/*      $OpenBSD: msdosfs_vnops.c,v 1.143 2024/10/18 05:52:32 miod Exp $        */
/*      $NetBSD: msdosfs_vnops.c,v 1.63 1997/10/17 11:24:19 ws Exp $    */

/*-
 * Copyright (C) 2005 Thomas Wang.
 * Copyright (C) 1994, 1995, 1997 Wolfgang Solfrank.
 * Copyright (C) 1994, 1995, 1997 TooLs GmbH.
 * All rights reserved.
 * Original code by Paul Popelka (paulp@uts.amdahl.com) (see below).
 *
 * 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 TooLs GmbH.
 * 4. The name of TooLs GmbH may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY TOOLS GMBH ``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 TOOLS GMBH 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.
 */
/*
 * Written by Paul Popelka (paulp@uts.amdahl.com)
 *
 * You can do anything you want with this software, just don't say you wrote
 * it, and don't remove this notice.
 *
 * This software is provided "as is".
 *
 * The author supplies this software to be publicly redistributed on the
 * understanding that the author is not responsible for the correct
 * functioning of this software in any circumstances and is not liable for
 * any damages caused by this software.
 *
 * October 1992
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/namei.h>
#include <sys/resourcevar.h>    /* defines plimit structure in proc struct */
#include <sys/fcntl.h>          /* define FWRITE ... */
#include <sys/file.h>
#include <sys/stat.h>
#include <sys/buf.h>
#include <sys/proc.h>
#include <sys/mount.h>
#include <sys/vnode.h>
#include <sys/lock.h>
#include <sys/signalvar.h>
#include <sys/specdev.h> /* XXX */      /* defines v_rdev */
#include <sys/malloc.h>
#include <sys/pool.h>
#include <sys/dirent.h>         /* defines dirent structure */
#include <sys/lockf.h>
#include <sys/unistd.h>

#include <msdosfs/bpb.h>
#include <msdosfs/direntry.h>
#include <msdosfs/denode.h>
#include <msdosfs/msdosfsmount.h>
#include <msdosfs/fat.h>

static uint32_t fileidhash(uint64_t);

int msdosfs_bmaparray(struct vnode *, uint32_t, daddr_t *, int *);
int msdosfs_kqfilter(void *);
int filt_msdosfsread(struct knote *, long);
int filt_msdosfswrite(struct knote *, long);
int filt_msdosfsvnode(struct knote *, long);
void filt_msdosfsdetach(struct knote *);

/*
 * Some general notes:
 *
 * In the ufs filesystem the inodes, superblocks, and indirect blocks are
 * read/written using the vnode for the filesystem. Blocks that represent
 * the contents of a file are read/written using the vnode for the file
 * (including directories when they are read/written as files). This
 * presents problems for the dos filesystem because data that should be in
 * an inode (if dos had them) resides in the directory itself.  Since we
 * must update directory entries without the benefit of having the vnode
 * for the directory we must use the vnode for the filesystem.  This means
 * that when a directory is actually read/written (via read, write, or
 * readdir, or seek) we must use the vnode for the filesystem instead of
 * the vnode for the directory as would happen in ufs. This is to insure we
 * retrieve the correct block from the buffer cache since the hash value is
 * based upon the vnode address and the desired block number.
 */

/*
 * Create a regular file. On entry the directory to contain the file being
 * created is locked.  We must release before we return. We must also free
 * the pathname buffer pointed at by cnp->cn_pnbuf, always on error, or
 * only if the SAVESTART bit in cn_flags is clear on success.
 */
int
msdosfs_create(void *v)
{
        struct vop_create_args *ap = v;
        struct componentname *cnp = ap->a_cnp;
        struct denode ndirent;
        struct denode *dep;
        struct denode *pdep = VTODE(ap->a_dvp);
        int error;
        struct timespec ts;

#ifdef MSDOSFS_DEBUG
        printf("msdosfs_create(cnp %p, vap %p\n", cnp, ap->a_vap);
#endif

        /*
         * If this is the root directory and there is no space left we
         * can't do anything.  This is because the root directory can not
         * change size.
         */
        if (pdep->de_StartCluster == MSDOSFSROOT
            && pdep->de_fndoffset >= pdep->de_FileSize) {
                error = ENOSPC;
                goto bad;
        }

        /*
         * Create a directory entry for the file, then call createde() to
         * have it installed. NOTE: DOS files are always executable.  We
         * use the absence of the owner write bit to make the file
         * readonly.
         */
#ifdef DIAGNOSTIC
        if ((cnp->cn_flags & HASBUF) == 0)
                panic("msdosfs_create: no name");
#endif
        bzero(&ndirent, sizeof(ndirent));
        if ((error = uniqdosname(pdep, cnp, ndirent.de_Name)) != 0)
                goto bad;

        ndirent.de_Attributes = (ap->a_vap->va_mode & VWRITE) ?
                                ATTR_ARCHIVE : ATTR_ARCHIVE | ATTR_READONLY;
        ndirent.de_StartCluster = 0;
        ndirent.de_FileSize = 0;
        ndirent.de_dev = pdep->de_dev;
        ndirent.de_devvp = pdep->de_devvp;
        ndirent.de_pmp = pdep->de_pmp;
        ndirent.de_flag = DE_ACCESS | DE_CREATE | DE_UPDATE;
        getnanotime(&ts);
        DETIMES(&ndirent, &ts, &ts, &ts);
        if ((error = createde(&ndirent, pdep, &dep, cnp)) != 0)
                goto bad;
        if ((cnp->cn_flags & SAVESTART) == 0)
                pool_put(&namei_pool, cnp->cn_pnbuf);
        VN_KNOTE(ap->a_dvp, NOTE_WRITE);
        *ap->a_vpp = DETOV(dep);
        return (0);

bad:
        pool_put(&namei_pool, cnp->cn_pnbuf);
        return (error);
}

int
msdosfs_mknod(void *v)
{
        struct vop_mknod_args *ap = v;

        pool_put(&namei_pool, ap->a_cnp->cn_pnbuf);
        VN_KNOTE(ap->a_dvp, NOTE_WRITE);
        return (EINVAL);
}

int
msdosfs_open(void *v)
{
        return (0);
}

int
msdosfs_close(void *v)
{
        struct vop_close_args *ap = v;
        struct vnode *vp = ap->a_vp;
        struct denode *dep = VTODE(vp);
        struct timespec ts;

        if (vp->v_usecount > 1 && !VOP_ISLOCKED(vp)) {
                getnanotime(&ts);
                DETIMES(dep, &ts, &ts, &ts);
        }
        return (0);
}

int
msdosfs_access(void *v)
{
        struct vop_access_args *ap = v;
        struct denode *dep = VTODE(ap->a_vp);
        struct msdosfsmount *pmp = dep->de_pmp;
        mode_t dosmode;

        dosmode = (S_IRUSR | S_IRGRP | S_IROTH);
        if ((dep->de_Attributes & ATTR_READONLY) == 0)
                dosmode |= (S_IWUSR | S_IWGRP | S_IWOTH);
        if (dep->de_Attributes & ATTR_DIRECTORY)
                dosmode |= (S_IXUSR | S_IXGRP | S_IXOTH);
        dosmode &= pmp->pm_mask;

        return (vaccess(ap->a_vp->v_type, dosmode, pmp->pm_uid, pmp->pm_gid,
            ap->a_mode, ap->a_cred));
}

int
msdosfs_getattr(void *v)
{
        struct vop_getattr_args *ap = v;
        struct denode *dep = VTODE(ap->a_vp);
        struct msdosfsmount *pmp = dep->de_pmp;
        struct vattr *vap = ap->a_vap;
        struct timespec ts;
        uint32_t fileid;

        getnanotime(&ts);
        DETIMES(dep, &ts, &ts, &ts);
        vap->va_fsid = dep->de_dev;

        /*
         * The following computation of the fileid must be the same as
         * that used in msdosfs_readdir() to compute d_fileno. If not,
         * pwd doesn't work.
         *
         * We now use the starting cluster number as the fileid/fileno.
         * This works for both files and directories (including the root
         * directory, on FAT32).  Even on FAT32, this will at most be a
         * 28-bit number, as the high 4 bits of FAT32 cluster numbers
         * are reserved.
         *
         * However, we do need to do something for 0-length files, which
         * will not have a starting cluster number.
         *
         * These files cannot be directories, since (except for /, which
         * is special-cased anyway) directories contain entries for . and
         * .., so must have non-zero length.
         *
         * In this case, we just create a non-cryptographic hash of the
         * original fileid calculation, and set the top bit.
         *
         * This algorithm has the benefit that all directories, and all
         * non-zero-length files, will have fileids that are persistent
         * across mounts and reboots, and that cannot collide (as long
         * as the filesystem is not corrupt).  Zero-length files will
         * have fileids that are persistent, but that may collide.  We
         * will just have to live with that.
         */
        fileid = dep->de_StartCluster;

        if (dep->de_Attributes & ATTR_DIRECTORY) {
                /* Special-case root */
                if (dep->de_StartCluster == MSDOSFSROOT)
                        fileid = FAT32(pmp) ? pmp->pm_rootdirblk : 1;
        } else {
                if (dep->de_FileSize == 0) {
                        uint32_t dirsperblk;
                        uint64_t fileid64;

                        dirsperblk = pmp->pm_BytesPerSec /
                            sizeof(struct direntry);

                        fileid64 = (dep->de_dirclust == MSDOSFSROOT) ?
                            roottobn(pmp, 0) : cntobn(pmp, dep->de_dirclust);
                        fileid64 *= dirsperblk;
                        fileid64 += dep->de_diroffset / sizeof(struct direntry);

                        fileid = fileidhash(fileid64);
                }
        }

        vap->va_fileid = fileid;
        vap->va_mode = (S_IRUSR|S_IRGRP|S_IROTH);
        if ((dep->de_Attributes & ATTR_READONLY) == 0)
                vap->va_mode |= (S_IWUSR|S_IWGRP|S_IWOTH);
        if (dep->de_Attributes & ATTR_DIRECTORY) {
                vap->va_mode |= S_IFDIR;
                vap->va_mode |= (vap->va_mode & S_IRUSR) ? S_IXUSR : 0;
                vap->va_mode |= (vap->va_mode & S_IRGRP) ? S_IXGRP : 0;
                vap->va_mode |= (vap->va_mode & S_IROTH) ? S_IXOTH : 0;
        }
        vap->va_mode &= dep->de_pmp->pm_mask;
        vap->va_nlink = 1;
        vap->va_gid = dep->de_pmp->pm_gid;
        vap->va_uid = dep->de_pmp->pm_uid;
        vap->va_rdev = 0;
        vap->va_size = dep->de_FileSize;
        dos2unixtime(dep->de_MDate, dep->de_MTime, 0, &vap->va_mtime);
        if (dep->de_pmp->pm_flags & MSDOSFSMNT_LONGNAME) {
                dos2unixtime(dep->de_ADate, 0, 0, &vap->va_atime);
                dos2unixtime(dep->de_CDate, dep->de_CTime, dep->de_CTimeHundredth, &vap->va_ctime);
        } else {
                vap->va_atime = vap->va_mtime;
                vap->va_ctime = vap->va_mtime;
        }
        vap->va_flags = 0;
        if ((dep->de_Attributes & ATTR_ARCHIVE) == 0)
                vap->va_flags |= SF_ARCHIVED;
        vap->va_gen = 0;
        vap->va_blocksize = dep->de_pmp->pm_bpcluster;
        vap->va_bytes = (dep->de_FileSize + dep->de_pmp->pm_crbomask) &
                                ~(dep->de_pmp->pm_crbomask);
        vap->va_type = ap->a_vp->v_type;
        return (0);
}

int
msdosfs_setattr(void *v)
{
        struct vop_setattr_args *ap = v;
        struct vnode *vp = ap->a_vp;
        struct denode *dep = VTODE(ap->a_vp);
        struct msdosfsmount *pmp = dep->de_pmp;
        struct vattr *vap = ap->a_vap;
        struct ucred *cred = ap->a_cred;
        int error = 0;

#ifdef MSDOSFS_DEBUG
        printf("msdosfs_setattr(): vp %p, vap %p, cred %p, p %p\n",
            ap->a_vp, vap, cred, ap->a_p);
#endif
        if ((vap->va_type != VNON) || (vap->va_nlink != VNOVAL) ||
            (vap->va_fsid != VNOVAL) || (vap->va_fileid != VNOVAL) ||
            (vap->va_blocksize != VNOVAL) || (vap->va_rdev != VNOVAL) ||
            (vap->va_bytes != VNOVAL) || (vap->va_gen != VNOVAL)) {
#ifdef MSDOSFS_DEBUG
                printf("msdosfs_setattr(): returning EINVAL\n");
                printf("    va_type %d, va_nlink %x, va_fsid %ld, "
                    "va_fileid %llx\n", vap->va_type, vap->va_nlink,
                    vap->va_fsid, (unsigned long long)vap->va_fileid);
                printf("    va_blocksize %lx, va_rdev %x, va_bytes %llx, "
                    "va_gen %lx\n", vap->va_blocksize,
                    (unsigned int)vap->va_rdev,
                    (unsigned long long)vap->va_bytes, vap->va_gen);
#endif
                return (EINVAL);
        }
        if (vap->va_flags != VNOVAL) {
                if (vp->v_mount->mnt_flag & MNT_RDONLY)
                        return (EINVAL);
                if (cred->cr_uid != pmp->pm_uid) {
                        error = suser_ucred(cred);
                        if (error)
                                return (error);
                }
                /*
                 * We are very inconsistent about handling unsupported
                 * attributes.  We ignored the access time and the
                 * read and execute bits.  We were strict for the other
                 * attributes.
                 *
                 * Here we are strict, stricter than ufs in not allowing
                 * users to attempt to set SF_SETTABLE bits or anyone to
                 * set unsupported bits.  However, we ignore attempts to
                 * set ATTR_ARCHIVE for directories `cp -pr' from a more
                 * sensible filesystem attempts it a lot.
                 */
                if (vap->va_flags & SF_SETTABLE) {
                        error = suser_ucred(cred);
                        if (error)
                                return (error);
                }
                if (vap->va_flags & ~SF_ARCHIVED)
                        return EOPNOTSUPP;
                if (vap->va_flags & SF_ARCHIVED)
                        dep->de_Attributes &= ~ATTR_ARCHIVE;
                else if (!(dep->de_Attributes & ATTR_DIRECTORY))
                        dep->de_Attributes |= ATTR_ARCHIVE;
                dep->de_flag |= DE_MODIFIED;
        }

        if (vap->va_uid != (uid_t)VNOVAL || vap->va_gid != (gid_t)VNOVAL) {
                uid_t uid;
                gid_t gid;

                if (vp->v_mount->mnt_flag & MNT_RDONLY)
                        return (EINVAL);
                uid = vap->va_uid;
                if (uid == (uid_t)VNOVAL)
                        uid = pmp->pm_uid;
                gid = vap->va_gid;
                if (gid == (gid_t)VNOVAL)
                        gid = pmp->pm_gid;
                if (cred->cr_uid != pmp->pm_uid || uid != pmp->pm_uid ||
                    (gid != pmp->pm_gid && !groupmember(gid, cred))) {
                        error = suser_ucred(cred);
                        if (error)
                                return (error);
                }
                if (uid != pmp->pm_uid || gid != pmp->pm_gid)
                        return EINVAL;
        }

        if (vap->va_size != VNOVAL) {
                switch (vp->v_type) {
                case VDIR:
                        return (EISDIR);
                case VREG:
                        /*
                         * Truncation is only supported for regular files,
                         * Disallow it if the filesystem is read-only.
                         */
                        if (vp->v_mount->mnt_flag & MNT_RDONLY)
                                return (EINVAL);
                        break;
                default:
                        /*
                         * According to POSIX, the result is unspecified
                         * for file types other than regular files,
                         * directories and shared memory objects.  We
                         * don't support any file types except regular
                         * files and directories in this file system, so
                         * this (default) case is unreachable and can do
                         * anything.  Keep falling through to detrunc()
                         * for now.
                         */
                        break;
                }
                error = detrunc(dep, vap->va_size, 0, cred, ap->a_p);
                if (error)
                        return error;
        }
        if ((vap->va_vaflags & VA_UTIMES_CHANGE) ||
            vap->va_atime.tv_nsec != VNOVAL ||
            vap->va_mtime.tv_nsec != VNOVAL) {
                if (vp->v_mount->mnt_flag & MNT_RDONLY)
                        return (EINVAL);
                if (cred->cr_uid != pmp->pm_uid &&
                    (error = suser_ucred(cred)) &&
                    ((vap->va_vaflags & VA_UTIMES_NULL) == 0 ||
                    (error = VOP_ACCESS(ap->a_vp, VWRITE, cred, ap->a_p))))
                        return (error);
                if (vp->v_type != VDIR) {
                        if ((pmp->pm_flags & MSDOSFSMNT_NOWIN95) == 0 &&
                            vap->va_atime.tv_nsec != VNOVAL) {
                                dep->de_flag &= ~DE_ACCESS;
                                unix2dostime(&vap->va_atime, &dep->de_ADate,
                                    NULL, NULL);
                        }
                        if (vap->va_mtime.tv_nsec != VNOVAL) {
                                dep->de_flag &= ~DE_UPDATE;
                                unix2dostime(&vap->va_mtime, &dep->de_MDate,
                                    &dep->de_MTime, NULL);
                        }
                        dep->de_Attributes |= ATTR_ARCHIVE;
                        dep->de_flag |= DE_MODIFIED;
                }
        }
        /*
         * DOS files only have the ability to have their writability
         * attribute set, so we use the owner write bit to set the readonly
         * attribute.
         */
        if (vap->va_mode != (mode_t)VNOVAL) {
                if (vp->v_mount->mnt_flag & MNT_RDONLY)
                        return (EINVAL);
                if (cred->cr_uid != pmp->pm_uid) {
                        error = suser_ucred(cred);
                        if (error)
                                return (error);
                }
                if (vp->v_type != VDIR) {
                        /* We ignore the read and execute bits. */
                        if (vap->va_mode & VWRITE)
                                dep->de_Attributes &= ~ATTR_READONLY;
                        else
                                dep->de_Attributes |= ATTR_READONLY;
                        dep->de_Attributes |= ATTR_ARCHIVE;
                        dep->de_flag |= DE_MODIFIED;
                }
        }
        VN_KNOTE(ap->a_vp, NOTE_ATTRIB);
        return (deupdat(dep, 1));
}

int
msdosfs_read(void *v)
{
        struct vop_read_args *ap = v;
        struct vnode *vp = ap->a_vp;
        struct denode *dep = VTODE(vp);
        struct msdosfsmount *pmp = dep->de_pmp;
        struct uio *uio = ap->a_uio;
        int isadir, error = 0;
        uint32_t n, diff, size, on;
        struct buf *bp;
        uint32_t cn;
        daddr_t bn;

        /*
         * If they didn't ask for any data, then we are done.
         */
        if (uio->uio_resid == 0)
                return (0);
        if (uio->uio_offset < 0)
                return (EINVAL);

        isadir = dep->de_Attributes & ATTR_DIRECTORY;
        do {
                if (uio->uio_offset >= dep->de_FileSize)
                        return (0);

                cn = de_cluster(pmp, uio->uio_offset);
                size = pmp->pm_bpcluster;
                on = uio->uio_offset & pmp->pm_crbomask;
                n = ulmin(pmp->pm_bpcluster - on, uio->uio_resid);

                /*
                 * de_FileSize is uint32_t, and we know that uio_offset <
                 * de_FileSize, so uio->uio_offset < 2^32.  Therefore
                 * the cast to uint32_t on the next line is safe.
                 */
                diff = dep->de_FileSize - (uint32_t)uio->uio_offset;
                if (diff < n)
                        n = diff;

                /*
                 * If we are operating on a directory file then be sure to
                 * do i/o with the vnode for the filesystem instead of the
                 * vnode for the directory.
                 */
                if (isadir) {
                        /* convert cluster # to block # */
                        error = pcbmap(dep, cn, &bn, 0, &size);
                        if (error)
                                return (error);
                        error = bread(pmp->pm_devvp, bn, size, &bp);
                } else {
                        if (de_cn2off(pmp, cn + 1) >= dep->de_FileSize)
                                error = bread(vp, cn, size, &bp);
                        else
                                error = bread_cluster(vp, cn, size, &bp);
                }
                n = min(n, pmp->pm_bpcluster - bp->b_resid);
                if (error) {
                        brelse(bp);
                        return (error);
                }
                error = uiomove(bp->b_data + on, n, uio);
                brelse(bp);
        } while (error == 0 && uio->uio_resid > 0 && n != 0);
        if (!isadir && !(vp->v_mount->mnt_flag & MNT_NOATIME))
                dep->de_flag |= DE_ACCESS;
        return (error);
}

/*
 * Write data to a file or directory.
 */
int
msdosfs_write(void *v)
{
        struct vop_write_args *ap = v;
        uint32_t n, croffset;
        size_t resid;
        ssize_t overrun;
        int extended = 0;
        uint32_t osize;
        int error = 0;
        uint32_t count, lastcn, cn;
        struct buf *bp;
        int ioflag = ap->a_ioflag;
        struct uio *uio = ap->a_uio;
        struct vnode *vp = ap->a_vp;
        struct vnode *thisvp;
        struct denode *dep = VTODE(vp);
        struct msdosfsmount *pmp = dep->de_pmp;
        struct ucred *cred = ap->a_cred;

#ifdef MSDOSFS_DEBUG
        printf("msdosfs_write(vp %p, uio %p, ioflag %08x, cred %p\n",
            vp, uio, ioflag, cred);
        printf("msdosfs_write(): diroff %d, dirclust %d, startcluster %d\n",
            dep->de_diroffset, dep->de_dirclust, dep->de_StartCluster);
#endif

        switch (vp->v_type) {
        case VREG:
                if (ioflag & IO_APPEND)
                        uio->uio_offset = dep->de_FileSize;
                thisvp = vp;
                break;
        case VDIR:
                return EISDIR;
        default:
                panic("msdosfs_write(): bad file type");
        }

        if (uio->uio_offset < 0)
                return (EINVAL);

        if (uio->uio_resid == 0)
                return (0);

        /* Don't bother to try to write files larger than the f/s limit */
        if (uio->uio_offset > MSDOSFS_FILESIZE_MAX ||
            uio->uio_resid > (MSDOSFS_FILESIZE_MAX - uio->uio_offset))
                return (EFBIG);

        /* do the filesize rlimit check */
        if ((error = vn_fsizechk(vp, uio, ioflag, &overrun)))
                return (error);

        /*
         * If the offset we are starting the write at is beyond the end of
         * the file, then they've done a seek.  Unix filesystems allow
         * files with holes in them, DOS doesn't so we must fill the hole
         * with zeroed blocks.
         */
        if (uio->uio_offset > dep->de_FileSize) {
                if ((error = deextend(dep, uio->uio_offset, cred)) != 0)
                        goto out;
        }

        /*
         * Remember some values in case the write fails.
         */
        resid = uio->uio_resid;
        osize = dep->de_FileSize;

        /*
         * If we write beyond the end of the file, extend it to its ultimate
         * size ahead of the time to hopefully get a contiguous area.
         */
        if (uio->uio_offset + resid > osize) {
                extended = 1;
                count = de_clcount(pmp, uio->uio_offset + resid) -
                        de_clcount(pmp, osize);
                if ((error = extendfile(dep, count, NULL, NULL, 0)) &&
                    (error != ENOSPC || (ioflag & IO_UNIT)))
                        goto errexit;
                lastcn = dep->de_fc[FC_LASTFC].fc_frcn;
        } else
                lastcn = de_clcount(pmp, osize) - 1;

        do {
                croffset = uio->uio_offset & pmp->pm_crbomask;
                cn = de_cluster(pmp, uio->uio_offset);

                if (cn > lastcn) {
                        error = ENOSPC;
                        break;
                }

                if (croffset == 0 &&
                    (de_cluster(pmp, uio->uio_offset + uio->uio_resid) > cn ||
                     (uio->uio_offset + uio->uio_resid) >= dep->de_FileSize)) {
                        /*
                         * If either the whole cluster gets written,
                         * or we write the cluster from its start beyond EOF,
                         * then no need to read data from disk.
                         */
                        bp = getblk(thisvp, cn, pmp->pm_bpcluster, 0, INFSLP);
                        clrbuf(bp);
                        /*
                         * Do the bmap now, since pcbmap needs buffers
                         * for the fat table. (see msdosfs_strategy)
                         */
                        if (bp->b_blkno == bp->b_lblkno) {
                                error = pcbmap(dep, bp->b_lblkno, &bp->b_blkno, 0, 0);
                                if (error)
                                        bp->b_blkno = -1;
                        }
                        if (bp->b_blkno == -1) {
                                brelse(bp);
                                if (!error)
                                        error = EIO;            /* XXX */
                                break;
                        }
                } else {
                        /*
                         * The block we need to write into exists, so
                         * read it in.
                         */
                        error = bread(thisvp, cn, pmp->pm_bpcluster, &bp);
                        if (error) {
                                brelse(bp);
                                break;
                        }
                }

                n = ulmin(uio->uio_resid, pmp->pm_bpcluster - croffset);
                if (uio->uio_offset + n > dep->de_FileSize) {
                        dep->de_FileSize = uio->uio_offset + n;
                        uvm_vnp_setsize(vp, dep->de_FileSize);
                }
                uvm_vnp_uncache(vp);
                /*
                 * Should these vnode_pager_* functions be done on dir
                 * files?
                 */

                /*
                 * Copy the data from user space into the buf header.
                 */
                error = uiomove(bp->b_data + croffset, n, uio);

                /*
                 * If they want this synchronous then write it and wait for
                 * it.  Otherwise, if on a cluster boundary write it
                 * asynchronously so we can move on to the next block
                 * without delay.  Otherwise do a delayed write because we
                 * may want to write some more into the block later.
                 */
#if 0
                if (ioflag & IO_NOCACHE)
                        bp->b_flags |= B_NOCACHE;
#endif
                if (ioflag & IO_SYNC)
                        (void) bwrite(bp);
                else if (n + croffset == pmp->pm_bpcluster)
                        bawrite(bp);
                else
                        bdwrite(bp);
                dep->de_flag |= DE_UPDATE;
        } while (error == 0 && uio->uio_resid > 0);

        if (resid > uio->uio_resid)
                 VN_KNOTE(ap->a_vp, NOTE_WRITE | (extended ? NOTE_EXTEND : 0));

        if (dep->de_FileSize < osize)
                VN_KNOTE(ap->a_vp, NOTE_TRUNCATE);

        /*
         * If the write failed and they want us to, truncate the file back
         * to the size it was before the write was attempted.
         */
errexit:
        if (error) {
                if (ioflag & IO_UNIT) {
                        detrunc(dep, osize, ioflag & IO_SYNC, NOCRED, curproc);
                        uio->uio_offset -= resid - uio->uio_resid;
                        uio->uio_resid = resid;
                } else {
                        detrunc(dep, dep->de_FileSize, ioflag & IO_SYNC, NOCRED, curproc);
                        if (uio->uio_resid != resid)
                                error = 0;
                }
        } else if (ioflag & IO_SYNC)
                error = deupdat(dep, 1);

out:
        /* correct the result for writes clamped by vn_fsizechk() */
        uio->uio_resid += overrun;
        return (error);
}

int
msdosfs_ioctl(void *v)
{
        return (ENOTTY);
}

/*
 * Flush the blocks of a file to disk.
 *
 * This function is worthless for vnodes that represent directories. Maybe we
 * could just do a sync if they try an fsync on a directory file.
 */
int
msdosfs_fsync(void *v)
{
        struct vop_fsync_args *ap = v;
        struct vnode *vp = ap->a_vp;

        vflushbuf(vp, ap->a_waitfor == MNT_WAIT);
        return (deupdat(VTODE(vp), ap->a_waitfor == MNT_WAIT));
}

/*
 * Flush the blocks of a file to disk.
 *
 * This function is worthless for vnodes that represent directories. Maybe we
 * could just do a sync if they try an fsync on a directory file.
 */
int
msdosfs_remove(void *v)
{
        struct vop_remove_args *ap = v;
        struct denode *dep = VTODE(ap->a_vp);
        struct denode *ddep = VTODE(ap->a_dvp);
        int error;

        if (ap->a_vp->v_type == VDIR)
                error = EPERM;
        else
                error = removede(ddep, dep);

        VN_KNOTE(ap->a_vp, NOTE_DELETE);
        VN_KNOTE(ap->a_dvp, NOTE_WRITE);

#ifdef MSDOSFS_DEBUG
        printf("msdosfs_remove(), dep %p, v_usecount %d\n", dep,
            ap->a_vp->v_usecount);
#endif
        return (error);
}

/*
 * DOS filesystems don't know what links are. But since we already called
 * msdosfs_lookup() with create and lockparent, the parent is locked so we
 * have to free it before we return the error.
 */
int
msdosfs_link(void *v)
{
        struct vop_link_args *ap = v;

        VOP_ABORTOP(ap->a_dvp, ap->a_cnp);
        vput(ap->a_dvp);
        return (EOPNOTSUPP);
}

/*
 * Renames on files require moving the denode to a new hash queue since the
 * denode's location is used to compute which hash queue to put the file
 * in. Unless it is a rename in place.  For example "mv a b".
 *
 * What follows is the basic algorithm:
 *
 * if (file move) {
 *      if (dest file exists) {
 *              remove dest file
 *      }
 *      if (dest and src in same directory) {
 *              rewrite name in existing directory slot
 *      } else {
 *              write new entry in dest directory
 *              update offset and dirclust in denode
 *              move denode to new hash chain
 *              clear old directory entry
 *      }
 * } else {
 *      directory move
 *      if (dest directory exists) {
 *              if (dest is not empty) {
 *                      return ENOTEMPTY
 *              }
 *              remove dest directory
 *      }
 *      if (dest and src in same directory) {
 *              rewrite name in existing entry
 *      } else {
 *              be sure dest is not a child of src directory
 *              write entry in dest directory
 *              update "." and ".." in moved directory
 *              update offset and dirclust in denode
 *              move denode to new hash chain
 *              clear old directory entry for moved directory
 *      }
 * }
 *
 * On entry:
 *      source's parent directory is unlocked
 *      source file or directory is unlocked
 *      destination's parent directory is locked
 *      destination file or directory is locked if it exists
 *
 * On exit:
 *      all denodes should be released
 *
 * Notes:
 * I'm not sure how the memory containing the pathnames pointed at by the
 * componentname structures is freed, there may be some memory bleeding
 * for each rename done.
 */
int
msdosfs_rename(void *v)
{
        struct vop_rename_args *ap = v;
        struct vnode *tvp = ap->a_tvp;
        struct vnode *tdvp = ap->a_tdvp;
        struct vnode *fvp = ap->a_fvp;
        struct vnode *fdvp = ap->a_fdvp;
        struct componentname *tcnp = ap->a_tcnp;
        struct componentname *fcnp = ap->a_fcnp;
        struct denode *ip, *xp, *dp, *zp;
        u_char toname[11], oldname[11];
        uint32_t from_diroffset, to_diroffset;
        u_char to_count;
        int doingdirectory = 0, newparent = 0;
        int error;
        uint32_t cn, pcl;
        daddr_t bn;
        struct msdosfsmount *pmp;
        struct direntry *dotdotp;
        struct buf *bp;

        pmp = VFSTOMSDOSFS(fdvp->v_mount);

#ifdef DIAGNOSTIC
        if ((tcnp->cn_flags & HASBUF) == 0 ||
            (fcnp->cn_flags & HASBUF) == 0)
                panic("msdosfs_rename: no name");
#endif
        /*
         * Check for cross-device rename.
         */
        if ((fvp->v_mount != tdvp->v_mount) ||
            (tvp && (fvp->v_mount != tvp->v_mount))) {
                error = EXDEV;
abortit:
                VOP_ABORTOP(tdvp, tcnp);
                if (tdvp == tvp)
                        vrele(tdvp);
                else
                        vput(tdvp);
                if (tvp)
                        vput(tvp);
                VOP_ABORTOP(fdvp, fcnp);
                vrele(fdvp);
                vrele(fvp);
                return (error);
        }

        /*
         * If source and dest are the same, do nothing.
         */
        if (tvp == fvp) {
                error = 0;
                goto abortit;
        }

        /* */
        if ((error = vn_lock(fvp, LK_EXCLUSIVE | LK_RETRY)) != 0)
                goto abortit;
        dp = VTODE(fdvp);
        ip = VTODE(fvp);

        /*
         * Be sure we are not renaming ".", "..", or an alias of ".". This
         * leads to a crippled directory tree.  It's pretty tough to do a
         * "ls" or "pwd" with the "." directory entry missing, and "cd .."
         * doesn't work if the ".." entry is missing.
         */
        if (ip->de_Attributes & ATTR_DIRECTORY) {
                /*
                 * Avoid ".", "..", and aliases of "." for obvious reasons.
                 */
                if ((fcnp->cn_namelen == 1 && fcnp->cn_nameptr[0] == '.') ||
                    dp == ip ||
                    (fcnp->cn_flags & ISDOTDOT) ||
                    (tcnp->cn_flags & ISDOTDOT) ||
                    (ip->de_flag & DE_RENAME)) {
                        VOP_UNLOCK(fvp);
                        error = EINVAL;
                        goto abortit;
                }
                ip->de_flag |= DE_RENAME;
                doingdirectory++;
        }
        VN_KNOTE(fdvp, NOTE_WRITE);     /* XXX right place? */

        /*
         * When the target exists, both the directory
         * and target vnodes are returned locked.
         */
        dp = VTODE(tdvp);
        xp = tvp ? VTODE(tvp) : NULL;
        /*
         * Remember direntry place to use for destination
         */
        to_diroffset = dp->de_fndoffset;
        to_count = dp->de_fndcnt;

        /*
         * If ".." must be changed (ie the directory gets a new
         * parent) then the source directory must not be in the
         * directory hierarchy above the target, as this would
         * orphan everything below the source directory. Also
         * the user must have write permission in the source so
         * as to be able to change "..". We must repeat the call
         * to namei, as the parent directory is unlocked by the
         * call to doscheckpath().
         */
        error = VOP_ACCESS(fvp, VWRITE, tcnp->cn_cred, tcnp->cn_proc);
        VOP_UNLOCK(fvp);
        if (VTODE(fdvp)->de_StartCluster != VTODE(tdvp)->de_StartCluster)
                newparent = 1;
        vrele(fdvp);
        if (doingdirectory && newparent) {
                if (error)      /* write access check above */
                        goto bad1;
                if (xp != NULL)
                        vput(tvp);
                /*
                 * doscheckpath() vput()'s dp,
                 * so we have to do a relookup afterwards
                 */
                if ((error = doscheckpath(ip, dp)) != 0)
                        goto out;
                if ((tcnp->cn_flags & SAVESTART) == 0)
                        panic("msdosfs_rename: lost to startdir");
                if ((error = vfs_relookup(tdvp, &tvp, tcnp)) != 0)
                        goto out;
                dp = VTODE(tdvp);
                xp = tvp ? VTODE(tvp) : NULL;
        }

        VN_KNOTE(tdvp, NOTE_WRITE);

        if (xp != NULL) {
                /*
                 * Target must be empty if a directory and have no links
                 * to it. Also, ensure source and target are compatible
                 * (both directories, or both not directories).
                 */
                if (xp->de_Attributes & ATTR_DIRECTORY) {
                        if (!dosdirempty(xp)) {
                                error = ENOTEMPTY;
                                goto bad1;
                        }
                        if (!doingdirectory) {
                                error = ENOTDIR;
                                goto bad1;
                        }
                        cache_purge(tdvp);
                } else if (doingdirectory) {
                        error = EISDIR;
                        goto bad1;
                }
                if ((error = removede(dp, xp)) != 0)
                        goto bad1;
                VN_KNOTE(tvp, NOTE_DELETE);
                vput(tvp);
                xp = NULL;
        }

        /*
         * Convert the filename in tcnp into a dos filename. We copy this
         * into the denode and directory entry for the destination
         * file/directory.
         */
        if ((error = uniqdosname(VTODE(tdvp), tcnp, toname)) != 0)
                goto bad1;

        /*
         * Since from wasn't locked at various places above,
         * have to do a relookup here.
         */
        fcnp->cn_flags &= ~MODMASK;
        fcnp->cn_flags |= LOCKPARENT | LOCKLEAF;
        if ((fcnp->cn_flags & SAVESTART) == 0)
                panic("msdosfs_rename: lost from startdir");
        if (!newparent)
                VOP_UNLOCK(tdvp);
        (void) vfs_relookup(fdvp, &fvp, fcnp);
        if (fvp == NULL) {
                /*
                 * From name has disappeared.
                 */
                if (doingdirectory)
                        panic("rename: lost dir entry");
                vrele(ap->a_fvp);
                if (newparent)
                        VOP_UNLOCK(tdvp);
                vrele(tdvp);
                return 0;
        }
        xp = VTODE(fvp);
        zp = VTODE(fdvp);
        from_diroffset = zp->de_fndoffset;

        /*
         * Ensure that the directory entry still exists and has not
         * changed till now. If the source is a file the entry may
         * have been unlinked or renamed. In either case there is
         * no further work to be done. If the source is a directory
         * then it cannot have been rmdir'ed or renamed; this is
         * prohibited by the DE_RENAME flag.
         */
        if (xp != ip) {
                if (doingdirectory)
                        panic("rename: lost dir entry");
                vrele(ap->a_fvp);
                if (newparent)
                        VOP_UNLOCK(fdvp);
                xp = NULL;
        } else {
                vrele(fvp);
                xp = NULL;

                /*
                 * First write a new entry in the destination
                 * directory and mark the entry in the source directory
                 * as deleted.  Then move the denode to the correct hash
                 * chain for its new location in the filesystem.  And, if
                 * we moved a directory, then update its .. entry to point
                 * to the new parent directory.
                 */
                bcopy(ip->de_Name, oldname, 11);
                bcopy(toname, ip->de_Name, 11); /* update denode */
                dp->de_fndoffset = to_diroffset;
                dp->de_fndcnt = to_count;
                error = createde(ip, dp, NULL, tcnp);
                if (error) {
                        bcopy(oldname, ip->de_Name, 11);
                        if (newparent)
                                VOP_UNLOCK(fdvp);
                        goto bad;
                }
                ip->de_refcnt++;
                zp->de_fndoffset = from_diroffset;
                if ((error = removede(zp, ip)) != 0) {
                        /* XXX should really panic here, fs is corrupt */
                        if (newparent)
                                VOP_UNLOCK(fdvp);
                        goto bad;
                }

                cache_purge(fvp);

                if (!doingdirectory) {
                        error = pcbmap(dp, de_cluster(pmp, to_diroffset), 0,
                                       &ip->de_dirclust, 0);
                        if (error) {
                                /* XXX should really panic here, fs is corrupt */
                                if (newparent)
                                        VOP_UNLOCK(fdvp);
                                goto bad;
                        }
                        ip->de_diroffset = to_diroffset;
                        if (ip->de_dirclust != MSDOSFSROOT)
                                ip->de_diroffset &= pmp->pm_crbomask;
                }
                reinsert(ip);
                if (newparent)
                        VOP_UNLOCK(fdvp);
        }

        /*
         * If we moved a directory to a new parent directory, then we must
         * fixup the ".." entry in the moved directory.
         */
        if (doingdirectory && newparent) {
                cn = ip->de_StartCluster;
                if (cn == MSDOSFSROOT) {
                        /* this should never happen */
                        panic("msdosfs_rename: updating .. in root directory?");
                } else
                        bn = cntobn(pmp, cn);
                error = bread(pmp->pm_devvp, bn, pmp->pm_bpcluster, &bp);
                if (error) {
                        /* XXX should really panic here, fs is corrupt */
                        brelse(bp);
                        goto bad;
                }
                dotdotp = (struct direntry *)bp->b_data;
                putushort(dotdotp[0].deStartCluster, cn);
                pcl = dp->de_StartCluster;
                if (FAT32(pmp) && pcl == pmp->pm_rootdirblk)
                        pcl = 0;
                putushort(dotdotp[1].deStartCluster, pcl);
                if (FAT32(pmp)) {
                        putushort(dotdotp[0].deHighClust, cn >> 16);
                        putushort(dotdotp[1].deHighClust, pcl >> 16);
                }
                if ((error = bwrite(bp)) != 0) {
                        /* XXX should really panic here, fs is corrupt */
                        goto bad;
                }
        }

        VN_KNOTE(fvp, NOTE_RENAME);

bad:
        VOP_UNLOCK(fvp);
        vrele(fdvp);
bad1:
        if (xp)
                vput(tvp);
        vput(tdvp);
out:
        ip->de_flag &= ~DE_RENAME;
        vrele(fvp);
        return (error);

}

struct {
        struct direntry dot;
        struct direntry dotdot;
} dosdirtemplate = {
        {       ".       ", "   ",                      /* the . entry */
                ATTR_DIRECTORY,                         /* file attribute */
                CASE_LOWER_BASE | CASE_LOWER_EXT,       /* lower case */
                0,                                      /* create time 100ths */
                { 0, 0 }, { 0, 0 },                     /* create time & date */
                { 0, 0 },                               /* access date */
                { 0, 0 },                               /* high bits of start cluster */
                { 210, 4 }, { 210, 4 },                 /* modify time & date */
                { 0, 0 },                               /* startcluster */
                { 0, 0, 0, 0 }                          /* filesize */
        },
        {       "..      ", "   ",                      /* the .. entry */
                ATTR_DIRECTORY,                         /* file attribute */
                CASE_LOWER_BASE | CASE_LOWER_EXT,       /* lower case */
                0,                                      /* create time 100ths */
                { 0, 0 }, { 0, 0 },                     /* create time & date */
                { 0, 0 },                               /* access date */
                { 0, 0 },                               /* high bits of start cluster */
                { 210, 4 }, { 210, 4 },                 /* modify time & date */
                { 0, 0 },                               /* startcluster */
                { 0, 0, 0, 0 }                          /* filesize */
        }
};

int
msdosfs_mkdir(void *v)
{
        struct vop_mkdir_args *ap = v;
        struct componentname *cnp = ap->a_cnp;
        struct denode ndirent;
        struct denode *dep;
        struct denode *pdep = VTODE(ap->a_dvp);
        int error;
        daddr_t bn;
        uint32_t newcluster, pcl;
        struct direntry *denp;
        struct msdosfsmount *pmp = pdep->de_pmp;
        struct buf *bp;
        struct timespec ts;

        /*
         * If this is the root directory and there is no space left we
         * can't do anything.  This is because the root directory can not
         * change size.
         */
        if (pdep->de_StartCluster == MSDOSFSROOT
            && pdep->de_fndoffset >= pdep->de_FileSize) {
                error = ENOSPC;
                goto bad2;
        }

        /*
         * Allocate a cluster to hold the about to be created directory.
         */
        error = clusteralloc(pmp, 0, 1, &newcluster, NULL);
        if (error)
                goto bad2;

        bzero(&ndirent, sizeof(ndirent));
        ndirent.de_pmp = pmp;
        ndirent.de_flag = DE_ACCESS | DE_CREATE | DE_UPDATE;
        getnanotime(&ts);
        DETIMES(&ndirent, &ts, &ts, &ts);

        /*
         * Now fill the cluster with the "." and ".." entries. And write
         * the cluster to disk.  This way it is there for the parent
         * directory to be pointing at if there were a crash.
         */
        bn = cntobn(pmp, newcluster);
        /* always succeeds */
        bp = getblk(pmp->pm_devvp, bn, pmp->pm_bpcluster, 0, INFSLP);
        bzero(bp->b_data, pmp->pm_bpcluster);
        bcopy(&dosdirtemplate, bp->b_data, sizeof dosdirtemplate);
        denp = (struct direntry *)bp->b_data;
        putushort(denp[0].deStartCluster, newcluster);
        putushort(denp[0].deCDate, ndirent.de_CDate);
        putushort(denp[0].deCTime, ndirent.de_CTime);
        denp[0].deCTimeHundredth = ndirent.de_CTimeHundredth;
        putushort(denp[0].deADate, ndirent.de_ADate);
        putushort(denp[0].deMDate, ndirent.de_MDate);
        putushort(denp[0].deMTime, ndirent.de_MTime);
        pcl = pdep->de_StartCluster;
        if (FAT32(pmp) && pcl == pmp->pm_rootdirblk)
                pcl = 0;
        putushort(denp[1].deStartCluster, pcl);
        putushort(denp[1].deCDate, ndirent.de_CDate);
        putushort(denp[1].deCTime, ndirent.de_CTime);
        denp[1].deCTimeHundredth = ndirent.de_CTimeHundredth;
        putushort(denp[1].deADate, ndirent.de_ADate);
        putushort(denp[1].deMDate, ndirent.de_MDate);
        putushort(denp[1].deMTime, ndirent.de_MTime);
        if (FAT32(pmp)) {
                putushort(denp[0].deHighClust, newcluster >> 16);
                putushort(denp[1].deHighClust, pdep->de_StartCluster >> 16);
        }

        if ((error = bwrite(bp)) != 0)
                goto bad;

        /*
         * Now build up a directory entry pointing to the newly allocated
         * cluster.  This will be written to an empty slot in the parent
         * directory.
         */
#ifdef DIAGNOSTIC
        if ((cnp->cn_flags & HASBUF) == 0)
                panic("msdosfs_mkdir: no name");
#endif
        if ((error = uniqdosname(pdep, cnp, ndirent.de_Name)) != 0)
                goto bad;

        ndirent.de_Attributes = ATTR_DIRECTORY;
        ndirent.de_StartCluster = newcluster;
        ndirent.de_FileSize = 0;
        ndirent.de_dev = pdep->de_dev;
        ndirent.de_devvp = pdep->de_devvp;
        if ((error = createde(&ndirent, pdep, &dep, cnp)) != 0)
                goto bad;
        if ((cnp->cn_flags & SAVESTART) == 0)
                pool_put(&namei_pool, cnp->cn_pnbuf);
        VN_KNOTE(ap->a_dvp, NOTE_WRITE | NOTE_LINK);
        vput(ap->a_dvp);
        *ap->a_vpp = DETOV(dep);
        return (0);

bad:
        clusterfree(pmp, newcluster, NULL);
bad2:
        pool_put(&namei_pool, cnp->cn_pnbuf);
        vput(ap->a_dvp);
        return (error);
}

int
msdosfs_rmdir(void *v)
{
        struct vop_rmdir_args *ap = v;
        struct vnode *vp = ap->a_vp;
        struct vnode *dvp = ap->a_dvp;
        struct componentname *cnp = ap->a_cnp;
        struct denode *ip, *dp;
        int error;

        ip = VTODE(vp);
        dp = VTODE(dvp);
        /*
         * Verify the directory is empty (and valid).
         * (Rmdir ".." won't be valid since
         *  ".." will contain a reference to
         *  the current directory and thus be
         *  non-empty.)
         */
        error = 0;
        if (!dosdirempty(ip) || ip->de_flag & DE_RENAME) {
                error = ENOTEMPTY;
                goto out;
        }

        VN_KNOTE(dvp, NOTE_WRITE | NOTE_LINK);

        /*
         * Delete the entry from the directory.  For dos filesystems this
         * gets rid of the directory entry on disk, the in memory copy
         * still exists but the de_refcnt is <= 0.  This prevents it from
         * being found by deget().  When the vput() on dep is done we give
         * up access and eventually msdosfs_reclaim() will be called which
         * will remove it from the denode cache.
         */
        if ((error = removede(dp, ip)) != 0)
                goto out;
        /*
         * This is where we decrement the link count in the parent
         * directory.  Since dos filesystems don't do this we just purge
         * the name cache and let go of the parent directory denode.
         */
        cache_purge(dvp);
        vput(dvp);
        dvp = NULL;
        /*
         * Truncate the directory that is being deleted.
         */
        error = detrunc(ip, (uint32_t)0, IO_SYNC, cnp->cn_cred, cnp->cn_proc);
        cache_purge(vp);
out:
        if (dvp)
                vput(dvp);
        VN_KNOTE(vp, NOTE_DELETE);
        vput(vp);
        return (error);
}

/*
 * DOS filesystems don't know what symlinks are.
 */
int
msdosfs_symlink(void *v)
{
        struct vop_symlink_args *ap = v;

        VOP_ABORTOP(ap->a_dvp, ap->a_cnp);
        vput(ap->a_dvp);
        return (EOPNOTSUPP);
}

int
msdosfs_readdir(void *v)
{
        struct vop_readdir_args *ap = v;
        int error = 0;
        int diff;
        long n;
        int blsize;
        long on;
        long lost;
        long count;
        uint32_t dirsperblk;
        uint32_t cn, lbn;
        uint32_t fileno;
        long bias = 0;
        daddr_t bn;
        struct buf *bp;
        struct denode *dep = VTODE(ap->a_vp);
        struct msdosfsmount *pmp = dep->de_pmp;
        struct direntry *dentp;
        struct dirent dirbuf;
        struct uio *uio = ap->a_uio;
        off_t offset, wlast = -1;
        int chksum = -1;

#ifdef MSDOSFS_DEBUG
        printf("msdosfs_readdir(): vp %p, uio %p, cred %p, eofflagp %p\n",
            ap->a_vp, uio, ap->a_cred, ap->a_eofflag);
#endif

        /*
         * msdosfs_readdir() won't operate properly on regular files since
         * it does i/o only with the filesystem vnode, and hence can
         * retrieve the wrong block from the buffer cache for a plain file.
         * So, fail attempts to readdir() on a plain file.
         */
        if ((dep->de_Attributes & ATTR_DIRECTORY) == 0)
                return (ENOTDIR);

        /*
         * To be safe, initialize dirbuf
         */
        bzero(&dirbuf, sizeof(dirbuf));

        /*
         * If the user buffer is smaller than the size of one dos directory
         * entry or the file offset is not a multiple of the size of a
         * directory entry, then we fail the read.
         */
        count = uio->uio_resid & ~(sizeof(struct direntry) - 1);
        offset = uio->uio_offset;
        if (count < sizeof(struct direntry) ||
            (offset & (sizeof(struct direntry) - 1)))
                return (EINVAL);
        lost = uio->uio_resid - count;
        uio->uio_resid = count;

        dirsperblk = pmp->pm_BytesPerSec / sizeof(struct direntry);

        /*
         * If they are reading from the root directory then, we simulate
         * the . and .. entries since these don't exist in the root
         * directory.  We also set the offset bias to make up for having to
         * simulate these entries. By this I mean that at file offset 64 we
         * read the first entry in the root directory that lives on disk.
         */
        if (dep->de_StartCluster == MSDOSFSROOT
            || (FAT32(pmp) && dep->de_StartCluster == pmp->pm_rootdirblk)) {
#if 0
                printf("msdosfs_readdir(): going after . or .. in root dir, offset %d\n",
                    offset);
#endif
                bias = 2 * sizeof(struct direntry);
                if (offset < bias) {
                        for (n = (int)offset / sizeof(struct direntry);
                             n < 2; n++) {
                                if (FAT32(pmp))
                                        dirbuf.d_fileno = pmp->pm_rootdirblk;
                                else
                                        dirbuf.d_fileno = 1;
                                dirbuf.d_type = DT_DIR;
                                switch (n) {
                                case 0:
                                        dirbuf.d_namlen = 1;
                                        strlcpy(dirbuf.d_name, ".",
                                            sizeof dirbuf.d_name);
                                        break;
                                case 1:
                                        dirbuf.d_namlen = 2;
                                        strlcpy(dirbuf.d_name, "..",
                                            sizeof dirbuf.d_name);
                                        break;
                                }
                                dirbuf.d_reclen = DIRENT_SIZE(&dirbuf);
                                dirbuf.d_off = offset +
                                    sizeof(struct direntry);
                                if (uio->uio_resid < dirbuf.d_reclen)
                                        goto out;
                                error = uiomove(&dirbuf, dirbuf.d_reclen, uio);
                                if (error)
                                        goto out;
                                offset = dirbuf.d_off;
                        }
                }
        }

        while (uio->uio_resid > 0) {
                lbn = de_cluster(pmp, offset - bias);
                on = (offset - bias) & pmp->pm_crbomask;
                n = min(pmp->pm_bpcluster - on, uio->uio_resid);
                diff = dep->de_FileSize - (offset - bias);
                if (diff <= 0)
                        break;
                n = min(n, diff);
                if ((error = pcbmap(dep, lbn, &bn, &cn, &blsize)) != 0)
                        break;
                error = bread(pmp->pm_devvp, bn, blsize, &bp);
                if (error) {
                        brelse(bp);
                        return (error);
                }
                n = min(n, blsize - bp->b_resid);

                /*
                 * Convert from dos directory entries to fs-independent
                 * directory entries.
                 */
                for (dentp = (struct direntry *)(bp->b_data + on);
                     (char *)dentp < bp->b_data + on + n;
                     dentp++, offset += sizeof(struct direntry)) {
#if 0
                        printf("rd: dentp %08x prev %08x crnt %08x deName %02x attr %02x\n",
                            dentp, prev, crnt, dentp->deName[0], dentp->deAttributes);
#endif
                        /*
                         * If this is an unused entry, we can stop.
                         */
                        if (dentp->deName[0] == SLOT_EMPTY) {
                                brelse(bp);
                                goto out;
                        }
                        /*
                         * Skip deleted entries.
                         */
                        if (dentp->deName[0] == SLOT_DELETED) {
                                chksum = -1;
                                wlast = -1;
                                continue;
                        }

                        /*
                         * Handle Win95 long directory entries
                         */
                        if (dentp->deAttributes == ATTR_WIN95) {
                                struct winentry *wep;
                                if (pmp->pm_flags & MSDOSFSMNT_SHORTNAME)
                                        continue;
                                wep = (struct winentry *)dentp;
                                chksum = win2unixfn(wep, &dirbuf, chksum);
                                if (wep->weCnt & WIN_LAST)
                                        wlast = offset;
                                continue;
                        }

                        /*
                         * Skip volume labels
                         */
                        if (dentp->deAttributes & ATTR_VOLUME) {
                                chksum = -1;
                                wlast = -1;
                                continue;
                        }

                        /*
                         * This computation of d_fileno must match
                         * the computation of va_fileid in
                         * msdosfs_getattr.
                         */
                        fileno = getushort(dentp->deStartCluster);
                        if (FAT32(pmp))
                            fileno |= getushort(dentp->deHighClust) << 16;

                        if (dentp->deAttributes & ATTR_DIRECTORY) {
                                /* Special-case root */
                                if (fileno == MSDOSFSROOT)  {
                                        fileno = FAT32(pmp) ?
                                            pmp->pm_rootdirblk : 1;
                                }

                                dirbuf.d_fileno = fileno;
                                dirbuf.d_type = DT_DIR;
                        } else {
                                if (getulong(dentp->deFileSize) == 0) {
                                        uint64_t fileno64;

                                        fileno64 = (cn == MSDOSFSROOT) ?
                                            roottobn(pmp, 0) : cntobn(pmp, cn);

                                        fileno64 *= dirsperblk;
                                        fileno64 += dentp -
                                            (struct direntry *)bp->b_data;

                                        fileno = fileidhash(fileno64);
                                }

                                dirbuf.d_fileno = fileno;
                                dirbuf.d_type = DT_REG;
                        }

                        if (chksum != winChksum(dentp->deName))
                                dirbuf.d_namlen = dos2unixfn(dentp->deName,
                                    (u_char *)dirbuf.d_name,
                                    pmp->pm_flags & MSDOSFSMNT_SHORTNAME);
                        else
                                dirbuf.d_name[dirbuf.d_namlen] = 0;
                        chksum = -1;
                        dirbuf.d_reclen = DIRENT_SIZE(&dirbuf);
                        dirbuf.d_off = offset + sizeof(struct direntry);
                        if (uio->uio_resid < dirbuf.d_reclen) {
                                brelse(bp);
                                /* Remember long-name offset. */
                                if (wlast != -1)
                                        offset = wlast;
                                goto out;
                        }
                        wlast = -1;
                        error = uiomove(&dirbuf, dirbuf.d_reclen, uio);
                        if (error) {
                                brelse(bp);
                                goto out;
                        }
                }
                brelse(bp);
        }

out:
        uio->uio_offset = offset;
        uio->uio_resid += lost;
        if (dep->de_FileSize - (offset - bias) <= 0)
                *ap->a_eofflag = 1;
        else
                *ap->a_eofflag = 0;
        return (error);
}

/*
 * DOS filesystems don't know what symlinks are.
 */
int
msdosfs_readlink(void *v)
{
#if 0
        struct vop_readlink_args /* {
                struct vnode *a_vp;
                struct uio *a_uio;
                struct ucred *a_cred;
        } */ *ap;
#endif

        return (EINVAL);
}

int
msdosfs_lock(void *v)
{
        struct vop_lock_args *ap = v;
        struct vnode *vp = ap->a_vp;

        return rrw_enter(&VTODE(vp)->de_lock, ap->a_flags & LK_RWFLAGS);
}

int
msdosfs_unlock(void *v)
{
        struct vop_unlock_args *ap = v;
        struct vnode *vp = ap->a_vp;

        rrw_exit(&VTODE(vp)->de_lock);
        return 0;
}

int
msdosfs_islocked(void *v)
{
        struct vop_islocked_args *ap = v;

        return rrw_status(&VTODE(ap->a_vp)->de_lock);
}

/*
 * vp  - address of vnode file the file
 * bn  - which cluster we are interested in mapping to a filesystem block number
 * vpp - returns the vnode for the block special file holding the filesystem
 *       containing the file of interest
 * bnp - address of where to return the filesystem relative block number
 */
int
msdosfs_bmap(void *v)
{
        struct vop_bmap_args *ap = v;
        struct denode *dep = VTODE(ap->a_vp);
        uint32_t cn;

        if (ap->a_vpp != NULL)
                *ap->a_vpp = dep->de_devvp;
        if (ap->a_bnp == NULL)
                return (0);

        cn = ap->a_bn;
        if (cn != ap->a_bn)
                return (EFBIG);

        return (msdosfs_bmaparray(ap->a_vp, cn, ap->a_bnp, ap->a_runp));
}

int
msdosfs_bmaparray(struct vnode *vp, uint32_t cn, daddr_t *bnp, int *runp)
{
        struct denode *dep = VTODE(vp);
        struct msdosfsmount *pmp = dep->de_pmp;
        struct mount *mp;
        int error, maxrun = 0, run;
        daddr_t runbn;

        mp = vp->v_mount;

        if (runp) {
                /*
                 * XXX
                 * If MAXBSIZE is the largest transfer the disks can handle,
                 * we probably want maxrun to be 1 block less so that we
                 * don't create a block larger than the device can handle.
                 */
                *runp = 0;
                maxrun = min(MAXBSIZE / mp->mnt_stat.f_iosize - 1,
                    pmp->pm_maxcluster - cn);
        }

        if ((error = pcbmap(dep, cn, bnp, 0, 0)) != 0)
                return (error);

        for (run = 1; run <= maxrun; run++) {
                error = pcbmap(dep, cn + run, &runbn, 0, 0);
                if (error != 0 || (runbn != *bnp + de_cn2bn(pmp, run)))
                        break;
        }

        if (runp)
                *runp = run - 1;

        return (0);
}

int
msdosfs_strategy(void *v)
{
        struct vop_strategy_args *ap = v;
        struct buf *bp = ap->a_bp;
        struct denode *dep = VTODE(bp->b_vp);
        struct vnode *vp;
        int error = 0;
        int s;

        if (bp->b_vp->v_type == VBLK || bp->b_vp->v_type == VCHR)
                panic("msdosfs_strategy: spec");
        /*
         * If we don't already know the filesystem relative block number
         * then get it using pcbmap().  If pcbmap() returns the block
         * number as -1 then we've got a hole in the file.  DOS filesystems
         * don't allow files with holes, so we shouldn't ever see this.
         */
        if (bp->b_blkno == bp->b_lblkno) {
                error = pcbmap(dep, bp->b_lblkno, &bp->b_blkno, 0, 0);
                if (error)
                        bp->b_blkno = -1;
                if (bp->b_blkno == -1)
                        clrbuf(bp);
        }
        if (bp->b_blkno == -1) {
                s = splbio();
                biodone(bp);
                splx(s);
                return (error);
        }

        /*
         * Read/write the block from/to the disk that contains the desired
         * file block.
         */

        vp = dep->de_devvp;
        bp->b_dev = vp->v_rdev;
        VOP_STRATEGY(vp, bp);
        return (0);
}

int
msdosfs_print(void *v)
{
#if defined(DEBUG) || defined(DIAGNOSTIC) || defined(VFSLCKDEBUG)
        struct vop_print_args *ap = v;
        struct denode *dep = VTODE(ap->a_vp);

        printf(
            "tag VT_MSDOSFS, startcluster %u, dircluster %u, diroffset %u ",
            dep->de_StartCluster, dep->de_dirclust, dep->de_diroffset);
        printf(" dev %d, %d, %s\n",
            major(dep->de_dev), minor(dep->de_dev),
            VOP_ISLOCKED(ap->a_vp) ? "(LOCKED)" : "");
#ifdef DIAGNOSTIC
        printf("\n");
#endif
#endif

        return (0);
}

int
msdosfs_advlock(void *v)
{
        struct vop_advlock_args *ap = v;
        struct denode *dep = VTODE(ap->a_vp);

        return (lf_advlock(&dep->de_lockf, dep->de_FileSize, ap->a_id, ap->a_op,
            ap->a_fl, ap->a_flags));
}

int
msdosfs_pathconf(void *v)
{
        struct vop_pathconf_args *ap = v;
        struct msdosfsmount *pmp = VTODE(ap->a_vp)->de_pmp;
        int error = 0;

        switch (ap->a_name) {
        case _PC_LINK_MAX:
                *ap->a_retval = 1;
                break;
        case _PC_NAME_MAX:
                *ap->a_retval = pmp->pm_flags & MSDOSFSMNT_LONGNAME ? WIN_MAXLEN : 12;
                break;
        case _PC_CHOWN_RESTRICTED:
                *ap->a_retval = 1;
                break;
        case _PC_NO_TRUNC:
                *ap->a_retval = 0;
                break;
        case _PC_TIMESTAMP_RESOLUTION:
                *ap->a_retval = 2000000000;     /* 2 billion nanoseconds */
                break;
        default:
                error = EINVAL;
                break;
        }

        return (error);
}

/*
 * Thomas Wang's hash function, severely hacked to always set the high
 * bit on the number it returns (so no longer a proper hash function).
 */
static uint32_t
fileidhash(uint64_t fileid)
{
        uint64_t c1 = 0x6e5ea73858134343LL;
        uint64_t c2 = 0xb34e8f99a2ec9ef5LL;

        /*
         * We now have the original fileid value, as 64-bit value.
         * We need to reduce it to 32-bits, with the top bit set.
         */
        fileid ^= ((c1 ^ fileid) >> 32);
        fileid *= c1;
        fileid ^= ((c2 ^ fileid) >> 31);
        fileid *= c2;
        fileid ^= ((c1 ^ fileid) >> 32);

        return (uint32_t)(fileid | 0x80000000);
}

/* Global vfs data structures for msdosfs */
const struct vops msdosfs_vops = {
        .vop_lookup     = msdosfs_lookup,
        .vop_create     = msdosfs_create,
        .vop_mknod      = msdosfs_mknod,
        .vop_open       = msdosfs_open,
        .vop_close      = msdosfs_close,
        .vop_access     = msdosfs_access,
        .vop_getattr    = msdosfs_getattr,
        .vop_setattr    = msdosfs_setattr,
        .vop_read       = msdosfs_read,
        .vop_write      = msdosfs_write,
        .vop_ioctl      = msdosfs_ioctl,
        .vop_kqfilter   = msdosfs_kqfilter,
        .vop_fsync      = msdosfs_fsync,
        .vop_remove     = msdosfs_remove,
        .vop_link       = msdosfs_link,
        .vop_rename     = msdosfs_rename,
        .vop_mkdir      = msdosfs_mkdir,
        .vop_rmdir      = msdosfs_rmdir,
        .vop_symlink    = msdosfs_symlink,
        .vop_readdir    = msdosfs_readdir,
        .vop_readlink   = msdosfs_readlink,
        .vop_abortop    = vop_generic_abortop,
        .vop_inactive   = msdosfs_inactive,
        .vop_reclaim    = msdosfs_reclaim,
        .vop_lock       = msdosfs_lock,
        .vop_unlock     = msdosfs_unlock,
        .vop_bmap       = msdosfs_bmap,
        .vop_strategy   = msdosfs_strategy,
        .vop_print      = msdosfs_print,
        .vop_islocked   = msdosfs_islocked,
        .vop_pathconf   = msdosfs_pathconf,
        .vop_advlock    = msdosfs_advlock,
        .vop_bwrite     = vop_generic_bwrite,
        .vop_revoke     = vop_generic_revoke,
};

const struct filterops msdosfsread_filtops = {
        .f_flags        = FILTEROP_ISFD,
        .f_attach       = NULL,
        .f_detach       = filt_msdosfsdetach,
        .f_event        = filt_msdosfsread,
};

const struct filterops msdosfswrite_filtops = {
        .f_flags        = FILTEROP_ISFD,
        .f_attach       = NULL,
        .f_detach       = filt_msdosfsdetach,
        .f_event        = filt_msdosfswrite,
};

const struct filterops msdosfsvnode_filtops = {
        .f_flags        = FILTEROP_ISFD,
        .f_attach       = NULL,
        .f_detach       = filt_msdosfsdetach,
        .f_event        = filt_msdosfsvnode,
};

int
msdosfs_kqfilter(void *v)
{
        struct vop_kqfilter_args *ap = v;
        struct vnode *vp = ap->a_vp;
        struct knote *kn = ap->a_kn;

        switch (kn->kn_filter) {
        case EVFILT_READ:
                kn->kn_fop = &msdosfsread_filtops;
                break;
        case EVFILT_WRITE:
                kn->kn_fop = &msdosfswrite_filtops;
                break;
        case EVFILT_VNODE:
                kn->kn_fop = &msdosfsvnode_filtops;
                break;
        default:
                return (EINVAL);
        }

        kn->kn_hook = (caddr_t)vp;

        klist_insert_locked(&vp->v_klist, kn);

        return (0);
}

void
filt_msdosfsdetach(struct knote *kn)
{
        struct vnode *vp = (struct vnode *)kn->kn_hook;

        klist_remove_locked(&vp->v_klist, kn);
}

int
filt_msdosfsread(struct knote *kn, long hint)
{
        struct vnode *vp = (struct vnode *)kn->kn_hook;
        struct denode *dep = VTODE(vp);

        /*
         * filesystem is gone, so set the EOF flag and schedule
         * the knote for deletion.
         */
        if (hint == NOTE_REVOKE) {
                kn->kn_flags |= (EV_EOF | EV_ONESHOT);
                return (1);
        }

        kn->kn_data = dep->de_FileSize - foffset(kn->kn_fp);
        if (kn->kn_data == 0 && kn->kn_sfflags & NOTE_EOF) {
                kn->kn_fflags |= NOTE_EOF;
                return (1);
        }

        if (kn->kn_flags & (__EV_POLL | __EV_SELECT))
                return (1);

        return (kn->kn_data != 0);
}

int
filt_msdosfswrite(struct knote *kn, long hint)
{
        /*
         * filesystem is gone, so set the EOF flag and schedule
         * the knote for deletion.
         */
        if (hint == NOTE_REVOKE) {
                kn->kn_flags |= (EV_EOF | EV_ONESHOT);
                return (1);
        }

        kn->kn_data = 0;
        return (1);
}

int
filt_msdosfsvnode(struct knote *kn, long hint)
{
        if (kn->kn_sfflags & hint)
                kn->kn_fflags |= hint;
        if (hint == NOTE_REVOKE) {
                kn->kn_flags |= EV_EOF;
                return (1);
        }
        return (kn->kn_fflags != 0);
}