/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */
/*
 * Copyright (c) 2017 by Delphix. All rights reserved.
 * Copyright 2024 Oxide Computer Company
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kmem.h>
#include <sys/user.h>
#include <sys/proc.h>
#include <sys/cred.h>
#include <sys/disp.h>
#include <sys/buf.h>
#include <sys/vfs.h>
#include <sys/vfs_opreg.h>
#include <sys/vnode.h>
#include <sys/fdio.h>
#include <sys/file.h>
#include <sys/uio.h>
#include <sys/conf.h>
#include <sys/statvfs.h>
#include <sys/mount.h>
#include <sys/pathname.h>
#include <sys/cmn_err.h>
#include <sys/debug.h>
#include <sys/sysmacros.h>
#include <sys/conf.h>
#include <sys/mkdev.h>
#include <sys/swap.h>
#include <sys/sunddi.h>
#include <sys/sunldi.h>
#include <sys/dktp/fdisk.h>
#include <sys/fs/pc_label.h>
#include <sys/fs/pc_fs.h>
#include <sys/fs/pc_dir.h>
#include <sys/fs/pc_node.h>
#include <fs/fs_subr.h>
#include <sys/modctl.h>
#include <sys/dkio.h>
#include <sys/open.h>
#include <sys/mntent.h>
#include <sys/policy.h>
#include <sys/atomic.h>
#include <sys/sdt.h>

/*
 * The majority of PC media use a 512 sector size, but
 * occasionally you will run across a 1k sector size.
 * For media with a 1k sector size, fd_strategy() requires
 * the I/O size to be a 1k multiple; so when the sector size
 * is not yet known, always read 1k.
 */
#define PC_SAFESECSIZE  (PC_SECSIZE * 2)

static int pcfs_pseudo_floppy(dev_t);

static int pcfsinit(int, char *);
static int pcfs_mount(struct vfs *, struct vnode *, struct mounta *,
        struct cred *);
static int pcfs_unmount(struct vfs *, int, struct cred *);
static int pcfs_root(struct vfs *, struct vnode **);
static int pcfs_statvfs(struct vfs *, struct statvfs64 *);
static int pc_syncfsnodes(struct pcfs *);
static int pcfs_sync(struct vfs *, short, struct cred *);
static int pcfs_vget(struct vfs *vfsp, struct vnode **vpp, struct fid *fidp);
static void pcfs_freevfs(vfs_t *vfsp);
static int pcfs_syncfs(struct vfs *, uint64_t, struct cred *);

static int pc_readfat(struct pcfs *fsp, uchar_t *fatp);
static int pc_writefat(struct pcfs *fsp, daddr_t start);

static int pc_getfattype(struct pcfs *fsp);
static void pcfs_parse_mntopts(struct pcfs *fsp);


/*
 * pcfs mount options table
 */

static char *nohidden_cancel[] = { MNTOPT_PCFS_HIDDEN, NULL };
static char *hidden_cancel[] = { MNTOPT_PCFS_NOHIDDEN, NULL };
static char *nofoldcase_cancel[] = { MNTOPT_PCFS_FOLDCASE, NULL };
static char *foldcase_cancel[] = { MNTOPT_PCFS_NOFOLDCASE, NULL };
static char *clamptime_cancel[] = { MNTOPT_PCFS_NOCLAMPTIME, NULL };
static char *noclamptime_cancel[] = { MNTOPT_PCFS_CLAMPTIME, NULL };
static char *atime_cancel[] = { MNTOPT_NOATIME, NULL };
static char *noatime_cancel[] = { MNTOPT_ATIME, NULL };

static mntopt_t mntopts[] = {
/*
 *      option name     cancel option   default arg     flags   opt data
 */
        { MNTOPT_PCFS_NOHIDDEN, nohidden_cancel, NULL, 0, NULL },
        { MNTOPT_PCFS_HIDDEN, hidden_cancel, NULL, MO_DEFAULT, NULL },
        { MNTOPT_PCFS_NOFOLDCASE, nofoldcase_cancel, NULL, MO_DEFAULT, NULL },
        { MNTOPT_PCFS_FOLDCASE, foldcase_cancel, NULL, 0, NULL },
        { MNTOPT_PCFS_CLAMPTIME, clamptime_cancel, NULL, MO_DEFAULT, NULL },
        { MNTOPT_PCFS_NOCLAMPTIME, noclamptime_cancel, NULL, 0, NULL },
        { MNTOPT_NOATIME, noatime_cancel, NULL, 0, NULL },
        { MNTOPT_ATIME, atime_cancel, NULL, 0, NULL },
        { MNTOPT_PCFS_TIMEZONE, NULL, "+0", MO_DEFAULT | MO_HASVALUE, NULL },
        { MNTOPT_PCFS_SECSIZE, NULL, NULL, MO_HASVALUE, NULL }
};

static mntopts_t pcfs_mntopts = {
        sizeof (mntopts) / sizeof (mntopt_t),
        mntopts
};

int pcfsdebuglevel = 0;

/*
 * pcfslock:    protects the list of mounted pc filesystems "pc_mounttab.
 * pcfs_lock:   (inside per filesystem structure "pcfs")
 *              per filesystem lock. Most of the vfsops and vnodeops are
 *              protected by this lock.
 * pcnodes_lock: protects the pcnode hash table "pcdhead", "pcfhead".
 *
 * Lock hierarchy: pcfslock > pcfs_lock > pcnodes_lock
 *
 * pcfs_mountcount:     used to prevent module unloads while there is still
 *                      pcfs state from a former mount hanging around. With
 *                      forced umount support, the filesystem module must not
 *                      be allowed to go away before the last VFS_FREEVFS()
 *                      call has been made.
 *                      Since this is just an atomic counter, there's no need
 *                      for locking.
 */
kmutex_t        pcfslock;
krwlock_t       pcnodes_lock;
uint32_t        pcfs_mountcount;

static int pcfstype;

static vfsdef_t vfw = {
        VFSDEF_VERSION,
        "pcfs",
        pcfsinit,
        VSW_HASPROTO|VSW_CANREMOUNT|VSW_STATS|VSW_CANLOFI|VSW_MOUNTDEV,
        &pcfs_mntopts
};

extern struct mod_ops mod_fsops;

static struct modlfs modlfs = {
        &mod_fsops,
        "PC filesystem",
        &vfw
};

static struct modlinkage modlinkage = {
        MODREV_1,
        &modlfs,
        NULL
};

int
_init(void)
{
        int     error;

#if !defined(lint)
        /* make sure the on-disk structures are sane */
        ASSERT(sizeof (struct pcdir) == 32);
        ASSERT(sizeof (struct pcdir_lfn) == 32);
#endif
        mutex_init(&pcfslock, NULL, MUTEX_DEFAULT, NULL);
        rw_init(&pcnodes_lock, NULL, RW_DEFAULT, NULL);
        error = mod_install(&modlinkage);
        if (error) {
                mutex_destroy(&pcfslock);
                rw_destroy(&pcnodes_lock);
        }
        return (error);
}

int
_fini(void)
{
        int     error;

        /*
         * If a forcedly unmounted instance is still hanging around,
         * we cannot allow the module to be unloaded because that would
         * cause panics once the VFS framework decides it's time to call
         * into VFS_FREEVFS().
         */
        if (pcfs_mountcount)
                return (EBUSY);

        error = mod_remove(&modlinkage);
        if (error)
                return (error);
        mutex_destroy(&pcfslock);
        rw_destroy(&pcnodes_lock);
        /*
         * Tear down the operations vectors
         */
        (void) vfs_freevfsops_by_type(pcfstype);
        vn_freevnodeops(pcfs_fvnodeops);
        vn_freevnodeops(pcfs_dvnodeops);
        return (0);
}

int
_info(struct modinfo *modinfop)
{
        return (mod_info(&modlinkage, modinfop));
}

/* ARGSUSED1 */
static int
pcfsinit(int fstype, char *name)
{
        static const fs_operation_def_t pcfs_vfsops_template[] = {
                VFSNAME_MOUNT,          { .vfs_mount = pcfs_mount },
                VFSNAME_UNMOUNT,        { .vfs_unmount = pcfs_unmount },
                VFSNAME_ROOT,           { .vfs_root = pcfs_root },
                VFSNAME_STATVFS,        { .vfs_statvfs = pcfs_statvfs },
                VFSNAME_SYNC,           { .vfs_sync = pcfs_sync },
                VFSNAME_VGET,           { .vfs_vget = pcfs_vget },
                VFSNAME_FREEVFS,        { .vfs_freevfs = pcfs_freevfs },
                VFSNAME_SYNCFS,         { .vfs_syncfs = pcfs_syncfs },
                NULL,                   NULL
        };
        int error;

        error = vfs_setfsops(fstype, pcfs_vfsops_template, NULL);
        if (error != 0) {
                cmn_err(CE_WARN, "pcfsinit: bad vfs ops template");
                return (error);
        }

        error = vn_make_ops("pcfs", pcfs_fvnodeops_template, &pcfs_fvnodeops);
        if (error != 0) {
                (void) vfs_freevfsops_by_type(fstype);
                cmn_err(CE_WARN, "pcfsinit: bad file vnode ops template");
                return (error);
        }

        error = vn_make_ops("pcfsd", pcfs_dvnodeops_template, &pcfs_dvnodeops);
        if (error != 0) {
                (void) vfs_freevfsops_by_type(fstype);
                vn_freevnodeops(pcfs_fvnodeops);
                cmn_err(CE_WARN, "pcfsinit: bad dir vnode ops template");
                return (error);
        }

        pcfstype = fstype;
        (void) pc_init();
        pcfs_mountcount = 0;
        return (0);
}

static struct pcfs *pc_mounttab = NULL;

extern struct pcfs_args pc_tz;

/*
 *  Define some special logical drives we use internal to this file.
 */
#define BOOT_PARTITION_DRIVE    99
#define PRIMARY_DOS_DRIVE       1
#define UNPARTITIONED_DRIVE     0

static int
pcfs_device_identify(
        struct vfs *vfsp,
        struct mounta *uap,
        struct cred *cr,
        int *dos_ldrive,
        dev_t *xdev)
{
        struct pathname special;
        char *c;
        struct vnode *svp = NULL;
        struct vnode *lvp = NULL;
        int oflag, aflag;
        int error;

        /*
         * Resolve path name of special file being mounted.
         */
        if (error = pn_get(uap->spec, UIO_USERSPACE, &special)) {
                return (error);
        }

        *dos_ldrive = -1;

        if (error =
            lookupname(special.pn_path, UIO_SYSSPACE, FOLLOW, NULLVPP, &svp)) {
                /*
                 * If there's no device node, the name specified most likely
                 * maps to a PCFS-style "partition specifier" to select a
                 * harddisk primary/logical partition. Disable floppy-specific
                 * checks in such cases unless an explicit :A or :B is
                 * requested.
                 */

                /*
                 * Split the pathname string at the last ':' separator.
                 * If there's no ':' in the device name, or the ':' is the
                 * last character in the string, the name is invalid and
                 * the error from the previous lookup will be returned.
                 */
                c = strrchr(special.pn_path, ':');
                if (c == NULL || strlen(c) == 0)
                        goto devlookup_done;

                *c++ = '\0';

                /*
                 * PCFS partition name suffixes can be:
                 *      - "boot" to indicate the X86BOOT partition
                 *      - a drive letter [c-z] for the "DOS logical drive"
                 *      - a drive number 1..24 for the "DOS logical drive"
                 *      - a "floppy name letter", 'a' or 'b' (just strip this)
                 */
                if (strcasecmp(c, "boot") == 0) {
                        /*
                         * The Solaris boot partition is requested.
                         */
                        *dos_ldrive = BOOT_PARTITION_DRIVE;
                } else if (strspn(c, "0123456789") == strlen(c)) {
                        /*
                         * All digits - parse the partition number.
                         */
                        long drvnum = 0;

                        if ((error = ddi_strtol(c, NULL, 10, &drvnum)) == 0) {
                                /*
                                 * A number alright - in the allowed range ?
                                 */
                                if (drvnum > 24 || drvnum == 0)
                                        error = ENXIO;
                        }
                        if (error)
                                goto devlookup_done;
                        *dos_ldrive = (int)drvnum;
                } else if (strlen(c) == 1) {
                        /*
                         * A single trailing character was specified.
                         *      - [c-zC-Z] means a harddisk partition, and
                         *        we retrieve the partition number.
                         *      - [abAB] means a floppy drive, so we swallow
                         *        the "drive specifier" and test later
                         *        whether the physical device is a floppy.
                         */
                        *c = tolower(*c);
                        if (*c == 'a' || *c == 'b') {
                                *dos_ldrive = UNPARTITIONED_DRIVE;
                        } else if (*c < 'c' || *c > 'z') {
                                error = ENXIO;
                                goto devlookup_done;
                        } else {
                                *dos_ldrive = 1 + *c - 'c';
                        }
                } else {
                        /*
                         * Can't parse this - pass through previous error.
                         */
                        goto devlookup_done;
                }


                error = lookupname(special.pn_path, UIO_SYSSPACE, FOLLOW,
                    NULLVPP, &svp);
        } else {
                *dos_ldrive = UNPARTITIONED_DRIVE;
        }
devlookup_done:
        pn_free(&special);
        if (error)
                return (error);

        ASSERT(*dos_ldrive >= UNPARTITIONED_DRIVE);

        /*
         * Verify caller's permission to open the device special file.
         */
        if ((vfsp->vfs_flag & VFS_RDONLY) != 0 ||
            ((uap->flags & MS_RDONLY) != 0)) {
                oflag = FREAD;
                aflag = VREAD;
        } else {
                oflag = FREAD | FWRITE;
                aflag = VREAD | VWRITE;
        }

        error = vfs_get_lofi(vfsp, &lvp);

        if (error > 0) {
                if (error == ENOENT)
                        error = ENODEV;
                goto out;
        } else if (error == 0) {
                *xdev = lvp->v_rdev;
        } else {
                *xdev = svp->v_rdev;

                if (svp->v_type != VBLK) {
                        error = ENOTBLK;
                        goto out;
                }

                if ((error = secpolicy_spec_open(cr, svp, oflag)) != 0)
                        goto out;
        }

        if (getmajor(*xdev) >= devcnt) {
                error = ENXIO;
                goto out;
        }

        if ((error = VOP_ACCESS(svp, aflag, 0, cr, NULL)) != 0)
                goto out;

out:
        if (svp != NULL)
                VN_RELE(svp);
        if (lvp != NULL)
                VN_RELE(lvp);
        return (error);
}

static int
pcfs_device_ismounted(
        struct vfs *vfsp,
        int dos_ldrive,
        dev_t xdev,
        int *remounting,
        dev_t *pseudodev)
{
        struct pcfs *fsp;
        int remount = *remounting;

        /*
         * Ensure that this logical drive isn't already mounted, unless
         * this is a REMOUNT request.
         * Note: The framework will perform this check if the "...:c"
         * PCFS-style "logical drive" syntax has not been used and an
         * actually existing physical device is backing this filesystem.
         * Once all block device drivers support PC-style partitioning,
         * this codeblock can be dropped.
         */
        *pseudodev = xdev;

        if (dos_ldrive) {
                mutex_enter(&pcfslock);
                for (fsp = pc_mounttab; fsp; fsp = fsp->pcfs_nxt)
                        if (fsp->pcfs_xdev == xdev &&
                            fsp->pcfs_ldrive == dos_ldrive) {
                                mutex_exit(&pcfslock);
                                if (remount) {
                                        return (0);
                                } else {
                                        return (EBUSY);
                                }
                        }
                /*
                 * Assign a unique device number for the vfs
                 * The old way (getudev() + a constantly incrementing
                 * major number) was wrong because it changes vfs_dev
                 * across mounts and reboots, which breaks nfs file handles.
                 * UFS just uses the real dev_t. We can't do that because
                 * of the way pcfs opens fdisk partitons (the :c and :d
                 * partitions are on the same dev_t). Though that _might_
                 * actually be ok, since the file handle contains an
                 * absolute block number, it's probably better to make them
                 * different. So I think we should retain the original
                 * dev_t, but come up with a different minor number based
                 * on the logical drive that will _always_ come up the same.
                 * For now, we steal the upper 6 bits.
                 */
#ifdef notdef
                /* what should we do here? */
                if (((getminor(xdev) >> 12) & 0x3F) != 0)
                        printf("whoops - upper bits used!\n");
#endif
                *pseudodev = makedevice(getmajor(xdev),
                    ((dos_ldrive << 12) | getminor(xdev)) & MAXMIN32);
                if (vfs_devmounting(*pseudodev, vfsp)) {
                        mutex_exit(&pcfslock);
                        return (EBUSY);
                }
                if (vfs_devismounted(*pseudodev)) {
                        mutex_exit(&pcfslock);
                        if (remount) {
                                return (0);
                        } else {
                                return (EBUSY);
                        }
                }
                mutex_exit(&pcfslock);
        } else {
                *pseudodev = xdev;
                if (vfs_devmounting(*pseudodev, vfsp)) {
                        return (EBUSY);
                }
                if (vfs_devismounted(*pseudodev))
                        if (remount) {
                                return (0);
                        } else {
                                return (EBUSY);
                        }
        }

        /*
         * This is not a remount. Even if MS_REMOUNT was requested,
         * the caller needs to proceed as it would on an ordinary
         * mount.
         */
        *remounting = 0;

        ASSERT(*pseudodev);
        return (0);
}

/*
 * Get the PCFS-specific mount options from the VFS framework.
 * For "timezone" and "secsize", we need to parse the number
 * ourselves and ensure its validity.
 * Note: "secsize" is deliberately undocumented at this time,
 * it's a workaround for devices (particularly: lofi image files)
 * that don't support the DKIOCGMEDIAINFO ioctl for autodetection.
 */
static void
pcfs_parse_mntopts(struct pcfs *fsp)
{
        char *c;
        char *endptr;
        long l;
        struct vfs *vfsp = fsp->pcfs_vfs;

        ASSERT(fsp->pcfs_secondswest == 0);
        ASSERT(fsp->pcfs_secsize == 0);

        if (vfs_optionisset(vfsp, MNTOPT_PCFS_HIDDEN, NULL))
                fsp->pcfs_flags |= PCFS_HIDDEN;
        if (vfs_optionisset(vfsp, MNTOPT_PCFS_FOLDCASE, NULL))
                fsp->pcfs_flags |= PCFS_FOLDCASE;
        if (vfs_optionisset(vfsp, MNTOPT_PCFS_NOCLAMPTIME, NULL))
                fsp->pcfs_flags |= PCFS_NOCLAMPTIME;
        if (vfs_optionisset(vfsp, MNTOPT_NOATIME, NULL))
                fsp->pcfs_flags |= PCFS_NOATIME;

        if (vfs_optionisset(vfsp, MNTOPT_PCFS_TIMEZONE, &c)) {
                if (ddi_strtol(c, &endptr, 10, &l) == 0 &&
                    endptr == c + strlen(c)) {
                        /*
                         * A number alright - in the allowed range ?
                         */
                        if (l <= -12*3600 || l >= 12*3600) {
                                cmn_err(CE_WARN, "!pcfs: invalid use of "
                                    "'timezone' mount option - %ld "
                                    "is out of range. Assuming 0.", l);
                                l = 0;
                        }
                } else {
                        cmn_err(CE_WARN, "!pcfs: invalid use of "
                            "'timezone' mount option - argument %s "
                            "is not a valid number. Assuming 0.", c);
                        l = 0;
                }
                fsp->pcfs_secondswest = l;
        }

        /*
         * The "secsize=..." mount option is a workaround for the lack of
         * lofi(4D) support for DKIOCGMEDIAINFO. If PCFS wants to parse the
         * partition table of a disk image and it has been partitioned with
         * sector sizes other than 512 bytes, we'd fail on loopback'ed disk
         * images.
         * That should really be fixed in lofi ... this is a workaround.
         */
        if (vfs_optionisset(vfsp, MNTOPT_PCFS_SECSIZE, &c)) {
                if (ddi_strtol(c, &endptr, 10, &l) == 0 &&
                    endptr == c + strlen(c)) {
                        /*
                         * A number alright - a valid sector size as well ?
                         */
                        if (!VALID_SECSIZE(l)) {
                                cmn_err(CE_WARN, "!pcfs: invalid use of "
                                    "'secsize' mount option - %ld is "
                                    "unsupported. Autodetecting.", l);
                                l = 0;
                        }
                } else {
                        cmn_err(CE_WARN, "!pcfs: invalid use of "
                            "'secsize' mount option - argument %s "
                            "is not a valid number. Autodetecting.", c);
                        l = 0;
                }
                fsp->pcfs_secsize = l;
                fsp->pcfs_sdshift = ddi_ffs(l / DEV_BSIZE) - 1;
        }
}

/*
 * vfs operations
 */

/*
 * pcfs_mount - backend for VFS_MOUNT() on PCFS.
 */
static int
pcfs_mount(
        struct vfs *vfsp,
        struct vnode *mvp,
        struct mounta *uap,
        struct cred *cr)
{
        struct pcfs *fsp;
        struct vnode *devvp;
        dev_t pseudodev;
        dev_t xdev;
        int dos_ldrive = 0;
        int error;
        int remounting;

        if ((error = secpolicy_fs_mount(cr, mvp, vfsp)) != 0)
                return (error);

        if (mvp->v_type != VDIR)
                return (ENOTDIR);

        mutex_enter(&mvp->v_lock);
        if ((uap->flags & MS_REMOUNT) == 0 &&
            (uap->flags & MS_OVERLAY) == 0 &&
            (mvp->v_count != 1 || (mvp->v_flag & VROOT))) {
                mutex_exit(&mvp->v_lock);
                return (EBUSY);
        }
        mutex_exit(&mvp->v_lock);

        /*
         * PCFS doesn't do mount arguments anymore - everything's a mount
         * option these days. In order not to break existing callers, we
         * don't reject it yet, just warn that the data (if any) is ignored.
         */
        if (uap->datalen != 0)
                cmn_err(CE_WARN, "!pcfs: deprecated use of mount(2) with "
                    "mount argument structures instead of mount options. "
                    "Ignoring mount(2) 'dataptr' argument.");

        /*
         * This is needed early, to make sure the access / open calls
         * are done using the correct mode. Processing this mount option
         * only when calling pcfs_parse_mntopts() would lead us to attempt
         * a read/write access to a possibly writeprotected device, and
         * a readonly mount attempt might fail because of that.
         */
        if (uap->flags & MS_RDONLY) {
                vfsp->vfs_flag |= VFS_RDONLY;
                vfs_setmntopt(vfsp, MNTOPT_RO, NULL, 0);
        }

        /*
         * For most filesystems, this is just a lookupname() on the
         * mount pathname string. PCFS historically has to do its own
         * partition table parsing because not all Solaris architectures
         * support all styles of partitioning that PC media can have, and
         * hence PCFS understands "device names" that don't map to actual
         * physical device nodes. Parsing the "PCFS syntax" for device
         * names is done in pcfs_device_identify() - see there.
         *
         * Once all block device drivers that can host FAT filesystems have
         * been enhanced to create device nodes for all PC-style partitions,
         * this code can go away.
         */
        if (error = pcfs_device_identify(vfsp, uap, cr, &dos_ldrive, &xdev))
                return (error);

        /*
         * As with looking up the actual device to mount, PCFS cannot rely
         * on just the checks done by vfs_ismounted() whether a given device
         * is mounted already. The additional check against the "PCFS syntax"
         * is done in  pcfs_device_ismounted().
         */
        remounting = (uap->flags & MS_REMOUNT);

        if (error = pcfs_device_ismounted(vfsp, dos_ldrive, xdev, &remounting,
            &pseudodev))
                return (error);

        if (remounting)
                return (0);

        /*
         * Mount the filesystem.
         * An instance structure is required before the attempt to locate
         * and parse the FAT BPB. This is because mount options may change
         * the behaviour of the filesystem type matching code. Precreate
         * it and fill it in to a degree that allows parsing the mount
         * options.
         */
        devvp = makespecvp(xdev, VBLK);
        if (IS_SWAPVP(devvp)) {
                VN_RELE(devvp);
                return (EBUSY);
        }
        error = VOP_OPEN(&devvp,
            (vfsp->vfs_flag & VFS_RDONLY) ? FREAD : FREAD | FWRITE, cr, NULL);
        if (error) {
                VN_RELE(devvp);
                return (error);
        }

        fsp = kmem_zalloc(sizeof (*fsp), KM_SLEEP);
        fsp->pcfs_vfs = vfsp;
        fsp->pcfs_xdev = xdev;
        fsp->pcfs_devvp = devvp;
        fsp->pcfs_ldrive = dos_ldrive;
        mutex_init(&fsp->pcfs_lock, NULL, MUTEX_DEFAULT, NULL);

        pcfs_parse_mntopts(fsp);

        /*
         * This is the actual "mount" - the PCFS superblock check.
         *
         * Find the requested logical drive and the FAT BPB therein.
         * Check device type and flag the instance if media is removeable.
         *
         * Initializes most members of the filesystem instance structure.
         * Returns EINVAL if no valid BPB can be found. Other errors may
         * occur after I/O failures, or when invalid / unparseable partition
         * tables are encountered.
         */
        if (error = pc_getfattype(fsp))
                goto errout;

        /*
         * Now that the BPB has been parsed, this structural information
         * is available and known to be valid. Initialize the VFS.
         */
        vfsp->vfs_data = fsp;
        vfsp->vfs_dev = pseudodev;
        vfsp->vfs_fstype = pcfstype;
        vfs_make_fsid(&vfsp->vfs_fsid, pseudodev, pcfstype);
        vfsp->vfs_bcount = 0;
        vfsp->vfs_bsize = fsp->pcfs_clsize;

        /*
         * Validate that we can access the FAT and that it is, to the
         * degree we can verify here, self-consistent.
         */
        if (error = pc_verify(fsp))
                goto errout;

        /*
         * Record the time of the mount, to return as an "approximate"
         * timestamp for the FAT root directory. Since FAT roots don't
         * have timestamps, this is less confusing to the user than
         * claiming "zero" / Jan/01/1970.
         */
        gethrestime(&fsp->pcfs_mounttime);

        /*
         * Fix up the mount options. Because "noatime" is made default on
         * removeable media only, a fixed disk will have neither "atime"
         * nor "noatime" set. We set the options explicitly depending on
         * the PCFS_NOATIME flag, to inform the user of what applies.
         * Mount option cancellation will take care that the mutually
         * exclusive 'other' is cleared.
         */
        vfs_setmntopt(vfsp,
            fsp->pcfs_flags & PCFS_NOATIME ? MNTOPT_NOATIME : MNTOPT_ATIME,
            NULL, 0);

        /*
         * All clear - insert the FS instance into PCFS' list.
         */
        mutex_enter(&pcfslock);
        fsp->pcfs_nxt = pc_mounttab;
        pc_mounttab = fsp;
        mutex_exit(&pcfslock);
        atomic_inc_32(&pcfs_mountcount);
        return (0);

errout:
        (void) VOP_CLOSE(devvp,
            vfsp->vfs_flag & VFS_RDONLY ? FREAD : FREAD | FWRITE,
            1, (offset_t)0, cr, NULL);
        VN_RELE(devvp);
        mutex_destroy(&fsp->pcfs_lock);
        kmem_free(fsp, sizeof (*fsp));
        return (error);

}

static int
pcfs_unmount(
        struct vfs *vfsp,
        int flag,
        struct cred *cr)
{
        struct pcfs *fsp, *fsp1;

        if (secpolicy_fs_unmount(cr, vfsp) != 0)
                return (EPERM);

        fsp = VFSTOPCFS(vfsp);

        /*
         * We don't have to lock fsp because the VVFSLOCK in vfs layer will
         * prevent lookuppn from crossing the mount point.
         * If this is not a forced umount request and there's ongoing I/O,
         * don't allow the mount to proceed.
         */
        if (flag & MS_FORCE)
                vfsp->vfs_flag |= VFS_UNMOUNTED;
        else if (fsp->pcfs_nrefs)
                return (EBUSY);

        mutex_enter(&pcfslock);

        /*
         * If this is a forced umount request or if the fs instance has
         * been marked as beyond recovery, allow the umount to proceed
         * regardless of state. pc_diskchanged() forcibly releases all
         * inactive vnodes/pcnodes.
         */
        if (flag & MS_FORCE || fsp->pcfs_flags & PCFS_IRRECOV) {
                rw_enter(&pcnodes_lock, RW_WRITER);
                pc_diskchanged(fsp);
                rw_exit(&pcnodes_lock);
        }

        /* now there should be no pcp node on pcfhead or pcdhead. */

        if (fsp == pc_mounttab) {
                pc_mounttab = fsp->pcfs_nxt;
        } else {
                for (fsp1 = pc_mounttab; fsp1 != NULL; fsp1 = fsp1->pcfs_nxt)
                        if (fsp1->pcfs_nxt == fsp)
                                fsp1->pcfs_nxt = fsp->pcfs_nxt;
        }

        mutex_exit(&pcfslock);

        /*
         * Since we support VFS_FREEVFS(), there's no need to
         * free the fsp right now. The framework will tell us
         * when the right time to do so has arrived by calling
         * into pcfs_freevfs.
         */
        return (0);
}

/*
 * find root of pcfs
 */
static int
pcfs_root(
        struct vfs *vfsp,
        struct vnode **vpp)
{
        struct pcfs *fsp;
        struct pcnode *pcp;
        int error;

        fsp = VFSTOPCFS(vfsp);
        if (error = pc_lockfs(fsp, 0, 0))
                return (error);

        pcp = pc_getnode(fsp, (daddr_t)0, 0, NULL);
        pc_unlockfs(fsp);
        *vpp = PCTOV(pcp);
        pcp->pc_flags |= PC_EXTERNAL;
        return (0);
}

/*
 * Get file system statistics.
 */
static int
pcfs_statvfs(
        struct vfs *vfsp,
        struct statvfs64 *sp)
{
        struct pcfs *fsp;
        int error;
        dev32_t d32;

        fsp = VFSTOPCFS(vfsp);
        error = pc_getfat(fsp);
        if (error)
                return (error);
        bzero(sp, sizeof (*sp));
        sp->f_bsize = sp->f_frsize = fsp->pcfs_clsize;
        sp->f_blocks = (fsblkcnt64_t)fsp->pcfs_ncluster;
        sp->f_bavail = sp->f_bfree = (fsblkcnt64_t)pc_freeclusters(fsp);
        sp->f_files = (fsfilcnt64_t)-1;
        sp->f_ffree = (fsfilcnt64_t)-1;
        sp->f_favail = (fsfilcnt64_t)-1;
#ifdef notdef
        (void) cmpldev(&d32, fsp->pcfs_devvp->v_rdev);
#endif /* notdef */
        (void) cmpldev(&d32, vfsp->vfs_dev);
        sp->f_fsid = d32;
        (void) strcpy(sp->f_basetype, vfssw[vfsp->vfs_fstype].vsw_name);
        sp->f_flag = vf_to_stf(vfsp->vfs_flag);
        sp->f_namemax = PCMAXNAMLEN;
        return (0);
}

static int
pc_syncfsnodes(struct pcfs *fsp)
{
        struct pchead *hp;
        struct pcnode *pcp;
        int error;

        if (error = pc_lockfs(fsp, 0, 0))
                return (error);

        if (!(error = pc_syncfat(fsp))) {
                hp = pcfhead;
                while (hp < & pcfhead [ NPCHASH ]) {
                        rw_enter(&pcnodes_lock, RW_READER);
                        pcp = hp->pch_forw;
                        while (pcp != (struct pcnode *)hp) {
                                if (VFSTOPCFS(PCTOV(pcp) -> v_vfsp) == fsp)
                                        if (error = pc_nodesync(pcp))
                                                break;
                                pcp = pcp -> pc_forw;
                        }
                        rw_exit(&pcnodes_lock);
                        if (error)
                                break;
                        hp++;
                }
        }
        pc_unlockfs(fsp);
        return (error);
}

/*
 * Flush any pending I/O.
 */
static int
pcfs_sync(struct vfs *vfsp, short flag, struct cred *cr)
{
        struct pcfs *fsp;
        int error = 0;

        /* this prevents the filesystem from being umounted. */
        mutex_enter(&pcfslock);
        if (vfsp != NULL) {
                fsp = VFSTOPCFS(vfsp);
                if (!(fsp->pcfs_flags & PCFS_IRRECOV)) {
                        error = pc_syncfsnodes(fsp);
                } else {
                        rw_enter(&pcnodes_lock, RW_WRITER);
                        pc_diskchanged(fsp);
                        rw_exit(&pcnodes_lock);
                        error = EIO;
                }
        } else {
                fsp = pc_mounttab;
                while (fsp != NULL) {
                        if (fsp->pcfs_flags & PCFS_IRRECOV) {
                                rw_enter(&pcnodes_lock, RW_WRITER);
                                pc_diskchanged(fsp);
                                rw_exit(&pcnodes_lock);
                                error = EIO;
                                break;
                        }
                        error = pc_syncfsnodes(fsp);
                        if (error) break;
                        fsp = fsp->pcfs_nxt;
                }
        }
        mutex_exit(&pcfslock);
        return (error);
}

static int
pcfs_syncfs(vfs_t *vfsp, uint64_t flags, cred_t *cr)
{
        int ret;
        struct pcfs *fsp;

        if (flags != 0) {
                return (ENOTSUP);
        }

        fsp = VFSTOPCFS(vfsp);
        if ((fsp->pcfs_flags & PCFS_IRRECOV) == 0) {
                ret = pc_syncfsnodes(fsp);
        } else {
                rw_enter(&pcnodes_lock, RW_WRITER);
                pc_diskchanged(fsp);
                rw_exit(&pcnodes_lock);
                ret = EIO;
        }

        return (ret);
}

int
pc_lockfs(struct pcfs *fsp, int diskchanged, int releasing)
{
        int err;

        if ((fsp->pcfs_flags & PCFS_IRRECOV) && !releasing)
                return (EIO);

        if ((fsp->pcfs_flags & PCFS_LOCKED) && (fsp->pcfs_owner == curthread)) {
                fsp->pcfs_count++;
        } else {
                mutex_enter(&fsp->pcfs_lock);
                if (fsp->pcfs_flags & PCFS_LOCKED)
                        panic("pc_lockfs");
                /*
                 * We check the IRRECOV bit again just in case somebody
                 * snuck past the initial check but then got held up before
                 * they could grab the lock.  (And in the meantime someone
                 * had grabbed the lock and set the bit)
                 */
                if (!diskchanged && !(fsp->pcfs_flags & PCFS_IRRECOV)) {
                        if ((err = pc_getfat(fsp))) {
                                mutex_exit(&fsp->pcfs_lock);
                                return (err);
                        }
                }
                fsp->pcfs_flags |= PCFS_LOCKED;
                fsp->pcfs_owner = curthread;
                fsp->pcfs_count++;
        }
        return (0);
}

void
pc_unlockfs(struct pcfs *fsp)
{

        if ((fsp->pcfs_flags & PCFS_LOCKED) == 0)
                panic("pc_unlockfs");
        if (--fsp->pcfs_count < 0)
                panic("pc_unlockfs: count");
        if (fsp->pcfs_count == 0) {
                fsp->pcfs_flags &= ~PCFS_LOCKED;
                fsp->pcfs_owner = 0;
                mutex_exit(&fsp->pcfs_lock);
        }
}

int
pc_syncfat(struct pcfs *fsp)
{
        struct buf *bp;
        int nfat;
        int     error = 0;
        struct fat_od_fsi *fsinfo_disk;

        if ((fsp->pcfs_fatp == NULL) ||
            !(fsp->pcfs_flags & PCFS_FATMOD))
                return (0);
        /*
         * write out all copies of FATs
         */
        fsp->pcfs_flags &= ~PCFS_FATMOD;
        fsp->pcfs_fattime = gethrestime_sec() + PCFS_DISKTIMEOUT;
        for (nfat = 0; nfat < fsp->pcfs_numfat; nfat++) {
                error = pc_writefat(fsp, pc_dbdaddr(fsp,
                    fsp->pcfs_fatstart + nfat * fsp->pcfs_fatsec));
                if (error) {
                        pc_mark_irrecov(fsp);
                        return (EIO);
                }
        }
        pc_clear_fatchanges(fsp);

        /*
         * Write out fsinfo sector.
         */
        if (IS_FAT32(fsp)) {
                bp = bread(fsp->pcfs_xdev,
                    pc_dbdaddr(fsp, fsp->pcfs_fsistart), fsp->pcfs_secsize);
                if (bp->b_flags & (B_ERROR | B_STALE)) {
                        error = geterror(bp);
                }
                fsinfo_disk = (fat_od_fsi_t *)(bp->b_un.b_addr);
                if (!error && FSISIG_OK(fsinfo_disk)) {
                        fsinfo_disk->fsi_incore.fs_free_clusters =
                            LE_32(fsp->pcfs_fsinfo.fs_free_clusters);
                        fsinfo_disk->fsi_incore.fs_next_free =
                            LE_32(FSINFO_UNKNOWN);
                        bwrite2(bp);
                        error = geterror(bp);
                }
                brelse(bp);
                if (error) {
                        pc_mark_irrecov(fsp);
                        return (EIO);
                }
        }
        return (0);
}

void
pc_invalfat(struct pcfs *fsp)
{
        struct pcfs *xfsp;
        int mount_cnt = 0;

        if (fsp->pcfs_fatp == NULL)
                panic("pc_invalfat");
        /*
         * Release FAT
         */
        kmem_free(fsp->pcfs_fatp, fsp->pcfs_fatsec * fsp->pcfs_secsize);
        fsp->pcfs_fatp = NULL;
        kmem_free(fsp->pcfs_fat_changemap, fsp->pcfs_fat_changemapsize);
        fsp->pcfs_fat_changemap = NULL;
        /*
         * Invalidate all the blocks associated with the device.
         * Not needed if stateless.
         */
        for (xfsp = pc_mounttab; xfsp; xfsp = xfsp->pcfs_nxt)
                if (xfsp != fsp && xfsp->pcfs_xdev == fsp->pcfs_xdev)
                        mount_cnt++;

        if (!mount_cnt)
                binval(fsp->pcfs_xdev);
        /*
         * close mounted device
         */
        (void) VOP_CLOSE(fsp->pcfs_devvp,
            (PCFSTOVFS(fsp)->vfs_flag & VFS_RDONLY) ? FREAD : FREAD|FWRITE,
            1, (offset_t)0, CRED(), NULL);
}

void
pc_badfs(struct pcfs *fsp)
{
        cmn_err(CE_WARN, "corrupted PC file system on dev (%x.%x):%d\n",
            getmajor(fsp->pcfs_devvp->v_rdev),
            getminor(fsp->pcfs_devvp->v_rdev), fsp->pcfs_ldrive);
}

/*
 * The problem with supporting NFS on the PCFS filesystem is that there
 * is no good place to keep the generation number. The only possible
 * place is inside a directory entry. There are a few words that we
 * don't use - they store NT & OS/2 attributes, and the creation/last access
 * time of the file - but it seems wrong to use them. In addition, directory
 * entries come and go. If a directory is removed completely, its directory
 * blocks are freed and the generation numbers are lost. Whereas in ufs,
 * inode blocks are dedicated for inodes, so the generation numbers are
 * permanently kept on the disk.
 */
static int
pcfs_vget(struct vfs *vfsp, struct vnode **vpp, struct fid *fidp)
{
        struct pcnode *pcp;
        struct pc_fid *pcfid;
        struct pcfs *fsp;
        struct pcdir *ep;
        daddr_t eblkno;
        int eoffset;
        struct buf *bp;
        int error;
        pc_cluster32_t  cn;

        pcfid = (struct pc_fid *)fidp;
        fsp = VFSTOPCFS(vfsp);

        error = pc_lockfs(fsp, 0, 0);
        if (error) {
                *vpp = NULL;
                return (error);
        }

        if (pcfid->pcfid_block == 0) {
                pcp = pc_getnode(fsp, (daddr_t)0, 0, NULL);
                pcp->pc_flags |= PC_EXTERNAL;
                *vpp = PCTOV(pcp);
                pc_unlockfs(fsp);
                return (0);
        }
        eblkno = pcfid->pcfid_block;
        eoffset = pcfid->pcfid_offset;

        if ((pc_dbtocl(fsp,
            eblkno - fsp->pcfs_dosstart) >= fsp->pcfs_ncluster) ||
            (eoffset > fsp->pcfs_clsize)) {
                pc_unlockfs(fsp);
                *vpp = NULL;
                return (EINVAL);
        }

        if (eblkno >= fsp->pcfs_datastart || (eblkno - fsp->pcfs_rdirstart)
            < (fsp->pcfs_rdirsec & ~(fsp->pcfs_spcl - 1))) {
                bp = bread(fsp->pcfs_xdev, pc_dbdaddr(fsp, eblkno),
                    fsp->pcfs_clsize);
        } else {
                /*
                 * This is an access "backwards" into the FAT12/FAT16
                 * root directory. A better code structure would
                 * significantly improve maintainability here ...
                 */
                bp = bread(fsp->pcfs_xdev, pc_dbdaddr(fsp, eblkno),
                    (int)(fsp->pcfs_datastart - eblkno) * fsp->pcfs_secsize);
        }
        if (bp->b_flags & (B_ERROR | B_STALE)) {
                error = geterror(bp);
                brelse(bp);
                if (error)
                        pc_mark_irrecov(fsp);
                *vpp = NULL;
                pc_unlockfs(fsp);
                return (error);
        }
        ep = (struct pcdir *)(bp->b_un.b_addr + eoffset);
        /*
         * Ok, if this is a valid file handle that we gave out,
         * then simply ensuring that the creation time matches,
         * the entry has not been deleted, and it has a valid first
         * character should be enough.
         *
         * Unfortunately, verifying that the <blkno, offset> _still_
         * refers to a directory entry is not easy, since we'd have
         * to search _all_ directories starting from root to find it.
         * That's a high price to pay just in case somebody is forging
         * file handles. So instead we verify that as much of the
         * entry is valid as we can:
         *
         * 1. The starting cluster is 0 (unallocated) or valid
         * 2. It is not an LFN entry
         * 3. It is not hidden (unless mounted as such)
         * 4. It is not the label
         */
        cn = pc_getstartcluster(fsp, ep);
        /*
         * if the starting cluster is valid, but not valid according
         * to pc_validcl(), force it to be to simplify the following if.
         */
        if (cn == 0)
                cn = PCF_FIRSTCLUSTER;
        if (IS_FAT32(fsp)) {
                if (cn >= PCF_LASTCLUSTER32)
                        cn = PCF_FIRSTCLUSTER;
        } else {
                if (cn >= PCF_LASTCLUSTER)
                        cn = PCF_FIRSTCLUSTER;
        }
        if ((!pc_validcl(fsp, cn)) ||
            (PCDL_IS_LFN(ep)) ||
            (PCA_IS_HIDDEN(fsp, ep->pcd_attr)) ||
            ((ep->pcd_attr & PCA_LABEL) == PCA_LABEL)) {
                bp->b_flags |= B_STALE | B_AGE;
                brelse(bp);
                pc_unlockfs(fsp);
                return (EINVAL);
        }
        if ((ep->pcd_crtime.pct_time == pcfid->pcfid_ctime) &&
            (ep->pcd_filename[0] != PCD_ERASED) &&
            (pc_validchar(ep->pcd_filename[0]) ||
            (ep->pcd_filename[0] == '.' && ep->pcd_filename[1] == '.'))) {
                pcp = pc_getnode(fsp, eblkno, eoffset, ep);
                pcp->pc_flags |= PC_EXTERNAL;
                *vpp = PCTOV(pcp);
        } else {
                *vpp = NULL;
        }
        bp->b_flags |= B_STALE | B_AGE;
        brelse(bp);
        pc_unlockfs(fsp);
        return (0);
}

/*
 * Unfortunately, FAT32 fat's can be pretty big (On a 1 gig jaz drive, about
 * a meg), so we can't bread() it all in at once. This routine reads a
 * fat a chunk at a time.
 */
static int
pc_readfat(struct pcfs *fsp, uchar_t *fatp)
{
        struct buf *bp;
        size_t off;
        size_t readsize;
        daddr_t diskblk;
        size_t fatsize = fsp->pcfs_fatsec * fsp->pcfs_secsize;
        daddr_t start = fsp->pcfs_fatstart;

        readsize = fsp->pcfs_clsize;
        for (off = 0; off < fatsize; off += readsize, fatp += readsize) {
                if (readsize > (fatsize - off))
                        readsize = fatsize - off;
                diskblk = pc_dbdaddr(fsp, start +
                    pc_cltodb(fsp, pc_lblkno(fsp, off)));
                bp = bread(fsp->pcfs_xdev, diskblk, readsize);
                if (bp->b_flags & (B_ERROR | B_STALE)) {
                        brelse(bp);
                        return (EIO);
                }
                bp->b_flags |= B_STALE | B_AGE;
                bcopy(bp->b_un.b_addr, fatp, readsize);
                brelse(bp);
        }
        return (0);
}

/*
 * We write the FAT out a _lot_, in order to make sure that it
 * is up-to-date. But on a FAT32 system (large drive, small clusters)
 * the FAT might be a couple of megabytes, and writing it all out just
 * because we created or deleted a small file is painful (especially
 * since we do it for each alternate FAT too). So instead, for FAT16 and
 * FAT32 we only write out the bit that has changed. We don't clear
 * the 'updated' fields here because the caller might be writing out
 * several FATs, so the caller must use pc_clear_fatchanges() after
 * all FATs have been updated.
 * This function doesn't take "start" from fsp->pcfs_dosstart because
 * callers can use it to write either the primary or any of the alternate
 * FAT tables.
 */
static int
pc_writefat(struct pcfs *fsp, daddr_t start)
{
        struct buf *bp;
        size_t off;
        size_t writesize;
        int     error;
        uchar_t *fatp = fsp->pcfs_fatp;
        size_t fatsize = fsp->pcfs_fatsec * fsp->pcfs_secsize;

        writesize = fsp->pcfs_clsize;
        for (off = 0; off < fatsize; off += writesize, fatp += writesize) {
                if (writesize > (fatsize - off))
                        writesize = fatsize - off;
                if (!pc_fat_is_changed(fsp, pc_lblkno(fsp, off))) {
                        continue;
                }
                bp = ngeteblk(writesize);
                bp->b_edev = fsp->pcfs_xdev;
                bp->b_dev = cmpdev(bp->b_edev);
                bp->b_blkno = start + pc_dbdaddr(fsp,
                    pc_cltodb(fsp, pc_lblkno(fsp, off)));
                DTRACE_PROBE3(pc_writefat, longlong_t, bp->b_blkno,
                    uchar_t *, fatp,
                    size_t, writesize);
                bcopy(fatp, bp->b_un.b_addr, writesize);
                bwrite2(bp);
                error = geterror(bp);
                brelse(bp);
                if (error) {
                        return (error);
                }
        }
        return (0);
}

/*
 * Mark the FAT cluster that 'cn' is stored in as modified.
 */
void
pc_mark_fat_updated(struct pcfs *fsp, pc_cluster32_t cn)
{
        pc_cluster32_t  bn;
        size_t          size;

        /* which fat block is the cluster number stored in? */
        if (IS_FAT32(fsp)) {
                size = sizeof (pc_cluster32_t);
                bn = pc_lblkno(fsp, cn * size);
                fsp->pcfs_fat_changemap[bn] = 1;
        } else if (IS_FAT16(fsp)) {
                size = sizeof (pc_cluster16_t);
                bn = pc_lblkno(fsp, cn * size);
                fsp->pcfs_fat_changemap[bn] = 1;
        } else {
                offset_t off;
                pc_cluster32_t nbn;

                ASSERT(IS_FAT12(fsp));
                off = cn + (cn >> 1);
                bn = pc_lblkno(fsp, off);
                fsp->pcfs_fat_changemap[bn] = 1;
                /* does this field wrap into the next fat cluster? */
                nbn = pc_lblkno(fsp, off + 1);
                if (nbn != bn) {
                        fsp->pcfs_fat_changemap[nbn] = 1;
                }
        }
}

/*
 * return whether the FAT cluster 'bn' is updated and needs to
 * be written out.
 */
int
pc_fat_is_changed(struct pcfs *fsp, pc_cluster32_t bn)
{
        return (fsp->pcfs_fat_changemap[bn] == 1);
}

/*
 * Implementation of VFS_FREEVFS() to support forced umounts.
 * This is called by the vfs framework after umount, to trigger
 * the release of any resources still associated with the given
 * vfs_t once the need to keep them has gone away.
 */
void
pcfs_freevfs(vfs_t *vfsp)
{
        struct pcfs *fsp = VFSTOPCFS(vfsp);

        mutex_enter(&pcfslock);
        /*
         * Purging the FAT closes the device - can't do any more
         * I/O after this.
         */
        if (fsp->pcfs_fatp != NULL)
                pc_invalfat(fsp);
        mutex_exit(&pcfslock);

        VN_RELE(fsp->pcfs_devvp);
        mutex_destroy(&fsp->pcfs_lock);
        kmem_free(fsp, sizeof (*fsp));

        /*
         * Allow _fini() to succeed now, if so desired.
         */
        atomic_dec_32(&pcfs_mountcount);
}


/*
 * PC-style partition parsing and FAT BPB identification/validation code.
 * The partition parsers here assume:
 *      - a FAT filesystem will be in a partition that has one of a set of
 *        recognized partition IDs
 *      - the user wants the 'numbering' (C:, D:, ...) that one would get
 *        on MSDOS 6.x.
 *        That means any non-FAT partition type (NTFS, HPFS, or any Linux fs)
 *        will not factor in the enumeration.
 * These days, such assumptions should be revisited. FAT is no longer the
 * only game in 'PC town'.
 */
/*
 * isDosDrive()
 *      Boolean function.  Give it the systid field for an fdisk partition
 *      and it decides if that's a systid that describes a DOS drive.  We
 *      use systid values defined in sys/dktp/fdisk.h.
 */
static int
isDosDrive(uchar_t checkMe)
{
        return ((checkMe == DOSOS12) || (checkMe == DOSOS16) ||
            (checkMe == DOSHUGE) || (checkMe == FDISK_WINDOWS) ||
            (checkMe == FDISK_EXT_WIN) || (checkMe == FDISK_FAT95) ||
            (checkMe == DIAGPART));
}


/*
 * isDosExtended()
 *      Boolean function.  Give it the systid field for an fdisk partition
 *      and it decides if that's a systid that describes an extended DOS
 *      partition.
 */
static int
isDosExtended(uchar_t checkMe)
{
        return ((checkMe == EXTDOS) || (checkMe == FDISK_EXTLBA));
}


/*
 * isBootPart()
 *      Boolean function.  Give it the systid field for an fdisk partition
 *      and it decides if that's a systid that describes a Solaris boot
 *      partition.
 */
static int
isBootPart(uchar_t checkMe)
{
        return (checkMe == X86BOOT);
}


/*
 * noLogicalDrive()
 *      Display error message about not being able to find a logical
 *      drive.
 */
static void
noLogicalDrive(int ldrive)
{
        if (ldrive == BOOT_PARTITION_DRIVE) {
                cmn_err(CE_NOTE, "!pcfs: no boot partition");
        } else {
                cmn_err(CE_NOTE, "!pcfs: %d: no such logical drive", ldrive);
        }
}


/*
 * findTheDrive()
 *      Discover offset of the requested logical drive, and return
 *      that offset (startSector), the systid of that drive (sysid),
 *      and a buffer pointer (bp), with the buffer contents being
 *      the first sector of the logical drive (i.e., the sector that
 *      contains the BPB for that drive).
 *
 * Note: this code is not capable of addressing >2TB disks, as it uses
 *       daddr_t not diskaddr_t, some of the calculations would overflow
 */
#define COPY_PTBL(mbr, ptblp)                                   \
        bcopy(&(((struct mboot *)(mbr))->parts), (ptblp),       \
            FD_NUMPART * sizeof (struct ipart))

static int
findTheDrive(struct pcfs *fsp, buf_t **bp)
{
        int ldrive = fsp->pcfs_ldrive;
        dev_t dev = fsp->pcfs_devvp->v_rdev;

        struct ipart dosp[FD_NUMPART];  /* incore fdisk partition structure */
        daddr_t lastseek = 0;           /* Disk block we sought previously */
        daddr_t diskblk = 0;            /* Disk block to get */
        daddr_t xstartsect;             /* base of Extended DOS partition */
        int logicalDriveCount = 0;      /* Count of logical drives seen */
        int extendedPart = -1;          /* index of extended dos partition */
        int primaryPart = -1;           /* index of primary dos partition */
        int bootPart = -1;              /* index of a Solaris boot partition */
        uint32_t xnumsect = 0;          /* length of extended DOS partition */
        int driveIndex;                 /* computed FDISK table index */
        daddr_t startsec;
        len_t mediasize;
        int i;
        /*
         * Count of drives in the current extended partition's
         * FDISK table, and indexes of the drives themselves.
         */
        int extndDrives[FD_NUMPART];
        int numDrives = 0;

        /*
         * Count of drives (beyond primary) in master boot record's
         * FDISK table, and indexes of the drives themselves.
         */
        int extraDrives[FD_NUMPART];
        int numExtraDrives = 0;

        /*
         * "ldrive == 0" should never happen, as this is a request to
         * mount the physical device (and ignore partitioning). The code
         * in pcfs_mount() should have made sure that a logical drive number
         * is at least 1, meaning we're looking for drive "C:". It is not
         * safe (and a bug in the callers of this function) to request logical
         * drive number 0; we could ASSERT() but a graceful EIO is a more
         * polite way.
         */
        if (ldrive == 0) {
                cmn_err(CE_NOTE, "!pcfs: request for logical partition zero");
                noLogicalDrive(ldrive);
                return (EIO);
        }

        /*
         *  Copy from disk block into memory aligned structure for fdisk usage.
         */
        COPY_PTBL((*bp)->b_un.b_addr, dosp);

        /*
         * This check is ok because a FAT BPB and a master boot record (MBB)
         * have the same signature, in the same position within the block.
         */
        if (bpb_get_BPBSig((*bp)->b_un.b_addr) != MBB_MAGIC) {
                cmn_err(CE_NOTE, "!pcfs: MBR partition table signature err, "
                    "device (%x.%x):%d\n",
                    getmajor(dev), getminor(dev), ldrive);
                return (EINVAL);
        }

        /*
         * Get a summary of what is in the Master FDISK table.
         * Normally we expect to find one partition marked as a DOS drive.
         * This partition is the one Windows calls the primary dos partition.
         * If the machine has any logical drives then we also expect
         * to find a partition marked as an extended DOS partition.
         *
         * Sometimes we'll find multiple partitions marked as DOS drives.
         * The Solaris fdisk program allows these partitions
         * to be created, but Windows fdisk no longer does.  We still need
         * to support these, though, since Windows does.  We also need to fix
         * our fdisk to behave like the Windows version.
         *
         * It turns out that some off-the-shelf media have *only* an
         * Extended partition, so we need to deal with that case as well.
         *
         * Only a single (the first) Extended or Boot Partition will
         * be recognized.  Any others will be ignored.
         */
        for (i = 0; i < FD_NUMPART; i++) {
                DTRACE_PROBE4(primarypart, struct pcfs *, fsp,
                    uint_t, (uint_t)dosp[i].systid,
                    uint_t, LE_32(dosp[i].relsect),
                    uint_t, LE_32(dosp[i].numsect));

                if (isDosDrive(dosp[i].systid)) {
                        if (primaryPart < 0) {
                                logicalDriveCount++;
                                primaryPart = i;
                        } else {
                                extraDrives[numExtraDrives++] = i;
                        }
                        continue;
                }
                if ((extendedPart < 0) && isDosExtended(dosp[i].systid)) {
                        extendedPart = i;
                        continue;
                }
                if ((bootPart < 0) && isBootPart(dosp[i].systid)) {
                        bootPart = i;
                        continue;
                }
        }

        if (ldrive == BOOT_PARTITION_DRIVE) {
                if (bootPart < 0) {
                        noLogicalDrive(ldrive);
                        return (EINVAL);
                }
                startsec = LE_32(dosp[bootPart].relsect);
                mediasize = LE_32(dosp[bootPart].numsect);
                goto found;
        }

        if (ldrive == PRIMARY_DOS_DRIVE && primaryPart >= 0) {
                startsec = LE_32(dosp[primaryPart].relsect);
                mediasize = LE_32(dosp[primaryPart].numsect);
                goto found;
        }

        /*
         * We are not looking for the C: drive (or the primary drive
         * was not found), so we had better have an extended partition
         * or extra drives in the Master FDISK table.
         */
        if ((extendedPart < 0) && (numExtraDrives == 0)) {
                cmn_err(CE_NOTE, "!pcfs: no extended dos partition");
                noLogicalDrive(ldrive);
                return (EINVAL);
        }

        if (extendedPart >= 0) {
                diskblk = xstartsect = LE_32(dosp[extendedPart].relsect);
                xnumsect = LE_32(dosp[extendedPart].numsect);
                do {
                        /*
                         *  If the seek would not cause us to change
                         *  position on the drive, then we're out of
                         *  extended partitions to examine.
                         */
                        if (diskblk == lastseek)
                                break;
                        logicalDriveCount += numDrives;
                        /*
                         *  Seek the next extended partition, and find
                         *  logical drives within it.
                         */
                        brelse(*bp);
                        /*
                         * bread() block numbers are multiples of DEV_BSIZE
                         * but the device sector size (the unit of partitioning)
                         * might be larger than that; pcfs_get_device_info()
                         * has calculated the multiplicator for us.
                         */
                        *bp = bread(dev,
                            pc_dbdaddr(fsp, diskblk), fsp->pcfs_secsize);
                        if ((*bp)->b_flags & B_ERROR) {
                                return (EIO);
                        }

                        lastseek = diskblk;
                        COPY_PTBL((*bp)->b_un.b_addr, dosp);
                        if (bpb_get_BPBSig((*bp)->b_un.b_addr) != MBB_MAGIC) {
                                cmn_err(CE_NOTE, "!pcfs: "
                                    "extended partition table signature err, "
                                    "device (%x.%x):%d, LBA %u",
                                    getmajor(dev), getminor(dev), ldrive,
                                    (uint_t)pc_dbdaddr(fsp, diskblk));
                                return (EINVAL);
                        }
                        /*
                         *  Count up drives, and track where the next
                         *  extended partition is in case we need it.  We
                         *  are expecting only one extended partition.  If
                         *  there is more than one we'll only go to the
                         *  first one we see, but warn about ignoring.
                         */
                        numDrives = 0;
                        for (i = 0; i < FD_NUMPART; i++) {
                                DTRACE_PROBE4(extendedpart,
                                    struct pcfs *, fsp,
                                    uint_t, (uint_t)dosp[i].systid,
                                    uint_t, LE_32(dosp[i].relsect),
                                    uint_t, LE_32(dosp[i].numsect));
                                if (isDosDrive(dosp[i].systid)) {
                                        extndDrives[numDrives++] = i;
                                } else if (isDosExtended(dosp[i].systid)) {
                                        if (diskblk != lastseek) {
                                                /*
                                                 * Already found an extended
                                                 * partition in this table.
                                                 */
                                                cmn_err(CE_NOTE,
                                                    "!pcfs: ignoring unexpected"
                                                    " additional extended"
                                                    " partition");
                                        } else {
                                                diskblk = xstartsect +
                                                    LE_32(dosp[i].relsect);
                                        }
                                }
                        }
                } while (ldrive > logicalDriveCount + numDrives);

                ASSERT(numDrives <= FD_NUMPART);

                if (ldrive <= logicalDriveCount + numDrives) {
                        /*
                         * The number of logical drives we've found thus
                         * far is enough to get us to the one we were
                         * searching for.
                         */
                        driveIndex = logicalDriveCount + numDrives - ldrive;
                        mediasize =
                            LE_32(dosp[extndDrives[driveIndex]].numsect);
                        startsec =
                            LE_32(dosp[extndDrives[driveIndex]].relsect) +
                            lastseek;
                        if (startsec > (xstartsect + xnumsect)) {
                                cmn_err(CE_NOTE, "!pcfs: extended partition "
                                    "values bad");
                                return (EINVAL);
                        }
                        goto found;
                } else {
                        /*
                         * We ran out of extended dos partition
                         * drives.  The only hope now is to go
                         * back to extra drives defined in the master
                         * fdisk table.  But we overwrote that table
                         * already, so we must load it in again.
                         */
                        logicalDriveCount += numDrives;
                        brelse(*bp);
                        ASSERT(fsp->pcfs_dosstart == 0);
                        *bp = bread(dev, pc_dbdaddr(fsp, fsp->pcfs_dosstart),
                            fsp->pcfs_secsize);
                        if ((*bp)->b_flags & B_ERROR) {
                                return (EIO);
                        }
                        COPY_PTBL((*bp)->b_un.b_addr, dosp);
                }
        }
        /*
         *  Still haven't found the drive, is it an extra
         *  drive defined in the main FDISK table?
         */
        if (ldrive <= logicalDriveCount + numExtraDrives) {
                driveIndex = logicalDriveCount + numExtraDrives - ldrive;
                ASSERT(driveIndex < MIN(numExtraDrives, FD_NUMPART));
                mediasize = LE_32(dosp[extraDrives[driveIndex]].numsect);
                startsec = LE_32(dosp[extraDrives[driveIndex]].relsect);
                goto found;
        }
        /*
         *  Still haven't found the drive, and there is
         *  nowhere else to look.
         */
        noLogicalDrive(ldrive);
        return (EINVAL);

found:
        /*
         * We need this value in units of sectorsize, because PCFS' internal
         * offset calculations go haywire for > 512Byte sectors unless all
         * pcfs_.*start values are in units of sectors.
         * So, assign before the capacity check (that's done in DEV_BSIZE)
         */
        fsp->pcfs_dosstart = startsec;

        /*
         * convert from device sectors to proper units:
         *      - starting sector: DEV_BSIZE (as argument to bread())
         *      - media size: Bytes
         */
        startsec = pc_dbdaddr(fsp, startsec);
        mediasize *= fsp->pcfs_secsize;

        /*
         * some additional validation / warnings in case the partition table
         * and the actual media capacity are not in accordance ...
         */
        if (fsp->pcfs_mediasize != 0) {
                diskaddr_t startoff =
                    (diskaddr_t)startsec * (diskaddr_t)DEV_BSIZE;

                if (startoff >= fsp->pcfs_mediasize ||
                    startoff + mediasize > fsp->pcfs_mediasize) {
                        cmn_err(CE_WARN,
                            "!pcfs: partition size (LBA start %u, %lld bytes, "
                            "device (%x.%x):%d) smaller than "
                            "mediasize (%lld bytes).\n"
                            "filesystem may be truncated, access errors "
                            "may result.\n",
                            (uint_t)startsec, (long long)mediasize,
                            getmajor(fsp->pcfs_xdev), getminor(fsp->pcfs_xdev),
                            fsp->pcfs_ldrive, (long long)fsp->pcfs_mediasize);
                }
        } else {
                fsp->pcfs_mediasize = mediasize;
        }

        return (0);
}


static fattype_t
secondaryBPBChecks(struct pcfs *fsp, uchar_t *bpb, size_t secsize)
{
        uint32_t ncl = fsp->pcfs_ncluster;

        if (ncl <= 4096) {
                if (bpb_get_FatSz16(bpb) == 0)
                        return (FAT_UNKNOWN);

                if (bpb_get_FatSz16(bpb) * secsize < ncl * 2 &&
                    bpb_get_FatSz16(bpb) * secsize >= (3 * ncl / 2))
                        return (FAT12);
                if (bcmp(bpb_FilSysType16(bpb), "FAT12", 5) == 0)
                        return (FAT12);
                if (bcmp(bpb_FilSysType16(bpb), "FAT16", 5) == 0)
                        return (FAT16);

                switch (bpb_get_Media(bpb)) {
                        case SS8SPT:
                        case DS8SPT:
                        case SS9SPT:
                        case DS9SPT:
                        case DS18SPT:
                        case DS9_15SPT:
                                /*
                                 * Is this reliable - all floppies are FAT12 ?
                                 */
                                return (FAT12);
                        case MD_FIXED:
                                /*
                                 * Is this reliable - disks are always FAT16 ?
                                 */
                                return (FAT16);
                        default:
                                break;
                }
        } else if (ncl <= 65536) {
                if (bpb_get_FatSz16(bpb) == 0 && bpb_get_FatSz32(bpb) > 0)
                        return (FAT32);
                if (VALID_BOOTSIG(bpb_get_BootSig32(bpb)))
                        return (FAT32);
                if (VALID_FSTYPSTR32(bpb_FilSysType32(bpb)))
                        return (FAT32);

                if (VALID_BOOTSIG(bpb_get_BootSig16(bpb)))
                        return (FAT16);
                if (bpb_get_FatSz16(bpb) * secsize < ncl * 4)
                        return (FAT16);
        }

        /*
         * We don't know
         */
        return (FAT_UNKNOWN);
}

/*
 * Check to see if the BPB we found is correct.
 *
 * This looks far more complicated that it needs to be for pure structural
 * validation. The reason for this is that parseBPB() is also used for
 * debugging purposes (mdb dcmd) and we therefore want a bitmap of which
 * BPB fields (do not) have 'known good' values, even if we (do not) reject
 * the BPB when attempting to mount the filesystem.
 *
 * Real-world usage of FAT shows there are a lot of corner-case situations
 * and, following the specification strictly, invalid filesystems out there.
 * Known are situations such as:
 *      - FAT12/FAT16 filesystems with garbage in either totsec16/32
 *        instead of the zero in one of the fields mandated by the spec
 *      - filesystems that claim to be larger than the partition they're in
 *      - filesystems without valid media descriptor
 *      - FAT32 filesystems with RootEntCnt != 0
 *      - FAT32 filesystems with less than 65526 clusters
 *      - FAT32 filesystems without valid FSI sector
 *      - FAT32 filesystems with FAT size in fatsec16 instead of fatsec32
 *
 * Such filesystems are accessible by PCFS - if it'd know to start with that
 * the filesystem should be treated as a specific FAT type. Before S10, it
 * relied on the PC/fdisk partition type for the purpose and almost completely
 * ignored the BPB; now it ignores the partition type for anything else but
 * logical drive enumeration, which can result in rejection of (invalid)
 * FAT32 - if the partition ID says FAT32, but the filesystem, for example
 * has less than 65526 clusters.
 *
 * Without a "force this fs as FAT{12,16,32}" tunable or mount option, it's
 * not possible to allow all such mostly-compliant filesystems in unless one
 * accepts false positives (definitely invalid filesystems that cause problems
 * later). This at least allows to pinpoint why the mount failed.
 *
 * Due to the use of FAT on removeable media, all relaxations of the rules
 * here need to be carefully evaluated wrt. to potential effects on PCFS
 * resilience. A faulty/"mis-crafted" filesystem must not cause a panic, so
 * beware.
 */
static int
parseBPB(struct pcfs *fsp, uchar_t *bpb, int *valid)
{
        fattype_t type;

        uint32_t        ncl;    /* number of clusters in file area */
        uint32_t        rec;
        uint32_t        reserved;
        uint32_t        fsisec, bkbootsec;
        blkcnt_t        totsec, totsec16, totsec32, datasec;
        size_t          fatsec, fatsec16, fatsec32, rdirsec;
        size_t          secsize;
        len_t           mediasize;
        uint64_t        validflags = 0;

        if (VALID_BPBSIG(bpb_get_BPBSig(bpb)))
                validflags |= BPB_BPBSIG_OK;

        rec = bpb_get_RootEntCnt(bpb);
        reserved = bpb_get_RsvdSecCnt(bpb);
        fsisec = bpb_get_FSInfo32(bpb);
        bkbootsec = bpb_get_BkBootSec32(bpb);
        totsec16 = (blkcnt_t)bpb_get_TotSec16(bpb);
        totsec32 = (blkcnt_t)bpb_get_TotSec32(bpb);
        fatsec16 = bpb_get_FatSz16(bpb);
        fatsec32 = bpb_get_FatSz32(bpb);

        totsec = totsec16 ? totsec16 : totsec32;
        fatsec = fatsec16 ? fatsec16 : fatsec32;

        secsize = bpb_get_BytesPerSec(bpb);
        if (!VALID_SECSIZE(secsize))
                secsize = fsp->pcfs_secsize;
        if (secsize != fsp->pcfs_secsize) {
                PC_DPRINTF3(3, "!pcfs: parseBPB, device (%x.%x):%d:\n",
                    getmajor(fsp->pcfs_xdev),
                    getminor(fsp->pcfs_xdev), fsp->pcfs_ldrive);
                PC_DPRINTF2(3, "!BPB secsize %d != "
                    "autodetected media block size %d\n",
                    (int)secsize, (int)fsp->pcfs_secsize);
                if (fsp->pcfs_ldrive) {
                        /*
                         * We've already attempted to parse the partition
                         * table. If the block size used for that don't match
                         * the PCFS sector size, we're hosed one way or the
                         * other. Just try what happens.
                         */
                        secsize = fsp->pcfs_secsize;
                        PC_DPRINTF1(3,
                            "!pcfs: Using autodetected secsize %d\n",
                            (int)secsize);
                } else {
                        /*
                         * This allows mounting lofi images of PCFS partitions
                         * with sectorsize != DEV_BSIZE. We can't parse the
                         * partition table on whole-disk images unless the
                         * (undocumented) "secsize=..." mount option is used,
                         * but at least this allows us to mount if we have
                         * an image of a partition.
                         */
                        PC_DPRINTF1(3,
                            "!pcfs: Using BPB secsize %d\n", (int)secsize);
                }
        }

        if (fsp->pcfs_mediasize == 0) {
                mediasize = (len_t)totsec * (len_t)secsize;
                /*
                 * This is not an error because not all devices support the
                 * dkio(4I) mediasize queries, and/or not all devices are
                 * partitioned. If we have not been able to figure out the
                 * size of the underlaying medium, we have to trust the BPB.
                 */
                PC_DPRINTF4(3, "!pcfs: parseBPB: mediasize autodetect failed "
                    "on device (%x.%x):%d, trusting BPB totsec (%lld Bytes)\n",
                    getmajor(fsp->pcfs_xdev), getminor(fsp->pcfs_xdev),
                    fsp->pcfs_ldrive, (long long)fsp->pcfs_mediasize);
        } else if ((len_t)totsec * (len_t)secsize > fsp->pcfs_mediasize) {
                cmn_err(CE_WARN,
                    "!pcfs: autodetected mediasize (%lld Bytes) smaller than "
                    "FAT BPB mediasize (%lld Bytes).\n"
                    "truncated filesystem on device (%x.%x):%d, access errors "
                    "possible.\n",
                    (long long)fsp->pcfs_mediasize,
                    (long long)(totsec * (blkcnt_t)secsize),
                    getmajor(fsp->pcfs_xdev), getminor(fsp->pcfs_xdev),
                    fsp->pcfs_ldrive);
                mediasize = fsp->pcfs_mediasize;
        } else {
                /*
                 * This is actually ok. A FAT needs not occupy the maximum
                 * space available in its partition, it can be shorter.
                 */
                mediasize = (len_t)totsec * (len_t)secsize;
        }

        /*
         * Since we let just about anything pass through this function,
         * fence against divide-by-zero here.
         */
        if (secsize)
                rdirsec = roundup(rec * 32, secsize) / secsize;
        else
                rdirsec = 0;

        /*
         * This assignment is necessary before pc_dbdaddr() can first be
         * used. Must initialize the value here.
         */
        fsp->pcfs_secsize = secsize;
        fsp->pcfs_sdshift = ddi_ffs(secsize / DEV_BSIZE) - 1;

        fsp->pcfs_mediasize = mediasize;

        fsp->pcfs_spcl = bpb_get_SecPerClus(bpb);
        fsp->pcfs_numfat = bpb_get_NumFATs(bpb);
        fsp->pcfs_mediadesc = bpb_get_Media(bpb);
        fsp->pcfs_clsize = secsize * fsp->pcfs_spcl;
        fsp->pcfs_rdirsec = rdirsec;

        /*
         * Remember: All PCFS offset calculations in sectors. Before I/O
         * is done, convert to DEV_BSIZE units via pc_dbdaddr(). This is
         * necessary so that media with > 512Byte sector sizes work correctly.
         */
        fsp->pcfs_fatstart = fsp->pcfs_dosstart + reserved;
        fsp->pcfs_rdirstart = fsp->pcfs_fatstart + fsp->pcfs_numfat * fatsec;
        fsp->pcfs_datastart = fsp->pcfs_rdirstart + rdirsec;
        datasec = totsec -
            (blkcnt_t)fatsec * fsp->pcfs_numfat -
            (blkcnt_t)rdirsec -
            (blkcnt_t)reserved;

        DTRACE_PROBE4(fatgeometry,
            blkcnt_t, totsec, size_t, fatsec,
            size_t, rdirsec, blkcnt_t, datasec);

        /*
         * 'totsec' is taken directly from the BPB and guaranteed to fit
         * into a 32bit unsigned integer. The calculation of 'datasec',
         * on the other hand, could underflow for incorrect values in
         * rdirsec/reserved/fatsec. Check for that.
         * We also check that the BPB conforms to the FAT specification's
         * requirement that either of the 16/32bit total sector counts
         * must be zero.
         */
        if (totsec != 0 &&
            (totsec16 == totsec32 || totsec16 == 0 || totsec32 == 0) &&
            datasec < totsec && datasec <= UINT32_MAX)
                validflags |= BPB_TOTSEC_OK;

        if ((len_t)totsec * (len_t)secsize <= mediasize)
                validflags |= BPB_MEDIASZ_OK;

        if (VALID_SECSIZE(secsize))
                validflags |= BPB_SECSIZE_OK;
        if (VALID_SPCL(fsp->pcfs_spcl))
                validflags |= BPB_SECPERCLUS_OK;
        if (VALID_CLSIZE(fsp->pcfs_clsize))
                validflags |= BPB_CLSIZE_OK;
        if (VALID_NUMFATS(fsp->pcfs_numfat))
                validflags |= BPB_NUMFAT_OK;
        if (VALID_RSVDSEC(reserved) && reserved < totsec)
                validflags |= BPB_RSVDSECCNT_OK;
        if (VALID_MEDIA(fsp->pcfs_mediadesc))
                validflags |= BPB_MEDIADESC_OK;
        if (VALID_BOOTSIG(bpb_get_BootSig16(bpb)))
                validflags |= BPB_BOOTSIG16_OK;
        if (VALID_BOOTSIG(bpb_get_BootSig32(bpb)))
                validflags |= BPB_BOOTSIG32_OK;
        if (VALID_FSTYPSTR16(bpb_FilSysType16(bpb)))
                validflags |= BPB_FSTYPSTR16_OK;
        if (VALID_FSTYPSTR32(bpb_FilSysType32(bpb)))
                validflags |= BPB_FSTYPSTR32_OK;
        if (VALID_OEMNAME(bpb_OEMName(bpb)))
                validflags |= BPB_OEMNAME_OK;
        if (bkbootsec > 0 && bkbootsec <= reserved && fsisec != bkbootsec)
                validflags |= BPB_BKBOOTSEC_OK;
        if (fsisec > 0 && fsisec <= reserved)
                validflags |= BPB_FSISEC_OK;
        if (VALID_JMPBOOT(bpb_jmpBoot(bpb)))
                validflags |= BPB_JMPBOOT_OK;
        if (VALID_FSVER32(bpb_get_FSVer32(bpb)))
                validflags |= BPB_FSVER_OK;
        if (VALID_VOLLAB(bpb_VolLab16(bpb)))
                validflags |= BPB_VOLLAB16_OK;
        if (VALID_VOLLAB(bpb_VolLab32(bpb)))
                validflags |= BPB_VOLLAB32_OK;
        if (VALID_EXTFLAGS(bpb_get_ExtFlags32(bpb)))
                validflags |= BPB_EXTFLAGS_OK;

        /*
         * Try to determine which FAT format to use.
         *
         * Calculate the number of clusters in order to determine
         * the type of FAT we are looking at.  This is the only
         * recommended way of determining FAT type, though there
         * are other hints in the data, this is the best way.
         *
         * Since we let just about "anything" pass through this function
         * without early exits, fence against divide-by-zero here.
         *
         * datasec was already validated against UINT32_MAX so we know
         * the result will not overflow the 32bit calculation.
         */
        if (fsp->pcfs_spcl)
                ncl = (uint32_t)datasec / fsp->pcfs_spcl;
        else
                ncl = 0;

        fsp->pcfs_ncluster = ncl;

        /*
         * From the Microsoft FAT specification:
         * In the following example, when it says <, it does not mean <=.
         * Note also that the numbers are correct.  The first number for
         * FAT12 is 4085; the second number for FAT16 is 65525. These numbers
         * and the '<' signs are not wrong.
         *
         * We "specialdetect" the corner cases, and use at least one "extra"
         * criterion to decide whether it's FAT16 or FAT32 if the cluster
         * count is dangerously close to the boundaries.
         */

        if (ncl <= PCF_FIRSTCLUSTER) {
                type = FAT_UNKNOWN;
        } else if (ncl < 4085) {
                type = FAT12;
        } else if (ncl <= 4096) {
                type = FAT_QUESTIONABLE;
        } else if (ncl < 65525) {
                type = FAT16;
        } else if (ncl <= 65536) {
                type = FAT_QUESTIONABLE;
        } else if (ncl < PCF_LASTCLUSTER32) {
                type = FAT32;
        } else {
                type = FAT_UNKNOWN;
        }

        DTRACE_PROBE4(parseBPB__initial,
            struct pcfs *, fsp, unsigned char *, bpb,
            int, validflags, fattype_t, type);

recheck:
        fsp->pcfs_fatsec = fatsec;

        /* Do some final sanity checks for each specific type of FAT */
        switch (type) {
                case FAT12:
                        if (rec != 0)
                                validflags |= BPB_ROOTENTCNT_OK;
                        if ((blkcnt_t)bpb_get_TotSec16(bpb) == totsec ||
                            bpb_get_TotSec16(bpb) == 0)
                                validflags |= BPB_TOTSEC16_OK;
                        if ((blkcnt_t)bpb_get_TotSec32(bpb) == totsec ||
                            bpb_get_TotSec32(bpb) == 0)
                                validflags |= BPB_TOTSEC32_OK;
                        if (bpb_get_FatSz16(bpb) == fatsec)
                                validflags |= BPB_FATSZ16_OK;
                        if (fatsec * secsize >= (ncl + PCF_FIRSTCLUSTER)
                            * 3 / 2)
                                validflags |= BPB_FATSZ_OK;
                        if (ncl < 4085)
                                validflags |= BPB_NCLUSTERS_OK;

                        fsp->pcfs_lastclmark = (PCF_LASTCLUSTER & 0xfff);
                        fsp->pcfs_rootblksize =
                            fsp->pcfs_rdirsec * secsize;
                        fsp->pcfs_fsistart = 0;

                        if ((validflags & FAT12_VALIDMSK) != FAT12_VALIDMSK)
                                type = FAT_UNKNOWN;
                        break;
                case FAT16:
                        if (rec != 0)
                                validflags |= BPB_ROOTENTCNT_OK;
                        if ((blkcnt_t)bpb_get_TotSec16(bpb) == totsec ||
                            bpb_get_TotSec16(bpb) == 0)
                                validflags |= BPB_TOTSEC16_OK;
                        if ((blkcnt_t)bpb_get_TotSec32(bpb) == totsec ||
                            bpb_get_TotSec32(bpb) == 0)
                                validflags |= BPB_TOTSEC32_OK;
                        if (bpb_get_FatSz16(bpb) == fatsec)
                                validflags |= BPB_FATSZ16_OK;
                        if (fatsec * secsize >= (ncl + PCF_FIRSTCLUSTER) * 2)
                                validflags |= BPB_FATSZ_OK;
                        if (ncl >= 4085 && ncl < 65525)
                                validflags |= BPB_NCLUSTERS_OK;

                        fsp->pcfs_lastclmark = PCF_LASTCLUSTER;
                        fsp->pcfs_rootblksize =
                            fsp->pcfs_rdirsec * secsize;
                        fsp->pcfs_fsistart = 0;

                        if ((validflags & FAT16_VALIDMSK) != FAT16_VALIDMSK)
                                type = FAT_UNKNOWN;
                        break;
                case FAT32:
                        if (rec == 0)
                                validflags |= BPB_ROOTENTCNT_OK;
                        if (bpb_get_TotSec16(bpb) == 0)
                                validflags |= BPB_TOTSEC16_OK;
                        if ((blkcnt_t)bpb_get_TotSec32(bpb) == totsec)
                                validflags |= BPB_TOTSEC32_OK;
                        if (bpb_get_FatSz16(bpb) == 0)
                                validflags |= BPB_FATSZ16_OK;
                        if (bpb_get_FatSz32(bpb) == fatsec)
                                validflags |= BPB_FATSZ32_OK;
                        if (fatsec * secsize >= (ncl + PCF_FIRSTCLUSTER) * 4)
                                validflags |= BPB_FATSZ_OK;
                        if (ncl >= 65525 && ncl < PCF_LASTCLUSTER32)
                                validflags |= BPB_NCLUSTERS_OK;

                        fsp->pcfs_lastclmark = PCF_LASTCLUSTER32;
                        fsp->pcfs_rootblksize = fsp->pcfs_clsize;
                        fsp->pcfs_fsistart = fsp->pcfs_dosstart + fsisec;
                        if (validflags & BPB_FSISEC_OK)
                                fsp->pcfs_flags |= PCFS_FSINFO_OK;
                        fsp->pcfs_rootclnum = bpb_get_RootClus32(bpb);
                        if (pc_validcl(fsp, fsp->pcfs_rootclnum))
                                validflags |= BPB_ROOTCLUSTER_OK;

                        /*
                         * Current PCFS code only works if 'pcfs_rdirstart'
                         * contains the root cluster number on FAT32.
                         * That's a mis-use and would better be changed.
                         */
                        fsp->pcfs_rdirstart = (daddr_t)fsp->pcfs_rootclnum;

                        if ((validflags & FAT32_VALIDMSK) != FAT32_VALIDMSK)
                                type = FAT_UNKNOWN;
                        break;
                case FAT_QUESTIONABLE:
                        type = secondaryBPBChecks(fsp, bpb, secsize);
                        goto recheck;
                default:
                        ASSERT(type == FAT_UNKNOWN);
                        break;
        }

        ASSERT(type != FAT_QUESTIONABLE);

        fsp->pcfs_fattype = type;

        if (valid)
                *valid = validflags;

        DTRACE_PROBE4(parseBPB__final,
            struct pcfs *, fsp, unsigned char *, bpb,
            int, validflags, fattype_t, type);

        if (type != FAT_UNKNOWN) {
                ASSERT((secsize & (DEV_BSIZE - 1)) == 0);
                ASSERT(ISP2(secsize / DEV_BSIZE));
                return (1);
        }

        return (0);
}


/*
 * Detect the device's native block size (sector size).
 *
 * Test whether the device is:
 *      - a floppy device from a known controller type via DKIOCINFO
 *      - a real floppy using the fd(4D) driver and capable of fdio(4I) ioctls
 *      - a USB floppy drive (identified by drive geometry)
 *
 * Detecting a floppy will make PCFS metadata updates on such media synchronous,
 * to minimize risks due to slow I/O and user hotplugging / device ejection.
 *
 * This might be a bit wasteful on kernel stack space; if anyone's
 * bothered by this, kmem_alloc/kmem_free the ioctl arguments...
 */
static void
pcfs_device_getinfo(struct pcfs *fsp)
{
        dev_t                   rdev = fsp->pcfs_xdev;
        int                     error;
        union {
                struct dk_minfo         mi;
                struct dk_cinfo         ci;
                struct dk_geom          gi;
                struct fd_char          fc;
        } arg;                          /* save stackspace ... */
        intptr_t argp = (intptr_t)&arg;
        ldi_handle_t            lh;
        ldi_ident_t             li;
        int isfloppy, isremoveable, ishotpluggable;
        cred_t                  *cr = CRED();

        if (ldi_ident_from_dev(rdev, &li))
                goto out;

        error = ldi_open_by_dev(&rdev, OTYP_CHR, FREAD, cr, &lh, li);
        ldi_ident_release(li);
        if (error)
                goto out;

        /*
         * Not sure if this could possibly happen. It'd be a bit like
         * VOP_OPEN() changing the passed-in vnode ptr. We're just not
         * expecting it, needs some thought if triggered ...
         */
        ASSERT(fsp->pcfs_xdev == rdev);

        /*
         * Check for removeable/hotpluggable media.
         */
        if (ldi_ioctl(lh, DKIOCREMOVABLE,
            (intptr_t)&isremoveable, FKIOCTL, cr, NULL)) {
                isremoveable = 0;
        }
        if (ldi_ioctl(lh, DKIOCHOTPLUGGABLE,
            (intptr_t)&ishotpluggable, FKIOCTL, cr, NULL)) {
                ishotpluggable = 0;
        }

        /*
         * Make sure we don't use "half-initialized" values if the ioctls fail.
         */
        if (ldi_ioctl(lh, DKIOCGMEDIAINFO, argp, FKIOCTL, cr, NULL)) {
                bzero(&arg, sizeof (arg));
                fsp->pcfs_mediasize = 0;
        } else {
                fsp->pcfs_mediasize =
                    (len_t)arg.mi.dki_lbsize *
                    (len_t)arg.mi.dki_capacity;
        }

        if (VALID_SECSIZE(arg.mi.dki_lbsize)) {
                if (fsp->pcfs_secsize == 0) {
                        fsp->pcfs_secsize = arg.mi.dki_lbsize;
                        fsp->pcfs_sdshift =
                            ddi_ffs(arg.mi.dki_lbsize / DEV_BSIZE) - 1;
                } else {
                        PC_DPRINTF4(1, "!pcfs: autodetected media block size "
                            "%d, device (%x.%x), different from user-provided "
                            "%d. User override - ignoring autodetect result.\n",
                            arg.mi.dki_lbsize,
                            getmajor(fsp->pcfs_xdev), getminor(fsp->pcfs_xdev),
                            fsp->pcfs_secsize);
                }
        } else if (arg.mi.dki_lbsize) {
                PC_DPRINTF3(1, "!pcfs: autodetected media block size "
                    "%d, device (%x.%x), invalid (not 512, 1024, 2048, 4096). "
                    "Ignoring autodetect result.\n",
                    arg.mi.dki_lbsize,
                    getmajor(fsp->pcfs_xdev), getminor(fsp->pcfs_xdev));
        }

        /*
         * We treat the following media types as a floppy by default.
         */
        isfloppy =
            (arg.mi.dki_media_type == DK_FLOPPY ||
            arg.mi.dki_media_type == DK_ZIP ||
            arg.mi.dki_media_type == DK_JAZ);

        /*
         * if this device understands fdio(4I) requests it's
         * obviously a floppy drive.
         */
        if (!isfloppy &&
            !ldi_ioctl(lh, FDIOGCHAR, argp, FKIOCTL, cr, NULL))
                isfloppy = 1;

        /*
         * some devices we like to treat as floppies, but they don't
         * understand fdio(4I) requests.
         */
        if (!isfloppy &&
            !ldi_ioctl(lh, DKIOCINFO, argp, FKIOCTL, cr, NULL) &&
            (arg.ci.dki_ctype == DKC_WDC2880 ||
            arg.ci.dki_ctype == DKC_NCRFLOPPY ||
            arg.ci.dki_ctype == DKC_SMSFLOPPY ||
            arg.ci.dki_ctype == DKC_INTEL82077))
                isfloppy = 1;

        /*
         * This is the "final fallback" test - media with
         * 2 heads and 80 cylinders are assumed to be floppies.
         * This is normally true for USB floppy drives ...
         */
        if (!isfloppy &&
            !ldi_ioctl(lh, DKIOCGGEOM, argp, FKIOCTL, cr, NULL) &&
            (arg.gi.dkg_ncyl == 80 && arg.gi.dkg_nhead == 2))
                isfloppy = 1;

        /*
         * This is similar to the "old" PCFS code that sets this flag
         * just based on the media descriptor being 0xf8 (MD_FIXED).
         * Should be re-worked. We really need some specialcasing for
         * removeable media.
         */
        if (!isfloppy) {
                fsp->pcfs_flags |= PCFS_NOCHK;
        }

        /*
         * We automatically disable access time updates if the medium is
         * removeable and/or hotpluggable, and the admin did not explicitly
         * request access time updates (via the "atime" mount option).
         * The majority of flash-based media should fit this category.
         * Minimizing write access extends the lifetime of your memory stick !
         */
        if (!vfs_optionisset(fsp->pcfs_vfs, MNTOPT_ATIME, NULL) &&
            (isremoveable || ishotpluggable | isfloppy)) {
                fsp->pcfs_flags |= PCFS_NOATIME;
        }

        (void) ldi_close(lh, FREAD, cr);
out:
        if (fsp->pcfs_secsize == 0) {
                PC_DPRINTF3(1, "!pcfs: media block size autodetection "
                    "device (%x.%x) failed, no user-provided fallback. "
                    "Using %d bytes.\n",
                    getmajor(fsp->pcfs_xdev), getminor(fsp->pcfs_xdev),
                    DEV_BSIZE);
                fsp->pcfs_secsize = DEV_BSIZE;
                fsp->pcfs_sdshift = 0;
        }
        ASSERT(fsp->pcfs_secsize % DEV_BSIZE == 0);
        ASSERT(VALID_SECSIZE(fsp->pcfs_secsize));
}

/*
 * Get the FAT type for the DOS medium.
 *
 * -------------------------
 * According to Microsoft:
 *   The FAT type one of FAT12, FAT16, or FAT32 is determined by the
 * count of clusters on the volume and nothing else.
 * -------------------------
 *
 */
static int
pc_getfattype(struct pcfs *fsp)
{
        int error = 0;
        buf_t *bp = NULL;
        struct vnode *devvp = fsp->pcfs_devvp;
        dev_t   dev = devvp->v_rdev;

        /*
         * Detect the native block size of the medium, and attempt to
         * detect whether the medium is removeable.
         * We do treat removable media (floppies, USB and FireWire disks)
         * differently wrt. to the frequency and synchronicity of FAT updates.
         * We need to know the media block size in order to be able to
         * parse the partition table.
         */
        pcfs_device_getinfo(fsp);

        /*
         * Unpartitioned media (floppies and some removeable devices)
         * don't have a partition table, the FAT BPB is at disk block 0.
         * Start out by reading block 0.
         */
        fsp->pcfs_dosstart = 0;
        bp = bread(dev, pc_dbdaddr(fsp, fsp->pcfs_dosstart), fsp->pcfs_secsize);

        if (error = geterror(bp))
                goto out;

        /*
         * If a logical drive number is requested, parse the partition table
         * and attempt to locate it. Otherwise, proceed immediately to the
         * BPB check. findTheDrive(), if successful, returns the disk block
         * number where the requested partition starts in "startsec".
         */
        if (fsp->pcfs_ldrive != 0) {
                PC_DPRINTF3(5, "!pcfs: pc_getfattype: using FDISK table on "
                    "device (%x,%x):%d to find BPB\n",
                    getmajor(dev), getminor(dev), fsp->pcfs_ldrive);

                if (error = findTheDrive(fsp, &bp))
                        goto out;

                ASSERT(fsp->pcfs_dosstart != 0);

                brelse(bp);
                bp = bread(dev, pc_dbdaddr(fsp, fsp->pcfs_dosstart),
                    fsp->pcfs_secsize);
                if (error = geterror(bp))
                        goto out;
        }

        /*
         * Validate the BPB and fill in the instance structure.
         */
        if (!parseBPB(fsp, (uchar_t *)bp->b_un.b_addr, NULL)) {
                PC_DPRINTF4(1, "!pcfs: pc_getfattype: No FAT BPB on "
                    "device (%x.%x):%d, disk LBA %u\n",
                    getmajor(dev), getminor(dev), fsp->pcfs_ldrive,
                    (uint_t)pc_dbdaddr(fsp, fsp->pcfs_dosstart));
                error = EINVAL;
                goto out;
        }

        ASSERT(fsp->pcfs_fattype != FAT_UNKNOWN);

out:
        /*
         * Release the buffer used
         */
        if (bp != NULL)
                brelse(bp);
        return (error);
}


/*
 * Get the file allocation table.
 * If there is an old FAT, invalidate it.
 */
int
pc_getfat(struct pcfs *fsp)
{
        struct buf *bp = NULL;
        uchar_t *fatp = NULL;
        uchar_t *fat_changemap = NULL;
        int error;
        int fat_changemapsize;
        int flags = 0;
        int nfat;
        int altfat_mustmatch = 0;
        int fatsize = fsp->pcfs_fatsec * fsp->pcfs_secsize;

        if (fsp->pcfs_fatp) {
                /*
                 * There is a FAT in core.
                 * If there are open file pcnodes or we have modified it or
                 * it hasn't timed out yet use the in core FAT.
                 * Otherwise invalidate it and get a new one
                 */
#ifdef notdef
                if (fsp->pcfs_frefs ||
                    (fsp->pcfs_flags & PCFS_FATMOD) ||
                    (gethrestime_sec() < fsp->pcfs_fattime)) {
                        return (0);
                } else {
                        mutex_enter(&pcfslock);
                        pc_invalfat(fsp);
                        mutex_exit(&pcfslock);
                }
#endif /* notdef */
                return (0);
        }

        /*
         * Get FAT and check it for validity
         */
        fatp = kmem_alloc(fatsize, KM_SLEEP);
        error = pc_readfat(fsp, fatp);
        if (error) {
                flags = B_ERROR;
                goto out;
        }
        fat_changemapsize = (fatsize / fsp->pcfs_clsize) + 1;
        fat_changemap = kmem_zalloc(fat_changemapsize, KM_SLEEP);
        fsp->pcfs_fatp = fatp;
        fsp->pcfs_fat_changemapsize = fat_changemapsize;
        fsp->pcfs_fat_changemap = fat_changemap;

        /*
         * The only definite signature check is that the
         * media descriptor byte should match the first byte
         * of the FAT block.
         */
        if (fatp[0] != fsp->pcfs_mediadesc) {
                cmn_err(CE_NOTE, "!pcfs: FAT signature mismatch, "
                    "media descriptor %x, FAT[0] lowbyte %x\n",
                    (uint32_t)fsp->pcfs_mediadesc, (uint32_t)fatp[0]);
                cmn_err(CE_NOTE, "!pcfs: Enforcing alternate FAT validation\n");
                altfat_mustmatch = 1;
        }

        /*
         * Get alternate FATs and check for consistency
         * This is an inlined version of pc_readfat().
         * Since we're only comparing FAT and alternate FAT,
         * there's no reason to let pc_readfat() copy data out
         * of the buf. Instead, compare in-situ, one cluster
         * at a time.
         */
        for (nfat = 1; nfat < fsp->pcfs_numfat; nfat++) {
                size_t startsec;
                size_t off;

                startsec = pc_dbdaddr(fsp,
                    fsp->pcfs_fatstart + nfat * fsp->pcfs_fatsec);

                for (off = 0; off < fatsize; off += fsp->pcfs_clsize) {
                        daddr_t fatblk = startsec + pc_dbdaddr(fsp,
                            pc_cltodb(fsp, pc_lblkno(fsp, off)));

                        bp = bread(fsp->pcfs_xdev, fatblk,
                            MIN(fsp->pcfs_clsize, fatsize - off));
                        if (bp->b_flags & (B_ERROR | B_STALE)) {
                                cmn_err(CE_NOTE,
                                    "!pcfs: alternate FAT #%d (start LBA %p)"
                                    " read error at offset %ld on device"
                                    " (%x.%x):%d",
                                    nfat, (void *)(uintptr_t)startsec, off,
                                    getmajor(fsp->pcfs_xdev),
                                    getminor(fsp->pcfs_xdev),
                                    fsp->pcfs_ldrive);
                                flags = B_ERROR;
                                error = EIO;
                                goto out;
                        }
                        bp->b_flags |= B_STALE | B_AGE;
                        if (bcmp(bp->b_un.b_addr, fatp + off,
                            MIN(fsp->pcfs_clsize, fatsize - off))) {
                                cmn_err(CE_NOTE,
                                    "!pcfs: alternate FAT #%d (start LBA %p)"
                                    " corrupted at offset %ld on device"
                                    " (%x.%x):%d",
                                    nfat, (void *)(uintptr_t)startsec, off,
                                    getmajor(fsp->pcfs_xdev),
                                    getminor(fsp->pcfs_xdev),
                                    fsp->pcfs_ldrive);
                                if (altfat_mustmatch) {
                                        flags = B_ERROR;
                                        error = EIO;
                                        goto out;
                                }
                        }
                        brelse(bp);
                        bp = NULL;      /* prevent double release */
                }
        }

        fsp->pcfs_fattime = gethrestime_sec() + PCFS_DISKTIMEOUT;
        fsp->pcfs_fatjustread = 1;

        /*
         * Retrieve FAT32 fsinfo sector.
         * A failure to read this is not fatal to accessing the volume.
         * It simply means operations that count or search free blocks
         * will have to do a full FAT walk, vs. a possibly quicker lookup
         * of the summary information.
         * Hence, we log a message but return success overall after this point.
         */
        if (IS_FAT32(fsp) && (fsp->pcfs_flags & PCFS_FSINFO_OK)) {
                struct fat_od_fsi *fsinfo_disk;

                bp = bread(fsp->pcfs_xdev,
                    pc_dbdaddr(fsp, fsp->pcfs_fsistart), fsp->pcfs_secsize);
                fsinfo_disk = (struct fat_od_fsi *)bp->b_un.b_addr;
                if (bp->b_flags & (B_ERROR | B_STALE) ||
                    !FSISIG_OK(fsinfo_disk)) {
                        cmn_err(CE_NOTE,
                            "!pcfs: error reading fat32 fsinfo from "
                            "device (%x.%x):%d, block %lld",
                            getmajor(fsp->pcfs_xdev), getminor(fsp->pcfs_xdev),
                            fsp->pcfs_ldrive,
                            (long long)pc_dbdaddr(fsp, fsp->pcfs_fsistart));
                        fsp->pcfs_flags &= ~PCFS_FSINFO_OK;
                        fsp->pcfs_fsinfo.fs_free_clusters = FSINFO_UNKNOWN;
                        fsp->pcfs_fsinfo.fs_next_free = FSINFO_UNKNOWN;
                } else {
                        bp->b_flags |= B_STALE | B_AGE;
                        fsinfo_disk = (fat_od_fsi_t *)(bp->b_un.b_addr);
                        fsp->pcfs_fsinfo.fs_free_clusters =
                            LE_32(fsinfo_disk->fsi_incore.fs_free_clusters);
                        fsp->pcfs_fsinfo.fs_next_free =
                            LE_32(fsinfo_disk->fsi_incore.fs_next_free);
                }
                brelse(bp);
                bp = NULL;
        }

        if (pc_validcl(fsp, (pc_cluster32_t)fsp->pcfs_fsinfo.fs_next_free))
                fsp->pcfs_nxfrecls = fsp->pcfs_fsinfo.fs_next_free;
        else
                fsp->pcfs_nxfrecls = PCF_FIRSTCLUSTER;

        return (0);

out:
        cmn_err(CE_NOTE, "!pcfs: illegal disk format");
        if (bp)
                brelse(bp);
        if (fatp)
                kmem_free(fatp, fatsize);
        if (fat_changemap)
                kmem_free(fat_changemap, fat_changemapsize);

        if (flags) {
                pc_mark_irrecov(fsp);
        }
        return (error);
}