[apple/xnu.git] / bsd / nfs / nfs_bio.c

/*
 * Copyright (c) 2000-2005 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * The contents of this file constitute Original Code as defined in and
 * are subject to the Apple Public Source License Version 1.1 (the
 * "License").  You may not use this file except in compliance with the
 * License.  Please obtain a copy of the License at
 * http://www.apple.com/publicsource and read it before using this file.
 * 
 * This 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 OR NON-INFRINGEMENT.  Please see the
 * License for the specific language governing rights and limitations
 * under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */
/* Copyright (c) 1995 NeXT Computer, Inc. All Rights Reserved */
/*
 * Copyright (c) 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Rick Macklem at The University of Guelph.
 *
 * 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.
 *
 *      @(#)nfs_bio.c   8.9 (Berkeley) 3/30/95
 * FreeBSD-Id: nfs_bio.c,v 1.44 1997/09/10 19:52:25 phk Exp $
 */
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/resourcevar.h>
#include <sys/signalvar.h>
#include <sys/proc_internal.h>
#include <sys/kauth.h>
#include <sys/malloc.h>
#include <sys/vnode.h>
#include <sys/dirent.h>
#include <sys/mount_internal.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/ubc_internal.h>
#include <sys/uio_internal.h>

#include <sys/vm.h>
#include <sys/vmparam.h>

#include <sys/time.h>
#include <kern/clock.h>
#include <libkern/OSAtomic.h>
#include <kern/kalloc.h>

#include <nfs/rpcv2.h>
#include <nfs/nfsproto.h>
#include <nfs/nfs.h>
#include <nfs/nfsmount.h>
#include <nfs/nfsnode.h>
#include <sys/buf_internal.h>

#include <sys/kdebug.h>

#define FSDBG(A, B, C, D, E) \
        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, (A))) | DBG_FUNC_NONE, \
                (int)(B), (int)(C), (int)(D), (int)(E), 0)
#define FSDBG_TOP(A, B, C, D, E) \
        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, (A))) | DBG_FUNC_START, \
                (int)(B), (int)(C), (int)(D), (int)(E), 0)
#define FSDBG_BOT(A, B, C, D, E) \
        KERNEL_DEBUG((FSDBG_CODE(DBG_FSRW, (A))) | DBG_FUNC_END, \
                (int)(B), (int)(C), (int)(D), (int)(E), 0)

extern int nfs_numasync;
extern int nfs_ioddelwri;
extern struct nfsstats nfsstats;

#define NFSBUFHASH(np, lbn)     \
        (&nfsbufhashtbl[((long)(np) / sizeof(*(np)) + (int)(lbn)) & nfsbufhash])
LIST_HEAD(nfsbufhashhead, nfsbuf) *nfsbufhashtbl;
struct nfsbuffreehead nfsbuffree, nfsbuffreemeta, nfsbufdelwri;
u_long nfsbufhash;
int nfsbufcnt, nfsbufmin, nfsbufmax, nfsbufmetacnt, nfsbufmetamax;
int nfsbuffreecnt, nfsbuffreemetacnt, nfsbufdelwricnt, nfsneedbuffer;
int nfs_nbdwrite;
time_t nfsbuffreeuptimestamp;

lck_grp_t *nfs_buf_lck_grp;
lck_grp_attr_t *nfs_buf_lck_grp_attr;
lck_attr_t *nfs_buf_lck_attr;
lck_mtx_t *nfs_buf_mutex;

#define NFSBUFWRITE_THROTTLE    9
#define NFSBUF_LRU_STALE        120
#define NFSBUF_META_STALE       240

/* number of nfsbufs nfs_buf_freeup() should attempt to free from nfsbuffree list */
#define LRU_TO_FREEUP                   6
/* number of nfsbufs nfs_buf_freeup() should attempt to free from nfsbuffreemeta list */
#define META_TO_FREEUP                  3
/* total number of nfsbufs nfs_buf_freeup() should attempt to free */
#define TOTAL_TO_FREEUP                 (LRU_TO_FREEUP+META_TO_FREEUP)
/* fraction of nfsbufs nfs_buf_freeup() should attempt to free from nfsbuffree list when called from nfs_timer() */
#define LRU_FREEUP_FRAC_ON_TIMER        8
/* fraction of nfsbufs nfs_buf_freeup() should attempt to free from nfsbuffreemeta list when called from nfs_timer() */
#define META_FREEUP_FRAC_ON_TIMER       16
/* fraction of total nfsbufs that nfsbuffreecnt should exceed before bothering to call nfs_buf_freeup() */
#define LRU_FREEUP_MIN_FRAC             4
/* fraction of total nfsbufs that nfsbuffreemetacnt should exceed before bothering to call nfs_buf_freeup() */
#define META_FREEUP_MIN_FRAC            2

#define NFS_BUF_FREEUP() \
        do { \
                /* only call nfs_buf_freeup() if it has work to do: */ \
                if (((nfsbuffreecnt > nfsbufcnt/LRU_FREEUP_MIN_FRAC) || \
                     (nfsbuffreemetacnt > nfsbufcnt/META_FREEUP_MIN_FRAC)) && \
                    ((nfsbufcnt - TOTAL_TO_FREEUP) > nfsbufmin)) \
                        nfs_buf_freeup(0); \
        } while (0)

/*
 * Initialize nfsbuf lists
 */
void
nfs_nbinit(void)
{
        nfs_buf_lck_grp_attr = lck_grp_attr_alloc_init();
        lck_grp_attr_setstat(nfs_buf_lck_grp_attr);
        nfs_buf_lck_grp = lck_grp_alloc_init("nfs_buf", nfs_buf_lck_grp_attr);

        nfs_buf_lck_attr = lck_attr_alloc_init();

        nfs_buf_mutex = lck_mtx_alloc_init(nfs_buf_lck_grp, nfs_buf_lck_attr);

        nfsbufcnt = nfsbufmetacnt =
        nfsbuffreecnt = nfsbuffreemetacnt = nfsbufdelwricnt = 0;
        nfsbufmin = 128;
        nfsbufmax = (sane_size >> PAGE_SHIFT) / 4;
        nfsbufmetamax = (sane_size >> PAGE_SHIFT) / 16;
        nfsneedbuffer = 0;
        nfs_nbdwrite = 0;
        nfsbuffreeuptimestamp = 0;

        nfsbufhashtbl = hashinit(nfsbufmax/4, M_TEMP, &nfsbufhash);
        TAILQ_INIT(&nfsbuffree);
        TAILQ_INIT(&nfsbuffreemeta);
        TAILQ_INIT(&nfsbufdelwri);

}

/*
 * try to free up some excess, unused nfsbufs
 */
void
nfs_buf_freeup(int timer)
{
        struct nfsbuf *fbp;
        struct timeval now;
        int count;
        struct nfsbuffreehead nfsbuffreeup;

        TAILQ_INIT(&nfsbuffreeup);

        lck_mtx_lock(nfs_buf_mutex);

        microuptime(&now);
        nfsbuffreeuptimestamp = now.tv_sec;

        FSDBG(320, nfsbufcnt, nfsbuffreecnt, nfsbuffreemetacnt, 0);

        count = timer ? nfsbuffreecnt/LRU_FREEUP_FRAC_ON_TIMER : LRU_TO_FREEUP;
        while ((nfsbufcnt > nfsbufmin) && (count-- > 0)) {
                fbp = TAILQ_FIRST(&nfsbuffree);
                if (!fbp)
                        break;
                if (fbp->nb_refs)
                        break;
                if (NBUFSTAMPVALID(fbp) &&
                    (fbp->nb_timestamp + (2*NFSBUF_LRU_STALE)) > now.tv_sec)
                        break;
                nfs_buf_remfree(fbp);
                /* disassociate buffer from any vnode */
                if (fbp->nb_vp) {
                        if (fbp->nb_vnbufs.le_next != NFSNOLIST) {
                                LIST_REMOVE(fbp, nb_vnbufs);
                                fbp->nb_vnbufs.le_next = NFSNOLIST;
                        }
                        fbp->nb_vp = NULL;
                }
                LIST_REMOVE(fbp, nb_hash);
                TAILQ_INSERT_TAIL(&nfsbuffreeup, fbp, nb_free);
                nfsbufcnt--;
        }

        count = timer ? nfsbuffreemetacnt/META_FREEUP_FRAC_ON_TIMER : META_TO_FREEUP;
        while ((nfsbufcnt > nfsbufmin) && (count-- > 0)) {
                fbp = TAILQ_FIRST(&nfsbuffreemeta);
                if (!fbp)
                        break;
                if (fbp->nb_refs)
                        break;
                if (NBUFSTAMPVALID(fbp) &&
                    (fbp->nb_timestamp + (2*NFSBUF_META_STALE)) > now.tv_sec)
                        break;
                nfs_buf_remfree(fbp);
                /* disassociate buffer from any vnode */
                if (fbp->nb_vp) {
                        if (fbp->nb_vnbufs.le_next != NFSNOLIST) {
                                LIST_REMOVE(fbp, nb_vnbufs);
                                fbp->nb_vnbufs.le_next = NFSNOLIST;
                        }
                        fbp->nb_vp = NULL;
                }
                LIST_REMOVE(fbp, nb_hash);
                TAILQ_INSERT_TAIL(&nfsbuffreeup, fbp, nb_free);
                nfsbufcnt--;
                nfsbufmetacnt--;
        }

        FSDBG(320, nfsbufcnt, nfsbuffreecnt, nfsbuffreemetacnt, 0);
        NFSBUFCNTCHK(1);

        lck_mtx_unlock(nfs_buf_mutex);

        while ((fbp = TAILQ_FIRST(&nfsbuffreeup))) {
                TAILQ_REMOVE(&nfsbuffreeup, fbp, nb_free);
                /* nuke any creds */
                if (fbp->nb_rcred != NOCRED) {
                        kauth_cred_rele(fbp->nb_rcred);
                        fbp->nb_rcred = NOCRED;
                }
                if (fbp->nb_wcred != NOCRED) {
                        kauth_cred_rele(fbp->nb_wcred);
                        fbp->nb_wcred = NOCRED;
                }
                /* if buf was NB_META, dump buffer */
                if (ISSET(fbp->nb_flags, NB_META) && fbp->nb_data)
                        kfree(fbp->nb_data, fbp->nb_bufsize);
                FREE(fbp, M_TEMP);
        }

}

/*
 * remove a buffer from the freelist
 * (must be called with nfs_buf_mutex held)
 */
void
nfs_buf_remfree(struct nfsbuf *bp)
{
        if (bp->nb_free.tqe_next == NFSNOLIST)
                panic("nfsbuf not on free list");
        if (ISSET(bp->nb_flags, NB_DELWRI)) {
                nfsbufdelwricnt--;
                TAILQ_REMOVE(&nfsbufdelwri, bp, nb_free);
        } else if (ISSET(bp->nb_flags, NB_META)) {
                nfsbuffreemetacnt--;
                TAILQ_REMOVE(&nfsbuffreemeta, bp, nb_free);
        } else {
                nfsbuffreecnt--;
                TAILQ_REMOVE(&nfsbuffree, bp, nb_free);
        }
        bp->nb_free.tqe_next = NFSNOLIST;
        NFSBUFCNTCHK(1);
}

/*
 * check for existence of nfsbuf in cache
 */
boolean_t
nfs_buf_is_incore(vnode_t vp, daddr64_t blkno)
{
        boolean_t rv;
        lck_mtx_lock(nfs_buf_mutex);
        if (nfs_buf_incore(vp, blkno))
                rv = TRUE;
        else
                rv = FALSE;
        lck_mtx_unlock(nfs_buf_mutex);
        return (rv);
}

/*
 * return incore buffer (must be called with nfs_buf_mutex held)
 */
struct nfsbuf *
nfs_buf_incore(vnode_t vp, daddr64_t blkno)
{
        /* Search hash chain */
        struct nfsbuf * bp = NFSBUFHASH(VTONFS(vp), blkno)->lh_first;
        for (; bp != NULL; bp = bp->nb_hash.le_next)
                if (bp->nb_lblkno == blkno && bp->nb_vp == vp) {
                        if (!ISSET(bp->nb_flags, NB_INVAL)) {
                                FSDBG(547, bp, blkno, bp->nb_flags, bp->nb_vp);
                                return (bp);
                        }
                }
        return (NULL);
}

/*
 * Check if it's OK to drop a page.
 *
 * Called by vnode_pager() on pageout request of non-dirty page.
 * We need to make sure that it's not part of a delayed write.
 * If it is, we can't let the VM drop it because we may need it
 * later when/if we need to write the data (again).
 */
int
nfs_buf_page_inval(vnode_t vp, off_t offset)
{
        struct nfsbuf *bp;
        int error = 0;

        lck_mtx_lock(nfs_buf_mutex);
        bp = nfs_buf_incore(vp, ubc_offtoblk(vp, offset));
        if (!bp)
                goto out;
        FSDBG(325, bp, bp->nb_flags, bp->nb_dirtyoff, bp->nb_dirtyend);
        if (ISSET(bp->nb_lflags, NBL_BUSY)) {
                error = EBUSY;
                goto out;
        }
        /*
         * If there's a dirty range in the buffer, check to
         * see if this page intersects with the dirty range.
         * If it does, we can't let the pager drop the page.
         */
        if (bp->nb_dirtyend > 0) {
                int start = offset - NBOFF(bp);
                if (bp->nb_dirtyend <= start ||
                    bp->nb_dirtyoff >= (start + PAGE_SIZE))
                        error = 0;
                else
                        error = EBUSY;
        }
out:
        lck_mtx_unlock(nfs_buf_mutex);
        return (error);
}

/*
 * set up the UPL for a buffer
 * (must NOT be called with nfs_buf_mutex held)
 */
int
nfs_buf_upl_setup(struct nfsbuf *bp)
{
        kern_return_t kret;
        upl_t upl;
        int upl_flags;

        if (ISSET(bp->nb_flags, NB_PAGELIST))
                return (0);

        upl_flags = UPL_PRECIOUS;
        if (! ISSET(bp->nb_flags, NB_READ)) {
                /*
                 * We're doing a "write", so we intend to modify
                 * the pages we're gathering.
                 */
                upl_flags |= UPL_WILL_MODIFY;
        }
        kret = ubc_create_upl(bp->nb_vp, NBOFF(bp), bp->nb_bufsize,
                                &upl, NULL, upl_flags);
        if (kret == KERN_INVALID_ARGUMENT) {
                /* vm object probably doesn't exist any more */
                bp->nb_pagelist = NULL;
                return (EINVAL);
        }
        if (kret != KERN_SUCCESS) {
                printf("nfs_buf_upl_setup(): failed to get pagelist %d\n", kret);
                bp->nb_pagelist = NULL;
                return (EIO);
        }

        FSDBG(538, bp, NBOFF(bp), bp->nb_bufsize, bp->nb_vp);

        bp->nb_pagelist = upl;
        SET(bp->nb_flags, NB_PAGELIST);
        return (0);
}

/*
 * update buffer's valid/dirty info from UBC
 * (must NOT be called with nfs_buf_mutex held)
 */
void
nfs_buf_upl_check(struct nfsbuf *bp)
{
        upl_page_info_t *pl;
        off_t filesize, fileoffset;
        int i, npages;

        if (!ISSET(bp->nb_flags, NB_PAGELIST))
                return;

        npages = round_page_32(bp->nb_bufsize) / PAGE_SIZE;
        filesize = ubc_getsize(bp->nb_vp);
        fileoffset = NBOFF(bp);
        if (fileoffset < filesize)
                SET(bp->nb_flags, NB_CACHE);
        else
                CLR(bp->nb_flags, NB_CACHE);

        pl = ubc_upl_pageinfo(bp->nb_pagelist);
        bp->nb_valid = bp->nb_dirty = 0;

        for (i=0; i < npages; i++, fileoffset += PAGE_SIZE_64) {
                /* anything beyond the end of the file is not valid or dirty */
                if (fileoffset >= filesize)
                        break;
                if (!upl_valid_page(pl, i)) {
                        CLR(bp->nb_flags, NB_CACHE);
                        continue;
                }
                NBPGVALID_SET(bp,i);
                if (upl_dirty_page(pl, i)) {
                        NBPGDIRTY_SET(bp, i);
                        if (!ISSET(bp->nb_flags, NB_WASDIRTY))
                                SET(bp->nb_flags, NB_WASDIRTY);
                }
        }
        fileoffset = NBOFF(bp);
        if (ISSET(bp->nb_flags, NB_CACHE)) {
                bp->nb_validoff = 0;
                bp->nb_validend = bp->nb_bufsize;
                if (fileoffset + bp->nb_validend > filesize)
                        bp->nb_validend = filesize - fileoffset;
        } else {
                bp->nb_validoff = bp->nb_validend = -1;
        }
        FSDBG(539, bp, fileoffset, bp->nb_valid, bp->nb_dirty);
        FSDBG(539, bp->nb_validoff, bp->nb_validend, bp->nb_dirtyoff, bp->nb_dirtyend);
}

/*
 * make sure that a buffer is mapped
 * (must NOT be called with nfs_buf_mutex held)
 */
static int
nfs_buf_map(struct nfsbuf *bp)
{
        kern_return_t kret;

        if (bp->nb_data)
                return (0);
        if (!ISSET(bp->nb_flags, NB_PAGELIST))
                return (EINVAL);

        kret = ubc_upl_map(bp->nb_pagelist, (vm_address_t *)&(bp->nb_data));
        if (kret != KERN_SUCCESS)
                panic("nfs_buf_map: ubc_upl_map() failed with (%d)", kret);
        if (bp->nb_data == 0)
                panic("ubc_upl_map mapped 0");
        FSDBG(540, bp, bp->nb_flags, NBOFF(bp), bp->nb_data);
        return (0);
}

/*
 * check range of pages in nfsbuf's UPL for validity
 */
static int
nfs_buf_upl_valid_range(struct nfsbuf *bp, int off, int size)
{
        off_t fileoffset, filesize;
        int pg, lastpg;
        upl_page_info_t *pl;

        if (!ISSET(bp->nb_flags, NB_PAGELIST))
                return (0);
        pl = ubc_upl_pageinfo(bp->nb_pagelist);

        size += off & PAGE_MASK;
        off &= ~PAGE_MASK;
        fileoffset = NBOFF(bp);
        filesize = VTONFS(bp->nb_vp)->n_size;
        if ((fileoffset + off + size) > filesize)
                size = filesize - (fileoffset + off);

        pg = off/PAGE_SIZE;
        lastpg = (off + size - 1)/PAGE_SIZE;
        while (pg <= lastpg) {
                if (!upl_valid_page(pl, pg))
                        return (0);
                pg++;
        }
        return (1);
}

/*
 * normalize an nfsbuf's valid range
 *
 * the read/write code guarantees that we'll always have a valid
 * region that is an integral number of pages.  If either end
 * of the valid range isn't page-aligned, it gets corrected
 * here as we extend the valid range through all of the
 * contiguous valid pages.
 */
static void
nfs_buf_normalize_valid_range(struct nfsnode *np, struct nfsbuf *bp)
{
        int pg, npg;
        /* pull validoff back to start of contiguous valid page range */
        pg = bp->nb_validoff/PAGE_SIZE;
        while (pg >= 0 && NBPGVALID(bp,pg))
                pg--;
        bp->nb_validoff = (pg+1) * PAGE_SIZE;
        /* push validend forward to end of contiguous valid page range */
        npg = bp->nb_bufsize/PAGE_SIZE;
        pg = bp->nb_validend/PAGE_SIZE;
        while (pg < npg && NBPGVALID(bp,pg))
                pg++;
        bp->nb_validend = pg * PAGE_SIZE;
        /* clip to EOF */
        if (NBOFF(bp) + bp->nb_validend > (off_t)np->n_size)
                bp->nb_validend = np->n_size % bp->nb_bufsize;
}

/*
 * try to push out some delayed/uncommitted writes
 * ("locked" indicates whether nfs_buf_mutex is already held)
 */
static void
nfs_buf_delwri_push(int locked)
{
        struct nfsbuf *bp;
        int i, error;

        if (TAILQ_EMPTY(&nfsbufdelwri))
                return;

        /* first try to tell the nfsiods to do it */
        if (nfs_asyncio(NULL, NULL) == 0)
                return;

        /* otherwise, try to do some of the work ourselves */
        i = 0;
        if (!locked)
                lck_mtx_lock(nfs_buf_mutex);
        while (i < 8 && (bp = TAILQ_FIRST(&nfsbufdelwri)) != NULL) {
                struct nfsnode *np = VTONFS(bp->nb_vp);
                nfs_buf_remfree(bp);
                nfs_buf_refget(bp);
                while ((error = nfs_buf_acquire(bp, 0, 0, 0)) == EAGAIN);
                nfs_buf_refrele(bp);
                if (error)
                        break;
                if (!bp->nb_vp) {
                        /* buffer is no longer valid */
                        nfs_buf_drop(bp);
                        continue;
                }
                if (ISSET(bp->nb_flags, NB_NEEDCOMMIT))
                        nfs_buf_check_write_verifier(np, bp);
                if (ISSET(bp->nb_flags, NB_NEEDCOMMIT)) {
                        /* put buffer at end of delwri list */
                        TAILQ_INSERT_TAIL(&nfsbufdelwri, bp, nb_free);
                        nfsbufdelwricnt++;
                        nfs_buf_drop(bp);
                        lck_mtx_unlock(nfs_buf_mutex);
                        nfs_flushcommits(np->n_vnode, NULL, 1);
                } else {
                        SET(bp->nb_flags, NB_ASYNC);
                        lck_mtx_unlock(nfs_buf_mutex);
                        nfs_buf_write(bp);
                }
                i++;
                lck_mtx_lock(nfs_buf_mutex);
        }
        if (!locked)
                lck_mtx_unlock(nfs_buf_mutex);
}

/*
 * Get an nfs buffer.
 *
 * Returns errno on error, 0 otherwise.
 * Any buffer is returned in *bpp.
 *
 * If NBLK_ONLYVALID is set, only return buffer if found in cache.
 * If NBLK_NOWAIT is set, don't wait for the buffer if it's marked BUSY.
 *
 * Check for existence of buffer in cache.
 * Or attempt to reuse a buffer from one of the free lists.
 * Or allocate a new buffer if we haven't already hit max allocation.
 * Or wait for a free buffer.
 *
 * If available buffer found, prepare it, and return it.
 *
 * If the calling process is interrupted by a signal for
 * an interruptible mount point, return EINTR.
 */
int
nfs_buf_get(
        vnode_t vp,
        daddr64_t blkno,
        int size,
        proc_t p,
        int flags,
        struct nfsbuf **bpp)
{
        struct nfsnode *np = VTONFS(vp);
        struct nfsbuf *bp;
        int biosize, bufsize;
        kauth_cred_t cred;
        int slpflag = PCATCH;
        int operation = (flags & NBLK_OPMASK);
        int error = 0;
        struct timespec ts;

        FSDBG_TOP(541, vp, blkno, size, flags);
        *bpp = NULL;

        bufsize = size;
        if (bufsize > MAXBSIZE)
                panic("nfs_buf_get: buffer larger than MAXBSIZE requested");

        biosize = vfs_statfs(vnode_mount(vp))->f_iosize;

        if (UBCINVALID(vp) || !UBCINFOEXISTS(vp)) {
                operation = NBLK_META;
        } else if (bufsize < biosize) {
                /* reg files should always have biosize blocks */
                bufsize = biosize;
        }

        /* if NBLK_WRITE, check for too many delayed/uncommitted writes */
        if ((operation == NBLK_WRITE) && (nfs_nbdwrite > ((nfsbufcnt*3)/4))) {
                FSDBG_TOP(542, vp, blkno, nfs_nbdwrite, ((nfsbufcnt*3)/4));

                /* poke the delwri list */
                nfs_buf_delwri_push(0);

                /* sleep to let other threads run... */
                tsleep(&nfs_nbdwrite, PCATCH, "nfs_nbdwrite", 1);
                FSDBG_BOT(542, vp, blkno, nfs_nbdwrite, ((nfsbufcnt*3)/4));
        }

loop:
        lck_mtx_lock(nfs_buf_mutex);

        /* check for existence of nfsbuf in cache */
        if ((bp = nfs_buf_incore(vp, blkno))) {
                /* if busy, set wanted and wait */
                if (ISSET(bp->nb_lflags, NBL_BUSY)) {
                        if (flags & NBLK_NOWAIT) {
                                lck_mtx_unlock(nfs_buf_mutex);
                                FSDBG_BOT(541, vp, blkno, bp, 0xbcbcbcbc);
                                return (0);
                        }
                        FSDBG_TOP(543, vp, blkno, bp, bp->nb_flags);
                        SET(bp->nb_lflags, NBL_WANTED);

                        ts.tv_sec = 2;
                        ts.tv_nsec = 0;
                        msleep(bp, nfs_buf_mutex, slpflag|(PRIBIO+1)|PDROP,
                                "nfsbufget", (slpflag == PCATCH) ? 0 : &ts);
                        slpflag = 0;
                        FSDBG_BOT(543, vp, blkno, bp, bp->nb_flags);
                        if ((error = nfs_sigintr(VFSTONFS(vnode_mount(vp)), NULL, p))) {
                                FSDBG_BOT(541, vp, blkno, 0, error);
                                return (error);
                        }
                        goto loop;
                }
                if (bp->nb_bufsize != bufsize)
                        panic("nfsbuf size mismatch");
                SET(bp->nb_lflags, NBL_BUSY);
                SET(bp->nb_flags, NB_CACHE);
                nfs_buf_remfree(bp);
                /* additional paranoia: */
                if (ISSET(bp->nb_flags, NB_PAGELIST))
                        panic("pagelist buffer was not busy");
                goto buffer_setup;
        }

        if (flags & NBLK_ONLYVALID) {
                lck_mtx_unlock(nfs_buf_mutex);
                FSDBG_BOT(541, vp, blkno, 0, 0x0000cace);
                return (0);
        }

        /*
         * where to get a free buffer:
         * - if meta and maxmeta reached, must reuse meta
         * - alloc new if we haven't reached min bufs
         * - if free lists are NOT empty
         *   - if free list is stale, use it
         *   - else if freemeta list is stale, use it
         *   - else if max bufs allocated, use least-time-to-stale
         * - alloc new if we haven't reached max allowed
         * - start clearing out delwri list and try again
         */

        if ((operation == NBLK_META) && (nfsbufmetacnt >= nfsbufmetamax)) {
                /* if we've hit max meta buffers, must reuse a meta buffer */
                bp = TAILQ_FIRST(&nfsbuffreemeta);
        } else if ((nfsbufcnt > nfsbufmin) &&
            (!TAILQ_EMPTY(&nfsbuffree) || !TAILQ_EMPTY(&nfsbuffreemeta))) {
                /* try to pull an nfsbuf off a free list */
                struct nfsbuf *lrubp, *metabp;
                struct timeval now;
                microuptime(&now);

                /* if the next LRU or META buffer is invalid or stale, use it */
                lrubp = TAILQ_FIRST(&nfsbuffree);
                if (lrubp && (!NBUFSTAMPVALID(lrubp) ||
                    ((lrubp->nb_timestamp + NFSBUF_LRU_STALE) < now.tv_sec)))
                        bp = lrubp;
                metabp = TAILQ_FIRST(&nfsbuffreemeta);
                if (!bp && metabp && (!NBUFSTAMPVALID(metabp) ||
                    ((metabp->nb_timestamp + NFSBUF_META_STALE) < now.tv_sec)))
                        bp = metabp;

                if (!bp && (nfsbufcnt >= nfsbufmax)) {
                        /* we've already allocated all bufs, so */
                        /* choose the buffer that'll go stale first */
                        if (!metabp)
                                bp = lrubp;
                        else if (!lrubp)
                                bp = metabp;
                        else {
                                int32_t lru_stale_time, meta_stale_time;
                                lru_stale_time = lrubp->nb_timestamp + NFSBUF_LRU_STALE;
                                meta_stale_time = metabp->nb_timestamp + NFSBUF_META_STALE;
                                if (lru_stale_time <= meta_stale_time)
                                        bp = lrubp;
                                else
                                        bp = metabp;
                        }
                }
        }

        if (bp) {
                /* we have a buffer to reuse */
                FSDBG(544, vp, blkno, bp, bp->nb_flags);
                nfs_buf_remfree(bp);
                if (ISSET(bp->nb_flags, NB_DELWRI))
                        panic("nfs_buf_get: delwri");
                SET(bp->nb_lflags, NBL_BUSY);
                /* disassociate buffer from previous vnode */
                if (bp->nb_vp) {
                        if (bp->nb_vnbufs.le_next != NFSNOLIST) {
                                LIST_REMOVE(bp, nb_vnbufs);
                                bp->nb_vnbufs.le_next = NFSNOLIST;
                        }
                        bp->nb_vp = NULL;
                }
                LIST_REMOVE(bp, nb_hash);
                /* nuke any creds we're holding */
                cred = bp->nb_rcred;
                if (cred != NOCRED) {
                        bp->nb_rcred = NOCRED; 
                        kauth_cred_rele(cred);
                }
                cred = bp->nb_wcred;
                if (cred != NOCRED) {
                        bp->nb_wcred = NOCRED; 
                        kauth_cred_rele(cred);
                }
                /* if buf will no longer be NB_META, dump old buffer */
                if (operation == NBLK_META) {
                        if (!ISSET(bp->nb_flags, NB_META))
                                nfsbufmetacnt++;
                } else if (ISSET(bp->nb_flags, NB_META)) {
                        if (bp->nb_data) {
                                kfree(bp->nb_data, bp->nb_bufsize);
                                bp->nb_data = NULL;
                        }
                        nfsbufmetacnt--;
                }
                /* re-init buf fields */
                bp->nb_error = 0;
                bp->nb_validoff = bp->nb_validend = -1;
                bp->nb_dirtyoff = bp->nb_dirtyend = 0;
                bp->nb_valid = 0;
                bp->nb_dirty = 0;
                bp->nb_verf = 0;
        } else {
                /* no buffer to reuse */
                if ((nfsbufcnt < nfsbufmax) &&
                    ((operation != NBLK_META) || (nfsbufmetacnt < nfsbufmetamax))) {
                        /* just alloc a new one */
                        MALLOC(bp, struct nfsbuf *, sizeof(struct nfsbuf), M_TEMP, M_WAITOK);
                        if (!bp) {
                                lck_mtx_unlock(nfs_buf_mutex);
                                FSDBG_BOT(541, vp, blkno, 0, error);
                                return (ENOMEM);
                        }
                        nfsbufcnt++;
                        if (operation == NBLK_META)
                                nfsbufmetacnt++;
                        NFSBUFCNTCHK(1);
                        /* init nfsbuf */
                        bzero(bp, sizeof(*bp));
                        bp->nb_free.tqe_next = NFSNOLIST;
                        bp->nb_validoff = bp->nb_validend = -1;
                        FSDBG(545, vp, blkno, bp, 0);
                } else {
                        /* too many bufs... wait for buffers to free up */
                        FSDBG_TOP(546, vp, blkno, nfsbufcnt, nfsbufmax);

                        /* poke the delwri list */
                        nfs_buf_delwri_push(1);

                        nfsneedbuffer = 1;
                        msleep(&nfsneedbuffer, nfs_buf_mutex, PCATCH|PDROP,
                                "nfsbufget", 0);
                        FSDBG_BOT(546, vp, blkno, nfsbufcnt, nfsbufmax);
                        if ((error = nfs_sigintr(VFSTONFS(vnode_mount(vp)), NULL, p))) {
                                FSDBG_BOT(541, vp, blkno, 0, error);
                                return (error);
                        }
                        goto loop;
                }
        }

        /* setup nfsbuf */
        bp->nb_lflags = NBL_BUSY;
        bp->nb_flags = 0;
        bp->nb_lblkno = blkno;
        /* insert buf in hash */
        LIST_INSERT_HEAD(NFSBUFHASH(np, blkno), bp, nb_hash);
        /* associate buffer with new vnode */
        bp->nb_vp = vp;
        LIST_INSERT_HEAD(&np->n_cleanblkhd, bp, nb_vnbufs);

buffer_setup:

        /* unlock hash */
        lck_mtx_unlock(nfs_buf_mutex);

        switch (operation) {
        case NBLK_META:
                SET(bp->nb_flags, NB_META);
                if ((bp->nb_bufsize != bufsize) && bp->nb_data) {
                        kfree(bp->nb_data, bp->nb_bufsize);
                        bp->nb_data = NULL;
                        bp->nb_validoff = bp->nb_validend = -1;
                        bp->nb_dirtyoff = bp->nb_dirtyend = 0;
                        bp->nb_valid = 0;
                        bp->nb_dirty = 0;
                        CLR(bp->nb_flags, NB_CACHE);
                }
                if (!bp->nb_data)
                        bp->nb_data = kalloc(bufsize);
                if (!bp->nb_data) {
                        /* Ack! couldn't allocate the data buffer! */
                        /* cleanup buffer and return error */
                        lck_mtx_lock(nfs_buf_mutex);
                        LIST_REMOVE(bp, nb_vnbufs);
                        bp->nb_vnbufs.le_next = NFSNOLIST;
                        bp->nb_vp = NULL;
                        /* invalidate usage timestamp to allow immediate freeing */
                        NBUFSTAMPINVALIDATE(bp);
                        if (bp->nb_free.tqe_next != NFSNOLIST)
                                panic("nfsbuf on freelist");
                        TAILQ_INSERT_HEAD(&nfsbuffree, bp, nb_free);
                        nfsbuffreecnt++;
                        lck_mtx_unlock(nfs_buf_mutex);
                        FSDBG_BOT(541, vp, blkno, 0xb00, ENOMEM);
                        return (ENOMEM);
                }
                bp->nb_bufsize = bufsize;
                break;

        case NBLK_READ:
        case NBLK_WRITE:
                /*
                 * Set or clear NB_READ now to let the UPL subsystem know
                 * if we intend to modify the pages or not.
                 */
                if (operation == NBLK_READ) {
                        SET(bp->nb_flags, NB_READ);
                } else {
                        CLR(bp->nb_flags, NB_READ);
                }
                if (bufsize < PAGE_SIZE)
                        bufsize = PAGE_SIZE;
                bp->nb_bufsize = bufsize;
                bp->nb_validoff = bp->nb_validend = -1;

                if (UBCINFOEXISTS(vp)) {
                        /* setup upl */
                        if (nfs_buf_upl_setup(bp)) {
                                /* unable to create upl */
                                /* vm object must no longer exist */
                                /* cleanup buffer and return error */
                                lck_mtx_lock(nfs_buf_mutex);
                                LIST_REMOVE(bp, nb_vnbufs);
                                bp->nb_vnbufs.le_next = NFSNOLIST;
                                bp->nb_vp = NULL;
                                /* invalidate usage timestamp to allow immediate freeing */
                                NBUFSTAMPINVALIDATE(bp);
                                if (bp->nb_free.tqe_next != NFSNOLIST)
                                        panic("nfsbuf on freelist");
                                TAILQ_INSERT_HEAD(&nfsbuffree, bp, nb_free);
                                nfsbuffreecnt++;
                                lck_mtx_unlock(nfs_buf_mutex);
                                FSDBG_BOT(541, vp, blkno, 0x2bc, EIO);
                                return (EIO);
                        }
                        nfs_buf_upl_check(bp);
                }
                break;

        default:
                panic("nfs_buf_get: %d unknown operation", operation);
        }

        *bpp = bp;

        FSDBG_BOT(541, vp, blkno, bp, bp->nb_flags);

        return (0);
}

void
nfs_buf_release(struct nfsbuf *bp, int freeup)
{
        vnode_t vp = bp->nb_vp;
        struct timeval now;
        int wakeup_needbuffer, wakeup_buffer, wakeup_nbdwrite;

        FSDBG_TOP(548, bp, NBOFF(bp), bp->nb_flags, bp->nb_data);
        FSDBG(548, bp->nb_validoff, bp->nb_validend, bp->nb_dirtyoff, bp->nb_dirtyend);
        FSDBG(548, bp->nb_valid, 0, bp->nb_dirty, 0);

        if (UBCINFOEXISTS(vp) && bp->nb_bufsize) {
                int upl_flags;
                upl_t upl;
                int i, rv;

                if (!ISSET(bp->nb_flags, NB_PAGELIST) && !ISSET(bp->nb_flags, NB_INVAL)) {
                        rv = nfs_buf_upl_setup(bp);
                        if (rv)
                                printf("nfs_buf_release: upl create failed %d\n", rv);
                        else
                                nfs_buf_upl_check(bp);
                }
                upl = bp->nb_pagelist;
                if (!upl)
                        goto pagelist_cleanup_done;
                if (bp->nb_data) {
                        if (ubc_upl_unmap(upl) != KERN_SUCCESS)
                                panic("ubc_upl_unmap failed");
                        bp->nb_data = NULL;
                }
                if (bp->nb_flags & (NB_ERROR | NB_INVAL | NB_NOCACHE)) {
                        if (bp->nb_flags & (NB_READ | NB_INVAL | NB_NOCACHE))
                                upl_flags = UPL_ABORT_DUMP_PAGES;
                        else
                                upl_flags = 0;
                        ubc_upl_abort(upl, upl_flags);
                        goto pagelist_cleanup_done;
                }
                for (i=0; i <= (bp->nb_bufsize - 1)/PAGE_SIZE; i++) {
                        if (!NBPGVALID(bp,i))
                                ubc_upl_abort_range(upl,
                                        i*PAGE_SIZE, PAGE_SIZE,
                                        UPL_ABORT_DUMP_PAGES |
                                        UPL_ABORT_FREE_ON_EMPTY);
                        else {
                                if (NBPGDIRTY(bp,i))
                                        upl_flags = UPL_COMMIT_SET_DIRTY;
                                else
                                        upl_flags = UPL_COMMIT_CLEAR_DIRTY;
                                ubc_upl_commit_range(upl,
                                        i*PAGE_SIZE, PAGE_SIZE,
                                        upl_flags |
                                        UPL_COMMIT_INACTIVATE |
                                        UPL_COMMIT_FREE_ON_EMPTY);
                        }
                }
pagelist_cleanup_done:
                /* was this the last buffer in the file? */
                if (NBOFF(bp) + bp->nb_bufsize > (off_t)(VTONFS(vp)->n_size)) {
                        /* if so, invalidate all pages of last buffer past EOF */
                        int biosize = vfs_statfs(vnode_mount(vp))->f_iosize;
                        off_t start, end;
                        start = trunc_page_64(VTONFS(vp)->n_size) + PAGE_SIZE_64;
                        end = trunc_page_64(NBOFF(bp) + biosize);
                        if (end > start) {
                                if (!(rv = ubc_sync_range(vp, start, end, UBC_INVALIDATE)))
                                        printf("nfs_buf_release(): ubc_sync_range failed!\n");
                        }
                }
                CLR(bp->nb_flags, NB_PAGELIST);
                bp->nb_pagelist = NULL;
        }

        lck_mtx_lock(nfs_buf_mutex);

        wakeup_needbuffer = wakeup_buffer = wakeup_nbdwrite = 0;

        /* Wake up any processes waiting for any buffer to become free. */
        if (nfsneedbuffer) {
                nfsneedbuffer = 0;
                wakeup_needbuffer = 1;
        }
        /* Wake up any processes waiting for _this_ buffer to become free. */
        if (ISSET(bp->nb_lflags, NBL_WANTED)) {
                CLR(bp->nb_lflags, NBL_WANTED);
                wakeup_buffer = 1;
        }

        /* If it's not cacheable, or an error, mark it invalid. */
        if (ISSET(bp->nb_flags, (NB_NOCACHE|NB_ERROR)))
                SET(bp->nb_flags, NB_INVAL);

        if ((bp->nb_bufsize <= 0) || ISSET(bp->nb_flags, NB_INVAL)) {
                /* If it's invalid or empty, dissociate it from its vnode */
                if (bp->nb_vnbufs.le_next != NFSNOLIST) {
                        LIST_REMOVE(bp, nb_vnbufs);
                        bp->nb_vnbufs.le_next = NFSNOLIST;
                }
                bp->nb_vp = NULL;
                /* if this was a delayed write, wakeup anyone */
                /* waiting for delayed writes to complete */
                if (ISSET(bp->nb_flags, NB_DELWRI)) {
                        CLR(bp->nb_flags, NB_DELWRI);
                        OSAddAtomic(-1, (SInt32*)&nfs_nbdwrite);
                        NFSBUFCNTCHK(1);
                        wakeup_nbdwrite = 1;
                }
                /* invalidate usage timestamp to allow immediate freeing */
                NBUFSTAMPINVALIDATE(bp);
                /* put buffer at head of free list */
                if (bp->nb_free.tqe_next != NFSNOLIST)
                        panic("nfsbuf on freelist");
                SET(bp->nb_flags, NB_INVAL);
                if (ISSET(bp->nb_flags, NB_META)) {
                        TAILQ_INSERT_HEAD(&nfsbuffreemeta, bp, nb_free);
                        nfsbuffreemetacnt++;
                } else {
                        TAILQ_INSERT_HEAD(&nfsbuffree, bp, nb_free);
                        nfsbuffreecnt++;
                }
        } else if (ISSET(bp->nb_flags, NB_DELWRI)) {
                /* put buffer at end of delwri list */
                if (bp->nb_free.tqe_next != NFSNOLIST)
                        panic("nfsbuf on freelist");
                TAILQ_INSERT_TAIL(&nfsbufdelwri, bp, nb_free);
                nfsbufdelwricnt++;
                freeup = 0;
        } else {
                /* update usage timestamp */
                microuptime(&now);
                bp->nb_timestamp = now.tv_sec;
                /* put buffer at end of free list */
                if (bp->nb_free.tqe_next != NFSNOLIST)
                        panic("nfsbuf on freelist");
                if (ISSET(bp->nb_flags, NB_META)) {
                        TAILQ_INSERT_TAIL(&nfsbuffreemeta, bp, nb_free);
                        nfsbuffreemetacnt++;
                } else {
                        TAILQ_INSERT_TAIL(&nfsbuffree, bp, nb_free);
                        nfsbuffreecnt++;
                }
        }

        NFSBUFCNTCHK(1);

        /* Unlock the buffer. */
        CLR(bp->nb_flags, (NB_ASYNC | NB_NOCACHE | NB_STABLE | NB_IOD));
        CLR(bp->nb_lflags, NBL_BUSY);

        FSDBG_BOT(548, bp, NBOFF(bp), bp->nb_flags, bp->nb_data);

        lck_mtx_unlock(nfs_buf_mutex);

        if (wakeup_needbuffer)
                wakeup(&nfsneedbuffer);
        if (wakeup_buffer)
                wakeup(bp);
        if (wakeup_nbdwrite)
                wakeup(&nfs_nbdwrite);
        if (freeup)
                NFS_BUF_FREEUP();
}

/*
 * Wait for operations on the buffer to complete.
 * When they do, extract and return the I/O's error value.
 */
int
nfs_buf_iowait(struct nfsbuf *bp)
{
        FSDBG_TOP(549, bp, NBOFF(bp), bp->nb_flags, bp->nb_error);

        lck_mtx_lock(nfs_buf_mutex);

        while (!ISSET(bp->nb_flags, NB_DONE))
                msleep(bp, nfs_buf_mutex, PRIBIO + 1, "nfs_buf_iowait", 0);

        lck_mtx_unlock(nfs_buf_mutex);

        FSDBG_BOT(549, bp, NBOFF(bp), bp->nb_flags, bp->nb_error);

        /* check for interruption of I/O, then errors. */
        if (ISSET(bp->nb_flags, NB_EINTR)) {
                CLR(bp->nb_flags, NB_EINTR);
                return (EINTR);
        } else if (ISSET(bp->nb_flags, NB_ERROR))
                return (bp->nb_error ? bp->nb_error : EIO);
        return (0);
}

/*
 * Mark I/O complete on a buffer.
 */
void
nfs_buf_iodone(struct nfsbuf *bp)
{

        FSDBG_TOP(550, bp, NBOFF(bp), bp->nb_flags, bp->nb_error);

        if (ISSET(bp->nb_flags, NB_DONE))
                panic("nfs_buf_iodone already");
        /*
         * I/O was done, so don't believe
         * the DIRTY state from VM anymore
         */
        CLR(bp->nb_flags, NB_WASDIRTY);

        if (!ISSET(bp->nb_flags, NB_READ)) {
                CLR(bp->nb_flags, NB_WRITEINPROG);
                /*
                 * vnode_writedone() takes care of waking up
                 * any throttled write operations
                 */
                vnode_writedone(bp->nb_vp);
        }
        if (ISSET(bp->nb_flags, NB_ASYNC)) {    /* if async, release it */
                SET(bp->nb_flags, NB_DONE);             /* note that it's done */
                nfs_buf_release(bp, 1);
        } else {                                        /* or just wakeup the buffer */ 
                lck_mtx_lock(nfs_buf_mutex);
                SET(bp->nb_flags, NB_DONE);             /* note that it's done */
                CLR(bp->nb_lflags, NBL_WANTED);
                lck_mtx_unlock(nfs_buf_mutex);
                wakeup(bp);
        }

        FSDBG_BOT(550, bp, NBOFF(bp), bp->nb_flags, bp->nb_error);
}

void
nfs_buf_write_delayed(struct nfsbuf *bp, proc_t p)
{
        vnode_t vp = bp->nb_vp;

        FSDBG_TOP(551, bp, NBOFF(bp), bp->nb_flags, 0);
        FSDBG(551, bp, bp->nb_dirtyoff, bp->nb_dirtyend, bp->nb_dirty);

        /*
         * 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->nb_flags, NB_DELWRI)) {
                SET(bp->nb_flags, NB_DELWRI);
                if (p && p->p_stats) 
                        p->p_stats->p_ru.ru_oublock++;          /* XXX */
                OSAddAtomic(1, (SInt32*)&nfs_nbdwrite);
                NFSBUFCNTCHK(0);
                /* move to dirty list */
                lck_mtx_lock(nfs_buf_mutex);
                if (bp->nb_vnbufs.le_next != NFSNOLIST)
                        LIST_REMOVE(bp, nb_vnbufs);
                LIST_INSERT_HEAD(&VTONFS(vp)->n_dirtyblkhd, bp, nb_vnbufs);
                lck_mtx_unlock(nfs_buf_mutex);
        }

        /*
         * 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, "nfs_buf_write_delayed");

        /*
         * If we have too many delayed write buffers, 
         * more than we can "safely" handle, just fall back to
         * doing the async write
         */
        if (nfs_nbdwrite < 0)
                panic("nfs_buf_write_delayed: Negative nfs_nbdwrite");

        if (nfs_nbdwrite > ((nfsbufcnt/4)*3)) {
                /* issue async write */
                SET(bp->nb_flags, NB_ASYNC);
                nfs_buf_write(bp);
                FSDBG_BOT(551, bp, NBOFF(bp), bp->nb_flags, bp->nb_error);
                return;
        }
         
        /* Otherwise, the "write" is done, so mark and release the buffer. */
        SET(bp->nb_flags, NB_DONE);
        nfs_buf_release(bp, 1);
        FSDBG_BOT(551, bp, NBOFF(bp), bp->nb_flags, 0);
        return;
}

/*
 * Check that a "needcommit" buffer can still be committed.
 * If the write verifier has changed, we need to clear the
 * the needcommit flag.
 */
void
nfs_buf_check_write_verifier(struct nfsnode *np, struct nfsbuf *bp)
{
        struct nfsmount *nmp;

        if (!ISSET(bp->nb_flags, NB_NEEDCOMMIT))
                return;

        nmp = VFSTONFS(vnode_mount(NFSTOV(np)));
        if (!nmp || (bp->nb_verf == nmp->nm_verf))
                return;

        /* write verifier changed, clear commit flag */
        bp->nb_flags &= ~NB_NEEDCOMMIT;
        np->n_needcommitcnt--;
        CHECK_NEEDCOMMITCNT(np);
}

/*
 * add a reference to a buffer so it doesn't disappear while being used
 * (must be called with nfs_buf_mutex held)
 */
void
nfs_buf_refget(struct nfsbuf *bp)
{
        bp->nb_refs++;
}
/*
 * release a reference on a buffer
 * (must be called with nfs_buf_mutex held)
 */
void
nfs_buf_refrele(struct nfsbuf *bp)
{
        bp->nb_refs--;
}

/*
 * mark a particular buffer as BUSY
 * (must be called with nfs_buf_mutex held)
 */
errno_t
nfs_buf_acquire(struct nfsbuf *bp, int flags, int slpflag, int slptimeo)
{
        errno_t error;
        struct timespec ts;

        if (ISSET(bp->nb_lflags, NBL_BUSY)) {
                /*      
                 * since the mutex_lock may block, the buffer
                 * may become BUSY, so we need to recheck for
                 * a NOWAIT request
                 */
                if (flags & NBAC_NOWAIT)
                        return (EBUSY);
                SET(bp->nb_lflags, NBL_WANTED);

                        ts.tv_sec = (slptimeo/100);
                        /* the hz value is 100; which leads to 10ms */
                        ts.tv_nsec = (slptimeo % 100) * 10  * NSEC_PER_USEC * 1000;

                        error = msleep(bp, nfs_buf_mutex, slpflag | (PRIBIO + 1),
                                "nfs_buf_acquire", &ts);
                        if (error)
                                return (error);
                        return (EAGAIN);
        }
        if (flags & NBAC_REMOVE)
                nfs_buf_remfree(bp);
        SET(bp->nb_lflags, NBL_BUSY);

        return (0);
}

/*
 * simply drop the BUSY status of a buffer
 * (must be called with nfs_buf_mutex held)
 */
void
nfs_buf_drop(struct nfsbuf *bp)
{
        int need_wakeup = 0;

        if (!ISSET(bp->nb_lflags, NBL_BUSY))
                panic("nfs_buf_drop: buffer not busy!");
        if (ISSET(bp->nb_lflags, NBL_WANTED)) {
                /*      
                 * delay the actual wakeup until after we
                 * clear NBL_BUSY and we've dropped nfs_buf_mutex
                 */
                need_wakeup = 1;
        }
        /* Unlock the buffer. */
        CLR(bp->nb_lflags, (NBL_BUSY | NBL_WANTED));

        if (need_wakeup)
                wakeup(bp);
}

/*
 * prepare for iterating over an nfsnode's buffer list
 * this lock protects the queue manipulation
 * (must be called with nfs_buf_mutex held)
 */
int
nfs_buf_iterprepare(struct nfsnode *np, struct nfsbuflists *iterheadp, int flags)
{
        struct nfsbuflists *listheadp;

        if (flags & NBI_DIRTY)
                listheadp = &np->n_dirtyblkhd;
        else
                listheadp = &np->n_cleanblkhd;

        if ((flags & NBI_NOWAIT) && (np->n_bufiterflags & NBI_ITER)) {
                LIST_INIT(iterheadp);
                return(EWOULDBLOCK);
        }

        while (np->n_bufiterflags & NBI_ITER)   {
                np->n_bufiterflags |= NBI_ITERWANT;
                msleep(&np->n_bufiterflags, nfs_buf_mutex, 0, "nfs_buf_iterprepare", 0);        
        }
        if (LIST_EMPTY(listheadp)) {
                LIST_INIT(iterheadp);
                return(EINVAL);
        }
        np->n_bufiterflags |= NBI_ITER;

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

        return(0);
}

/*
 * cleanup after iterating over an nfsnode's buffer list
 * this lock protects the queue manipulation
 * (must be called with nfs_buf_mutex held)
 */
void
nfs_buf_itercomplete(struct nfsnode *np, struct nfsbuflists *iterheadp, int flags)
{
        struct nfsbuflists * listheadp;
        struct nfsbuf *bp;

        if (flags & NBI_DIRTY)
                listheadp = &np->n_dirtyblkhd;
        else
                listheadp = &np->n_cleanblkhd;

        while (!LIST_EMPTY(iterheadp)) {
                bp = LIST_FIRST(iterheadp);
                LIST_REMOVE(bp, nb_vnbufs);
                LIST_INSERT_HEAD(listheadp, bp, nb_vnbufs);
        }

        np->n_bufiterflags &= ~NBI_ITER;
        if (np->n_bufiterflags & NBI_ITERWANT) {
                np->n_bufiterflags &= ~NBI_ITERWANT;
                wakeup(&np->n_bufiterflags);
        }
}


/*
 * Vnode op for read using bio
 * Any similarity to readip() is purely coincidental
 */
int
nfs_bioread(
        vnode_t vp,
        struct uio *uio,
        __unused int ioflag,
        kauth_cred_t cred,
        proc_t p)
{
        struct nfsnode *np = VTONFS(vp);
        int biosize;
        off_t diff;
        struct nfsbuf *bp = NULL, *rabp;
        struct nfs_vattr nvattr;
        struct nfsmount *nmp = VFSTONFS(vnode_mount(vp));
        daddr64_t lbn, rabn, lastrabn = -1, tlbn;
        int bufsize;
        int nra, error = 0, n = 0, on = 0;
        caddr_t dp;
        struct dirent *direntp = NULL;
        enum vtype vtype;
        int nocachereadahead = 0;

        FSDBG_TOP(514, vp, uio->uio_offset, uio_uio_resid(uio), ioflag);

#if DIAGNOSTIC
        if (uio->uio_rw != UIO_READ)
                panic("nfs_read mode");
#endif
        if (uio_uio_resid(uio) == 0) {
                FSDBG_BOT(514, vp, 0xd1e0001, 0, 0);
                return (0);
        }
        if (uio->uio_offset < 0) {
                FSDBG_BOT(514, vp, 0xd1e0002, 0, EINVAL);
                return (EINVAL);
        }

        if ((nmp->nm_flag & NFSMNT_NFSV3) && !(nmp->nm_state & NFSSTA_GOTFSINFO))
                nfs_fsinfo(nmp, vp, cred, p);
        biosize = vfs_statfs(vnode_mount(vp))->f_iosize;
        vtype = vnode_vtype(vp);
        /*
         * For nfs, cache consistency can only be maintained approximately.
         * Although RFC1094 does not specify the criteria, the following is
         * believed to be compatible with the reference port.
         * For nfs:
         * If the file's modify time on the server has changed since the
         * last read rpc or you have written to the file,
         * you may have lost data cache consistency with the
         * server, so flush all of the file's data out of the cache.
         * Then force a getattr rpc to ensure that you have up to date
         * attributes.
         * NB: This implies that cache data can be read when up to
         * NFS_MAXATTRTIMEO seconds out of date. If you find that you need
         * current attributes this could be forced by setting calling
         * NATTRINVALIDATE() before the nfs_getattr() call.
         */
        if (np->n_flag & NNEEDINVALIDATE) {
                np->n_flag &= ~NNEEDINVALIDATE;
                nfs_vinvalbuf(vp, V_SAVE|V_IGNORE_WRITEERR, cred, p, 1);
        }
        if (np->n_flag & NMODIFIED) {
                if (vtype != VREG) {
                        if (vtype != VDIR)
                                panic("nfs: bioread, not dir");
                        nfs_invaldir(vp);
                        error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
                        if (error) {
                                FSDBG_BOT(514, vp, 0xd1e0003, 0, error);
                                return (error);
                        }
                }
                NATTRINVALIDATE(np);
                error = nfs_getattr(vp, &nvattr, cred, p);
                if (error) {
                        FSDBG_BOT(514, vp, 0xd1e0004, 0, error);
                        return (error);
                }
                if (vtype == VDIR) {
                        /* if directory changed, purge any name cache entries */
                        if (nfstimespeccmp(&np->n_ncmtime, &nvattr.nva_mtime, !=))
                                cache_purge(vp);
                        np->n_ncmtime = nvattr.nva_mtime;
                }
                np->n_mtime = nvattr.nva_mtime;
        } else {
                error = nfs_getattr(vp, &nvattr, cred, p);
                if (error) {
                        FSDBG_BOT(514, vp, 0xd1e0005, 0, error);
                        return (error);
                }
                if (nfstimespeccmp(&np->n_mtime, &nvattr.nva_mtime, !=)) {
                        if (vtype == VDIR) {
                                nfs_invaldir(vp);
                                /* purge name cache entries */
                                if (nfstimespeccmp(&np->n_ncmtime, &nvattr.nva_mtime, !=))
                                        cache_purge(vp);
                        }
                        error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
                        if (error) {
                                FSDBG_BOT(514, vp, 0xd1e0006, 0, error);
                                return (error);
                        }
                        if (vtype == VDIR)
                                np->n_ncmtime = nvattr.nva_mtime;
                        np->n_mtime = nvattr.nva_mtime;
                }
        }

        if (vnode_isnocache(vp)) {
                if (!(np->n_flag & NNOCACHE)) {
                        if (NVALIDBUFS(np)) {
                                error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
                                if (error) {
                                        FSDBG_BOT(514, vp, 0xd1e000a, 0, error);
                                        return (error);
                                }
                        }
                        np->n_flag |= NNOCACHE;
                }
        } else if (np->n_flag & NNOCACHE) {
                np->n_flag &= ~NNOCACHE;
        }

        do {
            if (np->n_flag & NNOCACHE) {
                switch (vtype) {
                case VREG:
                        /*
                         * If we have only a block or so to read,
                         *     just do the rpc directly.
                         * If we have a couple blocks or more to read,
                         *     then we'll take advantage of readahead within
                         *     this loop to try to fetch all the data in parallel
                         */
                        if (!nocachereadahead && (uio_uio_resid(uio) < 2*biosize)) {
                                error = nfs_readrpc(vp, uio, cred, p);
                                FSDBG_BOT(514, vp, uio->uio_offset, uio_uio_resid(uio), error);
                                return (error);
                        }
                        nocachereadahead = 1;
                        break;
                case VLNK:
                        error = nfs_readlinkrpc(vp, uio, cred, p);
                        FSDBG_BOT(514, vp, uio->uio_offset, uio_uio_resid(uio), error);
                        return (error);
                case VDIR:
                        break;
                default:
                        printf(" NFSNOCACHE: type %x unexpected\n", vtype);
                };
            }
            switch (vtype) {
            case VREG:
                lbn = uio->uio_offset / biosize;

                /*
                 * Copy directly from any cached pages without grabbing the bufs.
                 *
                 * Note: for "nocache" reads, we don't copy directly from UBC
                 * because any cached pages will be for readahead buffers that
                 * need to be invalidated anyway before we finish this request.
                 */
                if (!(np->n_flag & NNOCACHE) &&
                        (uio->uio_segflg == UIO_USERSPACE32 || 
                         uio->uio_segflg == UIO_USERSPACE64 ||
                         uio->uio_segflg == UIO_USERSPACE)) {
                        // LP64todo - fix this!
                        int io_resid = uio_uio_resid(uio);
                        diff = np->n_size - uio->uio_offset;
                        if (diff < io_resid)
                                io_resid = diff;
                        if (io_resid > 0) {
                                error = cluster_copy_ubc_data(vp, uio, &io_resid, 0);
                                if (error) {
                                        FSDBG_BOT(514, vp, uio->uio_offset, 0xcacefeed, error);
                                        return (error);
                                }
                        }
                        /* count any biocache reads that we just copied directly */
                        if (lbn != uio->uio_offset / biosize) {
                                OSAddAtomic((uio->uio_offset / biosize) - lbn, (SInt32*)&nfsstats.biocache_reads);
                                FSDBG(514, vp, 0xcacefeed, uio->uio_offset, error);
                        }
                }

                lbn = uio->uio_offset / biosize;
                on = uio->uio_offset % biosize;

                /*
                 * Start the read ahead(s), as required.
                 */
                if (nfs_numasync > 0 && nmp->nm_readahead > 0) {
                        for (nra = 0; nra < nmp->nm_readahead; nra++) {
                                rabn = lbn + 1 + nra;
                                if (rabn <= lastrabn) {
                                        /* we've already (tried to) read this block */
                                        /* no need to try it again... */
                                        continue;
                                }
                                lastrabn = rabn;
                                if ((off_t)rabn * biosize >= (off_t)np->n_size)
                                        break;
                                if ((np->n_flag & NNOCACHE) &&
                                   (((off_t)rabn * biosize) >= (uio->uio_offset + uio_uio_resid(uio))))
                                        /* for uncached readahead, don't go beyond end of request */
                                        break;
                                /* check if block exists and is valid. */
                                error = nfs_buf_get(vp, rabn, biosize, p, NBLK_READ|NBLK_NOWAIT, &rabp);
                                if (error) {
                                        FSDBG_BOT(514, vp, 0xd1e000b, 1, error);
                                        return (error);
                                }
                                if (!rabp)
                                        continue;
                                if (nfs_buf_upl_valid_range(rabp, 0, rabp->nb_bufsize)) {
                                        nfs_buf_release(rabp, 1);
                                        continue;
                                }
                                if (!ISSET(rabp->nb_flags, (NB_CACHE|NB_DELWRI))) {
                                        SET(rabp->nb_flags, (NB_READ|NB_ASYNC));
                                        if (nfs_asyncio(rabp, cred)) {
                                                SET(rabp->nb_flags, (NB_INVAL|NB_ERROR));
                                                rabp->nb_error = EIO;
                                                nfs_buf_release(rabp, 1);
                                        }
                                } else
                                        nfs_buf_release(rabp, 1);
                        }
                }

                if ((uio_uio_resid(uio) <= 0) || (uio->uio_offset >= (off_t)np->n_size)) {
                        FSDBG_BOT(514, vp, uio->uio_offset, uio_uio_resid(uio), 0xaaaaaaaa);
                        return (0);
                }

                OSAddAtomic(1, (SInt32*)&nfsstats.biocache_reads);

                /*
                 * If the block is in the cache and has the required data
                 * in a valid region, just copy it out.
                 * Otherwise, get the block and write back/read in,
                 * as required.
                 */
again:
                bufsize = biosize;
                // LP64todo - fix this!
                n = min((unsigned)(bufsize - on), uio_uio_resid(uio));
                diff = np->n_size - uio->uio_offset;
                if (diff < n)
                        n = diff;

                error = nfs_buf_get(vp, lbn, bufsize, p, NBLK_READ, &bp);
                if (error) {
                        FSDBG_BOT(514, vp, 0xd1e000c, 0, EINTR);
                        return (EINTR);
                }

                /* if any pages are valid... */
                if (bp->nb_valid) {
                        /* ...check for any invalid pages in the read range */
                        int pg, firstpg, lastpg, dirtypg;
                        dirtypg = firstpg = lastpg = -1;
                        pg = on/PAGE_SIZE;
                        while (pg <= (on + n - 1)/PAGE_SIZE) {
                                if (!NBPGVALID(bp,pg)) {
                                        if (firstpg < 0)
                                                firstpg = pg;
                                        lastpg = pg;
                                } else if (firstpg >= 0 && dirtypg < 0 && NBPGDIRTY(bp,pg))
                                        dirtypg = pg;
                                pg++;
                        }

                        /* if there are no invalid pages, we're all set */
                        if (firstpg < 0) {
                                if (bp->nb_validoff < 0) {
                                        /* valid range isn't set up, so */
                                        /* set it to what we know is valid */
                                        bp->nb_validoff = trunc_page(on);
                                        bp->nb_validend = round_page(on+n);
                                        nfs_buf_normalize_valid_range(np, bp);
                                }
                                goto buffer_ready;
                        }

                        /* there are invalid pages in the read range */
                        if ((dirtypg > firstpg) && (dirtypg < lastpg)) {
                                /* there are also dirty page(s) in the range, */
                                /* so write the buffer out and try again */
                                CLR(bp->nb_flags, (NB_DONE | NB_ERROR | NB_INVAL));
                                SET(bp->nb_flags, NB_ASYNC);
                                if (bp->nb_wcred == NOCRED)  {
                                        kauth_cred_ref(cred);
                                        bp->nb_wcred = cred;
                                }
                                error = nfs_buf_write(bp);
                                if (error) {
                                        FSDBG_BOT(514, vp, 0xd1e000d, 0, error);
                                        return (error);
                                }
                                goto again;
                        }
                        if (!bp->nb_dirty && bp->nb_dirtyend <= 0 &&
                            (lastpg - firstpg + 1) > (bufsize/PAGE_SIZE)/2) {
                                /* we need to read in more than half the buffer and the */
                                /* buffer's not dirty, so just fetch the whole buffer */
                                bp->nb_valid = 0;
                        } else {
                                /* read the page range in */
                                uio_t auio;
                                char uio_buf[ UIO_SIZEOF(1) ];
                                
                                NFS_BUF_MAP(bp);
                                auio = uio_createwithbuffer(1, (NBOFF(bp) + firstpg * PAGE_SIZE_64), 
                                                UIO_SYSSPACE, UIO_READ, &uio_buf[0], sizeof(uio_buf));
                                if (!auio) {
                                        error = ENOMEM;
                                } else {
                                        uio_addiov(auio, CAST_USER_ADDR_T((bp->nb_data + firstpg * PAGE_SIZE)), 
                                                        ((lastpg - firstpg + 1) * PAGE_SIZE));
                                        error = nfs_readrpc(vp, auio, cred, p);
                                }
                                if (error) {
                                        if (np->n_flag & NNOCACHE)
                                                SET(bp->nb_flags, NB_NOCACHE);
                                        nfs_buf_release(bp, 1);
                                        FSDBG_BOT(514, vp, 0xd1e000e, 0, error);
                                        return (error);
                                }
                                /* Make sure that the valid range is set to cover this read. */
                                bp->nb_validoff = trunc_page_32(on);
                                bp->nb_validend = round_page_32(on+n);
                                nfs_buf_normalize_valid_range(np, bp);
                                if (uio_resid(auio) > 0) {
                                        /* if short read, must have hit EOF, */
                                        /* so zero the rest of the range */
                                        bzero(CAST_DOWN(caddr_t, uio_curriovbase(auio)), uio_resid(auio));
                                }
                                /* mark the pages (successfully read) as valid */
                                for (pg=firstpg; pg <= lastpg; pg++)
                                        NBPGVALID_SET(bp,pg);
                        }
                }
                /* if no pages are valid, read the whole block */
                if (!bp->nb_valid) {
                        SET(bp->nb_flags, NB_READ);
                        CLR(bp->nb_flags, (NB_DONE | NB_ERROR | NB_INVAL));
                        error = nfs_doio(bp, cred, p);
                        if (error) {
                                if (np->n_flag & NNOCACHE)
                                        SET(bp->nb_flags, NB_NOCACHE);
                                nfs_buf_release(bp, 1);
                                FSDBG_BOT(514, vp, 0xd1e000f, 0, error);
                                return (error);
                        }
                }
buffer_ready:
                /* validate read range against valid range and clip */
                if (bp->nb_validend > 0) {
                        diff = (on >= bp->nb_validend) ? 0 : (bp->nb_validend - on);
                        if (diff < n)
                                n = diff;
                }
                if (n > 0)
                        NFS_BUF_MAP(bp);
                break;
            case VLNK:
                OSAddAtomic(1, (SInt32*)&nfsstats.biocache_readlinks);
                error = nfs_buf_get(vp, 0, NFS_MAXPATHLEN, p, NBLK_READ, &bp);
                if (error) {
                        FSDBG_BOT(514, vp, 0xd1e0010, 0, error);
                        return (error);
                }
                if (!ISSET(bp->nb_flags, NB_CACHE)) {
                        SET(bp->nb_flags, NB_READ);
                        error = nfs_doio(bp, cred, p);
                        if (error) {
                                SET(bp->nb_flags, NB_ERROR);
                                nfs_buf_release(bp, 1);
                                FSDBG_BOT(514, vp, 0xd1e0011, 0, error);
                                return (error);
                        }
                }
                // LP64todo - fix this!
                n = min(uio_uio_resid(uio), bp->nb_validend);
                on = 0;
                break;
            case VDIR:
                OSAddAtomic(1, (SInt32*)&nfsstats.biocache_readdirs);
                if (np->n_direofoffset && uio->uio_offset >= np->n_direofoffset) {
                        FSDBG_BOT(514, vp, 0xde0f0001, 0, 0);
                        return (0);
                }
                lbn = uio->uio_offset / NFS_DIRBLKSIZ;
                on = uio->uio_offset & (NFS_DIRBLKSIZ - 1);
                error = nfs_buf_get(vp, lbn, NFS_DIRBLKSIZ, p, NBLK_READ, &bp);
                if (error) {
                        FSDBG_BOT(514, vp, 0xd1e0012, 0, error);
                        return (error);
                }
                if (!ISSET(bp->nb_flags, NB_CACHE)) {
                    SET(bp->nb_flags, NB_READ);
                    error = nfs_doio(bp, cred, p);
                    if (error) {
                        nfs_buf_release(bp, 1);
                    }
                    while (error == NFSERR_BAD_COOKIE) {
                        nfs_invaldir(vp);
                        error = nfs_vinvalbuf(vp, 0, cred, p, 1);
                        /*
                         * Yuck! The directory has been modified on the
                         * server. The only way to get the block is by
                         * reading from the beginning to get all the
                         * offset cookies.
                         */
                        for (tlbn = 0; tlbn <= lbn && !error; tlbn++) {
                            if (np->n_direofoffset
                                && (tlbn * NFS_DIRBLKSIZ) >= np->n_direofoffset) {
                                    FSDBG_BOT(514, vp, 0xde0f0002, 0, 0);
                                    return (0);
                            }
                            error = nfs_buf_get(vp, tlbn, NFS_DIRBLKSIZ, p, NBLK_READ, &bp);
                            if (error) {
                                    FSDBG_BOT(514, vp, 0xd1e0013, 0, error);
                                    return (error);
                            }
                            if (!ISSET(bp->nb_flags, NB_CACHE)) {
                                    SET(bp->nb_flags, NB_READ);
                                    error = nfs_doio(bp, cred, p);
                                    /*
                                     * no error + NB_INVAL == directory EOF,
                                     * use the block.
                                     */
                                    if (error == 0 && (bp->nb_flags & NB_INVAL))
                                            break;
                            }
                            /*
                             * An error will throw away the block and the
                             * for loop will break out.  If no error and this
                             * is not the block we want, we throw away the
                             * block and go for the next one via the for loop.
                             */
                            if (error || tlbn < lbn)
                                    nfs_buf_release(bp, 1);
                        }
                    }
                    /*
                     * The above while is repeated if we hit another cookie
                     * error.  If we hit an error and it wasn't a cookie error,
                     * we give up.
                     */
                    if (error) {
                        FSDBG_BOT(514, vp, 0xd1e0014, 0, error);
                        return (error);
                    }
                }

                /*
                 * If not eof and read aheads are enabled, start one.
                 * (You need the current block first, so that you have the
                 *  directory offset cookie of the next block.)
                 */
                if (nfs_numasync > 0 && nmp->nm_readahead > 0 &&
                    (np->n_direofoffset == 0 ||
                    (lbn + 1) * NFS_DIRBLKSIZ < np->n_direofoffset) &&
                    !nfs_buf_is_incore(vp, lbn + 1)) {
                        error = nfs_buf_get(vp, lbn + 1, NFS_DIRBLKSIZ, p, NBLK_READ|NBLK_NOWAIT, &rabp);
                        if (error) {
                            FSDBG_BOT(514, vp, 0xd1e0015, 0, error);
                            return (error);
                        }
                        if (rabp) {
                            if (!ISSET(rabp->nb_flags, (NB_CACHE))) {
                                SET(rabp->nb_flags, (NB_READ | NB_ASYNC));
                                if (nfs_asyncio(rabp, cred)) {
                                    SET(rabp->nb_flags, (NB_INVAL|NB_ERROR));
                                    rabp->nb_error = EIO;
                                    nfs_buf_release(rabp, 1);
                                }
                            } else {
                                nfs_buf_release(rabp, 1);
                            }
                        }
                }
                /*
                 * Make sure we use a signed variant of min() since
                 * the second term may be negative.
                 */
                // LP64todo - fix this!
                n = lmin(uio_uio_resid(uio), bp->nb_validend - on);
                /*
                 * We keep track of the directory eof in
                 * np->n_direofoffset and chop it off as an
                 * extra step right here.
                 */
                if (np->n_direofoffset &&
                    n > np->n_direofoffset - uio->uio_offset)
                        n = np->n_direofoffset - uio->uio_offset;
                /*
                 * Make sure that we return an integral number of entries so
                 * that any subsequent calls will start copying from the start
                 * of the next entry.
                 *
                 * If the current value of n has the last entry cut short,
                 * set n to copy everything up to the last entry instead.
                 */
                if (n > 0) {
                        dp = bp->nb_data + on;
                        while (dp < (bp->nb_data + on + n)) {
                                direntp = (struct dirent *)dp;
                                dp += direntp->d_reclen;
                        }
                        if (dp > (bp->nb_data + on + n))
                                n = (dp - direntp->d_reclen) - (bp->nb_data + on);
                }
                break;
            default:
                printf("nfs_bioread: type %x unexpected\n", vtype);
                FSDBG_BOT(514, vp, 0xd1e0016, 0, EINVAL);
                return (EINVAL);
            };

            if (n > 0) {
                error = uiomove(bp->nb_data + on, (int)n, uio);
            }
            switch (vtype) {
            case VREG:
                if (np->n_flag & NNOCACHE)
                        SET(bp->nb_flags, NB_NOCACHE);
                break;
            case VLNK:
                n = 0;
                break;
            case VDIR:
                break;
            default:
                break;
            }
            nfs_buf_release(bp, 1);
        } while (error == 0 && uio_uio_resid(uio) > 0 && n > 0);
        FSDBG_BOT(514, vp, uio->uio_offset, uio_uio_resid(uio), error);
        return (error);
}


/*
 * Vnode op for write using bio
 */
int
nfs_write(ap)
        struct vnop_write_args /* {
                struct vnodeop_desc *a_desc;
                vnode_t a_vp;
                struct uio *a_uio;
                int a_ioflag;
                vfs_context_t a_context;
        } */ *ap;
{
        struct uio *uio = ap->a_uio;
        vnode_t vp = ap->a_vp;
        struct nfsnode *np = VTONFS(vp);
        proc_t p;
        kauth_cred_t cred;
        int ioflag = ap->a_ioflag;
        struct nfsbuf *bp;
        struct nfs_vattr nvattr;
        struct nfsmount *nmp = VFSTONFS(vnode_mount(vp));
        daddr64_t lbn;
        int biosize, bufsize;
        int n, on, error = 0;
        off_t boff, start, end, cureof;
        struct iovec_32 iov;
        struct uio auio;

        FSDBG_TOP(515, vp, uio->uio_offset, uio_uio_resid(uio), ioflag);

#if DIAGNOSTIC
        if (uio->uio_rw != UIO_WRITE)
                panic("nfs_write mode");
        if (UIO_SEG_IS_USER_SPACE(uio->uio_segflg))
                panic("nfs_write proc");
#endif

        p = vfs_context_proc(ap->a_context);
        cred = vfs_context_ucred(ap->a_context);

        if (vnode_vtype(vp) != VREG)
                return (EIO);

        np->n_flag |= NWRBUSY;

        if (np->n_flag & NNEEDINVALIDATE) {
                np->n_flag &= ~NNEEDINVALIDATE;
                nfs_vinvalbuf(vp, V_SAVE|V_IGNORE_WRITEERR, cred, p, 1);
        }
        if (np->n_flag & NWRITEERR) {
                np->n_flag &= ~(NWRITEERR | NWRBUSY);
                FSDBG_BOT(515, vp, uio->uio_offset, uio_uio_resid(uio), np->n_error);
                return (np->n_error);
        }
        if ((nmp->nm_flag & NFSMNT_NFSV3) &&
            !(nmp->nm_state & NFSSTA_GOTFSINFO))
                (void)nfs_fsinfo(nmp, vp, cred, p);
        if (ioflag & (IO_APPEND | IO_SYNC)) {
                if (np->n_flag & NMODIFIED) {
                        NATTRINVALIDATE(np);
                        error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
                        if (error) {
                                np->n_flag &= ~NWRBUSY;
                                FSDBG_BOT(515, vp, uio->uio_offset, 0x10bad01, error);
                                return (error);
                        }
                }
                if (ioflag & IO_APPEND) {
                        NATTRINVALIDATE(np);
                        error = nfs_getattr(vp, &nvattr, cred, p);
                        if (error) {
                                np->n_flag &= ~NWRBUSY;
                                FSDBG_BOT(515, vp, uio->uio_offset, 0x10bad02, error);
                                return (error);
                        }
                        uio->uio_offset = np->n_size;
                }
        }
        if (uio->uio_offset < 0) {
                np->n_flag &= ~NWRBUSY;
                FSDBG_BOT(515, vp, uio->uio_offset, 0xbad0ff, EINVAL);
                return (EINVAL);
        }
        if (uio_uio_resid(uio) == 0) {
                np->n_flag &= ~NWRBUSY;
                FSDBG_BOT(515, vp, uio->uio_offset, uio_uio_resid(uio), 0);
                return (0);
        }

        biosize = vfs_statfs(vnode_mount(vp))->f_iosize;

        if (vnode_isnocache(vp)) {
                if (!(np->n_flag & NNOCACHE)) {
                        if (NVALIDBUFS(np)) {
                                error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
                                if (error) {
                                        np->n_flag &= ~NWRBUSY;
                                        FSDBG_BOT(515, vp, 0, 0, error);
                                        return (error);
                                }
                        }
                        np->n_flag |= NNOCACHE;
                }
        } else if (np->n_flag & NNOCACHE) {
                np->n_flag &= ~NNOCACHE;
        }

        do {
                OSAddAtomic(1, (SInt32*)&nfsstats.biocache_writes);
                lbn = uio->uio_offset / biosize;
                on = uio->uio_offset % biosize;
                // LP64todo - fix this
                n = min((unsigned)(biosize - on), uio_uio_resid(uio));
again:
                bufsize = biosize;
                /*
                 * Get a cache block for writing.  The range to be written is
                 * (off..off+n) within the block.  We ensure that the block
                 * either has no dirty region or that the given range is
                 * contiguous with the existing dirty region.
                 */
                error = nfs_buf_get(vp, lbn, bufsize, p, NBLK_WRITE, &bp);
                if (error) {
                        np->n_flag &= ~NWRBUSY;
                        FSDBG_BOT(515, vp, uio->uio_offset, uio_uio_resid(uio), error);
                        return (error);
                }
                /* map the block because we know we're going to write to it */
                NFS_BUF_MAP(bp);

                if (np->n_flag & NNOCACHE)
                        SET(bp->nb_flags, (NB_NOCACHE|NB_STABLE));

                if (bp->nb_wcred == NOCRED) {
                        kauth_cred_ref(cred);
                        bp->nb_wcred = cred;
                }

                /*
                 * If there's already a dirty range AND dirty pages in this block we
                 * need to send a commit AND write the dirty pages before continuing.
                 *
                 * If there's already a dirty range OR dirty pages in this block
                 * and the new write range is not contiguous with the existing range,
                 * then force the buffer to be written out now.
                 * (We used to just extend the dirty range to cover the valid,
                 * but unwritten, data in between also.  But writing ranges
                 * of data that weren't actually written by an application
                 * risks overwriting some other client's data with stale data
                 * that's just masquerading as new written data.)
                 */
                if (bp->nb_dirtyend > 0) {
                    if (on > bp->nb_dirtyend || (on + n) < bp->nb_dirtyoff || bp->nb_dirty) {
                        FSDBG(515, vp, uio->uio_offset, bp, 0xd15c001);
                        /* write/commit buffer "synchronously" */
                        /* (NB_STABLE indicates that data writes should be FILESYNC) */
                        CLR(bp->nb_flags, (NB_DONE | NB_ERROR | NB_INVAL));
                        SET(bp->nb_flags, (NB_ASYNC | NB_STABLE));
                        error = nfs_buf_write(bp);
                        if (error) {
                            np->n_flag &= ~NWRBUSY;
                            FSDBG_BOT(515, vp, uio->uio_offset, uio_uio_resid(uio), error);
                            return (error);
                        }
                        goto again;
                    }
                } else if (bp->nb_dirty) {
                    int firstpg, lastpg;
                    u_int32_t pagemask;
                    /* calculate write range pagemask */
                    firstpg = on/PAGE_SIZE;
                    lastpg = (on+n-1)/PAGE_SIZE;
                    pagemask = ((1 << (lastpg+1)) - 1) & ~((1 << firstpg) - 1);
                    /* check if there are dirty pages outside the write range */
                    if (bp->nb_dirty & ~pagemask) {
                        FSDBG(515, vp, uio->uio_offset, bp, 0xd15c002);
                        /* write/commit buffer "synchronously" */
                        /* (NB_STABLE indicates that data writes should be FILESYNC) */
                        CLR(bp->nb_flags, (NB_DONE | NB_ERROR | NB_INVAL));
                        SET(bp->nb_flags, (NB_ASYNC | NB_STABLE));
                        error = nfs_buf_write(bp);
                        if (error) {
                            np->n_flag &= ~NWRBUSY;
                            FSDBG_BOT(515, vp, uio->uio_offset, uio_uio_resid(uio), error);
                            return (error);
                        }
                        goto again;
                    }
                    /* if the first or last pages are already dirty */
                    /* make sure that the dirty range encompasses those pages */
                    if (NBPGDIRTY(bp,firstpg) || NBPGDIRTY(bp,lastpg)) {
                        FSDBG(515, vp, uio->uio_offset, bp, 0xd15c003);
                        bp->nb_dirtyoff = min(on, firstpg * PAGE_SIZE);
                        if (NBPGDIRTY(bp,lastpg)) {
                            bp->nb_dirtyend = (lastpg+1) * PAGE_SIZE;
                            /* clip to EOF */
                            if (NBOFF(bp) + bp->nb_dirtyend > (off_t)np->n_size)
                                    bp->nb_dirtyend = np->n_size - NBOFF(bp);
                        } else
                            bp->nb_dirtyend = on+n;
                    }
                }

                /*
                 * Are we extending the size of the file with this write?
                 * If so, update file size now that we have the block.
                 * If there was a partial buf at the old eof, validate
                 * and zero the new bytes. 
                 */
                cureof = (off_t)np->n_size;
                if (uio->uio_offset + n > (off_t)np->n_size) {
                        struct nfsbuf *eofbp = NULL;
                        daddr64_t eofbn = np->n_size / biosize;
                        int eofoff = np->n_size % biosize;
                        int neweofoff = (uio->uio_offset + n) % biosize;

                        FSDBG(515, 0xb1ffa000, uio->uio_offset + n, eofoff, neweofoff);

                        if (eofoff && (eofbn < lbn)) {
                                error = nfs_buf_get(vp, eofbn, biosize, p, NBLK_WRITE|NBLK_ONLYVALID, &eofbp);
                                if (error) {
                                        np->n_flag &= ~NWRBUSY;
                                        FSDBG_BOT(515, vp, uio->uio_offset, uio_uio_resid(uio), error);
                                        return (error);
                                }
                        }

                        /* if we're extending within the same last block */
                        /* and the block is flagged as being cached... */
                        if ((lbn == eofbn) && ISSET(bp->nb_flags, NB_CACHE)) {
                                /* ...check that all pages in buffer are valid */
                                int endpg = ((neweofoff ? neweofoff : biosize) - 1)/PAGE_SIZE;
                                u_int32_t pagemask;
                                /* pagemask only has to extend to last page being written to */
                                pagemask = (1 << (endpg+1)) - 1;
                                FSDBG(515, 0xb1ffa001, bp->nb_valid, pagemask, 0);
                                if ((bp->nb_valid & pagemask) != pagemask) {
                                        /* zerofill any hole */
                                        if (on > bp->nb_validend) {
                                                int i;
                                                for (i=bp->nb_validend/PAGE_SIZE; i <= (on - 1)/PAGE_SIZE; i++)
                                                        NBPGVALID_SET(bp, i);
                                                NFS_BUF_MAP(bp);
                                                FSDBG(516, bp, bp->nb_validend, on - bp->nb_validend, 0xf01e);
                                                bzero((char *)bp->nb_data + bp->nb_validend,
                                                        on - bp->nb_validend);
                                        }
                                        /* zerofill any trailing data in the last page */
                                        if (neweofoff) {
                                                NFS_BUF_MAP(bp);
                                                FSDBG(516, bp, neweofoff, PAGE_SIZE - (neweofoff & PAGE_MASK), 0xe0f);
                                                bzero((char *)bp->nb_data + neweofoff,
                                                        PAGE_SIZE - (neweofoff & PAGE_MASK));
                                        }
                                }
                        }
                        np->n_flag |= NMODIFIED;
                        np->n_size = uio->uio_offset + n;
                        ubc_setsize(vp, (off_t)np->n_size); /* XXX errors */
                        if (eofbp) {
                                /*
                                 * We may need to zero any previously invalid data
                                 * after the old EOF in the previous EOF buffer.
                                 *
                                 * For the old last page, don't zero bytes if there
                                 * are invalid bytes in that page (i.e. the page isn't
                                 * currently valid).
                                 * For pages after the old last page, zero them and
                                 * mark them as valid.
                                 */
                                char *d;
                                int i;
                                if (np->n_flag & NNOCACHE)
                                        SET(eofbp->nb_flags, (NB_NOCACHE|NB_STABLE));
                                NFS_BUF_MAP(eofbp);
                                FSDBG(516, eofbp, eofoff, biosize - eofoff, 0xe0fff01e);
                                d = eofbp->nb_data;
                                i = eofoff/PAGE_SIZE;
                                while (eofoff < biosize) {
                                        int poff = eofoff & PAGE_MASK;
                                        if (!poff || NBPGVALID(eofbp,i)) {
                                                bzero(d + eofoff, PAGE_SIZE - poff);
                                                NBPGVALID_SET(eofbp, i);
                                        }
                                        if (bp->nb_validend == eofoff)
                                                bp->nb_validend += PAGE_SIZE - poff;
                                        eofoff += PAGE_SIZE - poff;
                                        i++;
                                }
                                nfs_buf_release(eofbp, 1);
                        }
                }
                /*
                 * If dirtyend exceeds file size, chop it down.  This should
                 * not occur unless there is a race.
                 */
                if (NBOFF(bp) + bp->nb_dirtyend > (off_t)np->n_size)
                        bp->nb_dirtyend = np->n_size - NBOFF(bp);
                /*
                 * UBC doesn't handle partial pages, so we need to make sure
                 * that any pages left in the page cache are completely valid.
                 *
                 * Writes that are smaller than a block are delayed if they
                 * don't extend to the end of the block.
                 *
                 * If the block isn't (completely) cached, we may need to read
                 * in some parts of pages that aren't covered by the write.
                 * If the write offset (on) isn't page aligned, we'll need to
                 * read the start of the first page being written to.  Likewise,
                 * if the offset of the end of the write (on+n) isn't page aligned,
                 * we'll need to read the end of the last page being written to.
                 *
                 * Notes:
                 * We don't want to read anything we're just going to write over.
                 * We don't want to issue multiple I/Os if we don't have to
                 *   (because they're synchronous rpcs).
                 * We don't want to read anything we already have modified in the
                 *   page cache.
                 */
                if (!ISSET(bp->nb_flags, NB_CACHE) && n < biosize) {
                        int firstpg, lastpg, dirtypg;
                        int firstpgoff, lastpgoff;
                        start = end = -1;
                        firstpg = on/PAGE_SIZE;
                        firstpgoff = on & PAGE_MASK;
                        lastpg = (on+n-1)/PAGE_SIZE;
                        lastpgoff = (on+n) & PAGE_MASK;
                        if (firstpgoff && !NBPGVALID(bp,firstpg)) {
                                /* need to read start of first page */
                                start = firstpg * PAGE_SIZE;
                                end = start + firstpgoff;
                        }
                        if (lastpgoff && !NBPGVALID(bp,lastpg)) {
                                /* need to read end of last page */
                                if (start < 0)
                                        start = (lastpg * PAGE_SIZE) + lastpgoff;
                                end = (lastpg + 1) * PAGE_SIZE;
                        }
                        if (end > start) {
                                /* need to read the data in range: start...end-1 */

                                /* first, check for dirty pages in between */
                                /* if there are, we'll have to do two reads because */
                                /* we don't want to overwrite the dirty pages. */
                                for (dirtypg=start/PAGE_SIZE; dirtypg <= (end-1)/PAGE_SIZE; dirtypg++)
                                        if (NBPGDIRTY(bp,dirtypg))
                                                break;

                                /* if start is at beginning of page, try */
                                /* to get any preceeding pages as well. */
                                if (!(start & PAGE_MASK)) {
                                        /* stop at next dirty/valid page or start of block */
                                        for (; start > 0; start-=PAGE_SIZE)
                                                if (NBPGVALID(bp,((start-1)/PAGE_SIZE)))
                                                        break;
                                }

                                NFS_BUF_MAP(bp);
                                /* setup uio for read(s) */
                                boff = NBOFF(bp);
                                auio.uio_iovs.iov32p = &iov;
                                auio.uio_iovcnt = 1;
#if 1   /* LP64todo - can't use new segment flags until the drivers are ready */
                                auio.uio_segflg = UIO_SYSSPACE;
#else
                                auio.uio_segflg = UIO_SYSSPACE32;
#endif 
                                auio.uio_rw = UIO_READ;

                                if (dirtypg <= (end-1)/PAGE_SIZE) {
                                        /* there's a dirty page in the way, so just do two reads */
                                        /* we'll read the preceding data here */
                                        auio.uio_offset = boff + start;
                                        iov.iov_len = on - start;
                                        uio_uio_resid_set(&auio, iov.iov_len);
                                        iov.iov_base = (uintptr_t) bp->nb_data + start;
                                        error = nfs_readrpc(vp, &auio, cred, p);
                                        if (error) {
                                                bp->nb_error = error;
                                                SET(bp->nb_flags, NB_ERROR);
                                                printf("nfs_write: readrpc %d", error);
                                        }
                                        if (uio_uio_resid(&auio) > 0) {
                                                FSDBG(516, bp, iov.iov_base - bp->nb_data, uio_uio_resid(&auio), 0xd00dee01);
                                                // LP64todo - fix this
                                                bzero((caddr_t)iov.iov_base, uio_uio_resid(&auio));
                                        }
                                        /* update validoff/validend if necessary */
                                        if ((bp->nb_validoff < 0) || (bp->nb_validoff > start))
                                                bp->nb_validoff = start;
                                        if ((bp->nb_validend < 0) || (bp->nb_validend < on))
                                                bp->nb_validend = on;
                                        if ((off_t)np->n_size > boff + bp->nb_validend)
                                                bp->nb_validend = min(np->n_size - (boff + start), biosize);
                                        /* validate any pages before the write offset */
                                        for (; start < on/PAGE_SIZE; start+=PAGE_SIZE)
                                                NBPGVALID_SET(bp, start/PAGE_SIZE);
                                        /* adjust start to read any trailing data */
                                        start = on+n;
                                }

                                /* if end is at end of page, try to */
                                /* get any following pages as well. */
                                if (!(end & PAGE_MASK)) {
                                        /* stop at next valid page or end of block */
                                        for (; end < bufsize; end+=PAGE_SIZE)
                                                if (NBPGVALID(bp,end/PAGE_SIZE))
                                                        break;
                                }

                                if (((boff+start) >= cureof) || ((start >= on) && ((boff + on + n) >= cureof))) {
                                        /*
                                         * Either this entire read is beyond the current EOF
                                         * or the range that we won't be modifying (on+n...end)
                                         * is all beyond the current EOF.
                                         * No need to make a trip across the network to
                                         * read nothing.  So, just zero the buffer instead.
                                         */
                                        FSDBG(516, bp, start, end - start, 0xd00dee00);
                                        bzero(bp->nb_data + start, end - start);
                                } else {
                                        /* now we'll read the (rest of the) data */
                                        auio.uio_offset = boff + start;
                                        iov.iov_len = end - start;
                                        uio_uio_resid_set(&auio, iov.iov_len);
                                        iov.iov_base = (uintptr_t) (bp->nb_data + start);
                                        error = nfs_readrpc(vp, &auio, cred, p);
                                        if (error) {
                                                bp->nb_error = error;
                                                SET(bp->nb_flags, NB_ERROR);
                                                printf("nfs_write: readrpc %d", error);
                                        }
                                        if (uio_uio_resid(&auio) > 0) {
                                                FSDBG(516, bp, iov.iov_base - bp->nb_data, uio_uio_resid(&auio), 0xd00dee02);
                                                // LP64todo - fix this
                                                bzero((caddr_t)iov.iov_base, uio_uio_resid(&auio));
                                        }
                                }
                                /* update validoff/validend if necessary */
                                if ((bp->nb_validoff < 0) || (bp->nb_validoff > start))
                                        bp->nb_validoff = start;
                                if ((bp->nb_validend < 0) || (bp->nb_validend < end))
                                        bp->nb_validend = end;
                                if ((off_t)np->n_size > boff + bp->nb_validend)
                                        bp->nb_validend = min(np->n_size - (boff + start), biosize);
                                /* validate any pages before the write offset's page */
                                for (; start < trunc_page_32(on); start+=PAGE_SIZE)
                                        NBPGVALID_SET(bp, start/PAGE_SIZE);
                                /* validate any pages after the range of pages being written to */
                                for (; (end - 1) > round_page_32(on+n-1); end-=PAGE_SIZE)
                                        NBPGVALID_SET(bp, (end-1)/PAGE_SIZE);
                                /* Note: pages being written to will be validated when written */
                        }
                }

                if (ISSET(bp->nb_flags, NB_ERROR)) {
                        error = bp->nb_error;
                        nfs_buf_release(bp, 1);
                        np->n_flag &= ~NWRBUSY;
                        FSDBG_BOT(515, vp, uio->uio_offset, uio_uio_resid(uio), error);
                        return (error);
                }

                np->n_flag |= NMODIFIED;

                NFS_BUF_MAP(bp);
                error = uiomove((char *)bp->nb_data + on, n, uio);
                if (error) {
                        SET(bp->nb_flags, NB_ERROR);
                        nfs_buf_release(bp, 1);
                        np->n_flag &= ~NWRBUSY;
                        FSDBG_BOT(515, vp, uio->uio_offset, uio_uio_resid(uio), error);
                        return (error);
                }

                /* validate any pages written to */
                start = on & ~PAGE_MASK;
                for (; start < on+n; start += PAGE_SIZE) {
                        NBPGVALID_SET(bp, start/PAGE_SIZE);
                        /*
                         * This may seem a little weird, but we don't actually set the
                         * dirty bits for writes.  This is because we keep the dirty range
                         * in the nb_dirtyoff/nb_dirtyend fields.  Also, particularly for
                         * delayed writes, when we give the pages back to the VM we don't
                         * want to keep them marked dirty, because when we later write the
                         * buffer we won't be able to tell which pages were written dirty
                         * and which pages were mmapped and dirtied.
                         */
                }
                if (bp->nb_dirtyend > 0) {
                        bp->nb_dirtyoff = min(on, bp->nb_dirtyoff);
                        bp->nb_dirtyend = max((on + n), bp->nb_dirtyend);
                } else {
                        bp->nb_dirtyoff = on;
                        bp->nb_dirtyend = on + n;
                }
                if (bp->nb_validend <= 0 || bp->nb_validend < bp->nb_dirtyoff ||
                    bp->nb_validoff > bp->nb_dirtyend) {
                        bp->nb_validoff = bp->nb_dirtyoff;
                        bp->nb_validend = bp->nb_dirtyend;
                } else {
                        bp->nb_validoff = min(bp->nb_validoff, bp->nb_dirtyoff);
                        bp->nb_validend = max(bp->nb_validend, bp->nb_dirtyend);
                }
                if (!ISSET(bp->nb_flags, NB_CACHE))
                        nfs_buf_normalize_valid_range(np, bp);

                /*
                 * Since this block is being modified, it must be written
                 * again and not just committed.
                 */
                if (ISSET(bp->nb_flags, NB_NEEDCOMMIT)) {
                        np->n_needcommitcnt--;
                        CHECK_NEEDCOMMITCNT(np);
                }
                CLR(bp->nb_flags, NB_NEEDCOMMIT);

                if (ioflag & IO_SYNC) {
                        bp->nb_proc = p;
                        error = nfs_buf_write(bp);
                        if (error) {
                                np->n_flag &= ~NWRBUSY;
                                FSDBG_BOT(515, vp, uio->uio_offset,
                                        uio_uio_resid(uio), error);
                                return (error);
                        }
                } else if (((n + on) == biosize) || (np->n_flag & NNOCACHE)) {
                        bp->nb_proc = NULL;
                        SET(bp->nb_flags, NB_ASYNC);
                        nfs_buf_write(bp);
                } else
                        nfs_buf_write_delayed(bp, p);

                if (np->n_needcommitcnt > (nfsbufcnt/16))
                        nfs_flushcommits(vp, p, 1);

        } while (uio_uio_resid(uio) > 0 && n > 0);

        np->n_flag &= ~NWRBUSY;
        FSDBG_BOT(515, vp, uio->uio_offset, uio_uio_resid(uio), 0);
        return (0);
}

/*
 * Flush out and invalidate all buffers associated with a vnode.
 * Called with the underlying object locked.
 */
static int
nfs_vinvalbuf_internal(
        vnode_t vp,
        int flags,
        kauth_cred_t cred,
        proc_t p,
        int slpflag,
        int slptimeo)
{
        struct nfsbuf *bp;
        struct nfsbuflists blist;
        int list, error = 0;
        struct nfsnode *np = VTONFS(vp);

        if (flags & V_SAVE) {
                if ((error = nfs_flush(vp, MNT_WAIT, cred, p,
                                        (flags & V_IGNORE_WRITEERR))))
                        return (error);
                if (!LIST_EMPTY(&np->n_dirtyblkhd))
                        panic("nfs_vinvalbuf: dirty bufs (vp 0x%x, bp 0x%x)",
                                vp, LIST_FIRST(&np->n_dirtyblkhd));
        }

        lck_mtx_lock(nfs_buf_mutex);
        for (;;) {
                list = NBI_CLEAN;
                if (nfs_buf_iterprepare(np, &blist, list)) {
                        list = NBI_DIRTY;
                        if (nfs_buf_iterprepare(np, &blist, list))
                                break;
                }
                while ((bp = LIST_FIRST(&blist))) {
                        LIST_REMOVE(bp, nb_vnbufs);
                        if (list == NBI_CLEAN)
                                LIST_INSERT_HEAD(&np->n_cleanblkhd, bp, nb_vnbufs);
                        else
                                LIST_INSERT_HEAD(&np->n_dirtyblkhd, bp, nb_vnbufs);
                        nfs_buf_refget(bp);
                        while ((error = nfs_buf_acquire(bp, NBAC_REMOVE, slpflag, slptimeo))) {
                                FSDBG(556, vp, bp, NBOFF(bp), bp->nb_flags);
                                if (error != EAGAIN) {
                                        FSDBG(554, vp, bp, -1, error);
                                        nfs_buf_refrele(bp);
                                        nfs_buf_itercomplete(np, &blist, list);
                                        lck_mtx_unlock(nfs_buf_mutex);
                                        return (error);
                                }
                        }
                        nfs_buf_refrele(bp);
                        FSDBG(554, vp, bp, NBOFF(bp), bp->nb_flags);
                        lck_mtx_unlock(nfs_buf_mutex);
                        if ((flags & V_SAVE) && UBCINFOEXISTS(vp) && bp->nb_vp &&
                            (NBOFF(bp) < (off_t)np->n_size)) {
                                /* XXX extra paranoia: make sure we're not */
                                /* somehow leaving any dirty data around */
                                int mustwrite = 0;
                                int end = (NBOFF(bp) + bp->nb_bufsize > (off_t)np->n_size) ?
                                    ((off_t)np->n_size - NBOFF(bp)) : bp->nb_bufsize;
                                if (!ISSET(bp->nb_flags, NB_PAGELIST)) {
                                        error = nfs_buf_upl_setup(bp);
                                        if (error == EINVAL) {
                                                /* vm object must no longer exist */
                                                /* hopefully we don't need to do */
                                                /* anything for this buffer */
                                        } else if (error)
                                                printf("nfs_vinvalbuf: upl setup failed %d\n", error);
                                        bp->nb_valid = bp->nb_dirty = 0;
                                }
                                nfs_buf_upl_check(bp);
                                /* check for any dirty data before the EOF */
                                if (bp->nb_dirtyend && bp->nb_dirtyoff < end) {
                                        /* clip dirty range to EOF */
                                        if (bp->nb_dirtyend > end)
                                                bp->nb_dirtyend = end;
                                        mustwrite++;
                                }
                                bp->nb_dirty &= (1 << (round_page_32(end)/PAGE_SIZE)) - 1;
                                /* also make sure we'll have a credential to do the write */
                                if (mustwrite && (bp->nb_wcred == NOCRED) && (cred == NOCRED)) {
                                        printf("nfs_vinvalbuf: found dirty buffer with no write creds\n");
                                        mustwrite = 0;
                                }
                                if (mustwrite) {
                                        FSDBG(554, vp, bp, 0xd00dee, bp->nb_flags);
                                        if (!ISSET(bp->nb_flags, NB_PAGELIST))
                                                panic("nfs_vinvalbuf: dirty buffer without upl");
                                        /* gotta write out dirty data before invalidating */
                                        /* (NB_STABLE indicates that data writes should be FILESYNC) */
                                        /* (NB_NOCACHE indicates buffer should be discarded) */
                                        CLR(bp->nb_flags, (NB_DONE | NB_ERROR | NB_INVAL | NB_ASYNC));
                                        SET(bp->nb_flags, NB_STABLE | NB_NOCACHE);
                                        if (bp->nb_wcred == NOCRED) {
                                                kauth_cred_ref(cred);
                                                bp->nb_wcred = cred;
                                        }
                                        error = nfs_buf_write(bp);
                                        // Note: bp has been released
                                        if (error) {
                                                FSDBG(554, bp, 0xd00dee, 0xbad, error);
                                                np->n_error = error;
                                                np->n_flag |= NWRITEERR;
                                                /*
                                                 * There was a write error and we need to
                                                 * invalidate attrs to sync with server.
                                                 * (if this write was extending the file,
                                                 * we may no longer know the correct size)
                                                 */
                                                NATTRINVALIDATE(np);
                                                error = 0;
                                        }
                                        lck_mtx_lock(nfs_buf_mutex);
                                        continue;
                                }
                        }
                        SET(bp->nb_flags, NB_INVAL);
                        // hold off on FREEUPs until we're done here
                        nfs_buf_release(bp, 0);
                        lck_mtx_lock(nfs_buf_mutex);
                }
                nfs_buf_itercomplete(np, &blist, list);
        }
        lck_mtx_unlock(nfs_buf_mutex);
        NFS_BUF_FREEUP();
        if (NVALIDBUFS(np))
                panic("nfs_vinvalbuf: flush failed");
        return (0);
}


/*
 * Flush and invalidate all dirty buffers. If another process is already
 * doing the flush, just wait for completion.
 */
int
nfs_vinvalbuf(
        vnode_t vp,
        int flags,
        kauth_cred_t cred,
        proc_t p,
        int intrflg)
{
        struct nfsnode *np = VTONFS(vp);
        struct nfsmount *nmp = VFSTONFS(vnode_mount(vp));
        int error = 0, slpflag, slptimeo;
        off_t size;

        FSDBG_TOP(554, vp, flags, intrflg, 0);

        if (nmp && ((nmp->nm_flag & NFSMNT_INT) == 0))
                intrflg = 0;
        if (intrflg) {
                slpflag = PCATCH;
                slptimeo = 2 * hz;
        } else {
                slpflag = 0;
                slptimeo = 0;
        }
        /*
         * First wait for any other process doing a flush to complete.
         */
        while (np->n_flag & NFLUSHINPROG) {
                np->n_flag |= NFLUSHWANT;
                FSDBG_TOP(555, vp, flags, intrflg, np->n_flag);
                error = tsleep((caddr_t)&np->n_flag, PRIBIO + 2, "nfsvinval", slptimeo);
                FSDBG_BOT(555, vp, flags, intrflg, np->n_flag);
                if (error && (error = nfs_sigintr(VFSTONFS(vnode_mount(vp)), NULL, p))) {
                        FSDBG_BOT(554, vp, flags, intrflg, error);
                        return (error);
                }
        }

        /*
         * Now, flush as required.
         */
        np->n_flag |= NFLUSHINPROG;
        error = nfs_vinvalbuf_internal(vp, flags, cred, p, slpflag, 0);
        while (error) {
                FSDBG(554, vp, 0, 0, error);
                error = nfs_sigintr(VFSTONFS(vnode_mount(vp)), NULL, p);
                if (error) {
                        np->n_flag &= ~NFLUSHINPROG;
                        if (np->n_flag & NFLUSHWANT) {
                                np->n_flag &= ~NFLUSHWANT;
                                wakeup((caddr_t)&np->n_flag);
                        }
                        FSDBG_BOT(554, vp, flags, intrflg, error);
                        return (error);
                }
                error = nfs_vinvalbuf_internal(vp, flags, cred, p, 0, slptimeo);
        }
        np->n_flag &= ~(NMODIFIED | NFLUSHINPROG);
        if (np->n_flag & NFLUSHWANT) {
                np->n_flag &= ~NFLUSHWANT;
                wakeup((caddr_t)&np->n_flag);
        }
        /*
         * get the pages out of vm also
         */
        if (UBCINFOEXISTS(vp) && (size = ubc_getsize(vp))) {
                int rv = ubc_sync_range(vp, 0, size, UBC_PUSHALL | UBC_INVALIDATE);
                if (!rv)
                        panic("nfs_vinvalbuf(): ubc_sync_range failed!");
        }

        FSDBG_BOT(554, vp, flags, intrflg, 0);
        return (0);
}

/*
 * Initiate asynchronous I/O. Return an error if no nfsiods are available.
 * This is mainly to avoid queueing async I/O requests when the nfsiods
 * are all hung on a dead server.
 */
int
nfs_asyncio(bp, cred)
        struct nfsbuf *bp;
        kauth_cred_t cred;
{
        struct nfsmount *nmp;
        int i;
        int gotiod;
        int slpflag = 0;
        int slptimeo = 0;
        int error, error2;
        void *wakeme = NULL;
        struct timespec ts;

        if (nfs_numasync == 0)
                return (EIO);

        FSDBG_TOP(552, bp, bp ? NBOFF(bp) : 0, bp ? bp->nb_flags : 0, 0);

        nmp = ((bp != NULL) ? VFSTONFS(vnode_mount(bp->nb_vp)) : NULL);
again:
        if (nmp && nmp->nm_flag & NFSMNT_INT)
                slpflag = PCATCH;
        gotiod = FALSE;

        lck_mtx_lock(nfs_iod_mutex);

        /* no nfsbuf means tell nfsiod to process delwri list */
        if (!bp)
                nfs_ioddelwri = 1;

        /*
         * Find a free iod to process this request.
         */
        for (i = 0; i < NFS_MAXASYNCDAEMON; i++)
                if (nfs_iodwant[i]) {
                        /*
                         * Found one, so wake it up and tell it which
                         * mount to process.
                         */
                        nfs_iodwant[i] = NULL;
                        nfs_iodmount[i] = nmp;
                        if (nmp)
                                nmp->nm_bufqiods++;
                        wakeme = &nfs_iodwant[i];
                        gotiod = TRUE;
                        break;
                }

        /* if we're just poking the delwri list, we're done */
        if (!bp) {
                lck_mtx_unlock(nfs_iod_mutex);
                if (wakeme)
                        wakeup(wakeme);
                FSDBG_BOT(552, bp, 0x10101010, wakeme, 0);
                return (0);
        }

        /*
         * If none are free, we may already have an iod working on this mount
         * point.  If so, it will process our request.
         */
        if (!gotiod) {
                if (nmp->nm_bufqiods > 0) {
                        gotiod = TRUE;
                }
        }

        /*
         * If we have an iod which can process the request, then queue
         * the buffer.
         */
        FSDBG(552, bp, gotiod, i, nmp->nm_bufqiods);
        if (gotiod) {
                /*
                 * Ensure that the queue never grows too large.
                 */
                while (nmp->nm_bufqlen >= 2*nfs_numasync) {
                        if (ISSET(bp->nb_flags, NB_IOD)) {
                                /* An nfsiod is attempting this async operation so */
                                /* we must not fall asleep on the bufq because we */
                                /* could be waiting on ourself.  Just return error */
                                /* and we'll do this operation syncrhonously. */
                                goto out;
                        }
                        FSDBG(552, bp, nmp->nm_bufqlen, 2*nfs_numasync, -1);
                        nmp->nm_bufqwant = TRUE;

                        ts.tv_sec = (slptimeo/100);
                        /* the hz value is 100; which leads to 10ms */
                        ts.tv_nsec = (slptimeo % 100) * 10  * NSEC_PER_USEC * 1000;

                        error = msleep(&nmp->nm_bufq, nfs_iod_mutex, slpflag | PRIBIO,
                                       "nfsaio", &ts);
                        if (error) {
                                error2 = nfs_sigintr(nmp, NULL, bp->nb_proc);
                                if (error2) {
                                        lck_mtx_unlock(nfs_iod_mutex);
                                        FSDBG_BOT(552, bp, NBOFF(bp), bp->nb_flags, error2);
                                        return (error2);
                                }
                                if (slpflag == PCATCH) {
                                        slpflag = 0;
                                        slptimeo = 2 * hz;
                                }
                        }
                        /*
                         * We might have lost our iod while sleeping,
                         * so check and loop if nescessary.
                         */
                        if (nmp->nm_bufqiods == 0) {
                                lck_mtx_unlock(nfs_iod_mutex);
                                goto again;
                        }
                }

                if (ISSET(bp->nb_flags, NB_READ)) {
                        if (bp->nb_rcred == NOCRED && cred != NOCRED) {
                                kauth_cred_ref(cred);
                                bp->nb_rcred = cred;
                        }
                } else {
                        SET(bp->nb_flags, NB_WRITEINPROG);
                        if (bp->nb_wcred == NOCRED && cred != NOCRED) {
                                kauth_cred_ref(cred);
                                bp->nb_wcred = cred;
                        }
                }

                TAILQ_INSERT_TAIL(&nmp->nm_bufq, bp, nb_free);
                nmp->nm_bufqlen++;
                lck_mtx_unlock(nfs_iod_mutex);
                if (wakeme)
                        wakeup(wakeme);
                FSDBG_BOT(552, bp, NBOFF(bp), bp->nb_flags, 0);
                return (0);
        }

out:
        lck_mtx_unlock(nfs_iod_mutex);
        /*
         * All the iods are busy on other mounts, so return EIO to
         * force the caller to process the i/o synchronously.
         */
        FSDBG_BOT(552, bp, NBOFF(bp), bp->nb_flags, EIO);
        return (EIO);
}

/*
 * Do an I/O operation to/from a cache block. This may be called
 * synchronously or from an nfsiod.
 */
int
nfs_doio(struct nfsbuf *bp, kauth_cred_t cr, proc_t p)
{
        struct uio *uiop;
        vnode_t vp;
        struct nfsnode *np;
        struct nfsmount *nmp;
        int error = 0, diff, len, iomode, invalidate = 0;
        struct uio uio;
        struct iovec_32 io;
        enum vtype vtype;

        vp = bp->nb_vp;
        vtype = vnode_vtype(vp);
        np = VTONFS(vp);
        nmp = VFSTONFS(vnode_mount(vp));
        uiop = &uio;
        uiop->uio_iovs.iov32p = &io;
        uiop->uio_iovcnt = 1;
#if 1   /* LP64todo - can't use new segment flags until the drivers are ready */
        uiop->uio_segflg = UIO_SYSSPACE;
#else
        uiop->uio_segflg = UIO_SYSSPACE32;
#endif 

        /*
         * we've decided to perform I/O for this block,
         * so we couldn't possibly NB_DONE.  So, clear it.
         */
        if (ISSET(bp->nb_flags, NB_DONE)) {
                if (!ISSET(bp->nb_flags, NB_ASYNC))
                        panic("nfs_doio: done and not async");
                CLR(bp->nb_flags, NB_DONE);
        }
        FSDBG_TOP(256, np->n_size, NBOFF(bp), bp->nb_bufsize, bp->nb_flags);
        FSDBG(257, bp->nb_validoff, bp->nb_validend, bp->nb_dirtyoff,
              bp->nb_dirtyend);

        if (ISSET(bp->nb_flags, NB_READ)) {
            if (vtype == VREG)
                    NFS_BUF_MAP(bp);
            io.iov_len = bp->nb_bufsize;
            uio_uio_resid_set(uiop, io.iov_len);
            io.iov_base = (uintptr_t) bp->nb_data;
            uiop->uio_rw = UIO_READ;
            switch (vtype) {
            case VREG:
                uiop->uio_offset = NBOFF(bp);
                OSAddAtomic(1, (SInt32*)&nfsstats.read_bios);
                error = nfs_readrpc(vp, uiop, cr, p);
                FSDBG(262, np->n_size, NBOFF(bp), uio_uio_resid(uiop), error);
                if (!error) {
                    /* update valid range */
                    bp->nb_validoff = 0;
                    if (uio_uio_resid(uiop) != 0) {
                        /*
                         * If len > 0, there is a hole in the file and
                         * no writes after the hole have been pushed to
                         * the server yet.
                         * Just zero fill the rest of the valid area.
                         */
                        // LP64todo - fix this
                        diff = bp->nb_bufsize - uio_uio_resid(uiop);
                        len = np->n_size - (NBOFF(bp) + diff);
                        if (len > 0) {
                                // LP64todo - fix this
                                len = min(len, uio_uio_resid(uiop));
                                bzero((char *)bp->nb_data + diff, len);
                                bp->nb_validend = diff + len;
                                FSDBG(258, diff, len, 0, 1);
                        } else
                                bp->nb_validend = diff;
                    } else
                                bp->nb_validend = bp->nb_bufsize;
                    bp->nb_valid = (1 << (round_page_32(bp->nb_validend)/PAGE_SIZE)) - 1;
                    if (bp->nb_validend & PAGE_MASK) {
                            /* valid range ends in the middle of a page so we */
                            /* need to zero-fill any invalid data at the end */
                            /* of the last page */
                            bzero((caddr_t)(bp->nb_data + bp->nb_validend),
                                  bp->nb_bufsize - bp->nb_validend);
                            FSDBG(258, bp->nb_validend,
                                  bp->nb_bufsize - bp->nb_validend, 0, 2);
                    }
                }
                break;
            case VLNK:
                uiop->uio_offset = (off_t)0;
                OSAddAtomic(1, (SInt32*)&nfsstats.readlink_bios);
                error = nfs_readlinkrpc(vp, uiop, cr, p);
                if (!error) {
                        bp->nb_validoff = 0;
                        bp->nb_validend = uiop->uio_offset;
                }
                break;
            case VDIR:
                OSAddAtomic(1, (SInt32*)&nfsstats.readdir_bios);
                uiop->uio_offset = NBOFF(bp);
                if (!(nmp->nm_flag & NFSMNT_NFSV3))
                        nmp->nm_flag &= ~NFSMNT_RDIRPLUS; /* dk@farm.org */
                if (nmp->nm_flag & NFSMNT_RDIRPLUS) {
                        error = nfs_readdirplusrpc(vp, uiop, cr, p);
                        if (error == NFSERR_NOTSUPP)
                                nmp->nm_flag &= ~NFSMNT_RDIRPLUS;
                }
                if ((nmp->nm_flag & NFSMNT_RDIRPLUS) == 0)
                        error = nfs_readdirrpc(vp, uiop, cr, p);
                if (!error) {
                        bp->nb_validoff = 0;
                        bp->nb_validend = uiop->uio_offset - NBOFF(bp);
                        bp->nb_valid = (1 << (round_page_32(bp->nb_validend)/PAGE_SIZE)) - 1;
                }
                break;
            default:
                printf("nfs_doio: type %x unexpected\n", vtype);
                break;
            };
            if (error) {
                SET(bp->nb_flags, NB_ERROR);
                bp->nb_error = error;
            }

        } else {
            /* we're doing a write */
            int doff, dend = 0;

            /* We need to make sure the pages are locked before doing I/O.  */
            if (!ISSET(bp->nb_flags, NB_META) && UBCINFOEXISTS(vp)) {
                if (!ISSET(bp->nb_flags, NB_PAGELIST)) {
                    error = nfs_buf_upl_setup(bp);
                    if (error) {
                        printf("nfs_doio: upl create failed %d\n", error);
                        SET(bp->nb_flags, NB_ERROR);
                        bp->nb_error = EIO;
                        return (EIO);
                    }
                    nfs_buf_upl_check(bp);
                }
            }

            if (ISSET(bp->nb_flags, NB_WASDIRTY)) {
                FSDBG(256, bp, NBOFF(bp), bp->nb_dirty, 0xd00dee);
                /*
                 * There are pages marked dirty that need to be written out.
                 *
                 * We don't want to just combine the write range with the
                 * range of pages that are dirty because that could cause us
                 * to write data that wasn't actually written to.
                 * We also don't want to write data more than once.
                 *
                 * If the dirty range just needs to be committed, we do that.
                 * Otherwise, we write the dirty range and clear the dirty bits
                 * for any COMPLETE pages covered by that range.
                 * If there are dirty pages left after that, we write out the
                 * parts that we haven't written yet.
                 */
            }

            /*
             * If NB_NEEDCOMMIT is set, a commit rpc may do the trick. If not
             * an actual write will have to be done.
             * If NB_WRITEINPROG is already set, then push it with a write anyhow.
             */
            if (ISSET(bp->nb_flags, NB_NEEDCOMMIT))
                nfs_buf_check_write_verifier(np, bp);
            if ((bp->nb_flags & (NB_NEEDCOMMIT | NB_WRITEINPROG)) == NB_NEEDCOMMIT) {
                doff = NBOFF(bp) + bp->nb_dirtyoff;
                SET(bp->nb_flags, NB_WRITEINPROG);
                error = nfs_commit(vp, doff, bp->nb_dirtyend - bp->nb_dirtyoff,
                                bp->nb_wcred, bp->nb_proc);
                CLR(bp->nb_flags, NB_WRITEINPROG);
                if (!error) {
                    bp->nb_dirtyoff = bp->nb_dirtyend = 0;
                    CLR(bp->nb_flags, NB_NEEDCOMMIT);
                    np->n_needcommitcnt--;
                    CHECK_NEEDCOMMITCNT(np);
                }
            }

            if (!error && bp->nb_dirtyend > 0) {
                /* there's a dirty range that needs to be written out */
                u_int32_t pagemask;
                int firstpg, lastpg;

                if (NBOFF(bp) + bp->nb_dirtyend > (off_t)np->n_size)
                    bp->nb_dirtyend = np->n_size - NBOFF(bp);

                NFS_BUF_MAP(bp);

                doff = bp->nb_dirtyoff;
                dend = bp->nb_dirtyend;

                /* if doff page is dirty, move doff to start of page */
                if (NBPGDIRTY(bp,doff/PAGE_SIZE))
                    doff -= doff & PAGE_MASK;
                /* try to expand write range to include preceding dirty pages */
                if (!(doff & PAGE_MASK))
                    while (doff > 0 && NBPGDIRTY(bp,(doff-1)/PAGE_SIZE))
                        doff -= PAGE_SIZE;
                /* if dend page is dirty, move dend to start of next page */
                if ((dend & PAGE_MASK) && NBPGDIRTY(bp,dend/PAGE_SIZE))
                    dend = round_page_32(dend);
                /* try to expand write range to include trailing dirty pages */
                if (!(dend & PAGE_MASK))
                    while (dend < bp->nb_bufsize && NBPGDIRTY(bp,dend/PAGE_SIZE))
                        dend += PAGE_SIZE;
                /* make sure to keep dend clipped to EOF */
                if (NBOFF(bp) + dend > (off_t)np->n_size)
                    dend = np->n_size - NBOFF(bp);
                /* calculate range of complete pages being written */
                firstpg = round_page_32(doff) / PAGE_SIZE;
                lastpg = (trunc_page_32(dend) - 1)/ PAGE_SIZE;
                /* calculate mask for that page range */
                pagemask = ((1 << (lastpg+1)) - 1) & ~((1 << firstpg) - 1);

                /* compare page mask to nb_dirty; if there are other dirty pages */
                /* then write FILESYNC; otherwise, write UNSTABLE if async and */
                /* not needcommit/nocache/call; otherwise write FILESYNC */
                if (bp->nb_dirty & ~pagemask)
                    iomode = NFSV3WRITE_FILESYNC;
                else if ((bp->nb_flags & (NB_ASYNC | NB_NEEDCOMMIT | NB_NOCACHE | NB_STABLE)) == NB_ASYNC)
                    iomode = NFSV3WRITE_UNSTABLE;
                else
                    iomode = NFSV3WRITE_FILESYNC;

                /* write the dirty range */
                io.iov_len = dend - doff;
                uio_uio_resid_set(uiop, io.iov_len);
                uiop->uio_offset = NBOFF(bp) + doff;
                io.iov_base = (uintptr_t) bp->nb_data + doff;
                uiop->uio_rw = UIO_WRITE;

                OSAddAtomic(1, (SInt32*)&nfsstats.write_bios);

                SET(bp->nb_flags, NB_WRITEINPROG);
                error = nfs_writerpc(vp, uiop, cr, p, &iomode, &bp->nb_verf);
                /* clear dirty bits for pages we've written */
                if (!error)
                    bp->nb_dirty &= ~pagemask;
                /* set/clear needcommit flag */
                if (!error && iomode == NFSV3WRITE_UNSTABLE) {
                    if (!ISSET(bp->nb_flags, NB_NEEDCOMMIT))
                        np->n_needcommitcnt++;
                    SET(bp->nb_flags, NB_NEEDCOMMIT);
                    /* make sure nb_dirtyoff/nb_dirtyend reflect actual range written */
                    bp->nb_dirtyoff = doff;
                    bp->nb_dirtyend = dend;
                } else {
                    if (ISSET(bp->nb_flags, NB_NEEDCOMMIT)) {
                        np->n_needcommitcnt--;
                        CHECK_NEEDCOMMITCNT(np);
                    }
                    CLR(bp->nb_flags, NB_NEEDCOMMIT);
                }
                CLR(bp->nb_flags, NB_WRITEINPROG);
                /*
                 * For an interrupted write, the buffer is still valid and the write
                 * hasn't been pushed to the server yet, so we can't set NB_ERROR and
                 * report the interruption by setting NB_EINTR.  For the NB_ASYNC case,
                 * NB_EINTR is not relevant.
                 *
                 * For the case of a V3 write rpc not being committed to stable
                 * storage, the block is still dirty and requires either a commit rpc
                 * or another write rpc with iomode == NFSV3WRITE_FILESYNC before the
                 * block is reused. This is indicated by setting the NB_DELWRI and
                 * NB_NEEDCOMMIT flags.
                 */
                if (error == EINTR || (!error && bp->nb_flags & NB_NEEDCOMMIT)) {
                    CLR(bp->nb_flags, NB_INVAL | NB_NOCACHE);
                    if (!ISSET(bp->nb_flags, NB_DELWRI)) {
                        SET(bp->nb_flags, NB_DELWRI);
                        OSAddAtomic(1, (SInt32*)&nfs_nbdwrite);
                        NFSBUFCNTCHK(0);
                    }
                    FSDBG(261, bp->nb_validoff, bp->nb_validend,
                          bp->nb_bufsize, 0);
                    /*
                     * Since for the NB_ASYNC case, nfs_bwrite() has
                     * reassigned the buffer to the clean list, we have to
                     * reassign it back to the dirty one. Ugh.
                     */
                    if (ISSET(bp->nb_flags, NB_ASYNC)) {
                        /* move to dirty list */
                        lck_mtx_lock(nfs_buf_mutex);
                        if (bp->nb_vnbufs.le_next != NFSNOLIST)
                            LIST_REMOVE(bp, nb_vnbufs);
                        LIST_INSERT_HEAD(&np->n_dirtyblkhd, bp, nb_vnbufs);
                        lck_mtx_unlock(nfs_buf_mutex);
                    } else {
                        SET(bp->nb_flags, NB_EINTR);
                    }
                } else {
                        /* either there's an error or we don't need to commit */
                        if (error) {
                            SET(bp->nb_flags, NB_ERROR);
                            bp->nb_error = np->n_error = error;
                            np->n_flag |= NWRITEERR;
                            /*
                             * There was a write error and we need to
                             * invalidate attrs and flush buffers in
                             * order to sync up with the server.
                             * (if this write was extending the file,
                             * we may no longer know the correct size)
                             *
                             * But we can't call vinvalbuf while holding
                             * this buffer busy.  Set a flag to do it after
                             * releasing the buffer.
                             *
                             * Note we can only invalidate in this function
                             * if this is an async write and so the iodone
                             * below will release the buffer.  Also, we
                             * shouldn't call vinvalbuf from nfsiod because
                             * that may deadlock waiting for the completion
                             * of writes that are queued up behind this one.
                             */
                            if (ISSET(bp->nb_flags, NB_ASYNC) &&
                                !ISSET(bp->nb_flags, NB_IOD)) {
                                    invalidate = 1;
                            } else {
                                    /* invalidate later */
                                    np->n_flag |= NNEEDINVALIDATE;
                            }
                            NATTRINVALIDATE(np);
                        }
                        /* clear the dirty range */
                        bp->nb_dirtyoff = bp->nb_dirtyend = 0;
                }
            }

            if (!error && bp->nb_dirty) {
                /* there are pages marked dirty that need to be written out */
                int pg, count, npages, off;

                OSAddAtomic(1, (SInt32*)&nfsstats.write_bios);

                NFS_BUF_MAP(bp);

                /*
                 * we do these writes synchronously because we can't really
                 * support the unstable/needommit method.  We could write
                 * them unstable, clear the dirty bits, and then commit the
                 * whole block later, but if we need to rewrite the data, we
                 * won't have any idea which pages were written because that
                 * info can't be stored in the nb_dirtyoff/nb_dirtyend.  We
                 * also can't leave the dirty bits set because then we wouldn't
                 * be able to tell if the pages were re-dirtied between the end
                 * of the write and the commit.
                 */
                iomode = NFSV3WRITE_FILESYNC;
                uiop->uio_rw = UIO_WRITE;

                SET(bp->nb_flags, NB_WRITEINPROG);
                npages = bp->nb_bufsize/PAGE_SIZE;
                for (pg=0; pg < npages; pg++) {
                    if (!NBPGDIRTY(bp,pg))
                        continue;
                    count = 1;
                    while (((pg+count) < npages) && NBPGDIRTY(bp,pg+count))
                            count++;
                    /* write count pages starting with page pg */
                    off = pg * PAGE_SIZE;
                    len = count * PAGE_SIZE;

                    /* clip writes to EOF */
                    if (NBOFF(bp) + off + len > (off_t)np->n_size)
                        len -= (NBOFF(bp) + off + len) - np->n_size;
                    if (len > 0) {
                        io.iov_len = len;
                        uio_uio_resid_set(uiop, io.iov_len);
                        uiop->uio_offset = NBOFF(bp) + off;
                        io.iov_base = (uintptr_t) bp->nb_data + off;
                        error = nfs_writerpc(vp, uiop, cr, p, &iomode, &bp->nb_verf);
                        if (error)
                            break;
                    }
                    /* clear dirty bits */
                    while (count--) {
                           bp->nb_dirty &= ~(1 << pg);
                           /* leave pg on last page */
                           if (count) pg++;
                    }
                }
                if (!error) {
                    if (ISSET(bp->nb_flags, NB_NEEDCOMMIT)) {
                        np->n_needcommitcnt--;
                        CHECK_NEEDCOMMITCNT(np);
                    }
                    CLR(bp->nb_flags, NB_NEEDCOMMIT);
                }
                CLR(bp->nb_flags, NB_WRITEINPROG);
                FSDBG_BOT(256, bp->nb_validoff, bp->nb_validend, bp->nb_bufsize,
                          np->n_size);
            }

            if (error) {
                SET(bp->nb_flags, NB_ERROR);
                bp->nb_error = error;
            }
        }

        FSDBG_BOT(256, bp->nb_validoff, bp->nb_validend, bp->nb_bufsize, error);

        nfs_buf_iodone(bp);

        if (invalidate) {
                /*
                 * There was a write error and we need to
                 * invalidate attrs and flush buffers in
                 * order to sync up with the server.
                 * (if this write was extending the file,
                 * we may no longer know the correct size)
                 *
                 * But we couldn't call vinvalbuf while holding
                 * the buffer busy.  So we call vinvalbuf() after
                 * releasing the buffer.
                 *
                 * Note: we don't bother calling nfs_vinvalbuf() if
                 * there's already a flush in progress.
                 */
                if (!(np->n_flag & NFLUSHINPROG))
                        nfs_vinvalbuf(vp, V_SAVE|V_IGNORE_WRITEERR, cr, p, 1);
        }

        return (error);
}