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/smp.h>
    #include <sys/devctl.h>
    #include <sys/eventhandler.h>
    #include <sys/fcntl.h>
    #include <sys/jail.h>
    #include <sys/kernel.h>
    #include <sys/ktr.h>
    #include <sys/libkern.h>
    #include <sys/limits.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/systm.h>
    #include <sys/taskqueue.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");
    
    static bool     recursive_forced_unmount = false;
    SYSCTL_BOOL(_vfs, OID_AUTO, recursive_forced_unmount, CTLFLAG_RW,
        &recursive_forced_unmount, 0, "Recursively unmount stacked upper mounts"
        " when a file system is forcibly unmounted");
    
    static SYSCTL_NODE(_vfs, OID_AUTO, deferred_unmount,
        CTLFLAG_RD | CTLFLAG_MPSAFE, 0, "deferred unmount controls");
    
   static unsigned int     deferred_unmount_retry_limit = 10;
   SYSCTL_UINT(_vfs_deferred_unmount, OID_AUTO, retry_limit, CTLFLAG_RW,
       &deferred_unmount_retry_limit, 0,
       "Maximum number of retries for deferred unmount failure");
   
   static int      deferred_unmount_retry_delay_hz;
   SYSCTL_INT(_vfs_deferred_unmount, OID_AUTO, retry_delay_hz, CTLFLAG_RW,
       &deferred_unmount_retry_delay_hz, 0,
       "Delay in units of [1/kern.hz]s when retrying a failed deferred unmount");
   
   static int      deferred_unmount_total_retries = 0;
   SYSCTL_INT(_vfs_deferred_unmount, OID_AUTO, total_retries, CTLFLAG_RD,
       &deferred_unmount_total_retries, 0,
       "Total number of retried deferred unmounts");
   
   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_padalign __exclusive_cache_line mountlist_mtx;
   
   EVENTHANDLER_LIST_DEFINE(vfs_mounted);
   EVENTHANDLER_LIST_DEFINE(vfs_unmounted);
   
   static void vfs_deferred_unmount(void *arg, int pending);
   static struct timeout_task deferred_unmount_task;
   static struct mtx deferred_unmount_lock;
   MTX_SYSINIT(deferred_unmount, &deferred_unmount_lock, "deferred_unmount",
       MTX_DEF);
   static STAILQ_HEAD(, mount) deferred_unmount_list =
       STAILQ_HEAD_INITIALIZER(deferred_unmount_list);
   TASKQUEUE_DEFINE_THREAD(deferred_unmount);
   
   static void mount_devctl_event(const char *type, struct mount *mp, bool donew);
   
   /*
    * 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);
           mp->mnt_pcpu = uma_zalloc_pcpu(pcpu_zone_16, M_WAITOK | M_ZERO);
           mp->mnt_ref = 0;
           mp->mnt_vfs_ops = 1;
           mp->mnt_rootvnode = NULL;
           return (0);
   }
   
   static void
   mount_fini(void *mem, int size)
   {
           struct mount *mp;
   
           mp = (struct mount *)mem;
           uma_zfree_pcpu(pcpu_zone_16, mp->mnt_pcpu);
           lockdestroy(&mp->mnt_explock);
           mtx_destroy(&mp->mnt_listmtx);
           mtx_destroy(&mp->mnt_mtx);
   }
   
   static void
   vfs_mount_init(void *dummy __unused)
   {
           TIMEOUT_TASK_INIT(taskqueue_deferred_unmount, &deferred_unmount_task,
               0, vfs_deferred_unmount, NULL);
           deferred_unmount_retry_delay_hz = hz;
           mount_zone = uma_zcreate("Mountpoints", sizeof(struct mount), NULL,
               NULL, mount_init, mount_fini, UMA_ALIGN_CACHE, UMA_ZONE_NOFREE);
           mtx_init(&mountlist_mtx, "mountlist", NULL, MTX_DEF);
   }
   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
    */
   
   /*
    * Get a reference on a mount point from a vnode.
    *
    * The vnode is allowed to be passed unlocked and race against dooming. Note in
    * such case there are no guarantees the referenced mount point will still be
    * associated with it after the function returns.
    */
   struct mount *
   vfs_ref_from_vp(struct vnode *vp)
   {
           struct mount *mp;
           struct mount_pcpu *mpcpu;
   
           mp = atomic_load_ptr(&vp->v_mount);
           if (__predict_false(mp == NULL)) {
                   return (mp);
           }
           if (vfs_op_thread_enter(mp, mpcpu)) {
                   if (__predict_true(mp == vp->v_mount)) {
                           vfs_mp_count_add_pcpu(mpcpu, ref, 1);
                           vfs_op_thread_exit(mp, mpcpu);
                   } else {
                           vfs_op_thread_exit(mp, mpcpu);
                           mp = NULL;
                   }
           } else {
                   MNT_ILOCK(mp);
                   if (mp == vp->v_mount) {
                           MNT_REF(mp);
                           MNT_IUNLOCK(mp);
                   } else {
                           MNT_IUNLOCK(mp);
                           mp = NULL;
                   }
           }
           return (mp);
   }
   
   void
   vfs_ref(struct mount *mp)
   {
           struct mount_pcpu *mpcpu;
   
           CTR2(KTR_VFS, "%s: mp %p", __func__, mp);
           if (vfs_op_thread_enter(mp, mpcpu)) {
                   vfs_mp_count_add_pcpu(mpcpu, ref, 1);
                   vfs_op_thread_exit(mp, mpcpu);
                   return;
           }
   
           MNT_ILOCK(mp);
           MNT_REF(mp);
           MNT_IUNLOCK(mp);
   }
   
   /*
    * Register ump as an upper mount of the mount associated with
    * vnode vp.  This registration will be tracked through
    * mount_upper_node upper, which should be allocated by the
    * caller and stored in per-mount data associated with mp.
    *
    * If successful, this function will return the mount associated
    * with vp, and will ensure that it cannot be unmounted until
    * ump has been unregistered as one of its upper mounts.
    * 
    * Upon failure this function will return NULL.
    */
   struct mount *
   vfs_register_upper_from_vp(struct vnode *vp, struct mount *ump,
       struct mount_upper_node *upper)
   {
           struct mount *mp;
   
           mp = atomic_load_ptr(&vp->v_mount);
           if (mp == NULL)
                   return (NULL);
           MNT_ILOCK(mp);
           if (mp != vp->v_mount ||
               ((mp->mnt_kern_flag & (MNTK_UNMOUNT | MNTK_RECURSE)) != 0)) {
                   MNT_IUNLOCK(mp);
                   return (NULL);
           }
           KASSERT(ump != mp, ("upper and lower mounts are identical"));
           upper->mp = ump;
           MNT_REF(mp);
           TAILQ_INSERT_TAIL(&mp->mnt_uppers, upper, mnt_upper_link);
           MNT_IUNLOCK(mp);
           return (mp);
   }
   
   /*
    * Register upper mount ump to receive vnode unlink/reclaim
    * notifications from lower mount mp. This registration will
    * be tracked through mount_upper_node upper, which should be
    * allocated by the caller and stored in per-mount data
    * associated with mp.
    *
    * ump must already be registered as an upper mount of mp
    * through a call to vfs_register_upper_from_vp().
    */
   void
   vfs_register_for_notification(struct mount *mp, struct mount *ump,
       struct mount_upper_node *upper)
   {
           upper->mp = ump;
           MNT_ILOCK(mp);
           TAILQ_INSERT_TAIL(&mp->mnt_notify, upper, mnt_upper_link);
           MNT_IUNLOCK(mp);
   }
   
   static void
   vfs_drain_upper_locked(struct mount *mp)
   {
           mtx_assert(MNT_MTX(mp), MA_OWNED);
           while (mp->mnt_upper_pending != 0) {
                   mp->mnt_kern_flag |= MNTK_UPPER_WAITER;
                   msleep(&mp->mnt_uppers, MNT_MTX(mp), 0, "mntupw", 0);
           }
   }
   
   /*
    * Undo a previous call to vfs_register_for_notification().
    * The mount represented by upper must be currently registered
    * as an upper mount for mp.
    */
   void
   vfs_unregister_for_notification(struct mount *mp,
       struct mount_upper_node *upper)
   {
           MNT_ILOCK(mp);
           vfs_drain_upper_locked(mp);
           TAILQ_REMOVE(&mp->mnt_notify, upper, mnt_upper_link);
           MNT_IUNLOCK(mp);
   }
   
   /*
    * Undo a previous call to vfs_register_upper_from_vp().
    * This must be done before mp can be unmounted.
    */
   void
   vfs_unregister_upper(struct mount *mp, struct mount_upper_node *upper)
   {
           MNT_ILOCK(mp);
           KASSERT((mp->mnt_kern_flag & MNTK_UNMOUNT) == 0,
               ("registered upper with pending unmount"));
           vfs_drain_upper_locked(mp);
           TAILQ_REMOVE(&mp->mnt_uppers, upper, mnt_upper_link);
           if ((mp->mnt_kern_flag & MNTK_TASKQUEUE_WAITER) != 0 &&
               TAILQ_EMPTY(&mp->mnt_uppers)) {
                   mp->mnt_kern_flag &= ~MNTK_TASKQUEUE_WAITER;
                   wakeup(&mp->mnt_taskqueue_link);
           }
           MNT_REL(mp);
           MNT_IUNLOCK(mp);
   }
   
   void
   vfs_rel(struct mount *mp)
   {
           struct mount_pcpu *mpcpu;
   
           CTR2(KTR_VFS, "%s: mp %p", __func__, mp);
           if (vfs_op_thread_enter(mp, mpcpu)) {
                   vfs_mp_count_sub_pcpu(mpcpu, ref, 1);
                   vfs_op_thread_exit(mp, mpcpu);
                   return;
           }
   
           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));
           mp->mnt_kern_flag = 0;
           mp->mnt_flag = 0;
           mp->mnt_rootvnode = NULL;
           mp->mnt_vnodecovered = NULL;
           mp->mnt_op = NULL;
           mp->mnt_vfc = NULL;
           TAILQ_INIT(&mp->mnt_nvnodelist);
           mp->mnt_nvnodelistsize = 0;
           TAILQ_INIT(&mp->mnt_lazyvnodelist);
           mp->mnt_lazyvnodelistsize = 0;
           MPPASS(mp->mnt_ref == 0 && mp->mnt_lockref == 0 &&
               mp->mnt_writeopcount == 0, mp);
           MPASSERT(mp->mnt_vfs_ops == 1, mp,
               ("vfs_ops should be 1 but %d found", mp->mnt_vfs_ops));
           (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);
           mp->mnt_upper_pending = 0;
           TAILQ_INIT(&mp->mnt_uppers);
           TAILQ_INIT(&mp->mnt_notify);
           mp->mnt_taskqueue_flags = 0;
           mp->mnt_unmount_retries = 0;
           return (mp);
   }
   
   /*
    * Destroy the mount struct previously allocated by vfs_mount_alloc().
    */
   void
   vfs_mount_destroy(struct mount *mp)
   {
   
           MPPASS(mp->mnt_vfs_ops != 0, mp);
   
           vfs_assert_mount_counters(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__));
           MPPASS(mp->mnt_writeopcount == 0, mp);
           MPPASS(mp->mnt_secondary_writes == 0, mp);
           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(mp->mnt_upper_pending == 0, ("mnt_upper_pending"));
           KASSERT(TAILQ_EMPTY(&mp->mnt_uppers), ("mnt_uppers"));
           KASSERT(TAILQ_EMPTY(&mp->mnt_notify), ("mnt_notify"));
           MPPASS(mp->mnt_nvnodelistsize == 0, mp);
           MPPASS(mp->mnt_lazyvnodelistsize == 0, mp);
           MPPASS(mp->mnt_lockref == 0, mp);
           MNT_IUNLOCK(mp);
   
           MPASSERT(mp->mnt_vfs_ops == 1, mp,
               ("vfs_ops should be 1 but %d found", mp->mnt_vfs_ops));
   
           MPASSERT(mp->mnt_rootvnode == NULL, mp,
               ("mount point still has a root vnode %p", mp->mnt_rootvnode));
   
           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) {
                   int do_freeopt = 0;
   
                   if (strcmp(opt->name, "update") == 0) {
                           fsflags |= MNT_UPDATE;
                           do_freeopt = 1;
                   }
                   else if (strcmp(opt->name, "async") == 0)
                           fsflags |= MNT_ASYNC;
                   else if (strcmp(opt->name, "force") == 0) {
                           fsflags |= MNT_FORCE;
                           do_freeopt = 1;
                   }
                   else if (strcmp(opt->name, "reload") == 0) {
                           fsflags |= MNT_RELOAD;
                           do_freeopt = 1;
                   }
                   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) {
                           do_freeopt = 1;
                           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, "export") == 0)
                           fsflags |= MNT_EXPORTED;
                   else if (strcmp(opt->name, "automounted") == 0) {
                           fsflags |= MNT_AUTOMOUNTED;
                           do_freeopt = 1;
                   } else if (strcmp(opt->name, "nocover") == 0) {
                           fsflags |= MNT_NOCOVER;
                           do_freeopt = 1;
                   } else if (strcmp(opt->name, "cover") == 0) {
                           fsflags &= ~MNT_NOCOVER;
                           do_freeopt = 1;
                   } else if (strcmp(opt->name, "emptydir") == 0) {
                           fsflags |= MNT_EMPTYDIR;
                           do_freeopt = 1;
                   } else if (strcmp(opt->name, "noemptydir") == 0) {
                           fsflags &= ~MNT_EMPTYDIR;
                           do_freeopt = 1;
                   }
                   if (do_freeopt)
                           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);
           if (error == ENOENT) {
                   error = EINVAL;
                   if (errmsg != NULL)
                           strncpy(errmsg, "Invalid fstype", errmsg_len);
                   goto bail;
           }
   
           /*
            * 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_flags & VFCF_SBDRY) != 0 &&
              vfsp->vfc_vfsops_sd->vfs_cmount == NULL) ||
              ((vfsp->vfc_flags & VFCF_SBDRY) == 0 &&
              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");
  
          if ((vfsp->vfc_flags & VFCF_SBDRY) != 0)
                  return (vfsp->vfc_vfsops_sd->vfs_cmount(ma, uap->data, flags));
          return (vfsp->vfc_vfsops->vfs_cmount(ma, uap->data, flags));
  }
  
  /*
   * 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, *rootvp;
          int error, error1;
          bool unmounted;
  
          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);
          if (error == 0)
                  error = vinvalbuf(vp, V_SAVE, 0, 0);
          if (vfsp->vfc_flags & VFCF_FILEMOUNT) {
                  if (error == 0 && vp->v_type != VDIR && vp->v_type != VREG)
                          error = EINVAL;
                  /*
                   * For file mounts, ensure that there is only one hardlink to the file.
                   */
                  if (error == 0 && vp->v_type == VREG && va.va_nlink != 1)
                          error = EINVAL;
          } else {
                  if (error == 0 && vp->v_type != VDIR)
                          error = ENOTDIR;
          }
          if (error == 0 && (fsflags & MNT_EMPTYDIR) != 0)
                  error = vfs_emptydir(vp);
          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);
          }
          vn_seqc_write_begin(vp);
          VOP_UNLOCK(vp);
  
          /* 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 | MNT_FORCE));
  
          /*
           * Mount the filesystem.
           * XXX The final recipients of VFS_MOUNT just overwrite the ndp they
           * get.  No freeing of cn_pnbuf.
           */
          error1 = 0;
          unmounted = true;
          if ((error = VFS_MOUNT(mp)) != 0 ||
              (error1 = VFS_STATFS(mp, &mp->mnt_stat)) != 0 ||
              (error1 = VFS_ROOT(mp, LK_EXCLUSIVE, &newdp)) != 0) {
                  rootvp = NULL;
                  if (error1 != 0) {
                          MPASS(error == 0);
                          rootvp = vfs_cache_root_clear(mp);
                          if (rootvp != NULL) {
                                  vhold(rootvp);
                                  vrele(rootvp);
                          }
                          (void)vn_start_write(NULL, &mp, V_WAIT);
                          MNT_ILOCK(mp);
                          mp->mnt_kern_flag |= MNTK_UNMOUNT | MNTK_UNMOUNTF;
                          MNT_IUNLOCK(mp);
                          VFS_PURGE(mp);
                          error = VFS_UNMOUNT(mp, 0);
                          vn_finished_write(mp);
                          if (error != 0) {
                                  printf(
                      "failed post-mount (%d): rollback unmount returned %d\n",
                                      error1, error);
                                  unmounted = false;
                          }
                          error = error1;
                  }
                  vfs_unbusy(mp);
                  mp->mnt_vnodecovered = NULL;
                  if (unmounted) {
                          /* XXXKIB wait for mnt_lockref drain? */
                          vfs_mount_destroy(mp);
                  }
                  VI_LOCK(vp);
                  vp->v_iflag &= ~VI_MOUNT;
                  VI_UNLOCK(vp);
                  if (rootvp != NULL) {
                          vn_seqc_write_end(rootvp);
                          vdrop(rootvp);
                  }
                  vn_seqc_write_end(vp);
                  vrele(vp);
                  return (error);
          }
          vn_seqc_write_begin(newdp);
          VOP_UNLOCK(newdp);
  
          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);
  
          /*
           * VIRF_MOUNTPOINT and v_mountedhere need to be set under the
           * vp lock to satisfy vfs_lookup() requirements.
           */
          VOP_LOCK(vp, LK_EXCLUSIVE | LK_RETRY);
          VI_LOCK(vp);
          vn_irflag_set_locked(vp, VIRF_MOUNTPOINT);
          vp->v_mountedhere = mp;
          VI_UNLOCK(vp);
          VOP_UNLOCK(vp);
          cache_purge(vp);
  
          /*
           * We need to lock both vnodes.
           *
           * Use vn_lock_pair to avoid establishing an ordering between vnodes
           * from different filesystems.
           */
          vn_lock_pair(vp, false, newdp, false);
  
          VI_LOCK(vp);
          vp->v_iflag &= ~VI_MOUNT;
          VI_UNLOCK(vp);
          /* 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);
          VOP_UNLOCK(vp);
          EVENTHANDLER_DIRECT_INVOKE(vfs_mounted, mp, newdp, td);
          VOP_UNLOCK(newdp);
          mount_devctl_event("MOUNT", mp, false);
          mountcheckdirs(vp, newdp);
          vn_seqc_write_end(vp);
          vn_seqc_write_end(newdp);
          vrele(newdp);
          if ((mp->mnt_flag & MNT_RDONLY) == 0)
                  vfs_allocate_syncvnode(mp);
          vfs_op_exit(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;
          struct o2export_args o2export;
          struct vnode *rootvp;
          void *bufp;
          struct mount *mp;
          int error, export_error, i, len;
          uint64_t flag;
          gid_t *grps;
  
          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);
  
          vfs_op_enter(mp);
          vn_seqc_write_begin(vp);
  
          rootvp = NULL;
          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;
          rootvp = vfs_cache_root_clear(mp);
          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(&o2export, sizeof(o2export));
                          /* FALLTHROUGH */
                  case (sizeof(o2export)):
                          bcopy(bufp, &o2export, len);
                          export.ex_flags = (uint64_t)o2export.ex_flags;
                          export.ex_root = o2export.ex_root;
                          export.ex_uid = o2export.ex_anon.cr_uid;
                          export.ex_groups = NULL;
                          export.ex_ngroups = o2export.ex_anon.cr_ngroups;
                          if (export.ex_ngroups > 0) {
                                  if (export.ex_ngroups <= XU_NGROUPS) {
                                          export.ex_groups = malloc(
                                              export.ex_ngroups * sizeof(gid_t),
                                              M_TEMP, M_WAITOK);
                                          for (i = 0; i < export.ex_ngroups; i++)
                                                  export.ex_groups[i] =
                                                    o2export.ex_anon.cr_groups[i];
                                  } else
                                          export_error = EINVAL;
                          } else if (export.ex_ngroups < 0)
                                  export_error = EINVAL;
                          export.ex_addr = o2export.ex_addr;
                          export.ex_addrlen = o2export.ex_addrlen;
                          export.ex_mask = o2export.ex_mask;
                          export.ex_masklen = o2export.ex_masklen;
                          export.ex_indexfile = o2export.ex_indexfile;
                          export.ex_numsecflavors = o2export.ex_numsecflavors;
                          if (export.ex_numsecflavors < MAXSECFLAVORS) {
                                  for (i = 0; i < export.ex_numsecflavors; i++)
                                          export.ex_secflavors[i] =
                                              o2export.ex_secflavors[i];
                          } else
                                  export_error = EINVAL;
                          if (export_error == 0)
                                  export_error = vfs_export(mp, &export);
                          free(export.ex_groups, M_TEMP);
                          break;
                  case (sizeof(export)):
                          bcopy(bufp, &export, len);
                          grps = NULL;
                          if (export.ex_ngroups > 0) {
                                  if (export.ex_ngroups <= NGROUPS_MAX) {
                                          grps = malloc(export.ex_ngroups *
                                              sizeof(gid_t), M_TEMP, M_WAITOK);
                                          export_error = copyin(export.ex_groups,
                                              grps, export.ex_ngroups *
                                              sizeof(gid_t));
                                          if (export_error == 0)
                                                  export.ex_groups = grps;
                                  } else
                                          export_error = EINVAL;
                          } else if (export.ex_ngroups == 0)
                                  export.ex_groups = NULL;
                          else
                                  export_error = EINVAL;
                          if (export_error == 0)
                                  export_error = vfs_export(mp, &export);
                          free(grps, M_TEMP);
                          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;
  
          mount_devctl_event("REMOUNT", mp, true);
          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_op_exit(mp);
          if (rootvp != NULL) {
                  vn_seqc_write_end(rootvp);
                  vrele(rootvp);
          }
          vn_seqc_write_end(vp);
          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) {
                          if ((vfsp = vfs_byname(fstype)) == NULL)
                                  return (ENODEV);
                  } else {
                          if ((vfsp = vfs_byname_kld(fstype, td, &error)) == NULL)
                                  return (error);
                  }
          }
  
          /*
           * Get vnode to be covered or mount point's vnode in case of MNT_UPDATE.
           */
          NDINIT(&nd, LOOKUP, FOLLOW | LOCKLEAF | AUDITVNODE1 | WANTPARENT,
              UIO_SYSSPACE, fspath);
          error = namei(&nd);
          if (error != 0)
                  return (error);
          vp = nd.ni_vp;
          /*
           * Don't allow stacking file mounts to work around problems with the way
           * that namei sets nd.ni_dvp to vp_crossmp for these.
           */
          if (vp->v_type == VREG)
                  fsflags |= MNT_NOCOVER;
          if ((fsflags & MNT_UPDATE) == 0) {
                  if ((vp->v_vflag & VV_ROOT) != 0 &&
                      (fsflags & MNT_NOCOVER) != 0) {
                          vput(vp);
                          error = EBUSY;
                          goto out;
                  }
                  pathbuf = malloc(MNAMELEN, M_TEMP, M_WAITOK);
                  strcpy(pathbuf, fspath);
                  /*
                   * Note: we allow any vnode type here. If the path sanity check
                   * succeeds, the type will be validated in vfs_domount_first
                   * above.
                   */
                  if (vp->v_type == VDIR)
                          error = vn_path_to_global_path(td, vp, pathbuf,
                              MNAMELEN);
                  else
                          error = vn_path_to_global_path_hardlink(td, vp,
                              nd.ni_dvp, pathbuf, MNAMELEN,
                              nd.ni_cnd.cn_nameptr, nd.ni_cnd.cn_namelen);
                  if (error == 0) {
                          error = vfs_domount_first(td, vfsp, pathbuf, vp,
                              fsflags, optlist);
                  }
                  free(pathbuf, M_TEMP);
          } else
                  error = vfs_domount_update(td, vp, fsflags, optlist);
  
  out:
          NDFREE_PNBUF(&nd);
          vrele(nd.ni_dvp);
  
          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)
  {
  
          return (kern_unmount(td, uap->path, uap->flags));
  }
  
  int
  kern_unmount(struct thread *td, const char *path, int flags)
  {
          struct nameidata nd;
          struct mount *mp;
          char *fsidbuf, *pathbuf;
          fsid_t fsid;
          int error;
  
          AUDIT_ARG_VALUE(flags);
          if (jailed(td->td_ucred) || usermount == 0) {
                  error = priv_check(td, PRIV_VFS_UNMOUNT);
                  if (error)
                          return (error);
          }
  
          if (flags & MNT_BYFSID) {
                  fsidbuf = malloc(MNAMELEN, M_TEMP, M_WAITOK);
                  error = copyinstr(path, fsidbuf, MNAMELEN, NULL);
                  if (error) {
                          free(fsidbuf, M_TEMP);
                          return (error);
                  }
  
                  AUDIT_ARG_TEXT(fsidbuf);
                  /* Decode the filesystem ID. */
                  if (sscanf(fsidbuf, "FSID:%d:%d", &fsid.val[0], &fsid.val[1]) != 2) {
                          free(fsidbuf, M_TEMP);
                          return (EINVAL);
                  }
  
                  mp = vfs_getvfs(&fsid);
                  free(fsidbuf, M_TEMP);
                  if (mp == NULL) {
                          return (ENOENT);
                  }
          } else {
                  pathbuf = malloc(MNAMELEN, M_TEMP, M_WAITOK);
                  error = copyinstr(path, pathbuf, MNAMELEN, NULL);
                  if (error) {
                          free(pathbuf, M_TEMP);
                          return (error);
                  }
  
                  /*
                   * Try to find global path for path argument.
                   */
                  NDINIT(&nd, LOOKUP, FOLLOW | LOCKLEAF | AUDITVNODE1,
                      UIO_SYSSPACE, pathbuf);
                  if (namei(&nd) == 0) {
                          NDFREE_PNBUF(&nd);
                          error = vn_path_to_global_path(td, nd.ni_vp, pathbuf,
                              MNAMELEN);
                          if (error == 0)
                                  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 (EINVAL);
                  }
          }
  
          /*
           * Don't allow unmounting the root filesystem.
           */
          if (mp->mnt_flag & MNT_ROOTFS) {
                  vfs_rel(mp);
                  return (EINVAL);
          }
          error = dounmount(mp, 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);
          }
          vfs_op_exit_locked(mp);
          MNT_IUNLOCK(mp);
          if (coveredvp != NULL) {
                  VOP_UNLOCK(coveredvp);
                  vdrop(coveredvp);
          }
          vn_finished_write(mp);
          vfs_rel(mp);
  }
  
  /*
   * There are various reference counters associated with the mount point.
   * Normally it is permitted to modify them without taking the mnt ilock,
   * but this behavior can be temporarily disabled if stable value is needed
   * or callers are expected to block (e.g. to not allow new users during
   * forced unmount).
   */
  void
  vfs_op_enter(struct mount *mp)
  {
          struct mount_pcpu *mpcpu;
          int cpu;
  
          MNT_ILOCK(mp);
          mp->mnt_vfs_ops++;
          if (mp->mnt_vfs_ops > 1) {
                  MNT_IUNLOCK(mp);
                  return;
          }
          vfs_op_barrier_wait(mp);
          CPU_FOREACH(cpu) {
                  mpcpu = vfs_mount_pcpu_remote(mp, cpu);
  
                  mp->mnt_ref += mpcpu->mntp_ref;
                  mpcpu->mntp_ref = 0;
  
                  mp->mnt_lockref += mpcpu->mntp_lockref;
                  mpcpu->mntp_lockref = 0;
  
                  mp->mnt_writeopcount += mpcpu->mntp_writeopcount;
                  mpcpu->mntp_writeopcount = 0;
          }
          MPASSERT(mp->mnt_ref > 0 && mp->mnt_lockref >= 0 &&
              mp->mnt_writeopcount >= 0, mp,
              ("invalid count(s): ref %d lockref %d writeopcount %d",
              mp->mnt_ref, mp->mnt_lockref, mp->mnt_writeopcount));
          MNT_IUNLOCK(mp);
          vfs_assert_mount_counters(mp);
  }
  
  void
  vfs_op_exit_locked(struct mount *mp)
  {
  
          mtx_assert(MNT_MTX(mp), MA_OWNED);
  
          MPASSERT(mp->mnt_vfs_ops > 0, mp,
              ("invalid vfs_ops count %d", mp->mnt_vfs_ops));
          MPASSERT(mp->mnt_vfs_ops > 1 ||
              (mp->mnt_kern_flag & (MNTK_UNMOUNT | MNTK_SUSPEND)) == 0, mp,
              ("vfs_ops too low %d in unmount or suspend", mp->mnt_vfs_ops));
          mp->mnt_vfs_ops--;
  }
  
  void
  vfs_op_exit(struct mount *mp)
  {
  
          MNT_ILOCK(mp);
          vfs_op_exit_locked(mp);
          MNT_IUNLOCK(mp);
  }
  
  struct vfs_op_barrier_ipi {
          struct mount *mp;
          struct smp_rendezvous_cpus_retry_arg srcra;
  };
  
  static void
  vfs_op_action_func(void *arg)
  {
          struct vfs_op_barrier_ipi *vfsopipi;
          struct mount *mp;
  
          vfsopipi = __containerof(arg, struct vfs_op_barrier_ipi, srcra);
          mp = vfsopipi->mp;
  
          if (!vfs_op_thread_entered(mp))
                  smp_rendezvous_cpus_done(arg);
  }
  
  static void
  vfs_op_wait_func(void *arg, int cpu)
  {
          struct vfs_op_barrier_ipi *vfsopipi;
          struct mount *mp;
          struct mount_pcpu *mpcpu;
  
          vfsopipi = __containerof(arg, struct vfs_op_barrier_ipi, srcra);
          mp = vfsopipi->mp;
  
          mpcpu = vfs_mount_pcpu_remote(mp, cpu);
          while (atomic_load_int(&mpcpu->mntp_thread_in_ops))
                  cpu_spinwait();
  }
  
  void
  vfs_op_barrier_wait(struct mount *mp)
  {
          struct vfs_op_barrier_ipi vfsopipi;
  
          vfsopipi.mp = mp;
  
          smp_rendezvous_cpus_retry(all_cpus,
              smp_no_rendezvous_barrier,
              vfs_op_action_func,
              smp_no_rendezvous_barrier,
              vfs_op_wait_func,
              &vfsopipi.srcra);
  }
  
  #ifdef DIAGNOSTIC
  void
  vfs_assert_mount_counters(struct mount *mp)
  {
          struct mount_pcpu *mpcpu;
          int cpu;
  
          if (mp->mnt_vfs_ops == 0)
                  return;
  
          CPU_FOREACH(cpu) {
                  mpcpu = vfs_mount_pcpu_remote(mp, cpu);
                  if (mpcpu->mntp_ref != 0 ||
                      mpcpu->mntp_lockref != 0 ||
                      mpcpu->mntp_writeopcount != 0)
                          vfs_dump_mount_counters(mp);
          }
  }
  
  void
  vfs_dump_mount_counters(struct mount *mp)
  {
          struct mount_pcpu *mpcpu;
          int ref, lockref, writeopcount;
          int cpu;
  
          printf("%s: mp %p vfs_ops %d\n", __func__, mp, mp->mnt_vfs_ops);
  
          printf("        ref : ");
          ref = mp->mnt_ref;
          CPU_FOREACH(cpu) {
                  mpcpu = vfs_mount_pcpu_remote(mp, cpu);
                  printf("%d ", mpcpu->mntp_ref);
                  ref += mpcpu->mntp_ref;
          }
          printf("\n");
          printf("    lockref : ");
          lockref = mp->mnt_lockref;
          CPU_FOREACH(cpu) {
                  mpcpu = vfs_mount_pcpu_remote(mp, cpu);
                  printf("%d ", mpcpu->mntp_lockref);
                  lockref += mpcpu->mntp_lockref;
          }
          printf("\n");
          printf("writeopcount: ");
          writeopcount = mp->mnt_writeopcount;
          CPU_FOREACH(cpu) {
                  mpcpu = vfs_mount_pcpu_remote(mp, cpu);
                  printf("%d ", mpcpu->mntp_writeopcount);
                  writeopcount += mpcpu->mntp_writeopcount;
          }
          printf("\n");
  
          printf("counter       struct total\n");
          printf("ref             %-5d  %-5d\n", mp->mnt_ref, ref);
          printf("lockref         %-5d  %-5d\n", mp->mnt_lockref, lockref);
          printf("writeopcount    %-5d  %-5d\n", mp->mnt_writeopcount, writeopcount);
  
          panic("invalid counts on struct mount");
  }
  #endif
  
  int
  vfs_mount_fetch_counter(struct mount *mp, enum mount_counter which)
  {
          struct mount_pcpu *mpcpu;
          int cpu, sum;
  
          switch (which) {
          case MNT_COUNT_REF:
                  sum = mp->mnt_ref;
                  break;
          case MNT_COUNT_LOCKREF:
                  sum = mp->mnt_lockref;
                  break;
          case MNT_COUNT_WRITEOPCOUNT:
                  sum = mp->mnt_writeopcount;
                  break;
          }
  
          CPU_FOREACH(cpu) {
                  mpcpu = vfs_mount_pcpu_remote(mp, cpu);
                  switch (which) {
                  case MNT_COUNT_REF:
                          sum += mpcpu->mntp_ref;
                          break;
                  case MNT_COUNT_LOCKREF:
                          sum += mpcpu->mntp_lockref;
                          break;
                  case MNT_COUNT_WRITEOPCOUNT:
                          sum += mpcpu->mntp_writeopcount;
                          break;
                  }
          }
          return (sum);
  }
  
  static bool
  deferred_unmount_enqueue(struct mount *mp, uint64_t flags, bool requeue,
      int timeout_ticks)
  {
          bool enqueued;
  
          enqueued = false;
          mtx_lock(&deferred_unmount_lock);
          if ((mp->mnt_taskqueue_flags & MNT_DEFERRED) == 0 || requeue) {
                  mp->mnt_taskqueue_flags = flags | MNT_DEFERRED;
                  STAILQ_INSERT_TAIL(&deferred_unmount_list, mp,
                      mnt_taskqueue_link);
                  enqueued = true;
          }
          mtx_unlock(&deferred_unmount_lock);
  
          if (enqueued) {
                  taskqueue_enqueue_timeout(taskqueue_deferred_unmount,
                      &deferred_unmount_task, timeout_ticks);
          }
  
          return (enqueued);
  }
  
  /*
   * Taskqueue handler for processing async/recursive unmounts
   */
  static void
  vfs_deferred_unmount(void *argi __unused, int pending __unused)
  {
          STAILQ_HEAD(, mount) local_unmounts;
          uint64_t flags;
          struct mount *mp, *tmp;
          int error;
          unsigned int retries;
          bool unmounted;
  
          STAILQ_INIT(&local_unmounts);
          mtx_lock(&deferred_unmount_lock);
          STAILQ_CONCAT(&local_unmounts, &deferred_unmount_list); 
          mtx_unlock(&deferred_unmount_lock);
  
          STAILQ_FOREACH_SAFE(mp, &local_unmounts, mnt_taskqueue_link, tmp) {
                  flags = mp->mnt_taskqueue_flags;
                  KASSERT((flags & MNT_DEFERRED) != 0,
                      ("taskqueue unmount without MNT_DEFERRED"));
                  error = dounmount(mp, flags, curthread);
                  if (error != 0) {
                          MNT_ILOCK(mp);
                          unmounted = ((mp->mnt_kern_flag & MNTK_REFEXPIRE) != 0);
                          MNT_IUNLOCK(mp);
  
                          /*
                           * The deferred unmount thread is the only thread that
                           * modifies the retry counts, so locking/atomics aren't
                           * needed here.
                           */
                          retries = (mp->mnt_unmount_retries)++;
                          deferred_unmount_total_retries++;
                          if (!unmounted && retries < deferred_unmount_retry_limit) {
                                  deferred_unmount_enqueue(mp, flags, true,
                                      -deferred_unmount_retry_delay_hz);
                          } else {
                                  if (retries >= deferred_unmount_retry_limit) {
                                          printf("giving up on deferred unmount "
                                              "of %s after %d retries, error %d\n",
                                              mp->mnt_stat.f_mntonname, retries, error);
                                  }
                                  vfs_rel(mp);
                          }
                  }
          }
  }
  
  /*
   * Do the actual filesystem unmount.
   */
  int
  dounmount(struct mount *mp, uint64_t flags, struct thread *td)
  {
          struct mount_upper_node *upper;
          struct vnode *coveredvp, *rootvp;
          int error;
          uint64_t async_flag;
          int mnt_gen_r;
          unsigned int retries;
  
          KASSERT((flags & MNT_DEFERRED) == 0 ||
              (flags & (MNT_RECURSE | MNT_FORCE)) == (MNT_RECURSE | MNT_FORCE),
              ("MNT_DEFERRED requires MNT_RECURSE | MNT_FORCE"));
  
          /*
           * If the caller has explicitly requested the unmount to be handled by
           * the taskqueue and we're not already in taskqueue context, queue
           * up the unmount request and exit.  This is done prior to any
           * credential checks; MNT_DEFERRED should be used only for kernel-
           * initiated unmounts and will therefore be processed with the
           * (kernel) credentials of the taskqueue thread.  Still, callers
           * should be sure this is the behavior they want.
           */
          if ((flags & MNT_DEFERRED) != 0 &&
              taskqueue_member(taskqueue_deferred_unmount, curthread) == 0) {
                  if (!deferred_unmount_enqueue(mp, flags, false, 0))
                          vfs_rel(mp);
                  return (EINPROGRESS);
          }
  
          /*
           * Only privileged root, or (if MNT_USER is set) the user that did the
           * original mount is permitted to unmount this filesystem.
           * This check should be made prior to queueing up any recursive
           * unmounts of upper filesystems.  Those unmounts will be executed
           * with kernel thread credentials and are expected to succeed, so
           * we must at least ensure the originating context has sufficient
           * privilege to unmount the base filesystem before proceeding with
           * the uppers.
           */
          error = vfs_suser(mp, td);
          if (error != 0) {
                  KASSERT((flags & MNT_DEFERRED) == 0,
                      ("taskqueue unmount with insufficient privilege"));
                  vfs_rel(mp);
                  return (error);
          }
  
          if (recursive_forced_unmount && ((flags & MNT_FORCE) != 0))
                  flags |= MNT_RECURSE;
  
          if ((flags & MNT_RECURSE) != 0) {
                  KASSERT((flags & MNT_FORCE) != 0,
                      ("MNT_RECURSE requires MNT_FORCE"));
  
                  MNT_ILOCK(mp);
                  /*
                   * Set MNTK_RECURSE to prevent new upper mounts from being
                   * added, and note that an operation on the uppers list is in
                   * progress.  This will ensure that unregistration from the
                   * uppers list, and therefore any pending unmount of the upper
                   * FS, can't complete until after we finish walking the list.
                   */
                  mp->mnt_kern_flag |= MNTK_RECURSE;
                  mp->mnt_upper_pending++;
                  TAILQ_FOREACH(upper, &mp->mnt_uppers, mnt_upper_link) {
                          retries = upper->mp->mnt_unmount_retries;
                          if (retries > deferred_unmount_retry_limit) {
                                  error = EBUSY;
                                  continue;
                          }
                          MNT_IUNLOCK(mp);
  
                          vfs_ref(upper->mp);
                          if (!deferred_unmount_enqueue(upper->mp, flags,
                              false, 0))
                                  vfs_rel(upper->mp);
                          MNT_ILOCK(mp);
                  }
                  mp->mnt_upper_pending--;
                  if ((mp->mnt_kern_flag & MNTK_UPPER_WAITER) != 0 &&
                      mp->mnt_upper_pending == 0) {
                          mp->mnt_kern_flag &= ~MNTK_UPPER_WAITER;
                          wakeup(&mp->mnt_uppers);
                  }
  
                  /*
                   * If we're not on the taskqueue, wait until the uppers list
                   * is drained before proceeding with unmount.  Otherwise, if
                   * we are on the taskqueue and there are still pending uppers,
                   * just re-enqueue on the end of the taskqueue.
                   */
                  if ((flags & MNT_DEFERRED) == 0) {
                          while (error == 0 && !TAILQ_EMPTY(&mp->mnt_uppers)) {
                                  mp->mnt_kern_flag |= MNTK_TASKQUEUE_WAITER;
                                  error = msleep(&mp->mnt_taskqueue_link,
                                      MNT_MTX(mp), PCATCH, "umntqw", 0);
                          }
                          if (error != 0) {
                                  MNT_REL(mp);
                                  MNT_IUNLOCK(mp);
                                  return (error);
                          }
                  } else if (!TAILQ_EMPTY(&mp->mnt_uppers)) {
                          MNT_IUNLOCK(mp);
                          if (error == 0)
                                  deferred_unmount_enqueue(mp, flags, true, 0);
                          return (error);
                  }
                  MNT_IUNLOCK(mp);
                  KASSERT(TAILQ_EMPTY(&mp->mnt_uppers), ("mnt_uppers not empty"));
          }
  
          /* Allow the taskqueue to safely re-enqueue on failure */
          if ((flags & MNT_DEFERRED) != 0)
                  vfs_ref(mp);
  
          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);
                          vdrop(coveredvp);
                          vfs_rel(mp);
                          return (EBUSY);
                  }
          }
  
          vfs_op_enter(mp);
  
          vn_start_write(NULL, &mp, V_WAIT);
          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;
          rootvp = vfs_cache_root_clear(mp);
          if (coveredvp != NULL)
                  vn_seqc_write_begin(coveredvp);
          if (flags & MNT_NONBUSY) {
                  MNT_IUNLOCK(mp);
                  error = vfs_check_usecounts(mp);
                  MNT_ILOCK(mp);
                  if (error != 0) {
                          vn_seqc_write_end(coveredvp);
                          dounmount_cleanup(mp, coveredvp, MNTK_UNMOUNT);
                          if (rootvp != NULL) {
                                  vn_seqc_write_end(rootvp);
                                  vrele(rootvp);
                          }
                          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__));
  
          /*
           * We want to keep the vnode around so that we can vn_seqc_write_end
           * after we are done with unmount. Downgrade our reference to a mere
           * hold count so that we don't interefere with anything.
           */
          if (rootvp != NULL) {
                  vhold(rootvp);
                  vrele(rootvp);
          }
  
          if (mp->mnt_flag & MNT_EXPUBLIC)
                  vfs_setpublicfs(NULL, NULL, NULL);
  
          vfs_periodic(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);
          vfs_deallocate_syncvnode(mp);
          error = VFS_UNMOUNT(mp, flags);
          vn_finished_write(mp);
          vfs_rel(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);
                  }
                  vfs_op_exit_locked(mp);
                  MNT_IUNLOCK(mp);
                  if (coveredvp) {
                          vn_seqc_write_end(coveredvp);
                          VOP_UNLOCK(coveredvp);
                          vdrop(coveredvp);
                  }
                  if (rootvp != NULL) {
                          vn_seqc_write_end(rootvp);
                          vdrop(rootvp);
                  }
                  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) {
                  VI_LOCK(coveredvp);
                  vn_irflag_unset_locked(coveredvp, VIRF_MOUNTPOINT);
                  coveredvp->v_mountedhere = NULL;
                  vn_seqc_write_end_locked(coveredvp);
                  VI_UNLOCK(coveredvp);
                  VOP_UNLOCK(coveredvp);
                  vdrop(coveredvp);
          }
          mount_devctl_event("UNMOUNT", mp, false);
          if (rootvp != NULL) {
                  vn_seqc_write_end(rootvp);
                  vdrop(rootvp);
          }
          vfs_event_signal(NULL, VQ_UNMOUNT, 0);
          if (rootvnode != NULL && mp == rootvnode->v_mount) {
                  vrele(rootvnode);
                  rootvnode = NULL;
          }
          if (mp == rootdevmp)
                  rootdevmp = NULL;
          if ((flags & MNT_DEFERRED) != 0)
                  vfs_rel(mp);
          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)
  {
          /*
           * Filesystems only fill in part of the structure for updates, we
           * have to read the entirety first to get all content.
           */
          if (sbp != &mp->mnt_stat)
                  memcpy(sbp, &mp->mnt_stat, sizeof(*sbp));
  
          /*
           * Set these in case the underlying filesystem fails to do so.
           */
          sbp->f_version = STATFS_VERSION;
          sbp->f_namemax = NAME_MAX;
          sbp->f_flags = mp->mnt_flag & MNT_VISFLAGMASK;
          sbp->f_nvnodelistsize = mp->mnt_nvnodelistsize;
  
          return (mp->mnt_op->vfs_statfs(mp, sbp));
  }
  
  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->error != 0 || ma->v != NULL, ("kernel_mount NULL ma->v"));
          KASSERT(!(ma->len & 1), ("kernel_mount odd ma->len (%d)", ma->len));
  
          error = ma->error;
          if (error == 0) {
                  auio.uio_iov = ma->v;
                  auio.uio_iovcnt = ma->len;
                  auio.uio_segflg = UIO_SYSSPACE;
                  error = vfs_donmount(curthread, flags, &auio);
          }
          free_mntarg(ma);
          return (error);
  }
  
  /* Map from mount options to printable formats. */
  static struct mntoptnames optnames[] = {
          MNTOPT_NAMES
  };
  
  #define DEVCTL_LEN 1024
  static void
  mount_devctl_event(const char *type, struct mount *mp, bool donew)
  {
          const uint8_t *cp;
          struct mntoptnames *fp;
          struct sbuf sb;
          struct statfs *sfp = &mp->mnt_stat;
          char *buf;
  
          buf = malloc(DEVCTL_LEN, M_MOUNT, M_NOWAIT);
          if (buf == NULL)
                  return;
          sbuf_new(&sb, buf, DEVCTL_LEN, SBUF_FIXEDLEN);
          sbuf_cpy(&sb, "mount-point=\"");
          devctl_safe_quote_sb(&sb, sfp->f_mntonname);
          sbuf_cat(&sb, "\" mount-dev=\"");
          devctl_safe_quote_sb(&sb, sfp->f_mntfromname);
          sbuf_cat(&sb, "\" mount-type=\"");
          devctl_safe_quote_sb(&sb, sfp->f_fstypename);
          sbuf_cat(&sb, "\" fsid=0x");
          cp = (const uint8_t *)&sfp->f_fsid.val[0];
          for (int i = 0; i < sizeof(sfp->f_fsid); i++)
                  sbuf_printf(&sb, "%02x", cp[i]);
          sbuf_printf(&sb, " owner=%u flags=\"", sfp->f_owner);
          for (fp = optnames; fp->o_opt != 0; fp++) {
                  if ((mp->mnt_flag & fp->o_opt) != 0) {
                          sbuf_cat(&sb, fp->o_name);
                          sbuf_putc(&sb, ';');
                  }
          }
          sbuf_putc(&sb, '"');
          sbuf_finish(&sb);
  
          /*
           * Options are not published because the form of the options depends on
           * the file system and may include binary data. In addition, they don't
           * necessarily provide enough useful information to be actionable when
           * devd processes them.
           */
  
          if (sbuf_error(&sb) == 0)
                  devctl_notify("VFS", "FS", type, sbuf_data(&sb));
          sbuf_delete(&sb);
          free(buf, M_MOUNT);
  }
  
  /*
   * Force remount specified mount point to read-only.  The argument
   * must be busied to avoid parallel unmount attempts.
   *
   * Intended use is to prevent further writes if some metadata
   * inconsistency is detected.  Note that the function still flushes
   * all cached metadata and data for the mount point, which might be
   * not always suitable.
   */
  int
  vfs_remount_ro(struct mount *mp)
  {
          struct vfsoptlist *opts;
          struct vfsopt *opt;
          struct vnode *vp_covered, *rootvp;
          int error;
  
          KASSERT(mp->mnt_lockref > 0,
              ("vfs_remount_ro: mp %p is not busied", mp));
          KASSERT((mp->mnt_kern_flag & MNTK_UNMOUNT) == 0,
              ("vfs_remount_ro: mp %p is being unmounted (and busy?)", mp));
  
          rootvp = NULL;
          vp_covered = mp->mnt_vnodecovered;
          error = vget(vp_covered, LK_EXCLUSIVE | LK_NOWAIT);
          if (error != 0)
                  return (error);
          VI_LOCK(vp_covered);
          if ((vp_covered->v_iflag & VI_MOUNT) != 0) {
                  VI_UNLOCK(vp_covered);
                  vput(vp_covered);
                  return (EBUSY);
          }
          vp_covered->v_iflag |= VI_MOUNT;
          VI_UNLOCK(vp_covered);
          vfs_op_enter(mp);
          vn_seqc_write_begin(vp_covered);
  
          MNT_ILOCK(mp);
          if ((mp->mnt_flag & MNT_RDONLY) != 0) {
                  MNT_IUNLOCK(mp);
                  error = EBUSY;
                  goto out;
          }
          mp->mnt_flag |= MNT_UPDATE | MNT_FORCE | MNT_RDONLY;
          rootvp = vfs_cache_root_clear(mp);
          MNT_IUNLOCK(mp);
  
          opts = malloc(sizeof(struct vfsoptlist), M_MOUNT, M_WAITOK | M_ZERO);
          TAILQ_INIT(opts);
          opt = malloc(sizeof(struct vfsopt), M_MOUNT, M_WAITOK | M_ZERO);
          opt->name = strdup("ro", M_MOUNT);
          opt->value = NULL;
          TAILQ_INSERT_TAIL(opts, opt, link);
          vfs_mergeopts(opts, mp->mnt_opt);
          mp->mnt_optnew = opts;
  
          error = VFS_MOUNT(mp);
  
          if (error == 0) {
                  MNT_ILOCK(mp);
                  mp->mnt_flag &= ~(MNT_UPDATE | MNT_FORCE);
                  MNT_IUNLOCK(mp);
                  vfs_deallocate_syncvnode(mp);
                  if (mp->mnt_opt != NULL)
                          vfs_freeopts(mp->mnt_opt);
                  mp->mnt_opt = mp->mnt_optnew;
          } else {
                  MNT_ILOCK(mp);
                  mp->mnt_flag &= ~(MNT_UPDATE | MNT_FORCE | MNT_RDONLY);
                  MNT_IUNLOCK(mp);
                  vfs_freeopts(mp->mnt_optnew);
          }
          mp->mnt_optnew = NULL;
  
  out:
          vfs_op_exit(mp);
          VI_LOCK(vp_covered);
          vp_covered->v_iflag &= ~VI_MOUNT;
          VI_UNLOCK(vp_covered);
          vput(vp_covered);
          vn_seqc_write_end(vp_covered);
          if (rootvp != NULL) {
                  vn_seqc_write_end(rootvp);
                  vrele(rootvp);
          }
          return (error);
  }
  
  /*
   * 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: e7814fc474028e18cda091d7a7258251