NFS - Fix panic if the readdir base offset is beyond the directory EOF

[dragonfly.git] / sys / vfs / nfs / nfs_bio.c

/*
 * 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: /repoman/r/ncvs/src/sys/nfsclient/nfs_bio.c,v 1.130 2004/04/14 23:23:55 peadar Exp $
 * $DragonFly: src/sys/vfs/nfs/nfs_bio.c,v 1.45 2008/07/18 00:09:39 dillon 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/mbuf.h>
#include <sys/msfbuf.h>

#include <vm/vm.h>
#include <vm/vm_extern.h>
#include <vm/vm_page.h>
#include <vm/vm_object.h>
#include <vm/vm_pager.h>
#include <vm/vnode_pager.h>

#include <sys/buf2.h>
#include <sys/thread2.h>
#include <vm/vm_page2.h>

#include "rpcv2.h"
#include "nfsproto.h"
#include "nfs.h"
#include "nfsmount.h"
#include "nfsnode.h"
#include "xdr_subs.h"
#include "nfsm_subs.h"


static struct buf *nfs_getcacheblk(struct vnode *vp, off_t loffset,
                                   int size, struct thread *td);
static int nfs_check_dirent(struct nfs_dirent *dp, int maxlen);
static void nfsiodone_sync(struct bio *bio);
static void nfs_readrpc_bio_done(nfsm_info_t info);
static void nfs_writerpc_bio_done(nfsm_info_t info);
static void nfs_commitrpc_bio_done(nfsm_info_t info);

/*
 * Vnode op for VM getpages.
 *
 * nfs_getpages(struct vnode *a_vp, vm_page_t *a_m, int a_count,
 *              int a_reqpage, vm_ooffset_t a_offset)
 */
int
nfs_getpages(struct vop_getpages_args *ap)
{
        struct thread *td = curthread;          /* XXX */
        int i, error, nextoff, size, toff, count, npages;
        struct uio uio;
        struct iovec iov;
        char *kva;
        struct vnode *vp;
        struct nfsmount *nmp;
        vm_page_t *pages;
        vm_page_t m;
        struct msf_buf *msf;

        vp = ap->a_vp;
        nmp = VFSTONFS(vp->v_mount);
        pages = ap->a_m;
        count = ap->a_count;

        if (vp->v_object == NULL) {
                kprintf("nfs_getpages: called with non-merged cache vnode??\n");
                return VM_PAGER_ERROR;
        }

        if ((nmp->nm_flag & NFSMNT_NFSV3) != 0 &&
            (nmp->nm_state & NFSSTA_GOTFSINFO) == 0)
                (void)nfs_fsinfo(nmp, vp, td);

        npages = btoc(count);

        /*
         * NOTE that partially valid pages may occur in cases other
         * then file EOF, such as when a file is partially written and
         * ftruncate()-extended to a larger size.   It is also possible
         * for the valid bits to be set on garbage beyond the file EOF and
         * clear in the area before EOF (e.g. m->valid == 0xfc), which can
         * occur due to vtruncbuf() and the buffer cache's handling of
         * pages which 'straddle' buffers or when b_bufsize is not a 
         * multiple of PAGE_SIZE.... the buffer cache cannot normally
         * clear the extra bits.  This kind of situation occurs when you
         * make a small write() (m->valid == 0x03) and then mmap() and
         * fault in the buffer(m->valid = 0xFF).  When NFS flushes the
         * buffer (vinvalbuf() m->valid = 0xFC) we are left with a mess.
         *
         * This is combined with the possibility that the pages are partially
         * dirty or that there is a buffer backing the pages that is dirty
         * (even if m->dirty is 0).
         *
         * To solve this problem several hacks have been made:  (1) NFS
         * guarentees that the IO block size is a multiple of PAGE_SIZE and
         * (2) The buffer cache, when invalidating an NFS buffer, will
         * disregard the buffer's fragmentory b_bufsize and invalidate
         * the whole page rather then just the piece the buffer owns.
         *
         * This allows us to assume that a partially valid page found here
         * is fully valid (vm_fault will zero'd out areas of the page not
         * marked as valid).
         */
        m = pages[ap->a_reqpage];
        if (m->valid != 0) {
                for (i = 0; i < npages; ++i) {
                        if (i != ap->a_reqpage)
                                vnode_pager_freepage(pages[i]);
                }
                return(0);
        }

        /*
         * Use an MSF_BUF as a medium to retrieve data from the pages.
         */
        msf_map_pagelist(&msf, pages, npages, 0);
        KKASSERT(msf);
        kva = msf_buf_kva(msf);

        iov.iov_base = kva;
        iov.iov_len = count;
        uio.uio_iov = &iov;
        uio.uio_iovcnt = 1;
        uio.uio_offset = IDX_TO_OFF(pages[0]->pindex);
        uio.uio_resid = count;
        uio.uio_segflg = UIO_SYSSPACE;
        uio.uio_rw = UIO_READ;
        uio.uio_td = td;

        error = nfs_readrpc_uio(vp, &uio);
        msf_buf_free(msf);

        if (error && ((int)uio.uio_resid == count)) {
                kprintf("nfs_getpages: error %d\n", error);
                for (i = 0; i < npages; ++i) {
                        if (i != ap->a_reqpage)
                                vnode_pager_freepage(pages[i]);
                }
                return VM_PAGER_ERROR;
        }

        /*
         * Calculate the number of bytes read and validate only that number
         * of bytes.  Note that due to pending writes, size may be 0.  This
         * does not mean that the remaining data is invalid!
         */

        size = count - (int)uio.uio_resid;

        for (i = 0, toff = 0; i < npages; i++, toff = nextoff) {
                nextoff = toff + PAGE_SIZE;
                m = pages[i];

                m->flags &= ~PG_ZERO;

                /*
                 * NOTE: vm_page_undirty/clear_dirty etc do not clear the
                 *       pmap modified bit.
                 */
                if (nextoff <= size) {
                        /*
                         * Read operation filled an entire page
                         */
                        m->valid = VM_PAGE_BITS_ALL;
                        vm_page_undirty(m);
                } else if (size > toff) {
                        /*
                         * Read operation filled a partial page.
                         */
                        m->valid = 0;
                        vm_page_set_valid(m, 0, size - toff);
                        vm_page_clear_dirty_end_nonincl(m, 0, size - toff);
                        /* handled by vm_fault now        */
                        /* vm_page_zero_invalid(m, TRUE); */
                } else {
                        /*
                         * Read operation was short.  If no error occured
                         * we may have hit a zero-fill section.   We simply
                         * leave valid set to 0.
                         */
                        ;
                }
                if (i != ap->a_reqpage) {
                        /*
                         * Whether or not to leave the page activated is up in
                         * the air, but we should put the page on a page queue
                         * somewhere (it already is in the object).  Result:
                         * It appears that emperical results show that
                         * deactivating pages is best.
                         */

                        /*
                         * Just in case someone was asking for this page we
                         * now tell them that it is ok to use.
                         */
                        if (!error) {
                                if (m->flags & PG_WANTED)
                                        vm_page_activate(m);
                                else
                                        vm_page_deactivate(m);
                                vm_page_wakeup(m);
                        } else {
                                vnode_pager_freepage(m);
                        }
                }
        }
        return 0;
}

/*
 * Vnode op for VM putpages.
 *
 * The pmap modified bit was cleared prior to the putpages and probably
 * couldn't get set again until after our I/O completed, since the page
 * should not be mapped.  But don't count on it.  The m->dirty bits must
 * be completely cleared when we finish even if the count is truncated.
 *
 * nfs_putpages(struct vnode *a_vp, vm_page_t *a_m, int a_count, int a_sync,
 *              int *a_rtvals, vm_ooffset_t a_offset)
 */
int
nfs_putpages(struct vop_putpages_args *ap)
{
        struct thread *td = curthread;
        struct uio uio;
        struct iovec iov;
        char *kva;
        int iomode, must_commit, i, error, npages, count;
        off_t offset;
        int *rtvals;
        struct vnode *vp;
        struct nfsmount *nmp;
        struct nfsnode *np;
        vm_page_t *pages;
        struct msf_buf *msf;

        vp = ap->a_vp;
        np = VTONFS(vp);
        nmp = VFSTONFS(vp->v_mount);
        pages = ap->a_m;
        count = ap->a_count;
        rtvals = ap->a_rtvals;
        npages = btoc(count);
        offset = IDX_TO_OFF(pages[0]->pindex);

        if ((nmp->nm_flag & NFSMNT_NFSV3) != 0 &&
            (nmp->nm_state & NFSSTA_GOTFSINFO) == 0)
                (void)nfs_fsinfo(nmp, vp, td);

        for (i = 0; i < npages; i++) {
                rtvals[i] = VM_PAGER_AGAIN;
        }

        /*
         * When putting pages, do not extend file past EOF.
         */

        if (offset + count > np->n_size) {
                count = np->n_size - offset;
                if (count < 0)
                        count = 0;
        }

        /*
         * Use an MSF_BUF as a medium to retrieve data from the pages.
         */
        msf_map_pagelist(&msf, pages, npages, 0);
        KKASSERT(msf);
        kva = msf_buf_kva(msf);

        iov.iov_base = kva;
        iov.iov_len = count;
        uio.uio_iov = &iov;
        uio.uio_iovcnt = 1;
        uio.uio_offset = offset;
        uio.uio_resid = (size_t)count;
        uio.uio_segflg = UIO_SYSSPACE;
        uio.uio_rw = UIO_WRITE;
        uio.uio_td = td;

        if ((ap->a_sync & VM_PAGER_PUT_SYNC) == 0)
            iomode = NFSV3WRITE_UNSTABLE;
        else
            iomode = NFSV3WRITE_FILESYNC;

        error = nfs_writerpc_uio(vp, &uio, &iomode, &must_commit);

        msf_buf_free(msf);

        if (error == 0) {
                int nwritten;

                nwritten = round_page(count - (int)uio.uio_resid) / PAGE_SIZE;
                for (i = 0; i < nwritten; i++) {
                        rtvals[i] = VM_PAGER_OK;
                        vm_page_undirty(pages[i]);
                }
                if (must_commit)
                        nfs_clearcommit(vp->v_mount);
        }
        return rtvals[0];
}

/*
 * Vnode op for read using bio
 */
int
nfs_bioread(struct vnode *vp, struct uio *uio, int ioflag)
{
        struct nfsnode *np = VTONFS(vp);
        int biosize, i;
        struct buf *bp, *rabp;
        struct vattr vattr;
        struct thread *td;
        struct nfsmount *nmp = VFSTONFS(vp->v_mount);
        off_t lbn, rabn;
        off_t raoffset;
        off_t loffset;
        int seqcount;
        int nra, error = 0;
        int boff = 0;
        size_t n;

#ifdef DIAGNOSTIC
        if (uio->uio_rw != UIO_READ)
                panic("nfs_read mode");
#endif
        if (uio->uio_resid == 0)
                return (0);
        if (uio->uio_offset < 0)        /* XXX VDIR cookies can be negative */
                return (EINVAL);
        td = uio->uio_td;

        if ((nmp->nm_flag & NFSMNT_NFSV3) != 0 &&
            (nmp->nm_state & NFSSTA_GOTFSINFO) == 0)
                (void)nfs_fsinfo(nmp, vp, td);
        if (vp->v_type != VDIR &&
            (uio->uio_offset + uio->uio_resid) > nmp->nm_maxfilesize)
                return (EFBIG);
        biosize = vp->v_mount->mnt_stat.f_iosize;
        seqcount = (int)((off_t)(ioflag >> IO_SEQSHIFT) * biosize / BKVASIZE);

        /*
         * 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.
         *
         * NFS:         If local changes have been made and this is a
         *              directory, the directory must be invalidated and
         *              the attribute cache must be cleared.
         *
         *              GETATTR is called to synchronize the file size.
         *
         *              If remote changes are detected local data is flushed
         *              and the cache is invalidated.
         *
         *              NOTE: In the normal case the attribute cache is not
         *              cleared which means GETATTR may use cached data and
         *              not immediately detect changes made on the server.
         */
        if ((np->n_flag & NLMODIFIED) && vp->v_type == VDIR) {
                nfs_invaldir(vp);
                error = nfs_vinvalbuf(vp, V_SAVE, 1);
                if (error)
                        return (error);
                np->n_attrstamp = 0;
        }
        error = VOP_GETATTR(vp, &vattr);
        if (error)
                return (error);
        if (np->n_flag & NRMODIFIED) {
                if (vp->v_type == VDIR)
                        nfs_invaldir(vp);
                error = nfs_vinvalbuf(vp, V_SAVE, 1);
                if (error)
                        return (error);
                np->n_flag &= ~NRMODIFIED;
        }

        /*
         * Loop until uio exhausted or we hit EOF
         */
        do {
            bp = NULL;

            switch (vp->v_type) {
            case VREG:
                nfsstats.biocache_reads++;
                lbn = uio->uio_offset / biosize;
                boff = uio->uio_offset & (biosize - 1);
                loffset = (off_t)lbn * biosize;

                /*
                 * Start the read ahead(s), as required.
                 */
                if (nmp->nm_readahead > 0 && nfs_asyncok(nmp)) {
                    for (nra = 0; nra < nmp->nm_readahead && nra < seqcount &&
                        (off_t)(lbn + 1 + nra) * biosize < np->n_size; nra++) {
                        rabn = lbn + 1 + nra;
                        raoffset = (off_t)rabn * biosize;
                        if (findblk(vp, raoffset, FINDBLK_TEST) == NULL) {
                            rabp = nfs_getcacheblk(vp, raoffset, biosize, td);
                            if (!rabp)
                                return (EINTR);
                            if ((rabp->b_flags & (B_CACHE|B_DELWRI)) == 0) {
                                rabp->b_cmd = BUF_CMD_READ;
                                vfs_busy_pages(vp, rabp);
                                nfs_asyncio(vp, &rabp->b_bio2);
                            } else {
                                brelse(rabp);
                            }
                        }
                    }
                }

                /*
                 * Obtain the buffer cache block.  Figure out the buffer size
                 * when we are at EOF.  If we are modifying the size of the
                 * buffer based on an EOF condition we need to hold 
                 * nfs_rslock() through obtaining the buffer to prevent
                 * a potential writer-appender from messing with n_size.
                 * Otherwise we may accidently truncate the buffer and
                 * lose dirty data.
                 *
                 * Note that bcount is *not* DEV_BSIZE aligned.
                 */
                if (loffset + boff >= np->n_size) {
                        n = 0;
                        break;
                }
                bp = nfs_getcacheblk(vp, loffset, biosize, td);

                if (bp == NULL)
                        return (EINTR);

                /*
                 * If B_CACHE is not set, we must issue the read.  If this
                 * fails, we return an error.
                 */
                if ((bp->b_flags & B_CACHE) == 0) {
                        bp->b_cmd = BUF_CMD_READ;
                        bp->b_bio2.bio_done = nfsiodone_sync;
                        bp->b_bio2.bio_flags |= BIO_SYNC;
                        vfs_busy_pages(vp, bp);
                        error = nfs_doio(vp, &bp->b_bio2, td);
                        if (error) {
                                brelse(bp);
                                return (error);
                        }
                }

                /*
                 * on is the offset into the current bp.  Figure out how many
                 * bytes we can copy out of the bp.  Note that bcount is
                 * NOT DEV_BSIZE aligned.
                 *
                 * Then figure out how many bytes we can copy into the uio.
                 */
                n = biosize - boff;
                if (n > uio->uio_resid)
                        n = uio->uio_resid;
                if (loffset + boff + n > np->n_size)
                        n = np->n_size - loffset - boff;
                break;
            case VLNK:
                biosize = min(NFS_MAXPATHLEN, np->n_size);
                nfsstats.biocache_readlinks++;
                bp = nfs_getcacheblk(vp, (off_t)0, biosize, td);
                if (bp == NULL)
                        return (EINTR);
                if ((bp->b_flags & B_CACHE) == 0) {
                        bp->b_cmd = BUF_CMD_READ;
                        bp->b_bio2.bio_done = nfsiodone_sync;
                        bp->b_bio2.bio_flags |= BIO_SYNC;
                        vfs_busy_pages(vp, bp);
                        error = nfs_doio(vp, &bp->b_bio2, td);
                        if (error) {
                                bp->b_flags |= B_ERROR | B_INVAL;
                                brelse(bp);
                                return (error);
                        }
                }
                n = szmin(uio->uio_resid, (size_t)bp->b_bcount - bp->b_resid);
                boff = 0;
                break;
            case VDIR:
                nfsstats.biocache_readdirs++;
                if (np->n_direofoffset &&
                    uio->uio_offset >= np->n_direofoffset
                ) {
                        return (0);
                }
                lbn = (uoff_t)uio->uio_offset / NFS_DIRBLKSIZ;
                boff = uio->uio_offset & (NFS_DIRBLKSIZ - 1);
                loffset = uio->uio_offset - boff;
                bp = nfs_getcacheblk(vp, loffset, NFS_DIRBLKSIZ, td);
                if (bp == NULL)
                        return (EINTR);

                if ((bp->b_flags & B_CACHE) == 0) {
                    bp->b_cmd = BUF_CMD_READ;
                    bp->b_bio2.bio_done = nfsiodone_sync;
                    bp->b_bio2.bio_flags |= BIO_SYNC;
                    vfs_busy_pages(vp, bp);
                    error = nfs_doio(vp, &bp->b_bio2, td);
                    if (error)
                            brelse(bp);
                    while (error == NFSERR_BAD_COOKIE) {
                        kprintf("got bad cookie vp %p bp %p\n", vp, bp);
                        nfs_invaldir(vp);
                        error = nfs_vinvalbuf(vp, 0, 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.
                         *
                         * Leave the last bp intact unless there is an error.
                         * Loop back up to the while if the error is another
                         * NFSERR_BAD_COOKIE (double yuch!).
                         */
                        for (i = 0; i <= lbn && !error; i++) {
                            if (np->n_direofoffset
                                && (i * NFS_DIRBLKSIZ) >= np->n_direofoffset)
                                    return (0);
                            bp = nfs_getcacheblk(vp, (off_t)i * NFS_DIRBLKSIZ,
                                                 NFS_DIRBLKSIZ, td);
                            if (!bp)
                                return (EINTR);
                            if ((bp->b_flags & B_CACHE) == 0) {
                                    bp->b_cmd = BUF_CMD_READ;
                                    bp->b_bio2.bio_done = nfsiodone_sync;
                                    bp->b_bio2.bio_flags |= BIO_SYNC;
                                    vfs_busy_pages(vp, bp);
                                    error = nfs_doio(vp, &bp->b_bio2, td);
                                    /*
                                     * 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 (nmp->nm_readahead > 0 && nfs_asyncok(nmp) &&
                    (bp->b_flags & B_INVAL) == 0 &&
                    (np->n_direofoffset == 0 ||
                    loffset + NFS_DIRBLKSIZ < np->n_direofoffset) &&
                    findblk(vp, loffset + NFS_DIRBLKSIZ, FINDBLK_TEST) == NULL
                ) {
                        rabp = nfs_getcacheblk(vp, loffset + NFS_DIRBLKSIZ,
                                               NFS_DIRBLKSIZ, td);
                        if (rabp) {
                            if ((rabp->b_flags & (B_CACHE|B_DELWRI)) == 0) {
                                rabp->b_cmd = BUF_CMD_READ;
                                vfs_busy_pages(vp, rabp);
                                nfs_asyncio(vp, &rabp->b_bio2);
                            } else {
                                brelse(rabp);
                            }
                        }
                }
                /*
                 * 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 ( due to
                 * being VMIO ) later.  So we keep track of the directory eof
                 * in np->n_direofoffset and chop it off as an extra step 
                 * right here.
                 *
                 * NOTE: boff could already be beyond EOF.
                 */
                if ((size_t)boff > NFS_DIRBLKSIZ - bp->b_resid) {
                        n = 0;
                } else {
                        n = szmin(uio->uio_resid,
                                  NFS_DIRBLKSIZ - bp->b_resid - (size_t)boff);
                }
                if (np->n_direofoffset &&
                    n > (size_t)(np->n_direofoffset - uio->uio_offset)) {
                        n = (size_t)(np->n_direofoffset - uio->uio_offset);
                }
                break;
            default:
                kprintf(" nfs_bioread: type %x unexpected\n",vp->v_type);
                n = 0;
                break;
            };

            switch (vp->v_type) {
            case VREG:
                if (n > 0)
                    error = uiomove(bp->b_data + boff, n, uio);
                break;
            case VLNK:
                if (n > 0)
                    error = uiomove(bp->b_data + boff, n, uio);
                n = 0;
                break;
            case VDIR:
                if (n > 0) {
                    off_t old_off = uio->uio_offset;
                    caddr_t cpos, epos;
                    struct nfs_dirent *dp;

                    /*
                     * We are casting cpos to nfs_dirent, it must be
                     * int-aligned.
                     */
                    if (boff & 3) {
                        error = EINVAL;
                        break;
                    }

                    cpos = bp->b_data + boff;
                    epos = bp->b_data + boff + n;
                    while (cpos < epos && error == 0 && uio->uio_resid > 0) {
                            dp = (struct nfs_dirent *)cpos;
                            error = nfs_check_dirent(dp, (int)(epos - cpos));
                            if (error)
                                    break;
                            if (vop_write_dirent(&error, uio, dp->nfs_ino,
                                dp->nfs_type, dp->nfs_namlen, dp->nfs_name)) {
                                    break;
                            }
                            cpos += dp->nfs_reclen;
                    }
                    n = 0;
                    if (error == 0) {
                            uio->uio_offset = old_off + cpos -
                                              bp->b_data - boff;
                    }
                }
                break;
            default:
                kprintf(" nfs_bioread: type %x unexpected\n",vp->v_type);
            }
            if (bp)
                    brelse(bp);
        } while (error == 0 && uio->uio_resid > 0 && n > 0);
        return (error);
}

/*
 * Userland can supply any 'seek' offset when reading a NFS directory.
 * Validate the structure so we don't panic the kernel.  Note that
 * the element name is nul terminated and the nul is not included
 * in nfs_namlen.
 */
static
int
nfs_check_dirent(struct nfs_dirent *dp, int maxlen)
{
        int nfs_name_off = offsetof(struct nfs_dirent, nfs_name[0]);

        if (nfs_name_off >= maxlen)
                return (EINVAL);
        if (dp->nfs_reclen < nfs_name_off || dp->nfs_reclen > maxlen)
                return (EINVAL);
        if (nfs_name_off + dp->nfs_namlen >= dp->nfs_reclen)
                return (EINVAL);
        if (dp->nfs_reclen & 3)
                return (EINVAL);
        return (0);
}

/*
 * Vnode op for write using bio
 *
 * nfs_write(struct vnode *a_vp, struct uio *a_uio, int a_ioflag,
 *           struct ucred *a_cred)
 */
int
nfs_write(struct vop_write_args *ap)
{
        struct uio *uio = ap->a_uio;
        struct thread *td = uio->uio_td;
        struct vnode *vp = ap->a_vp;
        struct nfsnode *np = VTONFS(vp);
        int ioflag = ap->a_ioflag;
        struct buf *bp;
        struct vattr vattr;
        struct nfsmount *nmp = VFSTONFS(vp->v_mount);
        off_t loffset;
        int boff, bytes;
        int error = 0;
        int haverslock = 0;
        int bcount;
        int biosize;

#ifdef DIAGNOSTIC
        if (uio->uio_rw != UIO_WRITE)
                panic("nfs_write mode");
        if (uio->uio_segflg == UIO_USERSPACE && uio->uio_td != curthread)
                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) != 0 &&
            (nmp->nm_state & NFSSTA_GOTFSINFO) == 0)
                (void)nfs_fsinfo(nmp, vp, td);

        /*
         * Synchronously flush pending buffers if we are in synchronous
         * mode or if we are appending.
         */
        if (ioflag & (IO_APPEND | IO_SYNC)) {
                if (np->n_flag & NLMODIFIED) {
                        np->n_attrstamp = 0;
                        error = nfs_flush(vp, MNT_WAIT, td, 0);
                        /* error = nfs_vinvalbuf(vp, V_SAVE, 1); */
                        if (error)
                                return (error);
                }
        }

        /*
         * If IO_APPEND then load uio_offset.  We restart here if we cannot
         * get the append lock.
         */
restart:
        if (ioflag & IO_APPEND) {
                np->n_attrstamp = 0;
                error = VOP_GETATTR(vp, &vattr);
                if (error)
                        return (error);
                uio->uio_offset = np->n_size;
        }

        if (uio->uio_offset < 0)
                return (EINVAL);
        if ((uio->uio_offset + uio->uio_resid) > nmp->nm_maxfilesize)
                return (EFBIG);
        if (uio->uio_resid == 0)
                return (0);

        /*
         * We need to obtain the rslock if we intend to modify np->n_size
         * in order to guarentee the append point with multiple contending
         * writers, to guarentee that no other appenders modify n_size
         * while we are trying to obtain a truncated buffer (i.e. to avoid
         * accidently truncating data written by another appender due to
         * the race), and to ensure that the buffer is populated prior to
         * our extending of the file.  We hold rslock through the entire
         * operation.
         *
         * Note that we do not synchronize the case where someone truncates
         * the file while we are appending to it because attempting to lock
         * this case may deadlock other parts of the system unexpectedly.
         */
        if ((ioflag & IO_APPEND) ||
            uio->uio_offset + uio->uio_resid > np->n_size) {
                switch(nfs_rslock(np)) {
                case ENOLCK:
                        goto restart;
                        /* not reached */
                case EINTR:
                case ERESTART:
                        return(EINTR);
                        /* not reached */
                default:
                        break;
                }
                haverslock = 1;
        }

        /*
         * 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 (td->td_proc && uio->uio_offset + uio->uio_resid >
              td->td_proc->p_rlimit[RLIMIT_FSIZE].rlim_cur) {
                lwpsignal(td->td_proc, td->td_lwp, SIGXFSZ);
                if (haverslock)
                        nfs_rsunlock(np);
                return (EFBIG);
        }

        biosize = vp->v_mount->mnt_stat.f_iosize;

        do {
                nfsstats.biocache_writes++;
                boff = uio->uio_offset & (biosize-1);
                loffset = uio->uio_offset - boff;
                bytes = (int)szmin((unsigned)(biosize - boff), uio->uio_resid);
again:
                /*
                 * Handle direct append and file extension cases, calculate
                 * unaligned buffer size.  When extending B_CACHE will be
                 * set if possible.  See UIO_NOCOPY note below.
                 */
                if (uio->uio_offset + bytes > np->n_size) {
                        np->n_flag |= NLMODIFIED;
                        bp = nfs_meta_setsize(vp, td, loffset, boff, bytes);
                } else {
                        bp = nfs_getcacheblk(vp, loffset, biosize, td);
                }
                if (bp == NULL) {
                        error = EINTR;
                        break;
                }

                /*
                 * Actual bytes in buffer which we care about
                 */
                if (loffset + biosize < np->n_size)
                        bcount = biosize;
                else
                        bcount = (int)(np->n_size - loffset);

                /*
                 * Avoid a read by setting B_CACHE where the data we
                 * intend to write covers the entire buffer.  Note
                 * that the buffer may have been set to B_CACHE by
                 * nfs_meta_setsize() above or otherwise inherited the
                 * flag, but if B_CACHE isn't set the buffer may be
                 * uninitialized and must be zero'd to accomodate
                 * future seek+write's.
                 *
                 * See the comments in kern/vfs_bio.c's getblk() for
                 * more information.
                 *
                 * When doing a UIO_NOCOPY write the buffer is not
                 * overwritten and we cannot just set B_CACHE unconditionally
                 * for full-block writes.
                 */
                if (boff == 0 && bytes == biosize &&
                    uio->uio_segflg != UIO_NOCOPY) {
                        bp->b_flags |= B_CACHE;
                        bp->b_flags &= ~(B_ERROR | B_INVAL);
                }

                /*
                 * b_resid may be set due to file EOF if we extended out.
                 * The NFS bio code will zero the difference anyway so
                 * just acknowledged the fact and set b_resid to 0.
                 */
                if ((bp->b_flags & B_CACHE) == 0) {
                        bp->b_cmd = BUF_CMD_READ;
                        bp->b_bio2.bio_done = nfsiodone_sync;
                        bp->b_bio2.bio_flags |= BIO_SYNC;
                        vfs_busy_pages(vp, bp);
                        error = nfs_doio(vp, &bp->b_bio2, td);
                        if (error) {
                                brelse(bp);
                                break;
                        }
                        bp->b_resid = 0;
                }
                np->n_flag |= NLMODIFIED;

                /*
                 * If dirtyend exceeds file size, chop it down.  This should
                 * not normally occur but there is an append race where it
                 * might occur XXX, so we log it. 
                 *
                 * If the chopping creates a reverse-indexed or degenerate
                 * situation with dirtyoff/end, we 0 both of them.
                 */
                if (bp->b_dirtyend > bcount) {
                        kprintf("NFS append race @%08llx:%d\n", 
                            (long long)bp->b_bio2.bio_offset,
                            bp->b_dirtyend - bcount);
                        bp->b_dirtyend = bcount;
                }

                if (bp->b_dirtyoff >= bp->b_dirtyend)
                        bp->b_dirtyoff = bp->b_dirtyend = 0;

                /*
                 * If the new write will leave a contiguous dirty
                 * area, just update the b_dirtyoff and b_dirtyend,
                 * otherwise force a write rpc of the old dirty area.
                 *
                 * While it is possible to merge discontiguous writes due to 
                 * our having a B_CACHE buffer ( and thus valid read data
                 * for the hole), we don't because it could lead to 
                 * significant cache coherency problems with multiple clients,
                 * especially if locking is implemented later on.
                 *
                 * as an optimization we could theoretically maintain
                 * a linked list of discontinuous areas, but we would still
                 * have to commit them separately so there isn't much
                 * advantage to it except perhaps a bit of asynchronization.
                 */
                if (bp->b_dirtyend > 0 &&
                    (boff > bp->b_dirtyend ||
                     (boff + bytes) < bp->b_dirtyoff)
                ) {
                        if (bwrite(bp) == EINTR) {
                                error = EINTR;
                                break;
                        }
                        goto again;
                }

                error = uiomove(bp->b_data + boff, bytes, uio);

                /*
                 * Since this block is being modified, it must be written
                 * again and not just committed.  Since write clustering does
                 * not work for the stage 1 data write, only the stage 2
                 * commit rpc, we have to clear B_CLUSTEROK as well.
                 */
                bp->b_flags &= ~(B_NEEDCOMMIT | B_CLUSTEROK);

                if (error) {
                        brelse(bp);
                        break;
                }

                /*
                 * Only update dirtyoff/dirtyend if not a degenerate 
                 * condition.
                 *
                 * The underlying VM pages have been marked valid by
                 * virtue of acquiring the bp.  Because the entire buffer
                 * is marked dirty we do not have to worry about cleaning
                 * out the related dirty bits (and wouldn't really know
                 * how to deal with byte ranges anyway)
                 */
                if (bytes) {
                        if (bp->b_dirtyend > 0) {
                                bp->b_dirtyoff = imin(boff, bp->b_dirtyoff);
                                bp->b_dirtyend = imax(boff + bytes,
                                                      bp->b_dirtyend);
                        } else {
                                bp->b_dirtyoff = boff;
                                bp->b_dirtyend = boff + bytes;
                        }
                }

                /*
                 * If the lease is non-cachable or IO_SYNC do bwrite().
                 *
                 * IO_INVAL appears to be unused.  The idea appears to be
                 * to turn off caching in this case.  Very odd.  XXX
                 *
                 * If nfs_async is set bawrite() will use an unstable write
                 * (build dirty bufs on the server), so we might as well
                 * push it out with bawrite().  If nfs_async is not set we
                 * use bdwrite() to cache dirty bufs on the client.
                 */
                if (ioflag & IO_SYNC) {
                        if (ioflag & IO_INVAL)
                                bp->b_flags |= B_NOCACHE;
                        error = bwrite(bp);
                        if (error)
                                break;
                } else if (boff + bytes == biosize && nfs_async) {
                        bawrite(bp);
                } else {
                        bdwrite(bp);
                }
        } while (uio->uio_resid > 0 && bytes > 0);

        if (haverslock)
                nfs_rsunlock(np);

        return (error);
}

/*
 * 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.
 *
 * The caller must carefully deal with the possible B_INVAL state of
 * the buffer.  nfs_startio() clears B_INVAL (and nfs_asyncio() clears it
 * indirectly), so synchronous reads can be issued without worrying about
 * the B_INVAL state.  We have to be a little more careful when dealing
 * with writes (see comments in nfs_write()) when extending a file past
 * its EOF.
 */
static struct buf *
nfs_getcacheblk(struct vnode *vp, off_t loffset, int size, struct thread *td)
{
        struct buf *bp;
        struct mount *mp;
        struct nfsmount *nmp;

        mp = vp->v_mount;
        nmp = VFSTONFS(mp);

        if (nmp->nm_flag & NFSMNT_INT) {
                bp = getblk(vp, loffset, size, GETBLK_PCATCH, 0);
                while (bp == NULL) {
                        if (nfs_sigintr(nmp, NULL, td))
                                return (NULL);
                        bp = getblk(vp, loffset, size, 0, 2 * hz);
                }
        } else {
                bp = getblk(vp, loffset, size, 0, 0);
        }

        /*
         * bio2, the 'device' layer.  Since BIOs use 64 bit byte offsets
         * now, no translation is necessary.
         */
        bp->b_bio2.bio_offset = loffset;
        return (bp);
}

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

        if (vp->v_flag & VRECLAIMED)
                return (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, 0, "nfsvinval", slptimeo);
                if (error && intrflg && nfs_sigintr(nmp, NULL, td))
                        return (EINTR);
        }

        /*
         * Now, flush as required.
         */
        np->n_flag |= NFLUSHINPROG;
        error = vinvalbuf(vp, flags, slpflag, 0);
        while (error) {
                if (intrflg && nfs_sigintr(nmp, NULL, td)) {
                        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, 0, slptimeo);
        }
        np->n_flag &= ~(NLMODIFIED | NFLUSHINPROG);
        if (np->n_flag & NFLUSHWANT) {
                np->n_flag &= ~NFLUSHWANT;
                wakeup((caddr_t)&np->n_flag);
        }
        return (0);
}

/*
 * Return true (non-zero) if the txthread and rxthread are operational
 * and we do not already have too many not-yet-started BIO's built up.
 */
int
nfs_asyncok(struct nfsmount *nmp)
{
        return (nmp->nm_bioqlen < nfs_maxasyncbio &&
                nmp->nm_bioqlen < nmp->nm_maxasync_scaled / NFS_ASYSCALE &&
                nmp->nm_rxstate <= NFSSVC_PENDING &&
                nmp->nm_txstate <= NFSSVC_PENDING);
}

/*
 * The read-ahead code calls this to queue a bio to the txthread.
 *
 * We don't touch the bio otherwise... that is, we do not even
 * construct or send the initial rpc.  The txthread will do it
 * for us.
 *
 * NOTE!  nm_bioqlen is not decremented until the request completes,
 *        so it does not reflect the number of bio's on bioq.
 */
void
nfs_asyncio(struct vnode *vp, struct bio *bio)
{
        struct buf *bp = bio->bio_buf;
        struct nfsmount *nmp = VFSTONFS(vp->v_mount);

        KKASSERT(vp->v_tag == VT_NFS);
        BUF_KERNPROC(bp);
        bio->bio_driver_info = vp;
        crit_enter();
        TAILQ_INSERT_TAIL(&nmp->nm_bioq, bio, bio_act);
        atomic_add_int(&nmp->nm_bioqlen, 1);
        crit_exit();
        nfssvc_iod_writer_wakeup(nmp);
}

/*
 * nfs_dio()    - Execute a BIO operation synchronously.  The BIO will be
 *                completed and its error returned.  The caller is responsible
 *                for brelse()ing it.  ONLY USE FOR BIO_SYNC IOs!  Otherwise
 *                our error probe will be against an invalid pointer.
 *
 * nfs_startio()- Execute a BIO operation assynchronously.
 *
 * NOTE: nfs_asyncio() is used to initiate an asynchronous BIO operation,
 *       which basically just queues it to the txthread.  nfs_startio()
 *       actually initiates the I/O AFTER it has gotten to the txthread.
 *
 * NOTE: td might be NULL.
 *
 * NOTE: Caller has already busied the I/O.
 */
void
nfs_startio(struct vnode *vp, struct bio *bio, struct thread *td)
{
        struct buf *bp = bio->bio_buf;
        struct nfsnode *np;
        struct nfsmount *nmp;

        KKASSERT(vp->v_tag == VT_NFS);
        np = VTONFS(vp);
        nmp = VFSTONFS(vp->v_mount);

        /*
         * clear B_ERROR and B_INVAL state prior to initiating the I/O.  We
         * do this here so we do not have to do it in all the code that
         * calls us.
         */
        bp->b_flags &= ~(B_ERROR | B_INVAL);

        KASSERT(bp->b_cmd != BUF_CMD_DONE,
                ("nfs_doio: bp %p already marked done!", bp));

        if (bp->b_cmd == BUF_CMD_READ) {
            switch (vp->v_type) {
            case VREG:
                nfsstats.read_bios++;
                nfs_readrpc_bio(vp, bio);
                break;
            case VLNK:
#if 0
                bio->bio_offset = 0;
                nfsstats.readlink_bios++;
                nfs_readlinkrpc_bio(vp, bio);
#else
                nfs_doio(vp, bio, td);
#endif
                break;
            case VDIR:
                /*
                 * NOTE: If nfs_readdirplusrpc_bio() is requested but
                 *       not supported, it will chain to
                 *       nfs_readdirrpc_bio().
                 */
#if 0
                nfsstats.readdir_bios++;
                uiop->uio_offset = bio->bio_offset;
                if (nmp->nm_flag & NFSMNT_RDIRPLUS)
                        nfs_readdirplusrpc_bio(vp, bio);
                else
                        nfs_readdirrpc_bio(vp, bio);
#else
                nfs_doio(vp, bio, td);
#endif
                break;
            default:
                kprintf("nfs_doio:  type %x unexpected\n",vp->v_type);
                bp->b_flags |= B_ERROR;
                bp->b_error = EINVAL;
                biodone(bio);
                break;
            }
        } else {
            /*
             * If we only need to commit, try to commit.  If this fails
             * it will chain through to the write.  Basically all the logic
             * in nfs_doio() is replicated.
             */
            KKASSERT(bp->b_cmd == BUF_CMD_WRITE);
            if (bp->b_flags & B_NEEDCOMMIT)
                nfs_commitrpc_bio(vp, bio);
            else
                nfs_writerpc_bio(vp, bio);
        }
}

int
nfs_doio(struct vnode *vp, struct bio *bio, struct thread *td)
{
        struct buf *bp = bio->bio_buf;
        struct uio *uiop;
        struct nfsnode *np;
        struct nfsmount *nmp;
        int error = 0;
        int iomode, must_commit;
        size_t n;
        struct uio uio;
        struct iovec io;

        KKASSERT(vp->v_tag == VT_NFS);
        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_td = td;

        /*
         * clear B_ERROR and B_INVAL state prior to initiating the I/O.  We
         * do this here so we do not have to do it in all the code that
         * calls us.
         */
        bp->b_flags &= ~(B_ERROR | B_INVAL);

        KASSERT(bp->b_cmd != BUF_CMD_DONE, 
                ("nfs_doio: bp %p already marked done!", bp));

        if (bp->b_cmd == BUF_CMD_READ) {
            io.iov_len = uiop->uio_resid = (size_t)bp->b_bcount;
            io.iov_base = bp->b_data;
            uiop->uio_rw = UIO_READ;

            switch (vp->v_type) {
            case VREG:
                /*
                 * When reading from a regular file zero-fill any residual.
                 * Note that this residual has nothing to do with NFS short
                 * reads, which nfs_readrpc_uio() will handle for us.
                 *
                 * We have to do this because when we are write extending
                 * a file the server may not have the same notion of
                 * filesize as we do.  Our BIOs should already be sized
                 * (b_bcount) to account for the file EOF.
                 */
                nfsstats.read_bios++;
                uiop->uio_offset = bio->bio_offset;
                error = nfs_readrpc_uio(vp, uiop);
                if (error == 0 && uiop->uio_resid) {
                        n = (size_t)bp->b_bcount - uiop->uio_resid;
                        bzero(bp->b_data + n, bp->b_bcount - n);
                        uiop->uio_resid = 0;
                }
                if (td && td->td_proc && (vp->v_flag & VTEXT) &&
                    np->n_mtime != np->n_vattr.va_mtime.tv_sec) {
                        uprintf("Process killed due to text file modification\n");
                        ksignal(td->td_proc, SIGKILL);
                }
                break;
            case VLNK:
                uiop->uio_offset = 0;
                nfsstats.readlink_bios++;
                error = nfs_readlinkrpc_uio(vp, uiop);
                break;
            case VDIR:
                nfsstats.readdir_bios++;
                uiop->uio_offset = bio->bio_offset;
                if (nmp->nm_flag & NFSMNT_RDIRPLUS) {
                        error = nfs_readdirplusrpc_uio(vp, uiop);
                        if (error == NFSERR_NOTSUPP)
                                nmp->nm_flag &= ~NFSMNT_RDIRPLUS;
                }
                if ((nmp->nm_flag & NFSMNT_RDIRPLUS) == 0)
                        error = nfs_readdirrpc_uio(vp, uiop);
                /*
                 * end-of-directory sets B_INVAL but does not generate an
                 * error.
                 */
                if (error == 0 && uiop->uio_resid == bp->b_bcount)
                        bp->b_flags |= B_INVAL;
                break;
            default:
                kprintf("nfs_doio:  type %x unexpected\n",vp->v_type);
                break;
            };
            if (error) {
                bp->b_flags |= B_ERROR;
                bp->b_error = error;
            }
            bp->b_resid = uiop->uio_resid;
        } else {
            /* 
             * If we only need to commit, try to commit.
             *
             * NOTE: The I/O has already been staged for the write and
             *       its pages busied, so b_dirtyoff/end is valid.
             */
            KKASSERT(bp->b_cmd == BUF_CMD_WRITE);
            if (bp->b_flags & B_NEEDCOMMIT) {
                    int retv;
                    off_t off;

                    off = bio->bio_offset + bp->b_dirtyoff;
                    retv = nfs_commitrpc_uio(vp, off,
                                             bp->b_dirtyend - bp->b_dirtyoff,
                                             td);
                    if (retv == 0) {
                            bp->b_dirtyoff = bp->b_dirtyend = 0;
                            bp->b_flags &= ~(B_NEEDCOMMIT | B_CLUSTEROK);
                            bp->b_resid = 0;
                            biodone(bio);
                            return(0);
                    }
                    if (retv == NFSERR_STALEWRITEVERF) {
                            nfs_clearcommit(vp->v_mount);
                    }
            }

            /*
             * Setup for actual write
             */
            if (bio->bio_offset + bp->b_dirtyend > np->n_size)
                bp->b_dirtyend = np->n_size - bio->bio_offset;

            if (bp->b_dirtyend > bp->b_dirtyoff) {
                io.iov_len = uiop->uio_resid = bp->b_dirtyend
                    - bp->b_dirtyoff;
                uiop->uio_offset = bio->bio_offset + 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_NEEDCOMMIT | B_NOCACHE | B_CLUSTER)) == 0)
                    iomode = NFSV3WRITE_UNSTABLE;
                else
                    iomode = NFSV3WRITE_FILESYNC;

                must_commit = 0;
                error = nfs_writerpc_uio(vp, uiop, &iomode, &must_commit);

                /*
                 * When setting B_NEEDCOMMIT also set B_CLUSTEROK to try
                 * to cluster the buffers needing commit.  This will allow
                 * the system to submit a single commit rpc for the whole
                 * cluster.  We can do this even if the buffer is not 100% 
                 * dirty (relative to the NFS blocksize), so we optimize the
                 * append-to-file-case.
                 *
                 * (when clearing B_NEEDCOMMIT, B_CLUSTEROK must also be
                 * cleared because write clustering only works for commit
                 * rpc's, not for the data portion of the write).
                 */

                if (!error && iomode == NFSV3WRITE_UNSTABLE) {
                    bp->b_flags |= B_NEEDCOMMIT;
                    if (bp->b_dirtyoff == 0
                        && bp->b_dirtyend == bp->b_bcount)
                        bp->b_flags |= B_CLUSTEROK;
                } else {
                    bp->b_flags &= ~(B_NEEDCOMMIT | B_CLUSTEROK);
                }

                /*
                 * 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 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 the buffer is marked B_PAGING, it does not reside on
                 * the vp's paging queues so we cannot call bdirty().  The
                 * bp in this case is not an NFS cache block so we should
                 * be safe. XXX
                 */
                if (error == EINTR
                    || (!error && (bp->b_flags & B_NEEDCOMMIT))) {
                        crit_enter();
                        bp->b_flags &= ~(B_INVAL|B_NOCACHE);
                        if ((bp->b_flags & B_PAGING) == 0)
                            bdirty(bp);
                        if (error)
                            bp->b_flags |= B_EINTR;
                        crit_exit();
                } else {
                    if (error) {
                        bp->b_flags |= B_ERROR;
                        bp->b_error = np->n_error = error;
                        np->n_flag |= NWRITEERR;
                    }
                    bp->b_dirtyoff = bp->b_dirtyend = 0;
                }
                if (must_commit)
                    nfs_clearcommit(vp->v_mount);
                bp->b_resid = uiop->uio_resid;
            } else {
                bp->b_resid = 0;
            }
        }

        /*
         * I/O was run synchronously, biodone() it and calculate the
         * error to return.
         */
        biodone(bio);
        KKASSERT(bp->b_cmd == BUF_CMD_DONE);
        if (bp->b_flags & B_EINTR)
                return (EINTR);
        if (bp->b_flags & B_ERROR)
                return (bp->b_error ? bp->b_error : EIO);
        return (0);
}

/*
 * Used to aid in handling ftruncate() and non-trivial write-extend
 * operations on the NFS client side.  Note that trivial write-extend
 * operations (appending with no write hole) are handled by nfs_write()
 * directly to avoid silly flushes.
 *
 * Truncation creates a number of special problems for NFS.  We have to
 * throw away VM pages and buffer cache buffers that are beyond EOF, and
 * we have to properly handle VM pages or (potentially dirty) buffers
 * that straddle the truncation point.
 *
 * File extension no longer has an issue now that the buffer size is
 * fixed.  When extending the intended overwrite area is specified
 * by (boff, bytes).  This function uses the parameters to determine
 * what areas must be zerod.  If there are no gaps we set B_CACHE.
 */
struct buf *
nfs_meta_setsize(struct vnode *vp, struct thread *td, off_t nbase,
                 int boff, int bytes)
{

        struct nfsnode *np = VTONFS(vp);
        off_t osize = np->n_size;
        off_t nsize;
        int biosize = vp->v_mount->mnt_stat.f_iosize;
        int error = 0;
        struct buf *bp;

        nsize = nbase + boff + bytes;
        np->n_size = nsize;

        if (nsize < osize) {
                /*
                 * vtruncbuf() doesn't get the buffer overlapping the 
                 * truncation point, but it will invalidate pages in
                 * that buffer and zero the appropriate byte range in
                 * the page straddling EOF.
                 */
                error = vtruncbuf(vp, nsize, biosize);

                /*
                 * NFS doesn't do a good job tracking changes in the EOF
                 * so it may not revisit the buffer if the file is extended.
                 *
                 * After truncating just clear B_CACHE on the buffer
                 * straddling EOF.  If the buffer is dirty then clean
                 * out the portion beyond the file EOF.
                 */
                if (error) {
                        bp = NULL;
                } else {
                        bp = nfs_getcacheblk(vp, nbase, biosize, td);
                        if (bp->b_flags & B_DELWRI) {
                                if (bp->b_dirtyoff > bp->b_bcount)
                                        bp->b_dirtyoff = bp->b_bcount;
                                if (bp->b_dirtyend > bp->b_bcount)
                                        bp->b_dirtyend = bp->b_bcount;
                                boff = (int)nsize & (biosize - 1);
                                bzero(bp->b_data + boff, biosize - boff);
                        } else if (nsize != nbase) {
                                boff = (int)nsize & (biosize - 1);
                                bzero(bp->b_data + boff, biosize - boff);
                        }
                }
        } else {
                /*
                 * The newly expanded portions of the buffer should already
                 * be zero'd out if B_CACHE is set.  If B_CACHE is not
                 * set and the buffer is beyond osize we can safely zero it
                 * and set B_CACHE to avoid issuing unnecessary degenerate
                 * read rpcs.
                 *
                 * Don't do this if the caller is going to overwrite the
                 * entire buffer anyway (and also don't set B_CACHE!).
                 * This allows the caller to optimize the operation.
                 */
                KKASSERT(nsize >= 0);
                vnode_pager_setsize(vp, (vm_ooffset_t)nsize);

                bp = nfs_getcacheblk(vp, nbase, biosize, td);
                if ((bp->b_flags & B_CACHE) == 0 && nbase >= osize &&
                    !(boff == 0 && bytes == biosize)
                ) {
                        bzero(bp->b_data, biosize);
                        bp->b_flags |= B_CACHE;
                        bp->b_flags &= ~(B_ERROR | B_INVAL);
                }
        }
        return(bp);
}

/*
 * Synchronous completion for nfs_doio.  Call bpdone() with elseit=FALSE.
 * Caller is responsible for brelse()'ing the bp.
 */
static void
nfsiodone_sync(struct bio *bio)
{
        bio->bio_flags = 0;
        bpdone(bio->bio_buf, 0);
}

/*
 * nfs read rpc - BIO version
 */
void
nfs_readrpc_bio(struct vnode *vp, struct bio *bio)
{
        struct buf *bp = bio->bio_buf;
        u_int32_t *tl;
        struct nfsmount *nmp;
        int error = 0, len, tsiz;
        struct nfsm_info *info;

        info = kmalloc(sizeof(*info), M_NFSREQ, M_WAITOK);
        info->mrep = NULL;
        info->v3 = NFS_ISV3(vp);

        nmp = VFSTONFS(vp->v_mount);
        tsiz = bp->b_bcount;
        KKASSERT(tsiz <= nmp->nm_rsize);
        if (bio->bio_offset + tsiz > nmp->nm_maxfilesize) {
                error = EFBIG;
                goto nfsmout;
        }
        nfsstats.rpccnt[NFSPROC_READ]++;
        len = tsiz;
        nfsm_reqhead(info, vp, NFSPROC_READ,
                     NFSX_FH(info->v3) + NFSX_UNSIGNED * 3);
        ERROROUT(nfsm_fhtom(info, vp));
        tl = nfsm_build(info, NFSX_UNSIGNED * 3);
        if (info->v3) {
                txdr_hyper(bio->bio_offset, tl);
                *(tl + 2) = txdr_unsigned(len);
        } else {
                *tl++ = txdr_unsigned(bio->bio_offset);
                *tl++ = txdr_unsigned(len);
                *tl = 0;
        }
        info->bio = bio;
        info->done = nfs_readrpc_bio_done;
        nfsm_request_bio(info, vp, NFSPROC_READ, NULL,
                         nfs_vpcred(vp, ND_READ));
        return;
nfsmout:
        kfree(info, M_NFSREQ);
        bp->b_error = error;
        bp->b_flags |= B_ERROR;
        biodone(bio);
}

static void
nfs_readrpc_bio_done(nfsm_info_t info)
{
        struct nfsmount *nmp = VFSTONFS(info->vp->v_mount);
        struct bio *bio = info->bio;
        struct buf *bp = bio->bio_buf;
        u_int32_t *tl;
        int attrflag;
        int retlen;
        int eof;
        int error = 0;

        KKASSERT(info->state == NFSM_STATE_DONE);

        if (info->v3) {
                ERROROUT(nfsm_postop_attr(info, info->vp, &attrflag,
                                         NFS_LATTR_NOSHRINK));
                NULLOUT(tl = nfsm_dissect(info, 2 * NFSX_UNSIGNED));
                eof = fxdr_unsigned(int, *(tl + 1));
        } else {
                ERROROUT(nfsm_loadattr(info, info->vp, NULL));
                eof = 0;
        }
        NEGATIVEOUT(retlen = nfsm_strsiz(info, nmp->nm_rsize));
        ERROROUT(nfsm_mtobio(info, bio, retlen));
        m_freem(info->mrep);
        info->mrep = NULL;

        /*
         * No error occured, if retlen is less then bcount and no EOF
         * and NFSv3 a zero-fill short read occured.
         *
         * For NFSv2 a short-read indicates EOF.
         */
        if (retlen < bp->b_bcount && info->v3 && eof == 0) {
                bzero(bp->b_data + retlen, bp->b_bcount - retlen);
                retlen = bp->b_bcount;
        }

        /*
         * If we hit an EOF we still zero-fill, but return the expected
         * b_resid anyway.  This should normally not occur since async
         * BIOs are not used for read-before-write case.  Races against
         * the server can cause it though and we don't want to leave
         * garbage in the buffer.
         */
        if (retlen < bp->b_bcount) {
                bzero(bp->b_data + retlen, bp->b_bcount - retlen);
        }
        bp->b_resid = 0;
        /* bp->b_resid = bp->b_bcount - retlen; */
nfsmout:
        kfree(info, M_NFSREQ);
        if (error) {
                bp->b_error = error;
                bp->b_flags |= B_ERROR;
        }
        biodone(bio);
}

/*
 * nfs write call - BIO version
 *
 * NOTE: Caller has already busied the I/O.
 */
void
nfs_writerpc_bio(struct vnode *vp, struct bio *bio)
{
        struct nfsmount *nmp = VFSTONFS(vp->v_mount);
        struct nfsnode *np = VTONFS(vp);
        struct buf *bp = bio->bio_buf;
        u_int32_t *tl;
        int len;
        int iomode;
        int error = 0;
        struct nfsm_info *info;
        off_t offset;

        /*
         * Setup for actual write.  Just clean up the bio if there
         * is nothing to do.  b_dirtyoff/end have already been staged
         * by the bp's pages getting busied.
         */
        if (bio->bio_offset + bp->b_dirtyend > np->n_size)
                bp->b_dirtyend = np->n_size - bio->bio_offset;

        if (bp->b_dirtyend <= bp->b_dirtyoff) {
                bp->b_resid = 0;
                biodone(bio);
                return;
        }
        len = bp->b_dirtyend - bp->b_dirtyoff;
        offset = bio->bio_offset + bp->b_dirtyoff;
        if (offset + len > nmp->nm_maxfilesize) {
                bp->b_flags |= B_ERROR;
                bp->b_error = EFBIG;
                biodone(bio);
                return;
        }
        bp->b_resid = len;
        nfsstats.write_bios++;

        info = kmalloc(sizeof(*info), M_NFSREQ, M_WAITOK);
        info->mrep = NULL;
        info->v3 = NFS_ISV3(vp);
        info->info_writerpc.must_commit = 0;
        if ((bp->b_flags & (B_NEEDCOMMIT | B_NOCACHE | B_CLUSTER)) == 0)
                iomode = NFSV3WRITE_UNSTABLE;
        else
                iomode = NFSV3WRITE_FILESYNC;

        KKASSERT(len <= nmp->nm_wsize);

        nfsstats.rpccnt[NFSPROC_WRITE]++;
        nfsm_reqhead(info, vp, NFSPROC_WRITE,
                     NFSX_FH(info->v3) + 5 * NFSX_UNSIGNED + nfsm_rndup(len));
        ERROROUT(nfsm_fhtom(info, vp));
        if (info->v3) {
                tl = nfsm_build(info, 5 * NFSX_UNSIGNED);
                txdr_hyper(offset, tl);
                tl += 2;
                *tl++ = txdr_unsigned(len);
                *tl++ = txdr_unsigned(iomode);
                *tl = txdr_unsigned(len);
        } else {
                u_int32_t x;

                tl = nfsm_build(info, 4 * NFSX_UNSIGNED);
                /* Set both "begin" and "current" to non-garbage. */
                x = txdr_unsigned((u_int32_t)offset);
                *tl++ = x;      /* "begin offset" */
                *tl++ = x;      /* "current offset" */
                x = txdr_unsigned(len);
                *tl++ = x;      /* total to this offset */
                *tl = x;        /* size of this write */
        }
        ERROROUT(nfsm_biotom(info, bio, bp->b_dirtyoff, len));
        info->bio = bio;
        info->done = nfs_writerpc_bio_done;
        nfsm_request_bio(info, vp, NFSPROC_WRITE, NULL,
                         nfs_vpcred(vp, ND_WRITE));
        return;
nfsmout:
        kfree(info, M_NFSREQ);
        bp->b_error = error;
        bp->b_flags |= B_ERROR;
        biodone(bio);
}

static void
nfs_writerpc_bio_done(nfsm_info_t info)
{
        struct nfsmount *nmp = VFSTONFS(info->vp->v_mount);
        struct nfsnode *np = VTONFS(info->vp);
        struct bio *bio = info->bio;
        struct buf *bp = bio->bio_buf;
        int wccflag = NFSV3_WCCRATTR;
        int iomode = NFSV3WRITE_FILESYNC;
        int commit;
        int rlen;
        int error;
        int len = bp->b_resid;  /* b_resid was set to shortened length */
        u_int32_t *tl;

        if (info->v3) {
                /*
                 * The write RPC returns a before and after mtime.  The
                 * nfsm_wcc_data() macro checks the before n_mtime
                 * against the before time and stores the after time
                 * in the nfsnode's cached vattr and n_mtime field.
                 * The NRMODIFIED bit will be set if the before
                 * time did not match the original mtime.
                 */
                wccflag = NFSV3_WCCCHK;
                ERROROUT(nfsm_wcc_data(info, info->vp, &wccflag));
                if (error == 0) {
                        NULLOUT(tl = nfsm_dissect(info, 2 * NFSX_UNSIGNED + NFSX_V3WRITEVERF));
                        rlen = fxdr_unsigned(int, *tl++);
                        if (rlen == 0) {
                                error = NFSERR_IO;
                                m_freem(info->mrep);
                                info->mrep = NULL;
                                goto nfsmout;
                        } else if (rlen < len) {
#if 0
                                /*
                                 * XXX what do we do here?
                                 */
                                backup = len - rlen;
                                uiop->uio_iov->iov_base = (char *)uiop->uio_iov->iov_base - backup;
                                uiop->uio_iov->iov_len += backup;
                                uiop->uio_offset -= backup;
                                uiop->uio_resid += backup;
                                len = rlen;
#endif
                        }
                        commit = fxdr_unsigned(int, *tl++);

                        /*
                         * Return the lowest committment level
                         * obtained by any of the RPCs.
                         */
                        if (iomode == NFSV3WRITE_FILESYNC)
                                iomode = commit;
                        else if (iomode == NFSV3WRITE_DATASYNC &&
                                commit == NFSV3WRITE_UNSTABLE)
                                iomode = commit;
                        if ((nmp->nm_state & NFSSTA_HASWRITEVERF) == 0){
                            bcopy(tl, (caddr_t)nmp->nm_verf, NFSX_V3WRITEVERF);
                            nmp->nm_state |= NFSSTA_HASWRITEVERF;
                        } else if (bcmp(tl, nmp->nm_verf, NFSX_V3WRITEVERF)) {
                            info->info_writerpc.must_commit = 1;
                            bcopy(tl, (caddr_t)nmp->nm_verf, NFSX_V3WRITEVERF);
                        }
                }
        } else {
                ERROROUT(nfsm_loadattr(info, info->vp, NULL));
        }
        m_freem(info->mrep);
        info->mrep = NULL;
        len = 0;
nfsmout:
        if (info->vp->v_mount->mnt_flag & MNT_ASYNC)
                iomode = NFSV3WRITE_FILESYNC;
        bp->b_resid = len;

        /*
         * End of RPC.  Now clean up the bp.
         *
         * When setting B_NEEDCOMMIT also set B_CLUSTEROK to try
         * to cluster the buffers needing commit.  This will allow
         * the system to submit a single commit rpc for the whole
         * cluster.  We can do this even if the buffer is not 100%
         * dirty (relative to the NFS blocksize), so we optimize the
         * append-to-file-case.
         *
         * (when clearing B_NEEDCOMMIT, B_CLUSTEROK must also be
         * cleared because write clustering only works for commit
         * rpc's, not for the data portion of the write).
         */
        if (!error && iomode == NFSV3WRITE_UNSTABLE) {
                bp->b_flags |= B_NEEDCOMMIT;
                if (bp->b_dirtyoff == 0 && bp->b_dirtyend == bp->b_bcount)
                        bp->b_flags |= B_CLUSTEROK;
        } else {
                bp->b_flags &= ~(B_NEEDCOMMIT | B_CLUSTEROK);
        }

        /*
         * 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 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 the buffer is marked B_PAGING, it does not reside on
         * the vp's paging queues so we cannot call bdirty().  The
         * bp in this case is not an NFS cache block so we should
         * be safe. XXX
         */
        if (error == EINTR || (!error && (bp->b_flags & B_NEEDCOMMIT))) {
                crit_enter();
                bp->b_flags &= ~(B_INVAL|B_NOCACHE);
                if ((bp->b_flags & B_PAGING) == 0)
                        bdirty(bp);
                if (error)
                        bp->b_flags |= B_EINTR;
                crit_exit();
        } else {
                if (error) {
                        bp->b_flags |= B_ERROR;
                        bp->b_error = np->n_error = error;
                        np->n_flag |= NWRITEERR;
                }
                bp->b_dirtyoff = bp->b_dirtyend = 0;
        }
        if (info->info_writerpc.must_commit)
                nfs_clearcommit(info->vp->v_mount);
        kfree(info, M_NFSREQ);
        if (error) {
                bp->b_flags |= B_ERROR;
                bp->b_error = error;
        }
        biodone(bio);
}

/*
 * Nfs Version 3 commit rpc - BIO version
 *
 * This function issues the commit rpc and will chain to a write
 * rpc if necessary.
 */
void
nfs_commitrpc_bio(struct vnode *vp, struct bio *bio)
{
        struct nfsmount *nmp = VFSTONFS(vp->v_mount);
        struct buf *bp = bio->bio_buf;
        struct nfsm_info *info;
        int error = 0;
        u_int32_t *tl;

        if ((nmp->nm_state & NFSSTA_HASWRITEVERF) == 0) {
                bp->b_dirtyoff = bp->b_dirtyend = 0;
                bp->b_flags &= ~(B_NEEDCOMMIT | B_CLUSTEROK);
                bp->b_resid = 0;
                biodone(bio);
                return;
        }

        info = kmalloc(sizeof(*info), M_NFSREQ, M_WAITOK);
        info->mrep = NULL;
        info->v3 = 1;

        nfsstats.rpccnt[NFSPROC_COMMIT]++;
        nfsm_reqhead(info, vp, NFSPROC_COMMIT, NFSX_FH(1));
        ERROROUT(nfsm_fhtom(info, vp));
        tl = nfsm_build(info, 3 * NFSX_UNSIGNED);
        txdr_hyper(bio->bio_offset + bp->b_dirtyoff, tl);
        tl += 2;
        *tl = txdr_unsigned(bp->b_dirtyend - bp->b_dirtyoff);
        info->bio = bio;
        info->done = nfs_commitrpc_bio_done;
        nfsm_request_bio(info, vp, NFSPROC_COMMIT, NULL,
                         nfs_vpcred(vp, ND_WRITE));
        return;
nfsmout:
        /*
         * Chain to write RPC on (early) error
         */
        kfree(info, M_NFSREQ);
        nfs_writerpc_bio(vp, bio);
}

static void
nfs_commitrpc_bio_done(nfsm_info_t info)
{
        struct nfsmount *nmp = VFSTONFS(info->vp->v_mount);
        struct bio *bio = info->bio;
        struct buf *bp = bio->bio_buf;
        u_int32_t *tl;
        int wccflag = NFSV3_WCCRATTR;
        int error = 0;

        ERROROUT(nfsm_wcc_data(info, info->vp, &wccflag));
        if (error == 0) {
                NULLOUT(tl = nfsm_dissect(info, NFSX_V3WRITEVERF));
                if (bcmp(nmp->nm_verf, tl, NFSX_V3WRITEVERF)) {
                        bcopy(tl, nmp->nm_verf, NFSX_V3WRITEVERF);
                        error = NFSERR_STALEWRITEVERF;
                }
        }
        m_freem(info->mrep);
        info->mrep = NULL;

        /*
         * On completion we must chain to a write bio if an
         * error occurred.
         */
nfsmout:
        kfree(info, M_NFSREQ);
        if (error == 0) {
                bp->b_dirtyoff = bp->b_dirtyend = 0;
                bp->b_flags &= ~(B_NEEDCOMMIT | B_CLUSTEROK);
                bp->b_resid = 0;
                biodone(bio);
        } else {
                nfs_writerpc_bio(info->vp, bio);
        }
}