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

/*
 * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * The contents of this file constitute Original Code as defined in and
 * are subject to the Apple Public Source License Version 1.1 (the
 * "License").  You may not use this file except in compliance with the
 * License.  Please obtain a copy of the License at
 * http://www.apple.com/publicsource and read it before using this file.
 * 
 * This Original Code and all software distributed under the License are
 * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
 * License for the specific language governing rights and limitations
 * under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */
/* Copyright (c) 1995 NeXT Computer, Inc. All Rights Reserved */
/*
 * Copyright (c) 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Rick Macklem at The University of Guelph.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)nfs_bio.c   8.9 (Berkeley) 3/30/95
 * FreeBSD-Id: nfs_bio.c,v 1.44 1997/09/10 19:52:25 phk Exp $
 */
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/resourcevar.h>
#include <sys/signalvar.h>
#include <sys/proc.h>
#include <sys/buf.h>
#include <sys/vnode.h>
#include <sys/mount.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/ubc.h>

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

#include <sys/time.h>
#include <kern/clock.h>

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

#include <sys/kdebug.h>

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

static struct buf *nfs_getcacheblk __P((struct vnode *vp, daddr_t bn, int size,
                                        struct proc *p, int operation));

extern int nfs_numasync;
extern struct nfsstats nfsstats;
extern int nbdwrite;

/*
 * Vnode op for read using bio
 * Any similarity to readip() is purely coincidental
 */
int
nfs_bioread(vp, uio, ioflag, cred, getpages)
        register struct vnode *vp;
        register struct uio *uio;
        int ioflag;
        struct ucred *cred;
        int getpages;
{
        register struct nfsnode *np = VTONFS(vp);
        register int biosize, diff, i;
        struct buf *bp = 0, *rabp;
        struct vattr vattr;
        struct proc *p;
        struct nfsmount *nmp = VFSTONFS(vp->v_mount);
        daddr_t lbn, rabn;
        int bufsize;
        int nra, error = 0, n = 0, on = 0, not_readin;
        int operation = (getpages? BLK_PAGEIN : BLK_READ);

#if DIAGNOSTIC
        if (uio->uio_rw != UIO_READ)
                panic("nfs_read mode");
#endif
        if (uio->uio_resid == 0)
                return (0);
        if (uio->uio_offset < 0)
                return (EINVAL);
        p = uio->uio_procp;
        if ((nmp->nm_flag & (NFSMNT_NFSV3 | NFSMNT_GOTFSINFO)) == NFSMNT_NFSV3)
                (void)nfs_fsinfo(nmp, vp, cred, p);
        /*due to getblk/vm interractions, use vm page size or less values */
        biosize = min(vp->v_mount->mnt_stat.f_iosize, PAGE_SIZE);
        /*
         * For nfs, cache consistency can only be maintained approximately.
         * Although RFC1094 does not specify the criteria, the following is
         * believed to be compatible with the reference port.
         * For nqnfs, full cache consistency is maintained within the loop.
         * For nfs:
         * If the file's modify time on the server has changed since the
         * last read rpc or you have written to the file,
         * you may have lost data cache consistency with the
         * server, so flush all of the file's data out of the cache.
         * Then force a getattr rpc to ensure that you have up to date
         * attributes.
         * NB: This implies that cache data can be read when up to
         * NFS_ATTRTIMEO seconds out of date. If you find that you need current
         * attributes this could be forced by setting n_attrstamp to 0 before
         * the VOP_GETATTR() call.
         */
        if ((nmp->nm_flag & NFSMNT_NQNFS) == 0) {
                if (np->n_flag & NMODIFIED) {
                        if (vp->v_type != VREG) {
                                if (vp->v_type != VDIR)
                                        panic("nfs: bioread, not dir");
                                nfs_invaldir(vp);
                                error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
                                if (error)
                                        return (error);
                        }
                        np->n_attrstamp = 0;
                        error = VOP_GETATTR(vp, &vattr, cred, p);
                        if (error)
                                return (error);
                        np->n_mtime = vattr.va_mtime.tv_sec;
                } else {
                        error = VOP_GETATTR(vp, &vattr, cred, p);
                        if (error)
                                return (error);
                        if (np->n_mtime != vattr.va_mtime.tv_sec) {
                                if (vp->v_type == VDIR)
                                        nfs_invaldir(vp);
                                error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
                                if (error)
                                        return (error);
                                np->n_mtime = vattr.va_mtime.tv_sec;
                        }
                }
        }
        do {

            /*
             * Get a valid lease. If cached data is stale, flush it.
             */
            if (nmp->nm_flag & NFSMNT_NQNFS) {
                if (NQNFS_CKINVALID(vp, np, ND_READ)) {
                    do {
                        error = nqnfs_getlease(vp, ND_READ, cred, p);
                    } while (error == NQNFS_EXPIRED);
                    if (error)
                        return (error);
                    if (np->n_lrev != np->n_brev ||
                        (np->n_flag & NQNFSNONCACHE) ||
                        ((np->n_flag & NMODIFIED) && vp->v_type == VDIR)) {
                        if (vp->v_type == VDIR)
                            nfs_invaldir(vp);
                        error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
                        if (error)
                            return (error);
                        np->n_brev = np->n_lrev;
                    }
                } else if (vp->v_type == VDIR && (np->n_flag & NMODIFIED)) {
                    nfs_invaldir(vp);
                    error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
                    if (error)
                        return (error);
                }
            }
            if (np->n_flag & NQNFSNONCACHE) {
                switch (vp->v_type) {
                case VREG:
                        return (nfs_readrpc(vp, uio, cred));
                case VLNK:
                        return (nfs_readlinkrpc(vp, uio, cred));
                case VDIR:
                        break;
                default:
                        printf(" NQNFSNONCACHE: type %x unexpected\n",  
                                vp->v_type);
                };
            }
            switch (vp->v_type) {
            case VREG:
                nfsstats.biocache_reads++;
                lbn = uio->uio_offset / biosize;
                on = uio->uio_offset & (biosize - 1);
                not_readin = 1;

                /*
                 * Start the read ahead(s), as required.
                 */
                if (nfs_numasync > 0 && nmp->nm_readahead > 0) {
                    for (nra = 0; nra < nmp->nm_readahead &&
                                  (off_t)(lbn + 1 + nra) * biosize < np->n_size;
                         nra++) {
                                rabn = lbn + 1 + nra;
                                if (!incore(vp, rabn)) {
                                        rabp = nfs_getcacheblk(vp, rabn, biosize, p, operation);
                                        if (!rabp)
                                                return (EINTR);
                                        if (!ISSET(rabp->b_flags, (B_CACHE|B_DELWRI))) {
                                                SET(rabp->b_flags, (B_READ | B_ASYNC));
                                                if (nfs_asyncio(rabp, cred)) {
                                                        SET(rabp->b_flags, (B_INVAL|B_ERROR));
                                                        rabp->b_error = EIO;
                                                        brelse(rabp);
                                                }
                                        } else
                                                brelse(rabp);
                                }
                    }
                }

                /*
                 * If the block is in the cache and has the required data
                 * in a valid region, just copy it out.
                 * Otherwise, get the block and write back/read in,
                 * as required.
                 */
again:
                bufsize = biosize;
                if ((off_t)(lbn + 1) * biosize > np->n_size && 
                    (off_t)(lbn + 1) * biosize - np->n_size < biosize) {
                        bufsize = np->n_size - lbn * biosize;
                        bufsize = (bufsize + DEV_BSIZE - 1) & ~(DEV_BSIZE - 1);
                }
                bp = nfs_getcacheblk(vp, lbn, bufsize, p, operation);
                if (!bp)
                        return (EINTR);

                if (!ISSET(bp->b_flags, B_CACHE)) {
                        SET(bp->b_flags, B_READ);
                        CLR(bp->b_flags, (B_DONE | B_ERROR | B_INVAL));
                        not_readin = 0;
                        error = nfs_doio(bp, cred, p);
                        if (error) {
                            brelse(bp);
                            return (error);
                        }
                }
                if (bufsize > on) {
                        n = min((unsigned)(bufsize - on), uio->uio_resid);
                } else {
                        n = 0;
                }
                diff = np->n_size - uio->uio_offset;
                if (diff < n)
                        n = diff;
                if (not_readin && n > 0) {
                        if (on < bp->b_validoff || (on + n) > bp->b_validend) {
                                SET(bp->b_flags, (B_NOCACHE|B_INVAFTERWRITE));
                                if (bp->b_dirtyend > 0) {
                                        if (!ISSET(bp->b_flags, B_DELWRI))
                                                panic("nfsbioread");
                                        if (VOP_BWRITE(bp) == EINTR)
                                                return (EINTR);
                                } else
                                        brelse(bp);
                                goto again;
                        }
                }
                vp->v_lastr = lbn;
                diff = (on >= bp->b_validend) ? 0 : (bp->b_validend - on);
                if (diff < n)
                        n = diff;
                break;
            case VLNK:
                nfsstats.biocache_readlinks++;
                bp = nfs_getcacheblk(vp, (daddr_t)0, NFS_MAXPATHLEN, p, operation);
                if (!bp)
                        return (EINTR);
                if (!ISSET(bp->b_flags, B_CACHE)) {
                        SET(bp->b_flags, B_READ);
                        error = nfs_doio(bp, cred, p);
                        if (error) {
                                SET(bp->b_flags, B_ERROR);
                                brelse(bp);
                                return (error);
                        }
                }
                n = min(uio->uio_resid, NFS_MAXPATHLEN - bp->b_resid);
                on = 0;
                break;
            case VDIR:
                nfsstats.biocache_readdirs++;
                if (np->n_direofoffset
                    && uio->uio_offset >= np->n_direofoffset) {
                    return (0);
                }
                lbn = uio->uio_offset / NFS_DIRBLKSIZ;
                on = uio->uio_offset & (NFS_DIRBLKSIZ - 1);
                bp = nfs_getcacheblk(vp, lbn, NFS_DIRBLKSIZ, p, operation);
                if (!bp)
                    return (EINTR);
                if (!ISSET(bp->b_flags, B_CACHE)) {
                    SET(bp->b_flags, B_READ);
                    error = nfs_doio(bp, cred, p);
                    if (error) {
                        brelse(bp);
                    }
                    while (error == NFSERR_BAD_COOKIE) {
                        nfs_invaldir(vp);
                        error = nfs_vinvalbuf(vp, 0, cred, p, 1);
                        /*
                         * Yuck! The directory has been modified on the
                         * server. The only way to get the block is by
                         * reading from the beginning to get all the
                         * offset cookies.
                         */
                        for (i = 0; i <= lbn && !error; i++) {
                            if (np->n_direofoffset
                                && (i * NFS_DIRBLKSIZ) >= np->n_direofoffset)
                                    return (0);
                            bp = nfs_getcacheblk(vp, i, NFS_DIRBLKSIZ, p,
                                                 operation);
                            if (!bp)
                                    return (EINTR);
                            if (!ISSET(bp->b_flags, B_CACHE)) {
                                    SET(bp->b_flags, B_READ);
                                    error = nfs_doio(bp, cred, p);
                                    /*
                                     * no error + B_INVAL == directory EOF,
                                     * use the block.
                                     */
                                    if (error == 0 && (bp->b_flags & B_INVAL))
                                            break;
                            }
                            /*
                             * An error will throw away the block and the
                             * for loop will break out.  If no error and this
                             * is not the block we want, we throw away the
                             * block and go for the next one via the for loop.
                             */
                            if (error || i < lbn)
                                    brelse(bp);
                        }
                    }
                    /*
                     * The above while is repeated if we hit another cookie
                     * error.  If we hit an error and it wasn't a cookie error,
                     * we give up.
                     */
                    if (error)
                        return (error);
                }

                /*
                 * If not eof and read aheads are enabled, start one.
                 * (You need the current block first, so that you have the
                 *  directory offset cookie of the next block.)
                 */
                if (nfs_numasync > 0 && nmp->nm_readahead > 0 &&
                    (np->n_direofoffset == 0 ||
                    (lbn + 1) * NFS_DIRBLKSIZ < np->n_direofoffset) &&
                    !(np->n_flag & NQNFSNONCACHE) &&
                    !incore(vp, lbn + 1)) {
                        rabp = nfs_getcacheblk(vp, lbn + 1, NFS_DIRBLKSIZ, p,
                                               operation);
                        if (rabp) {
                            if (!ISSET(rabp->b_flags, (B_CACHE|B_DELWRI))) {
                                SET(rabp->b_flags, (B_READ | B_ASYNC));
                                if (nfs_asyncio(rabp, cred)) {
                                    SET(rabp->b_flags, (B_INVAL|B_ERROR));
                                    rabp->b_error = EIO;
                                    brelse(rabp);
                                }
                            } else {
                                brelse(rabp);
                            }
                        }
                }
                /*
                 * Make sure we use a signed variant of min() since
                 * the second term may be negative.
                 */
                n = lmin(uio->uio_resid, NFS_DIRBLKSIZ - bp->b_resid - on);
                /*
                 * Unlike VREG files, whos buffer size ( bp->b_bcount ) is
                 * chopped for the EOF condition, we cannot tell how large
                 * NFS directories are going to be until we hit EOF.  So
                 * an NFS directory buffer is *not* chopped to its EOF.  Now,
                 * it just so happens that b_resid will effectively chop it
                 * to EOF.  *BUT* this information is lost if the buffer goes
                 * away and is reconstituted into a B_CACHE state (recovered
                 * from VM) later.  So we keep track of the directory eof
                 * in np->n_direofoffset and chop it off as an extra step
                 * right here.
                 */
                if (np->n_direofoffset &&
                    n > np->n_direofoffset - uio->uio_offset)
                        n = np->n_direofoffset - uio->uio_offset;
                break;
            default:
                printf(" nfs_bioread: type %x unexpected\n",vp->v_type);
                break;
            };

            if (n > 0) {
                error = uiomove(bp->b_data + on, (int)n, uio);
            }
            switch (vp->v_type) {
            case VREG:
                break;
            case VLNK:
                n = 0;
                break;
            case VDIR:
                if (np->n_flag & NQNFSNONCACHE)
                        SET(bp->b_flags, B_INVAL);
                break;
            default:
                printf(" nfs_bioread: type %x unexpected\n",vp->v_type);
            }
            brelse(bp);
        } while (error == 0 && uio->uio_resid > 0 && n > 0);
        return (error);
}


/*
 * Vnode op for write using bio
 */
int
nfs_write(ap)
        struct vop_write_args /* {
                struct vnode *a_vp;
                struct uio *a_uio;
                int  a_ioflag;
                struct ucred *a_cred;
        } */ *ap;
{
        register int biosize;
        register struct uio *uio = ap->a_uio;
        struct proc *p = uio->uio_procp;
        register struct vnode *vp = ap->a_vp;
        struct nfsnode *np = VTONFS(vp);
        register struct ucred *cred = ap->a_cred;
        int ioflag = ap->a_ioflag;
        struct buf *bp;
        struct vattr vattr;
        struct nfsmount *nmp = VFSTONFS(vp->v_mount);
        daddr_t lbn;
        int bufsize;
        int n, on, error = 0, iomode, must_commit;
        off_t boff;
        struct iovec iov;
        struct uio auio;

#if DIAGNOSTIC
        if (uio->uio_rw != UIO_WRITE)
                panic("nfs_write mode");
        if (uio->uio_segflg == UIO_USERSPACE && uio->uio_procp != current_proc())
                panic("nfs_write proc");
#endif
        if (vp->v_type != VREG)
                return (EIO);
        if (np->n_flag & NWRITEERR) {
                np->n_flag &= ~NWRITEERR;
                return (np->n_error);
        }
        if ((nmp->nm_flag & (NFSMNT_NFSV3 | NFSMNT_GOTFSINFO)) == NFSMNT_NFSV3)
                (void)nfs_fsinfo(nmp, vp, cred, p);
        if (ioflag & (IO_APPEND | IO_SYNC)) {
                if (np->n_flag & NMODIFIED) {
                        np->n_attrstamp = 0;
                        error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
                        if (error)
                                return (error);
                }
                if (ioflag & IO_APPEND) {
                        np->n_attrstamp = 0;
                        error = VOP_GETATTR(vp, &vattr, cred, p);
                        if (error)
                                return (error);
                        uio->uio_offset = np->n_size;
                }
        }
        if (uio->uio_offset < 0)
                return (EINVAL);
        if (uio->uio_resid == 0)
                return (0);
        /*
         * Maybe this should be above the vnode op call, but so long as
         * file servers have no limits, i don't think it matters
         */
        if (p && uio->uio_offset + uio->uio_resid >
              p->p_rlimit[RLIMIT_FSIZE].rlim_cur) {
                psignal(p, SIGXFSZ);
                return (EFBIG);
        }
        /*
         * I use nm_rsize, not nm_wsize so that all buffer cache blocks
         * will be the same size within a filesystem. nfs_writerpc will
         * still use nm_wsize when sizing the rpc's.
         */
        /*due to getblk/vm interractions, use vm page size or less values */
        biosize = min(vp->v_mount->mnt_stat.f_iosize, PAGE_SIZE);

        do {
                /*
                 * Check for a valid write lease.
                 */
                if ((nmp->nm_flag & NFSMNT_NQNFS) &&
                    NQNFS_CKINVALID(vp, np, ND_WRITE)) {
                        do {
                                error = nqnfs_getlease(vp, ND_WRITE, cred, p);
                        } while (error == NQNFS_EXPIRED);
                        if (error)
                                return (error);
                        if (np->n_lrev != np->n_brev ||
                            (np->n_flag & NQNFSNONCACHE)) {
                                error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
                                if (error)
                                        return (error);
                                np->n_brev = np->n_lrev;
                        }
                }
                if ((np->n_flag & NQNFSNONCACHE) && uio->uio_iovcnt == 1) {
                    iomode = NFSV3WRITE_FILESYNC;
                    error = nfs_writerpc(vp, uio, cred, &iomode, &must_commit);
                    if (must_commit)
                        nfs_clearcommit(vp->v_mount);
                    return (error);
                }
                nfsstats.biocache_writes++;
                lbn = uio->uio_offset / biosize;
                on = uio->uio_offset & (biosize-1);
                n = min((unsigned)(biosize - on), uio->uio_resid);
again:
                bufsize = biosize;
#if 0
/* (removed for UBC) */
                if ((lbn + 1) * biosize > np->n_size) {
                        bufsize = np->n_size - lbn * biosize;
                        bufsize = (bufsize + DEV_BSIZE - 1) & ~(DEV_BSIZE - 1);
                }
#endif
                /*
                 * Get a cache block for writing.  The range to be written is
                 * (off..off+len) within the block.  We ensure that the block
                 * either has no dirty region or that the given range is
                 * contiguous with the existing dirty region.
                 */
                bp = nfs_getcacheblk(vp, lbn, bufsize, p, BLK_WRITE);
                if (!bp)
                        return (EINTR);
                /*
                 * Resize nfsnode *after* we busy the buffer to prevent
                 * readers from reading garbage.
                 * If there was a partial buf at the old eof, validate
                 * and zero the new bytes. 
                 */
                if (uio->uio_offset + n > np->n_size) {
                        struct buf *bp0 = NULL;
                        daddr_t bn = np->n_size / biosize;
                        int off = np->n_size & (biosize - 1);

                        if (off && bn < lbn && incore(vp, bn))
                                bp0 = nfs_getcacheblk(vp, bn, biosize, p,
                                                      BLK_WRITE);
                        np->n_flag |= NMODIFIED;
                        np->n_size = uio->uio_offset + n;
                        ubc_setsize(vp, (off_t)np->n_size); /* XXX errors */
                        if (bp0) {
                                bzero((char *)bp0->b_data + off, biosize - off);
                                bp0->b_validend = biosize;
                                brelse(bp0);
                        }
                }
                /*
                 * NFS has embedded ucred so crhold() risks zone corruption
                 */
                if (bp->b_wcred == NOCRED)
                        bp->b_wcred = crdup(cred);
                /*
                 * If dirtyend exceeds file size, chop it down.  This should
                 * not occur unless there is a race.
                 */
                if ((off_t)bp->b_blkno * DEV_BSIZE + bp->b_dirtyend >
                    np->n_size)
                        bp->b_dirtyend = np->n_size - (off_t)bp->b_blkno *
                                                      DEV_BSIZE;
                /*
                 * UBC doesn't (yet) handle partial pages so nfs_biowrite was
                 * hacked to never bdwrite, to start every little write right
                 * away.  Running IE Avie noticed the performance problem, thus
                 * this code, which permits those delayed writes by ensuring an
                 * initial read of the entire page.  The read may hit eof
                 * ("short read") but that we will handle.
                 *
                 * We are quite dependant on the correctness of B_CACHE so check
                 * that first in case of problems.
                 */
                if (!ISSET(bp->b_flags, B_CACHE) && n < PAGE_SIZE) {
                        boff = (off_t)bp->b_blkno * DEV_BSIZE;
                        auio.uio_iov = &iov;
                        auio.uio_iovcnt = 1;
                        auio.uio_offset = boff;
                        auio.uio_resid = PAGE_SIZE;
                        auio.uio_segflg = UIO_SYSSPACE;
                        auio.uio_rw = UIO_READ;
                        auio.uio_procp = p;
                        iov.iov_base = bp->b_data;
                        iov.iov_len = PAGE_SIZE;
                        error = nfs_readrpc(vp, &auio, cred);
                        if (error) {
                                bp->b_error = error;
                                SET(bp->b_flags, B_ERROR);
                                printf("nfs_write: readrpc %d", error);
                        }
                        if (auio.uio_resid > 0)
                                bzero(iov.iov_base, auio.uio_resid);
                        bp->b_validoff = 0;
                        bp->b_validend = PAGE_SIZE - auio.uio_resid;
                        if (np->n_size > boff + bp->b_validend)
                                bp->b_validend = min(np->n_size - boff,
                                                     PAGE_SIZE);
                        bp->b_dirtyoff = 0;
                        bp->b_dirtyend = 0;
                }
        
                /*
                 * If the new write will leave a contiguous dirty
                 * area, just update the b_dirtyoff and b_dirtyend,
                 * otherwise try to extend the dirty region.
                 */
                if (bp->b_dirtyend > 0 &&
                    (on > bp->b_dirtyend || (on + n) < bp->b_dirtyoff)) {
                        off_t start, end;
        
                        boff = (off_t)bp->b_blkno * DEV_BSIZE;
                        if (on > bp->b_dirtyend) {
                                start = boff + bp->b_validend;
                                end = boff + on;
                        } else {
                                start = boff + on + n;
                                end = boff + bp->b_validoff;
                        }
                        
                        /*
                         * It may be that the valid region in the buffer
                         * covers the region we want, in which case just
                         * extend the dirty region.  Otherwise we try to
                         * extend the valid region.
                         */
                        if (end > start) {
                                auio.uio_iov = &iov;
                                auio.uio_iovcnt = 1;
                                auio.uio_offset = start;
                                auio.uio_resid = end - start;
                                auio.uio_segflg = UIO_SYSSPACE;
                                auio.uio_rw = UIO_READ;
                                auio.uio_procp = p;
                                iov.iov_base = bp->b_data + (start - boff);
                                iov.iov_len = end - start;
                                error = nfs_readrpc(vp, &auio, cred);
                                /*
                                 * If we couldn't read, do not do a VOP_BWRITE
                                 * as originally coded. That could also error
                                 * and looping back to "again" as it was doing
                                 * could have us stuck trying to write same buf
                                 * again. nfs_write, will get the entire region
                                 * if nfs_readrpc succeeded. If unsuccessful
                                 * we should just error out. Errors like ESTALE
                                 * would keep us looping rather than transient
                                 * errors justifying a retry. We can return here
                                 * instead of altering dirty region later.  We
                                 * did not write old dirty region at this point.
                                 */
                                if (error) {
                                        bp->b_error = error;
                                        SET(bp->b_flags, B_ERROR);
                                        printf("nfs_write: readrpc2 %d", error);
                                        brelse(bp);
                                        return (error);
                                }
                                /*
                                 * The read worked.
                                 * If there was a short read, just zero fill.
                                 */
                                if (auio.uio_resid > 0)
                                        bzero(iov.iov_base, auio.uio_resid);
                                if (on > bp->b_dirtyend)
                                        bp->b_validend = on;
                                else
                                        bp->b_validoff = on + n;
                        }
                        /*
                         * We now have a valid region which extends up to the
                         * dirty region which we want.
                         */
                        if (on > bp->b_dirtyend)
                                bp->b_dirtyend = on;
                        else
                                bp->b_dirtyoff = on + n;
                }
                if (ISSET(bp->b_flags, B_ERROR)) {
                        error = bp->b_error;
                        brelse(bp);
                        return (error);
                }
                /*
                 * NFS has embedded ucred so crhold() risks zone corruption
                 */
                if (bp->b_wcred == NOCRED)
                        bp->b_wcred = crdup(cred);
                np->n_flag |= NMODIFIED;

                /*
                 * Check for valid write lease and get one as required.
                 * In case getblk() and/or bwrite() delayed us.
                 */
                if ((nmp->nm_flag & NFSMNT_NQNFS) &&
                    NQNFS_CKINVALID(vp, np, ND_WRITE)) {
                        do {
                                error = nqnfs_getlease(vp, ND_WRITE, cred, p);
                        } while (error == NQNFS_EXPIRED);
                        if (error) {
                                brelse(bp);
                                return (error);
                        }
                        if (np->n_lrev != np->n_brev ||
                            (np->n_flag & NQNFSNONCACHE)) {
                                brelse(bp);
                                error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
                                if (error)
                                        return (error);
                                np->n_brev = np->n_lrev;
                                goto again;
                        }
                }
                error = uiomove((char *)bp->b_data + on, n, uio);
                if (error) {
                        SET(bp->b_flags, B_ERROR);
                        brelse(bp);
                        return (error);
                }
                if (bp->b_dirtyend > 0) {
                        bp->b_dirtyoff = min(on, bp->b_dirtyoff);
                        bp->b_dirtyend = max((on + n), bp->b_dirtyend);
                } else {
                        bp->b_dirtyoff = on;
                        bp->b_dirtyend = on + n;
                }
                if (bp->b_validend == 0 || bp->b_validend < bp->b_dirtyoff ||
                    bp->b_validoff > bp->b_dirtyend) {
                        bp->b_validoff = bp->b_dirtyoff;
                        bp->b_validend = bp->b_dirtyend;
                } else {
                        bp->b_validoff = min(bp->b_validoff, bp->b_dirtyoff);
                        bp->b_validend = max(bp->b_validend, bp->b_dirtyend);
                }

                /*
                 * Since this block is being modified, it must be written
                 * again and not just committed.
                 */
                CLR(bp->b_flags, B_NEEDCOMMIT);

                /*
                 * If the lease is non-cachable or IO_SYNC do bwrite().
                 */
                if ((np->n_flag & NQNFSNONCACHE) || (ioflag & IO_SYNC)) {
                        bp->b_proc = p;
                        error = VOP_BWRITE(bp);
                        if (error)
                                return (error);
                        if (np->n_flag & NQNFSNONCACHE) {
                                error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
                                if (error)
                                        return (error);
                        }
                } else if ((n + on) == biosize &&
                        (nmp->nm_flag & NFSMNT_NQNFS) == 0) {
                        bp->b_proc = (struct proc *)0;
                        SET(bp->b_flags, B_ASYNC);
                        (void)nfs_writebp(bp, 0);
                } else
                        bdwrite(bp);
        } while (uio->uio_resid > 0 && n > 0);
        return (0);
}


/*
 * Get an nfs cache block.
 * Allocate a new one if the block isn't currently in the cache
 * and return the block marked busy. If the calling process is
 * interrupted by a signal for an interruptible mount point, return
 * NULL.
 */
static struct buf *
nfs_getcacheblk(vp, bn, size, p, operation)
        struct vnode *vp;
        daddr_t bn;
        int size;
        struct proc *p;
        int operation;  /* defined in sys/buf.h */
{
        register struct buf *bp;
        struct nfsmount *nmp = VFSTONFS(vp->v_mount);
        /*due to getblk/vm interractions, use vm page size or less values */
        int biosize = min(vp->v_mount->mnt_stat.f_iosize, PAGE_SIZE);

        if (nbdwrite > ((nbuf/4)*3) && operation == BLK_WRITE) {
#define __BUFFERS_RECLAIMED 2
                struct buf *tbp[__BUFFERS_RECLAIMED];
                int i;

                /* too many delayed writes, try to free up some buffers */
                for (i = 0; i < __BUFFERS_RECLAIMED; i++)
                        tbp[i] = geteblk(512);

                /* Yield to IO thread */
                (void)tsleep((caddr_t)&nbdwrite, PCATCH, "nbdwrite", 1);

                for (i = (__BUFFERS_RECLAIMED - 1); i >= 0; i--)
                         brelse(tbp[i]);
        }

        if (nmp->nm_flag & NFSMNT_INT) {
                bp = getblk(vp, bn, size, PCATCH, 0, operation);
                while (bp == (struct buf *)0) {
                        if (nfs_sigintr(nmp, (struct nfsreq *)0, p))
                                return ((struct buf *)0);
                        bp = getblk(vp, bn, size, 0, 2 * hz, operation);
                }
        } else
                bp = getblk(vp, bn, size, 0, 0, operation);

        if( vp->v_type == VREG)
                bp->b_blkno = (bn * biosize) / DEV_BSIZE;

        return (bp);
}

/*
 * Flush and invalidate all dirty buffers. If another process is already
 * doing the flush, just wait for completion.
 */
int
nfs_vinvalbuf(vp, flags, cred, p, intrflg)
        struct vnode *vp;
        int flags;
        struct ucred *cred;
        struct proc *p;
        int intrflg;
{
        register struct nfsnode *np = VTONFS(vp);
        struct nfsmount *nmp = VFSTONFS(vp->v_mount);
        int error = 0, slpflag, slptimeo;
        int didhold = 0;

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

        /*
         * Now, flush as required.
         */
        np->n_flag |= NFLUSHINPROG;
        error = vinvalbuf(vp, flags, cred, p, slpflag, 0);
        while (error) {
                /* we seem to be stuck in a loop here if the thread got aborted.
                 * nfs_flush will return EINTR. Not sure if that will cause
                 * other consequences due to EINTR having other meanings in NFS
                 * To handle, no dirty pages, it seems safe to just return from
                 * here. But if we did have dirty pages, how would we get them
                 * written out if thread was aborted? Some other strategy is
                 * necessary. -- EKN
                 */
                if ((intrflg && nfs_sigintr(nmp, (struct nfsreq *)0, p)) ||
                    (error == EINTR && current_thread_aborted())) {
                        np->n_flag &= ~NFLUSHINPROG;
                        if (np->n_flag & NFLUSHWANT) {
                                np->n_flag &= ~NFLUSHWANT;
                                wakeup((caddr_t)&np->n_flag);
                        }
                        return (EINTR);
                }
                error = vinvalbuf(vp, flags, cred, p, 0, slptimeo);
        }
        np->n_flag &= ~(NMODIFIED | NFLUSHINPROG);
        if (np->n_flag & NFLUSHWANT) {
                np->n_flag &= ~NFLUSHWANT;
                wakeup((caddr_t)&np->n_flag);
        }
        didhold = ubc_hold(vp);
        if (didhold) {
                (void) ubc_clean(vp, 1); /* get the pages out of vm also */
                ubc_rele(vp);
        }
        return (0);
}

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

        if (nfs_numasync == 0)
                return (EIO);
        
        nmp = VFSTONFS(bp->b_vp->v_mount);
again:
        if (nmp->nm_flag & NFSMNT_INT)
                slpflag = PCATCH;
        gotiod = FALSE;

        /*
         * Find a free iod to process this request.
         */
        for (i = 0; i < NFS_MAXASYNCDAEMON; i++)
                if (nfs_iodwant[i]) {
                        /*
                         * Found one, so wake it up and tell it which
                         * mount to process.
                         */
                        NFS_DPF(ASYNCIO,
                                ("nfs_asyncio: waking iod %d for mount %p\n",
                                 i, nmp));
                        nfs_iodwant[i] = (struct proc *)0;
                        nfs_iodmount[i] = nmp;
                        nmp->nm_bufqiods++;
                        wakeup((caddr_t)&nfs_iodwant[i]);
                        gotiod = TRUE;
                        break;
                }

        /*
         * If none are free, we may already have an iod working on this mount
         * point.  If so, it will process our request.
         */
        if (!gotiod) {
                if (nmp->nm_bufqiods > 0) {
                        NFS_DPF(ASYNCIO,
                                ("nfs_asyncio: %d iods are already processing mount %p\n",
                                 nmp->nm_bufqiods, nmp));
                        gotiod = TRUE;
                }
        }

        /*
         * If we have an iod which can process the request, then queue
         * the buffer.
         */
        if (gotiod) {
                /*
                 * Ensure that the queue never grows too large.
                 */
                while (nmp->nm_bufqlen >= 2*nfs_numasync) {
                        NFS_DPF(ASYNCIO,
                                ("nfs_asyncio: waiting for mount %p queue to drain\n", nmp));
                        nmp->nm_bufqwant = TRUE;
                        error = tsleep(&nmp->nm_bufq, slpflag | PRIBIO,
                                       "nfsaio", slptimeo);
                        if (error) {
                                if (nfs_sigintr(nmp, NULL, bp->b_proc))
                                        return (EINTR);
                                if (slpflag == PCATCH) {
                                        slpflag = 0;
                                        slptimeo = 2 * hz;
                                }
                        }
                        /*
                         * We might have lost our iod while sleeping,
                         * so check and loop if nescessary.
                         */
                        if (nmp->nm_bufqiods == 0) {
                                NFS_DPF(ASYNCIO,
                                        ("nfs_asyncio: no iods after mount %p queue was drained, looping\n", nmp));
                                goto again;
                        }
                }

                if (ISSET(bp->b_flags, B_READ)) {
                        if (bp->b_rcred == NOCRED && cred != NOCRED) {
                                /*
                                 * NFS has embedded ucred.
                                 * Can not crhold() here as that causes zone corruption
                                 */
                                bp->b_rcred = crdup(cred);
                        }
                } else {
                        SET(bp->b_flags, B_WRITEINPROG);
                        if (bp->b_wcred == NOCRED && cred != NOCRED) {
                                /*
                                 * NFS has embedded ucred.
                                 * Can not crhold() here as that causes zone corruption
                                 */
                                bp->b_wcred = crdup(cred);
                        }
                }

                TAILQ_INSERT_TAIL(&nmp->nm_bufq, bp, b_freelist);
                nmp->nm_bufqlen++;
                return (0);
        }

        /*
         * All the iods are busy on other mounts, so return EIO to
         * force the caller to process the i/o synchronously.
         */
        NFS_DPF(ASYNCIO, ("nfs_asyncio: no iods available, i/o is synchronous\n"));
        return (EIO);
}

/*
 * Do an I/O operation to/from a cache block. This may be called
 * synchronously or from an nfsiod.
 */
int
nfs_doio(bp, cr, p)
        register struct buf *bp;
        struct ucred *cr;
        struct proc *p;
{
        register struct uio *uiop;
        register struct vnode *vp;
        struct nfsnode *np;
        struct nfsmount *nmp;
        int error = 0, diff, len, iomode, must_commit = 0;
        struct uio uio;
        struct iovec io;

        vp = bp->b_vp;
        np = VTONFS(vp);
        nmp = VFSTONFS(vp->v_mount);
        uiop = &uio;
        uiop->uio_iov = &io;
        uiop->uio_iovcnt = 1;
        uiop->uio_segflg = UIO_SYSSPACE;
        uiop->uio_procp = p;

        /* 
         * With UBC, getblk() can return a buf with B_DONE set.
         * This indicates that the VM has valid data for that page.
         * NFS being stateless, this case poses a problem.
         * By definition, the NFS server should always be consulted
         * for the data in that page.
         * So we choose to clear the B_DONE and to do the IO.
         *
         * XXX revisit this if there is a performance issue.
         * XXX In that case, we could play the attribute cache games ...
         */
         if (ISSET(bp->b_flags, B_DONE)) {
                if (!ISSET(bp->b_flags, B_ASYNC))
                        panic("nfs_doio: done and not async");
                CLR(bp->b_flags, B_DONE);
        }
        FSDBG_TOP(256, np->n_size, bp->b_blkno * DEV_BSIZE, bp->b_bcount,
                  bp->b_flags);
        FSDBG(257, bp->b_validoff, bp->b_validend, bp->b_dirtyoff,
              bp->b_dirtyend);
        /*
         * Historically, paging was done with physio, but no more.
         */
        if (ISSET(bp->b_flags, B_PHYS)) {
            /*
             * ...though reading /dev/drum still gets us here.
             */
            io.iov_len = uiop->uio_resid = bp->b_bcount;
            /* mapping was done by vmapbuf() */
            io.iov_base = bp->b_data;
            uiop->uio_offset = (off_t)bp->b_blkno * DEV_BSIZE;
            if (ISSET(bp->b_flags, B_READ)) {
                        uiop->uio_rw = UIO_READ;
                        nfsstats.read_physios++;
                        error = nfs_readrpc(vp, uiop, cr);
            } else {
                        int com;

                        iomode = NFSV3WRITE_DATASYNC;
                        uiop->uio_rw = UIO_WRITE;
                        nfsstats.write_physios++;
                        error = nfs_writerpc(vp, uiop, cr, &iomode, &com);
            }
            if (error) {
                        SET(bp->b_flags, B_ERROR);
                        bp->b_error = error;
            }
        } else if (ISSET(bp->b_flags, B_READ)) {
            io.iov_len = uiop->uio_resid = bp->b_bcount;
            io.iov_base = bp->b_data;
            uiop->uio_rw = UIO_READ;
            switch (vp->v_type) {
            case VREG:
                uiop->uio_offset = (off_t)bp->b_blkno * DEV_BSIZE;
                nfsstats.read_bios++;
                error = nfs_readrpc(vp, uiop, cr);
                FSDBG(262, np->n_size, bp->b_blkno * DEV_BSIZE,
                      uiop->uio_resid, error);
                if (!error) {
                    bp->b_validoff = 0;
                    if (uiop->uio_resid) {
                        /*
                         * If len > 0, there is a hole in the file and
                         * no writes after the hole have been pushed to
                         * the server yet.
                         * Just zero fill the rest of the valid area.
                         */
                        diff = bp->b_bcount - uiop->uio_resid;
                        len = np->n_size - ((u_quad_t)bp->b_blkno * DEV_BSIZE +
                                            diff);
                        if (len > 0) {
                                len = min(len, uiop->uio_resid);
                                bzero((char *)bp->b_data + diff, len);
                                bp->b_validend = diff + len;
                                FSDBG(258, diff, len, 0, 1);
                        } else
                                bp->b_validend = diff;
                    } else
                                bp->b_validend = bp->b_bcount;

                    if (bp->b_validend < bp->b_bufsize) {
                            /*
                             * we're about to release a partial buffer after a
                             * read... the only way we should get here is if
                             * this buffer contains the EOF before releasing it,
                             * we'll zero out to the end of the buffer so that
                             * if a mmap of this page occurs, we'll see zero's
                             * even if a ftruncate extends the file in the
                             * meantime
                             */
                            bzero((caddr_t)(bp->b_data + bp->b_validend),
                                  bp->b_bufsize - bp->b_validend);
                            FSDBG(258, bp->b_validend,
                                  bp->b_bufsize - bp->b_validend, 0, 2);
                    }
                }
                if (p && (vp->v_flag & VTEXT) &&
                        (((nmp->nm_flag & NFSMNT_NQNFS) &&
                          NQNFS_CKINVALID(vp, np, ND_READ) &&
                          np->n_lrev != np->n_brev) ||
                         (!(nmp->nm_flag & NFSMNT_NQNFS) &&
                          np->n_mtime != np->n_vattr.va_mtime.tv_sec))) {
                        uprintf("Process killed due to text file modification\n");
                        psignal(p, SIGKILL);
                        p->p_flag |= P_NOSWAP;
                }
                break;
            case VLNK:
                uiop->uio_offset = (off_t)0;
                nfsstats.readlink_bios++;
                error = nfs_readlinkrpc(vp, uiop, cr);
                break;
            case VDIR:
                nfsstats.readdir_bios++;
                uiop->uio_offset = ((u_quad_t)bp->b_lblkno) * NFS_DIRBLKSIZ;
                if (!(nmp->nm_flag & NFSMNT_NFSV3))
                        nmp->nm_flag &= ~NFSMNT_RDIRPLUS; /* dk@farm.org */
                if (nmp->nm_flag & NFSMNT_RDIRPLUS) {
                        error = nfs_readdirplusrpc(vp, uiop, cr);
                        if (error == NFSERR_NOTSUPP)
                                nmp->nm_flag &= ~NFSMNT_RDIRPLUS;
                }
                if ((nmp->nm_flag & NFSMNT_RDIRPLUS) == 0)
                        error = nfs_readdirrpc(vp, uiop, cr);
                break;
            default:
                printf("nfs_doio: type %x unexpected\n", vp->v_type);
                break;
            };
            if (error) {
                SET(bp->b_flags, B_ERROR);
                bp->b_error = error;
            }
        } else {
            /*
             * mapped I/O may have altered any bytes, so we extend
             * the dirty zone to the valid zone.  For best performance
             * a better solution would be to save & restore page dirty bits
             * around the uiomove which brings write-data into the buffer.
             * Then here we'd check if the page is dirty rather than WASMAPPED
             * Also vnode_pager would change - if a page is clean it might
             * still need to be written due to DELWRI.
             */
            if (UBCINFOEXISTS(vp) && ubc_issetflags(vp, UI_WASMAPPED)) {
                bp->b_dirtyoff = min(bp->b_dirtyoff, bp->b_validoff);
                bp->b_dirtyend = max(bp->b_dirtyend, bp->b_validend);
            }
            if ((off_t)bp->b_blkno * DEV_BSIZE + bp->b_dirtyend > np->n_size)
                bp->b_dirtyend = np->n_size - (off_t)bp->b_blkno * DEV_BSIZE;

            if (bp->b_dirtyend > bp->b_dirtyoff) {
                io.iov_len = uiop->uio_resid = bp->b_dirtyend - bp->b_dirtyoff;
                uiop->uio_offset = (off_t)bp->b_blkno * DEV_BSIZE +
                                   bp->b_dirtyoff;
                io.iov_base = (char *)bp->b_data + bp->b_dirtyoff;
                uiop->uio_rw = UIO_WRITE;

                nfsstats.write_bios++;
                if ((bp->b_flags & (B_ASYNC | B_NEEDCOMMIT | B_NOCACHE)) ==
                    B_ASYNC)
                    iomode = NFSV3WRITE_UNSTABLE;
                else
                    iomode = NFSV3WRITE_FILESYNC;
                SET(bp->b_flags, B_WRITEINPROG);
                error = nfs_writerpc(vp, uiop, cr, &iomode, &must_commit);
                if (!error && iomode == NFSV3WRITE_UNSTABLE)
                    SET(bp->b_flags, B_NEEDCOMMIT);
                else
                    CLR(bp->b_flags, B_NEEDCOMMIT);
                CLR(bp->b_flags, B_WRITEINPROG);
                /*
                 * For an interrupted write, the buffer is still valid
                 * and the write hasn't been pushed to the server yet,
                 * so we can't set B_ERROR and report the interruption
                 * by setting B_EINTR. For the B_ASYNC case, B_EINTR
                 * is not relevant, so the rpc attempt is essentially
                 * a noop.  For the case of a V3 write rpc not being
                 * committed to stable storage, the block is still
                 * dirty and requires either a commit rpc or another
                 * write rpc with iomode == NFSV3WRITE_FILESYNC before
                 * the block is reused. This is indicated by setting
                 * the B_DELWRI and B_NEEDCOMMIT flags.
                 */
                if (error == EINTR || (!error && bp->b_flags & B_NEEDCOMMIT)) {
                        int s;

                        CLR(bp->b_flags, B_INVAL | B_NOCACHE);
                        if (!ISSET(bp->b_flags, B_DELWRI)) {
                                SET(bp->b_flags, B_DELWRI);
                                nbdwrite++;
                        }
                        FSDBG(261, bp->b_validoff, bp->b_validend,
                              bp->b_bufsize, bp->b_bcount);
                        /*
                         * Since for the B_ASYNC case, nfs_bwrite() has
                         * reassigned the buffer to the clean list, we have to
                         * reassign it back to the dirty one. Ugh.
                         */
                        if (ISSET(bp->b_flags, B_ASYNC)) {
                                s = splbio();
                                reassignbuf(bp, vp);
                                splx(s);
                        } else {
                                SET(bp->b_flags, B_EINTR);
                        }
                } else {
                        if (error) {
                                SET(bp->b_flags, B_ERROR);
                                bp->b_error = np->n_error = error;
                                np->n_flag |= NWRITEERR;
                        }
                        bp->b_dirtyoff = bp->b_dirtyend = 0;

                        /*
                         * validoff and validend represent the real data present
                         * in this buffer if validoff is non-zero, than we have
                         * to invalidate the buffer and kill the page when
                         * biodone is called... the same is also true when
                         * validend doesn't extend all the way to the end of the
                         * buffer and validend doesn't equate to the current
                         * EOF... eventually we need to deal with this in a more
                         * humane way (like keeping the partial buffer without
                         * making it immediately available to the VM page cache)
                         */
                        if (bp->b_validoff)
                                SET(bp->b_flags, B_INVAL);
                        else
                        if (bp->b_validend < bp->b_bufsize) {
                                if ((off_t)bp->b_blkno * DEV_BSIZE +
                                    bp->b_validend == np->n_size) {
                                        bzero((caddr_t)(bp->b_data +
                                                        bp->b_validend),
                                              bp->b_bufsize - bp->b_validend);
                                        FSDBG(259, bp->b_validend,
                                              bp->b_bufsize - bp->b_validend, 0,
                                              0);
                                } else
                                        SET(bp->b_flags, B_INVAL);
                        }
                }

            } else {
                if (bp->b_validoff ||
                    (bp->b_validend < bp->b_bufsize &&
                     (off_t)bp->b_blkno * DEV_BSIZE + bp->b_validend !=
                     np->n_size)) {
                        SET(bp->b_flags, B_INVAL);
                }
                if (bp->b_flags & B_INVAL) {
                        FSDBG(260, bp->b_validoff, bp->b_validend,
                              bp->b_bufsize, bp->b_bcount);
                }
                bp->b_resid = 0;
                biodone(bp);
                FSDBG_BOT(256, bp->b_validoff, bp->b_validend, bp->b_bufsize,
                          np->n_size);
                return (0);
            }
        }
        bp->b_resid = uiop->uio_resid;
        if (must_commit)
                nfs_clearcommit(vp->v_mount);

        if (bp->b_flags & B_INVAL) {
                FSDBG(260, bp->b_validoff, bp->b_validend, bp->b_bufsize,
                      bp->b_bcount);
        }
        FSDBG_BOT(256, bp->b_validoff, bp->b_validend, bp->b_bcount, error);

        biodone(bp);
        return (error);
}