xnu-1504.9.37.tar.gz

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

/*
 * Copyright (c) 2000-2008 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 * 
 * 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. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 * 
 * 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_OSREFERENCE_LICENSE_HEADER_END@
 */
/* Copyright (c) 1995 NeXT Computer, Inc. All Rights Reserved */
/*-
 * Copyright (c) 1994 Christopher G. Demetriou
 * Copyright (c) 1982, 1986, 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * 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_bio.c   8.6 (Berkeley) 1/11/94
 */

/*
 * Some references:
 *      Bach: The Design of the UNIX Operating System (Prentice Hall, 1986)
 *      Leffler, et al.: The Design and Implementation of the 4.3BSD
 *              UNIX Operating System (Addison Welley, 1989)
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc_internal.h>
#include <sys/buf_internal.h>
#include <sys/vnode_internal.h>
#include <sys/mount_internal.h>
#include <sys/trace.h>
#include <sys/malloc.h>
#include <sys/resourcevar.h>
#include <miscfs/specfs/specdev.h>
#include <sys/ubc.h>
#include <sys/kauth.h>
#if DIAGNOSTIC
#include <kern/assert.h>
#endif /* DIAGNOSTIC */
#include <kern/task.h>
#include <kern/zalloc.h>
#include <kern/lock.h>

#include <sys/fslog.h>          /* fslog_io_error() */

#include <mach/mach_types.h>
#include <mach/memory_object_types.h>
#include <kern/sched_prim.h>    /* thread_block() */

#include <vm/vm_kern.h>
#include <vm/vm_pageout.h>

#include <sys/kdebug.h>

#include <libkern/OSAtomic.h>
#include <libkern/OSDebug.h>
#include <sys/ubc_internal.h>

#include <sys/sdt.h>

#if BALANCE_QUEUES
static __inline__ void bufqinc(int q);
static __inline__ void bufqdec(int q);
#endif

static int      bcleanbuf(buf_t bp, boolean_t discard);
static int      brecover_data(buf_t bp);
static boolean_t incore(vnode_t vp, daddr64_t blkno);
/* timeout is in msecs */
static buf_t    getnewbuf(int slpflag, int slptimeo, int *queue);
static void     bremfree_locked(buf_t bp);
static void     buf_reassign(buf_t bp, vnode_t newvp);
static errno_t  buf_acquire_locked(buf_t bp, int flags, int slpflag, int slptimeo);
static int      buf_iterprepare(vnode_t vp, struct buflists *, int flags);
static void     buf_itercomplete(vnode_t vp, struct buflists *, int flags);
boolean_t buffer_cache_gc(int);

__private_extern__ int  bdwrite_internal(buf_t, int);

/* zone allocated buffer headers */
static void     bufzoneinit(void) __attribute__((section("__TEXT, initcode")));
static void     bcleanbuf_thread_init(void) __attribute__((section("__TEXT, initcode")));
static void     bcleanbuf_thread(void);

static zone_t   buf_hdr_zone;
static int      buf_hdr_count;


/*
 * Definitions for the buffer hash lists.
 */
#define BUFHASH(dvp, lbn)       \
        (&bufhashtbl[((long)(dvp) / sizeof(*(dvp)) + (int)(lbn)) & bufhash])
LIST_HEAD(bufhashhdr, buf) *bufhashtbl, invalhash;
u_long  bufhash;

static buf_t    incore_locked(vnode_t vp, daddr64_t blkno, struct bufhashhdr *dp);

/* Definitions for the buffer stats. */
struct bufstats bufstats;

/* Number of delayed write buffers */
long nbdwrite = 0;
int blaundrycnt = 0;
static int boot_nbuf_headers = 0;


static TAILQ_HEAD(ioqueue, buf) iobufqueue;
static TAILQ_HEAD(bqueues, buf) bufqueues[BQUEUES];
static int needbuffer;
static int need_iobuffer;

static lck_grp_t        *buf_mtx_grp;
static lck_attr_t       *buf_mtx_attr;
static lck_grp_attr_t   *buf_mtx_grp_attr;
static lck_mtx_t        *iobuffer_mtxp;
static lck_mtx_t        *buf_mtxp;

static int buf_busycount;

static __inline__ int
buf_timestamp(void)
{
        struct  timeval         t;
        microuptime(&t);
        return (t.tv_sec);
}

/*
 * Insq/Remq for the buffer free lists.
 */
#if BALANCE_QUEUES
#define binsheadfree(bp, dp, whichq)    do { \
                                    TAILQ_INSERT_HEAD(dp, bp, b_freelist); \
                                        bufqinc((whichq));      \
                                } while (0)

#define binstailfree(bp, dp, whichq)    do { \
                                    TAILQ_INSERT_TAIL(dp, bp, b_freelist); \
                                        bufqinc((whichq));      \
                                } while (0)
#else
#define binsheadfree(bp, dp, whichq)    do { \
                                    TAILQ_INSERT_HEAD(dp, bp, b_freelist); \
                                } while (0)

#define binstailfree(bp, dp, whichq)    do { \
                                    TAILQ_INSERT_TAIL(dp, bp, b_freelist); \
                                } while (0)
#endif


#define BHASHENTCHECK(bp)       \
        if ((bp)->b_hash.le_prev != (struct buf **)0xdeadbeef)  \
                panic("%p: b_hash.le_prev is not deadbeef", (bp));

#define BLISTNONE(bp)   \
        (bp)->b_hash.le_next = (struct buf *)0; \
        (bp)->b_hash.le_prev = (struct buf **)0xdeadbeef;

/*
 * Insq/Remq for the vnode usage lists.
 */
#define bufinsvn(bp, dp)        LIST_INSERT_HEAD(dp, bp, b_vnbufs)
#define bufremvn(bp) {                                                  \
        LIST_REMOVE(bp, b_vnbufs);                                      \
        (bp)->b_vnbufs.le_next = NOLIST;                                \
}

/*
 * Time in seconds before a buffer on a list is 
 * considered as a stale buffer 
 */
#define LRU_IS_STALE 120 /* default value for the LRU */
#define AGE_IS_STALE 60  /* default value for the AGE */
#define META_IS_STALE 180 /* default value for the BQ_META */

int lru_is_stale = LRU_IS_STALE;
int age_is_stale = AGE_IS_STALE;
int meta_is_stale = META_IS_STALE;



/* LIST_INSERT_HEAD() with assertions */
static __inline__ void
blistenterhead(struct bufhashhdr * head, buf_t bp)
{
        if ((bp->b_hash.le_next = (head)->lh_first) != NULL)
                (head)->lh_first->b_hash.le_prev = &(bp)->b_hash.le_next;
        (head)->lh_first = bp;
        bp->b_hash.le_prev = &(head)->lh_first;
        if (bp->b_hash.le_prev == (struct buf **)0xdeadbeef) 
                panic("blistenterhead: le_prev is deadbeef");
}

static __inline__ void 
binshash(buf_t bp, struct bufhashhdr *dp)
{
#if DIAGNOSTIC
        buf_t   nbp;
#endif /* DIAGNOSTIC */

        BHASHENTCHECK(bp);

#if DIAGNOSTIC
        nbp = dp->lh_first;
        for(; nbp != NULL; nbp = nbp->b_hash.le_next) {
                if(nbp == bp) 
                        panic("buf already in hashlist");
        }
#endif /* DIAGNOSTIC */

        blistenterhead(dp, bp);
}

static __inline__ void 
bremhash(buf_t  bp) 
{
        if (bp->b_hash.le_prev == (struct buf **)0xdeadbeef) 
                panic("bremhash le_prev is deadbeef");
        if (bp->b_hash.le_next == bp) 
                panic("bremhash: next points to self");

        if (bp->b_hash.le_next != NULL)
                bp->b_hash.le_next->b_hash.le_prev = bp->b_hash.le_prev;
        *bp->b_hash.le_prev = (bp)->b_hash.le_next;
}




int
buf_valid(buf_t bp) {

        if ( (bp->b_flags & (B_DONE | B_DELWRI)) )
                return 1;
        return 0;
}

int
buf_fromcache(buf_t bp) {

        if ( (bp->b_flags & B_CACHE) )
                return 1;
        return 0;
}

void
buf_markinvalid(buf_t bp) {
  
        SET(bp->b_flags, B_INVAL);
}

void
buf_markdelayed(buf_t bp) {
  
        if (!ISSET(bp->b_flags, B_DELWRI)) {
                SET(bp->b_flags, B_DELWRI);

                OSAddAtomicLong(1, &nbdwrite);
                buf_reassign(bp, bp->b_vp);
        }
        SET(bp->b_flags, B_DONE);
}

void
buf_markeintr(buf_t bp) {
  
        SET(bp->b_flags, B_EINTR);
}


void
buf_markaged(buf_t bp) {
  
        SET(bp->b_flags, B_AGE);
}

int
buf_fua(buf_t bp) {

        if ((bp->b_flags & B_FUA) == B_FUA)
                return 1;
        return 0;
}

void 
buf_markfua(buf_t bp) {

        SET(bp->b_flags, B_FUA);
}

#ifdef CONFIG_PROTECT
void *
buf_getcpaddr(buf_t bp) {
        return bp->b_cpentry;
}

void 
buf_setcpaddr(buf_t bp, void *cp_entry_addr) {
        bp->b_cpentry = (struct cprotect *) cp_entry_addr;
}

#else
void *
buf_getcpaddr(buf_t bp __unused) {
        return NULL;
}

void 
buf_setcpaddr(buf_t bp __unused, void *cp_entry_addr __unused) {
        return;
}
#endif /* CONFIG_PROTECT */

errno_t
buf_error(buf_t bp) {
        
        return (bp->b_error);
}

void
buf_seterror(buf_t bp, errno_t error) {

        if ((bp->b_error = error))
                SET(bp->b_flags, B_ERROR);
        else
                CLR(bp->b_flags, B_ERROR);
}

void
buf_setflags(buf_t bp, int32_t flags) {

        SET(bp->b_flags, (flags & BUF_X_WRFLAGS));
}

void
buf_clearflags(buf_t bp, int32_t flags) {

        CLR(bp->b_flags, (flags & BUF_X_WRFLAGS));
}

int32_t
buf_flags(buf_t bp) {
        
        return ((bp->b_flags & BUF_X_RDFLAGS));
}

void
buf_reset(buf_t bp, int32_t io_flags) {
        
        CLR(bp->b_flags, (B_READ | B_WRITE | B_ERROR | B_DONE | B_INVAL | B_ASYNC | B_NOCACHE | B_FUA));
        SET(bp->b_flags, (io_flags & (B_ASYNC | B_READ | B_WRITE | B_NOCACHE)));

        bp->b_error = 0;
}

uint32_t
buf_count(buf_t bp) {
        
        return (bp->b_bcount);
}

void
buf_setcount(buf_t bp, uint32_t bcount) {
        
        bp->b_bcount = bcount;
}

uint32_t
buf_size(buf_t bp) {
        
        return (bp->b_bufsize);
}

void
buf_setsize(buf_t bp, uint32_t bufsize) {
        
        bp->b_bufsize = bufsize;
}

uint32_t
buf_resid(buf_t bp) {
        
        return (bp->b_resid);
}

void
buf_setresid(buf_t bp, uint32_t resid) {
        
        bp->b_resid = resid;
}

uint32_t
buf_dirtyoff(buf_t bp) {

        return (bp->b_dirtyoff);
}

uint32_t
buf_dirtyend(buf_t bp) {

        return (bp->b_dirtyend);
}

void
buf_setdirtyoff(buf_t bp, uint32_t dirtyoff) {
        
        bp->b_dirtyoff = dirtyoff;
}

void
buf_setdirtyend(buf_t bp, uint32_t dirtyend) {
        
        bp->b_dirtyend = dirtyend;
}

uintptr_t
buf_dataptr(buf_t bp) {
        
        return (bp->b_datap);
}

void
buf_setdataptr(buf_t bp, uintptr_t data) {
        
        bp->b_datap = data;
}

vnode_t
buf_vnode(buf_t bp) {
        
        return (bp->b_vp);
}

void
buf_setvnode(buf_t bp, vnode_t vp) {
        
        bp->b_vp = vp;
}


void *
buf_callback(buf_t bp)
{
        if ( !(bp->b_flags & B_CALL) )
                return ((void *) NULL);

        return ((void *)bp->b_iodone);
}


errno_t
buf_setcallback(buf_t bp, void (*callback)(buf_t, void *), void *transaction)
{
        if (callback)
                bp->b_flags |= (B_CALL | B_ASYNC);
        else
                bp->b_flags &= ~B_CALL;
        bp->b_transaction = transaction;
        bp->b_iodone = callback;

        return (0);
}

errno_t
buf_setupl(buf_t bp, upl_t upl, uint32_t offset)
{

        if ( !(bp->b_lflags & BL_IOBUF) )
                return (EINVAL);

        if (upl)
                bp->b_flags |= B_CLUSTER;
        else
                bp->b_flags &= ~B_CLUSTER;
        bp->b_upl = upl;
        bp->b_uploffset = offset;

        return (0);
}

buf_t
buf_clone(buf_t bp, int io_offset, int io_size, void (*iodone)(buf_t, void *), void *arg)
{
        buf_t   io_bp;

        if (io_offset < 0 || io_size < 0)
                return (NULL);

        if ((unsigned)(io_offset + io_size) > (unsigned)bp->b_bcount)
                return (NULL);

        if (bp->b_flags & B_CLUSTER) {
                if (io_offset && ((bp->b_uploffset + io_offset) & PAGE_MASK))
                        return (NULL);

                if (((bp->b_uploffset + io_offset + io_size) & PAGE_MASK) && ((io_offset + io_size) < bp->b_bcount))
                        return (NULL);
        }
        io_bp = alloc_io_buf(bp->b_vp, 0);

        io_bp->b_flags = bp->b_flags & (B_COMMIT_UPL | B_META | B_PAGEIO | B_CLUSTER | B_PHYS | B_RAW | B_ASYNC | B_READ | B_FUA);

        if (iodone) {
                io_bp->b_transaction = arg;
                io_bp->b_iodone = iodone;
                io_bp->b_flags |= B_CALL;
        }
        if (bp->b_flags & B_CLUSTER) {
                io_bp->b_upl = bp->b_upl;
                io_bp->b_uploffset = bp->b_uploffset + io_offset;
        } else {
                io_bp->b_datap  = (uintptr_t)(((char *)bp->b_datap) + io_offset);
        }
        io_bp->b_bcount = io_size;

        return (io_bp);
}



void
buf_setfilter(buf_t bp, void (*filter)(buf_t, void *), void *transaction,
              void **old_iodone, void **old_transaction)
{
        if (old_iodone)
                *old_iodone = (void *)(bp->b_iodone);
        if (old_transaction)
                *old_transaction = (void *)(bp->b_transaction);

        bp->b_transaction = transaction;
        bp->b_iodone = filter;
        if (filter)
                bp->b_flags |= B_FILTER;
        else
                bp->b_flags &= ~B_FILTER;
}


daddr64_t
buf_blkno(buf_t bp) {

        return (bp->b_blkno);
}

daddr64_t
buf_lblkno(buf_t bp) {

        return (bp->b_lblkno);
}

void
buf_setblkno(buf_t bp, daddr64_t blkno) {

        bp->b_blkno = blkno;
}

void
buf_setlblkno(buf_t bp, daddr64_t lblkno) {

        bp->b_lblkno = lblkno;
}

dev_t
buf_device(buf_t bp) {
        
        return (bp->b_dev);
}

errno_t
buf_setdevice(buf_t bp, vnode_t vp) {

        if ((vp->v_type != VBLK) && (vp->v_type != VCHR))
                return EINVAL;
        bp->b_dev = vp->v_rdev;

        return 0;
}


void *
buf_drvdata(buf_t bp) {

        return (bp->b_drvdata);
}

void
buf_setdrvdata(buf_t bp, void *drvdata) {

        bp->b_drvdata = drvdata;
}

void *
buf_fsprivate(buf_t bp) {

        return (bp->b_fsprivate);
}

void
buf_setfsprivate(buf_t bp, void *fsprivate) {

        bp->b_fsprivate = fsprivate;
}

kauth_cred_t
buf_rcred(buf_t bp) {

        return (bp->b_rcred);
}

kauth_cred_t
buf_wcred(buf_t bp) {

        return (bp->b_wcred);
}

void *
buf_upl(buf_t bp) {

        return (bp->b_upl);
}

uint32_t
buf_uploffset(buf_t bp) {

        return ((uint32_t)(bp->b_uploffset));
}

proc_t
buf_proc(buf_t bp) {

        return (bp->b_proc);
}


errno_t
buf_map(buf_t bp, caddr_t *io_addr)
{
        buf_t           real_bp;
        vm_offset_t     vaddr;
        kern_return_t   kret;

        if ( !(bp->b_flags & B_CLUSTER)) {
                *io_addr = (caddr_t)bp->b_datap;
                return (0);
        }
        real_bp = (buf_t)(bp->b_real_bp);

        if (real_bp && real_bp->b_datap) {
                /*
                 * b_real_bp is only valid if B_CLUSTER is SET
                 * if it's non-zero, than someone did a cluster_bp call
                 * if the backing physical pages were already mapped
                 * in before the call to cluster_bp (non-zero b_datap),
                 * than we just use that mapping
                 */
                *io_addr = (caddr_t)real_bp->b_datap;
                return (0);
        }
        kret = ubc_upl_map(bp->b_upl, &vaddr);    /* Map it in */

        if (kret != KERN_SUCCESS) {
                *io_addr = NULL;

                return(ENOMEM);
        }
        vaddr += bp->b_uploffset;                                       

        *io_addr = (caddr_t)vaddr;

        return (0);
}

errno_t
buf_unmap(buf_t bp)
{
        buf_t           real_bp;
        kern_return_t   kret;

        if ( !(bp->b_flags & B_CLUSTER))
                return (0);
        /*
         * see buf_map for the explanation
         */
        real_bp = (buf_t)(bp->b_real_bp);

        if (real_bp && real_bp->b_datap)
                return (0);

        if ((bp->b_lflags & BL_IOBUF) &&
            ((bp->b_flags & (B_PAGEIO | B_READ)) != (B_PAGEIO | B_READ))) {
                /*
                 * ignore pageins... the 'right' thing will
                 * happen due to the way we handle speculative
                 * clusters...
                 *
                 * when we commit these pages, we'll hit
                 * it with UPL_COMMIT_INACTIVE which
                 * will clear the reference bit that got
                 * turned on when we touched the mapping
                 */
                bp->b_flags |= B_AGE;
        }
        kret = ubc_upl_unmap(bp->b_upl);

        if (kret != KERN_SUCCESS)
                return (EINVAL);
        return (0);
}


void
buf_clear(buf_t bp) {
        caddr_t baddr;
  
        if (buf_map(bp, &baddr) == 0) {
                bzero(baddr, bp->b_bcount);
                buf_unmap(bp);
        }
        bp->b_resid = 0;
}

/*
 * Read or write a buffer that is not contiguous on disk.
 * buffer is marked done/error at the conclusion
 */
static int
buf_strategy_fragmented(vnode_t devvp, buf_t bp, off_t f_offset, size_t contig_bytes)
{
        vnode_t vp = buf_vnode(bp);
        buf_t   io_bp;                   /* For reading or writing a single block */
        int     io_direction;
        int     io_resid;
        size_t  io_contig_bytes;
        daddr64_t io_blkno;
        int     error = 0;
        int     bmap_flags;

        /*
         * save our starting point... the bp was already mapped
         * in buf_strategy before we got called
         * no sense doing it again.
         */
        io_blkno = bp->b_blkno;
        /*
         * Make sure we redo this mapping for the next I/O
         * i.e. this can never be a 'permanent' mapping
         */
        bp->b_blkno = bp->b_lblkno;
        
        /*
         * Get an io buffer to do the deblocking
         */
        io_bp = alloc_io_buf(devvp, 0);

        io_bp->b_lblkno = bp->b_lblkno;
        io_bp->b_datap  = bp->b_datap;
        io_resid        = bp->b_bcount;
        io_direction    = bp->b_flags & B_READ;
        io_contig_bytes = contig_bytes;
        
        if (bp->b_flags & B_READ)
                bmap_flags = VNODE_READ;
        else
                bmap_flags = VNODE_WRITE;

        for (;;) {
                if (io_blkno == -1)
                        /*
                         * this is unexepected, but we'll allow for it
                         */
                        bzero((caddr_t)io_bp->b_datap, (int)io_contig_bytes);
                else {
                        io_bp->b_bcount  = io_contig_bytes;
                        io_bp->b_bufsize = io_contig_bytes;
                        io_bp->b_resid   = io_contig_bytes;
                        io_bp->b_blkno   = io_blkno;

                        buf_reset(io_bp, io_direction);

                        /*
                         * Call the device to do the I/O and wait for it.  Make sure the appropriate party is charged for write
                         */

                        if (!ISSET(bp->b_flags, B_READ))
                                OSAddAtomic(1, &devvp->v_numoutput);

                        if ((error = VNOP_STRATEGY(io_bp)))
                                break;
                        if ((error = (int)buf_biowait(io_bp)))
                                break;
                        if (io_bp->b_resid) {
                                io_resid -= (io_contig_bytes - io_bp->b_resid);
                                break;
                        }
                }
                if ((io_resid -= io_contig_bytes) == 0)
                        break;
                f_offset       += io_contig_bytes;
                io_bp->b_datap += io_contig_bytes;

                /*
                 * Map the current position to a physical block number
                 */
                if ((error = VNOP_BLOCKMAP(vp, f_offset, io_resid, &io_blkno, &io_contig_bytes, NULL, bmap_flags, NULL)))
                        break;
        }
        buf_free(io_bp);
        
        if (error)
                buf_seterror(bp, error);
        bp->b_resid = io_resid;
        /*
         * This I/O is now complete
         */
        buf_biodone(bp);

        return error;
}


/*
 * struct vnop_strategy_args {
 *      struct buf *a_bp;
 * } *ap;
 */
errno_t
buf_strategy(vnode_t devvp, void *ap)
{
        buf_t   bp = ((struct vnop_strategy_args *)ap)->a_bp;
        vnode_t vp = bp->b_vp;
        int     bmap_flags;
        errno_t error;

        if (vp == NULL || vp->v_type == VCHR || vp->v_type == VBLK)
                panic("buf_strategy: b_vp == NULL || vtype == VCHR | VBLK\n");
        /*
         * associate the physical device with
         * with this buf_t even if we don't
         * end up issuing the I/O...
         */
        bp->b_dev = devvp->v_rdev;
        DTRACE_IO1(start, buf_t, bp);

        if (bp->b_flags & B_READ)
                bmap_flags = VNODE_READ;
        else
                bmap_flags = VNODE_WRITE;

        if ( !(bp->b_flags & B_CLUSTER)) {

                if ( (bp->b_upl) ) {
                        /*
                         * we have a UPL associated with this bp
                         * go through cluster_bp which knows how
                         * to deal with filesystem block sizes
                         * that aren't equal to the page size
                         */
                        return (cluster_bp(bp));
                }
                if (bp->b_blkno == bp->b_lblkno) {
                        off_t   f_offset;
                        size_t  contig_bytes;
                  
                        if ((error = VNOP_BLKTOOFF(vp, bp->b_lblkno, &f_offset))) {
                                buf_seterror(bp, error);
                                buf_biodone(bp);

                                return (error);
                        }
                        if ((error = VNOP_BLOCKMAP(vp, f_offset, bp->b_bcount, &bp->b_blkno, &contig_bytes, NULL, bmap_flags, NULL))) {
                                buf_seterror(bp, error);
                                buf_biodone(bp);

                                return (error);
                        }
                        if ((bp->b_blkno == -1) || (contig_bytes == 0)) {
                                /* Set block number to force biodone later */
                                bp->b_blkno = -1;
                                buf_clear(bp);
                        }
                        else if ((long)contig_bytes < bp->b_bcount)
                                return (buf_strategy_fragmented(devvp, bp, f_offset, contig_bytes));
                }
                if (bp->b_blkno == -1) {
                        buf_biodone(bp);
                        return (0);
                }
        }
        /*
         * we can issue the I/O because...
         * either B_CLUSTER is set which
         * means that the I/O is properly set
         * up to be a multiple of the page size, or
         * we were able to successfully set up the
         * phsyical block mapping
         */
        return (VOCALL(devvp->v_op, VOFFSET(vnop_strategy), ap));
}



buf_t
buf_alloc(vnode_t vp)
{
        return(alloc_io_buf(vp, 0));
}

void
buf_free(buf_t bp) {
        
        free_io_buf(bp);
}


/*
 * iterate buffers for the specified vp. 
 *   if BUF_SCAN_DIRTY is set, do the dirty list
 *   if BUF_SCAN_CLEAN is set, do the clean list
 *   if neither flag is set, default to BUF_SCAN_DIRTY
 *   if BUF_NOTIFY_BUSY is set, call the callout function using a NULL bp for busy pages
 */

struct buf_iterate_info_t {
        int flag;
        struct buflists *listhead;
};

void
buf_iterate(vnode_t vp, int (*callout)(buf_t, void *), int flags, void *arg)
{
        buf_t   bp;
        int     retval;
        struct  buflists local_iterblkhd;
        int     lock_flags = BAC_NOWAIT | BAC_REMOVE;
        int     notify_busy = flags & BUF_NOTIFY_BUSY;
        struct buf_iterate_info_t list[2];
        int     num_lists, i;

        if (flags & BUF_SKIP_LOCKED)
                lock_flags |= BAC_SKIP_LOCKED;
        if (flags & BUF_SKIP_NONLOCKED)
                lock_flags |= BAC_SKIP_NONLOCKED;

        if ( !(flags & (BUF_SCAN_DIRTY | BUF_SCAN_CLEAN)))
                flags |= BUF_SCAN_DIRTY;

        num_lists = 0;

        if (flags & BUF_SCAN_DIRTY) {
                list[num_lists].flag = VBI_DIRTY;
                list[num_lists].listhead = &vp->v_dirtyblkhd;
                num_lists++;
        }
        if (flags & BUF_SCAN_CLEAN) {
                list[num_lists].flag = VBI_CLEAN;
                list[num_lists].listhead = &vp->v_cleanblkhd;
                num_lists++;
        }

        for (i = 0; i < num_lists; i++) {
                lck_mtx_lock(buf_mtxp);
        
                if (buf_iterprepare(vp, &local_iterblkhd, list[i].flag))  {
                        lck_mtx_unlock(buf_mtxp);
                        continue;
                }
                while (!LIST_EMPTY(&local_iterblkhd)) {
                        bp = LIST_FIRST(&local_iterblkhd);
                        LIST_REMOVE(bp, b_vnbufs);
                        LIST_INSERT_HEAD(list[i].listhead, bp, b_vnbufs);

                        if (buf_acquire_locked(bp, lock_flags, 0, 0)) {
                                if (notify_busy) {
                                        bp = NULL;
                                } else {
                                        continue;
                                }
                        }

                        lck_mtx_unlock(buf_mtxp);

                        retval = callout(bp, arg);

                        switch (retval) {
                        case BUF_RETURNED:
                                if (bp)
                                        buf_brelse(bp);
                                break;
                        case BUF_CLAIMED:
                                break;
                        case BUF_RETURNED_DONE:
                                if (bp)
                                        buf_brelse(bp);
                                lck_mtx_lock(buf_mtxp);
                                goto out;
                        case BUF_CLAIMED_DONE:
                                lck_mtx_lock(buf_mtxp);
                                goto out;
                        }
                        lck_mtx_lock(buf_mtxp);
                } /* while list has more nodes */
          out:
                buf_itercomplete(vp, &local_iterblkhd, list[i].flag);
                lck_mtx_unlock(buf_mtxp);
        } /* for each list */
} /* buf_iterate */


/*
 * Flush out and invalidate all buffers associated with a vnode.
 */
int
buf_invalidateblks(vnode_t vp, int flags, int slpflag, int slptimeo)
{
        buf_t   bp;
        int     error = 0;
        int     must_rescan = 1;
        struct  buflists local_iterblkhd;


        if (LIST_EMPTY(&vp->v_cleanblkhd) && LIST_EMPTY(&vp->v_dirtyblkhd))
                return (0);

        lck_mtx_lock(buf_mtxp);

        for (;;) {
                if (must_rescan == 0)
                        /*
                         * the lists may not be empty, but all that's left at this
                         * point are metadata or B_LOCKED buffers which are being
                         * skipped... we know this because we made it through both
                         * the clean and dirty lists without dropping buf_mtxp...
                         * each time we drop buf_mtxp we bump "must_rescan"
                         */
                        break;
                if (LIST_EMPTY(&vp->v_cleanblkhd) && LIST_EMPTY(&vp->v_dirtyblkhd))
                        break;
                must_rescan = 0;
                /*
                 * iterate the clean list
                 */
                if (buf_iterprepare(vp, &local_iterblkhd, VBI_CLEAN)) {
                        goto try_dirty_list;
                }
                while (!LIST_EMPTY(&local_iterblkhd)) {
                        bp = LIST_FIRST(&local_iterblkhd);

                        LIST_REMOVE(bp, b_vnbufs);
                        LIST_INSERT_HEAD(&vp->v_cleanblkhd, bp, b_vnbufs);

                        /*
                         * some filesystems distinguish meta data blocks with a negative logical block #
                         */
                        if ((flags & BUF_SKIP_META) && (bp->b_lblkno < 0 || ISSET(bp->b_flags, B_META)))
                                continue;

                        if ( (error = (int)buf_acquire_locked(bp, BAC_REMOVE | BAC_SKIP_LOCKED, slpflag, slptimeo)) ) {
                                if (error == EDEADLK)
                                        /*      
                                         * this buffer was marked B_LOCKED... 
                                         * we didn't drop buf_mtxp, so we
                                         * we don't need to rescan
                                         */
                                        continue;
                                if (error == EAGAIN) {
                                        /*
                                         * found a busy buffer... we blocked and
                                         * dropped buf_mtxp, so we're going to
                                         * need to rescan after this pass is completed
                                         */
                                        must_rescan++;
                                        continue;
                                }
                                /*
                                 * got some kind of 'real' error out of the msleep
                                 * in buf_acquire_locked, terminate the scan and return the error
                                 */
                                buf_itercomplete(vp, &local_iterblkhd, VBI_CLEAN);

                                lck_mtx_unlock(buf_mtxp);
                                return (error);
                        }
                        lck_mtx_unlock(buf_mtxp);

                        SET(bp->b_flags, B_INVAL);
                        buf_brelse(bp);

                        lck_mtx_lock(buf_mtxp);

                        /*
                         * by dropping buf_mtxp, we allow new
                         * buffers to be added to the vnode list(s)
                         * we'll have to rescan at least once more
                         * if the queues aren't empty
                         */
                        must_rescan++;
                }
                buf_itercomplete(vp, &local_iterblkhd, VBI_CLEAN);

try_dirty_list:
                /*
                 * Now iterate on dirty blks
                 */
                if (buf_iterprepare(vp, &local_iterblkhd, VBI_DIRTY)) {
                        continue;
                }
                while (!LIST_EMPTY(&local_iterblkhd)) {
                        bp = LIST_FIRST(&local_iterblkhd);

                        LIST_REMOVE(bp, b_vnbufs);
                        LIST_INSERT_HEAD(&vp->v_dirtyblkhd, bp, b_vnbufs);

                        /*
                         * some filesystems distinguish meta data blocks with a negative logical block #
                         */
                        if ((flags & BUF_SKIP_META) && (bp->b_lblkno < 0 || ISSET(bp->b_flags, B_META)))
                                continue;

                        if ( (error = (int)buf_acquire_locked(bp, BAC_REMOVE | BAC_SKIP_LOCKED, slpflag, slptimeo)) ) {
                                if (error == EDEADLK)
                                        /*      
                                         * this buffer was marked B_LOCKED... 
                                         * we didn't drop buf_mtxp, so we
                                         * we don't need to rescan
                                         */
                                        continue;
                                if (error == EAGAIN) {
                                        /*
                                         * found a busy buffer... we blocked and
                                         * dropped buf_mtxp, so we're going to
                                         * need to rescan after this pass is completed
                                         */
                                        must_rescan++;
                                        continue;
                                }
                                /*
                                 * got some kind of 'real' error out of the msleep
                                 * in buf_acquire_locked, terminate the scan and return the error
                                 */
                                buf_itercomplete(vp, &local_iterblkhd, VBI_DIRTY);

                                lck_mtx_unlock(buf_mtxp);
                                return (error);
                        }
                        lck_mtx_unlock(buf_mtxp);

                        SET(bp->b_flags, B_INVAL);

                        if (ISSET(bp->b_flags, B_DELWRI) && (flags & BUF_WRITE_DATA))
                                (void) VNOP_BWRITE(bp);
                        else
                                buf_brelse(bp);

                        lck_mtx_lock(buf_mtxp);
                        /*
                         * by dropping buf_mtxp, we allow new
                         * buffers to be added to the vnode list(s)
                         * we'll have to rescan at least once more
                         * if the queues aren't empty
                         */
                        must_rescan++;
                }
                buf_itercomplete(vp, &local_iterblkhd, VBI_DIRTY);
        }
        lck_mtx_unlock(buf_mtxp);

        return (0);
}

void
buf_flushdirtyblks(vnode_t vp, int wait, int flags, const char *msg) {
        buf_t   bp;
        int     writes_issued = 0;
        errno_t error;
        int     busy = 0;
        struct  buflists local_iterblkhd;
        int     lock_flags = BAC_NOWAIT | BAC_REMOVE;

        if (flags & BUF_SKIP_LOCKED)
                lock_flags |= BAC_SKIP_LOCKED;
        if (flags & BUF_SKIP_NONLOCKED)
                lock_flags |= BAC_SKIP_NONLOCKED;
loop:
        lck_mtx_lock(buf_mtxp);

        if (buf_iterprepare(vp, &local_iterblkhd, VBI_DIRTY) == 0)  {
                while (!LIST_EMPTY(&local_iterblkhd)) {
                        bp = LIST_FIRST(&local_iterblkhd);
                        LIST_REMOVE(bp, b_vnbufs);
                        LIST_INSERT_HEAD(&vp->v_dirtyblkhd, bp, b_vnbufs);
                        
                        if ((error = buf_acquire_locked(bp, lock_flags, 0, 0)) == EBUSY)
                                busy++;
                        if (error)
                                continue;
                        lck_mtx_unlock(buf_mtxp);

                        bp->b_flags &= ~B_LOCKED;

                        /*
                         * Wait for I/O associated with indirect blocks to complete,
                         * since there is no way to quickly wait for them below.
                         */
                        if ((bp->b_vp == vp) || (wait == 0))
                                (void) buf_bawrite(bp);
                        else
                                (void) VNOP_BWRITE(bp);
                        writes_issued++;

                        lck_mtx_lock(buf_mtxp);
                }
                buf_itercomplete(vp, &local_iterblkhd, VBI_DIRTY);
        }
        lck_mtx_unlock(buf_mtxp);
        
        if (wait) {
                (void)vnode_waitforwrites(vp, 0, 0, 0, msg);

                if (vp->v_dirtyblkhd.lh_first && busy) {
                        /*
                         * we had one or more BUSY buffers on
                         * the dirtyblock list... most likely
                         * these are due to delayed writes that
                         * were moved to the bclean queue but
                         * have not yet been 'written'.
                         * if we issued some writes on the 
                         * previous pass, we try again immediately
                         * if we didn't, we'll sleep for some time
                         * to allow the state to change...
                         */
                        if (writes_issued == 0) {
                                (void)tsleep((caddr_t)&vp->v_numoutput,
                                             PRIBIO + 1, "vnode_flushdirtyblks", hz/20);
                        }
                        writes_issued = 0;
                        busy = 0;

                        goto loop;
                }
        }
}


/*
 * called with buf_mtxp held...
 * this lock protects the queue manipulation
 */
static int
buf_iterprepare(vnode_t vp, struct buflists *iterheadp, int flags)
{
        struct buflists * listheadp;

        if (flags & VBI_DIRTY)
                listheadp = &vp->v_dirtyblkhd;
        else
                listheadp = &vp->v_cleanblkhd;
                
        while (vp->v_iterblkflags & VBI_ITER)   {
                vp->v_iterblkflags |= VBI_ITERWANT;
                msleep(&vp->v_iterblkflags, buf_mtxp, 0, "buf_iterprepare", NULL);      
        }
        if (LIST_EMPTY(listheadp)) {
                LIST_INIT(iterheadp);
                return(EINVAL);
        }
        vp->v_iterblkflags |= VBI_ITER;

        iterheadp->lh_first = listheadp->lh_first;
        listheadp->lh_first->b_vnbufs.le_prev = &iterheadp->lh_first;   
        LIST_INIT(listheadp);

        return(0);
}

/*
 * called with buf_mtxp held...
 * this lock protects the queue manipulation
 */
static void
buf_itercomplete(vnode_t vp, struct buflists *iterheadp, int flags)
{
        struct buflists * listheadp;
        buf_t bp;

        if (flags & VBI_DIRTY)
                listheadp = &vp->v_dirtyblkhd;
        else
                listheadp = &vp->v_cleanblkhd;

        while (!LIST_EMPTY(iterheadp)) {
                bp = LIST_FIRST(iterheadp);
                LIST_REMOVE(bp, b_vnbufs);
                LIST_INSERT_HEAD(listheadp, bp, b_vnbufs);
        }
        vp->v_iterblkflags &= ~VBI_ITER;

        if  (vp->v_iterblkflags & VBI_ITERWANT)         {
                vp->v_iterblkflags &= ~VBI_ITERWANT;
                wakeup(&vp->v_iterblkflags);
        }
}


static void
bremfree_locked(buf_t bp)
{
        struct bqueues *dp = NULL;
        int whichq;
        /*
         * We only calculate the head of the freelist when removing
         * the last element of the list as that is the only time that
         * it is needed (e.g. to reset the tail pointer).
         *
         * NB: This makes an assumption about how tailq's are implemented.
         */
        whichq = bp->b_whichq;

        if (bp->b_freelist.tqe_next == NULL) {
                dp = &bufqueues[whichq];

                if (dp->tqh_last != &bp->b_freelist.tqe_next)
                        panic("bremfree: lost tail");
        }
        TAILQ_REMOVE(dp, bp, b_freelist);

#if BALANCE_QUEUES
        bufqdec(whichq);
#endif
        if (whichq == BQ_LAUNDRY)
                blaundrycnt--;

        bp->b_whichq = -1;
        bp->b_timestamp = 0; 
}

/*
 * Associate a buffer with a vnode.
 * buf_mtxp must be locked on entry
 */
static void
bgetvp_locked(vnode_t vp, buf_t bp)
{

        if (bp->b_vp != vp)
                panic("bgetvp_locked: not free");

        if (vp->v_type == VBLK || vp->v_type == VCHR)
                bp->b_dev = vp->v_rdev;
        else
                bp->b_dev = NODEV;
        /*
         * Insert onto list for new vnode.
         */
        bufinsvn(bp, &vp->v_cleanblkhd);
}

/*
 * Disassociate a buffer from a vnode.
 * buf_mtxp must be locked on entry
 */
static void
brelvp_locked(buf_t bp)
{
        /*
         * Delete from old vnode list, if on one.
         */
        if (bp->b_vnbufs.le_next != NOLIST)
                bufremvn(bp);

        bp->b_vp = (vnode_t)NULL;
}

/*
 * Reassign a buffer from one vnode to another.
 * Used to assign file specific control information
 * (indirect blocks) to the vnode to which they belong.
 */
static void
buf_reassign(buf_t bp, vnode_t newvp)
{
        register struct buflists *listheadp;

        if (newvp == NULL) {
                printf("buf_reassign: NULL");
                return;
        }
        lck_mtx_lock_spin(buf_mtxp);

        /*
         * Delete from old vnode list, if on one.
         */
        if (bp->b_vnbufs.le_next != NOLIST)
                bufremvn(bp);
        /*
         * If dirty, put on list of dirty buffers;
         * otherwise insert onto list of clean buffers.
         */
        if (ISSET(bp->b_flags, B_DELWRI))
                listheadp = &newvp->v_dirtyblkhd;
        else
                listheadp = &newvp->v_cleanblkhd;
        bufinsvn(bp, listheadp);

        lck_mtx_unlock(buf_mtxp);
}

static __inline__ void
bufhdrinit(buf_t bp)
{
        bzero((char *)bp, sizeof *bp);
        bp->b_dev = NODEV;
        bp->b_rcred = NOCRED;
        bp->b_wcred = NOCRED;
        bp->b_vnbufs.le_next = NOLIST;
        bp->b_flags = B_INVAL;

        return;
}

/*
 * Initialize buffers and hash links for buffers.
 */
__private_extern__ void
bufinit(void)
{
        buf_t   bp;
        struct bqueues *dp;
        int     i;

        nbuf_headers = 0;
        /* Initialize the buffer queues ('freelists') and the hash table */
        for (dp = bufqueues; dp < &bufqueues[BQUEUES]; dp++)
                TAILQ_INIT(dp);
        bufhashtbl = hashinit(nbuf_hashelements, M_CACHE, &bufhash);

        buf_busycount = 0;

        /* Initialize the buffer headers */
        for (i = 0; i < max_nbuf_headers; i++) {
                nbuf_headers++;
                bp = &buf_headers[i];
                bufhdrinit(bp);

                BLISTNONE(bp);
                dp = &bufqueues[BQ_EMPTY];
                bp->b_whichq = BQ_EMPTY;
                bp->b_timestamp = buf_timestamp();
                binsheadfree(bp, dp, BQ_EMPTY);
                binshash(bp, &invalhash);
        }

        boot_nbuf_headers = nbuf_headers;
        for (; i < nbuf_headers + niobuf_headers; i++) {
                bp = &buf_headers[i];
                bufhdrinit(bp);
                bp->b_whichq = -1;
                binsheadfree(bp, &iobufqueue, -1);
        }

        /*
         * allocate lock group attribute and group
         */
        buf_mtx_grp_attr = lck_grp_attr_alloc_init();
        buf_mtx_grp = lck_grp_alloc_init("buffer cache", buf_mtx_grp_attr);
                
        /*
         * allocate the lock attribute
         */
        buf_mtx_attr = lck_attr_alloc_init();

        /*
         * allocate and initialize mutex's for the buffer and iobuffer pools
         */
        buf_mtxp        = lck_mtx_alloc_init(buf_mtx_grp, buf_mtx_attr);
        iobuffer_mtxp   = lck_mtx_alloc_init(buf_mtx_grp, buf_mtx_attr);

        if (iobuffer_mtxp == NULL)
                panic("couldn't create iobuffer mutex");

        if (buf_mtxp == NULL)
                panic("couldn't create buf mutex");

        /*
         * allocate and initialize cluster specific global locks...
         */
        cluster_init();

        printf("using %d buffer headers and %d cluster IO buffer headers\n",
                nbuf_headers, niobuf_headers);

        /* Set up zones used by the buffer cache */
        bufzoneinit();

        /* start the bcleanbuf() thread */
        bcleanbuf_thread_init();

        /* Register a callout for relieving vm pressure */
        if (vm_set_buffer_cleanup_callout(buffer_cache_gc) != KERN_SUCCESS) {
                panic("Couldn't register buffer cache callout for vm pressure!\n");
        }

#if BALANCE_QUEUES
        {
        static void bufq_balance_thread_init(void) __attribute__((section("__TEXT, initcode")));
        /* create a thread to do dynamic buffer queue balancing */
        bufq_balance_thread_init();
        }
#endif /* notyet */
}



/*
 * Zones for the meta data buffers
 */

#define MINMETA 512
#define MAXMETA 8192

struct meta_zone_entry {
        zone_t mz_zone;
        vm_size_t mz_size;
        vm_size_t mz_max;
        const char *mz_name;
};

struct meta_zone_entry meta_zones[] = {
        {NULL, (MINMETA * 1), 128 * (MINMETA * 1), "buf.512" },
        {NULL, (MINMETA * 2),  64 * (MINMETA * 2), "buf.1024" },
        {NULL, (MINMETA * 4),  16 * (MINMETA * 4), "buf.2048" },
        {NULL, (MINMETA * 8), 512 * (MINMETA * 8), "buf.4096" },
        {NULL, (MINMETA * 16), 512 * (MINMETA * 16), "buf.8192" },
        {NULL, 0, 0, "" } /* End */
};

/*
 * Initialize the meta data zones
 */
static void
bufzoneinit(void)
{
        int i;

        for (i = 0; meta_zones[i].mz_size != 0; i++) {
                meta_zones[i].mz_zone = 
                                zinit(meta_zones[i].mz_size,
                                        meta_zones[i].mz_max,
                                        PAGE_SIZE,
                                        meta_zones[i].mz_name);
        }
        buf_hdr_zone = zinit(sizeof(struct buf), 32, PAGE_SIZE, "buf headers");
}

static __inline__ zone_t
getbufzone(size_t size)
{
        int i;

        if ((size % 512) || (size < MINMETA) || (size > MAXMETA))
                panic("getbufzone: incorect size = %lu", size);

        for (i = 0; meta_zones[i].mz_size != 0; i++) {
                if (meta_zones[i].mz_size >= size)
                        break;
        }

        return (meta_zones[i].mz_zone);
}



static struct buf *
bio_doread(vnode_t vp, daddr64_t blkno, int size, kauth_cred_t cred, int async, int queuetype)
{
        buf_t   bp;

        bp = buf_getblk(vp, blkno, size, 0, 0, queuetype);

        /*
         * If buffer does not have data valid, start a read.
         * Note that if buffer is B_INVAL, buf_getblk() won't return it.
         * Therefore, it's valid if it's I/O has completed or been delayed.
         */
        if (!ISSET(bp->b_flags, (B_DONE | B_DELWRI))) {
                struct proc *p;

                p = current_proc();

                /* Start I/O for the buffer (keeping credentials). */
                SET(bp->b_flags, B_READ | async);
                if (IS_VALID_CRED(cred) && !IS_VALID_CRED(bp->b_rcred)) {
                        kauth_cred_ref(cred);
                        bp->b_rcred = cred;
                }

                VNOP_STRATEGY(bp);

                trace(TR_BREADMISS, pack(vp, size), blkno);

                /* Pay for the read. */
                if (p && p->p_stats) 
                        OSIncrementAtomicLong(&p->p_stats->p_ru.ru_inblock);            /* XXX */

                if (async) {
                        /*
                         * since we asked for an ASYNC I/O
                         * the biodone will do the brelse
                         * we don't want to pass back a bp
                         * that we don't 'own'
                         */
                        bp = NULL;
                }
        } else if (async) {
                buf_brelse(bp);
                bp = NULL;
        }

        trace(TR_BREADHIT, pack(vp, size), blkno);

        return (bp);
}

/*
 * Perform the reads for buf_breadn() and buf_meta_breadn(). 
 * Trivial modification to the breada algorithm presented in Bach (p.55). 
 */
static errno_t
do_breadn_for_type(vnode_t vp, daddr64_t blkno, int size, daddr64_t *rablks, int *rasizes, 
                   int nrablks, kauth_cred_t cred, buf_t *bpp, int queuetype)
{
        buf_t   bp;
        int     i;

        bp = *bpp = bio_doread(vp, blkno, size, cred, 0, queuetype);

        /*
         * For each of the read-ahead blocks, start a read, if necessary.
         */
        for (i = 0; i < nrablks; i++) {
                /* If it's in the cache, just go on to next one. */
                if (incore(vp, rablks[i]))
                        continue;

                /* Get a buffer for the read-ahead block */
                (void) bio_doread(vp, rablks[i], rasizes[i], cred, B_ASYNC, queuetype);
        }

        /* Otherwise, we had to start a read for it; wait until it's valid. */
        return (buf_biowait(bp));
}


/*
 * Read a disk block.
 * This algorithm described in Bach (p.54).
 */
errno_t
buf_bread(vnode_t vp, daddr64_t blkno, int size, kauth_cred_t cred, buf_t *bpp)
{
        buf_t   bp;

        /* Get buffer for block. */
        bp = *bpp = bio_doread(vp, blkno, size, cred, 0, BLK_READ);

        /* Wait for the read to complete, and return result. */
        return (buf_biowait(bp));
}

/*
 * Read a disk block. [bread() for meta-data]
 * This algorithm described in Bach (p.54).
 */
errno_t
buf_meta_bread(vnode_t vp, daddr64_t blkno, int size, kauth_cred_t cred, buf_t *bpp)
{
        buf_t   bp;

        /* Get buffer for block. */
        bp = *bpp = bio_doread(vp, blkno, size, cred, 0, BLK_META);

        /* Wait for the read to complete, and return result. */
        return (buf_biowait(bp));
}

/*
 * Read-ahead multiple disk blocks. The first is sync, the rest async.
 */
errno_t
buf_breadn(vnode_t vp, daddr64_t blkno, int size, daddr64_t *rablks, int *rasizes, int nrablks, kauth_cred_t cred, buf_t *bpp)
{
        return (do_breadn_for_type(vp, blkno, size, rablks, rasizes, nrablks, cred, bpp, BLK_READ));
}

/*
 * Read-ahead multiple disk blocks. The first is sync, the rest async.
 * [buf_breadn() for meta-data]
 */
errno_t
buf_meta_breadn(vnode_t vp, daddr64_t blkno, int size, daddr64_t *rablks, int *rasizes, int nrablks, kauth_cred_t cred, buf_t *bpp)
{
        return (do_breadn_for_type(vp, blkno, size, rablks, rasizes, nrablks, cred, bpp, BLK_META));
}

/*
 * Block write.  Described in Bach (p.56)
 */
errno_t
buf_bwrite(buf_t bp)
{
        int     sync, wasdelayed;
        errno_t rv;
        proc_t  p = current_proc();
        vnode_t vp = bp->b_vp;

        if (bp->b_datap == 0) {
                if (brecover_data(bp) == 0)
                        return (0);
        }
        /* Remember buffer type, to switch on it later. */
        sync = !ISSET(bp->b_flags, B_ASYNC);
        wasdelayed = ISSET(bp->b_flags, B_DELWRI);
        CLR(bp->b_flags, (B_READ | B_DONE | B_ERROR | B_DELWRI));

        if (wasdelayed)
                OSAddAtomicLong(-1, &nbdwrite);

        if (!sync) {
                /*
                 * If not synchronous, pay for the I/O operation and make
                 * sure the buf is on the correct vnode queue.  We have
                 * to do this now, because if we don't, the vnode may not
                 * be properly notified that its I/O has completed.
                 */
                if (wasdelayed)
                        buf_reassign(bp, vp);
                else
                if (p && p->p_stats) 
                        OSIncrementAtomicLong(&p->p_stats->p_ru.ru_oublock);    /* XXX */
        }
        trace(TR_BUFWRITE, pack(vp, bp->b_bcount), bp->b_lblkno);

        /* Initiate disk write.  Make sure the appropriate party is charged. */

        OSAddAtomic(1, &vp->v_numoutput);
        
        VNOP_STRATEGY(bp);

        if (sync) {
                /*
                 * If I/O was synchronous, wait for it to complete.
                 */
                rv = buf_biowait(bp);

                /*
                 * Pay for the I/O operation, if it's not been paid for, and
                 * make sure it's on the correct vnode queue. (async operatings
                 * were payed for above.)
                 */
                if (wasdelayed)
                        buf_reassign(bp, vp);
                else
                if (p && p->p_stats) 
                        OSIncrementAtomicLong(&p->p_stats->p_ru.ru_oublock);    /* XXX */

                /* Release the buffer. */
                // XXXdbg - only if the unused bit is set
                if (!ISSET(bp->b_flags, B_NORELSE)) {
                    buf_brelse(bp);
                } else {
                    CLR(bp->b_flags, B_NORELSE);
                }

                return (rv);
        } else {
                return (0);
        }
}

int
vn_bwrite(struct vnop_bwrite_args *ap)
{
        return (buf_bwrite(ap->a_bp));
}

/*
 * Delayed write.
 *
 * The buffer is marked dirty, but is not queued for I/O.
 * This routine should be used when the buffer is expected
 * to be modified again soon, typically a small write that
 * partially fills a buffer.
 *
 * NB: magnetic tapes cannot be delayed; they must be
 * written in the order that the writes are requested.
 *
 * Described in Leffler, et al. (pp. 208-213).
 *
 * Note: With the ability to allocate additional buffer
 * headers, we can get in to the situation where "too" many 
 * buf_bdwrite()s can create situation where the kernel can create
 * buffers faster than the disks can service. Doing a buf_bawrite() in
 * cases were we have "too many" outstanding buf_bdwrite()s avoids that.
 */
__private_extern__ int
bdwrite_internal(buf_t bp, int return_error)
{
        proc_t  p  = current_proc();
        vnode_t vp = bp->b_vp;

        /*
         * If the block hasn't been seen before:
         *      (1) Mark it as having been seen,
         *      (2) Charge for the write.
         *      (3) Make sure it's on its vnode's correct block list,
         */
        if (!ISSET(bp->b_flags, B_DELWRI)) {
                SET(bp->b_flags, B_DELWRI);
                if (p && p->p_stats) 
                        OSIncrementAtomicLong(&p->p_stats->p_ru.ru_oublock);    /* XXX */
                OSAddAtomicLong(1, &nbdwrite);
                buf_reassign(bp, vp);
        }

        /*
         * if we're not LOCKED, but the total number of delayed writes
         * has climbed above 75% of the total buffers in the system
         * return an error if the caller has indicated that it can 
         * handle one in this case, otherwise schedule the I/O now
         * this is done to prevent us from allocating tons of extra
         * buffers when dealing with virtual disks (i.e. DiskImages),
         * because additional buffers are dynamically allocated to prevent
         * deadlocks from occurring
         *
         * however, can't do a buf_bawrite() if the LOCKED bit is set because the
         * buffer is part of a transaction and can't go to disk until
         * the LOCKED bit is cleared.
         */
        if (!ISSET(bp->b_flags, B_LOCKED) && nbdwrite > ((nbuf_headers/4)*3)) {
                if (return_error)
                        return (EAGAIN);
                /*
                 * If the vnode has "too many" write operations in progress
                 * wait for them to finish the IO
                 */
                (void)vnode_waitforwrites(vp, VNODE_ASYNC_THROTTLE, 0, 0, "buf_bdwrite");

                return (buf_bawrite(bp));
        }
         
        /* Otherwise, the "write" is done, so mark and release the buffer. */
        SET(bp->b_flags, B_DONE);
        buf_brelse(bp);
        return (0);
}

errno_t
buf_bdwrite(buf_t bp)
{
        return (bdwrite_internal(bp, 0));
}
 

/*
 * Asynchronous block write; just an asynchronous buf_bwrite().
 *
 * Note: With the abilitty to allocate additional buffer
 * headers, we can get in to the situation where "too" many 
 * buf_bawrite()s can create situation where the kernel can create
 * buffers faster than the disks can service.
 * We limit the number of "in flight" writes a vnode can have to
 * avoid this.
 */
static int
bawrite_internal(buf_t bp, int throttle)
{
        vnode_t vp = bp->b_vp;

        if (vp) {
                if (throttle)
                        /*
                         * If the vnode has "too many" write operations in progress
                         * wait for them to finish the IO
                         */
                        (void)vnode_waitforwrites(vp, VNODE_ASYNC_THROTTLE, 0, 0, (const char *)"buf_bawrite");
                else if (vp->v_numoutput >= VNODE_ASYNC_THROTTLE)
                        /*
                         * return to the caller and 
                         * let him decide what to do
                         */
                        return (EWOULDBLOCK);
        }
        SET(bp->b_flags, B_ASYNC);

        return (VNOP_BWRITE(bp));
}

errno_t
buf_bawrite(buf_t bp)
{
        return (bawrite_internal(bp, 1));
}


/*
 * Release a buffer on to the free lists.
 * Described in Bach (p. 46).
 */
void
buf_brelse(buf_t bp)
{
        struct bqueues *bufq;
        long    whichq;
        upl_t   upl;
        int need_wakeup = 0;
        int need_bp_wakeup = 0;


        if (bp->b_whichq != -1 || !(bp->b_lflags & BL_BUSY))
                panic("buf_brelse: bad buffer = %p\n", bp);

#ifdef JOE_DEBUG
        (void) OSBacktrace(&bp->b_stackbrelse[0], 6);

        bp->b_lastbrelse = current_thread();
        bp->b_tag = 0;
#endif
        if (bp->b_lflags & BL_IOBUF) {
                free_io_buf(bp);
                return;
        }

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 388)) | DBG_FUNC_START,
                     bp->b_lblkno * PAGE_SIZE, bp, bp->b_datap,
                     bp->b_flags, 0);

        trace(TR_BRELSE, pack(bp->b_vp, bp->b_bufsize), bp->b_lblkno);

        /*
         * if we're invalidating a buffer that has the B_FILTER bit
         * set then call the b_iodone function so it gets cleaned
         * up properly.
         *
         * the HFS journal code depends on this
         */
        if (ISSET(bp->b_flags, B_META) && ISSET(bp->b_flags, B_INVAL)) {
                if (ISSET(bp->b_flags, B_FILTER)) {     /* if necessary, call out */
                        void    (*iodone_func)(struct buf *, void *) = bp->b_iodone;
                        void    *arg = (void *)bp->b_transaction;

                        CLR(bp->b_flags, B_FILTER);     /* but note callout done */
                        bp->b_iodone = NULL;
                        bp->b_transaction = NULL;

                        if (iodone_func == NULL) {
                                panic("brelse: bp @ %p has NULL b_iodone!\n", bp);
                        }
                        (*iodone_func)(bp, arg);
                }
        }
        /*
         * I/O is done. Cleanup the UPL state
         */
        upl = bp->b_upl;

        if ( !ISSET(bp->b_flags, B_META) && UBCINFOEXISTS(bp->b_vp) && bp->b_bufsize) {
                kern_return_t kret;
                int           upl_flags;

                if ( (upl == NULL) ) {
                        if ( !ISSET(bp->b_flags, B_INVAL)) {
                                kret = ubc_create_upl(bp->b_vp, 
                                                      ubc_blktooff(bp->b_vp, bp->b_lblkno),
                                                      bp->b_bufsize, 
                                                      &upl,
                                                      NULL,
                                                      UPL_PRECIOUS);

                                if (kret != KERN_SUCCESS)
                                        panic("brelse: Failed to create UPL");
#if  UPL_DEBUG
                                upl_ubc_alias_set(upl, (uintptr_t) bp, (uintptr_t) 5);
#endif /* UPL_DEBUG */
                        }
                } else {
                        if (bp->b_datap) {
                                kret = ubc_upl_unmap(upl);

                                if (kret != KERN_SUCCESS)
                                        panic("ubc_upl_unmap failed");
                                bp->b_datap = (uintptr_t)NULL;
                        }
                }
                if (upl) {
                        if (bp->b_flags & (B_ERROR | B_INVAL)) {
                                if (bp->b_flags & (B_READ | B_INVAL))
                                        upl_flags = UPL_ABORT_DUMP_PAGES;
                                else
                                        upl_flags = 0;

                                ubc_upl_abort(upl, upl_flags);
                        } else {
                                if (ISSET(bp->b_flags, B_DELWRI | B_WASDIRTY))
                                        upl_flags = UPL_COMMIT_SET_DIRTY ;
                                else
                                        upl_flags = UPL_COMMIT_CLEAR_DIRTY ;

                                ubc_upl_commit_range(upl, 0, bp->b_bufsize, upl_flags |
                                                     UPL_COMMIT_INACTIVATE | UPL_COMMIT_FREE_ON_EMPTY);
                        }
                        bp->b_upl = NULL;
                }
        } else {
                if ( (upl) )
                        panic("brelse: UPL set for non VREG; vp=%p", bp->b_vp);
        }       

        /*
         * If it's locked, don't report an error; try again later.
         */
        if (ISSET(bp->b_flags, (B_LOCKED|B_ERROR)) == (B_LOCKED|B_ERROR))
                CLR(bp->b_flags, B_ERROR);
        /*
         * If it's not cacheable, or an error, mark it invalid.
         */
        if (ISSET(bp->b_flags, (B_NOCACHE|B_ERROR)))
                SET(bp->b_flags, B_INVAL);
        
        if ((bp->b_bufsize <= 0) || 
                        ISSET(bp->b_flags, B_INVAL) || 
                        (ISSET(bp->b_lflags, BL_WANTDEALLOC) && !ISSET(bp->b_flags, B_DELWRI))) {
                /*
                 * If it's invalid or empty, dissociate it from its vnode,
                 * release its storage if B_META, and
                 * clean it up a bit and put it on the EMPTY queue
                 */
                if (ISSET(bp->b_flags, B_DELWRI))
                        OSAddAtomicLong(-1, &nbdwrite);

                if (ISSET(bp->b_flags, B_META)) {
                        if (bp->b_bufsize) {
                                if (ISSET(bp->b_flags, B_ZALLOC)) {
                                        zone_t z;

                                        z = getbufzone(bp->b_bufsize);
                                        zfree(z, (void *)bp->b_datap);
                                } else
                                        kmem_free(kernel_map, bp->b_datap, bp->b_bufsize); 

                                 bp->b_datap = (uintptr_t)NULL;
                                 bp->b_bufsize = 0;
                        }
                }
                /*
                 * nuke any credentials we were holding
                 */
                if (IS_VALID_CRED(bp->b_rcred)) {
                        kauth_cred_unref(&bp->b_rcred);
                }
                if (IS_VALID_CRED(bp->b_wcred)) {
                        kauth_cred_unref(&bp->b_wcred);
                }
                CLR(bp->b_flags, (B_META | B_ZALLOC | B_DELWRI | B_LOCKED | B_AGE | B_ASYNC | B_NOCACHE | B_FUA));

                bufq = &bufqueues[BQ_EMPTY];
                bp->b_whichq = BQ_EMPTY;

                lck_mtx_lock_spin(buf_mtxp);

                if (bp->b_vp)
                        brelvp_locked(bp);

                bremhash(bp);
                BLISTNONE(bp);
                binshash(bp, &invalhash);

                binsheadfree(bp, bufq, BQ_EMPTY);
        } else {
                /*
                 * It has valid data.  Put it on the end of the appropriate
                 * queue, so that it'll stick around for as long as possible.
                 */
                if (ISSET(bp->b_flags, B_LOCKED))
                        whichq = BQ_LOCKED;             /* locked in core */
                else if (ISSET(bp->b_flags, B_META))
                        whichq = BQ_META;               /* meta-data */
                else if (ISSET(bp->b_flags, B_AGE))
                        whichq = BQ_AGE;                /* stale but valid data */
                else
                        whichq = BQ_LRU;                /* valid data */
                bufq = &bufqueues[whichq];

                CLR(bp->b_flags, (B_AGE | B_ASYNC | B_NOCACHE));
                bp->b_whichq = whichq;
                bp->b_timestamp = buf_timestamp();

                lck_mtx_lock_spin(buf_mtxp);

                binstailfree(bp, bufq, whichq);
        }
        if (needbuffer) {
                /*
                 * needbuffer is a global
                 * we're currently using buf_mtxp to protect it
                 * delay doing the actual wakeup until after
                 * we drop buf_mtxp
                 */
                needbuffer = 0;
                need_wakeup = 1;
        }
        if (ISSET(bp->b_lflags, BL_WANTED)) {
                /*      
                 * delay the actual wakeup until after we
                 * clear BL_BUSY and we've dropped buf_mtxp
                 */
                need_bp_wakeup = 1;
        }
        /*
         * Unlock the buffer.
         */
        CLR(bp->b_lflags, (BL_BUSY | BL_WANTED));
        buf_busycount--;

        lck_mtx_unlock(buf_mtxp);

        if (need_wakeup) {
                /*
                 * Wake up any processes waiting for any buffer to become free.
                 */
                wakeup(&needbuffer);
        }
        if (need_bp_wakeup) {
                /*
                 * Wake up any proceeses waiting for _this_ buffer to become free.
                 */
                wakeup(bp);
        }
        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 388)) | DBG_FUNC_END,
                     bp, bp->b_datap, bp->b_flags, 0, 0);
}

/*
 * Determine if a block is in the cache.
 * Just look on what would be its hash chain.  If it's there, return
 * a pointer to it, unless it's marked invalid.  If it's marked invalid,
 * we normally don't return the buffer, unless the caller explicitly
 * wants us to.
 */
static boolean_t
incore(vnode_t vp, daddr64_t blkno)
{
        boolean_t retval;
        struct  bufhashhdr *dp;

        dp = BUFHASH(vp, blkno);

        lck_mtx_lock_spin(buf_mtxp);

        if (incore_locked(vp, blkno, dp))
                retval = TRUE;
        else
                retval = FALSE;
        lck_mtx_unlock(buf_mtxp);

        return (retval);
}


static buf_t
incore_locked(vnode_t vp, daddr64_t blkno, struct bufhashhdr *dp)
{
        struct buf *bp;

        /* Search hash chain */
        for (bp = dp->lh_first; bp != NULL; bp = bp->b_hash.le_next) {
                if (bp->b_lblkno == blkno && bp->b_vp == vp &&
                    !ISSET(bp->b_flags, B_INVAL)) {
                        return (bp);
                }
        }
        return (NULL);
}


/* XXX FIXME -- Update the comment to reflect the UBC changes (please) -- */
/*
 * Get a block of requested size that is associated with
 * a given vnode and block offset. If it is found in the
 * block cache, mark it as having been found, make it busy
 * and return it. Otherwise, return an empty block of the
 * correct size. It is up to the caller to insure that the
 * cached blocks be of the correct size.
 */
buf_t
buf_getblk(vnode_t vp, daddr64_t blkno, int size, int slpflag, int slptimeo, int operation)
{
        buf_t bp;
        int   err;
        upl_t upl;
        upl_page_info_t *pl;
        kern_return_t kret;
        int ret_only_valid;
        struct timespec ts;
        int upl_flags;
        struct  bufhashhdr *dp;

        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 386)) | DBG_FUNC_START,
                     (uintptr_t)(blkno * PAGE_SIZE), size, operation, 0, 0);

        ret_only_valid = operation & BLK_ONLYVALID;
        operation &= ~BLK_ONLYVALID;
        dp = BUFHASH(vp, blkno);
start:
        lck_mtx_lock_spin(buf_mtxp);

        if ((bp = incore_locked(vp, blkno, dp))) {
                /*
                 * Found in the Buffer Cache
                 */
                if (ISSET(bp->b_lflags, BL_BUSY)) {
                        /*
                         * but is busy
                         */
                        switch (operation) {
                        case BLK_READ:
                        case BLK_WRITE:
                        case BLK_META:
                                SET(bp->b_lflags, BL_WANTED);
                                bufstats.bufs_busyincore++;

                                /*
                                 * don't retake the mutex after being awakened...
                                 * the time out is in msecs 
                                 */
                                ts.tv_sec = (slptimeo/1000);
                                ts.tv_nsec = (slptimeo % 1000) * 10  * NSEC_PER_USEC * 1000;

                                KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 396)) | DBG_FUNC_NONE,
                                             (uintptr_t)blkno, size, operation, 0, 0);

                                err = msleep(bp, buf_mtxp, slpflag | PDROP | (PRIBIO + 1), "buf_getblk", &ts);

                                /*
                                 * Callers who call with PCATCH or timeout are
                                 * willing to deal with the NULL pointer
                                 */
                                if (err && ((slpflag & PCATCH) || ((err == EWOULDBLOCK) && slptimeo)))
                                        return (NULL);
                                goto start;
                                /*NOTREACHED*/
                                break;

                        default:
                                /*
                                 * unknown operation requested
                                 */
                                panic("getblk: paging or unknown operation for incore busy buffer - %x\n", operation);
                                /*NOTREACHED*/
                                break;
                        }               
                } else {
                        /*
                         * buffer in core and not busy
                         */
                        SET(bp->b_lflags, BL_BUSY);
                        SET(bp->b_flags, B_CACHE);
                        buf_busycount++;

                        bremfree_locked(bp);
                        bufstats.bufs_incore++;
                        
                        lck_mtx_unlock(buf_mtxp);
#ifdef JOE_DEBUG
                        bp->b_owner = current_thread();
                        bp->b_tag   = 1;
#endif
                        if ( (bp->b_upl) )
                                panic("buffer has UPL, but not marked BUSY: %p", bp);

                        if ( !ret_only_valid && bp->b_bufsize != size)
                                allocbuf(bp, size);

                        upl_flags = 0;
                        switch (operation) {
                        case BLK_WRITE:
                                /*
                                 * "write" operation:  let the UPL subsystem
                                 * know that we intend to modify the buffer
                                 * cache pages we're gathering.
                                 */
                                upl_flags |= UPL_WILL_MODIFY;
                        case BLK_READ:
                                upl_flags |= UPL_PRECIOUS;
                                if (UBCINFOEXISTS(bp->b_vp) && bp->b_bufsize) {
                                        kret = ubc_create_upl(vp,
                                                              ubc_blktooff(vp, bp->b_lblkno), 
                                                              bp->b_bufsize, 
                                                              &upl, 
                                                              &pl,
                                                              upl_flags);
                                        if (kret != KERN_SUCCESS)
                                                panic("Failed to create UPL");

                                        bp->b_upl = upl;

                                        if (upl_valid_page(pl, 0)) {
                                                if (upl_dirty_page(pl, 0))
                                                        SET(bp->b_flags, B_WASDIRTY);
                                                else
                                                        CLR(bp->b_flags, B_WASDIRTY);
                                        } else 
                                                CLR(bp->b_flags, (B_DONE | B_CACHE | B_WASDIRTY | B_DELWRI));

                                        kret = ubc_upl_map(upl, (vm_offset_t*)&(bp->b_datap));

                                        if (kret != KERN_SUCCESS)
                                                panic("getblk: ubc_upl_map() failed with (%d)", kret);
                                }
                                break;

                        case BLK_META:
                                /*
                                 * VM is not involved in IO for the meta data
                                 * buffer already has valid data 
                                 */
                                break;

                        default:
                                panic("getblk: paging or unknown operation for incore buffer- %d\n", operation);
                                /*NOTREACHED*/
                                break;
                        }
                }
        } else { /* not incore() */
                int queue = BQ_EMPTY; /* Start with no preference */
                
                if (ret_only_valid) {
                        lck_mtx_unlock(buf_mtxp);
                        return (NULL);
                }
                if ((vnode_isreg(vp) == 0) || (UBCINFOEXISTS(vp) == 0) /*|| (vnode_issystem(vp) == 1)*/)
                        operation = BLK_META;

                if ((bp = getnewbuf(slpflag, slptimeo, &queue)) == NULL)
                        goto start;

                /*
                 * getnewbuf may block for a number of different reasons...
                 * if it does, it's then possible for someone else to
                 * create a buffer for the same block and insert it into
                 * the hash... if we see it incore at this point we dump
                 * the buffer we were working on and start over
                 */
                if (incore_locked(vp, blkno, dp)) {
                        SET(bp->b_flags, B_INVAL);
                        binshash(bp, &invalhash);

                        lck_mtx_unlock(buf_mtxp);

                        buf_brelse(bp);
                        goto start;
                }
                /*
                 * NOTE: YOU CAN NOT BLOCK UNTIL binshash() HAS BEEN
                 *       CALLED!  BE CAREFUL.
                 */

                /*
                 * mark the buffer as B_META if indicated
                 * so that when buffer is released it will goto META queue
                 */
                if (operation == BLK_META)
                        SET(bp->b_flags, B_META);

                bp->b_blkno = bp->b_lblkno = blkno;
                bp->b_vp = vp;

                /*
                 * Insert in the hash so that incore() can find it 
                 */
                binshash(bp, BUFHASH(vp, blkno)); 

                bgetvp_locked(vp, bp);

                lck_mtx_unlock(buf_mtxp);

                allocbuf(bp, size);

                upl_flags = 0;
                switch (operation) {
                case BLK_META:
                        /*
                         * buffer data is invalid...
                         *
                         * I don't want to have to retake buf_mtxp,
                         * so the miss and vmhits counters are done
                         * with Atomic updates... all other counters
                         * in bufstats are protected with either
                         * buf_mtxp or iobuffer_mtxp
                         */
                        OSAddAtomicLong(1, &bufstats.bufs_miss);
                        break;

                case BLK_WRITE:
                        /*
                         * "write" operation:  let the UPL subsystem know
                         * that we intend to modify the buffer cache pages
                         * we're gathering.
                         */
                        upl_flags |= UPL_WILL_MODIFY;
                case BLK_READ:
                  {     off_t   f_offset;
                        size_t  contig_bytes;
                        int     bmap_flags;

                        if ( (bp->b_upl) )
                                panic("bp already has UPL: %p",bp);

                        f_offset = ubc_blktooff(vp, blkno);

                        upl_flags |= UPL_PRECIOUS;
                        kret = ubc_create_upl(vp,
                                              f_offset,
                                              bp->b_bufsize, 
                                              &upl,
                                              &pl,
                                              upl_flags);

                        if (kret != KERN_SUCCESS)
                                panic("Failed to create UPL");
#if  UPL_DEBUG
                        upl_ubc_alias_set(upl, (uintptr_t) bp, (uintptr_t) 4);
#endif /* UPL_DEBUG */
                        bp->b_upl = upl;

                        if (upl_valid_page(pl, 0)) {

                                if (operation == BLK_READ)
                                        bmap_flags = VNODE_READ;
                                else
                                        bmap_flags = VNODE_WRITE;

                                SET(bp->b_flags, B_CACHE | B_DONE);

                                OSAddAtomicLong(1, &bufstats.bufs_vmhits);

                                bp->b_validoff = 0;
                                bp->b_dirtyoff = 0;

                                if (upl_dirty_page(pl, 0)) {
                                        /* page is dirty */
                                        SET(bp->b_flags, B_WASDIRTY);

                                        bp->b_validend = bp->b_bcount;
                                        bp->b_dirtyend = bp->b_bcount;
                                } else {
                                        /* page is clean */
                                        bp->b_validend = bp->b_bcount;
                                        bp->b_dirtyend = 0;
                                }
                                /*
                                 * try to recreate the physical block number associated with
                                 * this buffer...
                                 */
                                if (VNOP_BLOCKMAP(vp, f_offset, bp->b_bcount, &bp->b_blkno, &contig_bytes, NULL, bmap_flags, NULL))
                                        panic("getblk: VNOP_BLOCKMAP failed");
                                /*
                                 * if the extent represented by this buffer
                                 * is not completely physically contiguous on
                                 * disk, than we can't cache the physical mapping
                                 * in the buffer header
                                 */
                                if ((long)contig_bytes < bp->b_bcount)
                                        bp->b_blkno = bp->b_lblkno;
                        } else {
                                OSAddAtomicLong(1, &bufstats.bufs_miss);
                        }
                        kret = ubc_upl_map(upl, (vm_offset_t *)&(bp->b_datap));

                        if (kret != KERN_SUCCESS)
                                panic("getblk: ubc_upl_map() failed with (%d)", kret);
                        break;
                  }
                default:
                        panic("getblk: paging or unknown operation - %x", operation);
                        /*NOTREACHED*/
                        break;
                }
        }
        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 386)) | DBG_FUNC_END,
                     bp, bp->b_datap, bp->b_flags, 3, 0);

#ifdef JOE_DEBUG
        (void) OSBacktrace(&bp->b_stackgetblk[0], 6);
#endif
        return (bp);
}

/*
 * Get an empty, disassociated buffer of given size.
 */
buf_t
buf_geteblk(int size)
{
        buf_t   bp = NULL;
        int queue = BQ_EMPTY;

        do {
                lck_mtx_lock_spin(buf_mtxp);

                bp = getnewbuf(0, 0, &queue);
        } while (bp == NULL);

        SET(bp->b_flags, (B_META|B_INVAL));

#if DIAGNOSTIC
        assert(queue == BQ_EMPTY);
#endif /* DIAGNOSTIC */
        /* XXX need to implement logic to deal with other queues */

        binshash(bp, &invalhash);
        bufstats.bufs_eblk++;

        lck_mtx_unlock(buf_mtxp);

        allocbuf(bp, size);

        return (bp);
}


/*
 * With UBC, there is no need to expand / shrink the file data 
 * buffer. The VM uses the same pages, hence no waste.
 * All the file data buffers can have one size.
 * In fact expand / shrink would be an expensive operation.
 *
 * Only exception to this is meta-data buffers. Most of the
 * meta data operations are smaller than PAGE_SIZE. Having the
 * meta-data buffers grow and shrink as needed, optimizes use
 * of the kernel wired memory.
 */

int
allocbuf(buf_t bp, int size)
{
        vm_size_t desired_size;

        desired_size = roundup(size, CLBYTES);

        if (desired_size < PAGE_SIZE)
                desired_size = PAGE_SIZE;
        if (desired_size > MAXBSIZE)
                panic("allocbuf: buffer larger than MAXBSIZE requested");

        if (ISSET(bp->b_flags, B_META)) {
                zone_t zprev, z;
                int    nsize = roundup(size, MINMETA);

                if (bp->b_datap) {
                        vm_offset_t elem = (vm_offset_t)bp->b_datap;

                        if (ISSET(bp->b_flags, B_ZALLOC)) {
                                if (bp->b_bufsize < nsize) {
                                        /* reallocate to a bigger size */

                                        zprev = getbufzone(bp->b_bufsize);
                                        if (nsize <= MAXMETA) {
                                                desired_size = nsize;
                                                z = getbufzone(nsize);
                                                /* b_datap not really a ptr */
                                                *(void **)(&bp->b_datap) = zalloc(z);
                                        } else {
                                                bp->b_datap = (uintptr_t)NULL;
                                                kmem_alloc_kobject(kernel_map, (vm_offset_t *)&bp->b_datap, desired_size);
                                                CLR(bp->b_flags, B_ZALLOC);
                                        }
                                        bcopy((void *)elem, (caddr_t)bp->b_datap, bp->b_bufsize);
                                        zfree(zprev, (void *)elem);
                                } else {
                                        desired_size = bp->b_bufsize;
                                }

                        } else {
                                if ((vm_size_t)bp->b_bufsize < desired_size) {
                                        /* reallocate to a bigger size */
                                        bp->b_datap = (uintptr_t)NULL;
                                        kmem_alloc_kobject(kernel_map, (vm_offset_t *)&bp->b_datap, desired_size);
                                        bcopy((const void *)elem, (caddr_t)bp->b_datap, bp->b_bufsize);
                                        kmem_free(kernel_map, elem, bp->b_bufsize); 
                                } else {
                                        desired_size = bp->b_bufsize;
                                }
                        }
                } else {
                        /* new allocation */
                        if (nsize <= MAXMETA) {
                                desired_size = nsize;
                                z = getbufzone(nsize);
                                /* b_datap not really a ptr */
                                *(void **)(&bp->b_datap) = zalloc(z);
                                SET(bp->b_flags, B_ZALLOC);
                        } else
                                kmem_alloc_kobject(kernel_map, (vm_offset_t *)&bp->b_datap, desired_size);
                }

                if (bp->b_datap == 0)
                        panic("allocbuf: NULL b_datap");
        }
        bp->b_bufsize = desired_size;
        bp->b_bcount = size;

        return (0);
}

/*
 *      Get a new buffer from one of the free lists.
 *
 *      Request for a queue is passes in. The queue from which the buffer was taken
 *      from is returned. Out of range queue requests get BQ_EMPTY. Request for
 *      BQUEUE means no preference. Use heuristics in that case.
 *      Heuristics is as follows:
 *      Try BQ_AGE, BQ_LRU, BQ_EMPTY, BQ_META in that order.
 *      If none available block till one is made available.
 *      If buffers available on both BQ_AGE and BQ_LRU, check the timestamps.
 *      Pick the most stale buffer.
 *      If found buffer was marked delayed write, start the async. write
 *      and restart the search.
 *      Initialize the fields and disassociate the buffer from the vnode.
 *      Remove the buffer from the hash. Return the buffer and the queue
 *      on which it was found.
 *
 *      buf_mtxp is held upon entry
 *      returns with buf_mtxp locked if new buf available
 *      returns with buf_mtxp UNlocked if new buf NOT available
 */

static buf_t
getnewbuf(int slpflag, int slptimeo, int * queue)
{
        buf_t   bp;
        buf_t   lru_bp;
        buf_t   age_bp;
        buf_t   meta_bp;
        int     age_time, lru_time, bp_time, meta_time;
        int     req = *queue;   /* save it for restarts */
        struct timespec ts;

start:
        /*
         * invalid request gets empty queue
         */
        if ((*queue >= BQUEUES) || (*queue < 0)
                || (*queue == BQ_LAUNDRY) || (*queue == BQ_LOCKED))
                *queue = BQ_EMPTY;


        if (*queue == BQ_EMPTY && (bp = bufqueues[*queue].tqh_first))
                goto found;

        /*
         * need to grow number of bufs, add another one rather than recycling
         */
        if (nbuf_headers < max_nbuf_headers) {
                /*
                 * Increment  count now as lock 
                 * is dropped for allocation.
                 * That avoids over commits
                 */
                nbuf_headers++;
                goto add_newbufs;
        }
        /* Try for the requested queue first */
        bp = bufqueues[*queue].tqh_first;
        if (bp)
                goto found;

        /* Unable to use requested queue */
        age_bp = bufqueues[BQ_AGE].tqh_first;
        lru_bp = bufqueues[BQ_LRU].tqh_first;
        meta_bp = bufqueues[BQ_META].tqh_first;

        if (!age_bp && !lru_bp && !meta_bp) {
                /*
                 * Unavailble on AGE or LRU or META queues
                 * Try the empty list first
                 */
                bp = bufqueues[BQ_EMPTY].tqh_first;
                if (bp) {
                        *queue = BQ_EMPTY;
                        goto found;
                }
                /*
                 * We have seen is this is hard to trigger.
                 * This is an overcommit of nbufs but needed 
                 * in some scenarios with diskiamges
                 */

add_newbufs:
                lck_mtx_unlock(buf_mtxp);

                /* Create a new temporary buffer header */
                bp = (struct buf *)zalloc(buf_hdr_zone);
                
                if (bp) {
                        bufhdrinit(bp);
                        bp->b_whichq = BQ_EMPTY;
                        bp->b_timestamp = buf_timestamp();
                        BLISTNONE(bp);
                        SET(bp->b_flags, B_HDRALLOC);
                        *queue = BQ_EMPTY;
                }
                lck_mtx_lock_spin(buf_mtxp);

                if (bp) {
                        binshash(bp, &invalhash);
                        binsheadfree(bp, &bufqueues[BQ_EMPTY], BQ_EMPTY);
                        buf_hdr_count++;
                        goto found;
                }
                /* subtract already accounted bufcount */
                nbuf_headers--;

                bufstats.bufs_sleeps++;

                /* wait for a free buffer of any kind */
                needbuffer = 1;
                /* hz value is 100 */
                ts.tv_sec = (slptimeo/1000);
                /* the hz value is 100; which leads to 10ms */
                ts.tv_nsec = (slptimeo % 1000) * NSEC_PER_USEC * 1000 * 10;

                msleep(&needbuffer, buf_mtxp, slpflag | PDROP | (PRIBIO+1), "getnewbuf", &ts);
                return (NULL);
        }

        /* Buffer available either on AGE or LRU or META */
        bp = NULL;
        *queue = -1;

        /* Buffer available either on AGE or LRU */
        if (!age_bp) {
                bp = lru_bp;
                *queue = BQ_LRU;
        } else if (!lru_bp) {
                bp = age_bp;
                *queue = BQ_AGE;
        } else { /* buffer available on both AGE and LRU */
                int             t = buf_timestamp();

                age_time = t - age_bp->b_timestamp;
                lru_time = t - lru_bp->b_timestamp;
                if ((age_time < 0) || (lru_time < 0)) { /* time set backwards */
                        bp = age_bp;
                        *queue = BQ_AGE;
                        /*
                         * we should probably re-timestamp eveything in the
                         * queues at this point with the current time
                         */
                } else {
                        if ((lru_time >= lru_is_stale) && (age_time < age_is_stale)) {
                                bp = lru_bp;
                                *queue = BQ_LRU;
                        } else {
                                bp = age_bp;
                                *queue = BQ_AGE;
                        }
                }
        }

        if (!bp) { /* Neither on AGE nor on LRU */
                bp = meta_bp;
                *queue = BQ_META;
        }  else if (meta_bp) {
                int             t = buf_timestamp();

                bp_time = t - bp->b_timestamp;
                meta_time = t - meta_bp->b_timestamp;

                if (!(bp_time < 0) && !(meta_time < 0)) {
                        /* time not set backwards */
                        int bp_is_stale;
                        bp_is_stale = (*queue == BQ_LRU) ? 
                                        lru_is_stale : age_is_stale;

                        if ((meta_time >= meta_is_stale) && 
                                        (bp_time < bp_is_stale)) {
                                bp = meta_bp;
                                *queue = BQ_META;
                        }
                }
        }
found:
        if (ISSET(bp->b_flags, B_LOCKED) || ISSET(bp->b_lflags, BL_BUSY))
                panic("getnewbuf: bp @ %p is LOCKED or BUSY! (flags 0x%x)\n", bp, bp->b_flags);

        /* Clean it */
        if (bcleanbuf(bp, FALSE)) {
                /*
                 * moved to the laundry thread, buffer not ready
                 */
                *queue = req;
                goto start;
        }
        return (bp); 
}


/* 
 * Clean a buffer.
 * Returns 0 is buffer is ready to use,
 * Returns 1 if issued a buf_bawrite() to indicate 
 * that the buffer is not ready.
 * 
 * buf_mtxp is held upon entry
 * returns with buf_mtxp locked
 */
static int
bcleanbuf(buf_t bp, boolean_t discard)
{
        /* Remove from the queue */
        bremfree_locked(bp);

#ifdef JOE_DEBUG
        bp->b_owner = current_thread();
        bp->b_tag   = 2;
#endif
        /*
         * If buffer was a delayed write, start the IO by queuing
         * it on the LAUNDRY queue, and return 1
         */
        if (ISSET(bp->b_flags, B_DELWRI)) {
                if (discard) {
                        SET(bp->b_lflags, BL_WANTDEALLOC);
                }

                bp->b_whichq = BQ_LAUNDRY;
                bp->b_timestamp = buf_timestamp();
                binstailfree(bp, &bufqueues[BQ_LAUNDRY], BQ_LAUNDRY);
                blaundrycnt++;

                lck_mtx_unlock(buf_mtxp);

                wakeup(&bufqueues[BQ_LAUNDRY]);
                /*
                 * and give it a chance to run
                 */
                (void)thread_block(THREAD_CONTINUE_NULL);

                lck_mtx_lock_spin(buf_mtxp);

                return (1);
        }
#ifdef JOE_DEBUG
        bp->b_owner = current_thread();
        bp->b_tag   = 8;
#endif
        /*
         * Buffer is no longer on any free list... we own it
         */
        SET(bp->b_lflags, BL_BUSY);
        buf_busycount++;
        
        bremhash(bp);

        /*
         * disassociate us from our vnode, if we had one...
         */
        if (bp->b_vp)
                brelvp_locked(bp);

        lck_mtx_unlock(buf_mtxp);

        BLISTNONE(bp);

        if (ISSET(bp->b_flags, B_META)) {
                vm_offset_t elem;

                elem = (vm_offset_t)bp->b_datap;
                bp->b_datap = (uintptr_t)0xdeadbeef;

                if (ISSET(bp->b_flags, B_ZALLOC)) {
                        zone_t z;

                        z = getbufzone(bp->b_bufsize);
                        zfree(z, (void *)elem);
                } else
                        kmem_free(kernel_map, elem, bp->b_bufsize); 
        }

        trace(TR_BRELSE, pack(bp->b_vp, bp->b_bufsize), bp->b_lblkno);

        /* nuke any credentials we were holding */
        if (IS_VALID_CRED(bp->b_rcred)) {
                kauth_cred_unref(&bp->b_rcred);
        }
        if (IS_VALID_CRED(bp->b_wcred)) {
                kauth_cred_unref(&bp->b_wcred);
        }

        /* If discarding, just move to the empty queue */
        if (discard) {
                lck_mtx_lock_spin(buf_mtxp);
                CLR(bp->b_flags, (B_META | B_ZALLOC | B_DELWRI | B_LOCKED | B_AGE | B_ASYNC | B_NOCACHE | B_FUA));
                bp->b_whichq = BQ_EMPTY;
                binshash(bp, &invalhash);
                binsheadfree(bp, &bufqueues[BQ_EMPTY], BQ_EMPTY);
                CLR(bp->b_lflags, BL_BUSY);
                buf_busycount--;
        } else {
                /* Not discarding: clean up and prepare for reuse */
                bp->b_bufsize = 0;
                bp->b_datap = (uintptr_t)NULL;
                bp->b_upl = (void *)NULL;
                /*
                 * preserve the state of whether this buffer
                 * was allocated on the fly or not...
                 * the only other flag that should be set at
                 * this point is BL_BUSY...
                 */
#ifdef JOE_DEBUG
                bp->b_owner = current_thread();
                bp->b_tag   = 3;
#endif
                bp->b_lflags = BL_BUSY;
                bp->b_flags = (bp->b_flags & B_HDRALLOC);
                bp->b_dev = NODEV;
                bp->b_blkno = bp->b_lblkno = 0;
                bp->b_iodone = NULL;
                bp->b_error = 0;
                bp->b_resid = 0;
                bp->b_bcount = 0;
                bp->b_dirtyoff = bp->b_dirtyend = 0;
                bp->b_validoff = bp->b_validend = 0;
#ifdef CONFIG_PROTECT
                bp->b_cpentry = 0;
#endif

                lck_mtx_lock_spin(buf_mtxp);
        }
        return (0);
}



errno_t
buf_invalblkno(vnode_t vp, daddr64_t lblkno, int flags)
{
        buf_t   bp;
        errno_t error;
        struct bufhashhdr *dp;

        dp = BUFHASH(vp, lblkno);

relook: 
        lck_mtx_lock_spin(buf_mtxp);

        if ((bp = incore_locked(vp, lblkno, dp)) == (struct buf *)0) {
                lck_mtx_unlock(buf_mtxp);
                return (0);
        }
        if (ISSET(bp->b_lflags, BL_BUSY)) {
                if ( !ISSET(flags, BUF_WAIT)) {
                        lck_mtx_unlock(buf_mtxp);
                        return (EBUSY);
                }
                SET(bp->b_lflags, BL_WANTED);

                error = msleep((caddr_t)bp, buf_mtxp, PDROP | (PRIBIO + 1), "buf_invalblkno", NULL);

                if (error) {
                        return (error);
                }
                goto relook;
        }
        bremfree_locked(bp);
        SET(bp->b_lflags, BL_BUSY);
        SET(bp->b_flags, B_INVAL);
        buf_busycount++;
#ifdef JOE_DEBUG
        bp->b_owner = current_thread();
        bp->b_tag   = 4;
#endif
        lck_mtx_unlock(buf_mtxp);
        buf_brelse(bp);

        return (0);
}


void
buf_drop(buf_t bp)
{
        int need_wakeup = 0;

        lck_mtx_lock_spin(buf_mtxp);

        if (ISSET(bp->b_lflags, BL_WANTED)) {
                /*      
                 * delay the actual wakeup until after we
                 * clear BL_BUSY and we've dropped buf_mtxp
                 */
                need_wakeup = 1;
        }
#ifdef JOE_DEBUG
        bp->b_owner = current_thread();
        bp->b_tag   = 9;
#endif
        /*
         * Unlock the buffer.
         */
        CLR(bp->b_lflags, (BL_BUSY | BL_WANTED));
        buf_busycount--;

        lck_mtx_unlock(buf_mtxp);

        if (need_wakeup) {
                /*
                 * Wake up any proceeses waiting for _this_ buffer to become free.
                 */
                wakeup(bp);
        }
}


errno_t
buf_acquire(buf_t bp, int flags, int slpflag, int slptimeo) {
        errno_t error;

        lck_mtx_lock_spin(buf_mtxp);

        error = buf_acquire_locked(bp, flags, slpflag, slptimeo);

        lck_mtx_unlock(buf_mtxp);

        return (error);
}


static errno_t
buf_acquire_locked(buf_t bp, int flags, int slpflag, int slptimeo)
{
        errno_t error;
        struct timespec ts;

        if (ISSET(bp->b_flags, B_LOCKED)) {
                if ((flags & BAC_SKIP_LOCKED))
                        return (EDEADLK);
        } else {
                if ((flags & BAC_SKIP_NONLOCKED))
                        return (EDEADLK);
        }
        if (ISSET(bp->b_lflags, BL_BUSY)) {
                /*      
                 * since the lck_mtx_lock may block, the buffer
                 * may become BUSY, so we need to
                 * recheck for a NOWAIT request
                 */
                if (flags & BAC_NOWAIT)
                        return (EBUSY);
                SET(bp->b_lflags, BL_WANTED);

                /* the hz value is 100; which leads to 10ms */
                ts.tv_sec = (slptimeo/100);
                ts.tv_nsec = (slptimeo % 100) * 10  * NSEC_PER_USEC * 1000;
                error = msleep((caddr_t)bp, buf_mtxp, slpflag | (PRIBIO + 1), "buf_acquire", &ts);

                if (error)
                        return (error);
                return (EAGAIN);
        }
        if (flags & BAC_REMOVE)
                bremfree_locked(bp);
        SET(bp->b_lflags, BL_BUSY);
        buf_busycount++;

#ifdef JOE_DEBUG
        bp->b_owner = current_thread();
        bp->b_tag   = 5;
#endif
        return (0);
}


/*
 * Wait for operations on the buffer to complete.
 * When they do, extract and return the I/O's error value.
 */
errno_t
buf_biowait(buf_t bp)
{
        while (!ISSET(bp->b_flags, B_DONE)) {

                lck_mtx_lock_spin(buf_mtxp);

                if (!ISSET(bp->b_flags, B_DONE)) {
                        DTRACE_IO1(wait__start, buf_t, bp);
                        (void) msleep(bp, buf_mtxp, PDROP | (PRIBIO+1), "buf_biowait", NULL);
                        DTRACE_IO1(wait__done, buf_t, bp);
                } else
                        lck_mtx_unlock(buf_mtxp);
        }
        /* check for interruption of I/O (e.g. via NFS), then errors. */
        if (ISSET(bp->b_flags, B_EINTR)) {
                CLR(bp->b_flags, B_EINTR);
                return (EINTR);
        } else if (ISSET(bp->b_flags, B_ERROR))
                return (bp->b_error ? bp->b_error : EIO);
        else
                return (0);
}

/*
 * Wait for the callback operation on a B_CALL buffer to complete.
 */
void
buf_biowait_callback(buf_t bp)
{
        while (!ISSET(bp->b_lflags, BL_CALLDONE)) {

                lck_mtx_lock_spin(buf_mtxp);

                if (!ISSET(bp->b_lflags, BL_CALLDONE)) {
                        DTRACE_IO1(wait__start, buf_t, bp);
                        (void) msleep(bp, buf_mtxp, PDROP | (PRIBIO+1), "buf_biowait", NULL);
                        DTRACE_IO1(wait__done, buf_t, bp);
                } else
                        lck_mtx_unlock(buf_mtxp);
        }
}

/*
 * Mark I/O complete on a buffer.
 *
 * If a callback has been requested, e.g. the pageout
 * daemon, do so. Otherwise, awaken waiting processes.
 *
 * [ Leffler, et al., says on p.247:
 *      "This routine wakes up the blocked process, frees the buffer
 *      for an asynchronous write, or, for a request by the pagedaemon
 *      process, invokes a procedure specified in the buffer structure" ]
 *
 * In real life, the pagedaemon (or other system processes) wants
 * to do async stuff to, and doesn't want the buffer buf_brelse()'d.
 * (for swap pager, that puts swap buffers on the free lists (!!!),
 * for the vn device, that puts malloc'd buffers on the free lists!)
 */
extern struct timeval priority_IO_timestamp_for_root;
extern int hard_throttle_on_root;

void
buf_biodone(buf_t bp)
{
        mount_t mp;
        
        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 387)) | DBG_FUNC_START,
                     bp, bp->b_datap, bp->b_flags, 0, 0);

        if (ISSET(bp->b_flags, B_DONE))
                panic("biodone already");

        if (ISSET(bp->b_flags, B_ERROR)) {
                fslog_io_error(bp);
        }

        if (bp->b_vp && bp->b_vp->v_mount) {
                mp = bp->b_vp->v_mount;
        } else {
                mp = NULL;
        }
        
        if (mp && (bp->b_flags & B_READ) == 0) {
                update_last_io_time(mp);
                INCR_PENDING_IO(-(pending_io_t)buf_count(bp), mp->mnt_pending_write_size);
        } else if (mp) {
                INCR_PENDING_IO(-(pending_io_t)buf_count(bp), mp->mnt_pending_read_size);
        }

        if (kdebug_enable) {
                int    code = DKIO_DONE;

                if (bp->b_flags & B_READ)
                        code |= DKIO_READ;
                if (bp->b_flags & B_ASYNC)
                        code |= DKIO_ASYNC;

                if (bp->b_flags & B_META)
                        code |= DKIO_META;
                else if (bp->b_flags & B_PAGEIO)
                        code |= DKIO_PAGING;

                KERNEL_DEBUG_CONSTANT(FSDBG_CODE(DBG_DKRW, code) | DBG_FUNC_NONE,
                              bp, (uintptr_t)bp->b_vp,
                                      bp->b_resid, bp->b_error, 0);
        }
        if ((bp->b_vp != NULLVP) &&
            ((bp->b_flags & (B_IOSTREAMING | B_PAGEIO | B_READ)) == (B_PAGEIO | B_READ)) &&
            (bp->b_vp->v_mount->mnt_kern_flag & MNTK_ROOTDEV)) {
                microuptime(&priority_IO_timestamp_for_root);
                hard_throttle_on_root = 0;
        }
        /*
         * I/O was done, so don't believe
         * the DIRTY state from VM anymore
         */
        CLR(bp->b_flags, B_WASDIRTY);
        DTRACE_IO1(done, buf_t, bp);

        if (!ISSET(bp->b_flags, B_READ) && !ISSET(bp->b_flags, B_RAW))
                /*
                 * wake up any writer's blocked
                 * on throttle or waiting for I/O
                 * to drain
                 */
                vnode_writedone(bp->b_vp);

        if (ISSET(bp->b_flags, (B_CALL | B_FILTER))) {  /* if necessary, call out */
                void    (*iodone_func)(struct buf *, void *) = bp->b_iodone;
                void    *arg = (void *)bp->b_transaction;
                int     callout = ISSET(bp->b_flags, B_CALL);

                CLR(bp->b_flags, (B_CALL | B_FILTER));  /* filters and callouts are one-shot */
                bp->b_iodone = NULL;
                bp->b_transaction = NULL;

                if (iodone_func == NULL) {
                        panic("biodone: bp @ %p has NULL b_iodone!\n", bp);                     
                } else { 
                        if (callout)
                                SET(bp->b_flags, B_DONE);       /* note that it's done */
                        (*iodone_func)(bp, arg);
                }
                if (callout) {
                        int need_wakeup = 0;

                        /*
                         * assumes that the callback function takes
                         * ownership of the bp and deals with releasing it if necessary
                         * BL_WANTED indicates that we've decided to wait on the
                         * completion of this I/O in a synchronous manner... we
                         * still call the callback function, but in addition we
                         * will do a wakeup... BL_CALLDONE indicates that the callback
                         * routine has completed and its ok for the waiter to take
                         * 'ownership' of this bp back
                         */
                        lck_mtx_lock_spin(buf_mtxp);

                        if (bp->b_lflags & BL_WANTED) {
                                CLR(bp->b_lflags, BL_WANTED);
                                need_wakeup = 1;
                        }
                        SET(bp->b_lflags, BL_CALLDONE);

                        lck_mtx_unlock(buf_mtxp);
                        
                        if (need_wakeup)
                                wakeup(bp);

                        goto biodone_done;
                }
                /*
                 * in this case the call back function is acting
                 * strictly as a filter... it does not take
                 * ownership of the bp and is expecting us
                 * to finish cleaning up... this is currently used
                 * by the HFS journaling code
                 */
        }
        if (ISSET(bp->b_flags, B_ASYNC)) {      /* if async, release it */
                SET(bp->b_flags, B_DONE);       /* note that it's done */

                buf_brelse(bp);
        } else {                                /* or just wakeup the buffer */ 
                /*
                 * by taking the mutex, we serialize
                 * the buf owner calling buf_biowait so that we'll
                 * only see him in one of 2 states...
                 * state 1: B_DONE wasn't set and he's
                 * blocked in msleep
                 * state 2: he's blocked trying to take the
                 * mutex before looking at B_DONE
                 * BL_WANTED is cleared in case anyone else
                 * is blocked waiting for the buffer... note
                 * that we haven't cleared B_BUSY yet, so if
                 * they do get to run, their going to re-set
                 * BL_WANTED and go back to sleep
                 */
                lck_mtx_lock_spin(buf_mtxp);

                CLR(bp->b_lflags, BL_WANTED);
                SET(bp->b_flags, B_DONE);               /* note that it's done */

                lck_mtx_unlock(buf_mtxp);

                wakeup(bp);
        }
biodone_done:
        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, 387)) | DBG_FUNC_END,
                 (uintptr_t)bp, (uintptr_t)bp->b_datap, bp->b_flags, 0, 0);
}

/*
 * Return a count of buffers on the "locked" queue.
 */
int
count_lock_queue(void)
{
        buf_t   bp;
        int     n = 0;

        lck_mtx_lock_spin(buf_mtxp);

        for (bp = bufqueues[BQ_LOCKED].tqh_first; bp;
            bp = bp->b_freelist.tqe_next)
                n++;
        lck_mtx_unlock(buf_mtxp);

        return (n);
}

/*
 * Return a count of 'busy' buffers. Used at the time of shutdown.
 */
int
count_busy_buffers(void)
{
        return buf_busycount + bufstats.bufs_iobufinuse;
}

#if DIAGNOSTIC
/*
 * Print out statistics on the current allocation of the buffer pool.
 * Can be enabled to print out on every ``sync'' by setting "syncprt"
 * in vfs_syscalls.c using sysctl.
 */
void
vfs_bufstats()
{
        int i, j, count;
        register struct buf *bp;
        register struct bqueues *dp;
        int counts[MAXBSIZE/CLBYTES+1];
        static char *bname[BQUEUES] =
                { "LOCKED", "LRU", "AGE", "EMPTY", "META", "LAUNDRY" };

        for (dp = bufqueues, i = 0; dp < &bufqueues[BQUEUES]; dp++, i++) {
                count = 0;
                for (j = 0; j <= MAXBSIZE/CLBYTES; j++)
                        counts[j] = 0;

                lck_mtx_lock(buf_mtxp);

                for (bp = dp->tqh_first; bp; bp = bp->b_freelist.tqe_next) {
                        counts[bp->b_bufsize/CLBYTES]++;
                        count++;
                }
                lck_mtx_unlock(buf_mtxp);

                printf("%s: total-%d", bname[i], count);
                for (j = 0; j <= MAXBSIZE/CLBYTES; j++)
                        if (counts[j] != 0)
                                printf(", %d-%d", j * CLBYTES, counts[j]);
                printf("\n");
        }
}
#endif /* DIAGNOSTIC */

#define NRESERVEDIOBUFS 64


buf_t
alloc_io_buf(vnode_t vp, int priv)
{
        buf_t   bp;

        lck_mtx_lock_spin(iobuffer_mtxp);

        while (((niobuf_headers - NRESERVEDIOBUFS < bufstats.bufs_iobufinuse) && !priv) || 
               (bp = iobufqueue.tqh_first) == NULL) {
                bufstats.bufs_iobufsleeps++;

                need_iobuffer = 1;
                (void) msleep(&need_iobuffer, iobuffer_mtxp, PDROP | (PRIBIO+1), (const char *)"alloc_io_buf", NULL);

                lck_mtx_lock_spin(iobuffer_mtxp);
        }
        TAILQ_REMOVE(&iobufqueue, bp, b_freelist);

        bufstats.bufs_iobufinuse++;
        if (bufstats.bufs_iobufinuse > bufstats.bufs_iobufmax)
                bufstats.bufs_iobufmax = bufstats.bufs_iobufinuse;

        lck_mtx_unlock(iobuffer_mtxp);

        /*
         * initialize various fields
         * we don't need to hold the mutex since the buffer
         * is now private... the vp should have a reference 
         * on it and is not protected by this mutex in any event
         */
        bp->b_timestamp = 0; 
        bp->b_proc = NULL;

        bp->b_datap = 0;
        bp->b_flags = 0;
        bp->b_lflags = BL_BUSY | BL_IOBUF;
        bp->b_blkno = bp->b_lblkno = 0;
#ifdef JOE_DEBUG
        bp->b_owner = current_thread();
        bp->b_tag   = 6;
#endif
        bp->b_iodone = NULL;
        bp->b_error = 0;
        bp->b_resid = 0;
        bp->b_bcount = 0;
        bp->b_bufsize = 0;
        bp->b_upl = NULL;
        bp->b_vp = vp;
#ifdef CONFIG_PROTECT
        bp->b_cpentry = 0;
#endif

        if (vp && (vp->v_type == VBLK || vp->v_type == VCHR))
                bp->b_dev = vp->v_rdev;
        else
                bp->b_dev = NODEV;

        return (bp);
}


void
free_io_buf(buf_t bp)
{
        int need_wakeup = 0;

        /*
         * put buffer back on the head of the iobufqueue
         */
        bp->b_vp = NULL;
        bp->b_flags = B_INVAL;

        lck_mtx_lock_spin(iobuffer_mtxp);

        binsheadfree(bp, &iobufqueue, -1);

        if (need_iobuffer) {
                /*
                 * Wake up any processes waiting because they need an io buffer
                 *
                 * do the wakeup after we drop the mutex... it's possible that the
                 * wakeup will be superfluous if need_iobuffer gets set again and
                 * another thread runs this path, but it's highly unlikely, doesn't
                 * hurt, and it means we don't hold up I/O progress if the wakeup blocks
                 * trying to grab a task related lock...
                 */
                need_iobuffer = 0;
                need_wakeup = 1;
        }
        if (bufstats.bufs_iobufinuse <= 0)
                panic("free_io_buf: bp(%p) - bufstats.bufs_iobufinuse < 0", bp);

        bufstats.bufs_iobufinuse--;

        lck_mtx_unlock(iobuffer_mtxp);

        if (need_wakeup)
                wakeup(&need_iobuffer);
}


void
buf_list_lock(void)
{
        lck_mtx_lock_spin(buf_mtxp);
}

void
buf_list_unlock(void)
{
        lck_mtx_unlock(buf_mtxp);
}

/*
 * If getnewbuf() calls bcleanbuf() on the same thread
 * there is a potential for stack overrun and deadlocks.
 * So we always handoff the work to a worker thread for completion
 */


static void
bcleanbuf_thread_init(void)
{
        thread_t        thread = THREAD_NULL;

        /* create worker thread */
        kernel_thread_start((thread_continue_t)bcleanbuf_thread, NULL, &thread);
        thread_deallocate(thread);
}

static void
bcleanbuf_thread(void)
{
        struct buf *bp;
        int error = 0;
        int loopcnt = 0;

        for (;;) {
                lck_mtx_lock_spin(buf_mtxp);

                while ( (bp = TAILQ_FIRST(&bufqueues[BQ_LAUNDRY])) == NULL) {
                        (void)msleep((void *)&bufqueues[BQ_LAUNDRY], buf_mtxp, PDROP | PRIBIO, "blaundry", NULL);

                        lck_mtx_lock_spin(buf_mtxp);
                }
                /*
                 * Remove from the queue
                 */
                bremfree_locked(bp);

                /*
                 * Buffer is no longer on any free list
                 */
                SET(bp->b_lflags, BL_BUSY);
                buf_busycount++;

#ifdef JOE_DEBUG
                bp->b_owner = current_thread();
                bp->b_tag   = 10;
#endif

                lck_mtx_unlock(buf_mtxp);
                /*
                 * do the IO
                 */
                error = bawrite_internal(bp, 0);

                if (error) {
                        bp->b_whichq = BQ_LAUNDRY;
                        bp->b_timestamp = buf_timestamp();

                        lck_mtx_lock_spin(buf_mtxp);

                        binstailfree(bp, &bufqueues[BQ_LAUNDRY], BQ_LAUNDRY);
                        blaundrycnt++;

                        /* we never leave a busy page on the laundary queue */
                        CLR(bp->b_lflags, BL_BUSY);
                        buf_busycount--;
#ifdef JOE_DEBUG
                        bp->b_owner = current_thread();
                        bp->b_tag   = 11;
#endif

                        lck_mtx_unlock(buf_mtxp);

                        if (loopcnt > 10) {
                                (void)tsleep((void *)&bufqueues[BQ_LAUNDRY], PRIBIO, "blaundry", 1);
                                loopcnt = 0;
                        } else {
                                (void)thread_block(THREAD_CONTINUE_NULL);
                                loopcnt++;
                        }
                }
        }
}


static int
brecover_data(buf_t bp)
{
        int     upl_offset;
        upl_t   upl;
        upl_page_info_t *pl;
        kern_return_t kret;
        vnode_t vp = bp->b_vp;
        int upl_flags;


        if ( !UBCINFOEXISTS(vp) || bp->b_bufsize == 0)
                goto dump_buffer;

        upl_flags = UPL_PRECIOUS;
        if (! (buf_flags(bp) & B_READ)) {
                /*
                 * "write" operation:  let the UPL subsystem know
                 * that we intend to modify the buffer cache pages we're
                 * gathering.
                 */
                upl_flags |= UPL_WILL_MODIFY;
        }
                
        kret = ubc_create_upl(vp,
                              ubc_blktooff(vp, bp->b_lblkno), 
                              bp->b_bufsize, 
                              &upl, 
                              &pl,
                              upl_flags);
        if (kret != KERN_SUCCESS)
                panic("Failed to create UPL");

        for (upl_offset = 0; upl_offset < bp->b_bufsize; upl_offset += PAGE_SIZE) {

                if (!upl_valid_page(pl, upl_offset / PAGE_SIZE) || !upl_dirty_page(pl, upl_offset / PAGE_SIZE)) {
                        ubc_upl_abort(upl, 0);
                        goto dump_buffer;
                }
        }
        bp->b_upl = upl;
                                        
        kret = ubc_upl_map(upl, (vm_offset_t *)&(bp->b_datap));

        if (kret != KERN_SUCCESS)
                panic("getblk: ubc_upl_map() failed with (%d)", kret);
        return (1);

dump_buffer:
        bp->b_bufsize = 0;
        SET(bp->b_flags, B_INVAL);
        buf_brelse(bp);

        return(0);
}

boolean_t 
buffer_cache_gc(int all)
{
        buf_t bp;
        boolean_t did_large_zfree = FALSE;
        int now = buf_timestamp();
        uint32_t count = 0;
        int thresh_hold = BUF_STALE_THRESHHOLD;

        if (all)
                thresh_hold = 0;

        lck_mtx_lock_spin(buf_mtxp);

        /* We only care about metadata (incore storage comes from zalloc()) */
        bp = TAILQ_FIRST(&bufqueues[BQ_META]);

        /* Only collect buffers unused in the last N seconds. Note: ordered by timestamp. */
        while ((bp != NULL) && ((now - bp->b_timestamp) > thresh_hold) && (all || (count < BUF_MAX_GC_COUNT))) {
                int result, size;
                boolean_t is_zalloc;

                size = buf_size(bp);
                is_zalloc = ISSET(bp->b_flags, B_ZALLOC);

                result = bcleanbuf(bp, TRUE);
                if ((result == 0) && is_zalloc && (size >= PAGE_SIZE)) {
                        /* We've definitely freed at least a page to a zone */
                        did_large_zfree = TRUE;
                }
                bp = TAILQ_FIRST(&bufqueues[BQ_META]);
                count++;
        } 

        lck_mtx_unlock(buf_mtxp);

        return did_large_zfree;
}


/*
 * disabled for now
 */

#if FLUSH_QUEUES

#define NFLUSH 32

static int
bp_cmp(void *a, void *b)
{
    buf_t *bp_a = *(buf_t **)a,
          *bp_b = *(buf_t **)b;
    daddr64_t res;

    // don't have to worry about negative block
    // numbers so this is ok to do.
    //
    res = (bp_a->b_blkno - bp_b->b_blkno);

    return (int)res;
}


int
bflushq(int whichq, mount_t mp)
{
        buf_t   bp, next;
        int     i, buf_count;
        int     total_writes = 0;
        static buf_t flush_table[NFLUSH];

        if (whichq < 0 || whichq >= BQUEUES) {
            return (0);
        }

  restart:
        lck_mtx_lock(buf_mtxp);

        bp = TAILQ_FIRST(&bufqueues[whichq]);

        for (buf_count = 0; bp; bp = next) {
            next = bp->b_freelist.tqe_next;
                        
            if (bp->b_vp == NULL || bp->b_vp->v_mount != mp) {
                continue;
            }

            if (ISSET(bp->b_flags, B_DELWRI) && !ISSET(bp->b_lflags, BL_BUSY)) {

                bremfree_locked(bp);
#ifdef JOE_DEBUG
                bp->b_owner = current_thread();
                bp->b_tag   = 7;
#endif
                SET(bp->b_lflags, BL_BUSY);
                buf_busycount++;

                flush_table[buf_count] = bp;
                buf_count++;
                total_writes++;

                if (buf_count >= NFLUSH) {
                    lck_mtx_unlock(buf_mtxp);

                    qsort(flush_table, buf_count, sizeof(struct buf *), bp_cmp);

                    for (i = 0; i < buf_count; i++) {
                        buf_bawrite(flush_table[i]);
                    }
                    goto restart;
                }
            }
        }
        lck_mtx_unlock(buf_mtxp);

        if (buf_count > 0) {
            qsort(flush_table, buf_count, sizeof(struct buf *), bp_cmp);

            for (i = 0; i < buf_count; i++) {
                buf_bawrite(flush_table[i]);
            }
        }

        return (total_writes);
}
#endif


#if BALANCE_QUEUES

/* XXX move this to a separate file */

/*
 * NOTE: THIS CODE HAS NOT BEEN UPDATED
 * WITH RESPECT TO THE NEW LOCKING MODEL
 */
   

/*
 * Dynamic Scaling of the Buffer Queues
 */

typedef long long blsize_t;

blsize_t MAXNBUF; /* initialize to (sane_size / PAGE_SIZE) */
/* Global tunable limits */
blsize_t nbufh;                 /* number of buffer headers */
blsize_t nbuflow;               /* minimum number of buffer headers required */
blsize_t nbufhigh;              /* maximum number of buffer headers allowed */
blsize_t nbuftarget;    /* preferred number of buffer headers */

/*
 * assertions:
 *
 * 1.   0 < nbuflow <= nbufh <= nbufhigh
 * 2.   nbufhigh <= MAXNBUF
 * 3.   0 < nbuflow <= nbuftarget <= nbufhigh
 * 4.   nbufh can not be set by sysctl().
 */

/* Per queue tunable limits */

struct bufqlim {
        blsize_t        bl_nlow;        /* minimum number of buffer headers required */
        blsize_t        bl_num;         /* number of buffer headers on the queue */
        blsize_t        bl_nlhigh;      /* maximum number of buffer headers allowed */
        blsize_t        bl_target;      /* preferred number of buffer headers */
        long    bl_stale;       /* Seconds after which a buffer is considered stale */
} bufqlim[BQUEUES];

/*
 * assertions:
 *
 * 1.   0 <= bl_nlow <= bl_num <= bl_nlhigh
 * 2.   bl_nlhigh <= MAXNBUF
 * 3.  bufqlim[BQ_META].bl_nlow != 0
 * 4.  bufqlim[BQ_META].bl_nlow > (number of possible concurrent 
 *                                                                      file system IO operations)
 * 5.   bl_num can not be set by sysctl().
 * 6.   bl_nhigh <= nbufhigh
 */

/*
 * Rationale:
 * ----------
 * Defining it blsize_t as long permits 2^31 buffer headers per queue.
 * Which can describe (2^31 * PAGE_SIZE) memory per queue.
 * 
 * These limits are exported to by means of sysctl().
 * It was decided to define blsize_t as a 64 bit quantity.
 * This will make sure that we will not be required to change it
 * as long as we do not exceed 64 bit address space for the kernel.
 * 
 * low and high numbers parameters initialized at compile time
 * and boot arguments can be used to override them. sysctl() 
 * would not change the value. sysctl() can get all the values 
 * but can set only target. num is the current level.
 *
 * Advantages of having a "bufqscan" thread doing the balancing are, 
 * Keep enough bufs on BQ_EMPTY.
 *      getnewbuf() by default will always select a buffer from the BQ_EMPTY.
 *              getnewbuf() perfoms best if a buffer was found there.
 *              Also this minimizes the possibility of starting IO
 *              from getnewbuf(). That's a performance win, too.
 *
 *      Localize complex logic [balancing as well as time aging]
 *              to balancebufq().
 *
 *      Simplify getnewbuf() logic by elimination of time aging code.
 */

/* 
 * Algorithm:
 * -----------
 * The goal of the dynamic scaling of the buffer queues to to keep
 * the size of the LRU close to bl_target. Buffers on a queue would
 * be time aged.
 *
 * There would be a thread which will be responsible for "balancing"
 * the buffer cache queues.
 *
 * The scan order would be:     AGE, LRU, META, EMPTY.
 */

long bufqscanwait = 0;

static void bufqscan_thread();
static int balancebufq(int q);
static int btrimempty(int n);
static __inline__ int initbufqscan(void);
static __inline__ int nextbufq(int q);
static void buqlimprt(int all);


static __inline__ void
bufqinc(int q)
{
        if ((q < 0) || (q >= BQUEUES))
                return;

        bufqlim[q].bl_num++;
        return;
}

static __inline__ void
bufqdec(int q)
{
        if ((q < 0) || (q >= BQUEUES))
                return; 

        bufqlim[q].bl_num--;
        return;
}

static void
bufq_balance_thread_init(void)
{
        thread_t        thread = THREAD_NULL;

        if (bufqscanwait++ == 0) {

                /* Initalize globals */
                MAXNBUF = (sane_size / PAGE_SIZE);
                nbufh = nbuf_headers;
                nbuflow = min(nbufh, 100);
                nbufhigh = min(MAXNBUF, max(nbufh, 2048));
                nbuftarget = (sane_size >> 5) / PAGE_SIZE;
                nbuftarget = max(nbuflow, nbuftarget);
                nbuftarget = min(nbufhigh, nbuftarget);

                /*
                 * Initialize the bufqlim 
                 */ 

                /* LOCKED queue */
                bufqlim[BQ_LOCKED].bl_nlow = 0;
                bufqlim[BQ_LOCKED].bl_nlhigh = 32;
                bufqlim[BQ_LOCKED].bl_target = 0;
                bufqlim[BQ_LOCKED].bl_stale = 30;

                /* LRU queue */
                bufqlim[BQ_LRU].bl_nlow = 0;
                bufqlim[BQ_LRU].bl_nlhigh = nbufhigh/4;
                bufqlim[BQ_LRU].bl_target = nbuftarget/4;
                bufqlim[BQ_LRU].bl_stale = LRU_IS_STALE;

                /* AGE queue */
                bufqlim[BQ_AGE].bl_nlow = 0;
                bufqlim[BQ_AGE].bl_nlhigh = nbufhigh/4;
                bufqlim[BQ_AGE].bl_target = nbuftarget/4;
                bufqlim[BQ_AGE].bl_stale = AGE_IS_STALE;

                /* EMPTY queue */
                bufqlim[BQ_EMPTY].bl_nlow = 0;
                bufqlim[BQ_EMPTY].bl_nlhigh = nbufhigh/4;
                bufqlim[BQ_EMPTY].bl_target = nbuftarget/4;
                bufqlim[BQ_EMPTY].bl_stale = 600000;

                /* META queue */
                bufqlim[BQ_META].bl_nlow = 0;
                bufqlim[BQ_META].bl_nlhigh = nbufhigh/4;
                bufqlim[BQ_META].bl_target = nbuftarget/4;
                bufqlim[BQ_META].bl_stale = META_IS_STALE;

                /* LAUNDRY queue */
                bufqlim[BQ_LOCKED].bl_nlow = 0;
                bufqlim[BQ_LOCKED].bl_nlhigh = 32;
                bufqlim[BQ_LOCKED].bl_target = 0;
                bufqlim[BQ_LOCKED].bl_stale = 30;

                buqlimprt(1);
        }

        /* create worker thread */
        kernel_thread_start((thread_continue_t)bufqscan_thread, NULL, &thread);
        thread_deallocate(thread);
}

/* The workloop for the buffer balancing thread */
static void
bufqscan_thread()
{
        int moretodo = 0;

        for(;;) {
                do {
                        int q;  /* buffer queue to process */
                
                        q = initbufqscan();
                        for (; q; ) {
                                moretodo |= balancebufq(q);
                                q = nextbufq(q);
                        }
                } while (moretodo);

#if DIAGNOSTIC
                vfs_bufstats();
                buqlimprt(0);
#endif
                (void)tsleep((void *)&bufqscanwait, PRIBIO, "bufqscanwait", 60 * hz);
                moretodo = 0;
        }
}

/* Seed for the buffer queue balancing */
static __inline__ int
initbufqscan()
{
        /* Start with AGE queue */
        return (BQ_AGE);
}

/* Pick next buffer queue to balance */
static __inline__ int
nextbufq(int q)
{
        int order[] = { BQ_AGE, BQ_LRU, BQ_META, BQ_EMPTY, 0 };
        
        q++;
        q %= sizeof(order);
        return (order[q]);
}

/* function to balance the buffer queues */
static int
balancebufq(int q)
{
        int moretodo = 0;
        int n, t;
        
        /* reject invalid q */
        if ((q < 0) || (q >= BQUEUES))
                goto out;

        /* LOCKED or LAUNDRY queue MUST not be balanced */
        if ((q == BQ_LOCKED) || (q == BQ_LAUNDRY))
                goto out;

        n = (bufqlim[q].bl_num - bufqlim[q].bl_target);

        /* If queue has less than target nothing more to do */
        if (n < 0)
                goto out;

        if ( n > 8 ) {
                /* Balance only a small amount (12.5%) at a time */
                n >>= 3;
        }

        /* EMPTY queue needs special handling */
        if (q == BQ_EMPTY) {
                moretodo |= btrimempty(n);
                goto out;
        }

        t = buf_timestamp():
        
        for (; n > 0; n--) {
                struct buf *bp = bufqueues[q].tqh_first;
                if (!bp)
                        break;
                
                /* check if it's stale */
                if ((t - bp->b_timestamp) > bufqlim[q].bl_stale) {
                        if (bcleanbuf(bp, FALSE)) {
                                /* buf_bawrite() issued, bp not ready */
                                moretodo = 1;
                        } else {
                                /* release the cleaned buffer to BQ_EMPTY */
                                SET(bp->b_flags, B_INVAL);
                                buf_brelse(bp);
                        }
                } else
                        break;          
        }

out:
        return (moretodo);              
}

static int
btrimempty(int n)
{
        /*
         * When struct buf are allocated dynamically, this would
         * reclaim upto 'n' struct buf from the empty queue.
         */
         
         return (0);
}

static void
buqlimprt(int all)
{
        int i;
    static char *bname[BQUEUES] =
                { "LOCKED", "LRU", "AGE", "EMPTY", "META", "LAUNDRY" };

        if (all)
                for (i = 0; i < BQUEUES; i++) {
                        printf("%s : ", bname[i]);
                        printf("min = %ld, ", (long)bufqlim[i].bl_nlow);
                        printf("cur = %ld, ", (long)bufqlim[i].bl_num);
                        printf("max = %ld, ", (long)bufqlim[i].bl_nlhigh);
                        printf("target = %ld, ", (long)bufqlim[i].bl_target);
                        printf("stale after %ld seconds\n", bufqlim[i].bl_stale);
                }
        else
                for (i = 0; i < BQUEUES; i++) {
                        printf("%s : ", bname[i]);
                        printf("cur = %ld, ", (long)bufqlim[i].bl_num);
                }
}

#endif