xnu-4570.1.46.tar.gz

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

/*
 * Copyright (c) 2000-2015 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 * 
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/* Copyright (c) 1995 NeXT Computer, Inc. All Rights Reserved */
/*
 * Copyright (c) 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/ubc_internal.h>
#include <sys/uio_internal.h>
#include <sys/kpi_mbuf.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 <kern/thread_call.h>

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

#define NFS_BIO_DBG(...) NFS_DBG(NFS_FAC_BIO, 7, ## __VA_ARGS__)

kern_return_t   thread_terminate(thread_t); /* XXX */

#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;
int nfs_buf_timer_on = 0;
thread_t nfsbufdelwrithd = NULL;

lck_grp_t *nfs_buf_lck_grp;
lck_mtx_t *nfs_buf_mutex;

#define NFSBUF_FREE_PERIOD      30      /* seconds */
#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 timer */
#define LRU_FREEUP_FRAC_ON_TIMER        8
/* fraction of nfsbufs nfs_buf_freeup() should attempt to free from nfsbuffreemeta list when called from 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 = lck_grp_alloc_init("nfs_buf", LCK_GRP_ATTR_NULL);
        nfs_buf_mutex = lck_mtx_alloc_init(nfs_buf_lck_grp, LCK_ATTR_NULL);

        nfsbufcnt = nfsbufmetacnt =
        nfsbuffreecnt = nfsbuffreemetacnt = nfsbufdelwricnt = 0;
        nfsbufmin = 128;
        /* size nfsbufmax to cover at most half sane_size (w/default buf size) */
        nfsbufmax = (sane_size >> PAGE_SHIFT) / (2 * (NFS_RWSIZE >> PAGE_SHIFT));
        nfsbufmetamax = nfsbufmax / 4;
        nfsneedbuffer = 0;
        nfs_nbdwrite = 0;

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

}

/*
 * Check periodically for stale/unused nfs bufs
 */
void
nfs_buf_timer(__unused void *param0, __unused void *param1)
{
        nfs_buf_freeup(1);

        lck_mtx_lock(nfs_buf_mutex);
        if (nfsbufcnt <= nfsbufmin) {
                nfs_buf_timer_on = 0;
                lck_mtx_unlock(nfs_buf_mutex);
                return;
        }
        lck_mtx_unlock(nfs_buf_mutex);

        nfs_interval_timer_start(nfs_buf_timer_call,
                NFSBUF_FREE_PERIOD * 1000);
}

/*
 * 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);

        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 nfsnode */
                if (fbp->nb_np) {
                        if (fbp->nb_vnbufs.le_next != NFSNOLIST) {
                                LIST_REMOVE(fbp, nb_vnbufs);
                                fbp->nb_vnbufs.le_next = NFSNOLIST;
                        }
                        fbp->nb_np = 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 nfsnode */
                if (fbp->nb_np) {
                        if (fbp->nb_vnbufs.le_next != NFSNOLIST) {
                                LIST_REMOVE(fbp, nb_vnbufs);
                                fbp->nb_vnbufs.le_next = NFSNOLIST;
                        }
                        fbp->nb_np = NULL;
                }
                LIST_REMOVE(fbp, nb_hash);
                TAILQ_INSERT_TAIL(&nfsbuffreeup, fbp, nb_free);
                nfsbufcnt--;
                nfsbufmetacnt--;
        }

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

        lck_mtx_unlock(nfs_buf_mutex);

        while ((fbp = TAILQ_FIRST(&nfsbuffreeup))) {
                TAILQ_REMOVE(&nfsbuffreeup, fbp, nb_free);
                /* nuke any creds */
                if (IS_VALID_CRED(fbp->nb_rcred))
                        kauth_cred_unref(&fbp->nb_rcred);
                if (IS_VALID_CRED(fbp->nb_wcred))
                        kauth_cred_unref(&fbp->nb_wcred);
                /* 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();
}

/*
 * check for existence of nfsbuf in cache
 */
boolean_t
nfs_buf_is_incore(nfsnode_t np, daddr64_t blkno)
{
        boolean_t rv;
        lck_mtx_lock(nfs_buf_mutex);
        if (nfs_buf_incore(np, 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(nfsnode_t np, daddr64_t blkno)
{
        /* Search hash chain */
        struct nfsbuf * bp = NFSBUFHASH(np, blkno)->lh_first;
        for (; bp != NULL; bp = bp->nb_hash.le_next)
                if ((bp->nb_lblkno == blkno) && (bp->nb_np == np)) {
                        if (!ISSET(bp->nb_flags, NB_INVAL)) {
                                FSDBG(547, bp, blkno, bp->nb_flags, bp->nb_np);
                                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 nfsmount *nmp = VTONMP(vp);
        struct nfsbuf *bp;
        int error = 0;

        if (nfs_mount_gone(nmp))
                return (ENXIO);

        lck_mtx_lock(nfs_buf_mutex);
        bp = nfs_buf_incore(VTONFS(vp), (daddr64_t)(offset / nmp->nm_biosize));
        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))) {
                        /*
                         * Before returning the bad news, move the
                         * buffer to the start of the delwri list and
                         * give the list a push to try to flush the
                         * buffer out.
                         */
                        error = EBUSY;
                        nfs_buf_remfree(bp);
                        TAILQ_INSERT_HEAD(&nfsbufdelwri, bp, nb_free);
                        nfsbufdelwricnt++;
                        nfs_buf_delwri_push(1);
                }
        }
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_kernel(NFSTOV(bp->nb_np), NBOFF(bp), bp->nb_bufsize,
                                &upl, NULL, upl_flags, VM_KERN_MEMORY_FILE);
        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_np);

        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(NFSTOV(bp->nb_np));
        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);
        }
        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)
 */
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_offset_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);
}

/*
 * 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.
 */
void
nfs_buf_normalize_valid_range(nfsnode_t 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;
}

/*
 * process some entries on the delayed write queue
 * (must be called with nfs_buf_mutex held)
 */
void
nfs_buf_delwri_service(void)
{
        struct nfsbuf *bp;
        nfsnode_t np;
        int error, i = 0;

        while (i < 8 && (bp = TAILQ_FIRST(&nfsbufdelwri)) != NULL) {
                np = bp->nb_np;
                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_np) {
                        /* 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, 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);
        }
}

/*
 * thread to service the delayed write queue when asked
 */
void
nfs_buf_delwri_thread(__unused void *arg, __unused wait_result_t wr)
{
        struct timespec ts = { 30, 0 };
        int error = 0;

        lck_mtx_lock(nfs_buf_mutex);
        while (!error) {
                nfs_buf_delwri_service();
                error = msleep(&nfsbufdelwrithd, nfs_buf_mutex, 0, "nfsbufdelwri", &ts);
        }
        nfsbufdelwrithd = NULL;
        lck_mtx_unlock(nfs_buf_mutex);
        thread_terminate(nfsbufdelwrithd);
}

/*
 * try to push out some delayed/uncommitted writes
 * ("locked" indicates whether nfs_buf_mutex is already held)
 */
void
nfs_buf_delwri_push(int locked)
{
        if (TAILQ_EMPTY(&nfsbufdelwri))
                return;
        if (!locked)
                lck_mtx_lock(nfs_buf_mutex);
        /* wake up the delayed write service thread */
        if (nfsbufdelwrithd)
                wakeup(&nfsbufdelwrithd);
        else if (kernel_thread_start(nfs_buf_delwri_thread, NULL, &nfsbufdelwrithd) == KERN_SUCCESS)
                thread_deallocate(nfsbufdelwrithd);
        /* otherwise, try to do some of the work ourselves */
        if (!nfsbufdelwrithd)
                nfs_buf_delwri_service();
        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(
        nfsnode_t np,
        daddr64_t blkno,
        uint32_t size,
        thread_t thd,
        int flags,
        struct nfsbuf **bpp)
{
        vnode_t vp = NFSTOV(np);
        struct nfsmount *nmp = VTONMP(vp);
        struct nfsbuf *bp;
        uint32_t bufsize;
        int slpflag = PCATCH;
        int operation = (flags & NBLK_OPMASK);
        int error = 0;
        struct timespec ts;

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

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

        if (nfs_mount_gone(nmp)) {
                FSDBG_BOT(541, np, blkno, 0, ENXIO);
                return (ENXIO);
        }

        if (!UBCINFOEXISTS(vp)) {
                operation = NBLK_META;
        } else if (bufsize < (uint32_t)nmp->nm_biosize) {
                /* reg files should always have biosize blocks */
                bufsize = nmp->nm_biosize;
        }

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

                /* 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, np, blkno, nfs_nbdwrite, NFS_A_LOT_OF_DELAYED_WRITES);
        }

loop:
        lck_mtx_lock(nfs_buf_mutex);

        /* wait for any buffer invalidation/flushing to complete */
        while (np->n_bflag & NBINVALINPROG) {
                np->n_bflag |= NBINVALWANT;
                ts.tv_sec = 2;
                ts.tv_nsec = 0;
                msleep(&np->n_bflag, nfs_buf_mutex, slpflag, "nfs_buf_get_invalwait", &ts);
                if ((error = nfs_sigintr(VTONMP(vp), NULL, thd, 0))) {
                        lck_mtx_unlock(nfs_buf_mutex);
                        FSDBG_BOT(541, np, blkno, 0, error);
                        return (error);
                }
                if (np->n_bflag & NBINVALINPROG)
                        slpflag = 0;
        }

        /* check for existence of nfsbuf in cache */
        if ((bp = nfs_buf_incore(np, 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, np, blkno, bp, 0xbcbcbcbc);
                                return (0);
                        }
                        FSDBG_TOP(543, np, 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) ? NULL : &ts);
                        slpflag = 0;
                        FSDBG_BOT(543, np, blkno, bp, bp->nb_flags);
                        if ((error = nfs_sigintr(VTONMP(vp), NULL, thd, 0))) {
                                FSDBG_BOT(541, np, 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, np, 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, np, 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 nfsnode */
                if (bp->nb_np) {
                        if (bp->nb_vnbufs.le_next != NFSNOLIST) {
                                LIST_REMOVE(bp, nb_vnbufs);
                                bp->nb_vnbufs.le_next = NFSNOLIST;
                        }
                        bp->nb_np = NULL;
                }
                LIST_REMOVE(bp, nb_hash);
                /* nuke any creds we're holding */
                if (IS_VALID_CRED(bp->nb_rcred))
                        kauth_cred_unref(&bp->nb_rcred);
                if (IS_VALID_CRED(bp->nb_wcred))
                        kauth_cred_unref(&bp->nb_wcred);
                /* 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, np, blkno, 0, error);
                                return (ENOMEM);
                        }
                        nfsbufcnt++;

                        /*
                         * If any excess bufs, make sure the timer
                         * is running to free them up later.
                         */
                        if (nfsbufcnt > nfsbufmin && !nfs_buf_timer_on) {
                                nfs_buf_timer_on = 1;
                                nfs_interval_timer_start(nfs_buf_timer_call,
                                        NFSBUF_FREE_PERIOD * 1000);
                        }

                        if (operation == NBLK_META)
                                nfsbufmetacnt++;
                        NFSBUFCNTCHK();
                        /* init nfsbuf */
                        bzero(bp, sizeof(*bp));
                        bp->nb_free.tqe_next = NFSNOLIST;
                        bp->nb_validoff = bp->nb_validend = -1;
                        FSDBG(545, np, blkno, bp, 0);
                } else {
                        /* too many bufs... wait for buffers to free up */
                        FSDBG_TOP(546, np, blkno, nfsbufcnt, nfsbufmax);

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

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

        /* set up nfsbuf */
        SET(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 nfsnode */
        bp->nb_np = np;
        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! */
                        /* clean up buffer and return error */
                        lck_mtx_lock(nfs_buf_mutex);
                        LIST_REMOVE(bp, nb_vnbufs);
                        bp->nb_vnbufs.le_next = NFSNOLIST;
                        bp->nb_np = 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, np, 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)) {
                        /* set up upl */
                        if (nfs_buf_upl_setup(bp)) {
                                /* unable to create upl */
                                /* vm object must no longer exist */
                                /* clean up buffer and return error */
                                lck_mtx_lock(nfs_buf_mutex);
                                LIST_REMOVE(bp, nb_vnbufs);
                                bp->nb_vnbufs.le_next = NFSNOLIST;
                                bp->nb_np = 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, np, 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, np, blkno, bp, bp->nb_flags);

        return (0);
}

void
nfs_buf_release(struct nfsbuf *bp, int freeup)
{
        nfsnode_t np = bp->nb_np;
        vnode_t 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);

        vp = np ? NFSTOV(np) : NULL;
        if (vp && UBCINFOEXISTS(vp) && bp->nb_bufsize) {
                int upl_flags, rv;
                upl_t upl;
                uint32_t i;

                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;
                }
                /*
                 * Abort the pages on error or: if this is an invalid or
                 * non-needcommit nocache buffer AND no pages are dirty.
                 */
                if (ISSET(bp->nb_flags, NB_ERROR) || (!bp->nb_dirty && (ISSET(bp->nb_flags, NB_INVAL) ||
                    (ISSET(bp->nb_flags, NB_NOCACHE) && !ISSET(bp->nb_flags, (NB_NEEDCOMMIT | NB_DELWRI)))))) {
                        if (ISSET(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;
                                
                                if (!ISSET(bp->nb_flags, (NB_NEEDCOMMIT | NB_DELWRI)))
                                        upl_flags |= UPL_COMMIT_CLEAR_PRECIOUS;

                                ubc_upl_commit_range(upl,
                                        i*PAGE_SIZE, PAGE_SIZE,
                                        upl_flags |
                                        UPL_COMMIT_INACTIVATE |
                                        UPL_COMMIT_FREE_ON_EMPTY);
                        }
                }
pagelist_cleanup_done:
                /* invalidate any pages past EOF */
                if (NBOFF(bp) + bp->nb_bufsize > (off_t)(np->n_size)) {
                        off_t start, end;
                        start = trunc_page_64(np->n_size) + PAGE_SIZE_64;
                        end = trunc_page_64(NBOFF(bp) + bp->nb_bufsize);
                        if (start < NBOFF(bp))
                                start = NBOFF(bp);
                        if (end > start) {
                                if ((rv = ubc_msync(vp, start, end, NULL, UBC_INVALIDATE)))
                                        printf("nfs_buf_release(): ubc_msync failed!, error %d\n", rv);
                        }
                }
                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 non-needcommit nocache, or an error, mark it invalid. */
        if (ISSET(bp->nb_flags, NB_ERROR) ||
            (ISSET(bp->nb_flags, NB_NOCACHE) && !ISSET(bp->nb_flags, (NB_NEEDCOMMIT | NB_DELWRI))))
                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 nfsnode */
                if (bp->nb_vnbufs.le_next != NFSNOLIST) {
                        LIST_REMOVE(bp, nb_vnbufs);
                        bp->nb_vnbufs.le_next = NFSNOLIST;
                }
                bp->nb_np = 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);
                        nfs_nbdwrite--;
                        NFSBUFCNTCHK();
                        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();

        /* Unlock the buffer. */
        CLR(bp->nb_flags, (NB_ASYNC | NB_STABLE));
        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", NULL);

        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");

        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(NFSTOV(bp->nb_np));
                nfs_node_lock_force(bp->nb_np);
                bp->nb_np->n_numoutput--;
                nfs_node_unlock(bp->nb_np);
        }
        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)
{
        nfsnode_t np = bp->nb_np;

        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) Make sure it's on its node's correct block list,
         */
        if (!ISSET(bp->nb_flags, NB_DELWRI)) {
                SET(bp->nb_flags, NB_DELWRI);
                /* move to dirty list */
                lck_mtx_lock(nfs_buf_mutex);
                nfs_nbdwrite++;
                NFSBUFCNTCHK();
                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);
        }

        /*
         * If the vnode has "too many" write operations in progress
         * wait for them to finish the IO
         */
        vnode_waitforwrites(NFSTOV(np), VNODE_ASYNC_THROTTLE, 0, 0, "nfs_buf_write_delayed");

        /* the file is in a modified state, so make sure the flag's set */
        nfs_node_lock_force(np);
        np->n_flag |= NMODIFIED;
        nfs_node_unlock(np);

        /*
         * If we have too many delayed write buffers,
         * just fall back to doing the async write.
         */
        if (nfs_nbdwrite < 0)
                panic("nfs_buf_write_delayed: Negative nfs_nbdwrite");
        if (nfs_nbdwrite > NFS_A_LOT_OF_DELAYED_WRITES) {
                /* 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(nfsnode_t np, struct nfsbuf *bp)
{
        struct nfsmount *nmp;

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

        nmp = NFSTONMP(np);
        if (nfs_mount_gone(nmp))
                return;
        if (!ISSET(bp->nb_flags, NB_STALEWVERF) && (bp->nb_verf == nmp->nm_verf))
                return;

        /* write verifier changed, clear commit/wverf flags */
        CLR(bp->nb_flags, (NB_NEEDCOMMIT | NB_STALEWVERF));
        bp->nb_verf = 0;
        nfs_node_lock_force(np);
        np->n_needcommitcnt--;
        CHECK_NEEDCOMMITCNT(np);
        nfs_node_unlock(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 lck_mtx_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 */
                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(nfsnode_t 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", NULL);
        }
        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);
}

/*
 * clean up 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(nfsnode_t 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);
        }
}


/*
 * Read an NFS buffer for a file.
 */
int
nfs_buf_read(struct nfsbuf *bp)
{
        int error = 0;
        nfsnode_t np;
        thread_t thd;
        kauth_cred_t cred;

        np = bp->nb_np;
        cred = bp->nb_rcred;
        if (IS_VALID_CRED(cred))
                kauth_cred_ref(cred);
        thd = ISSET(bp->nb_flags, NB_ASYNC) ? NULL : current_thread();

        /* sanity checks */
        if (!ISSET(bp->nb_flags, NB_READ))
                panic("nfs_buf_read: !NB_READ");
        if (ISSET(bp->nb_flags, NB_DONE))
                CLR(bp->nb_flags, NB_DONE);

        NFS_BUF_MAP(bp);

        OSAddAtomic64(1, &nfsstats.read_bios);

        error = nfs_buf_read_rpc(bp, thd, cred);
        /*
         * For async I/O, the callbacks will finish up the
         * read.  Otherwise, the read has already been finished.
         */

        if (IS_VALID_CRED(cred))
                kauth_cred_unref(&cred);
        return (error);
}

/*
 * finish the reading of a buffer
 */
void
nfs_buf_read_finish(struct nfsbuf *bp)
{
        nfsnode_t np = bp->nb_np;
        struct nfsmount *nmp;

        if (!ISSET(bp->nb_flags, NB_ERROR)) {
                /* update valid range */
                bp->nb_validoff = 0;
                bp->nb_validend = bp->nb_endio;
                if (bp->nb_endio < (int)bp->nb_bufsize) { 
                        /*
                         * The read may be short because we have unflushed writes
                         * that are extending the file size and the reads hit the
                         * (old) EOF on the server.  So, just make sure nb_validend
                         * correctly tracks EOF.
                         * Note that the missing data should have already been zeroed
                         * in nfs_buf_read_rpc_finish().
                         */
                        off_t boff = NBOFF(bp);
                        if ((off_t)np->n_size >= (boff + bp->nb_bufsize))
                                bp->nb_validend = bp->nb_bufsize;
                        else if ((off_t)np->n_size >= boff)
                                bp->nb_validend = np->n_size - boff;
                        else
                                bp->nb_validend = 0;
                }
                if ((nmp = NFSTONMP(np)) && (nmp->nm_vers == NFS_VER2) &&
                    ((NBOFF(bp) + bp->nb_validend) > 0x100000000LL))
                        bp->nb_validend = 0x100000000LL - NBOFF(bp);
                bp->nb_valid = (1 << (round_page_32(bp->nb_validend) / PAGE_SIZE)) - 1;
                if (bp->nb_validend & PAGE_MASK) {
                        /* zero-fill remainder of last page */
                        bzero(bp->nb_data + bp->nb_validend, PAGE_SIZE - (bp->nb_validend & PAGE_MASK));
                }
        }
        nfs_buf_iodone(bp);
}

/*
 * initiate the NFS READ RPC(s) for a buffer
 */
int
nfs_buf_read_rpc(struct nfsbuf *bp, thread_t thd, kauth_cred_t cred)
{
        struct nfsmount *nmp;
        nfsnode_t np = bp->nb_np;
        int error = 0, nfsvers, async;
        int offset, nrpcs;
        uint32_t nmrsize, length, len;
        off_t boff;
        struct nfsreq *req;
        struct nfsreq_cbinfo cb;

        nmp = NFSTONMP(np);
        if (nfs_mount_gone(nmp)) {
                bp->nb_error = error = ENXIO;
                SET(bp->nb_flags, NB_ERROR);
                nfs_buf_iodone(bp);
                return (error);
        }
        nfsvers = nmp->nm_vers;
        nmrsize = nmp->nm_rsize;

        boff = NBOFF(bp);
        offset = 0;
        length = bp->nb_bufsize;

        if (nfsvers == NFS_VER2) {
                if (boff > 0xffffffffLL) {
                        bp->nb_error = error = EFBIG;
                        SET(bp->nb_flags, NB_ERROR);
                        nfs_buf_iodone(bp);
                        return (error);
                }
                if ((boff + length - 1) > 0xffffffffLL)
                        length = 0x100000000LL - boff;
        }

        /* Note: Can only do async I/O if nfsiods are configured. */
        async = (bp->nb_flags & NB_ASYNC);
        cb.rcb_func = async ? nfs_buf_read_rpc_finish : NULL;
        cb.rcb_bp = bp;

        bp->nb_offio = bp->nb_endio = 0;
        bp->nb_rpcs = nrpcs = (length + nmrsize - 1) / nmrsize;
        if (async && (nrpcs > 1)) {
                SET(bp->nb_flags, NB_MULTASYNCRPC);
        } else {
                CLR(bp->nb_flags, NB_MULTASYNCRPC);
        }

        while (length > 0) {
                if (ISSET(bp->nb_flags, NB_ERROR)) {
                        error = bp->nb_error;
                        break;
                }
                len = (length > nmrsize) ? nmrsize : length;
                cb.rcb_args[0] = offset;
                cb.rcb_args[1] = len;
                if (nmp->nm_vers >= NFS_VER4)
                        cb.rcb_args[2] = nmp->nm_stategenid;
                req = NULL;
                error = nmp->nm_funcs->nf_read_rpc_async(np, boff + offset, len, thd, cred, &cb, &req);
                if (error)
                        break;
                offset += len;
                length -= len;
                if (async)
                        continue;
                nfs_buf_read_rpc_finish(req);
                if (ISSET(bp->nb_flags, NB_ERROR)) {
                        error = bp->nb_error;
                        break;
                }
        }

        if (length > 0) {
                /*
                 * Something bad happened while trying to send the RPC(s).
                 * Wait for any outstanding requests to complete.
                 */
                bp->nb_error = error;
                SET(bp->nb_flags, NB_ERROR);
                if (ISSET(bp->nb_flags, NB_MULTASYNCRPC)) {
                        nrpcs = (length + nmrsize - 1) / nmrsize;
                        lck_mtx_lock(nfs_buf_mutex);
                        bp->nb_rpcs -= nrpcs;
                        if (bp->nb_rpcs == 0) {
                                /* No RPCs left, so the buffer's done */
                                lck_mtx_unlock(nfs_buf_mutex);
                                nfs_buf_iodone(bp);
                        } else {
                                /* wait for the last RPC to mark it done */
                                while (bp->nb_rpcs > 0)
                                        msleep(&bp->nb_rpcs, nfs_buf_mutex, 0,
                                                "nfs_buf_read_rpc_cancel", NULL);
                                lck_mtx_unlock(nfs_buf_mutex);
                        }
                } else {
                        nfs_buf_iodone(bp);
                }
        }

        return (error);
}

/*
 * finish up an NFS READ RPC on a buffer
 */
void
nfs_buf_read_rpc_finish(struct nfsreq *req)
{
        struct nfsmount *nmp;
        size_t rlen;
        struct nfsreq_cbinfo cb;
        struct nfsbuf *bp;
        int error = 0, nfsvers, offset, length, eof = 0, multasyncrpc, finished;
        void *wakeme = NULL;
        struct nfsreq *rreq = NULL;
        nfsnode_t np;
        thread_t thd;
        kauth_cred_t cred;
        uio_t auio;
        char uio_buf [ UIO_SIZEOF(1) ];

finish:
        np = req->r_np;
        thd = req->r_thread;
        cred = req->r_cred;
        if (IS_VALID_CRED(cred))
                kauth_cred_ref(cred);
        cb = req->r_callback;
        bp = cb.rcb_bp;
        if (cb.rcb_func) /* take an extra reference on the nfsreq in case we want to resend it later due to grace error */
                nfs_request_ref(req, 0);

        nmp = NFSTONMP(np);
        if (nfs_mount_gone(nmp)) {
                SET(bp->nb_flags, NB_ERROR);
                bp->nb_error = error = ENXIO;
        }
        if (error || ISSET(bp->nb_flags, NB_ERROR)) {
                /* just drop it */
                nfs_request_async_cancel(req);
                goto out;
        }

        nfsvers = nmp->nm_vers;
        offset = cb.rcb_args[0];
        rlen = length = cb.rcb_args[1];

        auio = uio_createwithbuffer(1, NBOFF(bp) + offset, UIO_SYSSPACE,
                                UIO_READ, &uio_buf, sizeof(uio_buf));
        uio_addiov(auio, CAST_USER_ADDR_T(bp->nb_data + offset), length);

        /* finish the RPC */
        error = nmp->nm_funcs->nf_read_rpc_async_finish(np, req, auio, &rlen, &eof);
        if ((error == EINPROGRESS) && cb.rcb_func) {
                /* async request restarted */
                if (cb.rcb_func)
                        nfs_request_rele(req);
                if (IS_VALID_CRED(cred))
                        kauth_cred_unref(&cred);
                return;
        }
        if ((nmp->nm_vers >= NFS_VER4) && nfs_mount_state_error_should_restart(error) && !ISSET(bp->nb_flags, NB_ERROR)) {
                lck_mtx_lock(&nmp->nm_lock);
                if ((error != NFSERR_OLD_STATEID) && (error != NFSERR_GRACE) && (cb.rcb_args[2] == nmp->nm_stategenid)) {
                        NP(np, "nfs_buf_read_rpc_finish: error %d @ 0x%llx, 0x%x 0x%x, initiating recovery",
                                error, NBOFF(bp)+offset, cb.rcb_args[2], nmp->nm_stategenid);
                        nfs_need_recover(nmp, error);
                }
                lck_mtx_unlock(&nmp->nm_lock);
                if (np->n_flag & NREVOKE) {
                        error = EIO;
                } else {
                        if (error == NFSERR_GRACE) {
                                if (cb.rcb_func) {
                                        /*
                                         * For an async I/O request, handle a grace delay just like
                                         * jukebox errors.  Set the resend time and queue it up.
                                         */
                                        struct timeval now;
                                        if (req->r_nmrep.nmc_mhead) {
                                                mbuf_freem(req->r_nmrep.nmc_mhead);
                                                req->r_nmrep.nmc_mhead = NULL;
                                        }
                                        req->r_error = 0;
                                        microuptime(&now);
                                        lck_mtx_lock(&req->r_mtx);
                                        req->r_resendtime = now.tv_sec + 2;
                                        req->r_xid = 0;                 // get a new XID
                                        req->r_flags |= R_RESTART;
                                        req->r_start = 0;
                                        nfs_asyncio_resend(req);
                                        lck_mtx_unlock(&req->r_mtx);
                                        if (IS_VALID_CRED(cred))
                                                kauth_cred_unref(&cred);
                                        /* Note: nfsreq reference taken will be dropped later when finished */
                                        return;
                                }
                                /* otherwise, just pause a couple seconds and retry */
                                tsleep(&nmp->nm_state, (PZERO-1), "nfsgrace", 2*hz);
                        }
                        if (!(error = nfs_mount_state_wait_for_recovery(nmp))) {
                                rlen = 0;
                                goto readagain;
                        }
                }
        }
        if (error) {
                SET(bp->nb_flags, NB_ERROR);
                bp->nb_error = error;
                goto out;
        }

        if ((rlen > 0) && (bp->nb_endio < (offset + (int)rlen)))
                bp->nb_endio = offset + rlen;

        if ((nfsvers == NFS_VER2) || eof || (rlen == 0)) {
                /* zero out the remaining data (up to EOF) */
                off_t rpcrem, eofrem, rem;
                rpcrem = (length - rlen);
                eofrem = np->n_size - (NBOFF(bp) + offset + rlen);
                rem = (rpcrem < eofrem) ? rpcrem : eofrem;
                if (rem > 0)
                        bzero(bp->nb_data + offset + rlen, rem);
        } else if (((int)rlen < length) && !ISSET(bp->nb_flags, NB_ERROR)) {
                /*
                 * short read
                 *
                 * We haven't hit EOF and we didn't get all the data
                 * requested, so we need to issue another read for the rest.
                 * (Don't bother if the buffer already hit an error.)
                 */
readagain:
                offset += rlen;
                length -= rlen;
                cb.rcb_args[0] = offset;
                cb.rcb_args[1] = length;
                if (nmp->nm_vers >= NFS_VER4)
                        cb.rcb_args[2] = nmp->nm_stategenid;
                error = nmp->nm_funcs->nf_read_rpc_async(np, NBOFF(bp) + offset, length, thd, cred, &cb, &rreq);
                if (!error) {
                        if (IS_VALID_CRED(cred))
                                kauth_cred_unref(&cred);
                        if (!cb.rcb_func) {
                                /* if !async we'll need to wait for this RPC to finish */
                                req = rreq;
                                rreq = NULL;
                                goto finish;
                        }
                        nfs_request_rele(req);
                        /*
                         * We're done here.
                         * Outstanding RPC count is unchanged.
                         * Callback will be called when RPC is done.
                         */
                        return;
                }
                SET(bp->nb_flags, NB_ERROR);
                bp->nb_error = error;
        }

out:
        if (cb.rcb_func)
                nfs_request_rele(req);
        if (IS_VALID_CRED(cred))
                kauth_cred_unref(&cred);

        /*
         * Decrement outstanding RPC count on buffer
         * and call nfs_buf_read_finish on last RPC.
         *
         * (Note: when there are multiple async RPCs issued for a
         * buffer we need nfs_buffer_mutex to avoid problems when
         * aborting a partially-initiated set of RPCs)
         */

        multasyncrpc = ISSET(bp->nb_flags, NB_MULTASYNCRPC);
        if (multasyncrpc)
                lck_mtx_lock(nfs_buf_mutex);

        bp->nb_rpcs--;
        finished = (bp->nb_rpcs == 0);

        if (multasyncrpc)
                lck_mtx_unlock(nfs_buf_mutex);

        if (finished) {
                if (multasyncrpc)
                        wakeme = &bp->nb_rpcs;
                nfs_buf_read_finish(bp);
                if (wakeme)
                        wakeup(wakeme);
        }
}

/*
 * Do buffer readahead.
 * Initiate async I/O to read buffers not in cache.
 */
int
nfs_buf_readahead(nfsnode_t np, int ioflag, daddr64_t *rabnp, daddr64_t lastrabn, thread_t thd, kauth_cred_t cred)
{
        struct nfsmount *nmp = NFSTONMP(np);
        struct nfsbuf *bp;
        int error = 0;
        uint32_t nra;

        if (nfs_mount_gone(nmp))
                return (ENXIO);
        if (nmp->nm_readahead <= 0)
                return (0);
        if (*rabnp > lastrabn)
                return (0);

        for (nra = 0; (nra < nmp->nm_readahead) && (*rabnp <= lastrabn); nra++, *rabnp = *rabnp + 1) {
                /* check if block exists and is valid. */
                if ((*rabnp * nmp->nm_biosize) >= (off_t)np->n_size) {
                        /* stop reading ahead if we're beyond EOF */
                        *rabnp = lastrabn;
                        break;
                }
                error = nfs_buf_get(np, *rabnp, nmp->nm_biosize, thd, NBLK_READ|NBLK_NOWAIT, &bp);
                if (error)
                        break;
                nfs_node_lock_force(np);
                np->n_lastrahead = *rabnp;
                nfs_node_unlock(np);
                if (!bp)
                        continue;
                if ((ioflag & IO_NOCACHE) && ISSET(bp->nb_flags, NB_CACHE) &&
                    !bp->nb_dirty && !ISSET(bp->nb_flags, (NB_DELWRI|NB_NCRDAHEAD))) {
                        CLR(bp->nb_flags, NB_CACHE);
                        bp->nb_valid = 0;
                        bp->nb_validoff = bp->nb_validend = -1;
                }
                if ((bp->nb_dirtyend <= 0) && !bp->nb_dirty &&
                    !ISSET(bp->nb_flags, (NB_CACHE|NB_DELWRI))) {
                        SET(bp->nb_flags, (NB_READ|NB_ASYNC));
                        if (ioflag & IO_NOCACHE)
                                SET(bp->nb_flags, NB_NCRDAHEAD);
                        if (!IS_VALID_CRED(bp->nb_rcred) && IS_VALID_CRED(cred)) {
                                kauth_cred_ref(cred);
                                bp->nb_rcred = cred;
                        }
                        if ((error = nfs_buf_read(bp)))
                                break;
                        continue;
                }
                nfs_buf_release(bp, 1);
        }
        return (error);
}

/*
 * NFS buffer I/O for reading files.
 */
int
nfs_bioread(nfsnode_t np, uio_t uio, int ioflag, vfs_context_t ctx)
{
        vnode_t vp = NFSTOV(np);
        struct nfsbuf *bp = NULL;
        struct nfsmount *nmp = VTONMP(vp);
        daddr64_t lbn, rabn = 0, lastrabn, maxrabn = -1;
        off_t diff;
        int error = 0, n = 0, on = 0;
        int nfsvers, biosize, modified, readaheads = 0;
        thread_t thd;
        kauth_cred_t cred;
        int64_t io_resid;

        FSDBG_TOP(514, np, uio_offset(uio), uio_resid(uio), ioflag);

        nfsvers = nmp->nm_vers;
        biosize = nmp->nm_biosize;
        thd = vfs_context_thread(ctx);
        cred = vfs_context_ucred(ctx);

        if (vnode_vtype(vp) != VREG) {
                printf("nfs_bioread: type %x unexpected\n", vnode_vtype(vp));
                FSDBG_BOT(514, np, 0xd1e0016, 0, EINVAL);
                return (EINVAL);
        }

        /*
         * 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.
         * 
         * If the file 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, check for a change, and flush all of the
         * file's data out of the cache.
         * NB: This implies that cache data can be read when up to
         * NFS_MAXATTRTIMO seconds out of date. If you find that you
         * need current attributes, nfs_getattr() can be forced to fetch
         * new attributes (via NATTRINVALIDATE() or NGA_UNCACHED).
         */

        if (ISSET(np->n_flag, NUPDATESIZE))
                nfs_data_update_size(np, 0);

        if ((error = nfs_node_lock(np))) {
                FSDBG_BOT(514, np, 0xd1e0222, 0, error);
                return (error);
        }

        if (np->n_flag & NNEEDINVALIDATE) {
                np->n_flag &= ~NNEEDINVALIDATE;
                nfs_node_unlock(np);
                error = nfs_vinvalbuf(vp, V_SAVE|V_IGNORE_WRITEERR, ctx, 1);
                if (!error)
                        error = nfs_node_lock(np);
                if (error) {
                        FSDBG_BOT(514, np, 0xd1e0322, 0, error);
                        return (error);
                }
        }

        modified = (np->n_flag & NMODIFIED);
        nfs_node_unlock(np);
        /* nfs_getattr() will check changed and purge caches */
        error = nfs_getattr(np, NULL, ctx, modified ? NGA_UNCACHED : NGA_CACHED);
        if (error) {
                FSDBG_BOT(514, np, 0xd1e0004, 0, error);
                return (error);
        }

        if (uio_resid(uio) == 0) {
                FSDBG_BOT(514, np, 0xd1e0001, 0, 0);
                return (0);
        }
        if (uio_offset(uio) < 0) {
                FSDBG_BOT(514, np, 0xd1e0002, 0, EINVAL);
                return (EINVAL);
        }

        /*
         * set up readahead - which may be limited by:
         * + current request length (for IO_NOCACHE)
         * + readahead setting
         * + file size
         */
        if (nmp->nm_readahead > 0) {
                off_t end = uio_offset(uio) + uio_resid(uio);
                if (end > (off_t)np->n_size)
                        end = np->n_size;
                rabn = uio_offset(uio) / biosize;
                maxrabn = (end - 1) / biosize;
                nfs_node_lock_force(np);
                if (!(ioflag & IO_NOCACHE) &&
                    (!rabn || (rabn == np->n_lastread) || (rabn == (np->n_lastread+1)))) {
                        maxrabn += nmp->nm_readahead;
                        if ((maxrabn * biosize) >= (off_t)np->n_size)
                                maxrabn = ((off_t)np->n_size - 1)/biosize;
                }
                if (maxrabn < np->n_lastrahead)
                        np->n_lastrahead = -1;
                if (rabn < np->n_lastrahead)
                        rabn = np->n_lastrahead + 1;
                nfs_node_unlock(np);
        } else {
                rabn = maxrabn = 0;
        }

        do {

                nfs_data_lock(np, NFS_DATA_LOCK_SHARED);
                lbn = uio_offset(uio) / biosize;

                /*
                 * Copy directly from any cached pages without grabbing the bufs.
                 * (If we are NOCACHE and we've issued readahead requests, we need
                 * to grab the NB_NCRDAHEAD bufs to drop them.)
                 */
                if ((!(ioflag & IO_NOCACHE) || !readaheads) &&
                    ((uio->uio_segflg == UIO_USERSPACE32 ||
                      uio->uio_segflg == UIO_USERSPACE64 ||
                      uio->uio_segflg == UIO_USERSPACE))) {
                        io_resid = uio_resid(uio);
                        diff = np->n_size - uio_offset(uio);
                        if (diff < io_resid)
                                io_resid = diff;
                        if (io_resid > 0) {
                                int count = (io_resid > INT_MAX) ? INT_MAX : io_resid;
                                error = cluster_copy_ubc_data(vp, uio, &count, 0);
                                if (error) {
                                        nfs_data_unlock(np);
                                        FSDBG_BOT(514, np, uio_offset(uio), 0xcacefeed, error);
                                        return (error);
                                }
                        }
                        /* count any biocache reads that we just copied directly */
                        if (lbn != (uio_offset(uio)/biosize)) {
                                OSAddAtomic64((uio_offset(uio)/biosize) - lbn, &nfsstats.biocache_reads);
                                FSDBG(514, np, 0xcacefeed, uio_offset(uio), error);
                        }
                }

                lbn = uio_offset(uio) / biosize;
                on = uio_offset(uio) % biosize;
                nfs_node_lock_force(np);
                np->n_lastread = (uio_offset(uio) - 1) / biosize;
                nfs_node_unlock(np);

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

                /* adjust readahead block number, if necessary */
                if (rabn < lbn)
                        rabn = lbn;
                lastrabn = MIN(maxrabn, lbn + nmp->nm_readahead);
                if (rabn <= lastrabn) { /* start readaheads */
                        error = nfs_buf_readahead(np, ioflag, &rabn, lastrabn, thd, cred);
                        if (error) {
                                nfs_data_unlock(np);
                                FSDBG_BOT(514, np, 0xd1e000b, 1, error);
                                return (error);
                        }
                        readaheads = 1;
                }

                OSAddAtomic64(1, &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:
                io_resid = uio_resid(uio);
                n = (io_resid > (biosize - on)) ? (biosize - on) : io_resid;
                diff = np->n_size - uio_offset(uio);
                if (diff < n)
                        n = diff;

                error = nfs_buf_get(np, lbn, biosize, thd, NBLK_READ, &bp);
                if (error) {
                        nfs_data_unlock(np);
                        FSDBG_BOT(514, np, 0xd1e000c, 0, error);
                        return (error);
                }

                if ((ioflag & IO_NOCACHE) && ISSET(bp->nb_flags, NB_CACHE)) {
                        /*
                         * IO_NOCACHE found a cached buffer.
                         * Flush the buffer if it's dirty.
                         * Invalidate the data if it wasn't just read
                         * in as part of a "nocache readahead".
                         */
                        if (bp->nb_dirty || (bp->nb_dirtyend > 0)) {
                                /* so write the buffer out and try again */
                                SET(bp->nb_flags, NB_NOCACHE);
                                goto flushbuffer;
                        }
                        if (ISSET(bp->nb_flags, NB_NCRDAHEAD)) {
                                CLR(bp->nb_flags, NB_NCRDAHEAD);
                                SET(bp->nb_flags, NB_NOCACHE);
                        }
                }

                /* 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)) ||
                            (((firstpg*PAGE_SIZE) < bp->nb_dirtyend) && (((lastpg+1)*PAGE_SIZE) > bp->nb_dirtyoff))) {
                                /* there are also dirty page(s) (or range) in the read range, */
                                /* so write the buffer out and try again */
flushbuffer:
                                CLR(bp->nb_flags, (NB_DONE | NB_ERROR | NB_INVAL));
                                SET(bp->nb_flags, NB_ASYNC);
                                if (!IS_VALID_CRED(bp->nb_wcred)) {
                                        kauth_cred_ref(cred);
                                        bp->nb_wcred = cred;
                                }
                                error = nfs_buf_write(bp);
                                if (error) {
                                        nfs_data_unlock(np);
                                        FSDBG_BOT(514, np, 0xd1e000d, 0, error);
                                        return (error);
                                }
                                goto again;
                        }
                        if (!bp->nb_dirty && bp->nb_dirtyend <= 0 &&
                            (lastpg - firstpg + 1) > (biosize/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_read_rpc(np, auio, ctx);
                                }
                                if (error) {
                                        if (ioflag & IO_NOCACHE)
                                                SET(bp->nb_flags, NB_NOCACHE);
                                        nfs_buf_release(bp, 1);
                                        nfs_data_unlock(np);
                                        FSDBG_BOT(514, np, 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) {
                        if (!IS_VALID_CRED(bp->nb_rcred) && IS_VALID_CRED(cred)) {
                                kauth_cred_ref(cred);
                                bp->nb_rcred = cred;
                        }
                        SET(bp->nb_flags, NB_READ);
                        CLR(bp->nb_flags, (NB_DONE | NB_ERROR | NB_INVAL));
                        error = nfs_buf_read(bp);
                        if (ioflag & IO_NOCACHE)
                                SET(bp->nb_flags, NB_NOCACHE);
                        if (error) {
                                nfs_data_unlock(np);
                                nfs_buf_release(bp, 1);
                                FSDBG_BOT(514, np, 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);
                        error = uiomove(bp->nb_data + on, n, uio);
                }

                nfs_buf_release(bp, 1);
                nfs_data_unlock(np);
                nfs_node_lock_force(np);
                np->n_lastread = (uio_offset(uio) - 1) / biosize;
                nfs_node_unlock(np);
        } while (error == 0 && uio_resid(uio) > 0 && n > 0);
        FSDBG_BOT(514, np, uio_offset(uio), uio_resid(uio), error);
        return (error);
}

/*
 * limit the number of outstanding async I/O writes
 */
int
nfs_async_write_start(struct nfsmount *nmp)
{
        int error = 0, slpflag = NMFLAG(nmp, INTR) ? PCATCH : 0;
        struct timespec ts = {1, 0};

        if (nfs_max_async_writes <= 0)
                return (0);
        lck_mtx_lock(&nmp->nm_lock);
        while ((nfs_max_async_writes > 0) && (nmp->nm_asyncwrites >= nfs_max_async_writes)) {
                if ((error = nfs_sigintr(nmp, NULL, current_thread(), 1)))
                        break;
                msleep(&nmp->nm_asyncwrites, &nmp->nm_lock, slpflag|(PZERO-1), "nfsasyncwrites", &ts);
                slpflag = 0;
        }
        if (!error)
                nmp->nm_asyncwrites++;
        lck_mtx_unlock(&nmp->nm_lock);
        return (error);
}
void
nfs_async_write_done(struct nfsmount *nmp)
{
        if (nmp->nm_asyncwrites <= 0)
                return;
        lck_mtx_lock(&nmp->nm_lock);
        if (nmp->nm_asyncwrites-- >= nfs_max_async_writes)
                wakeup(&nmp->nm_asyncwrites);
        lck_mtx_unlock(&nmp->nm_lock);
}

/*
 * write (or commit) the given NFS buffer
 *
 * Commit the buffer if we can.
 * Write out any dirty range.
 * If any dirty pages remain, write them out.
 * Mark buffer done.
 *
 * For async requests, all the work beyond sending the initial
 * write RPC is handled in the RPC callback(s).
 */
int
nfs_buf_write(struct nfsbuf *bp)
{
        int error = 0, oldflags, async;
        nfsnode_t np;
        thread_t thd;
        kauth_cred_t cred;
        proc_t p = current_proc();
        int iomode, doff, dend, firstpg, lastpg;
        uint32_t pagemask;

        FSDBG_TOP(553, bp, NBOFF(bp), bp->nb_flags, 0);

        if (!ISSET(bp->nb_lflags, NBL_BUSY))
                panic("nfs_buf_write: buffer is not busy???");

        np = bp->nb_np;
        async = ISSET(bp->nb_flags, NB_ASYNC);
        oldflags = bp->nb_flags;

        CLR(bp->nb_flags, (NB_READ|NB_DONE|NB_ERROR|NB_DELWRI));
        if (ISSET(oldflags, NB_DELWRI)) {
                lck_mtx_lock(nfs_buf_mutex);
                nfs_nbdwrite--;
                NFSBUFCNTCHK();
                lck_mtx_unlock(nfs_buf_mutex);
                wakeup(&nfs_nbdwrite);
        }

        /* move to clean list */
        if (ISSET(oldflags, (NB_ASYNC|NB_DELWRI))) {
                lck_mtx_lock(nfs_buf_mutex);
                if (bp->nb_vnbufs.le_next != NFSNOLIST)
                        LIST_REMOVE(bp, nb_vnbufs);
                LIST_INSERT_HEAD(&np->n_cleanblkhd, bp, nb_vnbufs);
                lck_mtx_unlock(nfs_buf_mutex);
        }
        nfs_node_lock_force(np);
        np->n_numoutput++;
        nfs_node_unlock(np);
        vnode_startwrite(NFSTOV(np));

        if (p && p->p_stats)
                OSIncrementAtomicLong(&p->p_stats->p_ru.ru_oublock);

        cred = bp->nb_wcred;
        if (!IS_VALID_CRED(cred) && ISSET(bp->nb_flags, NB_READ))
                cred = bp->nb_rcred;  /* shouldn't really happen, but... */
        if (IS_VALID_CRED(cred))
                kauth_cred_ref(cred);
        thd = async ? NULL : current_thread();

        /* We need to make sure the pages are locked before doing I/O.  */
        if (!ISSET(bp->nb_flags, NB_META)) {
                if (UBCINFOEXISTS(NFSTOV(np))) {
                        if (!ISSET(bp->nb_flags, NB_PAGELIST)) {
                                error = nfs_buf_upl_setup(bp);
                                if (error) {
                                        printf("nfs_buf_write: upl create failed %d\n", error);
                                        SET(bp->nb_flags, NB_ERROR);
                                        bp->nb_error = error = EIO;
                                        nfs_buf_iodone(bp);
                                        goto out;
                                }
                                nfs_buf_upl_check(bp);
                        }
                } else {
                        /* We should never be in nfs_buf_write() with no UBCINFO. */
                        printf("nfs_buf_write: ubcinfo already gone\n");
                        SET(bp->nb_flags, NB_ERROR);
                        bp->nb_error = error = EIO;
                        nfs_buf_iodone(bp);
                        goto out;
                }
        }

        /* If NB_NEEDCOMMIT is set, a commit RPC may do the trick. */
        if (ISSET(bp->nb_flags, NB_NEEDCOMMIT))
                nfs_buf_check_write_verifier(np, bp);
        if (ISSET(bp->nb_flags, NB_NEEDCOMMIT)) {
                struct nfsmount *nmp = NFSTONMP(np);
                if (nfs_mount_gone(nmp)) {
                        SET(bp->nb_flags, NB_ERROR);
                        bp->nb_error = error = EIO;
                        nfs_buf_iodone(bp);
                        goto out;
                }
                SET(bp->nb_flags, NB_WRITEINPROG);
                error = nmp->nm_funcs->nf_commit_rpc(np, NBOFF(bp) + bp->nb_dirtyoff,
                                bp->nb_dirtyend - bp->nb_dirtyoff, bp->nb_wcred, bp->nb_verf);
                CLR(bp->nb_flags, NB_WRITEINPROG);
                if (error) {
                        if (error != NFSERR_STALEWRITEVERF) {
                                SET(bp->nb_flags, NB_ERROR);
                                bp->nb_error = error;
                        }
                        nfs_buf_iodone(bp);
                        goto out;
                }
                bp->nb_dirtyoff = bp->nb_dirtyend = 0;
                CLR(bp->nb_flags, NB_NEEDCOMMIT);
                nfs_node_lock_force(np);
                np->n_needcommitcnt--;
                CHECK_NEEDCOMMITCNT(np);
                nfs_node_unlock(np);
        }
        if (!error && (bp->nb_dirtyend > 0)) {
                /* sanity check the dirty range */
                if (NBOFF(bp) + bp->nb_dirtyend > (off_t) np->n_size) {
                        bp->nb_dirtyend = np->n_size - NBOFF(bp);
                        if (bp->nb_dirtyoff >= bp->nb_dirtyend)
                                bp->nb_dirtyoff = bp->nb_dirtyend = 0;
                }
        }
        if (!error && (bp->nb_dirtyend > 0)) {
                /* there's a dirty range that needs to be written out */
                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 < (int)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/stable; otherwise write FILESYNC
                 */
                if (bp->nb_dirty & ~pagemask)
                        iomode = NFS_WRITE_FILESYNC;
                else if ((bp->nb_flags & (NB_ASYNC | NB_NEEDCOMMIT | NB_STABLE)) == NB_ASYNC)
                        iomode = NFS_WRITE_UNSTABLE;
                else
                        iomode = NFS_WRITE_FILESYNC;

                /* write the whole contiguous dirty range */
                bp->nb_offio = doff;
                bp->nb_endio = dend;

                OSAddAtomic64(1, &nfsstats.write_bios);

                SET(bp->nb_flags, NB_WRITEINPROG);
                error = nfs_buf_write_rpc(bp, iomode, thd, cred);
                /*
                 * For async I/O, the callbacks will finish up the
                 * write and push out any dirty pages.  Otherwise,
                 * the write has already been finished and any dirty
                 * pages pushed out.
                 */
        } else {
                if (!error && bp->nb_dirty) /* write out any dirty pages */
                        error = nfs_buf_write_dirty_pages(bp, thd, cred);
                nfs_buf_iodone(bp);
        }
        /* note: bp is still valid only for !async case */
out:
        if (!async) {
                error = nfs_buf_iowait(bp);
                /* move to clean list */
                if (oldflags & NB_DELWRI) {
                        lck_mtx_lock(nfs_buf_mutex);
                        if (bp->nb_vnbufs.le_next != NFSNOLIST)
                                LIST_REMOVE(bp, nb_vnbufs);
                        LIST_INSERT_HEAD(&np->n_cleanblkhd, bp, nb_vnbufs);
                        lck_mtx_unlock(nfs_buf_mutex);
                }
                FSDBG_BOT(553, bp, NBOFF(bp), bp->nb_flags, error);
                nfs_buf_release(bp, 1);
                /* check if we need to invalidate (and we can) */
                if ((np->n_flag & NNEEDINVALIDATE) &&
                    !(np->n_bflag & (NBINVALINPROG|NBFLUSHINPROG))) {
                        int invalidate = 0;
                        nfs_node_lock_force(np);
                        if (np->n_flag & NNEEDINVALIDATE) {
                                invalidate = 1;
                                np->n_flag &= ~NNEEDINVALIDATE;
                        }
                        nfs_node_unlock(np);
                        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.
                                 */
                                nfs_vinvalbuf2(NFSTOV(np), V_SAVE|V_IGNORE_WRITEERR, thd, cred, 1);
                        }
                }
        }

        if (IS_VALID_CRED(cred))
                kauth_cred_unref(&cred);
        return (error);
}

/*
 * finish the writing of a buffer
 */
void
nfs_buf_write_finish(struct nfsbuf *bp, thread_t thd, kauth_cred_t cred)
{
        nfsnode_t np = bp->nb_np;
        int error = (bp->nb_flags & NB_ERROR) ? bp->nb_error : 0;
        int firstpg, lastpg;
        uint32_t pagemask;

        if ((error == EINTR) || (error == ERESTART)) {
                CLR(bp->nb_flags, NB_ERROR);
                SET(bp->nb_flags, NB_EINTR);
        }

        if (!error) {
                /* calculate range of complete pages being written */
                firstpg = round_page_32(bp->nb_offio) / PAGE_SIZE;
                lastpg = (trunc_page_32(bp->nb_endio) - 1) / PAGE_SIZE;
                /* calculate mask for that page range written */
                pagemask = ((1 << (lastpg + 1)) - 1) & ~((1 << firstpg) - 1);
                /* clear dirty bits for pages we've written */
                bp->nb_dirty &= ~pagemask;
        }

        /* manage needcommit state */
        if (!error && (bp->nb_commitlevel == NFS_WRITE_UNSTABLE)) {
                if (!ISSET(bp->nb_flags, NB_NEEDCOMMIT)) {
                        nfs_node_lock_force(np);
                        np->n_needcommitcnt++;
                        nfs_node_unlock(np);
                        SET(bp->nb_flags, NB_NEEDCOMMIT);
                }
                /* make sure nb_dirtyoff/nb_dirtyend reflect actual range written */
                bp->nb_dirtyoff = bp->nb_offio;
                bp->nb_dirtyend = bp->nb_endio;
        } else if (ISSET(bp->nb_flags, NB_NEEDCOMMIT)) {
                nfs_node_lock_force(np);
                np->n_needcommitcnt--;
                CHECK_NEEDCOMMITCNT(np);
                nfs_node_unlock(np);
                CLR(bp->nb_flags, NB_NEEDCOMMIT);
        }

        CLR(bp->nb_flags, NB_WRITEINPROG);

        /*
         * For an unstable write, the buffer is still treated as dirty until
         * a commit (or stable (re)write) is performed.  Buffers needing only
         * a commit are marked with the NB_DELWRI and NB_NEEDCOMMIT flags.
         *
         * If the write was interrupted we set NB_EINTR.  Don't set NB_ERROR
         * because that would cause the buffer to be dropped.  The buffer is
         * still valid and simply needs to be written again.
         */
        if ((error == EINTR) || (error == ERESTART) || (!error && (bp->nb_flags & NB_NEEDCOMMIT))) {
                CLR(bp->nb_flags, NB_INVAL);
                if (!ISSET(bp->nb_flags, NB_DELWRI)) {
                        SET(bp->nb_flags, NB_DELWRI);
                        lck_mtx_lock(nfs_buf_mutex);
                        nfs_nbdwrite++;
                        NFSBUFCNTCHK();
                        lck_mtx_unlock(nfs_buf_mutex);
                }
                /*
                 * Since for the NB_ASYNC case, we've 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 {
                /* either there's an error or we don't need to commit */
                if (error) {
                        /*
                         * 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.
                         */
                        nfs_node_lock_force(np);
                        np->n_error = error;
                        np->n_flag |= (NWRITEERR | NNEEDINVALIDATE);
                        NATTRINVALIDATE(np);
                        nfs_node_unlock(np);
                }
                /* clear the dirty range */
                bp->nb_dirtyoff = bp->nb_dirtyend = 0;
        }

        if (!error && bp->nb_dirty)
                nfs_buf_write_dirty_pages(bp, thd, cred);
        nfs_buf_iodone(bp);
}

/*
 * write out any pages marked dirty in a buffer
 *
 * We do use unstable writes and follow up with a commit.
 * If we catch the write verifier changing we'll restart
 * do the writes filesync.
 */
int
nfs_buf_write_dirty_pages(struct nfsbuf *bp, thread_t thd, kauth_cred_t cred)
{
        nfsnode_t np = bp->nb_np;
        struct nfsmount *nmp = NFSTONMP(np);
        int error = 0, commit, iomode, iomode2, len, pg, count, npages, off;
        uint32_t dirty = bp->nb_dirty;
        uint64_t wverf;
        uio_t auio;
        char uio_buf [ UIO_SIZEOF(1) ];

        if (!bp->nb_dirty)
                return (0);

        /* there are pages marked dirty that need to be written out */
        OSAddAtomic64(1, &nfsstats.write_bios);
        NFS_BUF_MAP(bp);
        SET(bp->nb_flags, NB_WRITEINPROG);
        npages = bp->nb_bufsize / PAGE_SIZE;
        iomode = NFS_WRITE_UNSTABLE;

        auio = uio_createwithbuffer(1, 0, UIO_SYSSPACE, UIO_WRITE,
                &uio_buf, sizeof(uio_buf));

again:
        dirty = bp->nb_dirty;
        wverf = bp->nb_verf;
        commit = NFS_WRITE_FILESYNC;
        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) {
                        iomode2 = iomode;
                        uio_reset(auio, NBOFF(bp) + off, UIO_SYSSPACE, UIO_WRITE);
                        uio_addiov(auio, CAST_USER_ADDR_T(bp->nb_data + off), len);
                        error = nfs_write_rpc2(np, auio, thd, cred, &iomode2, &bp->nb_verf);
                        if (error)
                                break;
                        if (iomode2 < commit) /* Retain the lowest commitment level returned. */
                                commit = iomode2;
                        if ((commit != NFS_WRITE_FILESYNC) && (wverf != bp->nb_verf)) {
                                /* verifier changed, redo all the writes filesync */
                                iomode = NFS_WRITE_FILESYNC;
                                goto again;
                        }
                }
                /* clear dirty bits */
                while (count--) {
                        dirty &= ~(1 << pg);
                        if (count) /* leave pg on last page */
                                pg++;
                }
        }
        CLR(bp->nb_flags, NB_WRITEINPROG);

        if (!error && (commit != NFS_WRITE_FILESYNC)) {
                error = nmp->nm_funcs->nf_commit_rpc(np, NBOFF(bp), bp->nb_bufsize, cred, wverf);
                if (error == NFSERR_STALEWRITEVERF) {
                        /* verifier changed, so we need to restart all the writes */
                        iomode = NFS_WRITE_FILESYNC;
                        goto again;
                }
        }
        if (!error) {
                bp->nb_dirty = dirty;
        } else {
                SET(bp->nb_flags, NB_ERROR);
                bp->nb_error = error;
        }
        return (error);
}

/*
 * initiate the NFS WRITE RPC(s) for a buffer
 */
int
nfs_buf_write_rpc(struct nfsbuf *bp, int iomode, thread_t thd, kauth_cred_t cred)
{
        struct nfsmount *nmp;
        nfsnode_t np = bp->nb_np;
        int error = 0, nfsvers, async;
        int offset, nrpcs;
        uint32_t nmwsize, length, len;
        struct nfsreq *req;
        struct nfsreq_cbinfo cb;
        uio_t auio;
        char uio_buf [ UIO_SIZEOF(1) ];

        nmp = NFSTONMP(np);
        if (nfs_mount_gone(nmp)) {
                bp->nb_error = error = ENXIO;
                SET(bp->nb_flags, NB_ERROR);
                nfs_buf_iodone(bp);
                return (error);
        }
        nfsvers = nmp->nm_vers;
        nmwsize = nmp->nm_wsize;

        offset = bp->nb_offio;
        length = bp->nb_endio - bp->nb_offio;

        /* Note: Can only do async I/O if nfsiods are configured. */
        async = (bp->nb_flags & NB_ASYNC) && (NFSIOD_MAX > 0);
        bp->nb_commitlevel = NFS_WRITE_FILESYNC;
        cb.rcb_func = async ? nfs_buf_write_rpc_finish : NULL;
        cb.rcb_bp = bp;

        if ((nfsvers == NFS_VER2) && ((NBOFF(bp) + bp->nb_endio) > 0xffffffffLL)) {
                bp->nb_error = error = EFBIG;
                SET(bp->nb_flags, NB_ERROR);
                nfs_buf_iodone(bp);
                return (error);
        }

        auio = uio_createwithbuffer(1, NBOFF(bp) + offset, UIO_SYSSPACE,
                UIO_WRITE, &uio_buf, sizeof(uio_buf));
        uio_addiov(auio, CAST_USER_ADDR_T(bp->nb_data + offset), length);

        bp->nb_rpcs = nrpcs = (length + nmwsize - 1) / nmwsize;
        if (async && (nrpcs > 1)) {
                SET(bp->nb_flags, NB_MULTASYNCRPC);
        } else {
                CLR(bp->nb_flags, NB_MULTASYNCRPC);
        }

        while (length > 0) {
                if (ISSET(bp->nb_flags, NB_ERROR)) {
                        error = bp->nb_error;
                        break;
                }
                len = (length > nmwsize) ? nmwsize : length;
                cb.rcb_args[0] = offset;
                cb.rcb_args[1] = len;
                if (nmp->nm_vers >= NFS_VER4)
                        cb.rcb_args[2] = nmp->nm_stategenid;
                if (async && ((error = nfs_async_write_start(nmp))))
                        break;
                req = NULL;
                error = nmp->nm_funcs->nf_write_rpc_async(np, auio, len, thd, cred,
                                iomode, &cb, &req);
                if (error) {
                        if (async)
                                nfs_async_write_done(nmp);
                        break;
                }
                offset += len;
                length -= len;
                if (async)
                        continue;
                nfs_buf_write_rpc_finish(req);
        }

        if (length > 0) {
                /*
                 * Something bad happened while trying to send the RPCs.
                 * Wait for any outstanding requests to complete.
                 */
                bp->nb_error = error;
                SET(bp->nb_flags, NB_ERROR);
                if (ISSET(bp->nb_flags, NB_MULTASYNCRPC)) {
                        nrpcs = (length + nmwsize - 1) / nmwsize;
                        lck_mtx_lock(nfs_buf_mutex);
                        bp->nb_rpcs -= nrpcs;
                        if (bp->nb_rpcs == 0) {
                                /* No RPCs left, so the buffer's done */
                                lck_mtx_unlock(nfs_buf_mutex);
                                nfs_buf_write_finish(bp, thd, cred);
                        } else {
                                /* wait for the last RPC to mark it done */
                                while (bp->nb_rpcs > 0)
                                        msleep(&bp->nb_rpcs, nfs_buf_mutex, 0,
                                                "nfs_buf_write_rpc_cancel", NULL);
                                lck_mtx_unlock(nfs_buf_mutex);
                        }
                } else {
                        nfs_buf_write_finish(bp, thd, cred);
                }
                /* It may have just been an interrupt... that's OK */
                if (!ISSET(bp->nb_flags, NB_ERROR))
                        error = 0;
        }

        return (error);
}

/*
 * finish up an NFS WRITE RPC on a buffer
 */
void
nfs_buf_write_rpc_finish(struct nfsreq *req)
{
        int error = 0, nfsvers, offset, length, multasyncrpc, finished;
        int committed = NFS_WRITE_FILESYNC;
        uint64_t wverf = 0;
        size_t rlen;
        void *wakeme = NULL;
        struct nfsreq_cbinfo cb;
        struct nfsreq *wreq = NULL;
        struct nfsbuf *bp;
        struct nfsmount *nmp;
        nfsnode_t np;
        thread_t thd;
        kauth_cred_t cred;
        uio_t auio;
        char uio_buf [ UIO_SIZEOF(1) ];

finish:
        np = req->r_np;
        thd = req->r_thread;
        cred = req->r_cred;
        if (IS_VALID_CRED(cred))
                kauth_cred_ref(cred);
        cb = req->r_callback;
        bp = cb.rcb_bp;
        if (cb.rcb_func) /* take an extra reference on the nfsreq in case we want to resend it later due to grace error */
                nfs_request_ref(req, 0);

        nmp = NFSTONMP(np);
        if (nfs_mount_gone(nmp)) {
                SET(bp->nb_flags, NB_ERROR);
                bp->nb_error = error = ENXIO;
        }
        if (error || ISSET(bp->nb_flags, NB_ERROR)) {
                /* just drop it */
                nfs_request_async_cancel(req);
                goto out;
        }
        nfsvers = nmp->nm_vers;

        offset = cb.rcb_args[0];
        rlen = length = cb.rcb_args[1];

        /* finish the RPC */
        error = nmp->nm_funcs->nf_write_rpc_async_finish(np, req, &committed, &rlen, &wverf);
        if ((error == EINPROGRESS) && cb.rcb_func) {
                /* async request restarted */
                if (cb.rcb_func)
                        nfs_request_rele(req);
                if (IS_VALID_CRED(cred))
                        kauth_cred_unref(&cred);
                return;
        }
        if ((nmp->nm_vers >= NFS_VER4) && nfs_mount_state_error_should_restart(error) && !ISSET(bp->nb_flags, NB_ERROR)) {
                lck_mtx_lock(&nmp->nm_lock);
                if ((error != NFSERR_OLD_STATEID) && (error != NFSERR_GRACE) && (cb.rcb_args[2] == nmp->nm_stategenid)) {
                        NP(np, "nfs_buf_write_rpc_finish: error %d @ 0x%llx, 0x%x 0x%x, initiating recovery",
                                error, NBOFF(bp)+offset, cb.rcb_args[2], nmp->nm_stategenid);
                        nfs_need_recover(nmp, error);
                }
                lck_mtx_unlock(&nmp->nm_lock);
                if (np->n_flag & NREVOKE) {
                        error = EIO;
                } else {
                        if (error == NFSERR_GRACE) {
                                if (cb.rcb_func) {
                                        /*
                                         * For an async I/O request, handle a grace delay just like
                                         * jukebox errors.  Set the resend time and queue it up.
                                         */
                                        struct timeval now;
                                        if (req->r_nmrep.nmc_mhead) {
                                                mbuf_freem(req->r_nmrep.nmc_mhead);
                                                req->r_nmrep.nmc_mhead = NULL;
                                        }
                                        req->r_error = 0;
                                        microuptime(&now);
                                        lck_mtx_lock(&req->r_mtx);
                                        req->r_resendtime = now.tv_sec + 2;
                                        req->r_xid = 0;                 // get a new XID
                                        req->r_flags |= R_RESTART;
                                        req->r_start = 0;
                                        nfs_asyncio_resend(req);
                                        lck_mtx_unlock(&req->r_mtx);
                                        if (IS_VALID_CRED(cred))
                                                kauth_cred_unref(&cred);
                                        /* Note: nfsreq reference taken will be dropped later when finished */
                                        return;
                                }
                                /* otherwise, just pause a couple seconds and retry */
                                tsleep(&nmp->nm_state, (PZERO-1), "nfsgrace", 2*hz);
                        }
                        if (!(error = nfs_mount_state_wait_for_recovery(nmp))) {
                                rlen = 0;
                                goto writeagain;
                        }
                }
        }
        if (error) {
                SET(bp->nb_flags, NB_ERROR);
                bp->nb_error = error;
        }
        if (error || (nfsvers == NFS_VER2))
                goto out;
        if (rlen <= 0) {
                SET(bp->nb_flags, NB_ERROR);
                bp->nb_error = error = EIO;
                goto out;
        }

        /* save lowest commit level returned */
        if (committed < bp->nb_commitlevel)
                bp->nb_commitlevel = committed;

        /* check the write verifier */
        if (!bp->nb_verf) {
                bp->nb_verf = wverf;
        } else if (bp->nb_verf != wverf) {
                /* verifier changed, so buffer will need to be rewritten */
                bp->nb_flags |= NB_STALEWVERF;
                bp->nb_commitlevel = NFS_WRITE_UNSTABLE;
                bp->nb_verf = wverf;
        }

        /*
         * check for a short write
         *
         * If the server didn't write all the data, then we
         * need to issue another write for the rest of it.
         * (Don't bother if the buffer hit an error or stale wverf.)
         */
        if (((int)rlen < length) && !(bp->nb_flags & (NB_STALEWVERF|NB_ERROR))) {
writeagain:
                offset += rlen;
                length -= rlen;

                auio = uio_createwithbuffer(1, NBOFF(bp) + offset, UIO_SYSSPACE,
                        UIO_WRITE, &uio_buf, sizeof(uio_buf));
                uio_addiov(auio, CAST_USER_ADDR_T(bp->nb_data + offset), length);

                cb.rcb_args[0] = offset;
                cb.rcb_args[1] = length;
                if (nmp->nm_vers >= NFS_VER4)
                        cb.rcb_args[2] = nmp->nm_stategenid;

                // XXX iomode should really match the original request
                error = nmp->nm_funcs->nf_write_rpc_async(np, auio, length, thd, cred,
                                NFS_WRITE_FILESYNC, &cb, &wreq);
                if (!error) {
                        if (IS_VALID_CRED(cred))
                                kauth_cred_unref(&cred);
                        if (!cb.rcb_func) {
                                /* if !async we'll need to wait for this RPC to finish */
                                req = wreq;
                                wreq = NULL;
                                goto finish;
                        }
                        nfs_request_rele(req);
                        /*
                         * We're done here.
                         * Outstanding RPC count is unchanged.
                         * Callback will be called when RPC is done.
                         */
                        return;
                }
                SET(bp->nb_flags, NB_ERROR);
                bp->nb_error = error;
        }

out:
        if (cb.rcb_func) {
                nfs_async_write_done(nmp);
                nfs_request_rele(req);
        }
        /*
         * Decrement outstanding RPC count on buffer
         * and call nfs_buf_write_finish on last RPC.
         *
         * (Note: when there are multiple async RPCs issued for a
         * buffer we need nfs_buffer_mutex to avoid problems when
         * aborting a partially-initiated set of RPCs)
         */
        multasyncrpc = ISSET(bp->nb_flags, NB_MULTASYNCRPC);
        if (multasyncrpc)
                lck_mtx_lock(nfs_buf_mutex);

        bp->nb_rpcs--;
        finished = (bp->nb_rpcs == 0);

        if (multasyncrpc)
                lck_mtx_unlock(nfs_buf_mutex);

        if (finished) {
                if (multasyncrpc)
                        wakeme = &bp->nb_rpcs;
                nfs_buf_write_finish(bp, thd, cred);
                if (wakeme)
                        wakeup(wakeme);
        }

        if (IS_VALID_CRED(cred))
                kauth_cred_unref(&cred);
}

/*
 * Send commit(s) for the given node's "needcommit" buffers 
 */
int
nfs_flushcommits(nfsnode_t np, int nowait)
{
        struct nfsmount *nmp;
        struct nfsbuf *bp, *prevlbp, *lbp;
        struct nfsbuflists blist, commitlist;
        int error = 0, retv, wcred_set, flags, dirty;
        u_quad_t off, endoff, toff;
        uint64_t wverf;
        u_int32_t count;
        kauth_cred_t wcred = NULL;

        FSDBG_TOP(557, np, 0, 0, 0);

        /*
         * A nb_flags == (NB_DELWRI | NB_NEEDCOMMIT) block has been written to the
         * server, but nas not been committed to stable storage on the server
         * yet. The byte range is worked out for as many nfsbufs as we can handle
         * and the commit rpc is done.
         */
        if (!LIST_EMPTY(&np->n_dirtyblkhd)) {
                error = nfs_node_lock(np);
                if (error)
                        goto done;
                np->n_flag |= NMODIFIED;
                nfs_node_unlock(np);
        }

        off = (u_quad_t)-1;
        endoff = 0;
        wcred_set = 0;
        LIST_INIT(&commitlist);

        nmp = NFSTONMP(np);
        if (nfs_mount_gone(nmp)) {
                error = ENXIO;
                goto done;
        }
        if (nmp->nm_vers == NFS_VER2) {
                error = EINVAL;
                goto done;
        }

        flags = NBI_DIRTY;
        if (nowait)
                flags |= NBI_NOWAIT;
        lck_mtx_lock(nfs_buf_mutex);
        wverf = nmp->nm_verf;
        if (!nfs_buf_iterprepare(np, &blist, flags)) {
                while ((bp = LIST_FIRST(&blist))) {
                        LIST_REMOVE(bp, nb_vnbufs);
                        LIST_INSERT_HEAD(&np->n_dirtyblkhd, bp, nb_vnbufs);
                        error = nfs_buf_acquire(bp, NBAC_NOWAIT, 0, 0);
                        if (error)
                                continue;
                        if (ISSET(bp->nb_flags, NB_NEEDCOMMIT))
                                nfs_buf_check_write_verifier(np, bp);
                        if (((bp->nb_flags & (NB_DELWRI | NB_NEEDCOMMIT)) != (NB_DELWRI | NB_NEEDCOMMIT)) ||
                            (bp->nb_verf != wverf)) {
                                nfs_buf_drop(bp);
                                continue;
                        }
                        nfs_buf_remfree(bp);

                        /* buffer UPLs will be grabbed *in order* below */

                        FSDBG(557, bp, bp->nb_flags, bp->nb_valid, bp->nb_dirty);
                        FSDBG(557, bp->nb_validoff, bp->nb_validend,
                              bp->nb_dirtyoff, bp->nb_dirtyend);

                        /*
                         * Work out if all buffers are using the same cred
                         * so we can deal with them all with one commit.
                         *
                         * Note: creds in bp's must be obtained by kauth_cred_ref
                         * on the same original cred in order for them to be equal.
                         */
                        if (wcred_set == 0) {
                                wcred = bp->nb_wcred;
                                if (!IS_VALID_CRED(wcred))
                                        panic("nfs: needcommit w/out wcred");
                                wcred_set = 1;
                        } else if ((wcred_set == 1) && wcred != bp->nb_wcred) {
                                wcred_set = -1;
                        }
                        SET(bp->nb_flags, NB_WRITEINPROG);

                        /*
                         * Add this buffer to the list of buffers we are committing.
                         * Buffers are inserted into the list in ascending order so that
                         * we can take the UPLs in order after the list is complete.
                         */
                        prevlbp = NULL;
                        LIST_FOREACH(lbp, &commitlist, nb_vnbufs) {
                                if (bp->nb_lblkno < lbp->nb_lblkno)
                                        break;
                                prevlbp = lbp;
                        }
                        LIST_REMOVE(bp, nb_vnbufs);
                        if (prevlbp)
                                LIST_INSERT_AFTER(prevlbp, bp, nb_vnbufs);
                        else
                                LIST_INSERT_HEAD(&commitlist, bp, nb_vnbufs);

                        /* update commit range start, end */
                        toff = NBOFF(bp) + bp->nb_dirtyoff;
                        if (toff < off)
                                off = toff;
                        toff += (u_quad_t)(bp->nb_dirtyend - bp->nb_dirtyoff);
                        if (toff > endoff)
                                endoff = toff;
                }
                nfs_buf_itercomplete(np, &blist, NBI_DIRTY);
        }
        lck_mtx_unlock(nfs_buf_mutex);

        if (LIST_EMPTY(&commitlist)) {
                error = ENOBUFS;
                goto done;
        }

        /*
         * We need a UPL to prevent others from accessing the buffers during
         * our commit RPC(s).
         *
         * We used to also check for dirty pages here; if there were any we'd
         * abort the commit and force the entire buffer to be written again.
         * Instead of doing that, we just go ahead and commit the dirty range,
         * and then leave the buffer around with dirty pages that will be
         * written out later.
         */
        LIST_FOREACH(bp, &commitlist, nb_vnbufs) {
                if (!ISSET(bp->nb_flags, NB_PAGELIST)) {
                        retv = nfs_buf_upl_setup(bp);
                        if (retv) {
                                /* Unable to create the UPL, the VM object probably no longer exists. */
                                printf("nfs_flushcommits: upl create failed %d\n", retv);
                                bp->nb_valid = bp->nb_dirty = 0;
                        }
                }
                nfs_buf_upl_check(bp);
        }

        /*
         * Commit data on the server, as required.
         * If all bufs are using the same wcred, then use that with
         * one call for all of them, otherwise commit each one
         * separately.
         */
        if (wcred_set == 1) {
                /*
                 * Note, it's possible the commit range could be >2^32-1.
                 * If it is, we'll send one commit that covers the whole file.
                 */
                if ((endoff - off) > 0xffffffff)
                        count = 0;
                else
                        count = (endoff - off);
                retv = nmp->nm_funcs->nf_commit_rpc(np, off, count, wcred, wverf);
        } else {
                retv = 0;
                LIST_FOREACH(bp, &commitlist, nb_vnbufs) {
                        toff = NBOFF(bp) + bp->nb_dirtyoff;
                        count = bp->nb_dirtyend - bp->nb_dirtyoff;
                        retv = nmp->nm_funcs->nf_commit_rpc(np, toff, count, bp->nb_wcred, wverf);
                        if (retv)
                                break;
                }
        }

        /*
         * Now, either mark the blocks I/O done or mark the
         * blocks dirty, depending on whether the commit
         * succeeded.
         */
        while ((bp = LIST_FIRST(&commitlist))) {
                LIST_REMOVE(bp, nb_vnbufs);
                FSDBG(557, bp, retv, bp->nb_flags, bp->nb_dirty);
                nfs_node_lock_force(np);
                CLR(bp->nb_flags, (NB_NEEDCOMMIT | NB_WRITEINPROG));
                np->n_needcommitcnt--;
                CHECK_NEEDCOMMITCNT(np);
                nfs_node_unlock(np);

                if (retv) {
                        /* move back to dirty list */
                        lck_mtx_lock(nfs_buf_mutex);
                        LIST_INSERT_HEAD(&np->n_dirtyblkhd, bp, nb_vnbufs);
                        lck_mtx_unlock(nfs_buf_mutex);
                        nfs_buf_release(bp, 1);
                        continue;
                }

                nfs_node_lock_force(np);
                np->n_numoutput++;
                nfs_node_unlock(np);
                vnode_startwrite(NFSTOV(np));
                if (ISSET(bp->nb_flags, NB_DELWRI)) {
                        lck_mtx_lock(nfs_buf_mutex);
                        nfs_nbdwrite--;
                        NFSBUFCNTCHK();
                        lck_mtx_unlock(nfs_buf_mutex);
                        wakeup(&nfs_nbdwrite);
                }
                CLR(bp->nb_flags, (NB_READ|NB_DONE|NB_ERROR|NB_DELWRI));
                /* if block still has dirty pages, we don't want it to */
                /* be released in nfs_buf_iodone().  So, don't set NB_ASYNC. */
                if (!(dirty = bp->nb_dirty))
                        SET(bp->nb_flags, NB_ASYNC);
                else
                        CLR(bp->nb_flags, NB_ASYNC);

                /* move to clean list */
                lck_mtx_lock(nfs_buf_mutex);
                LIST_INSERT_HEAD(&np->n_cleanblkhd, bp, nb_vnbufs);
                lck_mtx_unlock(nfs_buf_mutex);

                bp->nb_dirtyoff = bp->nb_dirtyend = 0;

                nfs_buf_iodone(bp);
                if (dirty) {
                        /* throw it back in as a delayed write buffer */
                        CLR(bp->nb_flags, NB_DONE);
                        nfs_buf_write_delayed(bp);
                }
        }

done:
        FSDBG_BOT(557, np, 0, 0, error);
        return (error);
}

/*
 * Flush all the blocks associated with a vnode.
 *      Walk through the buffer pool and push any dirty pages
 *      associated with the vnode.
 */
int
nfs_flush(nfsnode_t np, int waitfor, thread_t thd, int ignore_writeerr)
{
        struct nfsbuf *bp;
        struct nfsbuflists blist;
        struct nfsmount *nmp = NFSTONMP(np);
        int error = 0, error2, slptimeo = 0, slpflag = 0;
        int nfsvers, flags, passone = 1;

        FSDBG_TOP(517, np, waitfor, ignore_writeerr, 0);

        if (nfs_mount_gone(nmp)) {
                error = ENXIO;
                goto out;
        }
        nfsvers = nmp->nm_vers;
        if (NMFLAG(nmp, INTR))
                slpflag = PCATCH;

        if (!LIST_EMPTY(&np->n_dirtyblkhd)) {
                nfs_node_lock_force(np);
                np->n_flag |= NMODIFIED;
                nfs_node_unlock(np);
        }

        lck_mtx_lock(nfs_buf_mutex);
        while (np->n_bflag & NBFLUSHINPROG) {
                np->n_bflag |= NBFLUSHWANT;
                error = msleep(&np->n_bflag, nfs_buf_mutex, slpflag, "nfs_flush", NULL);
                if ((error && (error != EWOULDBLOCK)) ||
                    ((error = nfs_sigintr(NFSTONMP(np), NULL, thd, 0)))) {
                        lck_mtx_unlock(nfs_buf_mutex);
                        goto out;
                }
        }
        np->n_bflag |= NBFLUSHINPROG;

        /*
         * On the first pass, start async/unstable writes on all
         * delayed write buffers.  Then wait for all writes to complete
         * and call nfs_flushcommits() to commit any uncommitted buffers.
         * On all subsequent passes, start STABLE writes on any remaining
         * dirty buffers.  Then wait for all writes to complete.
         */
again:
        FSDBG(518, LIST_FIRST(&np->n_dirtyblkhd), np->n_flag, 0, 0);
        if (!NFSTONMP(np)) {
                lck_mtx_unlock(nfs_buf_mutex);
                error = ENXIO;
                goto done;
        }

        /* Start/do any write(s) that are required. */
        if (!nfs_buf_iterprepare(np, &blist, NBI_DIRTY)) {
                while ((bp = LIST_FIRST(&blist))) {
                        LIST_REMOVE(bp, nb_vnbufs);
                        LIST_INSERT_HEAD(&np->n_dirtyblkhd, bp, nb_vnbufs);
                        flags = (passone || !(waitfor == MNT_WAIT || waitfor == MNT_DWAIT)) ? NBAC_NOWAIT : 0;
                        if (flags != NBAC_NOWAIT)
                                nfs_buf_refget(bp);
                        while ((error = nfs_buf_acquire(bp, flags, slpflag, slptimeo))) {
                                FSDBG(524, bp, flags, bp->nb_lflags, bp->nb_flags);
                                if (error == EBUSY)
                                        break;
                                if (error) {
                                        error2 = nfs_sigintr(NFSTONMP(np), NULL, thd, 0);
                                        if (error2) {
                                                if (flags != NBAC_NOWAIT)
                                                        nfs_buf_refrele(bp);
                                                nfs_buf_itercomplete(np, &blist, NBI_DIRTY);
                                                lck_mtx_unlock(nfs_buf_mutex);
                                                error = error2;
                                                goto done;
                                        }
                                        if (slpflag == PCATCH) {
                                                slpflag = 0;
                                                slptimeo = 2 * hz;
                                        }
                                }
                        }
                        if (flags != NBAC_NOWAIT)
                                nfs_buf_refrele(bp);
                        if (error == EBUSY)
                                continue;
                        if (!bp->nb_np) {
                                /* 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_DELWRI)) {
                                /* buffer is no longer dirty */
                                nfs_buf_drop(bp);
                                continue;
                        }
                        FSDBG(525, bp, passone, bp->nb_lflags, bp->nb_flags);
                        if ((passone || !(waitfor == MNT_WAIT || waitfor == MNT_DWAIT)) &&
                            ISSET(bp->nb_flags, NB_NEEDCOMMIT)) {
                                nfs_buf_drop(bp);
                                continue;
                        }
                        nfs_buf_remfree(bp);
                        lck_mtx_unlock(nfs_buf_mutex);
                        if (ISSET(bp->nb_flags, NB_ERROR)) {
                                nfs_node_lock_force(np);
                                np->n_error = bp->nb_error ? bp->nb_error : EIO;
                                np->n_flag |= NWRITEERR;
                                nfs_node_unlock(np);
                                nfs_buf_release(bp, 1);
                                lck_mtx_lock(nfs_buf_mutex);
                                continue;
                        }
                        SET(bp->nb_flags, NB_ASYNC);
                        if (!passone) {
                                /* NB_STABLE forces this to be written FILESYNC */
                                SET(bp->nb_flags, NB_STABLE);
                        }
                        nfs_buf_write(bp);
                        lck_mtx_lock(nfs_buf_mutex);
                }
                nfs_buf_itercomplete(np, &blist, NBI_DIRTY);
        }
        lck_mtx_unlock(nfs_buf_mutex);

        if (waitfor == MNT_WAIT || waitfor == MNT_DWAIT) {
                while ((error = vnode_waitforwrites(NFSTOV(np), 0, slpflag, slptimeo, "nfsflush"))) {
                        error2 = nfs_sigintr(NFSTONMP(np), NULL, thd, 0);
                        if (error2) {
                                error = error2;
                                goto done;
                        }
                        if (slpflag == PCATCH) {
                                slpflag = 0;
                                slptimeo = 2 * hz;
                        }
                }
        }

        if (nfsvers != NFS_VER2) {
                /* loop while it looks like there are still buffers to be */
                /* commited and nfs_flushcommits() seems to be handling them. */
                while (np->n_needcommitcnt)
                        if (nfs_flushcommits(np, 0))
                                break;
        }

        if (passone) {
                passone = 0;
                if (!LIST_EMPTY(&np->n_dirtyblkhd)) {
                        nfs_node_lock_force(np);
                        np->n_flag |= NMODIFIED;
                        nfs_node_unlock(np);
                }
                lck_mtx_lock(nfs_buf_mutex);
                goto again;
        }

        if (waitfor == MNT_WAIT || waitfor == MNT_DWAIT) {
                if (!LIST_EMPTY(&np->n_dirtyblkhd)) {
                        nfs_node_lock_force(np);
                        np->n_flag |= NMODIFIED;
                        nfs_node_unlock(np);
                }
                lck_mtx_lock(nfs_buf_mutex);
                if (!LIST_EMPTY(&np->n_dirtyblkhd))
                        goto again;
                lck_mtx_unlock(nfs_buf_mutex);
                nfs_node_lock_force(np);
                /*
                 * OK, it looks like there are no dirty blocks.  If we have no
                 * writes in flight and no one in the write code, we can clear
                 * the modified flag.  In order to make sure we see the latest
                 * attributes and size, we also invalidate the attributes and
                 * advance the attribute cache XID to guarantee that attributes
                 * newer than our clearing of NMODIFIED will get loaded next.
                 * (If we don't do this, it's possible for the flush's final
                 * write/commit (xid1) to be executed in parallel with a subsequent
                 * getattr request (xid2).  The getattr could return attributes
                 * from *before* the write/commit completed but the stale attributes
                 * would be preferred because of the xid ordering.)
                 */
                if (!np->n_wrbusy && !np->n_numoutput) {
                        np->n_flag &= ~NMODIFIED;
                        NATTRINVALIDATE(np);
                        nfs_get_xid(&np->n_xid);
                }
        } else {
                nfs_node_lock_force(np);
        }

        FSDBG(526, np->n_flag, np->n_error, 0, 0);
        if (!ignore_writeerr && (np->n_flag & NWRITEERR)) {
                error = np->n_error;
                np->n_flag &= ~NWRITEERR;
        }
        nfs_node_unlock(np);
done:
        lck_mtx_lock(nfs_buf_mutex);
        flags = np->n_bflag;
        np->n_bflag &= ~(NBFLUSHINPROG|NBFLUSHWANT);
        lck_mtx_unlock(nfs_buf_mutex);
        if (flags & NBFLUSHWANT)
                wakeup(&np->n_bflag);
out:
        FSDBG_BOT(517, np, error, ignore_writeerr, 0);
        return (error);
}

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

        if (flags & V_SAVE) {
                if ((error = nfs_flush(np, MNT_WAIT, thd, (flags & V_IGNORE_WRITEERR))))
                        return (error);
        }

        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, np, bp, NBOFF(bp), bp->nb_flags);
                                if (error != EAGAIN) {
                                        FSDBG(554, np, 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, np, bp, NBOFF(bp), bp->nb_flags);
                        lck_mtx_unlock(nfs_buf_mutex);
                        if ((flags & V_SAVE) && UBCINFOEXISTS(NFSTOV(np)) && bp->nb_np &&
                            (NBOFF(bp) < (off_t)np->n_size)) {
                                /* 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 > 0) && (bp->nb_dirtyoff < end)) {
                                        /* clip dirty range to EOF */
                                        if (bp->nb_dirtyend > end) {
                                                bp->nb_dirtyend = end;
                                                if (bp->nb_dirtyoff >= bp->nb_dirtyend)
                                                        bp->nb_dirtyoff = bp->nb_dirtyend = 0;
                                        }
                                        if ((bp->nb_dirtyend > 0) && (bp->nb_dirtyoff < end))
                                                mustwrite++;
                                }
                                bp->nb_dirty &= (1 << (round_page_32(end)/PAGE_SIZE)) - 1;
                                if (bp->nb_dirty)
                                        mustwrite++;
                                /* also make sure we'll have a credential to do the write */
                                if (mustwrite && !IS_VALID_CRED(bp->nb_wcred) && !IS_VALID_CRED(cred)) {
                                        printf("nfs_vinvalbuf: found dirty buffer with no write creds\n");
                                        mustwrite = 0;
                                }
                                if (mustwrite) {
                                        FSDBG(554, np, 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 (!IS_VALID_CRED(bp->nb_wcred)) {
                                                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);
                                                nfs_node_lock_force(np);
                                                if ((error != EINTR) && (error != ERESTART)) {
                                                        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);
                                                nfs_node_unlock(np);
                                                if ((error == EINTR) || (error == ERESTART)) {
                                                        /*
                                                         * Abort on EINTR.  If we don't, we could
                                                         * be stuck in this loop forever because
                                                         * the buffer will continue to stay dirty.
                                                         */
                                                        lck_mtx_lock(nfs_buf_mutex);
                                                        nfs_buf_itercomplete(np, &blist, list);
                                                        lck_mtx_unlock(nfs_buf_mutex);
                                                        return (error);
                                                }
                                                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);
        }
        if (!LIST_EMPTY(&(np)->n_dirtyblkhd) || !LIST_EMPTY(&(np)->n_cleanblkhd))
                panic("nfs_vinvalbuf: flush/inval failed");
        lck_mtx_unlock(nfs_buf_mutex);
        nfs_node_lock_force(np);
        if (!(flags & V_SAVE))
                np->n_flag &= ~NMODIFIED;
        if (vnode_vtype(NFSTOV(np)) == VREG)
                np->n_lastrahead = -1;
        nfs_node_unlock(np);
        NFS_BUF_FREEUP();
        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, vfs_context_t ctx, int intrflg)
{
        return nfs_vinvalbuf2(vp, flags, vfs_context_thread(ctx), vfs_context_ucred(ctx), intrflg);
}

int
nfs_vinvalbuf2(vnode_t vp, int flags, thread_t thd, kauth_cred_t cred, int intrflg)
{
        nfsnode_t np = VTONFS(vp);
        struct nfsmount *nmp = VTONMP(vp);
        int error, slpflag, slptimeo, nflags, retry = 0;
        int ubcflags = UBC_PUSHALL | UBC_SYNC | UBC_INVALIDATE;
        struct timespec ts = { 2, 0 };
        off_t size;

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

        /*
         * If the mount is gone no sense to try and write anything.
         * and hang trying to do IO.
         */
        if (nfs_mount_gone(nmp)) {
                flags &= ~V_SAVE;
                ubcflags &= ~UBC_PUSHALL;
        }
        
        if (nmp && !NMFLAG(nmp, INTR))
                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.  */
        lck_mtx_lock(nfs_buf_mutex);
        while (np->n_bflag & NBINVALINPROG) {
                np->n_bflag |= NBINVALWANT;
                msleep(&np->n_bflag, nfs_buf_mutex, slpflag, "nfs_vinvalbuf", &ts);
                if ((error = nfs_sigintr(VTONMP(vp), NULL, thd, 0))) {
                        lck_mtx_unlock(nfs_buf_mutex);
                        return (error);
                }
                if (np->n_bflag & NBINVALINPROG)
                        slpflag = 0;
        }
        np->n_bflag |= NBINVALINPROG;
        lck_mtx_unlock(nfs_buf_mutex);

        /* Now, flush as required.  */
again:
        error = nfs_vinvalbuf_internal(np, flags, thd, cred, slpflag, 0);
        while (error) {
                FSDBG(554, np, 0, 0, error);
                if ((error = nfs_sigintr(VTONMP(vp), NULL, thd, 0)))
                        goto done;
                error = nfs_vinvalbuf_internal(np, flags, thd, cred, 0, slptimeo);
        }

        /* get the pages out of vm also */
        if (UBCINFOEXISTS(vp) && (size = ubc_getsize(vp)))
                if ((error = ubc_msync(vp, 0, size, NULL, ubcflags))) {
                        if (error == EINVAL)
                                panic("nfs_vinvalbuf(): ubc_msync failed!, error %d", error);
                        if (retry++ < 10) { /* retry invalidating a few times */
                                if (retry > 1 || error == ENXIO)
                                        ubcflags &= ~UBC_PUSHALL;
                                goto again;
                        }
                        /* give up */
                        printf("nfs_vinvalbuf(): ubc_msync failed!, error %d\n", error);
                }
done:
        lck_mtx_lock(nfs_buf_mutex);
        nflags = np->n_bflag;
        np->n_bflag &= ~(NBINVALINPROG|NBINVALWANT);
        lck_mtx_unlock(nfs_buf_mutex);
        if (nflags & NBINVALWANT)
                wakeup(&np->n_bflag);

        FSDBG_BOT(554, np, flags, intrflg, error);
        return (error);
}

/*
 * Wait for any busy buffers to complete.
 */
void
nfs_wait_bufs(nfsnode_t np)
{
        struct nfsbuf *bp;
        struct nfsbuflists blist;
        int error = 0;

        lck_mtx_lock(nfs_buf_mutex);
        if (!nfs_buf_iterprepare(np, &blist, NBI_CLEAN)) {
                while ((bp = LIST_FIRST(&blist))) {
                        LIST_REMOVE(bp, nb_vnbufs);
                        LIST_INSERT_HEAD(&np->n_cleanblkhd, bp, nb_vnbufs);
                        nfs_buf_refget(bp);
                        while ((error = nfs_buf_acquire(bp, 0, 0, 0))) {
                                if (error != EAGAIN) {
                                        nfs_buf_refrele(bp);
                                        nfs_buf_itercomplete(np, &blist, NBI_CLEAN);
                                        lck_mtx_unlock(nfs_buf_mutex);
                                        return;
                                }
                        }
                        nfs_buf_refrele(bp);
                        nfs_buf_drop(bp);
                }
                nfs_buf_itercomplete(np, &blist, NBI_CLEAN);
        }
        if (!nfs_buf_iterprepare(np, &blist, NBI_DIRTY)) {
                while ((bp = LIST_FIRST(&blist))) {
                        LIST_REMOVE(bp, nb_vnbufs);
                        LIST_INSERT_HEAD(&np->n_dirtyblkhd, bp, nb_vnbufs);
                        nfs_buf_refget(bp);
                        while ((error = nfs_buf_acquire(bp, 0, 0, 0))) {
                                if (error != EAGAIN) {
                                        nfs_buf_refrele(bp);
                                        nfs_buf_itercomplete(np, &blist, NBI_DIRTY);
                                        lck_mtx_unlock(nfs_buf_mutex);
                                        return;
                                }
                        }
                        nfs_buf_refrele(bp);
                        nfs_buf_drop(bp);
                }
                nfs_buf_itercomplete(np, &blist, NBI_DIRTY);
        }
        lck_mtx_unlock(nfs_buf_mutex);
}


/*
 * Add an async I/O request to the mount's async I/O queue and make
 * sure that an nfsiod will service it.
 */
void
nfs_asyncio_finish(struct nfsreq *req)
{
        struct nfsmount *nmp;
        struct nfsiod *niod;
        int started = 0;

        FSDBG_TOP(552, nmp, 0, 0, 0);
again:
        nmp = req->r_nmp;

        if (nmp == NULL)
                return;

        lck_mtx_lock(nfsiod_mutex);
        niod = nmp->nm_niod;

        /* grab an nfsiod if we don't have one already */
        if (!niod) {
                niod = TAILQ_FIRST(&nfsiodfree);
                if (niod) {
                        TAILQ_REMOVE(&nfsiodfree, niod, niod_link);
                        TAILQ_INSERT_TAIL(&nfsiodwork, niod, niod_link);
                        niod->niod_nmp = nmp;
                } else if (((nfsiod_thread_count < NFSIOD_MAX) || (nfsiod_thread_count <= 0)) && (started < 4)) {
                        /*
                         * Try starting a new thread.
                         * We may try a couple times if other callers
                         * get the new threads before we do.
                         */
                        lck_mtx_unlock(nfsiod_mutex);
                        started++;
                        if (!nfsiod_start())
                                goto again;
                        lck_mtx_lock(nfsiod_mutex);
                }
        }

        /*
         * If we got here while being on the resendq we need to get off. This
         * happens when the timer fires and errors out requests from nfs_sigintr
         * or we receive a reply (UDP case) while being on the resend queue so
         * we're just finishing up and are not going to be resent.
         */
        lck_mtx_lock(&req->r_mtx);
        if (req->r_flags & R_RESENDQ) {
                lck_mtx_lock(&nmp->nm_lock);
                if (req->r_rchain.tqe_next != NFSREQNOLIST) {
                        NFS_BIO_DBG("Proccessing async request on resendq. Removing");
                        TAILQ_REMOVE(&nmp->nm_resendq, req, r_rchain);
                        req->r_rchain.tqe_next = NFSREQNOLIST;
                        assert(req->r_refs > 1);
                        /* Remove resendq reference */
                        req->r_refs--;
                }
                lck_mtx_unlock(&nmp->nm_lock);
                req->r_flags &= ~R_RESENDQ;
        }
        lck_mtx_unlock(&req->r_mtx);

        if (req->r_achain.tqe_next == NFSREQNOLIST)
                TAILQ_INSERT_TAIL(&nmp->nm_iodq, req, r_achain);

        /* If this mount doesn't already have an nfsiod working on it... */
        if (!nmp->nm_niod) {
                if (niod) { /* give it the nfsiod we just grabbed */
                        nmp->nm_niod = niod;
                        lck_mtx_unlock(nfsiod_mutex);
                        wakeup(niod);
                } else if (nfsiod_thread_count > 0) {
                        /* just queue it up on nfsiod mounts queue if needed */
                        if (nmp->nm_iodlink.tqe_next == NFSNOLIST)
                                TAILQ_INSERT_TAIL(&nfsiodmounts, nmp, nm_iodlink);
                        lck_mtx_unlock(nfsiod_mutex);
                } else {
                        printf("nfs_asyncio(): no nfsiods? %d %d (%d)\n", nfsiod_thread_count, NFSIOD_MAX, started);
                        lck_mtx_unlock(nfsiod_mutex);
                        /* we have no other option but to be persistent */
                        started = 0;
                        goto again;
                }
        } else {
                lck_mtx_unlock(nfsiod_mutex);
        }

        FSDBG_BOT(552, nmp, 0, 0, 0);
}

/*
 * queue up async I/O request for resend
 */
void
nfs_asyncio_resend(struct nfsreq *req)
{
        struct nfsmount *nmp = req->r_nmp;

        if (nfs_mount_gone(nmp))
                return;

        nfs_gss_clnt_rpcdone(req);
        lck_mtx_lock(&nmp->nm_lock);
        if (!(req->r_flags & R_RESENDQ)) {
                TAILQ_INSERT_TAIL(&nmp->nm_resendq, req, r_rchain);
                req->r_flags |= R_RESENDQ;
                /*
                 * We take a reference on this request so that it can't be
                 * destroyed while a resend is queued or in progress.
                 */
                nfs_request_ref(req, 1);
        }
        nfs_mount_sock_thread_wake(nmp);
        lck_mtx_unlock(&nmp->nm_lock);
}

/*
 * Read directory data into a buffer.
 *
 * Buffer will be filled (unless EOF is hit).
 * Buffers after this one may also be completely/partially filled.
 */
int
nfs_buf_readdir(struct nfsbuf *bp, vfs_context_t ctx)
{
        nfsnode_t np = bp->nb_np;
        struct nfsmount *nmp = NFSTONMP(np);
        int error = 0;

        if (nfs_mount_gone(nmp))
                return (ENXIO);

        if (nmp->nm_vers < NFS_VER4)
                error = nfs3_readdir_rpc(np, bp, ctx);
        else
                error = nfs4_readdir_rpc(np, bp, ctx);

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