FreeBSD/Linux Kernel Cross Reference
sys/kern/vfs_mount.c

     /*-
      * SPDX-License-Identifier: BSD-3-Clause
      *
      * Copyright (c) 1999-2004 Poul-Henning Kamp
      * Copyright (c) 1999 Michael Smith
      * Copyright (c) 1989, 1993
      *      The Regents of the University of California.  All rights reserved.
      * (c) UNIX System Laboratories, Inc.
      * All or some portions of this file are derived from material licensed
     * to the University of California by American Telephone and Telegraph
     * Co. or Unix System Laboratories, Inc. and are reproduced herein with
     * the permission of UNIX System Laboratories, Inc.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include <sys/param.h>
    #include <sys/conf.h>
    #include <sys/eventhandler.h>
    #include <sys/fcntl.h>
    #include <sys/jail.h>
    #include <sys/kernel.h>
    #include <sys/libkern.h>
    #include <sys/malloc.h>
    #include <sys/mount.h>
    #include <sys/mutex.h>
    #include <sys/namei.h>
    #include <sys/priv.h>
    #include <sys/proc.h>
    #include <sys/filedesc.h>
    #include <sys/reboot.h>
    #include <sys/sbuf.h>
    #include <sys/syscallsubr.h>
    #include <sys/sysproto.h>
    #include <sys/sx.h>
    #include <sys/sysctl.h>
    #include <sys/sysent.h>
    #include <sys/systm.h>
    #include <sys/vnode.h>
    #include <vm/uma.h>
    
    #include <geom/geom.h>
    
    #include <machine/stdarg.h>
    
    #include <security/audit/audit.h>
    #include <security/mac/mac_framework.h>
    
    #define VFS_MOUNTARG_SIZE_MAX   (1024 * 64)
    
    static int      vfs_domount(struct thread *td, const char *fstype, char *fspath,
                        uint64_t fsflags, struct vfsoptlist **optlist);
    static void     free_mntarg(struct mntarg *ma);
    
    static int      usermount = 0;
    SYSCTL_INT(_vfs, OID_AUTO, usermount, CTLFLAG_RW, &usermount, 0,
        "Unprivileged users may mount and unmount file systems");
    
    static bool     default_autoro = false;
    SYSCTL_BOOL(_vfs, OID_AUTO, default_autoro, CTLFLAG_RW, &default_autoro, 0,
        "Retry failed r/w mount as r/o if no explicit ro/rw option is specified");
    
    MALLOC_DEFINE(M_MOUNT, "mount", "vfs mount structure");
    MALLOC_DEFINE(M_STATFS, "statfs", "statfs structure");
    static uma_zone_t mount_zone;
    
    /* List of mounted filesystems. */
    struct mntlist mountlist = TAILQ_HEAD_INITIALIZER(mountlist);
    
    /* For any iteration/modification of mountlist */
    struct mtx mountlist_mtx;
    MTX_SYSINIT(mountlist, &mountlist_mtx, "mountlist", MTX_DEF);
    
    EVENTHANDLER_LIST_DEFINE(vfs_mounted);
   EVENTHANDLER_LIST_DEFINE(vfs_unmounted);
   
   /*
    * Global opts, taken by all filesystems
    */
   static const char *global_opts[] = {
           "errmsg",
           "fstype",
           "fspath",
           "ro",
           "rw",
           "nosuid",
           "noexec",
           NULL
   };
   
   static int
   mount_init(void *mem, int size, int flags)
   {
           struct mount *mp;
   
           mp = (struct mount *)mem;
           mtx_init(&mp->mnt_mtx, "struct mount mtx", NULL, MTX_DEF);
           mtx_init(&mp->mnt_listmtx, "struct mount vlist mtx", NULL, MTX_DEF);
           lockinit(&mp->mnt_explock, PVFS, "explock", 0, 0);
           return (0);
   }
   
   static void
   mount_fini(void *mem, int size)
   {
           struct mount *mp;
   
           mp = (struct mount *)mem;
           lockdestroy(&mp->mnt_explock);
           mtx_destroy(&mp->mnt_listmtx);
           mtx_destroy(&mp->mnt_mtx);
   }
   
   static void
   vfs_mount_init(void *dummy __unused)
   {
   
           mount_zone = uma_zcreate("Mountpoints", sizeof(struct mount), NULL,
               NULL, mount_init, mount_fini, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
   }
   SYSINIT(vfs_mount, SI_SUB_VFS, SI_ORDER_ANY, vfs_mount_init, NULL);
   
   /*
    * ---------------------------------------------------------------------
    * Functions for building and sanitizing the mount options
    */
   
   /* Remove one mount option. */
   static void
   vfs_freeopt(struct vfsoptlist *opts, struct vfsopt *opt)
   {
   
           TAILQ_REMOVE(opts, opt, link);
           free(opt->name, M_MOUNT);
           if (opt->value != NULL)
                   free(opt->value, M_MOUNT);
           free(opt, M_MOUNT);
   }
   
   /* Release all resources related to the mount options. */
   void
   vfs_freeopts(struct vfsoptlist *opts)
   {
           struct vfsopt *opt;
   
           while (!TAILQ_EMPTY(opts)) {
                   opt = TAILQ_FIRST(opts);
                   vfs_freeopt(opts, opt);
           }
           free(opts, M_MOUNT);
   }
   
   void
   vfs_deleteopt(struct vfsoptlist *opts, const char *name)
   {
           struct vfsopt *opt, *temp;
   
           if (opts == NULL)
                   return;
           TAILQ_FOREACH_SAFE(opt, opts, link, temp)  {
                   if (strcmp(opt->name, name) == 0)
                           vfs_freeopt(opts, opt);
           }
   }
   
   static int
   vfs_isopt_ro(const char *opt)
   {
   
           if (strcmp(opt, "ro") == 0 || strcmp(opt, "rdonly") == 0 ||
               strcmp(opt, "norw") == 0)
                   return (1);
           return (0);
   }
   
   static int
   vfs_isopt_rw(const char *opt)
   {
   
           if (strcmp(opt, "rw") == 0 || strcmp(opt, "noro") == 0)
                   return (1);
           return (0);
   }
   
   /*
    * Check if options are equal (with or without the "no" prefix).
    */
   static int
   vfs_equalopts(const char *opt1, const char *opt2)
   {
           char *p;
   
           /* "opt" vs. "opt" or "noopt" vs. "noopt" */
           if (strcmp(opt1, opt2) == 0)
                   return (1);
           /* "noopt" vs. "opt" */
           if (strncmp(opt1, "no", 2) == 0 && strcmp(opt1 + 2, opt2) == 0)
                   return (1);
           /* "opt" vs. "noopt" */
           if (strncmp(opt2, "no", 2) == 0 && strcmp(opt1, opt2 + 2) == 0)
                   return (1);
           while ((p = strchr(opt1, '.')) != NULL &&
               !strncmp(opt1, opt2, ++p - opt1)) {
                   opt2 += p - opt1;
                   opt1 = p;
                   /* "foo.noopt" vs. "foo.opt" */
                   if (strncmp(opt1, "no", 2) == 0 && strcmp(opt1 + 2, opt2) == 0)
                           return (1);
                   /* "foo.opt" vs. "foo.noopt" */
                   if (strncmp(opt2, "no", 2) == 0 && strcmp(opt1, opt2 + 2) == 0)
                           return (1);
           }
           /* "ro" / "rdonly" / "norw" / "rw" / "noro" */
           if ((vfs_isopt_ro(opt1) || vfs_isopt_rw(opt1)) &&
               (vfs_isopt_ro(opt2) || vfs_isopt_rw(opt2)))
                   return (1);
           return (0);
   }
   
   /*
    * If a mount option is specified several times,
    * (with or without the "no" prefix) only keep
    * the last occurrence of it.
    */
   static void
   vfs_sanitizeopts(struct vfsoptlist *opts)
   {
           struct vfsopt *opt, *opt2, *tmp;
   
           TAILQ_FOREACH_REVERSE(opt, opts, vfsoptlist, link) {
                   opt2 = TAILQ_PREV(opt, vfsoptlist, link);
                   while (opt2 != NULL) {
                           if (vfs_equalopts(opt->name, opt2->name)) {
                                   tmp = TAILQ_PREV(opt2, vfsoptlist, link);
                                   vfs_freeopt(opts, opt2);
                                   opt2 = tmp;
                           } else {
                                   opt2 = TAILQ_PREV(opt2, vfsoptlist, link);
                           }
                   }
           }
   }
   
   /*
    * Build a linked list of mount options from a struct uio.
    */
   int
   vfs_buildopts(struct uio *auio, struct vfsoptlist **options)
   {
           struct vfsoptlist *opts;
           struct vfsopt *opt;
           size_t memused, namelen, optlen;
           unsigned int i, iovcnt;
           int error;
   
           opts = malloc(sizeof(struct vfsoptlist), M_MOUNT, M_WAITOK);
           TAILQ_INIT(opts);
           memused = 0;
           iovcnt = auio->uio_iovcnt;
           for (i = 0; i < iovcnt; i += 2) {
                   namelen = auio->uio_iov[i].iov_len;
                   optlen = auio->uio_iov[i + 1].iov_len;
                   memused += sizeof(struct vfsopt) + optlen + namelen;
                   /*
                    * Avoid consuming too much memory, and attempts to overflow
                    * memused.
                    */
                   if (memused > VFS_MOUNTARG_SIZE_MAX ||
                       optlen > VFS_MOUNTARG_SIZE_MAX ||
                       namelen > VFS_MOUNTARG_SIZE_MAX) {
                           error = EINVAL;
                           goto bad;
                   }
   
                   opt = malloc(sizeof(struct vfsopt), M_MOUNT, M_WAITOK);
                   opt->name = malloc(namelen, M_MOUNT, M_WAITOK);
                   opt->value = NULL;
                   opt->len = 0;
                   opt->pos = i / 2;
                   opt->seen = 0;
   
                   /*
                    * Do this early, so jumps to "bad" will free the current
                    * option.
                    */
                   TAILQ_INSERT_TAIL(opts, opt, link);
   
                   if (auio->uio_segflg == UIO_SYSSPACE) {
                           bcopy(auio->uio_iov[i].iov_base, opt->name, namelen);
                   } else {
                           error = copyin(auio->uio_iov[i].iov_base, opt->name,
                               namelen);
                           if (error)
                                   goto bad;
                   }
                   /* Ensure names are null-terminated strings. */
                   if (namelen == 0 || opt->name[namelen - 1] != '\0') {
                           error = EINVAL;
                           goto bad;
                   }
                   if (optlen != 0) {
                           opt->len = optlen;
                           opt->value = malloc(optlen, M_MOUNT, M_WAITOK);
                           if (auio->uio_segflg == UIO_SYSSPACE) {
                                   bcopy(auio->uio_iov[i + 1].iov_base, opt->value,
                                       optlen);
                           } else {
                                   error = copyin(auio->uio_iov[i + 1].iov_base,
                                       opt->value, optlen);
                                   if (error)
                                           goto bad;
                           }
                   }
           }
           vfs_sanitizeopts(opts);
           *options = opts;
           return (0);
   bad:
           vfs_freeopts(opts);
           return (error);
   }
   
   /*
    * Merge the old mount options with the new ones passed
    * in the MNT_UPDATE case.
    *
    * XXX: This function will keep a "nofoo" option in the new
    * options.  E.g, if the option's canonical name is "foo",
    * "nofoo" ends up in the mount point's active options.
    */
   static void
   vfs_mergeopts(struct vfsoptlist *toopts, struct vfsoptlist *oldopts)
   {
           struct vfsopt *opt, *new;
   
           TAILQ_FOREACH(opt, oldopts, link) {
                   new = malloc(sizeof(struct vfsopt), M_MOUNT, M_WAITOK);
                   new->name = strdup(opt->name, M_MOUNT);
                   if (opt->len != 0) {
                           new->value = malloc(opt->len, M_MOUNT, M_WAITOK);
                           bcopy(opt->value, new->value, opt->len);
                   } else
                           new->value = NULL;
                   new->len = opt->len;
                   new->seen = opt->seen;
                   TAILQ_INSERT_HEAD(toopts, new, link);
           }
           vfs_sanitizeopts(toopts);
   }
   
   /*
    * Mount a filesystem.
    */
   #ifndef _SYS_SYSPROTO_H_
   struct nmount_args {
           struct iovec *iovp;
           unsigned int iovcnt;
           int flags;
   };
   #endif
   int
   sys_nmount(struct thread *td, struct nmount_args *uap)
   {
           struct uio *auio;
           int error;
           u_int iovcnt;
           uint64_t flags;
   
           /*
            * Mount flags are now 64-bits. On 32-bit archtectures only
            * 32-bits are passed in, but from here on everything handles
            * 64-bit flags correctly.
            */
           flags = uap->flags;
   
           AUDIT_ARG_FFLAGS(flags);
           CTR4(KTR_VFS, "%s: iovp %p with iovcnt %d and flags %d", __func__,
               uap->iovp, uap->iovcnt, flags);
   
           /*
            * Filter out MNT_ROOTFS.  We do not want clients of nmount() in
            * userspace to set this flag, but we must filter it out if we want
            * MNT_UPDATE on the root file system to work.
            * MNT_ROOTFS should only be set by the kernel when mounting its
            * root file system.
            */
           flags &= ~MNT_ROOTFS;
   
           iovcnt = uap->iovcnt;
           /*
            * Check that we have an even number of iovec's
            * and that we have at least two options.
            */
           if ((iovcnt & 1) || (iovcnt < 4)) {
                   CTR2(KTR_VFS, "%s: failed for invalid iovcnt %d", __func__,
                       uap->iovcnt);
                   return (EINVAL);
           }
   
           error = copyinuio(uap->iovp, iovcnt, &auio);
           if (error) {
                   CTR2(KTR_VFS, "%s: failed for invalid uio op with %d errno",
                       __func__, error);
                   return (error);
           }
           error = vfs_donmount(td, flags, auio);
   
           free(auio, M_IOV);
           return (error);
   }
   
   /*
    * ---------------------------------------------------------------------
    * Various utility functions
    */
   
   void
   vfs_ref(struct mount *mp)
   {
   
           CTR2(KTR_VFS, "%s: mp %p", __func__, mp);
           MNT_ILOCK(mp);
           MNT_REF(mp);
           MNT_IUNLOCK(mp);
   }
   
   void
   vfs_rel(struct mount *mp)
   {
   
           CTR2(KTR_VFS, "%s: mp %p", __func__, mp);
           MNT_ILOCK(mp);
           MNT_REL(mp);
           MNT_IUNLOCK(mp);
   }
   
   /*
    * Allocate and initialize the mount point struct.
    */
   struct mount *
   vfs_mount_alloc(struct vnode *vp, struct vfsconf *vfsp, const char *fspath,
       struct ucred *cred)
   {
           struct mount *mp;
   
           mp = uma_zalloc(mount_zone, M_WAITOK);
           bzero(&mp->mnt_startzero,
               __rangeof(struct mount, mnt_startzero, mnt_endzero));
           TAILQ_INIT(&mp->mnt_nvnodelist);
           mp->mnt_nvnodelistsize = 0;
           TAILQ_INIT(&mp->mnt_activevnodelist);
           mp->mnt_activevnodelistsize = 0;
           TAILQ_INIT(&mp->mnt_tmpfreevnodelist);
           mp->mnt_tmpfreevnodelistsize = 0;
           mp->mnt_ref = 0;
           (void) vfs_busy(mp, MBF_NOWAIT);
           atomic_add_acq_int(&vfsp->vfc_refcount, 1);
           mp->mnt_op = vfsp->vfc_vfsops;
           mp->mnt_vfc = vfsp;
           mp->mnt_stat.f_type = vfsp->vfc_typenum;
           mp->mnt_gen++;
           strlcpy(mp->mnt_stat.f_fstypename, vfsp->vfc_name, MFSNAMELEN);
           mp->mnt_vnodecovered = vp;
           mp->mnt_cred = crdup(cred);
           mp->mnt_stat.f_owner = cred->cr_uid;
           strlcpy(mp->mnt_stat.f_mntonname, fspath, MNAMELEN);
           mp->mnt_iosize_max = DFLTPHYS;
   #ifdef MAC
           mac_mount_init(mp);
           mac_mount_create(cred, mp);
   #endif
           arc4rand(&mp->mnt_hashseed, sizeof mp->mnt_hashseed, 0);
           TAILQ_INIT(&mp->mnt_uppers);
           return (mp);
   }
   
   /*
    * Destroy the mount struct previously allocated by vfs_mount_alloc().
    */
   void
   vfs_mount_destroy(struct mount *mp)
   {
   
           MNT_ILOCK(mp);
           mp->mnt_kern_flag |= MNTK_REFEXPIRE;
           if (mp->mnt_kern_flag & MNTK_MWAIT) {
                   mp->mnt_kern_flag &= ~MNTK_MWAIT;
                   wakeup(mp);
           }
           while (mp->mnt_ref)
                   msleep(mp, MNT_MTX(mp), PVFS, "mntref", 0);
           KASSERT(mp->mnt_ref == 0,
               ("%s: invalid refcount in the drain path @ %s:%d", __func__,
               __FILE__, __LINE__));
           if (mp->mnt_writeopcount != 0)
                   panic("vfs_mount_destroy: nonzero writeopcount");
           if (mp->mnt_secondary_writes != 0)
                   panic("vfs_mount_destroy: nonzero secondary_writes");
           atomic_subtract_rel_int(&mp->mnt_vfc->vfc_refcount, 1);
           if (!TAILQ_EMPTY(&mp->mnt_nvnodelist)) {
                   struct vnode *vp;
   
                   TAILQ_FOREACH(vp, &mp->mnt_nvnodelist, v_nmntvnodes)
                           vn_printf(vp, "dangling vnode ");
                   panic("unmount: dangling vnode");
           }
           KASSERT(TAILQ_EMPTY(&mp->mnt_uppers), ("mnt_uppers"));
           if (mp->mnt_nvnodelistsize != 0)
                   panic("vfs_mount_destroy: nonzero nvnodelistsize");
           if (mp->mnt_activevnodelistsize != 0)
                   panic("vfs_mount_destroy: nonzero activevnodelistsize");
           if (mp->mnt_tmpfreevnodelistsize != 0)
                   panic("vfs_mount_destroy: nonzero tmpfreevnodelistsize");
           if (mp->mnt_lockref != 0)
                   panic("vfs_mount_destroy: nonzero lock refcount");
           MNT_IUNLOCK(mp);
           if (mp->mnt_vnodecovered != NULL)
                   vrele(mp->mnt_vnodecovered);
   #ifdef MAC
           mac_mount_destroy(mp);
   #endif
           if (mp->mnt_opt != NULL)
                   vfs_freeopts(mp->mnt_opt);
           crfree(mp->mnt_cred);
           uma_zfree(mount_zone, mp);
   }
   
   static bool
   vfs_should_downgrade_to_ro_mount(uint64_t fsflags, int error)
   {
           /* This is an upgrade of an exisiting mount. */
           if ((fsflags & MNT_UPDATE) != 0)
                   return (false);
           /* This is already an R/O mount. */
           if ((fsflags & MNT_RDONLY) != 0)
                   return (false);
   
           switch (error) {
           case ENODEV:    /* generic, geom, ... */
           case EACCES:    /* cam/scsi, ... */
           case EROFS:     /* md, mmcsd, ... */
                   /*
                    * These errors can be returned by the storage layer to signal
                    * that the media is read-only.  No harm in the R/O mount
                    * attempt if the error was returned for some other reason.
                    */
                   return (true);
           default:
                   return (false);
           }
   }
   
   int
   vfs_donmount(struct thread *td, uint64_t fsflags, struct uio *fsoptions)
   {
           struct vfsoptlist *optlist;
           struct vfsopt *opt, *tmp_opt;
           char *fstype, *fspath, *errmsg;
           int error, fstypelen, fspathlen, errmsg_len, errmsg_pos;
           bool autoro;
   
           errmsg = fspath = NULL;
           errmsg_len = fspathlen = 0;
           errmsg_pos = -1;
           autoro = default_autoro;
   
           error = vfs_buildopts(fsoptions, &optlist);
           if (error)
                   return (error);
   
           if (vfs_getopt(optlist, "errmsg", (void **)&errmsg, &errmsg_len) == 0)
                   errmsg_pos = vfs_getopt_pos(optlist, "errmsg");
   
           /*
            * We need these two options before the others,
            * and they are mandatory for any filesystem.
            * Ensure they are NUL terminated as well.
            */
           fstypelen = 0;
           error = vfs_getopt(optlist, "fstype", (void **)&fstype, &fstypelen);
           if (error || fstypelen <= 0 || fstype[fstypelen - 1] != '\0') {
                   error = EINVAL;
                   if (errmsg != NULL)
                           strncpy(errmsg, "Invalid fstype", errmsg_len);
                   goto bail;
           }
           fspathlen = 0;
           error = vfs_getopt(optlist, "fspath", (void **)&fspath, &fspathlen);
           if (error || fspathlen <= 0 || fspath[fspathlen - 1] != '\0') {
                   error = EINVAL;
                   if (errmsg != NULL)
                           strncpy(errmsg, "Invalid fspath", errmsg_len);
                   goto bail;
           }
   
           /*
            * We need to see if we have the "update" option
            * before we call vfs_domount(), since vfs_domount() has special
            * logic based on MNT_UPDATE.  This is very important
            * when we want to update the root filesystem.
            */
           TAILQ_FOREACH_SAFE(opt, optlist, link, tmp_opt) {
                   if (strcmp(opt->name, "update") == 0) {
                           fsflags |= MNT_UPDATE;
                           vfs_freeopt(optlist, opt);
                   }
                   else if (strcmp(opt->name, "async") == 0)
                           fsflags |= MNT_ASYNC;
                   else if (strcmp(opt->name, "force") == 0) {
                           fsflags |= MNT_FORCE;
                           vfs_freeopt(optlist, opt);
                   }
                   else if (strcmp(opt->name, "reload") == 0) {
                           fsflags |= MNT_RELOAD;
                           vfs_freeopt(optlist, opt);
                   }
                   else if (strcmp(opt->name, "multilabel") == 0)
                           fsflags |= MNT_MULTILABEL;
                   else if (strcmp(opt->name, "noasync") == 0)
                           fsflags &= ~MNT_ASYNC;
                   else if (strcmp(opt->name, "noatime") == 0)
                           fsflags |= MNT_NOATIME;
                   else if (strcmp(opt->name, "atime") == 0) {
                           free(opt->name, M_MOUNT);
                           opt->name = strdup("nonoatime", M_MOUNT);
                   }
                   else if (strcmp(opt->name, "noclusterr") == 0)
                           fsflags |= MNT_NOCLUSTERR;
                   else if (strcmp(opt->name, "clusterr") == 0) {
                           free(opt->name, M_MOUNT);
                           opt->name = strdup("nonoclusterr", M_MOUNT);
                   }
                   else if (strcmp(opt->name, "noclusterw") == 0)
                           fsflags |= MNT_NOCLUSTERW;
                   else if (strcmp(opt->name, "clusterw") == 0) {
                           free(opt->name, M_MOUNT);
                           opt->name = strdup("nonoclusterw", M_MOUNT);
                   }
                   else if (strcmp(opt->name, "noexec") == 0)
                           fsflags |= MNT_NOEXEC;
                   else if (strcmp(opt->name, "exec") == 0) {
                           free(opt->name, M_MOUNT);
                           opt->name = strdup("nonoexec", M_MOUNT);
                   }
                   else if (strcmp(opt->name, "nosuid") == 0)
                           fsflags |= MNT_NOSUID;
                   else if (strcmp(opt->name, "suid") == 0) {
                           free(opt->name, M_MOUNT);
                           opt->name = strdup("nonosuid", M_MOUNT);
                   }
                   else if (strcmp(opt->name, "nosymfollow") == 0)
                           fsflags |= MNT_NOSYMFOLLOW;
                   else if (strcmp(opt->name, "symfollow") == 0) {
                           free(opt->name, M_MOUNT);
                           opt->name = strdup("nonosymfollow", M_MOUNT);
                   }
                   else if (strcmp(opt->name, "noro") == 0) {
                           fsflags &= ~MNT_RDONLY;
                           autoro = false;
                   }
                   else if (strcmp(opt->name, "rw") == 0) {
                           fsflags &= ~MNT_RDONLY;
                           autoro = false;
                   }
                   else if (strcmp(opt->name, "ro") == 0) {
                           fsflags |= MNT_RDONLY;
                           autoro = false;
                   }
                   else if (strcmp(opt->name, "rdonly") == 0) {
                           free(opt->name, M_MOUNT);
                           opt->name = strdup("ro", M_MOUNT);
                           fsflags |= MNT_RDONLY;
                           autoro = false;
                   }
                   else if (strcmp(opt->name, "autoro") == 0) {
                           vfs_freeopt(optlist, opt);
                           autoro = true;
                   }
                   else if (strcmp(opt->name, "suiddir") == 0)
                           fsflags |= MNT_SUIDDIR;
                   else if (strcmp(opt->name, "sync") == 0)
                           fsflags |= MNT_SYNCHRONOUS;
                   else if (strcmp(opt->name, "union") == 0)
                           fsflags |= MNT_UNION;
                   else if (strcmp(opt->name, "automounted") == 0) {
                           fsflags |= MNT_AUTOMOUNTED;
                           vfs_freeopt(optlist, opt);
                   }
           }
   
           /*
            * Be ultra-paranoid about making sure the type and fspath
            * variables will fit in our mp buffers, including the
            * terminating NUL.
            */
           if (fstypelen > MFSNAMELEN || fspathlen > MNAMELEN) {
                   error = ENAMETOOLONG;
                   goto bail;
           }
   
           error = vfs_domount(td, fstype, fspath, fsflags, &optlist);
   
           /*
            * See if we can mount in the read-only mode if the error code suggests
            * that it could be possible and the mount options allow for that.
            * Never try it if "[no]{ro|rw}" has been explicitly requested and not
            * overridden by "autoro".
            */
           if (autoro && vfs_should_downgrade_to_ro_mount(fsflags, error)) {
                   printf("%s: R/W mount failed, possibly R/O media,"
                       " trying R/O mount\n", __func__);
                   fsflags |= MNT_RDONLY;
                   error = vfs_domount(td, fstype, fspath, fsflags, &optlist);
           }
   bail:
           /* copyout the errmsg */
           if (errmsg_pos != -1 && ((2 * errmsg_pos + 1) < fsoptions->uio_iovcnt)
               && errmsg_len > 0 && errmsg != NULL) {
                   if (fsoptions->uio_segflg == UIO_SYSSPACE) {
                           bcopy(errmsg,
                               fsoptions->uio_iov[2 * errmsg_pos + 1].iov_base,
                               fsoptions->uio_iov[2 * errmsg_pos + 1].iov_len);
                   } else {
                           copyout(errmsg,
                               fsoptions->uio_iov[2 * errmsg_pos + 1].iov_base,
                               fsoptions->uio_iov[2 * errmsg_pos + 1].iov_len);
                   }
           }
   
           if (optlist != NULL)
                   vfs_freeopts(optlist);
           return (error);
   }
   
   /*
    * Old mount API.
    */
   #ifndef _SYS_SYSPROTO_H_
   struct mount_args {
           char    *type;
           char    *path;
           int     flags;
           caddr_t data;
   };
   #endif
   /* ARGSUSED */
   int
   sys_mount(struct thread *td, struct mount_args *uap)
   {
           char *fstype;
           struct vfsconf *vfsp = NULL;
           struct mntarg *ma = NULL;
           uint64_t flags;
           int error;
   
           /*
            * Mount flags are now 64-bits. On 32-bit architectures only
            * 32-bits are passed in, but from here on everything handles
            * 64-bit flags correctly.
            */
           flags = uap->flags;
   
           AUDIT_ARG_FFLAGS(flags);
   
           /*
            * Filter out MNT_ROOTFS.  We do not want clients of mount() in
            * userspace to set this flag, but we must filter it out if we want
            * MNT_UPDATE on the root file system to work.
            * MNT_ROOTFS should only be set by the kernel when mounting its
            * root file system.
            */
           flags &= ~MNT_ROOTFS;
   
           fstype = malloc(MFSNAMELEN, M_TEMP, M_WAITOK);
           error = copyinstr(uap->type, fstype, MFSNAMELEN, NULL);
           if (error) {
                   free(fstype, M_TEMP);
                   return (error);
           }
   
           AUDIT_ARG_TEXT(fstype);
           vfsp = vfs_byname_kld(fstype, td, &error);
           free(fstype, M_TEMP);
           if (vfsp == NULL)
                   return (ENOENT);
           if (vfsp->vfc_vfsops->vfs_cmount == NULL)
                   return (EOPNOTSUPP);
   
           ma = mount_argsu(ma, "fstype", uap->type, MFSNAMELEN);
           ma = mount_argsu(ma, "fspath", uap->path, MNAMELEN);
           ma = mount_argb(ma, flags & MNT_RDONLY, "noro");
           ma = mount_argb(ma, !(flags & MNT_NOSUID), "nosuid");
           ma = mount_argb(ma, !(flags & MNT_NOEXEC), "noexec");
   
           error = vfsp->vfc_vfsops->vfs_cmount(ma, uap->data, flags);
           return (error);
   }
   
   /*
    * vfs_domount_first(): first file system mount (not update)
    */
   static int
   vfs_domount_first(
           struct thread *td,              /* Calling thread. */
           struct vfsconf *vfsp,           /* File system type. */
           char *fspath,                   /* Mount path. */
           struct vnode *vp,               /* Vnode to be covered. */
           uint64_t fsflags,               /* Flags common to all filesystems. */
           struct vfsoptlist **optlist     /* Options local to the filesystem. */
           )
   {
           struct vattr va;
           struct mount *mp;
           struct vnode *newdp;
           int error, error1;
   
           ASSERT_VOP_ELOCKED(vp, __func__);
           KASSERT((fsflags & MNT_UPDATE) == 0, ("MNT_UPDATE shouldn't be here"));
   
           /*
            * If the jail of the calling thread lacks permission for this type of
            * file system, or is trying to cover its own root, deny immediately.
            */
           if (jailed(td->td_ucred) && (!prison_allow(td->td_ucred,
               vfsp->vfc_prison_flag) || vp == td->td_ucred->cr_prison->pr_root)) {
                   vput(vp);
                   return (EPERM);
           }
   
           /*
            * If the user is not root, ensure that they own the directory
            * onto which we are attempting to mount.
            */
           error = VOP_GETATTR(vp, &va, td->td_ucred);
           if (error == 0 && va.va_uid != td->td_ucred->cr_uid)
                   error = priv_check_cred(td->td_ucred, PRIV_VFS_ADMIN, 0);
           if (error == 0)
                   error = vinvalbuf(vp, V_SAVE, 0, 0);
           if (error == 0 && vp->v_type != VDIR)
                   error = ENOTDIR;
           if (error == 0) {
                   VI_LOCK(vp);
                   if ((vp->v_iflag & VI_MOUNT) == 0 && vp->v_mountedhere == NULL)
                           vp->v_iflag |= VI_MOUNT;
                   else
                           error = EBUSY;
                   VI_UNLOCK(vp);
           }
           if (error != 0) {
                   vput(vp);
                   return (error);
           }
           VOP_UNLOCK(vp, 0);
   
           /* Allocate and initialize the filesystem. */
           mp = vfs_mount_alloc(vp, vfsp, fspath, td->td_ucred);
           /* XXXMAC: pass to vfs_mount_alloc? */
           mp->mnt_optnew = *optlist;
           /* Set the mount level flags. */
           mp->mnt_flag = (fsflags & (MNT_UPDATEMASK | MNT_ROOTFS | MNT_RDONLY));
   
           /*
            * Mount the filesystem.
            * XXX The final recipients of VFS_MOUNT just overwrite the ndp they
            * get.  No freeing of cn_pnbuf.
            */
           error1 = 0;
           if ((error = VFS_MOUNT(mp)) != 0 ||
               (error1 = VFS_STATFS(mp, &mp->mnt_stat)) != 0 ||
               (error1 = VFS_ROOT(mp, LK_EXCLUSIVE, &newdp)) != 0) {
                   if (error1 != 0) {
                           error = error1;
                           if ((error1 = VFS_UNMOUNT(mp, 0)) != 0)
                                   printf("VFS_UNMOUNT returned %d\n", error1);
                   }
                   vfs_unbusy(mp);
                   mp->mnt_vnodecovered = NULL;
                   vfs_mount_destroy(mp);
                   VI_LOCK(vp);
                   vp->v_iflag &= ~VI_MOUNT;
                   VI_UNLOCK(vp);
                   vrele(vp);
                   return (error);
           }
           VOP_UNLOCK(newdp, 0);
   
           if (mp->mnt_opt != NULL)
                   vfs_freeopts(mp->mnt_opt);
           mp->mnt_opt = mp->mnt_optnew;
           *optlist = NULL;
   
           /*
            * Prevent external consumers of mount options from reading mnt_optnew.
            */
           mp->mnt_optnew = NULL;
   
           MNT_ILOCK(mp);
           if ((mp->mnt_flag & MNT_ASYNC) != 0 &&
               (mp->mnt_kern_flag & MNTK_NOASYNC) == 0)
                   mp->mnt_kern_flag |= MNTK_ASYNC;
           else
                   mp->mnt_kern_flag &= ~MNTK_ASYNC;
           MNT_IUNLOCK(mp);
   
           vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
           cache_purge(vp);
           VI_LOCK(vp);
           vp->v_iflag &= ~VI_MOUNT;
           VI_UNLOCK(vp);
           vp->v_mountedhere = mp;
           /* Place the new filesystem at the end of the mount list. */
           mtx_lock(&mountlist_mtx);
           TAILQ_INSERT_TAIL(&mountlist, mp, mnt_list);
           mtx_unlock(&mountlist_mtx);
           vfs_event_signal(NULL, VQ_MOUNT, 0);
           vn_lock(newdp, LK_EXCLUSIVE | LK_RETRY);
           VOP_UNLOCK(vp, 0);
           EVENTHANDLER_DIRECT_INVOKE(vfs_mounted, mp, newdp, td);
           VOP_UNLOCK(newdp, 0);
           mountcheckdirs(vp, newdp);
           vrele(newdp);
           if ((mp->mnt_flag & MNT_RDONLY) == 0)
                   vfs_allocate_syncvnode(mp);
           vfs_unbusy(mp);
           return (0);
   }
   
   /*
    * vfs_domount_update(): update of mounted file system
    */
   static int
   vfs_domount_update(
           struct thread *td,              /* Calling thread. */
           struct vnode *vp,               /* Mount point vnode. */
           uint64_t fsflags,               /* Flags common to all filesystems. */
           struct vfsoptlist **optlist     /* Options local to the filesystem. */
           )
   {
           struct export_args export;
           void *bufp;
           struct mount *mp;
           int error, export_error, len;
           uint64_t flag;
   
           ASSERT_VOP_ELOCKED(vp, __func__);
           KASSERT((fsflags & MNT_UPDATE) != 0, ("MNT_UPDATE should be here"));
           mp = vp->v_mount;
   
           if ((vp->v_vflag & VV_ROOT) == 0) {
                   if (vfs_copyopt(*optlist, "export", &export, sizeof(export))
                       == 0)
                           error = EXDEV;
                   else
                           error = EINVAL;
                   vput(vp);
                   return (error);
           }
   
           /*
            * We only allow the filesystem to be reloaded if it
            * is currently mounted read-only.
            */
           flag = mp->mnt_flag;
           if ((fsflags & MNT_RELOAD) != 0 && (flag & MNT_RDONLY) == 0) {
                   vput(vp);
                   return (EOPNOTSUPP);    /* Needs translation */
           }
           /*
            * Only privileged root, or (if MNT_USER is set) the user that
            * did the original mount is permitted to update it.
            */
           error = vfs_suser(mp, td);
           if (error != 0) {
                   vput(vp);
                  return (error);
          }
          if (vfs_busy(mp, MBF_NOWAIT)) {
                  vput(vp);
                  return (EBUSY);
          }
          VI_LOCK(vp);
          if ((vp->v_iflag & VI_MOUNT) != 0 || vp->v_mountedhere != NULL) {
                  VI_UNLOCK(vp);
                  vfs_unbusy(mp);
                  vput(vp);
                  return (EBUSY);
          }
          vp->v_iflag |= VI_MOUNT;
          VI_UNLOCK(vp);
          VOP_UNLOCK(vp, 0);
  
          MNT_ILOCK(mp);
          if ((mp->mnt_kern_flag & MNTK_UNMOUNT) != 0) {
                  MNT_IUNLOCK(mp);
                  error = EBUSY;
                  goto end;
          }
          mp->mnt_flag &= ~MNT_UPDATEMASK;
          mp->mnt_flag |= fsflags & (MNT_RELOAD | MNT_FORCE | MNT_UPDATE |
              MNT_SNAPSHOT | MNT_ROOTFS | MNT_UPDATEMASK | MNT_RDONLY);
          if ((mp->mnt_flag & MNT_ASYNC) == 0)
                  mp->mnt_kern_flag &= ~MNTK_ASYNC;
          MNT_IUNLOCK(mp);
          mp->mnt_optnew = *optlist;
          vfs_mergeopts(mp->mnt_optnew, mp->mnt_opt);
  
          /*
           * Mount the filesystem.
           * XXX The final recipients of VFS_MOUNT just overwrite the ndp they
           * get.  No freeing of cn_pnbuf.
           */
          error = VFS_MOUNT(mp);
  
          export_error = 0;
          /* Process the export option. */
          if (error == 0 && vfs_getopt(mp->mnt_optnew, "export", &bufp,
              &len) == 0) {
                  /* Assume that there is only 1 ABI for each length. */
                  switch (len) {
                  case (sizeof(struct oexport_args)):
                          bzero(&export, sizeof(export));
                          /* FALLTHROUGH */
                  case (sizeof(export)):
                          bcopy(bufp, &export, len);
                          export_error = vfs_export(mp, &export);
                          break;
                  default:
                          export_error = EINVAL;
                          break;
                  }
          }
  
          MNT_ILOCK(mp);
          if (error == 0) {
                  mp->mnt_flag &= ~(MNT_UPDATE | MNT_RELOAD | MNT_FORCE |
                      MNT_SNAPSHOT);
          } else {
                  /*
                   * If we fail, restore old mount flags. MNT_QUOTA is special,
                   * because it is not part of MNT_UPDATEMASK, but it could have
                   * changed in the meantime if quotactl(2) was called.
                   * All in all we want current value of MNT_QUOTA, not the old
                   * one.
                   */
                  mp->mnt_flag = (mp->mnt_flag & MNT_QUOTA) | (flag & ~MNT_QUOTA);
          }
          if ((mp->mnt_flag & MNT_ASYNC) != 0 &&
              (mp->mnt_kern_flag & MNTK_NOASYNC) == 0)
                  mp->mnt_kern_flag |= MNTK_ASYNC;
          else
                  mp->mnt_kern_flag &= ~MNTK_ASYNC;
          MNT_IUNLOCK(mp);
  
          if (error != 0)
                  goto end;
  
          if (mp->mnt_opt != NULL)
                  vfs_freeopts(mp->mnt_opt);
          mp->mnt_opt = mp->mnt_optnew;
          *optlist = NULL;
          (void)VFS_STATFS(mp, &mp->mnt_stat);
          /*
           * Prevent external consumers of mount options from reading
           * mnt_optnew.
           */
          mp->mnt_optnew = NULL;
  
          if ((mp->mnt_flag & MNT_RDONLY) == 0)
                  vfs_allocate_syncvnode(mp);
          else
                  vfs_deallocate_syncvnode(mp);
  end:
          vfs_unbusy(mp);
          VI_LOCK(vp);
          vp->v_iflag &= ~VI_MOUNT;
          VI_UNLOCK(vp);
          vrele(vp);
          return (error != 0 ? error : export_error);
  }
  
  /*
   * vfs_domount(): actually attempt a filesystem mount.
   */
  static int
  vfs_domount(
          struct thread *td,              /* Calling thread. */
          const char *fstype,             /* Filesystem type. */
          char *fspath,                   /* Mount path. */
          uint64_t fsflags,               /* Flags common to all filesystems. */
          struct vfsoptlist **optlist     /* Options local to the filesystem. */
          )
  {
          struct vfsconf *vfsp;
          struct nameidata nd;
          struct vnode *vp;
          char *pathbuf;
          int error;
  
          /*
           * Be ultra-paranoid about making sure the type and fspath
           * variables will fit in our mp buffers, including the
           * terminating NUL.
           */
          if (strlen(fstype) >= MFSNAMELEN || strlen(fspath) >= MNAMELEN)
                  return (ENAMETOOLONG);
  
          if (jailed(td->td_ucred) || usermount == 0) {
                  if ((error = priv_check(td, PRIV_VFS_MOUNT)) != 0)
                          return (error);
          }
  
          /*
           * Do not allow NFS export or MNT_SUIDDIR by unprivileged users.
           */
          if (fsflags & MNT_EXPORTED) {
                  error = priv_check(td, PRIV_VFS_MOUNT_EXPORTED);
                  if (error)
                          return (error);
          }
          if (fsflags & MNT_SUIDDIR) {
                  error = priv_check(td, PRIV_VFS_MOUNT_SUIDDIR);
                  if (error)
                          return (error);
          }
          /*
           * Silently enforce MNT_NOSUID and MNT_USER for unprivileged users.
           */
          if ((fsflags & (MNT_NOSUID | MNT_USER)) != (MNT_NOSUID | MNT_USER)) {
                  if (priv_check(td, PRIV_VFS_MOUNT_NONUSER) != 0)
                          fsflags |= MNT_NOSUID | MNT_USER;
          }
  
          /* Load KLDs before we lock the covered vnode to avoid reversals. */
          vfsp = NULL;
          if ((fsflags & MNT_UPDATE) == 0) {
                  /* Don't try to load KLDs if we're mounting the root. */
                  if (fsflags & MNT_ROOTFS)
                          vfsp = vfs_byname(fstype);
                  else
                          vfsp = vfs_byname_kld(fstype, td, &error);
                  if (vfsp == NULL)
                          return (ENODEV);
          }
  
          /*
           * Get vnode to be covered or mount point's vnode in case of MNT_UPDATE.
           */
          NDINIT(&nd, LOOKUP, FOLLOW | LOCKLEAF | AUDITVNODE1,
              UIO_SYSSPACE, fspath, td);
          error = namei(&nd);
          if (error != 0)
                  return (error);
          NDFREE(&nd, NDF_ONLY_PNBUF);
          vp = nd.ni_vp;
          if ((fsflags & MNT_UPDATE) == 0) {
                  pathbuf = malloc(MNAMELEN, M_TEMP, M_WAITOK);
                  strcpy(pathbuf, fspath);
                  error = vn_path_to_global_path(td, vp, pathbuf, MNAMELEN);
                  /* debug.disablefullpath == 1 results in ENODEV */
                  if (error == 0 || error == ENODEV) {
                          error = vfs_domount_first(td, vfsp, pathbuf, vp,
                              fsflags, optlist);
                  }
                  free(pathbuf, M_TEMP);
          } else
                  error = vfs_domount_update(td, vp, fsflags, optlist);
  
          return (error);
  }
  
  /*
   * Unmount a filesystem.
   *
   * Note: unmount takes a path to the vnode mounted on as argument, not
   * special file (as before).
   */
  #ifndef _SYS_SYSPROTO_H_
  struct unmount_args {
          char    *path;
          int     flags;
  };
  #endif
  /* ARGSUSED */
  int
  sys_unmount(struct thread *td, struct unmount_args *uap)
  {
          struct nameidata nd;
          struct mount *mp;
          char *pathbuf;
          int error, id0, id1;
  
          AUDIT_ARG_VALUE(uap->flags);
          if (jailed(td->td_ucred) || usermount == 0) {
                  error = priv_check(td, PRIV_VFS_UNMOUNT);
                  if (error)
                          return (error);
          }
  
          pathbuf = malloc(MNAMELEN, M_TEMP, M_WAITOK);
          error = copyinstr(uap->path, pathbuf, MNAMELEN, NULL);
          if (error) {
                  free(pathbuf, M_TEMP);
                  return (error);
          }
          if (uap->flags & MNT_BYFSID) {
                  AUDIT_ARG_TEXT(pathbuf);
                  /* Decode the filesystem ID. */
                  if (sscanf(pathbuf, "FSID:%d:%d", &id0, &id1) != 2) {
                          free(pathbuf, M_TEMP);
                          return (EINVAL);
                  }
  
                  mtx_lock(&mountlist_mtx);
                  TAILQ_FOREACH_REVERSE(mp, &mountlist, mntlist, mnt_list) {
                          if (mp->mnt_stat.f_fsid.val[0] == id0 &&
                              mp->mnt_stat.f_fsid.val[1] == id1) {
                                  vfs_ref(mp);
                                  break;
                          }
                  }
                  mtx_unlock(&mountlist_mtx);
          } else {
                  /*
                   * Try to find global path for path argument.
                   */
                  NDINIT(&nd, LOOKUP, FOLLOW | LOCKLEAF | AUDITVNODE1,
                      UIO_SYSSPACE, pathbuf, td);
                  if (namei(&nd) == 0) {
                          NDFREE(&nd, NDF_ONLY_PNBUF);
                          error = vn_path_to_global_path(td, nd.ni_vp, pathbuf,
                              MNAMELEN);
                          if (error == 0 || error == ENODEV)
                                  vput(nd.ni_vp);
                  }
                  mtx_lock(&mountlist_mtx);
                  TAILQ_FOREACH_REVERSE(mp, &mountlist, mntlist, mnt_list) {
                          if (strcmp(mp->mnt_stat.f_mntonname, pathbuf) == 0) {
                                  vfs_ref(mp);
                                  break;
                          }
                  }
                  mtx_unlock(&mountlist_mtx);
          }
          free(pathbuf, M_TEMP);
          if (mp == NULL) {
                  /*
                   * Previously we returned ENOENT for a nonexistent path and
                   * EINVAL for a non-mountpoint.  We cannot tell these apart
                   * now, so in the !MNT_BYFSID case return the more likely
                   * EINVAL for compatibility.
                   */
                  return ((uap->flags & MNT_BYFSID) ? ENOENT : EINVAL);
          }
  
          /*
           * Don't allow unmounting the root filesystem.
           */
          if (mp->mnt_flag & MNT_ROOTFS) {
                  vfs_rel(mp);
                  return (EINVAL);
          }
          error = dounmount(mp, uap->flags, td);
          return (error);
  }
  
  /*
   * Return error if any of the vnodes, ignoring the root vnode
   * and the syncer vnode, have non-zero usecount.
   *
   * This function is purely advisory - it can return false positives
   * and negatives.
   */
  static int
  vfs_check_usecounts(struct mount *mp)
  {
          struct vnode *vp, *mvp;
  
          MNT_VNODE_FOREACH_ALL(vp, mp, mvp) {
                  if ((vp->v_vflag & VV_ROOT) == 0 && vp->v_type != VNON &&
                      vp->v_usecount != 0) {
                          VI_UNLOCK(vp);
                          MNT_VNODE_FOREACH_ALL_ABORT(mp, mvp);
                          return (EBUSY);
                  }
                  VI_UNLOCK(vp);
          }
  
          return (0);
  }
  
  static void
  dounmount_cleanup(struct mount *mp, struct vnode *coveredvp, int mntkflags)
  {
  
          mtx_assert(MNT_MTX(mp), MA_OWNED);
          mp->mnt_kern_flag &= ~mntkflags;
          if ((mp->mnt_kern_flag & MNTK_MWAIT) != 0) {
                  mp->mnt_kern_flag &= ~MNTK_MWAIT;
                  wakeup(mp);
          }
          MNT_IUNLOCK(mp);
          if (coveredvp != NULL) {
                  VOP_UNLOCK(coveredvp, 0);
                  vdrop(coveredvp);
          }
          vn_finished_write(mp);
  }
  
  /*
   * Do the actual filesystem unmount.
   */
  int
  dounmount(struct mount *mp, int flags, struct thread *td)
  {
          struct vnode *coveredvp;
          int error;
          uint64_t async_flag;
          int mnt_gen_r;
  
          if ((coveredvp = mp->mnt_vnodecovered) != NULL) {
                  mnt_gen_r = mp->mnt_gen;
                  VI_LOCK(coveredvp);
                  vholdl(coveredvp);
                  vn_lock(coveredvp, LK_EXCLUSIVE | LK_INTERLOCK | LK_RETRY);
                  /*
                   * Check for mp being unmounted while waiting for the
                   * covered vnode lock.
                   */
                  if (coveredvp->v_mountedhere != mp ||
                      coveredvp->v_mountedhere->mnt_gen != mnt_gen_r) {
                          VOP_UNLOCK(coveredvp, 0);
                          vdrop(coveredvp);
                          vfs_rel(mp);
                          return (EBUSY);
                  }
          }
  
          /*
           * Only privileged root, or (if MNT_USER is set) the user that did the
           * original mount is permitted to unmount this filesystem.
           */
          error = vfs_suser(mp, td);
          if (error != 0) {
                  if (coveredvp != NULL) {
                          VOP_UNLOCK(coveredvp, 0);
                          vdrop(coveredvp);
                  }
                  vfs_rel(mp);
                  return (error);
          }
  
          vn_start_write(NULL, &mp, V_WAIT | V_MNTREF);
          MNT_ILOCK(mp);
          if ((mp->mnt_kern_flag & MNTK_UNMOUNT) != 0 ||
              (mp->mnt_flag & MNT_UPDATE) != 0 ||
              !TAILQ_EMPTY(&mp->mnt_uppers)) {
                  dounmount_cleanup(mp, coveredvp, 0);
                  return (EBUSY);
          }
          mp->mnt_kern_flag |= MNTK_UNMOUNT;
          if (flags & MNT_NONBUSY) {
                  MNT_IUNLOCK(mp);
                  error = vfs_check_usecounts(mp);
                  MNT_ILOCK(mp);
                  if (error != 0) {
                          dounmount_cleanup(mp, coveredvp, MNTK_UNMOUNT);
                          return (error);
                  }
          }
          /* Allow filesystems to detect that a forced unmount is in progress. */
          if (flags & MNT_FORCE) {
                  mp->mnt_kern_flag |= MNTK_UNMOUNTF;
                  MNT_IUNLOCK(mp);
                  /*
                   * Must be done after setting MNTK_UNMOUNTF and before
                   * waiting for mnt_lockref to become 0.
                   */
                  VFS_PURGE(mp);
                  MNT_ILOCK(mp);
          }
          error = 0;
          if (mp->mnt_lockref) {
                  mp->mnt_kern_flag |= MNTK_DRAINING;
                  error = msleep(&mp->mnt_lockref, MNT_MTX(mp), PVFS,
                      "mount drain", 0);
          }
          MNT_IUNLOCK(mp);
          KASSERT(mp->mnt_lockref == 0,
              ("%s: invalid lock refcount in the drain path @ %s:%d",
              __func__, __FILE__, __LINE__));
          KASSERT(error == 0,
              ("%s: invalid return value for msleep in the drain path @ %s:%d",
              __func__, __FILE__, __LINE__));
  
          if (mp->mnt_flag & MNT_EXPUBLIC)
                  vfs_setpublicfs(NULL, NULL, NULL);
  
          /*
           * From now, we can claim that the use reference on the
           * coveredvp is ours, and the ref can be released only by
           * successfull unmount by us, or left for later unmount
           * attempt.  The previously acquired hold reference is no
           * longer needed to protect the vnode from reuse.
           */
          if (coveredvp != NULL)
                  vdrop(coveredvp);
  
          vfs_msync(mp, MNT_WAIT);
          MNT_ILOCK(mp);
          async_flag = mp->mnt_flag & MNT_ASYNC;
          mp->mnt_flag &= ~MNT_ASYNC;
          mp->mnt_kern_flag &= ~MNTK_ASYNC;
          MNT_IUNLOCK(mp);
          cache_purgevfs(mp, false); /* remove cache entries for this file sys */
          vfs_deallocate_syncvnode(mp);
          error = VFS_UNMOUNT(mp, flags);
          vn_finished_write(mp);
          /*
           * If we failed to flush the dirty blocks for this mount point,
           * undo all the cdir/rdir and rootvnode changes we made above.
           * Unless we failed to do so because the device is reporting that
           * it doesn't exist anymore.
           */
          if (error && error != ENXIO) {
                  MNT_ILOCK(mp);
                  if ((mp->mnt_flag & MNT_RDONLY) == 0) {
                          MNT_IUNLOCK(mp);
                          vfs_allocate_syncvnode(mp);
                          MNT_ILOCK(mp);
                  }
                  mp->mnt_kern_flag &= ~(MNTK_UNMOUNT | MNTK_UNMOUNTF);
                  mp->mnt_flag |= async_flag;
                  if ((mp->mnt_flag & MNT_ASYNC) != 0 &&
                      (mp->mnt_kern_flag & MNTK_NOASYNC) == 0)
                          mp->mnt_kern_flag |= MNTK_ASYNC;
                  if (mp->mnt_kern_flag & MNTK_MWAIT) {
                          mp->mnt_kern_flag &= ~MNTK_MWAIT;
                          wakeup(mp);
                  }
                  MNT_IUNLOCK(mp);
                  if (coveredvp)
                          VOP_UNLOCK(coveredvp, 0);
                  return (error);
          }
          mtx_lock(&mountlist_mtx);
          TAILQ_REMOVE(&mountlist, mp, mnt_list);
          mtx_unlock(&mountlist_mtx);
          EVENTHANDLER_DIRECT_INVOKE(vfs_unmounted, mp, td);
          if (coveredvp != NULL) {
                  coveredvp->v_mountedhere = NULL;
                  VOP_UNLOCK(coveredvp, 0);
          }
          vfs_event_signal(NULL, VQ_UNMOUNT, 0);
          if (rootvnode != NULL && mp == rootvnode->v_mount) {
                  vrele(rootvnode);
                  rootvnode = NULL;
          }
          if (mp == rootdevmp)
                  rootdevmp = NULL;
          vfs_mount_destroy(mp);
          return (0);
  }
  
  /*
   * Report errors during filesystem mounting.
   */
  void
  vfs_mount_error(struct mount *mp, const char *fmt, ...)
  {
          struct vfsoptlist *moptlist = mp->mnt_optnew;
          va_list ap;
          int error, len;
          char *errmsg;
  
          error = vfs_getopt(moptlist, "errmsg", (void **)&errmsg, &len);
          if (error || errmsg == NULL || len <= 0)
                  return;
  
          va_start(ap, fmt);
          vsnprintf(errmsg, (size_t)len, fmt, ap);
          va_end(ap);
  }
  
  void
  vfs_opterror(struct vfsoptlist *opts, const char *fmt, ...)
  {
          va_list ap;
          int error, len;
          char *errmsg;
  
          error = vfs_getopt(opts, "errmsg", (void **)&errmsg, &len);
          if (error || errmsg == NULL || len <= 0)
                  return;
  
          va_start(ap, fmt);
          vsnprintf(errmsg, (size_t)len, fmt, ap);
          va_end(ap);
  }
  
  /*
   * ---------------------------------------------------------------------
   * Functions for querying mount options/arguments from filesystems.
   */
  
  /*
   * Check that no unknown options are given
   */
  int
  vfs_filteropt(struct vfsoptlist *opts, const char **legal)
  {
          struct vfsopt *opt;
          char errmsg[255];
          const char **t, *p, *q;
          int ret = 0;
  
          TAILQ_FOREACH(opt, opts, link) {
                  p = opt->name;
                  q = NULL;
                  if (p[0] == 'n' && p[1] == 'o')
                          q = p + 2;
                  for(t = global_opts; *t != NULL; t++) {
                          if (strcmp(*t, p) == 0)
                                  break;
                          if (q != NULL) {
                                  if (strcmp(*t, q) == 0)
                                          break;
                          }
                  }
                  if (*t != NULL)
                          continue;
                  for(t = legal; *t != NULL; t++) {
                          if (strcmp(*t, p) == 0)
                                  break;
                          if (q != NULL) {
                                  if (strcmp(*t, q) == 0)
                                          break;
                          }
                  }
                  if (*t != NULL)
                          continue;
                  snprintf(errmsg, sizeof(errmsg),
                      "mount option <%s> is unknown", p);
                  ret = EINVAL;
          }
          if (ret != 0) {
                  TAILQ_FOREACH(opt, opts, link) {
                          if (strcmp(opt->name, "errmsg") == 0) {
                                  strncpy((char *)opt->value, errmsg, opt->len);
                                  break;
                          }
                  }
                  if (opt == NULL)
                          printf("%s\n", errmsg);
          }
          return (ret);
  }
  
  /*
   * Get a mount option by its name.
   *
   * Return 0 if the option was found, ENOENT otherwise.
   * If len is non-NULL it will be filled with the length
   * of the option. If buf is non-NULL, it will be filled
   * with the address of the option.
   */
  int
  vfs_getopt(struct vfsoptlist *opts, const char *name, void **buf, int *len)
  {
          struct vfsopt *opt;
  
          KASSERT(opts != NULL, ("vfs_getopt: caller passed 'opts' as NULL"));
  
          TAILQ_FOREACH(opt, opts, link) {
                  if (strcmp(name, opt->name) == 0) {
                          opt->seen = 1;
                          if (len != NULL)
                                  *len = opt->len;
                          if (buf != NULL)
                                  *buf = opt->value;
                          return (0);
                  }
          }
          return (ENOENT);
  }
  
  int
  vfs_getopt_pos(struct vfsoptlist *opts, const char *name)
  {
          struct vfsopt *opt;
  
          if (opts == NULL)
                  return (-1);
  
          TAILQ_FOREACH(opt, opts, link) {
                  if (strcmp(name, opt->name) == 0) {
                          opt->seen = 1;
                          return (opt->pos);
                  }
          }
          return (-1);
  }
  
  int
  vfs_getopt_size(struct vfsoptlist *opts, const char *name, off_t *value)
  {
          char *opt_value, *vtp;
          quad_t iv;
          int error, opt_len;
  
          error = vfs_getopt(opts, name, (void **)&opt_value, &opt_len);
          if (error != 0)
                  return (error);
          if (opt_len == 0 || opt_value == NULL)
                  return (EINVAL);
          if (opt_value[0] == '\0' || opt_value[opt_len - 1] != '\0')
                  return (EINVAL);
          iv = strtoq(opt_value, &vtp, 0);
          if (vtp == opt_value || (vtp[0] != '\0' && vtp[1] != '\0'))
                  return (EINVAL);
          if (iv < 0)
                  return (EINVAL);
          switch (vtp[0]) {
          case 't': case 'T':
                  iv *= 1024;
                  /* FALLTHROUGH */
          case 'g': case 'G':
                  iv *= 1024;
                  /* FALLTHROUGH */
          case 'm': case 'M':
                  iv *= 1024;
                  /* FALLTHROUGH */
          case 'k': case 'K':
                  iv *= 1024;
          case '\0':
                  break;
          default:
                  return (EINVAL);
          }
          *value = iv;
  
          return (0);
  }
  
  char *
  vfs_getopts(struct vfsoptlist *opts, const char *name, int *error)
  {
          struct vfsopt *opt;
  
          *error = 0;
          TAILQ_FOREACH(opt, opts, link) {
                  if (strcmp(name, opt->name) != 0)
                          continue;
                  opt->seen = 1;
                  if (opt->len == 0 ||
                      ((char *)opt->value)[opt->len - 1] != '\0') {
                          *error = EINVAL;
                          return (NULL);
                  }
                  return (opt->value);
          }
          *error = ENOENT;
          return (NULL);
  }
  
  int
  vfs_flagopt(struct vfsoptlist *opts, const char *name, uint64_t *w,
          uint64_t val)
  {
          struct vfsopt *opt;
  
          TAILQ_FOREACH(opt, opts, link) {
                  if (strcmp(name, opt->name) == 0) {
                          opt->seen = 1;
                          if (w != NULL)
                                  *w |= val;
                          return (1);
                  }
          }
          if (w != NULL)
                  *w &= ~val;
          return (0);
  }
  
  int
  vfs_scanopt(struct vfsoptlist *opts, const char *name, const char *fmt, ...)
  {
          va_list ap;
          struct vfsopt *opt;
          int ret;
  
          KASSERT(opts != NULL, ("vfs_getopt: caller passed 'opts' as NULL"));
  
          TAILQ_FOREACH(opt, opts, link) {
                  if (strcmp(name, opt->name) != 0)
                          continue;
                  opt->seen = 1;
                  if (opt->len == 0 || opt->value == NULL)
                          return (0);
                  if (((char *)opt->value)[opt->len - 1] != '\0')
                          return (0);
                  va_start(ap, fmt);
                  ret = vsscanf(opt->value, fmt, ap);
                  va_end(ap);
                  return (ret);
          }
          return (0);
  }
  
  int
  vfs_setopt(struct vfsoptlist *opts, const char *name, void *value, int len)
  {
          struct vfsopt *opt;
  
          TAILQ_FOREACH(opt, opts, link) {
                  if (strcmp(name, opt->name) != 0)
                          continue;
                  opt->seen = 1;
                  if (opt->value == NULL)
                          opt->len = len;
                  else {
                          if (opt->len != len)
                                  return (EINVAL);
                          bcopy(value, opt->value, len);
                  }
                  return (0);
          }
          return (ENOENT);
  }
  
  int
  vfs_setopt_part(struct vfsoptlist *opts, const char *name, void *value, int len)
  {
          struct vfsopt *opt;
  
          TAILQ_FOREACH(opt, opts, link) {
                  if (strcmp(name, opt->name) != 0)
                          continue;
                  opt->seen = 1;
                  if (opt->value == NULL)
                          opt->len = len;
                  else {
                          if (opt->len < len)
                                  return (EINVAL);
                          opt->len = len;
                          bcopy(value, opt->value, len);
                  }
                  return (0);
          }
          return (ENOENT);
  }
  
  int
  vfs_setopts(struct vfsoptlist *opts, const char *name, const char *value)
  {
          struct vfsopt *opt;
  
          TAILQ_FOREACH(opt, opts, link) {
                  if (strcmp(name, opt->name) != 0)
                          continue;
                  opt->seen = 1;
                  if (opt->value == NULL)
                          opt->len = strlen(value) + 1;
                  else if (strlcpy(opt->value, value, opt->len) >= opt->len)
                          return (EINVAL);
                  return (0);
          }
          return (ENOENT);
  }
  
  /*
   * Find and copy a mount option.
   *
   * The size of the buffer has to be specified
   * in len, if it is not the same length as the
   * mount option, EINVAL is returned.
   * Returns ENOENT if the option is not found.
   */
  int
  vfs_copyopt(struct vfsoptlist *opts, const char *name, void *dest, int len)
  {
          struct vfsopt *opt;
  
          KASSERT(opts != NULL, ("vfs_copyopt: caller passed 'opts' as NULL"));
  
          TAILQ_FOREACH(opt, opts, link) {
                  if (strcmp(name, opt->name) == 0) {
                          opt->seen = 1;
                          if (len != opt->len)
                                  return (EINVAL);
                          bcopy(opt->value, dest, opt->len);
                          return (0);
                  }
          }
          return (ENOENT);
  }
  
  int
  __vfs_statfs(struct mount *mp, struct statfs *sbp)
  {
          int error;
  
          error = mp->mnt_op->vfs_statfs(mp, &mp->mnt_stat);
          if (sbp != &mp->mnt_stat)
                  *sbp = mp->mnt_stat;
          return (error);
  }
  
  void
  vfs_mountedfrom(struct mount *mp, const char *from)
  {
  
          bzero(mp->mnt_stat.f_mntfromname, sizeof mp->mnt_stat.f_mntfromname);
          strlcpy(mp->mnt_stat.f_mntfromname, from,
              sizeof mp->mnt_stat.f_mntfromname);
  }
  
  /*
   * ---------------------------------------------------------------------
   * This is the api for building mount args and mounting filesystems from
   * inside the kernel.
   *
   * The API works by accumulation of individual args.  First error is
   * latched.
   *
   * XXX: should be documented in new manpage kernel_mount(9)
   */
  
  /* A memory allocation which must be freed when we are done */
  struct mntaarg {
          SLIST_ENTRY(mntaarg)    next;
  };
  
  /* The header for the mount arguments */
  struct mntarg {
          struct iovec *v;
          int len;
          int error;
          SLIST_HEAD(, mntaarg)   list;
  };
  
  /*
   * Add a boolean argument.
   *
   * flag is the boolean value.
   * name must start with "no".
   */
  struct mntarg *
  mount_argb(struct mntarg *ma, int flag, const char *name)
  {
  
          KASSERT(name[0] == 'n' && name[1] == 'o',
              ("mount_argb(...,%s): name must start with 'no'", name));
  
          return (mount_arg(ma, name + (flag ? 2 : 0), NULL, 0));
  }
  
  /*
   * Add an argument printf style
   */
  struct mntarg *
  mount_argf(struct mntarg *ma, const char *name, const char *fmt, ...)
  {
          va_list ap;
          struct mntaarg *maa;
          struct sbuf *sb;
          int len;
  
          if (ma == NULL) {
                  ma = malloc(sizeof *ma, M_MOUNT, M_WAITOK | M_ZERO);
                  SLIST_INIT(&ma->list);
          }
          if (ma->error)
                  return (ma);
  
          ma->v = realloc(ma->v, sizeof *ma->v * (ma->len + 2),
              M_MOUNT, M_WAITOK);
          ma->v[ma->len].iov_base = (void *)(uintptr_t)name;
          ma->v[ma->len].iov_len = strlen(name) + 1;
          ma->len++;
  
          sb = sbuf_new_auto();
          va_start(ap, fmt);
          sbuf_vprintf(sb, fmt, ap);
          va_end(ap);
          sbuf_finish(sb);
          len = sbuf_len(sb) + 1;
          maa = malloc(sizeof *maa + len, M_MOUNT, M_WAITOK | M_ZERO);
          SLIST_INSERT_HEAD(&ma->list, maa, next);
          bcopy(sbuf_data(sb), maa + 1, len);
          sbuf_delete(sb);
  
          ma->v[ma->len].iov_base = maa + 1;
          ma->v[ma->len].iov_len = len;
          ma->len++;
  
          return (ma);
  }
  
  /*
   * Add an argument which is a userland string.
   */
  struct mntarg *
  mount_argsu(struct mntarg *ma, const char *name, const void *val, int len)
  {
          struct mntaarg *maa;
          char *tbuf;
  
          if (val == NULL)
                  return (ma);
          if (ma == NULL) {
                  ma = malloc(sizeof *ma, M_MOUNT, M_WAITOK | M_ZERO);
                  SLIST_INIT(&ma->list);
          }
          if (ma->error)
                  return (ma);
          maa = malloc(sizeof *maa + len, M_MOUNT, M_WAITOK | M_ZERO);
          SLIST_INSERT_HEAD(&ma->list, maa, next);
          tbuf = (void *)(maa + 1);
          ma->error = copyinstr(val, tbuf, len, NULL);
          return (mount_arg(ma, name, tbuf, -1));
  }
  
  /*
   * Plain argument.
   *
   * If length is -1, treat value as a C string.
   */
  struct mntarg *
  mount_arg(struct mntarg *ma, const char *name, const void *val, int len)
  {
  
          if (ma == NULL) {
                  ma = malloc(sizeof *ma, M_MOUNT, M_WAITOK | M_ZERO);
                  SLIST_INIT(&ma->list);
          }
          if (ma->error)
                  return (ma);
  
          ma->v = realloc(ma->v, sizeof *ma->v * (ma->len + 2),
              M_MOUNT, M_WAITOK);
          ma->v[ma->len].iov_base = (void *)(uintptr_t)name;
          ma->v[ma->len].iov_len = strlen(name) + 1;
          ma->len++;
  
          ma->v[ma->len].iov_base = (void *)(uintptr_t)val;
          if (len < 0)
                  ma->v[ma->len].iov_len = strlen(val) + 1;
          else
                  ma->v[ma->len].iov_len = len;
          ma->len++;
          return (ma);
  }
  
  /*
   * Free a mntarg structure
   */
  static void
  free_mntarg(struct mntarg *ma)
  {
          struct mntaarg *maa;
  
          while (!SLIST_EMPTY(&ma->list)) {
                  maa = SLIST_FIRST(&ma->list);
                  SLIST_REMOVE_HEAD(&ma->list, next);
                  free(maa, M_MOUNT);
          }
          free(ma->v, M_MOUNT);
          free(ma, M_MOUNT);
  }
  
  /*
   * Mount a filesystem
   */
  int
  kernel_mount(struct mntarg *ma, uint64_t flags)
  {
          struct uio auio;
          int error;
  
          KASSERT(ma != NULL, ("kernel_mount NULL ma"));
          KASSERT(ma->v != NULL, ("kernel_mount NULL ma->v"));
          KASSERT(!(ma->len & 1), ("kernel_mount odd ma->len (%d)", ma->len));
  
          auio.uio_iov = ma->v;
          auio.uio_iovcnt = ma->len;
          auio.uio_segflg = UIO_SYSSPACE;
  
          error = ma->error;
          if (!error)
                  error = vfs_donmount(curthread, flags, &auio);
          free_mntarg(ma);
          return (error);
  }
  
  /*
   * A printflike function to mount a filesystem.
   */
  int
  kernel_vmount(int flags, ...)
  {
          struct mntarg *ma = NULL;
          va_list ap;
          const char *cp;
          const void *vp;
          int error;
  
          va_start(ap, flags);
          for (;;) {
                  cp = va_arg(ap, const char *);
                  if (cp == NULL)
                          break;
                  vp = va_arg(ap, const void *);
                  ma = mount_arg(ma, cp, vp, (vp != NULL ? -1 : 0));
          }
          va_end(ap);
  
          error = kernel_mount(ma, flags);
          return (error);
  }
  
  /*
   * Convert the old export args format into new export args.
   *
   * The old export args struct does not have security flavors.  Otherwise, the
   * structs are identical.  The default security flavor 'sys' is applied by
   * vfs_export when .ex_numsecflavors is 0.
   */
  void
  vfs_oexport_conv(const struct oexport_args *oexp, struct export_args *exp)
  {
  
          bcopy(oexp, exp, sizeof(*oexp));
          exp->ex_numsecflavors = 0;
  }
  
  /*
   * Suspend write operations on all local writeable filesystems.  Does
   * full sync of them in the process.
   *
   * Iterate over the mount points in reverse order, suspending most
   * recently mounted filesystems first.  It handles a case where a
   * filesystem mounted from a md(4) vnode-backed device should be
   * suspended before the filesystem that owns the vnode.
   */
  void
  suspend_all_fs(void)
  {
          struct mount *mp;
          int error;
  
          mtx_lock(&mountlist_mtx);
          TAILQ_FOREACH_REVERSE(mp, &mountlist, mntlist, mnt_list) {
                  error = vfs_busy(mp, MBF_MNTLSTLOCK | MBF_NOWAIT);
                  if (error != 0)
                          continue;
                  if ((mp->mnt_flag & (MNT_RDONLY | MNT_LOCAL)) != MNT_LOCAL ||
                      (mp->mnt_kern_flag & MNTK_SUSPEND) != 0) {
                          mtx_lock(&mountlist_mtx);
                          vfs_unbusy(mp);
                          continue;
                  }
                  error = vfs_write_suspend(mp, 0);
                  if (error == 0) {
                          MNT_ILOCK(mp);
                          MPASS((mp->mnt_kern_flag & MNTK_SUSPEND_ALL) == 0);
                          mp->mnt_kern_flag |= MNTK_SUSPEND_ALL;
                          MNT_IUNLOCK(mp);
                          mtx_lock(&mountlist_mtx);
                  } else {
                          printf("suspend of %s failed, error %d\n",
                              mp->mnt_stat.f_mntonname, error);
                          mtx_lock(&mountlist_mtx);
                          vfs_unbusy(mp);
                  }
          }
          mtx_unlock(&mountlist_mtx);
  }
  
  void
  resume_all_fs(void)
  {
          struct mount *mp;
  
          mtx_lock(&mountlist_mtx);
          TAILQ_FOREACH(mp, &mountlist, mnt_list) {
                  if ((mp->mnt_kern_flag & MNTK_SUSPEND_ALL) == 0)
                          continue;
                  mtx_unlock(&mountlist_mtx);
                  MNT_ILOCK(mp);
                  MPASS((mp->mnt_kern_flag & MNTK_SUSPEND) != 0);
                  mp->mnt_kern_flag &= ~MNTK_SUSPEND_ALL;
                  MNT_IUNLOCK(mp);
                  vfs_write_resume(mp, 0);
                  mtx_lock(&mountlist_mtx);
                  vfs_unbusy(mp);
          }
          mtx_unlock(&mountlist_mtx);
  }

Cache object: 5d2dd328feb9b115e60cca542501a5ac