xnu-517.3.15.tar.gz

[apple/xnu.git] / bsd / vfs / vfs_cluster.c

/*
 * Copyright (c) 2000-2002 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * Copyright (c) 1999-2003 Apple Computer, Inc.  All Rights Reserved.
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this
 * file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */
/* Copyright (c) 1995 NeXT Computer, Inc. All Rights Reserved */
/*
 * Copyright (c) 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)vfs_cluster.c       8.10 (Berkeley) 3/28/95
 */

#include <sys/param.h>
#include <sys/proc.h>
#include <sys/buf.h>
#include <sys/vnode.h>
#include <sys/mount.h>
#include <sys/trace.h>
#include <sys/malloc.h>
#include <sys/time.h>
#include <sys/kernel.h>
#include <sys/resourcevar.h>
#include <libkern/libkern.h>
#include <machine/machine_routines.h>

#include <sys/ubc.h>
#include <vm/vm_pageout.h>

#include <mach/mach_types.h>
#include <mach/memory_object_types.h>

#include <sys/kdebug.h>


#define CL_READ      0x01
#define CL_ASYNC     0x02
#define CL_COMMIT    0x04
#define CL_PAGEOUT   0x10
#define CL_AGE       0x20
#define CL_DUMP      0x40
#define CL_NOZERO    0x80
#define CL_PAGEIN    0x100
#define CL_DEV_MEMORY 0x200
#define CL_PRESERVE   0x400
#define CL_THROTTLE   0x800


struct clios {
        u_int  io_completed;       /* amount of io that has currently completed */
        u_int  io_issued;          /* amount of io that was successfully issued */
        int    io_error;           /* error code of first error encountered */
        int    io_wanted;          /* someone is sleeping waiting for a change in state */
};


static void cluster_zero(upl_t upl, vm_offset_t   upl_offset,
                int size, struct buf *bp);
static int cluster_read_x(struct vnode *vp, struct uio *uio,
                off_t filesize, int devblocksize, int flags);
static int cluster_write_x(struct vnode *vp, struct uio *uio,
                off_t oldEOF, off_t newEOF, off_t headOff,
                off_t tailOff, int devblocksize, int flags);
static int cluster_nocopy_read(struct vnode *vp, struct uio *uio,
                off_t filesize, int devblocksize, int flags);
static int cluster_nocopy_write(struct vnode *vp, struct uio *uio,
                off_t newEOF, int devblocksize, int flags);
static int cluster_phys_read(struct vnode *vp, struct uio *uio,
                off_t filesize, int devblocksize, int flags);
static int cluster_phys_write(struct vnode *vp, struct uio *uio,
                off_t newEOF, int devblocksize, int flags);
static int cluster_align_phys_io(struct vnode *vp, struct uio *uio,
                addr64_t usr_paddr, int xsize, int devblocksize, int flags);
static int cluster_push_x(struct vnode *vp, off_t EOF, daddr_t first, daddr_t last, int can_delay);
static int cluster_try_push(struct vnode *vp, off_t EOF, int can_delay, int push_all);

static int sparse_cluster_switch(struct vnode *vp, off_t EOF);
static int sparse_cluster_push(struct vnode *vp, off_t EOF, int push_all);
static int sparse_cluster_add(struct vnode *vp, off_t EOF, daddr_t first, daddr_t last);

static kern_return_t vfs_drt_mark_pages(void **cmapp, off_t offset, u_int length, int *setcountp);
static kern_return_t vfs_drt_unmark_pages(void **cmapp, off_t offset, u_int length);
static kern_return_t vfs_drt_get_cluster(void **cmapp, off_t *offsetp, u_int *lengthp);
static kern_return_t vfs_drt_control(void **cmapp, int op_type);

int     ubc_page_op_with_control __P((memory_object_control_t, off_t, int, ppnum_t *, int *));


/*
 * throttle the number of async writes that
 * can be outstanding on a single vnode
 * before we issue a synchronous write 
 */
#define ASYNC_THROTTLE  18
#define HARD_THROTTLE_MAXCNT 1
#define HARD_THROTTLE_MAXSIZE (64 * 1024)

int hard_throttle_on_root = 0;
struct timeval priority_IO_timestamp_for_root;


static int 
cluster_hard_throttle_on(vp)
        struct vnode *vp;
{
        static struct timeval hard_throttle_maxelapsed = { 0, 300000 };

        if (vp->v_mount->mnt_kern_flag & MNTK_ROOTDEV) {
                struct timeval elapsed;

                if (hard_throttle_on_root)
                        return(1);

                elapsed = time;
                timevalsub(&elapsed, &priority_IO_timestamp_for_root);

                if (timevalcmp(&elapsed, &hard_throttle_maxelapsed, <))
                        return(1);
        }
        return(0);
}


static int
cluster_iodone(bp)
        struct buf *bp;
{
        int         b_flags;
        int         error;
        int         total_size;
        int         total_resid;
        int         upl_offset;
        int         zero_offset;
        upl_t       upl;
        struct buf *cbp;
        struct buf *cbp_head;
        struct buf *cbp_next;
        struct buf *real_bp;
        struct vnode *vp;
        struct clios *iostate;
        int         commit_size;
        int         pg_offset;


        cbp_head = (struct buf *)(bp->b_trans_head);

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 20)) | DBG_FUNC_START,
                     (int)cbp_head, bp->b_lblkno, bp->b_bcount, bp->b_flags, 0);

        for (cbp = cbp_head; cbp; cbp = cbp->b_trans_next) {
                /*
                 * all I/O requests that are part of this transaction
                 * have to complete before we can process it
                 */
                if ( !(cbp->b_flags & B_DONE)) {

                        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 20)) | DBG_FUNC_END,
                                     (int)cbp_head, (int)cbp, cbp->b_bcount, cbp->b_flags, 0);

                        return 0;
                }
        }
        error       = 0;
        total_size  = 0;
        total_resid = 0;

        cbp        = cbp_head;
        upl_offset = cbp->b_uploffset;
        upl        = cbp->b_pagelist;
        b_flags    = cbp->b_flags;
        real_bp    = cbp->b_real_bp;
        vp         = cbp->b_vp;
        zero_offset= cbp->b_validend;
        iostate    = (struct clios *)cbp->b_iostate;

        while (cbp) {
                if ((cbp->b_flags & B_ERROR) && error == 0)
                        error = cbp->b_error;

                total_resid += cbp->b_resid;
                total_size  += cbp->b_bcount;

                cbp_next = cbp->b_trans_next;

                free_io_buf(cbp);

                cbp = cbp_next;
        }
        if (zero_offset)
                cluster_zero(upl, zero_offset, PAGE_SIZE - (zero_offset & PAGE_MASK), real_bp);

        if ((vp->v_flag & VTHROTTLED) && (vp->v_numoutput <= (ASYNC_THROTTLE / 3))) {
                vp->v_flag &= ~VTHROTTLED;
                wakeup((caddr_t)&vp->v_numoutput);
        }
        if (iostate) {
                /*
                 * someone has issued multiple I/Os asynchrounsly
                 * and is waiting for them to complete (streaming)
                 */
                if (error && iostate->io_error == 0)
                        iostate->io_error = error;

                iostate->io_completed += total_size;

                if (iostate->io_wanted) {
                        /*
                         * someone is waiting for the state of
                         * this io stream to change
                         */
                        iostate->io_wanted = 0;
                        wakeup((caddr_t)&iostate->io_wanted);
                }
        }
        if ((b_flags & B_NEED_IODONE) && real_bp) {
                if (error) {
                        real_bp->b_flags |= B_ERROR;
                        real_bp->b_error = error;
                }
                real_bp->b_resid = total_resid;

                biodone(real_bp);
        }
        if (error == 0 && total_resid)
                error = EIO;

        if (b_flags & B_COMMIT_UPL) {
                pg_offset   = upl_offset & PAGE_MASK;
                commit_size = (pg_offset + total_size + (PAGE_SIZE - 1)) & ~PAGE_MASK;

                if (error || (b_flags & B_NOCACHE)) {
                        int upl_abort_code;

                        if ((b_flags & B_PAGEOUT) && (error != ENXIO)) /* transient error */
                                upl_abort_code = UPL_ABORT_FREE_ON_EMPTY;
                        else if (b_flags & B_PGIN)
                                upl_abort_code = UPL_ABORT_FREE_ON_EMPTY | UPL_ABORT_ERROR;
                        else
                                upl_abort_code = UPL_ABORT_FREE_ON_EMPTY | UPL_ABORT_DUMP_PAGES;

                        ubc_upl_abort_range(upl, upl_offset - pg_offset, commit_size,
                                        upl_abort_code);
                        
                        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 20)) | DBG_FUNC_END,
                                     (int)upl, upl_offset - pg_offset, commit_size,
                                     0x80000000|upl_abort_code, 0);

                } else {
                        int upl_commit_flags = UPL_COMMIT_FREE_ON_EMPTY;

                        if (b_flags & B_PHYS) {
                                if (b_flags & B_READ)
                                        upl_commit_flags |= UPL_COMMIT_SET_DIRTY;
                        } else if ( !(b_flags & B_PAGEOUT))
                                upl_commit_flags |= UPL_COMMIT_CLEAR_DIRTY;

                        if (b_flags & B_AGE)
                                upl_commit_flags |= UPL_COMMIT_INACTIVATE;

                        ubc_upl_commit_range(upl, upl_offset - pg_offset, commit_size,
                                        upl_commit_flags);

                        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 20)) | DBG_FUNC_END,
                                     (int)upl, upl_offset - pg_offset, commit_size,
                                     upl_commit_flags, 0);
                }
        } else 
                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 20)) | DBG_FUNC_END,
                             (int)upl, upl_offset, 0, error, 0);

        return (error);
}


static void
cluster_zero(upl, upl_offset, size, bp)
        upl_t         upl;
        vm_offset_t   upl_offset;
        int           size;
        struct buf   *bp;
{
        upl_page_info_t *pl;

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 23)) | DBG_FUNC_START,
                     upl_offset, size, (int)bp, 0, 0);

        if (bp == NULL || bp->b_data == NULL) {

                pl = ubc_upl_pageinfo(upl);

                while (size) {
                        int           page_offset;
                        int           page_index;
                        addr64_t      zero_addr;
                        int           zero_cnt;

                        page_index  = upl_offset / PAGE_SIZE;
                        page_offset = upl_offset & PAGE_MASK;

                        zero_addr = ((addr64_t)upl_phys_page(pl, page_index) << 12) + page_offset;
                        zero_cnt  = min(PAGE_SIZE - page_offset, size);

                        bzero_phys(zero_addr, zero_cnt);

                        size       -= zero_cnt;
                        upl_offset += zero_cnt;
                }
        } else
                bzero((caddr_t)((vm_offset_t)bp->b_data + upl_offset), size);

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 23)) | DBG_FUNC_END,
                     upl_offset, size, 0, 0, 0);
}

static int
cluster_io(vp, upl, upl_offset, f_offset, non_rounded_size, devblocksize, flags, real_bp, iostate)
        struct vnode *vp;
        upl_t         upl;
        vm_offset_t   upl_offset;
        off_t         f_offset;
        int           non_rounded_size;
        int           devblocksize;
        int           flags;
        struct buf   *real_bp;
        struct clios *iostate;
{
        struct buf   *cbp;
        u_int         size;
        u_int         io_size;
        int           io_flags;
        int           error = 0;
        int           retval = 0;
        struct buf   *cbp_head = 0;
        struct buf   *cbp_tail = 0;
        int buf_count = 0;
        int pg_count;
        int pg_offset;
        u_int max_iosize;
        u_int max_vectors;
        int priv;
        int zero_offset = 0;
        int async_throttle;

        if (devblocksize)
                size = (non_rounded_size + (devblocksize - 1)) & ~(devblocksize - 1);
        else
                size = non_rounded_size;

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 22)) | DBG_FUNC_START,
                     (int)f_offset, size, upl_offset, flags, 0);


        if (flags & CL_READ) {
                io_flags = (B_VECTORLIST | B_READ);

                vfs_io_attributes(vp, B_READ, &max_iosize, &max_vectors);
        } else {
                io_flags = (B_VECTORLIST | B_WRITEINPROG);

                vfs_io_attributes(vp, B_WRITE, &max_iosize, &max_vectors);
        }
        /*
         * make sure the maximum iosize are at least the size of a page
         * and that they are multiples of the page size
         */
        max_iosize  &= ~PAGE_MASK;

        if (flags & CL_THROTTLE) {
                if ( !(flags & CL_PAGEOUT) && cluster_hard_throttle_on(vp)) {
                        if (max_iosize > HARD_THROTTLE_MAXSIZE)
                                max_iosize = HARD_THROTTLE_MAXSIZE;
                        async_throttle = HARD_THROTTLE_MAXCNT;
                } else
                        async_throttle = ASYNC_THROTTLE;
        }
        if (flags & CL_AGE)
                io_flags |= B_AGE;
        if (flags & CL_DUMP)
                io_flags |= B_NOCACHE;
        if (flags & CL_PAGEIN)
                io_flags |= B_PGIN;
        if (flags & CL_PAGEOUT)
                io_flags |= B_PAGEOUT;
        if (flags & CL_COMMIT)
                io_flags |= B_COMMIT_UPL;
        if (flags & CL_PRESERVE)
                io_flags |= B_PHYS;

        if ((flags & CL_READ) && ((upl_offset + non_rounded_size) & PAGE_MASK) && (!(flags & CL_NOZERO))) {
                /*
                 * then we are going to end up
                 * with a page that we can't complete (the file size wasn't a multiple
                 * of PAGE_SIZE and we're trying to read to the end of the file
                 * so we'll go ahead and zero out the portion of the page we can't
                 * read in from the file
                 */
                zero_offset = upl_offset + non_rounded_size;
        }
        while (size) {
                int vsize;
                int i;
                int pg_resid;
                int num_contig;
                daddr_t lblkno;
                daddr_t blkno;

                if (size > max_iosize)
                        io_size = max_iosize;
                else
                        io_size = size;

                if (error = VOP_CMAP(vp, f_offset, io_size, &blkno, (size_t *)&io_size, NULL)) {
                        if (error == EOPNOTSUPP)
                                panic("VOP_CMAP Unimplemented");
                        break;
                }

                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 24)) | DBG_FUNC_NONE,
                             (int)f_offset, (int)blkno, io_size, zero_offset, 0);

                if ( (!(flags & CL_READ) && (long)blkno == -1) || io_size == 0) {
                        if (flags & CL_PAGEOUT) {
                                error = EINVAL;
                                break;
                        };
                        
                        /* Try paging out the page individually before
                           giving up entirely and dumping it (it could
                           be mapped in a "hole" and require allocation
                           before the I/O:
                         */
                         ubc_upl_abort_range(upl, upl_offset, PAGE_SIZE, UPL_ABORT_FREE_ON_EMPTY);
                         if (ubc_pushdirty_range(vp, f_offset, PAGE_SIZE_64) == 0) {
                                error = EINVAL;
                                break;
                         };
                         
                        f_offset   += PAGE_SIZE_64;
                        upl_offset += PAGE_SIZE;
                        size       -= PAGE_SIZE;
                        continue;
                }
                lblkno = (daddr_t)(f_offset / PAGE_SIZE_64);
                /*
                 * we have now figured out how much I/O we can do - this is in 'io_size'
                 * pg_offset is the starting point in the first page for the I/O
                 * pg_count is the number of full and partial pages that 'io_size' encompasses
                 */
                pg_offset = upl_offset & PAGE_MASK;

                if (flags & CL_DEV_MEMORY) {
                        /*
                         * currently, can't deal with reading 'holes' in file
                         */
                        if ((long)blkno == -1) {
                                error = EINVAL;
                                break;
                        }
                        /*
                         * treat physical requests as one 'giant' page
                         */
                        pg_count = 1;
                } else
                        pg_count  = (io_size + pg_offset + (PAGE_SIZE - 1)) / PAGE_SIZE;

                if ((flags & CL_READ) && (long)blkno == -1) {
                        int bytes_to_zero;

                        /*
                         * if we're reading and blkno == -1, then we've got a
                         * 'hole' in the file that we need to deal with by zeroing
                         * out the affected area in the upl
                         */
                        if (zero_offset && io_size == size) {
                                /*
                                 * if this upl contains the EOF and it is not a multiple of PAGE_SIZE
                                 * than 'zero_offset' will be non-zero
                                 * if the 'hole' returned by VOP_CMAP extends all the way to the eof
                                 * (indicated by the io_size finishing off the I/O request for this UPL)
                                 * than we're not going to issue an I/O for the
                                 * last page in this upl... we need to zero both the hole and the tail
                                 * of the page beyond the EOF, since the delayed zero-fill won't kick in 
                                 */
                                bytes_to_zero = (((upl_offset + io_size) + (PAGE_SIZE - 1)) & ~PAGE_MASK) - upl_offset;

                                zero_offset = 0;
                        } else
                                bytes_to_zero = io_size;

                        cluster_zero(upl, upl_offset, bytes_to_zero, real_bp);
                          
                        if (cbp_head)
                                /*
                                 * if there is a current I/O chain pending
                                 * then the first page of the group we just zero'd
                                 * will be handled by the I/O completion if the zero
                                 * fill started in the middle of the page
                                 */
                                pg_count = (io_size - pg_offset) / PAGE_SIZE;
                        else {
                                /*
                                 * no pending I/O to pick up that first page
                                 * so, we have to make sure it gets committed
                                 * here.
                                 * set the pg_offset to 0 so that the upl_commit_range
                                 * starts with this page
                                 */
                                pg_count = (io_size + pg_offset) / PAGE_SIZE;
                                pg_offset = 0;
                        }
                        if (io_size == size && ((upl_offset + io_size) & PAGE_MASK))
                                /*
                                 * if we're done with the request for this UPL
                                 * then we have to make sure to commit the last page
                                 * even if we only partially zero-filled it
                                 */
                                pg_count++;

                        if (pg_count) {
                                if (pg_offset)
                                        pg_resid = PAGE_SIZE - pg_offset;
                                else
                                        pg_resid = 0;

                                if (flags & CL_COMMIT)
                                        ubc_upl_commit_range(upl,
                                                        (upl_offset + pg_resid) & ~PAGE_MASK, 
                                                        pg_count * PAGE_SIZE,
                                                        UPL_COMMIT_CLEAR_DIRTY | UPL_COMMIT_FREE_ON_EMPTY);
                        }
                        upl_offset += io_size;
                        f_offset   += io_size;
                        size       -= io_size;

                        if (cbp_head && pg_count) 
                                goto start_io;
                        continue;

                } else if (real_bp && (real_bp->b_blkno == real_bp->b_lblkno)) {
                        real_bp->b_blkno = blkno;
                }

                if (pg_count > max_vectors) {
                        io_size -= (pg_count - max_vectors) * PAGE_SIZE;

                        if (io_size < 0) {
                                io_size = PAGE_SIZE - pg_offset;
                                pg_count = 1;
                        } else
                                pg_count = max_vectors;
                }

                if ( !(vp->v_mount->mnt_kern_flag & MNTK_VIRTUALDEV))
                        /*
                         * if we're not targeting a virtual device i.e. a disk image
                         * it's safe to dip into the reserve pool since real devices
                         * can complete this I/O request without requiring additional
                         * bufs from the alloc_io_buf pool
                         */
                        priv = 1;
                else if ((flags & CL_ASYNC) && !(flags & CL_PAGEOUT))
                        /*
                         * Throttle the speculative IO
                         */
                        priv = 0;
                else
                        priv = 1;

                cbp = alloc_io_buf(vp, priv);


                if (flags & CL_PAGEOUT) {
                        for (i = 0; i < pg_count; i++) {
                                int         s;
                                struct buf *bp;

                                s = splbio();
                                if (bp = incore(vp, lblkno + i)) {
                                        if (!ISSET(bp->b_flags, B_BUSY)) {
                                                bremfree(bp);
                                                SET(bp->b_flags, (B_BUSY | B_INVAL));
                                                splx(s);
                                                brelse(bp);
                                        } else
                                                panic("BUSY bp found in cluster_io");
                                }
                                splx(s);
                        }
                }
                if (flags & CL_ASYNC) {
                        cbp->b_flags |= (B_CALL | B_ASYNC);
                        cbp->b_iodone = (void *)cluster_iodone;
                }
                cbp->b_flags |= io_flags;

                cbp->b_lblkno = lblkno;
                cbp->b_blkno  = blkno;
                cbp->b_bcount = io_size;
                cbp->b_pagelist  = upl;
                cbp->b_uploffset = upl_offset;
                cbp->b_trans_next = (struct buf *)0;

                if (cbp->b_iostate = (void *)iostate)
                        /*
                         * caller wants to track the state of this
                         * io... bump the amount issued against this stream
                         */
                        iostate->io_issued += io_size;

                if (flags & CL_READ)
                        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 26)) | DBG_FUNC_NONE,
                                     cbp->b_lblkno, cbp->b_blkno, upl_offset, io_size, 0);
                else
                        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 27)) | DBG_FUNC_NONE,
                                     cbp->b_lblkno, cbp->b_blkno, upl_offset, io_size, 0);

                if (cbp_head) {
                        cbp_tail->b_trans_next = cbp;
                        cbp_tail = cbp;
                } else {
                        cbp_head = cbp;
                        cbp_tail = cbp;
                }
                (struct buf *)(cbp->b_trans_head) = cbp_head;
                buf_count++;

                upl_offset += io_size;
                f_offset   += io_size;
                size       -= io_size;

                if ( (!(upl_offset & PAGE_MASK) && !(flags & CL_DEV_MEMORY) && ((flags & CL_ASYNC) || buf_count > 8)) || size == 0) {
                        /*
                         * if we have no more I/O to issue or
                         * the current I/O we've prepared fully
                         * completes the last page in this request
                         * and it's either an ASYNC request or 
                         * we've already accumulated more than 8 I/O's into
                         * this transaction and it's not an I/O directed to 
                         * special DEVICE memory
                         * then go ahead and issue the I/O
                         */
start_io:               
                        if (real_bp) {
                                cbp_head->b_flags |= B_NEED_IODONE;
                                cbp_head->b_real_bp = real_bp;
                        } else
                                cbp_head->b_real_bp = (struct buf *)NULL;

                        if (size == 0) {
                                /*
                                 * we're about to issue the last I/O for this upl
                                 * if this was a read to the eof and the eof doesn't
                                 * finish on a page boundary, than we need to zero-fill
                                 * the rest of the page....
                                 */
                                cbp_head->b_validend = zero_offset;
                        } else
                                cbp_head->b_validend = 0;
                          
                        if (flags & CL_THROTTLE) {
                                while (vp->v_numoutput >= async_throttle) {
                                        vp->v_flag |= VTHROTTLED;
                                        tsleep((caddr_t)&vp->v_numoutput, PRIBIO + 1, "cluster_io", 0);
                                }
                        }
                        for (cbp = cbp_head; cbp;) {
                                struct buf * cbp_next;

                                if (io_flags & B_WRITEINPROG)
                                        cbp->b_vp->v_numoutput++;

                                cbp_next = cbp->b_trans_next;
                                
                                (void) VOP_STRATEGY(cbp);
                                cbp = cbp_next;
                        }
                        if ( !(flags & CL_ASYNC)) {
                                for (cbp = cbp_head; cbp; cbp = cbp->b_trans_next)
                                        biowait(cbp);

                                if (error = cluster_iodone(cbp_head)) {
                                        if ((flags & CL_PAGEOUT) && (error == ENXIO))
                                                retval = 0;     /* drop the error */
                                        else
                                                retval = error;
                                        error  = 0;
                                }
                        }
                        cbp_head = (struct buf *)0;
                        cbp_tail = (struct buf *)0;

                        buf_count = 0;
                }
        }
        if (error) {
                int abort_size;

                io_size = 0;
                
                for (cbp = cbp_head; cbp;) {
                        struct buf * cbp_next;
 
                        upl_offset -= cbp->b_bcount;
                        size       += cbp->b_bcount;
                        io_size    += cbp->b_bcount;

                        cbp_next = cbp->b_trans_next;
                        free_io_buf(cbp);
                        cbp = cbp_next;
                }
                if (iostate) {
                        /*
                         * update the error condition for this stream
                         * since we never really issued the io
                         * just go ahead and adjust it back
                         */
                        if (iostate->io_error == 0)
                                iostate->io_error = error;
                        iostate->io_issued -= io_size;

                        if (iostate->io_wanted) {
                                /*
                                 * someone is waiting for the state of
                                 * this io stream to change
                                 */
                                iostate->io_wanted = 0;
                                wakeup((caddr_t)&iostate->io_wanted);
                        }
                }
                pg_offset  = upl_offset & PAGE_MASK;
                abort_size = (size + pg_offset + (PAGE_SIZE - 1)) & ~PAGE_MASK;

                if (flags & CL_COMMIT) {
                        int upl_abort_code;

                        if (flags & CL_PRESERVE) {
                                ubc_upl_commit_range(upl, upl_offset - pg_offset, abort_size,
                                                     UPL_COMMIT_FREE_ON_EMPTY);
                        } else {
                                if ((flags & CL_PAGEOUT) && (error != ENXIO)) /* transient error */
                                        upl_abort_code = UPL_ABORT_FREE_ON_EMPTY;
                                else if (flags & CL_PAGEIN)
                                        upl_abort_code = UPL_ABORT_FREE_ON_EMPTY | UPL_ABORT_ERROR;
                                else
                                        upl_abort_code = UPL_ABORT_FREE_ON_EMPTY | UPL_ABORT_DUMP_PAGES;

                                ubc_upl_abort_range(upl, upl_offset - pg_offset, abort_size,
                                                upl_abort_code);
                        }
                        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 28)) | DBG_FUNC_NONE,
                                     (int)upl, upl_offset - pg_offset, abort_size, error, 0);
                }
                if (real_bp) {
                        real_bp->b_flags |= B_ERROR;
                        real_bp->b_error  = error;

                        biodone(real_bp);
                }
                if (retval == 0)
                        retval = error;
        }
        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 22)) | DBG_FUNC_END,
                     (int)f_offset, size, upl_offset, retval, 0);

        return (retval);
}


static int
cluster_rd_prefetch(vp, f_offset, size, filesize, devblocksize)
        struct vnode *vp;
        off_t         f_offset;
        u_int         size;
        off_t         filesize;
        int           devblocksize;
{
        int           pages_in_prefetch;

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 49)) | DBG_FUNC_START,
                     (int)f_offset, size, (int)filesize, 0, 0);

        if (f_offset >= filesize) {
                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 49)) | DBG_FUNC_END,
                             (int)f_offset, 0, 0, 0, 0);
                return(0);
        }
        if (size > (MAX_UPL_TRANSFER * PAGE_SIZE))
                size = (MAX_UPL_TRANSFER * PAGE_SIZE);
        else
                size = (size + (PAGE_SIZE - 1)) & ~PAGE_MASK;

        if ((off_t)size > (filesize - f_offset))
                size = filesize - f_offset;
        pages_in_prefetch = (size + (PAGE_SIZE - 1)) / PAGE_SIZE;

        advisory_read(vp, filesize, f_offset, size, devblocksize);

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 49)) | DBG_FUNC_END,
                     (int)f_offset + size, pages_in_prefetch, 0, 1, 0);

        return (pages_in_prefetch);
}



static void
cluster_rd_ahead(vp, b_lblkno, e_lblkno, filesize, devblocksize)
        struct vnode *vp;
        daddr_t       b_lblkno;
        daddr_t       e_lblkno;
        off_t         filesize;
        int           devblocksize;
{
        daddr_t       r_lblkno;
        off_t         f_offset;
        int           size_of_prefetch;

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 48)) | DBG_FUNC_START,
                     b_lblkno, e_lblkno, vp->v_lastr, 0, 0);

        if (b_lblkno == vp->v_lastr && b_lblkno == e_lblkno) {
                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 48)) | DBG_FUNC_END,
                             vp->v_ralen, vp->v_maxra, vp->v_lastr, 0, 0);
                return;
        }
        if (vp->v_lastr == -1 || (b_lblkno != vp->v_lastr && b_lblkno != (vp->v_lastr + 1) &&
                                 (b_lblkno != (vp->v_maxra + 1) || vp->v_ralen == 0))) {
                vp->v_ralen = 0;
                vp->v_maxra = 0;

                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 48)) | DBG_FUNC_END,
                             vp->v_ralen, vp->v_maxra, vp->v_lastr, 1, 0);

                return;
        }
        if (e_lblkno < vp->v_maxra) {
                if ((vp->v_maxra - e_lblkno) > (MAX_UPL_TRANSFER / 4)) {

                        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 48)) | DBG_FUNC_END,
                                     vp->v_ralen, vp->v_maxra, vp->v_lastr, 2, 0);
                        return;
                }
        }
        r_lblkno = max(e_lblkno, vp->v_maxra) + 1;
        f_offset = (off_t)r_lblkno * PAGE_SIZE_64;

        size_of_prefetch = 0;

        ubc_range_op(vp, f_offset, f_offset + PAGE_SIZE_64, UPL_ROP_PRESENT, &size_of_prefetch);

        if (size_of_prefetch) {
                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 48)) | DBG_FUNC_END,
                             vp->v_ralen, vp->v_maxra, vp->v_lastr, 3, 0);
                return;
        }
        if (f_offset < filesize) {
                vp->v_ralen = vp->v_ralen ? min(MAX_UPL_TRANSFER, vp->v_ralen << 1) : 1;

                if (((e_lblkno + 1) - b_lblkno) > vp->v_ralen)
                        vp->v_ralen = min(MAX_UPL_TRANSFER, (e_lblkno + 1) - b_lblkno);

                size_of_prefetch = cluster_rd_prefetch(vp, f_offset, vp->v_ralen * PAGE_SIZE, filesize, devblocksize);

                if (size_of_prefetch)
                        vp->v_maxra = (r_lblkno + size_of_prefetch) - 1;
        }
        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 48)) | DBG_FUNC_END,
                     vp->v_ralen, vp->v_maxra, vp->v_lastr, 4, 0);
}

int
cluster_pageout(vp, upl, upl_offset, f_offset, size, filesize, devblocksize, flags)
        struct vnode *vp;
        upl_t         upl;
        vm_offset_t   upl_offset;
        off_t         f_offset;
        int           size;
        off_t         filesize;
        int           devblocksize;
        int           flags;
{
        int           io_size;
        int           rounded_size;
        off_t         max_size;
        int           local_flags;

        if (vp->v_mount->mnt_kern_flag & MNTK_VIRTUALDEV)
                /*
                 * if we know we're issuing this I/O to a virtual device (i.e. disk image)
                 * then we don't want to enforce this throttle... if we do, we can 
                 * potentially deadlock since we're stalling the pageout thread at a time
                 * when the disk image might need additional memory (which won't be available
                 * if the pageout thread can't run)... instead we'll just depend on the throttle
                 * that the pageout thread now has in place to deal with external files
                 */
                local_flags = CL_PAGEOUT;
        else
                local_flags = CL_PAGEOUT | CL_THROTTLE;

        if ((flags & UPL_IOSYNC) == 0) 
                local_flags |= CL_ASYNC;
        if ((flags & UPL_NOCOMMIT) == 0) 
                local_flags |= CL_COMMIT;


        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 52)) | DBG_FUNC_NONE,
                     (int)f_offset, size, (int)filesize, local_flags, 0);

        /*
         * If they didn't specify any I/O, then we are done...
         * we can't issue an abort because we don't know how
         * big the upl really is
         */
        if (size <= 0)
                return (EINVAL);

        if (vp->v_mount->mnt_flag & MNT_RDONLY) {
                if (local_flags & CL_COMMIT)
                        ubc_upl_abort_range(upl, upl_offset, size, UPL_ABORT_FREE_ON_EMPTY);
                return (EROFS);
        }
        /*
         * can't page-in from a negative offset
         * or if we're starting beyond the EOF
         * or if the file offset isn't page aligned
         * or the size requested isn't a multiple of PAGE_SIZE
         */
        if (f_offset < 0 || f_offset >= filesize ||
           (f_offset & PAGE_MASK_64) || (size & PAGE_MASK)) {
                if (local_flags & CL_COMMIT)
                        ubc_upl_abort_range(upl, upl_offset, size, UPL_ABORT_FREE_ON_EMPTY);
                return (EINVAL);
        }
        max_size = filesize - f_offset;

        if (size < max_size)
                io_size = size;
        else
                io_size = max_size;

        rounded_size = (io_size + (PAGE_SIZE - 1)) & ~PAGE_MASK;

        if (size > rounded_size) {
                if (local_flags & CL_COMMIT)
                        ubc_upl_abort_range(upl, upl_offset + rounded_size, size - rounded_size,
                                        UPL_ABORT_FREE_ON_EMPTY);
        }
        vp->v_flag |= VHASBEENPAGED;

        return (cluster_io(vp, upl, upl_offset, f_offset, io_size, devblocksize,
                           local_flags, (struct buf *)0, (struct clios *)0));
}

int
cluster_pagein(vp, upl, upl_offset, f_offset, size, filesize, devblocksize, flags)
        struct vnode *vp;
        upl_t         upl;
        vm_offset_t   upl_offset;
        off_t         f_offset;
        int           size;
        off_t         filesize;
        int           devblocksize;
        int           flags;
{
        u_int         io_size;
        int           rounded_size;
        off_t         max_size;
        int           retval;
        int           local_flags = 0;

        if (upl == NULL || size < 0)
                panic("cluster_pagein: NULL upl passed in");

        if ((flags & UPL_IOSYNC) == 0)
                local_flags |= CL_ASYNC;
        if ((flags & UPL_NOCOMMIT) == 0) 
                local_flags |= CL_COMMIT;


        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 56)) | DBG_FUNC_NONE,
                     (int)f_offset, size, (int)filesize, local_flags, 0);

        /*
         * can't page-in from a negative offset
         * or if we're starting beyond the EOF
         * or if the file offset isn't page aligned
         * or the size requested isn't a multiple of PAGE_SIZE
         */
        if (f_offset < 0 || f_offset >= filesize ||
           (f_offset & PAGE_MASK_64) || (size & PAGE_MASK) || (upl_offset & PAGE_MASK)) {
                if (local_flags & CL_COMMIT)
                        ubc_upl_abort_range(upl, upl_offset, size, UPL_ABORT_FREE_ON_EMPTY | UPL_ABORT_ERROR);
                return (EINVAL);
        }
        max_size = filesize - f_offset;

        if (size < max_size)
                io_size = size;
        else
                io_size = max_size;

        rounded_size = (io_size + (PAGE_SIZE - 1)) & ~PAGE_MASK;

        if (size > rounded_size && (local_flags & CL_COMMIT))
                ubc_upl_abort_range(upl, upl_offset + rounded_size,
                                    size - rounded_size, UPL_ABORT_FREE_ON_EMPTY | UPL_ABORT_ERROR);
        
        retval = cluster_io(vp, upl, upl_offset, f_offset, io_size, devblocksize,
                           local_flags | CL_READ | CL_PAGEIN, (struct buf *)0, (struct clios *)0);

        if (retval == 0) {
                int b_lblkno;
                int e_lblkno;

                b_lblkno = (int)(f_offset / PAGE_SIZE_64);
                e_lblkno = (int)
                        ((f_offset + ((off_t)io_size - 1)) / PAGE_SIZE_64);

                if (!(flags & UPL_NORDAHEAD) && !(vp->v_flag & VRAOFF) && rounded_size == PAGE_SIZE) {
                        /*
                         * we haven't read the last page in of the file yet
                         * so let's try to read ahead if we're in 
                         * a sequential access pattern
                         */
                        cluster_rd_ahead(vp, b_lblkno, e_lblkno, filesize, devblocksize);
                }
                vp->v_lastr = e_lblkno;
        }
        return (retval);
}

int
cluster_bp(bp)
        struct buf *bp;
{
        off_t  f_offset;
        int    flags;

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 19)) | DBG_FUNC_START,
                     (int)bp, bp->b_lblkno, bp->b_bcount, bp->b_flags, 0);

        if (bp->b_pagelist == (upl_t) 0)
                panic("cluster_bp: can't handle NULL upl yet\n");
        if (bp->b_flags & B_READ)
                flags = CL_ASYNC | CL_READ;
        else
                flags = CL_ASYNC;

        f_offset = ubc_blktooff(bp->b_vp, bp->b_lblkno);

        return (cluster_io(bp->b_vp, bp->b_pagelist, 0, f_offset, bp->b_bcount, 0, flags, bp, (struct clios *)0));
}

int
cluster_write(vp, uio, oldEOF, newEOF, headOff, tailOff, devblocksize, flags)
        struct vnode *vp;
        struct uio   *uio;
        off_t         oldEOF;
        off_t         newEOF;
        off_t         headOff;
        off_t         tailOff;
        int           devblocksize;
        int           flags;
{
        int           prev_resid;
        int           clip_size;
        off_t         max_io_size;
        struct iovec  *iov;
        int           upl_size;
        int           upl_flags;
        upl_t         upl;
        int           retval = 0;

        
        if (vp->v_flag & VHASBEENPAGED)
          {
            /*
             * this vnode had pages cleaned to it by
             * the pager which indicates that either
             * it's not very 'hot', or the system is
             * being overwhelmed by a lot of dirty 
             * data being delayed in the VM cache...
             * in either event, we'll push our remaining
             * delayed data at this point...  this will
             * be more efficient than paging out 1 page at 
             * a time, and will also act as a throttle
             * by delaying this client from writing any
             * more data until all his delayed data has
             * at least been queued to the uderlying driver.
             */
            cluster_push(vp);
          
            vp->v_flag &= ~VHASBEENPAGED;
          }

        if ( (!(vp->v_flag & VNOCACHE_DATA)) || (!uio) || (uio->uio_segflg != UIO_USERSPACE))
          {
            /*
             * go do a write through the cache if one of the following is true....
             *   NOCACHE is not true
             *   there is no uio structure or it doesn't target USERSPACE
             */
            return (cluster_write_x(vp, uio, oldEOF, newEOF, headOff, tailOff, devblocksize, flags));
          }
        
        while (uio->uio_resid && uio->uio_offset < newEOF && retval == 0)
          {
            /*
             * we know we have a resid, so this is safe
             * skip over any emtpy vectors
             */
            iov = uio->uio_iov;

            while (iov->iov_len == 0) {
              uio->uio_iov++;
              uio->uio_iovcnt--;
              iov = uio->uio_iov;
            }
            upl_size  = PAGE_SIZE;
            upl_flags = UPL_QUERY_OBJECT_TYPE;

            if ((vm_map_get_upl(current_map(),
                               (vm_offset_t)iov->iov_base & ~PAGE_MASK,
                               &upl_size, &upl, NULL, NULL, &upl_flags, 0)) != KERN_SUCCESS)
              {
                /*
                 * the user app must have passed in an invalid address
                 */
                return (EFAULT);
              }       

            /*
             * We check every vector target but if it is physically
             * contiguous space, we skip the sanity checks.
             */
            if (upl_flags & UPL_PHYS_CONTIG)
              {
                if (flags & IO_HEADZEROFILL)
                  {
                    flags &= ~IO_HEADZEROFILL;

                    if (retval = cluster_write_x(vp, (struct uio *)0, 0, uio->uio_offset, headOff, 0, devblocksize, IO_HEADZEROFILL))
                        return(retval);
                  }

                retval = cluster_phys_write(vp, uio, newEOF, devblocksize, flags);

                if (uio->uio_resid == 0 && (flags & IO_TAILZEROFILL))
                  {
                    return (cluster_write_x(vp, (struct uio *)0, 0, tailOff, uio->uio_offset, 0, devblocksize, IO_HEADZEROFILL));
                  }
              }
            else if ((uio->uio_resid < PAGE_SIZE) || (flags & (IO_TAILZEROFILL | IO_HEADZEROFILL)))
              {
                /*
                 * we're here because we're don't have a physically contiguous target buffer
                 * go do a write through the cache if one of the following is true....
                 *   the total xfer size is less than a page...
                 *   we're being asked to ZEROFILL either the head or the tail of the I/O...
                 */
                return (cluster_write_x(vp, uio, oldEOF, newEOF, headOff, tailOff, devblocksize, flags));
              }
            else if (((int)uio->uio_offset & PAGE_MASK) || ((int)iov->iov_base & PAGE_MASK))
              {
                if (((int)uio->uio_offset & PAGE_MASK) == ((int)iov->iov_base & PAGE_MASK))
                  {
                    /*
                     * Bring the file offset write up to a pagesize boundary
                     * this will also bring the base address to a page boundary
                     * since they both are currently on the same offset within a page
                     * note: if we get here, uio->uio_resid is greater than PAGE_SIZE
                     * so the computed clip_size must always be less than the current uio_resid
                     */
                    clip_size = (PAGE_SIZE - (uio->uio_offset & PAGE_MASK_64));

                    /* 
                     * Fake the resid going into the cluster_write_x call
                     * and restore it on the way out.
                     */
                    prev_resid = uio->uio_resid;
                    uio->uio_resid = clip_size;
                    retval = cluster_write_x(vp, uio, oldEOF, newEOF, headOff, tailOff, devblocksize, flags);
                    uio->uio_resid = prev_resid - (clip_size - uio->uio_resid);
                  }
                else 
                  {
                    /*
                     * can't get both the file offset and the buffer offset aligned to a page boundary
                     * so fire an I/O through the cache for this entire vector
                     */
                    clip_size = iov->iov_len;
                    prev_resid = uio->uio_resid;
                    uio->uio_resid = clip_size;
                    retval = cluster_write_x(vp, uio, oldEOF, newEOF, headOff, tailOff, devblocksize, flags);
                    uio->uio_resid = prev_resid - (clip_size - uio->uio_resid);
                  }
              }
            else
              {
                /* 
                 * If we come in here, we know the offset into
                 * the file is on a pagesize boundary and the
                 * target buffer address is also on a page boundary
                 */
                max_io_size = newEOF - uio->uio_offset;
                clip_size = uio->uio_resid;
                if (iov->iov_len < clip_size)
                  clip_size = iov->iov_len;
                if (max_io_size < clip_size)
                  clip_size = max_io_size;

                if (clip_size < PAGE_SIZE)
                  {
                    /*
                     * Take care of tail end of write in this vector
                     */
                    prev_resid = uio->uio_resid;
                    uio->uio_resid = clip_size;
                    retval = cluster_write_x(vp, uio, oldEOF, newEOF, headOff, tailOff, devblocksize, flags);
                    uio->uio_resid = prev_resid - (clip_size - uio->uio_resid);
                  }
                else
                  {
                    /* round clip_size down to a multiple of pagesize */
                    clip_size = clip_size & ~(PAGE_MASK);
                    prev_resid = uio->uio_resid;
                    uio->uio_resid = clip_size;
                    retval = cluster_nocopy_write(vp, uio, newEOF, devblocksize, flags);
                    if ((retval == 0) && uio->uio_resid)
                      retval = cluster_write_x(vp, uio, oldEOF, newEOF, headOff, tailOff, devblocksize, flags);
                    uio->uio_resid = prev_resid - (clip_size - uio->uio_resid);
                  }
              } /* end else */
          } /* end while */
        return(retval);
}


static int
cluster_nocopy_write(vp, uio, newEOF, devblocksize, flags)
        struct vnode *vp;
        struct uio   *uio;
        off_t         newEOF;
        int           devblocksize;
        int           flags;
{
        upl_t            upl;
        upl_page_info_t  *pl;
        off_t            upl_f_offset;
        vm_offset_t      upl_offset;
        off_t            max_io_size;
        int              io_size;
        int              io_flag;
        int              upl_size;
        int              upl_needed_size;
        int              pages_in_pl;
        int              upl_flags;
        kern_return_t    kret;
        struct iovec     *iov;
        int              i;
        int              force_data_sync;
        int              error  = 0;
        struct clios     iostate;

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 75)) | DBG_FUNC_START,
                     (int)uio->uio_offset, (int)uio->uio_resid, 
                     (int)newEOF, devblocksize, 0);

        /*
         * When we enter this routine, we know
         *  -- the offset into the file is on a pagesize boundary
         *  -- the resid is a page multiple
         *  -- the resid will not exceed iov_len
         */
        cluster_try_push(vp, newEOF, 0, 1);

        iostate.io_completed = 0;
        iostate.io_issued = 0;
        iostate.io_error = 0;
        iostate.io_wanted = 0;

        iov = uio->uio_iov;

        while (uio->uio_resid && uio->uio_offset < newEOF && error == 0) {
                io_size = uio->uio_resid;

                if (io_size > (MAX_UPL_TRANSFER * PAGE_SIZE))
                        io_size = MAX_UPL_TRANSFER * PAGE_SIZE;

                upl_offset = (vm_offset_t)iov->iov_base & PAGE_MASK;
                upl_needed_size = (upl_offset + io_size + (PAGE_SIZE -1)) & ~PAGE_MASK;

                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 76)) | DBG_FUNC_START,
                             (int)upl_offset, upl_needed_size, (int)iov->iov_base, io_size, 0);

                for (force_data_sync = 0; force_data_sync < 3; force_data_sync++) {
                        pages_in_pl = 0;
                        upl_size = upl_needed_size;
                        upl_flags = UPL_FILE_IO | UPL_COPYOUT_FROM | UPL_NO_SYNC |
                                    UPL_CLEAN_IN_PLACE | UPL_SET_INTERNAL | UPL_SET_LITE | UPL_SET_IO_WIRE;

                        kret = vm_map_get_upl(current_map(),
                                              (vm_offset_t)iov->iov_base & ~PAGE_MASK,
                                              &upl_size,
                                              &upl, 
                                              NULL, 
                                              &pages_in_pl,
                                              &upl_flags,
                                              force_data_sync);

                        if (kret != KERN_SUCCESS) {
                                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 76)) | DBG_FUNC_END,
                                             0, 0, 0, kret, 0);
                                /*
                                 * cluster_nocopy_write: failed to get pagelist
                                 *
                                 * we may have already spun some portion of this request
                                 * off as async requests... we need to wait for the I/O
                                 * to complete before returning
                                 */
                                goto wait_for_writes;
                        }
                        pl = UPL_GET_INTERNAL_PAGE_LIST(upl);
                        pages_in_pl = upl_size / PAGE_SIZE;

                        for (i = 0; i < pages_in_pl; i++) {
                                if (!upl_valid_page(pl, i))
                                        break;            
                        }
                        if (i == pages_in_pl)
                                break;

                        /*
                         * didn't get all the pages back that we
                         * needed... release this upl and try again
                         */
                        ubc_upl_abort_range(upl, (upl_offset & ~PAGE_MASK), upl_size, 
                                            UPL_ABORT_FREE_ON_EMPTY);
                }
                if (force_data_sync >= 3) {
                        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 76)) | DBG_FUNC_END,
                                     i, pages_in_pl, upl_size, kret, 0);
                        /*
                         * for some reason, we couldn't acquire a hold on all
                         * the pages needed in the user's address space
                         *
                         * we may have already spun some portion of this request
                         * off as async requests... we need to wait for the I/O
                         * to complete before returning
                         */
                        goto wait_for_writes;
                }

                /*
                 * Consider the possibility that upl_size wasn't satisfied.
                 */
                if (upl_size != upl_needed_size)
                        io_size = (upl_size - (int)upl_offset) & ~PAGE_MASK;

                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 76)) | DBG_FUNC_END,
                             (int)upl_offset, upl_size, (int)iov->iov_base, io_size, 0);                       

                if (io_size == 0) {
                        ubc_upl_abort_range(upl, (upl_offset & ~PAGE_MASK), upl_size, 
                                            UPL_ABORT_FREE_ON_EMPTY);
                        /*
                         * we may have already spun some portion of this request
                         * off as async requests... we need to wait for the I/O
                         * to complete before returning
                         */
                        goto wait_for_writes;
                }
                /*
                 * Now look for pages already in the cache
                 * and throw them away.
                 * uio->uio_offset is page aligned within the file
                 * io_size is a multiple of PAGE_SIZE
                 */
                ubc_range_op(vp, uio->uio_offset, uio->uio_offset + io_size, UPL_ROP_DUMP, NULL);

                /*
                 * we want push out these writes asynchronously so that we can overlap
                 * the preparation of the next I/O
                 * if there are already too many outstanding writes
                 * wait until some complete before issuing the next
                 */
                while ((iostate.io_issued - iostate.io_completed) > (2 * MAX_UPL_TRANSFER * PAGE_SIZE)) {
                        iostate.io_wanted = 1;
                        tsleep((caddr_t)&iostate.io_wanted, PRIBIO + 1, "cluster_nocopy_write", 0);
                }       
                if (iostate.io_error) {
                        /*
                         * one of the earlier writes we issued ran into a hard error
                         * don't issue any more writes, cleanup the UPL
                         * that was just created but not used, then
                         * go wait for all writes that are part of this stream
                         * to complete before returning the error to the caller
                         */
                        ubc_upl_abort_range(upl, (upl_offset & ~PAGE_MASK), upl_size, 
                                            UPL_ABORT_FREE_ON_EMPTY);

                        goto wait_for_writes;
                }
                io_flag = CL_ASYNC | CL_PRESERVE | CL_COMMIT | CL_THROTTLE;

                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 77)) | DBG_FUNC_START,
                             (int)upl_offset, (int)uio->uio_offset, io_size, io_flag, 0);

                error = cluster_io(vp, upl, upl_offset, uio->uio_offset,
                                   io_size, devblocksize, io_flag, (struct buf *)0, &iostate);

                iov->iov_len    -= io_size;
                iov->iov_base   += io_size;
                uio->uio_resid  -= io_size;
                uio->uio_offset += io_size;

                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 77)) | DBG_FUNC_END,
                             (int)upl_offset, (int)uio->uio_offset, (int)uio->uio_resid, error, 0);

        } /* end while */

wait_for_writes:
        /*
         * make sure all async writes issued as part of this stream
         * have completed before we return
         */
        while (iostate.io_issued != iostate.io_completed) {
                iostate.io_wanted = 1;
                tsleep((caddr_t)&iostate.io_wanted, PRIBIO + 1, "cluster_nocopy_write", 0);
        }       
        if (iostate.io_error)
                error = iostate.io_error;

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 75)) | DBG_FUNC_END,
                     (int)uio->uio_offset, (int)uio->uio_resid, error, 4, 0);

        return (error);
}


static int
cluster_phys_write(vp, uio, newEOF, devblocksize, flags)
        struct vnode *vp;
        struct uio   *uio;
        off_t        newEOF;
        int          devblocksize;
        int          flags;
{
        upl_page_info_t *pl;
        addr64_t         src_paddr;
        upl_t            upl;
        vm_offset_t      upl_offset;
        int              tail_size;
        int              io_size;
        int              upl_size;
        int              upl_needed_size;
        int              pages_in_pl;
        int              upl_flags;
        kern_return_t    kret;
        struct iovec     *iov;
        int              error  = 0;

        /*
         * When we enter this routine, we know
         *  -- the resid will not exceed iov_len
         *  -- the vector target address is physcially contiguous
         */
        cluster_try_push(vp, newEOF, 0, 1);

        iov = uio->uio_iov;
        io_size = iov->iov_len;
        upl_offset = (vm_offset_t)iov->iov_base & PAGE_MASK;
        upl_needed_size = upl_offset + io_size;

        pages_in_pl = 0;
        upl_size = upl_needed_size;
        upl_flags = UPL_FILE_IO | UPL_COPYOUT_FROM | UPL_NO_SYNC | 
                    UPL_CLEAN_IN_PLACE | UPL_SET_INTERNAL | UPL_SET_LITE | UPL_SET_IO_WIRE;

        kret = vm_map_get_upl(current_map(),
                              (vm_offset_t)iov->iov_base & ~PAGE_MASK,
                              &upl_size, &upl, NULL, &pages_in_pl, &upl_flags, 0);

        if (kret != KERN_SUCCESS) {
                /*
                 * cluster_phys_write: failed to get pagelist
                 * note: return kret here
                 */
              return(EINVAL);
        }
        /*
         * Consider the possibility that upl_size wasn't satisfied.
         * This is a failure in the physical memory case.
         */
        if (upl_size < upl_needed_size) {
                kernel_upl_abort_range(upl, 0, upl_size, UPL_ABORT_FREE_ON_EMPTY);
                return(EINVAL);
        }
        pl = ubc_upl_pageinfo(upl);

        src_paddr = ((addr64_t)upl_phys_page(pl, 0) << 12) + ((addr64_t)((u_int)iov->iov_base & PAGE_MASK));

        while (((uio->uio_offset & (devblocksize - 1)) || io_size < devblocksize) && io_size) {
                int   head_size;

                head_size = devblocksize - (int)(uio->uio_offset & (devblocksize - 1));

                if (head_size > io_size)
                        head_size = io_size;

                error = cluster_align_phys_io(vp, uio, src_paddr, head_size, devblocksize, 0);

                if (error) {
                        ubc_upl_abort_range(upl, 0, upl_size, UPL_ABORT_FREE_ON_EMPTY);

                        return(EINVAL);
                }
                upl_offset += head_size;
                src_paddr  += head_size;
                io_size    -= head_size;
        }
        tail_size = io_size & (devblocksize - 1);
        io_size  -= tail_size;

        if (io_size) {
                /*
                 * issue a synchronous write to cluster_io
                 */
                error = cluster_io(vp, upl, upl_offset, uio->uio_offset,
                                   io_size, 0, CL_DEV_MEMORY, (struct buf *)0, (struct clios *)0);
        }
        if (error == 0) {
                /*
                 * The cluster_io write completed successfully,
                 * update the uio structure
                 */
                uio->uio_resid  -= io_size;
                iov->iov_len    -= io_size;
                iov->iov_base   += io_size;
                uio->uio_offset += io_size;
                src_paddr       += io_size;

                if (tail_size)
                        error = cluster_align_phys_io(vp, uio, src_paddr, tail_size, devblocksize, 0);
        }
        /*
         * just release our hold on the physically contiguous
         * region without changing any state
         */
        ubc_upl_abort_range(upl, 0, upl_size, UPL_ABORT_FREE_ON_EMPTY);

        return (error);
}


static int
cluster_write_x(vp, uio, oldEOF, newEOF, headOff, tailOff, devblocksize, flags)
        struct vnode *vp;
        struct uio   *uio;
        off_t         oldEOF;
        off_t         newEOF;
        off_t         headOff;
        off_t         tailOff;
        int           devblocksize;
        int           flags;
{
        upl_page_info_t *pl;
        upl_t            upl;
        vm_offset_t      upl_offset;
        int              upl_size;
        off_t            upl_f_offset;
        int              pages_in_upl;
        int              start_offset;
        int              xfer_resid;
        int              io_size;
        int              io_flags;
        int              io_offset;
        int              bytes_to_zero;
        int              bytes_to_move;
        kern_return_t    kret;
        int              retval = 0;
        int              uio_resid;
        long long        total_size;
        long long        zero_cnt;
        off_t            zero_off;
        long long        zero_cnt1;
        off_t            zero_off1;
        daddr_t          start_blkno;
        daddr_t          last_blkno;
        int              intersection;


        if (uio) {
                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 40)) | DBG_FUNC_START,
                             (int)uio->uio_offset, uio->uio_resid, (int)oldEOF, (int)newEOF, 0);

                uio_resid = uio->uio_resid;
        } else {
                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 40)) | DBG_FUNC_START,
                             0, 0, (int)oldEOF, (int)newEOF, 0);

                uio_resid = 0;
        }
        zero_cnt  = 0;
        zero_cnt1 = 0;

        if (flags & IO_HEADZEROFILL) {
                /*
                 * some filesystems (HFS is one) don't support unallocated holes within a file...
                 * so we zero fill the intervening space between the old EOF and the offset
                 * where the next chunk of real data begins.... ftruncate will also use this
                 * routine to zero fill to the new EOF when growing a file... in this case, the
                 * uio structure will not be provided
                 */
                if (uio) {
                        if (headOff < uio->uio_offset) {
                                zero_cnt = uio->uio_offset - headOff;
                                zero_off = headOff;
                        }
                } else if (headOff < newEOF) {  
                        zero_cnt = newEOF - headOff;
                        zero_off = headOff;
                }
        }
        if (flags & IO_TAILZEROFILL) {
                if (uio) {
                        zero_off1 = uio->uio_offset + uio->uio_resid;

                        if (zero_off1 < tailOff)
                                zero_cnt1 = tailOff - zero_off1;
                }       
        }
        if (zero_cnt == 0 && uio == (struct uio *) 0) {
            KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 40)) | DBG_FUNC_END,
                         retval, 0, 0, 0, 0);
            return (0);
        }

        while ((total_size = (uio_resid + zero_cnt + zero_cnt1)) && retval == 0) {
                /*
                 * for this iteration of the loop, figure out where our starting point is
                 */
                if (zero_cnt) {
                        start_offset = (int)(zero_off & PAGE_MASK_64);
                        upl_f_offset = zero_off - start_offset;
                } else if (uio_resid) {
                        start_offset = (int)(uio->uio_offset & PAGE_MASK_64);
                        upl_f_offset = uio->uio_offset - start_offset;
                } else {
                        start_offset = (int)(zero_off1 & PAGE_MASK_64);
                        upl_f_offset = zero_off1 - start_offset;
                }
                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 46)) | DBG_FUNC_NONE,
                             (int)zero_off, (int)zero_cnt, (int)zero_off1, (int)zero_cnt1, 0);

                if (total_size > (MAX_UPL_TRANSFER * PAGE_SIZE))
                        total_size = MAX_UPL_TRANSFER * PAGE_SIZE;

                start_blkno = (daddr_t)(upl_f_offset / PAGE_SIZE_64);
                
                if (uio && !(vp->v_flag & VNOCACHE_DATA) &&
                   (flags & (IO_SYNC | IO_HEADZEROFILL | IO_TAILZEROFILL)) == 0) {
                        /*
                         * assumption... total_size <= uio_resid
                         * because IO_HEADZEROFILL and IO_TAILZEROFILL not set
                         */
                        if ((start_offset + total_size) > (MAX_UPL_TRANSFER * PAGE_SIZE))
                                total_size -= start_offset;
                        xfer_resid = total_size;

                        retval = cluster_copy_ubc_data(vp, uio, &xfer_resid, 1);
                        
                        if (retval)
                                break;

                        uio_resid   -= (total_size - xfer_resid);
                        total_size   = xfer_resid;
                        start_offset = (int)(uio->uio_offset & PAGE_MASK_64);
                        upl_f_offset = uio->uio_offset - start_offset;

                        if (total_size == 0) {
                                if (start_offset) {
                                        /*
                                         * the write did not finish on a page boundary
                                         * which will leave upl_f_offset pointing to the
                                         * beginning of the last page written instead of
                                         * the page beyond it... bump it in this case
                                         * so that the cluster code records the last page
                                         * written as dirty
                                         */
                                        upl_f_offset += PAGE_SIZE_64;
                                }
                                upl_size = 0;
                                
                                goto check_cluster;
                        }
                }
                /*
                 * compute the size of the upl needed to encompass
                 * the requested write... limit each call to cluster_io
                 * to the maximum UPL size... cluster_io will clip if
                 * this exceeds the maximum io_size for the device,
                 * make sure to account for 
                 * a starting offset that's not page aligned
                 */
                upl_size = (start_offset + total_size + (PAGE_SIZE - 1)) & ~PAGE_MASK;

                if (upl_size > (MAX_UPL_TRANSFER * PAGE_SIZE))
                        upl_size = MAX_UPL_TRANSFER * PAGE_SIZE;

                pages_in_upl = upl_size / PAGE_SIZE;
                io_size      = upl_size - start_offset;
                
                if ((long long)io_size > total_size)
                        io_size = total_size;

                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 41)) | DBG_FUNC_START, upl_size, io_size, total_size, 0, 0);
                        

                kret = ubc_create_upl(vp, 
                                                        upl_f_offset,
                                                        upl_size,
                                                        &upl,
                                                        &pl,
                                                        UPL_SET_LITE);
                if (kret != KERN_SUCCESS)
                        panic("cluster_write: failed to get pagelist");

                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 41)) | DBG_FUNC_END,
                        (int)upl, (int)upl_f_offset, start_offset, 0, 0);

                if (start_offset && !upl_valid_page(pl, 0)) {
                        int   read_size;

                        /*
                         * we're starting in the middle of the first page of the upl
                         * and the page isn't currently valid, so we're going to have
                         * to read it in first... this is a synchronous operation
                         */
                        read_size = PAGE_SIZE;

                        if ((upl_f_offset + read_size) > newEOF)
                                read_size = newEOF - upl_f_offset;

                        retval = cluster_io(vp, upl, 0, upl_f_offset, read_size, devblocksize,
                                            CL_READ, (struct buf *)0, (struct clios *)0);
                        if (retval) {
                                /*
                                 * we had an error during the read which causes us to abort
                                 * the current cluster_write request... before we do, we need
                                 * to release the rest of the pages in the upl without modifying
                                 * there state and mark the failed page in error
                                 */
                                ubc_upl_abort_range(upl, 0, PAGE_SIZE, UPL_ABORT_DUMP_PAGES);
                                ubc_upl_abort_range(upl, 0, upl_size,  UPL_ABORT_FREE_ON_EMPTY);

                                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 45)) | DBG_FUNC_NONE,
                                             (int)upl, 0, 0, retval, 0);
                                break;
                        }
                }
                if ((start_offset == 0 || upl_size > PAGE_SIZE) && ((start_offset + io_size) & PAGE_MASK)) {
                        /* 
                         * the last offset we're writing to in this upl does not end on a page
                         * boundary... if it's not beyond the old EOF, then we'll also need to
                         * pre-read this page in if it isn't already valid
                         */
                        upl_offset = upl_size - PAGE_SIZE;

                        if ((upl_f_offset + start_offset + io_size) < oldEOF &&
                            !upl_valid_page(pl, upl_offset / PAGE_SIZE)) {
                                int   read_size;

                                read_size = PAGE_SIZE;

                                if ((upl_f_offset + upl_offset + read_size) > newEOF)
                                        read_size = newEOF - (upl_f_offset + upl_offset);

                                retval = cluster_io(vp, upl, upl_offset, upl_f_offset + upl_offset, read_size, devblocksize,
                                                    CL_READ, (struct buf *)0, (struct clios *)0);
                                if (retval) {
                                        /*
                                         * we had an error during the read which causes us to abort
                                         * the current cluster_write request... before we do, we
                                         * need to release the rest of the pages in the upl without
                                         * modifying there state and mark the failed page in error
                                         */
                                        ubc_upl_abort_range(upl, upl_offset, PAGE_SIZE, UPL_ABORT_DUMP_PAGES);
                                        ubc_upl_abort_range(upl, 0,          upl_size,  UPL_ABORT_FREE_ON_EMPTY);

                                        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 45)) | DBG_FUNC_NONE,
                                                     (int)upl, 0, 0, retval, 0);
                                        break;
                                }
                        }
                }
                xfer_resid = io_size;
                io_offset = start_offset;

                while (zero_cnt && xfer_resid) {

                        if (zero_cnt < (long long)xfer_resid)
                                bytes_to_zero = zero_cnt;
                        else
                                bytes_to_zero = xfer_resid;

                        if ( !(flags & (IO_NOZEROVALID | IO_NOZERODIRTY))) {
                                cluster_zero(upl, io_offset, bytes_to_zero, NULL);
                        } else {
                                int zero_pg_index;

                                bytes_to_zero = min(bytes_to_zero, PAGE_SIZE - (int)(zero_off & PAGE_MASK_64));
                                zero_pg_index = (int)((zero_off - upl_f_offset) / PAGE_SIZE_64);

                                if ( !upl_valid_page(pl, zero_pg_index)) {
                                        cluster_zero(upl, io_offset, bytes_to_zero, NULL); 

                                } else if ((flags & (IO_NOZERODIRTY | IO_NOZEROVALID)) == IO_NOZERODIRTY &&
                                           !upl_dirty_page(pl, zero_pg_index)) {
                                        cluster_zero(upl, io_offset, bytes_to_zero, NULL); 
                                }
                        }
                        xfer_resid -= bytes_to_zero;
                        zero_cnt   -= bytes_to_zero;
                        zero_off   += bytes_to_zero;
                        io_offset  += bytes_to_zero;
                }
                if (xfer_resid && uio_resid) {
                        bytes_to_move = min(uio_resid, xfer_resid);

                        retval = cluster_copy_upl_data(uio, upl, io_offset, bytes_to_move);

                        if (retval) {

                                ubc_upl_abort_range(upl, 0, upl_size, UPL_ABORT_DUMP_PAGES | UPL_ABORT_FREE_ON_EMPTY);

                                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 45)) | DBG_FUNC_NONE,
                                             (int)upl, 0, 0, retval, 0);
                        } else {
                                uio_resid  -= bytes_to_move;
                                xfer_resid -= bytes_to_move;
                                io_offset  += bytes_to_move;
                        }
                }
                while (xfer_resid && zero_cnt1 && retval == 0) {

                        if (zero_cnt1 < (long long)xfer_resid)
                                bytes_to_zero = zero_cnt1;
                        else
                                bytes_to_zero = xfer_resid;

                        if ( !(flags & (IO_NOZEROVALID | IO_NOZERODIRTY))) {
                                cluster_zero(upl, io_offset, bytes_to_zero, NULL); 
                        } else {
                                int zero_pg_index;
                        
                                bytes_to_zero = min(bytes_to_zero, PAGE_SIZE - (int)(zero_off1 & PAGE_MASK_64));
                                zero_pg_index = (int)((zero_off1 - upl_f_offset) / PAGE_SIZE_64);

                                if ( !upl_valid_page(pl, zero_pg_index)) {
                                        cluster_zero(upl, io_offset, bytes_to_zero, NULL); 
                                } else if ((flags & (IO_NOZERODIRTY | IO_NOZEROVALID)) == IO_NOZERODIRTY &&
                                           !upl_dirty_page(pl, zero_pg_index)) {
                                        cluster_zero(upl, io_offset, bytes_to_zero, NULL); 
                                }
                        }
                        xfer_resid -= bytes_to_zero;
                        zero_cnt1  -= bytes_to_zero;
                        zero_off1  += bytes_to_zero;
                        io_offset  += bytes_to_zero;
                }

                if (retval == 0) {
                        int cl_index;
                        int can_delay;

                        io_size += start_offset;

                        if ((upl_f_offset + io_size) >= newEOF && io_size < upl_size) {
                                /*
                                 * if we're extending the file with this write
                                 * we'll zero fill the rest of the page so that
                                 * if the file gets extended again in such a way as to leave a
                                 * hole starting at this EOF, we'll have zero's in the correct spot
                                 */
                                cluster_zero(upl, io_size, upl_size - io_size, NULL); 
                        }
                        if (flags & IO_SYNC)
                                /*
                                 * if the IO_SYNC flag is set than we need to 
                                 * bypass any clusters and immediately issue
                                 * the I/O
                                 */
                                goto issue_io;
check_cluster:
                        /*
                         * calculate the last logical block number 
                         * that this delayed I/O encompassed
                         */
                        last_blkno = (upl_f_offset + (off_t)upl_size) / PAGE_SIZE_64;

                        if (vp->v_flag & VHASDIRTY) {

                                if ( !(vp->v_flag & VNOCACHE_DATA)) {
                                        /*
                                         * we've fallen into the sparse
                                         * cluster method of delaying dirty pages
                                         * first, we need to release the upl if we hold one
                                         * since pages in it may be present in the sparse cluster map
                                         * and may span 2 separate buckets there... if they do and 
                                         * we happen to have to flush a bucket to make room and it intersects
                                         * this upl, a deadlock may result on page BUSY
                                         */
                                        if (upl_size)
                                                ubc_upl_commit_range(upl, 0, upl_size,
                                                                     UPL_COMMIT_SET_DIRTY | UPL_COMMIT_INACTIVATE | UPL_COMMIT_FREE_ON_EMPTY);

                                        sparse_cluster_add(vp, newEOF, start_blkno, last_blkno);

                                        continue;
                                }
                                /*
                                 * must have done cached writes that fell into
                                 * the sparse cluster mechanism... we've switched
                                 * to uncached writes on the file, so go ahead
                                 * and push whatever's in the sparse map
                                 * and switch back to normal clustering
                                 *
                                 * see the comment above concerning a possible deadlock...
                                 */
                                if (upl_size) {
                                        ubc_upl_commit_range(upl, 0, upl_size,
                                                             UPL_COMMIT_SET_DIRTY | UPL_COMMIT_INACTIVATE | UPL_COMMIT_FREE_ON_EMPTY);
                                        /*
                                         * setting upl_size to 0 keeps us from committing a
                                         * second time in the start_new_cluster path
                                         */
                                        upl_size = 0;
                                }
                                sparse_cluster_push(vp, ubc_getsize(vp), 1);

                                /*
                                 * no clusters of either type present at this point
                                 * so just go directly to start_new_cluster since
                                 * we know we need to delay this I/O since we've
                                 * already released the pages back into the cache
                                 * to avoid the deadlock with sparse_cluster_push
                                 */
                                goto start_new_cluster;
                        }                   
                        upl_offset = 0;

                        if (vp->v_clen == 0)
                                /*
                                 * no clusters currently present
                                 */
                                goto start_new_cluster;

                        for (cl_index = 0; cl_index < vp->v_clen; cl_index++) {
                                /*
                                 * check each cluster that we currently hold
                                 * try to merge some or all of this write into
                                 * one or more of the existing clusters... if
                                 * any portion of the write remains, start a
                                 * new cluster
                                 */
                                if (start_blkno >= vp->v_clusters[cl_index].start_pg) {
                                        /*
                                         * the current write starts at or after the current cluster
                                         */
                                        if (last_blkno <= (vp->v_clusters[cl_index].start_pg + MAX_UPL_TRANSFER)) {
                                                /*
                                                 * we have a write that fits entirely
                                                 * within the existing cluster limits
                                                 */
                                                if (last_blkno > vp->v_clusters[cl_index].last_pg)
                                                        /*
                                                         * update our idea of where the cluster ends
                                                         */
                                                        vp->v_clusters[cl_index].last_pg = last_blkno;
                                                break;
                                        }
                                        if (start_blkno < (vp->v_clusters[cl_index].start_pg + MAX_UPL_TRANSFER)) {
                                                /*
                                                 * we have a write that starts in the middle of the current cluster
                                                 * but extends beyond the cluster's limit... we know this because
                                                 * of the previous checks
                                                 * we'll extend the current cluster to the max
                                                 * and update the start_blkno for the current write to reflect that
                                                 * the head of it was absorbed into this cluster...
                                                 * note that we'll always have a leftover tail in this case since
                                                 * full absorbtion would have occurred in the clause above
                                                 */
                                                vp->v_clusters[cl_index].last_pg = vp->v_clusters[cl_index].start_pg + MAX_UPL_TRANSFER;

                                                if (upl_size) {
                                                        int  start_pg_in_upl;

                                                        start_pg_in_upl = upl_f_offset / PAGE_SIZE_64;
                                                        
                                                        if (start_pg_in_upl < vp->v_clusters[cl_index].last_pg) {
                                                                intersection = (vp->v_clusters[cl_index].last_pg - start_pg_in_upl) * PAGE_SIZE;

                                                                ubc_upl_commit_range(upl, upl_offset, intersection,
                                                                                     UPL_COMMIT_SET_DIRTY | UPL_COMMIT_INACTIVATE | UPL_COMMIT_FREE_ON_EMPTY);
                                                                upl_f_offset += intersection;
                                                                upl_offset   += intersection;
                                                                upl_size     -= intersection;
                                                        }
                                                }
                                                start_blkno = vp->v_clusters[cl_index].last_pg;
                                        }
                                        /*
                                         * we come here for the case where the current write starts
                                         * beyond the limit of the existing cluster or we have a leftover
                                         * tail after a partial absorbtion
                                         *
                                         * in either case, we'll check the remaining clusters before 
                                         * starting a new one
                                         */
                                } else {
                                        /*
                                         * the current write starts in front of the cluster we're currently considering
                                         */
                                        if ((vp->v_clusters[cl_index].last_pg - start_blkno) <= MAX_UPL_TRANSFER) {
                                                /*
                                                 * we can just merge the new request into
                                                 * this cluster and leave it in the cache
                                                 * since the resulting cluster is still 
                                                 * less than the maximum allowable size
                                                 */
                                                vp->v_clusters[cl_index].start_pg = start_blkno;

                                                if (last_blkno > vp->v_clusters[cl_index].last_pg) {
                                                        /*
                                                         * the current write completely
                                                         * envelops the existing cluster and since
                                                         * each write is limited to at most MAX_UPL_TRANSFER bytes
                                                         * we can just use the start and last blocknos of the write
                                                         * to generate the cluster limits
                                                         */
                                                        vp->v_clusters[cl_index].last_pg = last_blkno;
                                                }
                                                break;
                                        }

                                        /*
                                         * if we were to combine this write with the current cluster
                                         * we would exceed the cluster size limit.... so,
                                         * let's see if there's any overlap of the new I/O with
                                         * the cluster we're currently considering... in fact, we'll
                                         * stretch the cluster out to it's full limit and see if we
                                         * get an intersection with the current write
                                         * 
                                         */
                                        if (last_blkno > vp->v_clusters[cl_index].last_pg - MAX_UPL_TRANSFER) {
                                                /*
                                                 * the current write extends into the proposed cluster
                                                 * clip the length of the current write after first combining it's
                                                 * tail with the newly shaped cluster
                                                 */
                                                vp->v_clusters[cl_index].start_pg = vp->v_clusters[cl_index].last_pg - MAX_UPL_TRANSFER;

                                                if (upl_size) {
                                                        intersection = (last_blkno - vp->v_clusters[cl_index].start_pg) * PAGE_SIZE;

                                                        if (intersection > upl_size)
                                                                /*
                                                                 * because the current write may consist of a number of pages found in the cache
                                                                 * which are not part of the UPL, we may have an intersection that exceeds
                                                                 * the size of the UPL that is also part of this write
                                                                 */
                                                                intersection = upl_size;

                                                        ubc_upl_commit_range(upl, upl_offset + (upl_size - intersection), intersection,
                                                                             UPL_COMMIT_SET_DIRTY | UPL_COMMIT_INACTIVATE | UPL_COMMIT_FREE_ON_EMPTY);
                                                        upl_size -= intersection;
                                                }
                                                last_blkno = vp->v_clusters[cl_index].start_pg;
                                        }
                                        /*
                                         * if we get here, there was no way to merge
                                         * any portion of this write with this cluster 
                                         * or we could only merge part of it which 
                                         * will leave a tail...
                                         * we'll check the remaining clusters before starting a new one
                                         */
                                }
                        }
                        if (cl_index < vp->v_clen)
                                /*
                                 * we found an existing cluster(s) that we
                                 * could entirely merge this I/O into
                                 */
                                goto delay_io;

                        if (vp->v_clen < MAX_CLUSTERS && !(vp->v_flag & VNOCACHE_DATA))
                                /*
                                 * we didn't find an existing cluster to
                                 * merge into, but there's room to start
                                 * a new one
                                 */
                                goto start_new_cluster;

                        /*
                         * no exisitng cluster to merge with and no
                         * room to start a new one... we'll try 
                         * pushing one of the existing ones... if none of
                         * them are able to be pushed, we'll switch
                         * to the sparse cluster mechanism
                         * cluster_try_push updates v_clen to the
                         * number of remaining clusters... and
                         * returns the number of currently unused clusters
                         */
                        if (vp->v_flag & VNOCACHE_DATA)
                                can_delay = 0;
                        else
                                can_delay = 1;

                        if (cluster_try_push(vp, newEOF, can_delay, 0) == 0) {
                                /*
                                 * no more room in the normal cluster mechanism
                                 * so let's switch to the more expansive but expensive
                                 * sparse mechanism....
                                 * first, we need to release the upl if we hold one
                                 * since pages in it may be present in the sparse cluster map (after the cluster_switch)
                                 * and may span 2 separate buckets there... if they do and 
                                 * we happen to have to flush a bucket to make room and it intersects
                                 * this upl, a deadlock may result on page BUSY
                                 */
                                if (upl_size)
                                        ubc_upl_commit_range(upl, upl_offset, upl_size,
                                                             UPL_COMMIT_SET_DIRTY | UPL_COMMIT_INACTIVATE | UPL_COMMIT_FREE_ON_EMPTY);

                                sparse_cluster_switch(vp, newEOF);
                                sparse_cluster_add(vp, newEOF, start_blkno, last_blkno);

                                continue;
                        }
                        /*
                         * we pushed one cluster successfully, so we must be sequentially writing this file
                         * otherwise, we would have failed and fallen into the sparse cluster support
                         * so let's take the opportunity to push out additional clusters as long as we
                         * remain below the throttle... this will give us better I/O locality if we're
                         * in a copy loop (i.e.  we won't jump back and forth between the read and write points
                         * however, we don't want to push so much out that the write throttle kicks in and
                         * hangs this thread up until some of the I/O completes...
                         */
                        while (vp->v_clen && (vp->v_numoutput <= (ASYNC_THROTTLE / 2)))
                                cluster_try_push(vp, newEOF, 0, 0);

start_new_cluster:
                        if (vp->v_clen == 0)
                                vp->v_ciosiz = devblocksize;

                        vp->v_clusters[vp->v_clen].start_pg = start_blkno;
                        vp->v_clusters[vp->v_clen].last_pg  = last_blkno;
                        vp->v_clen++;

delay_io:
                        if (upl_size)
                                ubc_upl_commit_range(upl, upl_offset, upl_size,
                                                     UPL_COMMIT_SET_DIRTY | UPL_COMMIT_INACTIVATE | UPL_COMMIT_FREE_ON_EMPTY);
                        continue;
issue_io:
                        /*
                         * in order to maintain some semblance of coherency with mapped writes
                         * we need to write the cluster back out as a multiple of the PAGESIZE
                         * unless the cluster encompasses the last page of the file... in this
                         * case we'll round out to the nearest device block boundary
                         */
                        io_size = upl_size;

                        if ((upl_f_offset + io_size) > newEOF) {
                                io_size = newEOF - upl_f_offset;
                                io_size = (io_size + (devblocksize - 1)) & ~(devblocksize - 1);
                        }

                        if (flags & IO_SYNC)
                                io_flags = CL_THROTTLE | CL_COMMIT | CL_AGE;
                        else
                                io_flags = CL_THROTTLE | CL_COMMIT | CL_AGE | CL_ASYNC;

                        if (vp->v_flag & VNOCACHE_DATA)
                                io_flags |= CL_DUMP;

                        retval = cluster_io(vp, upl, 0, upl_f_offset, io_size, devblocksize,
                                            io_flags, (struct buf *)0, (struct clios *)0);
                }
        }
        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 40)) | DBG_FUNC_END,
                     retval, 0, uio_resid, 0, 0);

        return (retval);
}

int
cluster_read(vp, uio, filesize, devblocksize, flags)
        struct vnode *vp;
        struct uio   *uio;
        off_t         filesize;
        int           devblocksize;
        int           flags;
{
        int           prev_resid;
        int           clip_size;
        off_t         max_io_size;
        struct iovec  *iov;
        int           upl_size;
        int           upl_flags;
        upl_t         upl;
        int           retval = 0;


        if (!((vp->v_flag & VNOCACHE_DATA) && (uio->uio_segflg == UIO_USERSPACE)))
          {
            /*
             * go do a read through the cache if one of the following is true....
             *   NOCACHE is not true
             *   the uio request doesn't target USERSPACE
             */
            return (cluster_read_x(vp, uio, filesize, devblocksize, flags));
          }

        while (uio->uio_resid && uio->uio_offset < filesize && retval == 0)
          {
            /*
             * we know we have a resid, so this is safe
             * skip over any emtpy vectors
             */
            iov = uio->uio_iov;

            while (iov->iov_len == 0) {
              uio->uio_iov++;
              uio->uio_iovcnt--;
              iov = uio->uio_iov;
            }
            upl_size  = PAGE_SIZE;
            upl_flags = UPL_QUERY_OBJECT_TYPE;
  
            if ((vm_map_get_upl(current_map(),
                               (vm_offset_t)iov->iov_base & ~PAGE_MASK,
                               &upl_size, &upl, NULL, NULL, &upl_flags, 0)) != KERN_SUCCESS)
              {
                /*
                 * the user app must have passed in an invalid address
                 */
                return (EFAULT);
              }

            /*
             * We check every vector target but if it is physically 
             * contiguous space, we skip the sanity checks.
             */
            if (upl_flags & UPL_PHYS_CONTIG)
              {
                retval = cluster_phys_read(vp, uio, filesize, devblocksize, flags);
              }
            else if (uio->uio_resid < PAGE_SIZE)
              {
                /*
                 * we're here because we're don't have a physically contiguous target buffer
                 * go do a read through the cache if
                 *   the total xfer size is less than a page...
                 */
                return (cluster_read_x(vp, uio, filesize, devblocksize, flags));
              }
            else if (((int)uio->uio_offset & PAGE_MASK) || ((int)iov->iov_base & PAGE_MASK))
              {
                if (((int)uio->uio_offset & PAGE_MASK) == ((int)iov->iov_base & PAGE_MASK))
                  {
                    /*
                     * Bring the file offset read up to a pagesize boundary
                     * this will also bring the base address to a page boundary
                     * since they both are currently on the same offset within a page
                     * note: if we get here, uio->uio_resid is greater than PAGE_SIZE
                     * so the computed clip_size must always be less than the current uio_resid
                     */
                    clip_size = (PAGE_SIZE - (int)(uio->uio_offset & PAGE_MASK_64));

                    /* 
                     * Fake the resid going into the cluster_read_x call
                     * and restore it on the way out.
                     */
                    prev_resid = uio->uio_resid;
                    uio->uio_resid = clip_size;
                    retval = cluster_read_x(vp, uio, filesize, devblocksize, flags);
                    uio->uio_resid = prev_resid - (clip_size - uio->uio_resid);
                  }
                else
                  {
                    /*
                     * can't get both the file offset and the buffer offset aligned to a page boundary
                     * so fire an I/O through the cache for this entire vector
                     */
                    clip_size = iov->iov_len;
                    prev_resid = uio->uio_resid;
                    uio->uio_resid = clip_size;
                    retval = cluster_read_x(vp, uio, filesize, devblocksize, flags);
                    uio->uio_resid = prev_resid - (clip_size - uio->uio_resid);
                  }
              }
            else
              {
                /* 
                 * If we come in here, we know the offset into
                 * the file is on a pagesize boundary
                 */

                max_io_size = filesize - uio->uio_offset;
                clip_size = uio->uio_resid;
                if (iov->iov_len < clip_size)
                  clip_size = iov->iov_len;
                if (max_io_size < clip_size)
                  clip_size = (int)max_io_size;

                if (clip_size < PAGE_SIZE)
                  {
                    /*
                     * Take care of the tail end of the read in this vector.
                     */
                    prev_resid = uio->uio_resid;
                    uio->uio_resid = clip_size;
                    retval = cluster_read_x(vp, uio, filesize, devblocksize, flags);
                    uio->uio_resid = prev_resid - (clip_size - uio->uio_resid);
                  }
                else
                  {
                    /* round clip_size down to a multiple of pagesize */
                    clip_size = clip_size & ~(PAGE_MASK);
                    prev_resid = uio->uio_resid;
                    uio->uio_resid = clip_size;
                    retval = cluster_nocopy_read(vp, uio, filesize, devblocksize, flags);
                    if ((retval==0) && uio->uio_resid)
                      retval = cluster_read_x(vp, uio, filesize, devblocksize, flags);
                    uio->uio_resid = prev_resid - (clip_size - uio->uio_resid);
                  }
              } /* end else */
          } /* end while */

        return(retval);
}

static int
cluster_read_x(vp, uio, filesize, devblocksize, flags)
        struct vnode *vp;
        struct uio   *uio;
        off_t         filesize;
        int           devblocksize;
        int           flags;
{
        upl_page_info_t *pl;
        upl_t            upl;
        vm_offset_t      upl_offset;
        int              upl_size;
        off_t            upl_f_offset;
        int              start_offset;
        int              start_pg;
        int              last_pg;
        int              uio_last;
        int              pages_in_upl;
        off_t            max_size;
        off_t            last_ioread_offset;
        off_t            last_request_offset;
        u_int            size_of_prefetch;
        int              io_size;
        kern_return_t    kret;
        int              error  = 0;
        int              retval = 0;
        u_int            b_lblkno;
        u_int            e_lblkno;
        struct clios     iostate;
        u_int            max_rd_size = MAX_UPL_TRANSFER * PAGE_SIZE;
        u_int            rd_ahead_enabled = 1;
        u_int            prefetch_enabled = 1;


        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 32)) | DBG_FUNC_START,
                     (int)uio->uio_offset, uio->uio_resid, (int)filesize, devblocksize, 0);

        if (cluster_hard_throttle_on(vp)) {
                rd_ahead_enabled = 0;
                prefetch_enabled = 0;

                max_rd_size = HARD_THROTTLE_MAXSIZE;
        }
        if (vp->v_flag & (VRAOFF|VNOCACHE_DATA))
                rd_ahead_enabled = 0;

        last_request_offset = uio->uio_offset + uio->uio_resid;

        if (last_request_offset > filesize)
                last_request_offset = filesize;
        b_lblkno = (u_int)(uio->uio_offset / PAGE_SIZE_64);
        e_lblkno = (u_int)((last_request_offset - 1) / PAGE_SIZE_64);

        if (vp->v_ralen && (vp->v_lastr == b_lblkno || (vp->v_lastr + 1) == b_lblkno)) {
                /*
                 * determine if we already have a read-ahead in the pipe courtesy of the
                 * last read systemcall that was issued...
                 * if so, pick up it's extent to determine where we should start
                 * with respect to any read-ahead that might be necessary to 
                 * garner all the data needed to complete this read systemcall
                 */
                last_ioread_offset = (vp->v_maxra * PAGE_SIZE_64) + PAGE_SIZE_64;

                if (last_ioread_offset < uio->uio_offset)
                        last_ioread_offset = (off_t)0;
                else if (last_ioread_offset > last_request_offset)
                        last_ioread_offset = last_request_offset;
        } else
                last_ioread_offset = (off_t)0;

        while (uio->uio_resid && uio->uio_offset < filesize && retval == 0) {
                /*
                 * compute the size of the upl needed to encompass
                 * the requested read... limit each call to cluster_io
                 * to the maximum UPL size... cluster_io will clip if
                 * this exceeds the maximum io_size for the device,
                 * make sure to account for 
                 * a starting offset that's not page aligned
                 */
                start_offset = (int)(uio->uio_offset & PAGE_MASK_64);
                upl_f_offset = uio->uio_offset - (off_t)start_offset;
                max_size     = filesize - uio->uio_offset;

                if ((off_t)((unsigned int)uio->uio_resid) < max_size)
                        io_size = uio->uio_resid;
                else
                        io_size = max_size;

                if (!(vp->v_flag & VNOCACHE_DATA)) {

                        while (io_size) {
                                u_int io_resid;
                                u_int io_requested;

                                /*
                                 * if we keep finding the pages we need already in the cache, then
                                 * don't bother to call cluster_rd_prefetch since it costs CPU cycles
                                 * to determine that we have all the pages we need... once we miss in
                                 * the cache and have issued an I/O, than we'll assume that we're likely
                                 * to continue to miss in the cache and it's to our advantage to try and prefetch
                                 */
                                if (last_request_offset && last_ioread_offset && (size_of_prefetch = (last_request_offset - last_ioread_offset))) {
                                        if ((last_ioread_offset - uio->uio_offset) <= max_rd_size && prefetch_enabled) {
                                                /*
                                                 * we've already issued I/O for this request and
                                                 * there's still work to do and
                                                 * our prefetch stream is running dry, so issue a
                                                 * pre-fetch I/O... the I/O latency will overlap
                                                 * with the copying of the data
                                                 */
                                                if (size_of_prefetch > max_rd_size)
                                                        size_of_prefetch = max_rd_size;

                                                size_of_prefetch = cluster_rd_prefetch(vp, last_ioread_offset, size_of_prefetch, filesize, devblocksize);

                                                last_ioread_offset += (off_t)(size_of_prefetch * PAGE_SIZE);
                                
                                                if (last_ioread_offset > last_request_offset)
                                                        last_ioread_offset = last_request_offset;
                                        }
                                }
                                /*
                                 * limit the size of the copy we're about to do so that 
                                 * we can notice that our I/O pipe is running dry and 
                                 * get the next I/O issued before it does go dry
                                 */
                                if (last_ioread_offset && io_size > ((MAX_UPL_TRANSFER * PAGE_SIZE) / 4))
                                        io_resid = ((MAX_UPL_TRANSFER * PAGE_SIZE) / 4);
                                else
                                        io_resid = io_size;

                                io_requested = io_resid;

                                retval = cluster_copy_ubc_data(vp, uio, &io_resid, 0);

                                io_size -= (io_requested - io_resid);

                                if (retval || io_resid)
                                        /*
                                         * if we run into a real error or
                                         * a page that is not in the cache
                                         * we need to leave streaming mode
                                         */
                                        break;
                                
                                if ((io_size == 0 || last_ioread_offset == last_request_offset) && rd_ahead_enabled) {
                                        /*
                                         * we're already finished the I/O for this read request
                                         * let's see if we should do a read-ahead
                                         */
                                        cluster_rd_ahead(vp, b_lblkno, e_lblkno, filesize, devblocksize);
                                }
                        }
                        if (retval)
                                break;
                        if (io_size == 0) {
                                if (e_lblkno < vp->v_lastr)
                                        vp->v_maxra = 0;
                                vp->v_lastr = e_lblkno;

                                break;
                        }
                        start_offset = (int)(uio->uio_offset & PAGE_MASK_64);
                        upl_f_offset = uio->uio_offset - (off_t)start_offset;
                        max_size     = filesize - uio->uio_offset;
                }
                if (io_size > max_rd_size)
                        io_size = max_rd_size;

                upl_size = (start_offset + io_size + (PAGE_SIZE - 1)) & ~PAGE_MASK;

                if (upl_size > (MAX_UPL_TRANSFER * PAGE_SIZE) / 4)
                        upl_size = (MAX_UPL_TRANSFER * PAGE_SIZE) / 4;
                pages_in_upl = upl_size / PAGE_SIZE;

                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 33)) | DBG_FUNC_START,
                             (int)upl, (int)upl_f_offset, upl_size, start_offset, 0);

                kret = ubc_create_upl(vp, 
                                                upl_f_offset,
                                                upl_size,
                                                &upl,
                                                &pl,
                                                UPL_SET_LITE);
                if (kret != KERN_SUCCESS)
                        panic("cluster_read: failed to get pagelist");

                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 33)) | DBG_FUNC_END,
                             (int)upl, (int)upl_f_offset, upl_size, start_offset, 0);

                /*
                 * scan from the beginning of the upl looking for the first
                 * non-valid page.... this will become the first page in
                 * the request we're going to make to 'cluster_io'... if all
                 * of the pages are valid, we won't call through to 'cluster_io'
                 */
                for (start_pg = 0; start_pg < pages_in_upl; start_pg++) {
                        if (!upl_valid_page(pl, start_pg))
                                break;
                }

                /*
                 * scan from the starting invalid page looking for a valid
                 * page before the end of the upl is reached, if we 
                 * find one, then it will be the last page of the request to
                 * 'cluster_io'
                 */
                for (last_pg = start_pg; last_pg < pages_in_upl; last_pg++) {
                        if (upl_valid_page(pl, last_pg))
                                break;
                }
                iostate.io_completed = 0;
                iostate.io_issued = 0;
                iostate.io_error = 0;
                iostate.io_wanted = 0;

                if (start_pg < last_pg) {               
                        /*
                         * we found a range of 'invalid' pages that must be filled
                         * if the last page in this range is the last page of the file
                         * we may have to clip the size of it to keep from reading past
                         * the end of the last physical block associated with the file
                         */
                        upl_offset = start_pg * PAGE_SIZE;
                        io_size    = (last_pg - start_pg) * PAGE_SIZE;

                        if ((upl_f_offset + upl_offset + io_size) > filesize)
                                io_size = filesize - (upl_f_offset + upl_offset);

                        /*
                         * issue an asynchronous read to cluster_io
                         */

                        error = cluster_io(vp, upl, upl_offset, upl_f_offset + upl_offset,
                                           io_size, devblocksize, CL_READ | CL_ASYNC, (struct buf *)0, &iostate);
                }
                if (error == 0) {
                        /*
                         * if the read completed successfully, or there was no I/O request
                         * issued, than copy the data into user land via 'cluster_upl_copy_data'
                         * we'll first add on any 'valid'
                         * pages that were present in the upl when we acquired it.
                         */
                        u_int  val_size;

                        for (uio_last = last_pg; uio_last < pages_in_upl; uio_last++) {
                                if (!upl_valid_page(pl, uio_last))
                                        break;
                        }
                        /*
                         * compute size to transfer this round,  if uio->uio_resid is
                         * still non-zero after this attempt, we'll loop around and
                         * set up for another I/O.
                         */
                        val_size = (uio_last * PAGE_SIZE) - start_offset;
                
                        if (val_size > max_size)
                                val_size = max_size;

                        if (val_size > uio->uio_resid)
                                val_size = uio->uio_resid;

                        if (last_ioread_offset == 0)
                                last_ioread_offset = uio->uio_offset + val_size;

                        if ((size_of_prefetch = (last_request_offset - last_ioread_offset)) && prefetch_enabled) {
                                /*
                                 * if there's still I/O left to do for this request, and...
                                 * we're not in hard throttle mode, then issue a
                                 * pre-fetch I/O... the I/O latency will overlap
                                 * with the copying of the data
                                 */
                                size_of_prefetch = cluster_rd_prefetch(vp, last_ioread_offset, size_of_prefetch, filesize, devblocksize);

                                last_ioread_offset += (off_t)(size_of_prefetch * PAGE_SIZE);
                                
                                if (last_ioread_offset > last_request_offset)
                                        last_ioread_offset = last_request_offset;

                        } else if ((uio->uio_offset + val_size) == last_request_offset) {
                                /*
                                 * this transfer will finish this request, so...
                                 * let's try to read ahead if we're in 
                                 * a sequential access pattern and we haven't
                                 * explicitly disabled it
                                 */
                                if (rd_ahead_enabled)
                                        cluster_rd_ahead(vp, b_lblkno, e_lblkno, filesize, devblocksize);

                                if (e_lblkno < vp->v_lastr)
                                        vp->v_maxra = 0;
                                vp->v_lastr = e_lblkno;
                        }
                        while (iostate.io_issued != iostate.io_completed) {
                                iostate.io_wanted = 1;
                                tsleep((caddr_t)&iostate.io_wanted, PRIBIO + 1, "cluster_read_x", 0);
                        }       
                        if (iostate.io_error)
                                error = iostate.io_error;
                        else
                                retval = cluster_copy_upl_data(uio, upl, start_offset, val_size);
                }
                if (start_pg < last_pg) {
                        /*
                         * compute the range of pages that we actually issued an I/O for
                         * and either commit them as valid if the I/O succeeded
                         * or abort them if the I/O failed
                         */
                        io_size = (last_pg - start_pg) * PAGE_SIZE;

                        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 35)) | DBG_FUNC_START,
                                     (int)upl, start_pg * PAGE_SIZE, io_size, error, 0);

                        if (error || (vp->v_flag & VNOCACHE_DATA))
                                ubc_upl_abort_range(upl, start_pg * PAGE_SIZE, io_size,
                                                UPL_ABORT_DUMP_PAGES | UPL_ABORT_FREE_ON_EMPTY);
                        else
                                ubc_upl_commit_range(upl, start_pg * PAGE_SIZE, io_size, 
                                                     UPL_COMMIT_CLEAR_DIRTY |
                                                     UPL_COMMIT_FREE_ON_EMPTY | 
                                                     UPL_COMMIT_INACTIVATE);

                        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 35)) | DBG_FUNC_END,
                                     (int)upl, start_pg * PAGE_SIZE, io_size, error, 0);
                }
                if ((last_pg - start_pg) < pages_in_upl) {
                        int cur_pg;
                        int commit_flags;

                        /*
                         * the set of pages that we issued an I/O for did not encompass
                         * the entire upl... so just release these without modifying
                         * their state
                         */
                        if (error)
                                ubc_upl_abort_range(upl, 0, upl_size, UPL_ABORT_FREE_ON_EMPTY);
                        else {
                                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 35)) | DBG_FUNC_START,
                                             (int)upl, -1, pages_in_upl - (last_pg - start_pg), 0, 0);

                                if (start_pg) {
                                        /*
                                         * we found some already valid pages at the beginning of
                                         * the upl commit these back to the inactive list with
                                         * reference cleared
                                         */
                                        for (cur_pg = 0; cur_pg < start_pg; cur_pg++) {
                                                commit_flags = UPL_COMMIT_FREE_ON_EMPTY 
                                                                   | UPL_COMMIT_INACTIVATE;
                                                
                                                if (upl_dirty_page(pl, cur_pg))
                                                        commit_flags |= UPL_COMMIT_SET_DIRTY;
                                                
                                                if ( !(commit_flags & UPL_COMMIT_SET_DIRTY) && (vp->v_flag & VNOCACHE_DATA))
                                                        ubc_upl_abort_range(upl, cur_pg * PAGE_SIZE, PAGE_SIZE,
                                                                UPL_ABORT_DUMP_PAGES | UPL_ABORT_FREE_ON_EMPTY);
                                                else
                                                        ubc_upl_commit_range(upl, cur_pg * PAGE_SIZE, 
                                                                PAGE_SIZE, commit_flags);
                                        }
                                }
                                if (last_pg < uio_last) {
                                        /*
                                         * we found some already valid pages immediately after the
                                         * pages we issued I/O for, commit these back to the
                                         * inactive list with reference cleared
                                         */
                                        for (cur_pg = last_pg; cur_pg < uio_last; cur_pg++) {
                                                commit_flags =  UPL_COMMIT_FREE_ON_EMPTY 
                                                                                | UPL_COMMIT_INACTIVATE;

                                                if (upl_dirty_page(pl, cur_pg))
                                                        commit_flags |= UPL_COMMIT_SET_DIRTY;
                                                
                                                if ( !(commit_flags & UPL_COMMIT_SET_DIRTY) && (vp->v_flag & VNOCACHE_DATA))
                                                        ubc_upl_abort_range(upl, cur_pg * PAGE_SIZE, PAGE_SIZE,
                                                                UPL_ABORT_DUMP_PAGES | UPL_ABORT_FREE_ON_EMPTY);
                                                else
                                                        ubc_upl_commit_range(upl, cur_pg * PAGE_SIZE, 
                                                                PAGE_SIZE, commit_flags);
                                        }
                                }
                                if (uio_last < pages_in_upl) {
                                        /*
                                         * there were some invalid pages beyond the valid pages
                                         * that we didn't issue an I/O for, just release them
                                         * unchanged
                                         */
                                        ubc_upl_abort_range(upl, uio_last * PAGE_SIZE,
                                                            (pages_in_upl - uio_last) * PAGE_SIZE, UPL_ABORT_FREE_ON_EMPTY);
                                }

                                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 35)) | DBG_FUNC_END,
                                        (int)upl, -1, -1, 0, 0);
                        }
                }
                if (retval == 0)
                        retval = error;
        }
        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 32)) | DBG_FUNC_END,
                     (int)uio->uio_offset, uio->uio_resid, vp->v_lastr, retval, 0);

        return (retval);
}


static int
cluster_nocopy_read(vp, uio, filesize, devblocksize, flags)
        struct vnode *vp;
        struct uio   *uio;
        off_t         filesize;
        int           devblocksize;
        int           flags;
{
        upl_t            upl;
        upl_page_info_t  *pl;
        vm_offset_t      upl_offset;
        off_t            max_io_size;
        int              io_size;
        int              upl_size;
        int              upl_needed_size;
        int              pages_in_pl;
        int              upl_flags;
        kern_return_t    kret;
        struct iovec     *iov;
        int              i;
        int              force_data_sync;
        int              retval = 0;
        struct clios     iostate;
        u_int            max_rd_size  = MAX_UPL_TRANSFER * PAGE_SIZE;
        u_int            max_rd_ahead = MAX_UPL_TRANSFER * PAGE_SIZE * 2;


        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 70)) | DBG_FUNC_START,
                     (int)uio->uio_offset, uio->uio_resid, (int)filesize, devblocksize, 0);

        /*
         * When we enter this routine, we know
         *  -- the offset into the file is on a pagesize boundary
         *  -- the resid is a page multiple
         *  -- the resid will not exceed iov_len
         */

        iostate.io_completed = 0;
        iostate.io_issued = 0;
        iostate.io_error = 0;
        iostate.io_wanted = 0;

        iov = uio->uio_iov;

        if (cluster_hard_throttle_on(vp)) {
                max_rd_size  = HARD_THROTTLE_MAXSIZE;
                max_rd_ahead = HARD_THROTTLE_MAXSIZE - 1;
        }
        while (uio->uio_resid && uio->uio_offset < filesize && retval == 0) {

                max_io_size = filesize - uio->uio_offset;

                if (max_io_size < (off_t)((unsigned int)uio->uio_resid))
                        io_size = max_io_size;
                else
                        io_size = uio->uio_resid;

                /*
                 * First look for pages already in the cache
                 * and move them to user space.
                 */
                retval = cluster_copy_ubc_data(vp, uio, &io_size, 0);
                        
                if (retval) {
                        /*
                         * we may have already spun some portion of this request
                         * off as async requests... we need to wait for the I/O
                         * to complete before returning
                         */
                        goto wait_for_reads;
                }
                /*
                 * If we are already finished with this read, then return
                 */
                if (io_size == 0) {
                        /*
                         * we may have already spun some portion of this request
                         * off as async requests... we need to wait for the I/O
                         * to complete before returning
                         */
                        goto wait_for_reads;
                }
                max_io_size = io_size;

                if (max_io_size > max_rd_size)
                        max_io_size = max_rd_size;

                io_size = 0;

                ubc_range_op(vp, uio->uio_offset, uio->uio_offset + max_io_size, UPL_ROP_ABSENT, &io_size);

                if (io_size == 0)
                        /*
                         * we may have already spun some portion of this request
                         * off as async requests... we need to wait for the I/O
                         * to complete before returning
                         */
                        goto wait_for_reads;

                upl_offset = (vm_offset_t)iov->iov_base & PAGE_MASK;
                upl_needed_size = (upl_offset + io_size + (PAGE_SIZE -1)) & ~PAGE_MASK;

                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 72)) | DBG_FUNC_START,
                             (int)upl_offset, upl_needed_size, (int)iov->iov_base, io_size, 0);

                for (force_data_sync = 0; force_data_sync < 3; force_data_sync++) {
                        pages_in_pl = 0;
                        upl_size = upl_needed_size;
                        upl_flags = UPL_FILE_IO | UPL_NO_SYNC | UPL_SET_INTERNAL | UPL_SET_LITE | UPL_SET_IO_WIRE;

                        kret = vm_map_get_upl(current_map(),
                                              (vm_offset_t)iov->iov_base & ~PAGE_MASK,
                                              &upl_size, &upl, NULL, &pages_in_pl, &upl_flags, force_data_sync);

                        if (kret != KERN_SUCCESS) {
                                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 72)) | DBG_FUNC_END,
                                             (int)upl_offset, upl_size, io_size, kret, 0);
                                /*
                                 * cluster_nocopy_read: failed to get pagelist
                                 *
                                 * we may have already spun some portion of this request
                                 * off as async requests... we need to wait for the I/O
                                 * to complete before returning
                                 */
                                goto wait_for_reads;
                        }
                        pages_in_pl = upl_size / PAGE_SIZE;
                        pl = UPL_GET_INTERNAL_PAGE_LIST(upl);

                        for (i = 0; i < pages_in_pl; i++) {
                                if (!upl_valid_page(pl, i))
                                        break;            
                        }
                        if (i == pages_in_pl)
                                break;

                        ubc_upl_abort_range(upl, (upl_offset & ~PAGE_MASK), upl_size, 
                                            UPL_ABORT_FREE_ON_EMPTY);
                }
                if (force_data_sync >= 3) {
                        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 72)) | DBG_FUNC_END,
                                     (int)upl_offset, upl_size, io_size, kret, 0);
                  
                        goto wait_for_reads;
                }
                /*
                 * Consider the possibility that upl_size wasn't satisfied.
                 */
                if (upl_size != upl_needed_size)
                        io_size = (upl_size - (int)upl_offset) & ~PAGE_MASK;

                if (io_size == 0) {
                        ubc_upl_abort_range(upl, (upl_offset & ~PAGE_MASK), upl_size, 
                                            UPL_ABORT_FREE_ON_EMPTY);
                        goto wait_for_reads;
                }
                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 72)) | DBG_FUNC_END,
                             (int)upl_offset, upl_size, io_size, kret, 0);

                /*
                 * request asynchronously so that we can overlap
                 * the preparation of the next I/O
                 * if there are already too many outstanding reads
                 * wait until some have completed before issuing the next read
                 */
                while ((iostate.io_issued - iostate.io_completed) > max_rd_ahead) {
                        iostate.io_wanted = 1;
                        tsleep((caddr_t)&iostate.io_wanted, PRIBIO + 1, "cluster_nocopy_read", 0);
                }       
                if (iostate.io_error) {
                        /*
                         * one of the earlier reads we issued ran into a hard error
                         * don't issue any more reads, cleanup the UPL
                         * that was just created but not used, then
                         * go wait for any other reads to complete before
                         * returning the error to the caller
                         */
                        ubc_upl_abort_range(upl, (upl_offset & ~PAGE_MASK), upl_size, 
                                            UPL_ABORT_FREE_ON_EMPTY);

                        goto wait_for_reads;
                }
                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 73)) | DBG_FUNC_START,
                             (int)upl, (int)upl_offset, (int)uio->uio_offset, io_size, 0);

                retval = cluster_io(vp, upl, upl_offset, uio->uio_offset,
                                   io_size, devblocksize,
                                   CL_PRESERVE | CL_COMMIT | CL_READ | CL_ASYNC | CL_NOZERO,
                                   (struct buf *)0, &iostate);

                /*
                 * update the uio structure
                 */
                iov->iov_base   += io_size;
                iov->iov_len    -= io_size;
                uio->uio_resid  -= io_size;
                uio->uio_offset += io_size;

                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 73)) | DBG_FUNC_END,
                             (int)upl, (int)uio->uio_offset, (int)uio->uio_resid, retval, 0);

        } /* end while */

wait_for_reads:
        /*
         * make sure all async reads that are part of this stream
         * have completed before we return
         */
        while (iostate.io_issued != iostate.io_completed) {
                iostate.io_wanted = 1;
                tsleep((caddr_t)&iostate.io_wanted, PRIBIO + 1, "cluster_nocopy_read", 0);
        }       
        if (iostate.io_error)
                retval = iostate.io_error;

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 70)) | DBG_FUNC_END,
                     (int)uio->uio_offset, (int)uio->uio_resid, 6, retval, 0);

        return (retval);
}


static int
cluster_phys_read(vp, uio, filesize, devblocksize, flags)
        struct vnode *vp;
        struct uio   *uio;
        off_t        filesize;
        int          devblocksize;
        int          flags;
{
        upl_page_info_t *pl;
        upl_t            upl;
        vm_offset_t      upl_offset;
        addr64_t         dst_paddr;
        off_t            max_size;
        int              io_size;
        int              tail_size;
        int              upl_size;
        int              upl_needed_size;
        int              pages_in_pl;
        int              upl_flags;
        kern_return_t    kret;
        struct iovec     *iov;
        struct clios     iostate;
        int              error;

        /*
         * When we enter this routine, we know
         *  -- the resid will not exceed iov_len
         *  -- the target address is physically contiguous
         */

        iov = uio->uio_iov;

        max_size = filesize - uio->uio_offset;

        if (max_size > (off_t)((unsigned int)iov->iov_len))
                io_size = iov->iov_len;
        else
                io_size = max_size;

        upl_offset = (vm_offset_t)iov->iov_base & PAGE_MASK;
        upl_needed_size = upl_offset + io_size;

        error       = 0;
        pages_in_pl = 0;
        upl_size = upl_needed_size;
        upl_flags = UPL_FILE_IO | UPL_NO_SYNC | UPL_CLEAN_IN_PLACE | UPL_SET_INTERNAL | UPL_SET_LITE | UPL_SET_IO_WIRE;

        kret = vm_map_get_upl(current_map(),
                              (vm_offset_t)iov->iov_base & ~PAGE_MASK,
                              &upl_size, &upl, NULL, &pages_in_pl, &upl_flags, 0);

        if (kret != KERN_SUCCESS) {
                /*
                 * cluster_phys_read: failed to get pagelist
                 */
                return(EINVAL);
        }
        if (upl_size < upl_needed_size) {
                /*
                 * The upl_size wasn't satisfied.
                 */
                ubc_upl_abort_range(upl, 0, upl_size, UPL_ABORT_FREE_ON_EMPTY);

                return(EINVAL);
        }
        pl = ubc_upl_pageinfo(upl);

        dst_paddr = ((addr64_t)upl_phys_page(pl, 0) << 12) + ((addr64_t)((u_int)iov->iov_base & PAGE_MASK));

        while (((uio->uio_offset & (devblocksize - 1)) || io_size < devblocksize) && io_size) {
                int   head_size;

                head_size = devblocksize - (int)(uio->uio_offset & (devblocksize - 1));

                if (head_size > io_size)
                        head_size = io_size;

                error = cluster_align_phys_io(vp, uio, dst_paddr, head_size, devblocksize, CL_READ);

                if (error) {
                        ubc_upl_abort_range(upl, 0, upl_size, UPL_ABORT_FREE_ON_EMPTY);

                        return(EINVAL);
                }
                upl_offset += head_size;
                dst_paddr  += head_size;
                io_size    -= head_size;
        }
        tail_size = io_size & (devblocksize - 1);
        io_size  -= tail_size;

        iostate.io_completed = 0;
        iostate.io_issued = 0;
        iostate.io_error = 0;
        iostate.io_wanted = 0;

        while (io_size && error == 0) {
                int  xsize;

                if (io_size > (MAX_UPL_TRANSFER * PAGE_SIZE))
                        xsize = MAX_UPL_TRANSFER * PAGE_SIZE;
                else
                        xsize = io_size;
                /*
                 * request asynchronously so that we can overlap
                 * the preparation of the next I/O... we'll do
                 * the commit after all the I/O has completed
                 * since its all issued against the same UPL
                 * if there are already too many outstanding reads
                 * wait until some have completed before issuing the next
                 */
                while ((iostate.io_issued - iostate.io_completed) > (2 * MAX_UPL_TRANSFER * PAGE_SIZE)) {
                        iostate.io_wanted = 1;
                        tsleep((caddr_t)&iostate.io_wanted, PRIBIO + 1, "cluster_phys_read", 0);
                }       

                error = cluster_io(vp, upl, upl_offset, uio->uio_offset, xsize, 0, 
                                   CL_READ | CL_NOZERO | CL_DEV_MEMORY | CL_ASYNC,
                                   (struct buf *)0, &iostate);
                /*
                 * The cluster_io read was issued successfully,
                 * update the uio structure
                 */
                if (error == 0) {
                        uio->uio_resid  -= xsize;
                        iov->iov_len    -= xsize;
                        iov->iov_base   += xsize;
                        uio->uio_offset += xsize;
                        dst_paddr       += xsize;
                        upl_offset      += xsize;
                        io_size         -= xsize;
                }
        }
        /*
         * make sure all async reads that are part of this stream
         * have completed before we proceed
         */
        while (iostate.io_issued != iostate.io_completed) {
                iostate.io_wanted = 1;
                tsleep((caddr_t)&iostate.io_wanted, PRIBIO + 1, "cluster_phys_read", 0);
        }       
        if (iostate.io_error) {
                error = iostate.io_error;
        }
        if (error == 0 && tail_size)
                error = cluster_align_phys_io(vp, uio, dst_paddr, tail_size, devblocksize, CL_READ);

        /*
         * just release our hold on the physically contiguous
         * region without changing any state
         */
        ubc_upl_abort_range(upl, 0, upl_size, UPL_ABORT_FREE_ON_EMPTY);
        
        return (error);
}


/*
 * generate advisory I/O's in the largest chunks possible
 * the completed pages will be released into the VM cache
 */
int
advisory_read(vp, filesize, f_offset, resid, devblocksize)
        struct vnode *vp;
        off_t         filesize;
        off_t         f_offset;
        int           resid;
        int           devblocksize;
{
        upl_page_info_t *pl;
        upl_t            upl;
        vm_offset_t      upl_offset;
        int              upl_size;
        off_t            upl_f_offset;
        int              start_offset;
        int              start_pg;
        int              last_pg;
        int              pages_in_upl;
        off_t            max_size;
        int              io_size;
        kern_return_t    kret;
        int              retval = 0;
        int              issued_io;
        int              skip_range;

        if (!UBCINFOEXISTS(vp))
                return(EINVAL);

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 60)) | DBG_FUNC_START,
                     (int)f_offset, resid, (int)filesize, devblocksize, 0);

        while (resid && f_offset < filesize && retval == 0) {
                /*
                 * compute the size of the upl needed to encompass
                 * the requested read... limit each call to cluster_io
                 * to the maximum UPL size... cluster_io will clip if
                 * this exceeds the maximum io_size for the device,
                 * make sure to account for 
                 * a starting offset that's not page aligned
                 */
                start_offset = (int)(f_offset & PAGE_MASK_64);
                upl_f_offset = f_offset - (off_t)start_offset;
                max_size     = filesize - f_offset;

                if (resid < max_size)
                        io_size = resid;
                else
                        io_size = max_size;

                upl_size = (start_offset + io_size + (PAGE_SIZE - 1)) & ~PAGE_MASK;
                if (upl_size > (MAX_UPL_TRANSFER * PAGE_SIZE))
                        upl_size = MAX_UPL_TRANSFER * PAGE_SIZE;

                skip_range = 0;
                /*
                 * return the number of contiguously present pages in the cache
                 * starting at upl_f_offset within the file
                 */
                ubc_range_op(vp, upl_f_offset, upl_f_offset + upl_size, UPL_ROP_PRESENT, &skip_range);

                if (skip_range) {
                        /*
                         * skip over pages already present in the cache
                         */
                        io_size = skip_range - start_offset;

                        f_offset += io_size;
                        resid    -= io_size;

                        if (skip_range == upl_size)
                                continue;
                        /*
                         * have to issue some real I/O
                         * at this point, we know it's starting on a page boundary
                         * because we've skipped over at least the first page in the request
                         */
                        start_offset = 0;
                        upl_f_offset += skip_range;
                        upl_size     -= skip_range;
                }
                pages_in_upl = upl_size / PAGE_SIZE;

                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 61)) | DBG_FUNC_START,
                             (int)upl, (int)upl_f_offset, upl_size, start_offset, 0);

                kret = ubc_create_upl(vp, 
                                                upl_f_offset,
                                                upl_size,
                                                &upl,
                                                &pl,
                                                UPL_RET_ONLY_ABSENT | UPL_SET_LITE);
                if (kret != KERN_SUCCESS)
                        return(retval);
                issued_io = 0;

                /*
                 * before we start marching forward, we must make sure we end on 
                 * a present page, otherwise we will be working with a freed
                 * upl
                 */
                for (last_pg = pages_in_upl - 1; last_pg >= 0; last_pg--) {
                        if (upl_page_present(pl, last_pg))
                                break;
                }
                pages_in_upl = last_pg + 1;


                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 61)) | DBG_FUNC_END,
                             (int)upl, (int)upl_f_offset, upl_size, start_offset, 0);


                for (last_pg = 0; last_pg < pages_in_upl; ) {
                        /*
                         * scan from the beginning of the upl looking for the first
                         * page that is present.... this will become the first page in
                         * the request we're going to make to 'cluster_io'... if all
                         * of the pages are absent, we won't call through to 'cluster_io'
                         */
                        for (start_pg = last_pg; start_pg < pages_in_upl; start_pg++) {
                                if (upl_page_present(pl, start_pg))
                                        break;
                        }

                        /*
                         * scan from the starting present page looking for an absent
                         * page before the end of the upl is reached, if we 
                         * find one, then it will terminate the range of pages being
                         * presented to 'cluster_io'
                         */
                        for (last_pg = start_pg; last_pg < pages_in_upl; last_pg++) {
                                if (!upl_page_present(pl, last_pg))
                                        break;
                        }

                        if (last_pg > start_pg) {               
                                /*
                                 * we found a range of pages that must be filled
                                 * if the last page in this range is the last page of the file
                                 * we may have to clip the size of it to keep from reading past
                                 * the end of the last physical block associated with the file
                                 */
                                upl_offset = start_pg * PAGE_SIZE;
                                io_size    = (last_pg - start_pg) * PAGE_SIZE;

                                if ((upl_f_offset + upl_offset + io_size) > filesize)
                                        io_size = filesize - (upl_f_offset + upl_offset);

                                /*
                                 * issue an asynchronous read to cluster_io
                                 */
                                retval = cluster_io(vp, upl, upl_offset, upl_f_offset + upl_offset, io_size, devblocksize,
                                                    CL_ASYNC | CL_READ | CL_COMMIT | CL_AGE, (struct buf *)0, (struct clios *)0);

                                issued_io = 1;
                        }
                }
                if (issued_io == 0)
                        ubc_upl_abort(upl, 0);

                io_size = upl_size - start_offset;
                
                if (io_size > resid)
                        io_size = resid;
                f_offset += io_size;
                resid    -= io_size;
        }

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 60)) | DBG_FUNC_END,
                     (int)f_offset, resid, retval, 0, 0);

        return(retval);
}


int
cluster_push(vp)
        struct vnode *vp;
{
        int  retval;

        if (!UBCINFOEXISTS(vp) || (vp->v_clen == 0 && !(vp->v_flag & VHASDIRTY)))
                return(0);

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 53)) | DBG_FUNC_START,
                     vp->v_flag & VHASDIRTY, vp->v_clen, 0, 0, 0);

        if (vp->v_flag & VHASDIRTY) {
                sparse_cluster_push(vp, ubc_getsize(vp), 1);

                vp->v_clen = 0;
                retval = 1;
        } else 
                retval = cluster_try_push(vp, ubc_getsize(vp), 0, 1);

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 53)) | DBG_FUNC_END,
                     vp->v_flag & VHASDIRTY, vp->v_clen, retval, 0, 0);

        return (retval);
}


int
cluster_release(vp)
        struct vnode *vp;
{
        off_t offset;
        u_int length;

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 81)) | DBG_FUNC_START, (int)vp, (int)vp->v_scmap, vp->v_scdirty, 0, 0);

        if (vp->v_flag & VHASDIRTY) {
                vfs_drt_control(&(vp->v_scmap), 0);

                vp->v_flag &= ~VHASDIRTY;
        }
        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 81)) | DBG_FUNC_END, (int)vp, (int)vp->v_scmap, vp->v_scdirty, 0, 0);
}


static int
cluster_try_push(vp, EOF, can_delay, push_all)
        struct vnode *vp;
        off_t  EOF;
        int    can_delay;
        int    push_all;
{
        int cl_index;
        int cl_index1;
        int min_index;
        int cl_len;
        int cl_total;
        int cl_pushed = 0;
        struct v_cluster l_clusters[MAX_CLUSTERS];

        /*
         * make a local 'sorted' copy of the clusters
         * and clear vp->v_clen so that new clusters can
         * be developed
         */
        for (cl_index = 0; cl_index < vp->v_clen; cl_index++) {
                for (min_index = -1, cl_index1 = 0; cl_index1 < vp->v_clen; cl_index1++) {
                        if (vp->v_clusters[cl_index1].start_pg == vp->v_clusters[cl_index1].last_pg)
                                continue;
                        if (min_index == -1)
                                min_index = cl_index1;
                        else if (vp->v_clusters[cl_index1].start_pg < vp->v_clusters[min_index].start_pg)
                                min_index = cl_index1;
                }
                if (min_index == -1)
                        break;
                l_clusters[cl_index].start_pg = vp->v_clusters[min_index].start_pg;
                l_clusters[cl_index].last_pg  = vp->v_clusters[min_index].last_pg;

                vp->v_clusters[min_index].start_pg = vp->v_clusters[min_index].last_pg;
        }
        cl_len     = cl_index;
        vp->v_clen = 0;

        if (can_delay && cl_len == MAX_CLUSTERS) {
                int   i;
                
                /*
                 * determine if we appear to be writing the file sequentially
                 * if not, by returning without having pushed any clusters
                 * we will cause this vnode to be pushed into the sparse cluster mechanism
                 * used for managing more random I/O patterns
                 *
                 * we know that we've got all clusters currently in use and the next write doesn't fit into one of them...
                 * that's why we're in try_push with can_delay true...
                 *
                 * check to make sure that all the clusters except the last one are 'full'... and that each cluster
                 * is adjacent to the next (i.e. we're looking for sequential writes) they were sorted above
                 * so we can just make a simple pass through up, to but not including the last one...
                 * note that last_pg is not inclusive, so it will be equal to the start_pg of the next cluster if they
                 * are sequential
                 * 
                 * we let the last one be partial as long as it was adjacent to the previous one...
                 * we need to do this to deal with multi-threaded servers that might write an I/O or 2 out
                 * of order... if this occurs at the tail of the last cluster, we don't want to fall into the sparse cluster world...
                 */
                for (i = 0; i < MAX_CLUSTERS - 1; i++) {
                        if ((l_clusters[i].last_pg - l_clusters[i].start_pg) != MAX_UPL_TRANSFER)
                                goto dont_try;
                        if (l_clusters[i].last_pg != l_clusters[i+1].start_pg)
                                goto dont_try;
                }
        }
        for (cl_index = 0; cl_index < cl_len; cl_index++) {
                /*
                 * try to push each cluster in turn...  cluster_push_x may not
                 * push the cluster if can_delay is TRUE and the cluster doesn't
                 * meet the critera for an immediate push
                 */
                if (cluster_push_x(vp, EOF, l_clusters[cl_index].start_pg, l_clusters[cl_index].last_pg, can_delay)) {
                        l_clusters[cl_index].start_pg = 0;
                        l_clusters[cl_index].last_pg  = 0;

                        cl_pushed++;

                        if (push_all == 0)
                                break;
                }
        }
dont_try:
        if (cl_len > cl_pushed) {
               /*
                * we didn't push all of the clusters, so
                * lets try to merge them back in to the vnode
                */
                if ((MAX_CLUSTERS - vp->v_clen) < (cl_len - cl_pushed)) {
                        /*
                         * we picked up some new clusters while we were trying to
                         * push the old ones (I don't think this can happen because
                         * I'm holding the lock, but just in case)... the sum of the
                         * leftovers plus the new cluster count exceeds our ability
                         * to represent them, so switch to the sparse cluster mechanism
                         */

                        /*
                         * first collect the new clusters sitting in the vp
                         */
                        sparse_cluster_switch(vp, EOF);

                        for (cl_index = 0, cl_index1 = 0; cl_index < cl_len; cl_index++) {
                                if (l_clusters[cl_index].start_pg == l_clusters[cl_index].last_pg)
                                        continue;
                                vp->v_clusters[cl_index1].start_pg = l_clusters[cl_index].start_pg;
                                vp->v_clusters[cl_index1].last_pg  = l_clusters[cl_index].last_pg;

                                cl_index1++;
                        }
                        /*
                         * update the cluster count
                         */
                        vp->v_clen = cl_index1;

                        /*
                         * and collect the original clusters that were moved into the 
                         * local storage for sorting purposes
                         */
                        sparse_cluster_switch(vp, EOF);

                } else {
                        /*
                         * we've got room to merge the leftovers back in
                         * just append them starting at the next 'hole'
                         * represented by vp->v_clen
                         */
                        for (cl_index = 0, cl_index1 = vp->v_clen; cl_index < cl_len; cl_index++) {
                                if (l_clusters[cl_index].start_pg == l_clusters[cl_index].last_pg)
                                        continue;

                                vp->v_clusters[cl_index1].start_pg = l_clusters[cl_index].start_pg;
                                vp->v_clusters[cl_index1].last_pg  = l_clusters[cl_index].last_pg;

                                cl_index1++;
                        }
                        /*
                         * update the cluster count
                         */
                        vp->v_clen = cl_index1;
                }
        }
        return(MAX_CLUSTERS - vp->v_clen);
}



static int
cluster_push_x(vp, EOF, first, last, can_delay)
        struct vnode *vp;
        off_t  EOF;
        daddr_t first;
        daddr_t last;
        int    can_delay;
{
        upl_page_info_t *pl;
        upl_t            upl;
        vm_offset_t      upl_offset;
        int              upl_size;
        off_t            upl_f_offset;
        int              pages_in_upl;
        int              start_pg;
        int              last_pg;
        int              io_size;
        int              io_flags;
        int              upl_flags;
        int              size;
        kern_return_t    kret;


        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 51)) | DBG_FUNC_START,
                     vp->v_clen, first, last, EOF, 0);

        if ((pages_in_upl = last - first) == 0) {
                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 51)) | DBG_FUNC_END, 1, 0, 0, 0, 0);

                return (1);
        }
        upl_size = pages_in_upl * PAGE_SIZE;
        upl_f_offset = ((off_t)first) * PAGE_SIZE_64;

        if (upl_f_offset + upl_size >= EOF) {

                if (upl_f_offset >= EOF) {
                        /*
                         * must have truncated the file and missed 
                         * clearing a dangling cluster (i.e. it's completely
                         * beyond the new EOF
                         */
                        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 51)) | DBG_FUNC_END, 1, 1, 0, 0, 0);

                        return(1);
                }
                size = EOF - upl_f_offset;

                upl_size = (size + (PAGE_SIZE - 1)) & ~PAGE_MASK;
                pages_in_upl = upl_size / PAGE_SIZE;
        } else
                size = upl_size;

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 41)) | DBG_FUNC_START, upl_size, size, 0, 0, 0);

        if (vp->v_flag & VNOCACHE_DATA)
                upl_flags = UPL_COPYOUT_FROM | UPL_RET_ONLY_DIRTY | UPL_SET_LITE | UPL_WILL_BE_DUMPED;
        else
                upl_flags = UPL_COPYOUT_FROM | UPL_RET_ONLY_DIRTY | UPL_SET_LITE;

        kret = ubc_create_upl(vp, 
                                upl_f_offset,
                                upl_size,
                                &upl,
                                &pl,
                                upl_flags);
        if (kret != KERN_SUCCESS)
                panic("cluster_push: failed to get pagelist");

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 41)) | DBG_FUNC_END, (int)upl, upl_f_offset, 0, 0, 0);

        /*
         * since we only asked for the dirty pages back
         * it's possible that we may only get a few or even none, so...
         * before we start marching forward, we must make sure we know
         * where the last present page is in the UPL, otherwise we could
         * end up working with a freed upl due to the FREE_ON_EMPTY semantics
         * employed by commit_range and abort_range.
         */
        for (last_pg = pages_in_upl - 1; last_pg >= 0; last_pg--) {
                if (upl_page_present(pl, last_pg))
                        break;
        }
        pages_in_upl = last_pg + 1;

        if (pages_in_upl == 0) {
                ubc_upl_abort(upl, 0);

                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 51)) | DBG_FUNC_END, 1, 2, 0, 0, 0);
                return(1);
        }         

        for (last_pg = 0; last_pg < pages_in_upl; ) {
                /*
                 * find the next dirty page in the UPL
                 * this will become the first page in the 
                 * next I/O to generate
                 */
                for (start_pg = last_pg; start_pg < pages_in_upl; start_pg++) {
                        if (upl_dirty_page(pl, start_pg))
                                break;
                        if (upl_page_present(pl, start_pg))
                                /*
                                 * RET_ONLY_DIRTY will return non-dirty 'precious' pages
                                 * just release these unchanged since we're not going
                                 * to steal them or change their state
                                 */
                                ubc_upl_abort_range(upl, start_pg * PAGE_SIZE, PAGE_SIZE, UPL_ABORT_FREE_ON_EMPTY);
                }
                if (start_pg >= pages_in_upl)
                        /*
                         * done... no more dirty pages to push
                         */
                        break;
                if (start_pg > last_pg)
                        /*
                         * skipped over some non-dirty pages
                         */
                        size -= ((start_pg - last_pg) * PAGE_SIZE);

                /*
                 * find a range of dirty pages to write
                 */
                for (last_pg = start_pg; last_pg < pages_in_upl; last_pg++) {
                        if (!upl_dirty_page(pl, last_pg))
                                break;
                }
                upl_offset = start_pg * PAGE_SIZE;

                io_size = min(size, (last_pg - start_pg) * PAGE_SIZE);

                if (vp->v_flag & VNOCACHE_DATA)
                        io_flags = CL_THROTTLE | CL_COMMIT | CL_ASYNC | CL_DUMP;
                else
                        io_flags = CL_THROTTLE | CL_COMMIT | CL_ASYNC;

                cluster_io(vp, upl, upl_offset, upl_f_offset + upl_offset, io_size, vp->v_ciosiz, io_flags, (struct buf *)0, (struct clios *)0);

                size -= io_size;
        }
        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 51)) | DBG_FUNC_END, 1, 3, 0, 0, 0);

        return(1);
}


static int
sparse_cluster_switch(struct vnode *vp, off_t EOF)
{
        int cl_index;

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 78)) | DBG_FUNC_START, (int)vp, (int)vp->v_scmap, vp->v_scdirty, 0, 0);

        if ( !(vp->v_flag & VHASDIRTY)) {
                vp->v_flag |= VHASDIRTY;
                vp->v_scdirty = 0;
                vp->v_scmap   = 0;
        }
        for (cl_index = 0; cl_index < vp->v_clen; cl_index++) {
                int    flags;
                int    start_pg;
                int    last_pg;

                for (start_pg = vp->v_clusters[cl_index].start_pg; start_pg < vp->v_clusters[cl_index].last_pg; start_pg++) {

                        if (ubc_page_op(vp, (off_t)(((off_t)start_pg) * PAGE_SIZE_64), 0, 0, &flags) == KERN_SUCCESS) {
                                if (flags & UPL_POP_DIRTY)
                                        sparse_cluster_add(vp, EOF, start_pg, start_pg + 1);
                        }
                }
        }
        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 78)) | DBG_FUNC_END, (int)vp, (int)vp->v_scmap, vp->v_scdirty, 0, 0);
}


static int
sparse_cluster_push(struct vnode *vp, off_t EOF, int push_all)
{
        daddr_t first;
        daddr_t last;
        off_t offset;
        u_int length;

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 79)) | DBG_FUNC_START, (int)vp, (int)vp->v_scmap, vp->v_scdirty, push_all, 0);

        if (push_all)
                vfs_drt_control(&(vp->v_scmap), 1);

        for (;;) {
                if (vfs_drt_get_cluster(&(vp->v_scmap), &offset, &length) != KERN_SUCCESS) {
                        vp->v_flag &= ~VHASDIRTY;
                        vp->v_clen = 0;
                        break;
                }
                first = (daddr_t)(offset / PAGE_SIZE_64);
                last  = (daddr_t)((offset + length) / PAGE_SIZE_64);

                cluster_push_x(vp, EOF, first, last, 0);

                vp->v_scdirty -= (last - first);

                if (push_all == 0)
                        break;
        }
        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 79)) | DBG_FUNC_END, (int)vp, (int)vp->v_scmap, vp->v_scdirty, 0, 0);
}


static int
sparse_cluster_add(struct vnode *vp, off_t EOF, daddr_t first, daddr_t last)
{
        u_int new_dirty;
        u_int length;
        off_t offset;

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 80)) | DBG_FUNC_START, (int)vp->v_scmap, vp->v_scdirty, first, last, 0);

        offset = (off_t)first * PAGE_SIZE_64;
        length = (last - first) * PAGE_SIZE;

        while (vfs_drt_mark_pages(&(vp->v_scmap), offset, length, &new_dirty) != KERN_SUCCESS) {
                /*
                 * no room left in the map
                 * only a partial update was done
                 * push out some pages and try again
                 */
                vp->v_scdirty += new_dirty;

                sparse_cluster_push(vp, EOF, 0);

                offset += (new_dirty * PAGE_SIZE_64);
                length -= (new_dirty * PAGE_SIZE);
        }
        vp->v_scdirty += new_dirty;

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 80)) | DBG_FUNC_END, (int)vp, (int)vp->v_scmap, vp->v_scdirty, 0, 0);
}


static int
cluster_align_phys_io(struct vnode *vp, struct uio *uio, addr64_t usr_paddr, int xsize, int devblocksize, int flags)
{
        struct iovec     *iov;
        upl_page_info_t  *pl;
        upl_t            upl;
        addr64_t         ubc_paddr;
        kern_return_t    kret;
        int              error = 0;

        iov = uio->uio_iov;

        kret = ubc_create_upl(vp,
                              uio->uio_offset & ~PAGE_MASK_64,
                              PAGE_SIZE,
                              &upl,
                              &pl,
                              UPL_SET_LITE);

        if (kret != KERN_SUCCESS)
                return(EINVAL);

        if (!upl_valid_page(pl, 0)) {
                /*
                 * issue a synchronous read to cluster_io
                 */
                error = cluster_io(vp, upl, 0, uio->uio_offset & ~PAGE_MASK_64, PAGE_SIZE, devblocksize,
                                   CL_READ, (struct buf *)0, (struct clios *)0);
                if (error) {
                          ubc_upl_abort_range(upl, 0, PAGE_SIZE, UPL_ABORT_DUMP_PAGES | UPL_ABORT_FREE_ON_EMPTY);

                          return(error);
                }
        }
        ubc_paddr = ((addr64_t)upl_phys_page(pl, 0) << 12) + (addr64_t)(uio->uio_offset & PAGE_MASK_64);

/*
 *      NOTE:  There is no prototype for the following in BSD. It, and the definitions
 *      of the defines for cppvPsrc, cppvPsnk, cppvFsnk, and cppvFsrc will be found in
 *      osfmk/ppc/mappings.h.  They are not included here because there appears to be no
 *      way to do so without exporting them to kexts as well.
 */
        if (flags & CL_READ)
//              copypv(ubc_paddr, usr_paddr, xsize, cppvPsrc | cppvPsnk | cppvFsnk);    /* Copy physical to physical and flush the destination */
                copypv(ubc_paddr, usr_paddr, xsize,        2 |        1 |        4);    /* Copy physical to physical and flush the destination */
        else
//              copypv(usr_paddr, ubc_paddr, xsize, cppvPsrc | cppvPsnk | cppvFsrc);    /* Copy physical to physical and flush the source */
                copypv(usr_paddr, ubc_paddr, xsize,        2 |        1 |        8);    /* Copy physical to physical and flush the source */
        
        if ( !(flags & CL_READ) || (upl_valid_page(pl, 0) && upl_dirty_page(pl, 0))) {
                /*
                 * issue a synchronous write to cluster_io
                 */
                error = cluster_io(vp, upl, 0, uio->uio_offset & ~PAGE_MASK_64, PAGE_SIZE, devblocksize,
                                        0, (struct buf *)0, (struct clios *)0);
        }
        if (error == 0) {
                uio->uio_offset += xsize;
                iov->iov_base   += xsize;
                iov->iov_len    -= xsize;
                uio->uio_resid  -= xsize;
        }
        ubc_upl_abort_range(upl, 0, PAGE_SIZE, UPL_ABORT_DUMP_PAGES | UPL_ABORT_FREE_ON_EMPTY);
        
        return (error);
}



int
cluster_copy_upl_data(struct uio *uio, upl_t upl, int upl_offset, int xsize)
{
        int       pg_offset;
        int       pg_index;
        int       csize;
        int       segflg;
        int       retval = 0;
        upl_page_info_t *pl;
        boolean_t funnel_state = FALSE;


        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 34)) | DBG_FUNC_START,
                     (int)uio->uio_offset, uio->uio_resid, upl_offset, xsize, 0);

        if (xsize >= (16 * 1024))
                funnel_state = thread_funnel_set(kernel_flock, FALSE);

        segflg = uio->uio_segflg;

        switch(segflg) {

          case UIO_USERSPACE:
          case UIO_USERISPACE:
                uio->uio_segflg = UIO_PHYS_USERSPACE;
                break;

          case UIO_SYSSPACE:
                uio->uio_segflg = UIO_PHYS_SYSSPACE;
                break;
        }
        pl = ubc_upl_pageinfo(upl);

        pg_index  = upl_offset / PAGE_SIZE;
        pg_offset = upl_offset & PAGE_MASK;
        csize     = min(PAGE_SIZE - pg_offset, xsize);

        while (xsize && retval == 0) {
                addr64_t  paddr;

                paddr = ((addr64_t)upl_phys_page(pl, pg_index) << 12) + pg_offset;

                retval = uiomove64(paddr, csize, uio);

                pg_index += 1;
                pg_offset = 0;
                xsize    -= csize;
                csize     = min(PAGE_SIZE, xsize);
        }
        uio->uio_segflg = segflg;

        if (funnel_state == TRUE)
                thread_funnel_set(kernel_flock, TRUE);

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 34)) | DBG_FUNC_END,
                     (int)uio->uio_offset, uio->uio_resid, retval, segflg, 0);

        return (retval);
}


int
cluster_copy_ubc_data(struct vnode *vp, struct uio *uio, int *io_resid, int mark_dirty)
{
        int       segflg;
        int       io_size;
        int       xsize;
        int       start_offset;
        off_t     f_offset;
        int       retval = 0;
        memory_object_control_t  control;
        int       op_flags = UPL_POP_SET | UPL_POP_BUSY;
        boolean_t funnel_state = FALSE;


        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 34)) | DBG_FUNC_START,
                     (int)uio->uio_offset, uio->uio_resid, 0, *io_resid, 0);

        control = ubc_getobject(vp, UBC_FLAGS_NONE);
        if (control == MEMORY_OBJECT_CONTROL_NULL) {
                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 34)) | DBG_FUNC_END,
                             (int)uio->uio_offset, uio->uio_resid, retval, 3, 0);

                return(0);
        }
        if (mark_dirty)
                op_flags |= UPL_POP_DIRTY;

        segflg = uio->uio_segflg;

        switch(segflg) {

          case UIO_USERSPACE:
          case UIO_USERISPACE:
                uio->uio_segflg = UIO_PHYS_USERSPACE;
                break;

          case UIO_SYSSPACE:
                uio->uio_segflg = UIO_PHYS_SYSSPACE;
                break;
        }
        io_size      = *io_resid;
        start_offset = (int)(uio->uio_offset & PAGE_MASK_64);
        f_offset     = uio->uio_offset - start_offset;
        xsize        = min(PAGE_SIZE - start_offset, io_size);

        while (io_size && retval == 0) {
                ppnum_t pgframe;

                if (ubc_page_op_with_control(control, f_offset, op_flags, &pgframe, 0) != KERN_SUCCESS)
                        break;

                if (funnel_state == FALSE && io_size >= (16 * 1024))
                        funnel_state = thread_funnel_set(kernel_flock, FALSE);

                retval = uiomove64((addr64_t)(((addr64_t)pgframe << 12) + start_offset), xsize, uio);

                ubc_page_op_with_control(control, f_offset, UPL_POP_CLR | UPL_POP_BUSY, 0, 0);

                io_size     -= xsize;
                start_offset = 0;
                f_offset     = uio->uio_offset;
                xsize        = min(PAGE_SIZE, io_size);
        }
        uio->uio_segflg = segflg;
        *io_resid       = io_size;

        if (funnel_state == TRUE)
                thread_funnel_set(kernel_flock, TRUE);

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 34)) | DBG_FUNC_END,
                     (int)uio->uio_offset, uio->uio_resid, retval, 0x80000000 | segflg, 0);

        return(retval);
}


int
is_file_clean(struct vnode *vp, off_t filesize)
{
        off_t f_offset;
        int   flags;
        int   total_dirty = 0;

        for (f_offset = 0; f_offset < filesize; f_offset += PAGE_SIZE_64) {
                if (ubc_page_op(vp, f_offset, 0, 0, &flags) == KERN_SUCCESS) {
                        if (flags & UPL_POP_DIRTY) {
                                total_dirty++;
                        }
                }
        }
        if (total_dirty)
                return(EINVAL);

        return (0);
}



/*
 * Dirty region tracking/clustering mechanism.
 *
 * This code (vfs_drt_*) provides a mechanism for tracking and clustering
 * dirty regions within a larger space (file).  It is primarily intended to
 * support clustering in large files with many dirty areas.
 *
 * The implementation assumes that the dirty regions are pages.
 *
 * To represent dirty pages within the file, we store bit vectors in a
 * variable-size circular hash.
 */

/*
 * Bitvector size.  This determines the number of pages we group in a
 * single hashtable entry.  Each hashtable entry is aligned to this
 * size within the file.
 */
#define DRT_BITVECTOR_PAGES             256

/*
 * File offset handling.
 *
 * DRT_ADDRESS_MASK is dependent on DRT_BITVECTOR_PAGES;
 * the correct formula is  (~(DRT_BITVECTOR_PAGES * PAGE_SIZE) - 1)
 */
#define DRT_ADDRESS_MASK                (~((1 << 20) - 1))
#define DRT_ALIGN_ADDRESS(addr)         ((addr) & DRT_ADDRESS_MASK)

/*
 * Hashtable address field handling.
 *
 * The low-order bits of the hashtable address are used to conserve
 * space.
 *
 * DRT_HASH_COUNT_MASK must be large enough to store the range
 * 0-DRT_BITVECTOR_PAGES inclusive, as well as have one value
 * to indicate that the bucket is actually unoccupied.
 */
#define DRT_HASH_GET_ADDRESS(scm, i)    ((scm)->scm_hashtable[(i)].dhe_control & DRT_ADDRESS_MASK)
#define DRT_HASH_SET_ADDRESS(scm, i, a)                                                                 \
        do {                                                                                            \
                (scm)->scm_hashtable[(i)].dhe_control =                                                 \
                    ((scm)->scm_hashtable[(i)].dhe_control & ~DRT_ADDRESS_MASK) | DRT_ALIGN_ADDRESS(a); \
        } while (0)
#define DRT_HASH_COUNT_MASK             0x1ff
#define DRT_HASH_GET_COUNT(scm, i)      ((scm)->scm_hashtable[(i)].dhe_control & DRT_HASH_COUNT_MASK)
#define DRT_HASH_SET_COUNT(scm, i, c)                                                                                   \
        do {                                                                                                            \
                (scm)->scm_hashtable[(i)].dhe_control =                                                                 \
                    ((scm)->scm_hashtable[(i)].dhe_control & ~DRT_HASH_COUNT_MASK) | ((c) & DRT_HASH_COUNT_MASK);       \
        } while (0)
#define DRT_HASH_CLEAR(scm, i)                                                                                          \
        do {                                                                                                            \
                (scm)->scm_hashtable[(i)].dhe_control = 0;                                                              \
        } while (0)
#define DRT_HASH_VACATE(scm, i)         DRT_HASH_SET_COUNT((scm), (i), DRT_HASH_COUNT_MASK)
#define DRT_HASH_VACANT(scm, i)         (DRT_HASH_GET_COUNT((scm), (i)) == DRT_HASH_COUNT_MASK)
#define DRT_HASH_COPY(oscm, oi, scm, i)                                                                 \
        do {                                                                                            \
                (scm)->scm_hashtable[(i)].dhe_control = (oscm)->scm_hashtable[(oi)].dhe_control;        \
                DRT_BITVECTOR_COPY(oscm, oi, scm, i);                                                   \
        } while(0);


/*
 * Hash table moduli.
 *
 * Since the hashtable entry's size is dependent on the size of
 * the bitvector, and since the hashtable size is constrained to
 * both being prime and fitting within the desired allocation
 * size, these values need to be manually determined.
 *
 * For DRT_BITVECTOR_SIZE = 256, the entry size is 40 bytes.
 *
 * The small hashtable allocation is 1024 bytes, so the modulus is 23.
 * The large hashtable allocation is 16384 bytes, so the modulus is 401.
 */
#define DRT_HASH_SMALL_MODULUS  23
#define DRT_HASH_LARGE_MODULUS  401

#define DRT_SMALL_ALLOCATION    1024    /* 104 bytes spare */
#define DRT_LARGE_ALLOCATION    16384   /* 344 bytes spare */

/* *** nothing below here has secret dependencies on DRT_BITVECTOR_PAGES *** */

/*
 * Hashtable bitvector handling.
 *
 * Bitvector fields are 32 bits long.
 */

#define DRT_HASH_SET_BIT(scm, i, bit)                           \
        (scm)->scm_hashtable[(i)].dhe_bitvector[(bit) / 32] |= (1 << ((bit) % 32))

#define DRT_HASH_CLEAR_BIT(scm, i, bit)                         \
        (scm)->scm_hashtable[(i)].dhe_bitvector[(bit) / 32] &= ~(1 << ((bit) % 32))
    
#define DRT_HASH_TEST_BIT(scm, i, bit)                          \
        ((scm)->scm_hashtable[(i)].dhe_bitvector[(bit) / 32] & (1 << ((bit) % 32)))
    
#define DRT_BITVECTOR_CLEAR(scm, i)                             \
        bzero(&(scm)->scm_hashtable[(i)].dhe_bitvector[0], (DRT_BITVECTOR_PAGES / 32) * sizeof(u_int32_t))

#define DRT_BITVECTOR_COPY(oscm, oi, scm, i)                    \
        bcopy(&(oscm)->scm_hashtable[(oi)].dhe_bitvector[0],    \
            &(scm)->scm_hashtable[(i)].dhe_bitvector[0],        \
            (DRT_BITVECTOR_PAGES / 32) * sizeof(u_int32_t))


 
/*
 * Hashtable entry.
 */
struct vfs_drt_hashentry {
        u_int64_t       dhe_control;
        u_int32_t       dhe_bitvector[DRT_BITVECTOR_PAGES / 32];
};

/*
 * Dirty Region Tracking structure.
 *
 * The hashtable is allocated entirely inside the DRT structure.
 *
 * The hash is a simple circular prime modulus arrangement, the structure
 * is resized from small to large if it overflows.
 */

struct vfs_drt_clustermap {
        u_int32_t               scm_magic;      /* sanity/detection */
#define DRT_SCM_MAGIC           0x12020003
        u_int32_t               scm_modulus;    /* current ring size */
        u_int32_t               scm_buckets;    /* number of occupied buckets */
        u_int32_t               scm_lastclean;  /* last entry we cleaned */
        u_int32_t               scm_iskips;     /* number of slot skips */

        struct vfs_drt_hashentry scm_hashtable[0];
};


#define DRT_HASH(scm, addr)             ((addr) % (scm)->scm_modulus)
#define DRT_HASH_NEXT(scm, addr)        (((addr) + 1) % (scm)->scm_modulus)

/*
 * Debugging codes and arguments.
 */
#define DRT_DEBUG_EMPTYFREE     (FSDBG_CODE(DBG_FSRW, 82)) /* nil */
#define DRT_DEBUG_RETCLUSTER    (FSDBG_CODE(DBG_FSRW, 83)) /* offset, length */
#define DRT_DEBUG_ALLOC         (FSDBG_CODE(DBG_FSRW, 84)) /* copycount */
#define DRT_DEBUG_INSERT        (FSDBG_CODE(DBG_FSRW, 85)) /* offset, iskip */
#define DRT_DEBUG_MARK          (FSDBG_CODE(DBG_FSRW, 86)) /* offset, length,
                                                            * dirty */
                                                           /* 0, setcount */
                                                           /* 1 (clean, no map) */
                                                           /* 2 (map alloc fail) */
                                                           /* 3, resid (partial) */
#define DRT_DEBUG_6             (FSDBG_CODE(DBG_FSRW, 87))
#define DRT_DEBUG_SCMDATA       (FSDBG_CODE(DBG_FSRW, 88)) /* modulus, buckets,
                                                            * lastclean, iskips */


static void             vfs_drt_sanity(struct vfs_drt_clustermap *cmap);
static kern_return_t    vfs_drt_alloc_map(struct vfs_drt_clustermap **cmapp);
static kern_return_t    vfs_drt_free_map(struct vfs_drt_clustermap *cmap);
static kern_return_t    vfs_drt_search_index(struct vfs_drt_clustermap *cmap,
        u_int64_t offset, int *indexp);
static kern_return_t    vfs_drt_get_index(struct vfs_drt_clustermap **cmapp,
        u_int64_t offset,
        int *indexp,
        int recursed);
static kern_return_t    vfs_drt_do_mark_pages(
        void            **cmapp,
        u_int64_t       offset,
        u_int           length,
        int             *setcountp,
        int             dirty);
static void             vfs_drt_trace(
        struct vfs_drt_clustermap *cmap,
        int code,
        int arg1,
        int arg2,
        int arg3,
        int arg4);


/*
 * Allocate and initialise a sparse cluster map.
 *
 * Will allocate a new map, resize or compact an existing map.
 *
 * XXX we should probably have at least one intermediate map size,
 * as the 1:16 ratio seems a bit drastic.
 */
static kern_return_t
vfs_drt_alloc_map(struct vfs_drt_clustermap **cmapp)
{
        struct vfs_drt_clustermap *cmap, *ocmap;
        kern_return_t   kret;
        u_int64_t       offset;
        int             nsize, i, active_buckets, index, copycount;

        ocmap = NULL;
        if (cmapp != NULL)
                ocmap = *cmapp;
        
        /*
         * Decide on the size of the new map.
         */
        if (ocmap == NULL) {
                nsize = DRT_HASH_SMALL_MODULUS;
        } else {
                /* count the number of active buckets in the old map */
                active_buckets = 0;
                for (i = 0; i < ocmap->scm_modulus; i++) {
                        if (!DRT_HASH_VACANT(ocmap, i) &&
                            (DRT_HASH_GET_COUNT(ocmap, i) != 0))
                                active_buckets++;
                }
                /*
                 * If we're currently using the small allocation, check to
                 * see whether we should grow to the large one.
                 */
                if (ocmap->scm_modulus == DRT_HASH_SMALL_MODULUS) {
                        /* if the ring is nearly full */
                        if (active_buckets > (DRT_HASH_SMALL_MODULUS - 5)) {
                                nsize = DRT_HASH_LARGE_MODULUS;
                        } else {
                                nsize = DRT_HASH_SMALL_MODULUS;
                        }
                } else {
                        /* already using the large modulus */
                        nsize = DRT_HASH_LARGE_MODULUS;
                        /*
                         * If the ring is completely full, there's
                         * nothing useful for us to do.  Behave as
                         * though we had compacted into the new
                         * array and return.
                         */
                        if (active_buckets >= DRT_HASH_LARGE_MODULUS)
                                return(KERN_SUCCESS);
                }
        }

        /*
         * Allocate and initialise the new map.
         */

        kret = kmem_alloc(kernel_map, (vm_offset_t *)&cmap,
            (nsize == DRT_HASH_SMALL_MODULUS) ? DRT_SMALL_ALLOCATION : DRT_LARGE_ALLOCATION);
        if (kret != KERN_SUCCESS)
                return(kret);
        cmap->scm_magic = DRT_SCM_MAGIC;
        cmap->scm_modulus = nsize;
        cmap->scm_buckets = 0;
        cmap->scm_lastclean = 0;
        cmap->scm_iskips = 0;
        for (i = 0; i < cmap->scm_modulus; i++) {
                DRT_HASH_CLEAR(cmap, i);
                DRT_HASH_VACATE(cmap, i);
                DRT_BITVECTOR_CLEAR(cmap, i);
        }

        /*
         * If there's an old map, re-hash entries from it into the new map.
         */
        copycount = 0;
        if (ocmap != NULL) {
                for (i = 0; i < ocmap->scm_modulus; i++) {
                        /* skip empty buckets */
                        if (DRT_HASH_VACANT(ocmap, i) ||
                            (DRT_HASH_GET_COUNT(ocmap, i) == 0))
                                continue;
                        /* get new index */
                        offset = DRT_HASH_GET_ADDRESS(ocmap, i);
                        kret = vfs_drt_get_index(&cmap, offset, &index, 1);
                        if (kret != KERN_SUCCESS) {
                                /* XXX need to bail out gracefully here */
                                panic("vfs_drt: new cluster map mysteriously too small");
                        }
                        /* copy */
                        DRT_HASH_COPY(ocmap, i, cmap, index);
                        copycount++;
                }
        }

        /* log what we've done */
        vfs_drt_trace(cmap, DRT_DEBUG_ALLOC, copycount, 0, 0, 0);
        
        /*
         * It's important to ensure that *cmapp always points to 
         * a valid map, so we must overwrite it before freeing
         * the old map.
         */
        *cmapp = cmap;
        if (ocmap != NULL) {
                /* emit stats into trace buffer */
                vfs_drt_trace(ocmap, DRT_DEBUG_SCMDATA,
                              ocmap->scm_modulus,
                              ocmap->scm_buckets,
                              ocmap->scm_lastclean,
                              ocmap->scm_iskips);

                vfs_drt_free_map(ocmap);
        }
        return(KERN_SUCCESS);
}


/*
 * Free a sparse cluster map.
 */
static kern_return_t
vfs_drt_free_map(struct vfs_drt_clustermap *cmap)
{
        kern_return_t   ret;

        kmem_free(kernel_map, (vm_offset_t)cmap, 
                  (cmap->scm_modulus == DRT_HASH_SMALL_MODULUS) ? DRT_SMALL_ALLOCATION : DRT_LARGE_ALLOCATION);
        return(KERN_SUCCESS);
}


/*
 * Find the hashtable slot currently occupied by an entry for the supplied offset.
 */
static kern_return_t
vfs_drt_search_index(struct vfs_drt_clustermap *cmap, u_int64_t offset, int *indexp)
{
        kern_return_t   kret;
        int             index, i, tries;

        offset = DRT_ALIGN_ADDRESS(offset);
        index = DRT_HASH(cmap, offset);

        /* traverse the hashtable */
        for (i = 0; i < cmap->scm_modulus; i++) {

                /*
                 * If the slot is vacant, we can stop.
                 */
                if (DRT_HASH_VACANT(cmap, index))
                        break;

                /*
                 * If the address matches our offset, we have success.
                 */
                if (DRT_HASH_GET_ADDRESS(cmap, index) == offset) {
                        *indexp = index;
                        return(KERN_SUCCESS);
                }

                /*
                 * Move to the next slot, try again.
                 */
                index = DRT_HASH_NEXT(cmap, index);
        }
        /*
         * It's not there.
         */
        return(KERN_FAILURE);
}

/*
 * Find the hashtable slot for the supplied offset.  If we haven't allocated
 * one yet, allocate one and populate the address field.  Note that it will
 * not have a nonzero page count and thus will still technically be free, so
 * in the case where we are called to clean pages, the slot will remain free.
 */
static kern_return_t
vfs_drt_get_index(struct vfs_drt_clustermap **cmapp, u_int64_t offset, int *indexp, int recursed)
{
        struct vfs_drt_clustermap *cmap;
        kern_return_t   kret;
        int             index, i;

        cmap = *cmapp;

        /* look for an existing entry */
        kret = vfs_drt_search_index(cmap, offset, indexp);
        if (kret == KERN_SUCCESS)
                return(kret);

        /* need to allocate an entry */
        offset = DRT_ALIGN_ADDRESS(offset);
        index = DRT_HASH(cmap, offset);

        /* scan from the index forwards looking for a vacant slot */
        for (i = 0; i < cmap->scm_modulus; i++) {
                /* slot vacant? */
                if (DRT_HASH_VACANT(cmap, index) || DRT_HASH_GET_COUNT(cmap,index) == 0) {
                        cmap->scm_buckets++;
                        if (index < cmap->scm_lastclean)
                                cmap->scm_lastclean = index;
                        DRT_HASH_SET_ADDRESS(cmap, index, offset);
                        DRT_HASH_SET_COUNT(cmap, index, 0);
                        DRT_BITVECTOR_CLEAR(cmap, index);
                        *indexp = index;
                        vfs_drt_trace(cmap, DRT_DEBUG_INSERT, (int)offset, i, 0, 0);
                        return(KERN_SUCCESS);
                }
                cmap->scm_iskips += i;
                index = DRT_HASH_NEXT(cmap, index);
        }

        /*
         * We haven't found a vacant slot, so the map is full.  If we're not
         * already recursed, try reallocating/compacting it.
         */
        if (recursed)
                return(KERN_FAILURE);
        kret = vfs_drt_alloc_map(cmapp);
        if (kret == KERN_SUCCESS) {
                /* now try to insert again */
                kret = vfs_drt_get_index(cmapp, offset, indexp, 1);
        }
        return(kret);
}

/*
 * Implementation of set dirty/clean.
 *
 * In the 'clean' case, not finding a map is OK.
 */
static kern_return_t
vfs_drt_do_mark_pages(
        void            **private,
        u_int64_t       offset,
        u_int           length,
        int             *setcountp,
        int             dirty)
{
        struct vfs_drt_clustermap *cmap, **cmapp;
        kern_return_t   kret;
        int             i, index, pgoff, pgcount, setcount, ecount;

        cmapp = (struct vfs_drt_clustermap **)private;
        cmap = *cmapp;

        vfs_drt_trace(cmap, DRT_DEBUG_MARK | DBG_FUNC_START, (int)offset, (int)length, dirty, 0);

        if (setcountp != NULL)
                *setcountp = 0;
        
        /* allocate a cluster map if we don't already have one */
        if (cmap == NULL) {
                /* no cluster map, nothing to clean */
                if (!dirty) {
                        vfs_drt_trace(cmap, DRT_DEBUG_MARK | DBG_FUNC_END, 1, 0, 0, 0);
                        return(KERN_SUCCESS);
                }
                kret = vfs_drt_alloc_map(cmapp);
                if (kret != KERN_SUCCESS) {
                        vfs_drt_trace(cmap, DRT_DEBUG_MARK | DBG_FUNC_END, 2, 0, 0, 0);
                        return(kret);
                }
        }
        setcount = 0;

        /*
         * Iterate over the length of the region.
         */
        while (length > 0) {
                /*
                 * Get the hashtable index for this offset.
                 *
                 * XXX this will add blank entries if we are clearing a range
                 * that hasn't been dirtied.
                 */
                kret = vfs_drt_get_index(cmapp, offset, &index, 0);
                cmap = *cmapp;  /* may have changed! */
                /* this may be a partial-success return */
                if (kret != KERN_SUCCESS) {
                        if (setcountp != NULL)
                                *setcountp = setcount;
                        vfs_drt_trace(cmap, DRT_DEBUG_MARK | DBG_FUNC_END, 3, (int)length, 0, 0);

                        return(kret);
                }

                /*
                 * Work out how many pages we're modifying in this
                 * hashtable entry.
                 */
                pgoff = (offset - DRT_ALIGN_ADDRESS(offset)) / PAGE_SIZE;
                pgcount = min((length / PAGE_SIZE), (DRT_BITVECTOR_PAGES - pgoff));

                /*
                 * Iterate over pages, dirty/clearing as we go.
                 */
                ecount = DRT_HASH_GET_COUNT(cmap, index);
                for (i = 0; i < pgcount; i++) {
                        if (dirty) {
                                if (!DRT_HASH_TEST_BIT(cmap, index, pgoff + i)) {
                                        DRT_HASH_SET_BIT(cmap, index, pgoff + i);
                                        ecount++;
                                        setcount++;
                                }
                        } else {
                                if (DRT_HASH_TEST_BIT(cmap, index, pgoff + i)) {
                                        DRT_HASH_CLEAR_BIT(cmap, index, pgoff + i);
                                        ecount--;
                                        setcount++;
                                }
                        }
                }
                DRT_HASH_SET_COUNT(cmap, index, ecount);
next:
                offset += pgcount * PAGE_SIZE;
                length -= pgcount * PAGE_SIZE;
        }
        if (setcountp != NULL)
                *setcountp = setcount;

        vfs_drt_trace(cmap, DRT_DEBUG_MARK | DBG_FUNC_END, 0, setcount, 0, 0);

        return(KERN_SUCCESS);
}

/*
 * Mark a set of pages as dirty/clean.
 *
 * This is a public interface.
 *
 * cmapp
 *      Pointer to storage suitable for holding a pointer.  Note that
 *      this must either be NULL or a value set by this function.
 *
 * size
 *      Current file size in bytes.
 *
 * offset
 *      Offset of the first page to be marked as dirty, in bytes.  Must be
 *      page-aligned.
 *
 * length
 *      Length of dirty region, in bytes.  Must be a multiple of PAGE_SIZE.
 *
 * setcountp
 *      Number of pages newly marked dirty by this call (optional).
 *
 * Returns KERN_SUCCESS if all the pages were successfully marked.
 */
static kern_return_t
vfs_drt_mark_pages(void **cmapp, off_t offset, u_int length, int *setcountp)
{
        /* XXX size unused, drop from interface */
        return(vfs_drt_do_mark_pages(cmapp, offset, length, setcountp, 1));
}

static kern_return_t
vfs_drt_unmark_pages(void **cmapp, off_t offset, u_int length)
{
        return(vfs_drt_do_mark_pages(cmapp, offset, length, NULL, 0));
}

/*
 * Get a cluster of dirty pages.
 *
 * This is a public interface.
 *
 * cmapp
 *      Pointer to storage managed by drt_mark_pages.  Note that this must
 *      be NULL or a value set by drt_mark_pages.
 *
 * offsetp
 *      Returns the byte offset into the file of the first page in the cluster.
 *
 * lengthp
 *      Returns the length in bytes of the cluster of dirty pages.
 *
 * Returns success if a cluster was found.  If KERN_FAILURE is returned, there
 * are no dirty pages meeting the minmum size criteria.  Private storage will
 * be released if there are no more dirty pages left in the map
 *
 */
static kern_return_t
vfs_drt_get_cluster(void **cmapp, off_t *offsetp, u_int *lengthp)
{
        struct vfs_drt_clustermap *cmap;
        u_int64_t       offset;
        u_int           length;
        int             index, i, j, fs, ls;

        /* sanity */
        if ((cmapp == NULL) || (*cmapp == NULL))
                return(KERN_FAILURE);
        cmap = *cmapp;

        /* walk the hashtable */
        for (offset = 0, j = 0; j < cmap->scm_modulus; offset += (DRT_BITVECTOR_PAGES * PAGE_SIZE), j++) {
                index = DRT_HASH(cmap, offset);

                if (DRT_HASH_VACANT(cmap, index) || (DRT_HASH_GET_COUNT(cmap, index) == 0))
                        continue;

                /* scan the bitfield for a string of bits */
                fs = -1;

                for (i = 0; i < DRT_BITVECTOR_PAGES; i++) {
                        if (DRT_HASH_TEST_BIT(cmap, index, i)) {
                                fs = i;
                                break;
                        }
                }
                if (fs == -1) {
                        /*  didn't find any bits set */
                        panic("vfs_drt: entry summary count > 0 but no bits set in map");
                }
                for (ls = 0; i < DRT_BITVECTOR_PAGES; i++, ls++) {
                        if (!DRT_HASH_TEST_BIT(cmap, index, i))
                                break;
                }
                
                /* compute offset and length, mark pages clean */
                offset = DRT_HASH_GET_ADDRESS(cmap, index) + (PAGE_SIZE * fs);
                length = ls * PAGE_SIZE;
                vfs_drt_do_mark_pages(cmapp, offset, length, NULL, 0);
                cmap->scm_lastclean = index;

                /* return successful */
                *offsetp = (off_t)offset;
                *lengthp = length;

                vfs_drt_trace(cmap, DRT_DEBUG_RETCLUSTER, (int)offset, (int)length, 0, 0);
                return(KERN_SUCCESS);
        }
        /*
         * We didn't find anything... hashtable is empty
         * emit stats into trace buffer and
         * then free it
         */
        vfs_drt_trace(cmap, DRT_DEBUG_SCMDATA,
                      cmap->scm_modulus,
                      cmap->scm_buckets,
                      cmap->scm_lastclean,
                      cmap->scm_iskips);
        
        vfs_drt_free_map(cmap);
        *cmapp = NULL;

        return(KERN_FAILURE);
}


static kern_return_t
vfs_drt_control(void **cmapp, int op_type)
{
        struct vfs_drt_clustermap *cmap;

        /* sanity */
        if ((cmapp == NULL) || (*cmapp == NULL))
                return(KERN_FAILURE);
        cmap = *cmapp;

        switch (op_type) {
        case 0:
                /* emit stats into trace buffer */
                vfs_drt_trace(cmap, DRT_DEBUG_SCMDATA,
                              cmap->scm_modulus,
                              cmap->scm_buckets,
                              cmap->scm_lastclean,
                              cmap->scm_iskips);

                vfs_drt_free_map(cmap);
                *cmapp = NULL;
                break;

        case 1:
                cmap->scm_lastclean = 0;
                break;
        }
        return(KERN_SUCCESS);
}



/*
 * Emit a summary of the state of the clustermap into the trace buffer
 * along with some caller-provided data.
 */
static void
vfs_drt_trace(struct vfs_drt_clustermap *cmap, int code, int arg1, int arg2, int arg3, int arg4)
{
        KERNEL_DEBUG(code, arg1, arg2, arg3, arg4, 0);
}

/*
 * Perform basic sanity check on the hash entry summary count
 * vs. the actual bits set in the entry.
 */
static void
vfs_drt_sanity(struct vfs_drt_clustermap *cmap)
{
        int index, i;
        int bits_on;
        
        for (index = 0; index < cmap->scm_modulus; index++) {
                if (DRT_HASH_VACANT(cmap, index))
                        continue;

                for (bits_on = 0, i = 0; i < DRT_BITVECTOR_PAGES; i++) {
                        if (DRT_HASH_TEST_BIT(cmap, index, i))
                                bits_on++;
                }
                if (bits_on != DRT_HASH_GET_COUNT(cmap, index))
                        panic("bits_on = %d,  index = %d\n", bits_on, index);
        }               
}