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

     /*
      * 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 REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      @(#)vfs_syscalls.c      8.13 (Berkeley) 4/15/94
     * $FreeBSD: src/sys/kern/vfs_syscalls.c,v 1.151.2.18 2003/04/04 20:35:58 tegge Exp $
     */
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/buf.h>
    #include <sys/conf.h>
    #include <sys/sysent.h>
    #include <sys/malloc.h>
    #include <sys/mount.h>
    #include <sys/mountctl.h>
    #include <sys/sysproto.h>
    #include <sys/filedesc.h>
    #include <sys/kernel.h>
    #include <sys/fcntl.h>
    #include <sys/file.h>
    #include <sys/linker.h>
    #include <sys/stat.h>
    #include <sys/unistd.h>
    #include <sys/vnode.h>
    #include <sys/proc.h>
    #include <sys/priv.h>
    #include <sys/jail.h>
    #include <sys/namei.h>
    #include <sys/nlookup.h>
    #include <sys/dirent.h>
    #include <sys/extattr.h>
    #include <sys/spinlock.h>
    #include <sys/kern_syscall.h>
    #include <sys/objcache.h>
    #include <sys/sysctl.h>
    
    #include <sys/buf2.h>
    #include <sys/file2.h>
    #include <sys/spinlock2.h>
    #include <sys/mplock2.h>
    
    #include <vm/vm.h>
    #include <vm/vm_object.h>
    #include <vm/vm_page.h>
    
    #include <machine/limits.h>
    #include <machine/stdarg.h>
    
    #include <vfs/union/union.h>
    
    static void mount_warning(struct mount *mp, const char *ctl, ...)
                    __printflike(2, 3);
    static int mount_path(struct proc *p, struct mount *mp, char **rb, char **fb);
    static int checkvp_chdir (struct vnode *vn, struct thread *td);
    static void checkdirs (struct nchandle *old_nch, struct nchandle *new_nch);
    static int chroot_refuse_vdir_fds (struct filedesc *fdp);
    static int chroot_visible_mnt(struct mount *mp, struct proc *p);
    static int getutimes (const struct timeval *, struct timespec *);
    static int setfown (struct mount *, struct vnode *, uid_t, gid_t);
    static int setfmode (struct vnode *, int);
    static int setfflags (struct vnode *, int);
    static int setutimes (struct vnode *, struct vattr *,
                            const struct timespec *, int);
    static int      usermount = 0;  /* if 1, non-root can mount fs. */
    
    int (*union_dircheckp) (struct thread *, struct vnode **, struct file *);
    
    SYSCTL_INT(_vfs, OID_AUTO, usermount, CTLFLAG_RW, &usermount, 0,
        "Allow non-root users to mount filesystems");
   
   /*
    * Virtual File System System Calls
    */
   
   /*
    * Mount a file system.
    *
    * mount_args(char *type, char *path, int flags, caddr_t data)
    *
    * MPALMOSTSAFE
    */
   int
   sys_mount(struct mount_args *uap)
   {
           struct thread *td = curthread;
           struct vnode *vp;
           struct nchandle nch;
           struct mount *mp, *nullmp;
           struct vfsconf *vfsp;
           int error, flag = 0, flag2 = 0;
           int hasmount;
           struct vattr va;
           struct nlookupdata nd;
           char fstypename[MFSNAMELEN];
           struct ucred *cred;
   
           cred = td->td_ucred;
           if (jailed(cred)) {
                   error = EPERM;
                   goto done;
           }
           if (usermount == 0 && (error = priv_check(td, PRIV_ROOT)))
                   goto done;
   
           /*
            * Do not allow NFS export by non-root users.
            */
           if (uap->flags & MNT_EXPORTED) {
                   error = priv_check(td, PRIV_ROOT);
                   if (error)
                           goto done;
           }
           /*
            * Silently enforce MNT_NOSUID and MNT_NODEV for non-root users
            */
           if (priv_check(td, PRIV_ROOT)) 
                   uap->flags |= MNT_NOSUID | MNT_NODEV;
   
           /*
            * Lookup the requested path and extract the nch and vnode.
            */
           error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
           if (error == 0) {
                   if ((error = nlookup(&nd)) == 0) {
                           if (nd.nl_nch.ncp->nc_vp == NULL)
                                   error = ENOENT;
                   }
           }
           if (error) {
                   nlookup_done(&nd);
                   goto done;
           }
   
           /*
            * If the target filesystem is resolved via a nullfs mount, then
            * nd.nl_nch.mount will be pointing to the nullfs mount structure
            * instead of the target file system. We need it in case we are
            * doing an update.
            */
           nullmp = nd.nl_nch.mount;
   
           /*
            * Extract the locked+refd ncp and cleanup the nd structure
            */
           nch = nd.nl_nch;
           cache_zero(&nd.nl_nch);
           nlookup_done(&nd);
   
           if ((nch.ncp->nc_flag & NCF_ISMOUNTPT) &&
               (mp = cache_findmount(&nch)) != NULL) {
                   cache_dropmount(mp);
                   hasmount = 1;
           } else {
                   hasmount = 0;
           }
   
   
           /*
            * now we have the locked ref'd nch and unreferenced vnode.
            */
           vp = nch.ncp->nc_vp;
           if ((error = vget(vp, LK_EXCLUSIVE)) != 0) {
                   cache_put(&nch);
                   goto done;
           }
           cache_unlock(&nch);
   
           /*
            * Extract the file system type. We need to know this early, to take
            * appropriate actions if we are dealing with a nullfs.
            */
           if ((error = copyinstr(uap->type, fstypename, MFSNAMELEN, NULL)) != 0) {
                   cache_drop(&nch);
                   vput(vp);
                   goto done;
           }
   
           /*
            * Now we have an unlocked ref'd nch and a locked ref'd vp
            */
           if (uap->flags & MNT_UPDATE) {
                   if ((vp->v_flag & (VROOT|VPFSROOT)) == 0) {
                           cache_drop(&nch);
                           vput(vp);
                           error = EINVAL;
                           goto done;
                   }
   
                   if (strncmp(fstypename, "null", 5) == 0) {
                           KKASSERT(nullmp);
                           mp = nullmp;
                   } else {
                           mp = vp->v_mount;
                   }
   
                   flag = mp->mnt_flag;
                   flag2 = mp->mnt_kern_flag;
                   /*
                    * We only allow the filesystem to be reloaded if it
                    * is currently mounted read-only.
                    */
                   if ((uap->flags & MNT_RELOAD) &&
                       ((mp->mnt_flag & MNT_RDONLY) == 0)) {
                           cache_drop(&nch);
                           vput(vp);
                           error = EOPNOTSUPP;     /* Needs translation */
                           goto done;
                   }
                   /*
                    * Only root, or the user that did the original mount is
                    * permitted to update it.
                    */
                   if (mp->mnt_stat.f_owner != cred->cr_uid &&
                       (error = priv_check(td, PRIV_ROOT))) {
                           cache_drop(&nch);
                           vput(vp);
                           goto done;
                   }
                   if (vfs_busy(mp, LK_NOWAIT)) {
                           cache_drop(&nch);
                           vput(vp);
                           error = EBUSY;
                           goto done;
                   }
                   if (hasmount) {
                           cache_drop(&nch);
                           vfs_unbusy(mp);
                           vput(vp);
                           error = EBUSY;
                           goto done;
                   }
                   mp->mnt_flag |=
                       uap->flags & (MNT_RELOAD | MNT_FORCE | MNT_UPDATE);
                   lwkt_gettoken(&mp->mnt_token);
                   vn_unlock(vp);
                   goto update;
           }
   
           /*
            * If the user is not root, ensure that they own the directory
            * onto which we are attempting to mount.
            */
           if ((error = VOP_GETATTR(vp, &va)) ||
               (va.va_uid != cred->cr_uid &&
                (error = priv_check(td, PRIV_ROOT)))) {
                   cache_drop(&nch);
                   vput(vp);
                   goto done;
           }
           if ((error = vinvalbuf(vp, V_SAVE, 0, 0)) != 0) {
                   cache_drop(&nch);
                   vput(vp);
                   goto done;
           }
           if (vp->v_type != VDIR) {
                   cache_drop(&nch);
                   vput(vp);
                   error = ENOTDIR;
                   goto done;
           }
           if (vp->v_mount->mnt_kern_flag & MNTK_NOSTKMNT) {
                   cache_drop(&nch);
                   vput(vp);
                   error = EPERM;
                   goto done;
           }
           vfsp = vfsconf_find_by_name(fstypename);
           if (vfsp == NULL) {
                   linker_file_t lf;
   
                   /* Only load modules for root (very important!) */
                   if ((error = priv_check(td, PRIV_ROOT)) != 0) {
                           cache_drop(&nch);
                           vput(vp);
                           goto done;
                   }
                   error = linker_load_file(fstypename, &lf);
                   if (error || lf == NULL) {
                           cache_drop(&nch);
                           vput(vp);
                           if (lf == NULL)
                                   error = ENODEV;
                           goto done;
                   }
                   lf->userrefs++;
                   /* lookup again, see if the VFS was loaded */
                   vfsp = vfsconf_find_by_name(fstypename);
                   if (vfsp == NULL) {
                           lf->userrefs--;
                           linker_file_unload(lf);
                           cache_drop(&nch);
                           vput(vp);
                           error = ENODEV;
                           goto done;
                   }
           }
           if (hasmount) {
                   cache_drop(&nch);
                   vput(vp);
                   error = EBUSY;
                   goto done;
           }
   
           /*
            * Allocate and initialize the filesystem.
            */
           mp = kmalloc(sizeof(struct mount), M_MOUNT, M_ZERO|M_WAITOK);
           mount_init(mp);
           vfs_busy(mp, LK_NOWAIT);
           mp->mnt_op = vfsp->vfc_vfsops;
           mp->mnt_vfc = vfsp;
           vfsp->vfc_refcount++;
           mp->mnt_stat.f_type = vfsp->vfc_typenum;
           mp->mnt_flag |= vfsp->vfc_flags & MNT_VISFLAGMASK;
           strncpy(mp->mnt_stat.f_fstypename, vfsp->vfc_name, MFSNAMELEN);
           mp->mnt_stat.f_owner = cred->cr_uid;
           lwkt_gettoken(&mp->mnt_token);
           vn_unlock(vp);
   update:
           /*
            * (per-mount token acquired at this point)
            *
            * Set the mount level flags.
            */
           if (uap->flags & MNT_RDONLY)
                   mp->mnt_flag |= MNT_RDONLY;
           else if (mp->mnt_flag & MNT_RDONLY)
                   mp->mnt_kern_flag |= MNTK_WANTRDWR;
           mp->mnt_flag &=~ (MNT_NOSUID | MNT_NOEXEC | MNT_NODEV |
               MNT_SYNCHRONOUS | MNT_UNION | MNT_ASYNC | MNT_NOATIME |
               MNT_NOSYMFOLLOW | MNT_IGNORE | MNT_TRIM |
               MNT_NOCLUSTERR | MNT_NOCLUSTERW | MNT_SUIDDIR);
           mp->mnt_flag |= uap->flags & (MNT_NOSUID | MNT_NOEXEC |
               MNT_NODEV | MNT_SYNCHRONOUS | MNT_UNION | MNT_ASYNC | MNT_FORCE |
               MNT_NOSYMFOLLOW | MNT_IGNORE | MNT_TRIM |
               MNT_NOATIME | MNT_NOCLUSTERR | MNT_NOCLUSTERW | MNT_SUIDDIR);
           /*
            * Mount the filesystem.
            * XXX The final recipients of VFS_MOUNT just overwrite the ndp they
            * get. 
            */
           error = VFS_MOUNT(mp, uap->path, uap->data, cred);
           if (mp->mnt_flag & MNT_UPDATE) {
                   if (mp->mnt_kern_flag & MNTK_WANTRDWR)
                           mp->mnt_flag &= ~MNT_RDONLY;
                   mp->mnt_flag &=~ (MNT_UPDATE | MNT_RELOAD | MNT_FORCE);
                   mp->mnt_kern_flag &=~ MNTK_WANTRDWR;
                   if (error) {
                           mp->mnt_flag = flag;
                           mp->mnt_kern_flag = flag2;
                   }
                   lwkt_reltoken(&mp->mnt_token);
                   vfs_unbusy(mp);
                   vrele(vp);
                   cache_drop(&nch);
                   goto done;
           }
           vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
   
           /*
            * Put the new filesystem on the mount list after root.  The mount
            * point gets its own mnt_ncmountpt (unless the VFS already set one
            * up) which represents the root of the mount.  The lookup code
            * detects the mount point going forward and checks the root of
            * the mount going backwards.
            *
            * It is not necessary to invalidate or purge the vnode underneath
            * because elements under the mount will be given their own glue
            * namecache record.
            */
           if (!error) {
                   if (mp->mnt_ncmountpt.ncp == NULL) {
                           /* 
                            * allocate, then unlock, but leave the ref intact 
                            */
                           cache_allocroot(&mp->mnt_ncmountpt, mp, NULL);
                           cache_unlock(&mp->mnt_ncmountpt);
                   }
                   mp->mnt_ncmounton = nch;                /* inherits ref */
                   nch.ncp->nc_flag |= NCF_ISMOUNTPT;
                   cache_ismounting(mp);
   
                   mountlist_insert(mp, MNTINS_LAST);
                   vn_unlock(vp);
                   checkdirs(&mp->mnt_ncmounton, &mp->mnt_ncmountpt);
                   error = vfs_allocate_syncvnode(mp);
                   lwkt_reltoken(&mp->mnt_token);
                   vfs_unbusy(mp);
                   error = VFS_START(mp, 0);
                   vrele(vp);
           } else {
                   vn_syncer_thr_stop(mp);
                   vfs_rm_vnodeops(mp, NULL, &mp->mnt_vn_coherency_ops);
                   vfs_rm_vnodeops(mp, NULL, &mp->mnt_vn_journal_ops);
                   vfs_rm_vnodeops(mp, NULL, &mp->mnt_vn_norm_ops);
                   vfs_rm_vnodeops(mp, NULL, &mp->mnt_vn_spec_ops);
                   vfs_rm_vnodeops(mp, NULL, &mp->mnt_vn_fifo_ops);
                   mp->mnt_vfc->vfc_refcount--;
                   lwkt_reltoken(&mp->mnt_token);
                   vfs_unbusy(mp);
                   kfree(mp, M_MOUNT);
                   cache_drop(&nch);
                   vput(vp);
           }
   done:
           return (error);
   }
   
   /*
    * Scan all active processes to see if any of them have a current
    * or root directory onto which the new filesystem has just been
    * mounted. If so, replace them with the new mount point.
    *
    * Both old_nch and new_nch are ref'd on call but not locked.
    * new_nch must be temporarily locked so it can be associated with the
    * vnode representing the root of the mount point.
    */
   struct checkdirs_info {
           struct nchandle old_nch;
           struct nchandle new_nch;
           struct vnode *old_vp;
           struct vnode *new_vp;
   };
   
   static int checkdirs_callback(struct proc *p, void *data);
   
   static void
   checkdirs(struct nchandle *old_nch, struct nchandle *new_nch)
   {
           struct checkdirs_info info;
           struct vnode *olddp;
           struct vnode *newdp;
           struct mount *mp;
   
           /*
            * If the old mount point's vnode has a usecount of 1, it is not
            * being held as a descriptor anywhere.
            */
           olddp = old_nch->ncp->nc_vp;
           if (olddp == NULL || VREFCNT(olddp) == 1)
                   return;
   
           /*
            * Force the root vnode of the new mount point to be resolved
            * so we can update any matching processes.
            */
           mp = new_nch->mount;
           if (VFS_ROOT(mp, &newdp))
                   panic("mount: lost mount");
           vn_unlock(newdp);
           cache_lock(new_nch);
           vn_lock(newdp, LK_EXCLUSIVE | LK_RETRY);
           cache_setunresolved(new_nch);
           cache_setvp(new_nch, newdp);
           cache_unlock(new_nch);
   
           /*
            * Special handling of the root node
            */
           if (rootvnode == olddp) {
                   vref(newdp);
                   vfs_cache_setroot(newdp, cache_hold(new_nch));
           }
   
           /*
            * Pass newdp separately so the callback does not have to access
            * it via new_nch->ncp->nc_vp.
            */
           info.old_nch = *old_nch;
           info.new_nch = *new_nch;
           info.new_vp = newdp;
           allproc_scan(checkdirs_callback, &info);
           vput(newdp);
   }
   
   /*
    * NOTE: callback is not MP safe because the scanned process's filedesc
    * structure can be ripped out from under us, amoung other things.
    */
   static int
   checkdirs_callback(struct proc *p, void *data)
   {
           struct checkdirs_info *info = data;
           struct filedesc *fdp;
           struct nchandle ncdrop1;
           struct nchandle ncdrop2;
           struct vnode *vprele1;
           struct vnode *vprele2;
   
           if ((fdp = p->p_fd) != NULL) {
                   cache_zero(&ncdrop1);
                   cache_zero(&ncdrop2);
                   vprele1 = NULL;
                   vprele2 = NULL;
   
                   /*
                    * MPUNSAFE - XXX fdp can be pulled out from under a
                    * foreign process.
                    *
                    * A shared filedesc is ok, we don't have to copy it
                    * because we are making this change globally.
                    */
                   spin_lock(&fdp->fd_spin);
                   if (fdp->fd_ncdir.mount == info->old_nch.mount &&
                       fdp->fd_ncdir.ncp == info->old_nch.ncp) {
                           vprele1 = fdp->fd_cdir;
                           vref(info->new_vp);
                           fdp->fd_cdir = info->new_vp;
                           ncdrop1 = fdp->fd_ncdir;
                           cache_copy(&info->new_nch, &fdp->fd_ncdir);
                   }
                   if (fdp->fd_nrdir.mount == info->old_nch.mount &&
                       fdp->fd_nrdir.ncp == info->old_nch.ncp) {
                           vprele2 = fdp->fd_rdir;
                           vref(info->new_vp);
                           fdp->fd_rdir = info->new_vp;
                           ncdrop2 = fdp->fd_nrdir;
                           cache_copy(&info->new_nch, &fdp->fd_nrdir);
                   }
                   spin_unlock(&fdp->fd_spin);
                   if (ncdrop1.ncp)
                           cache_drop(&ncdrop1);
                   if (ncdrop2.ncp)
                           cache_drop(&ncdrop2);
                   if (vprele1)
                           vrele(vprele1);
                   if (vprele2)
                           vrele(vprele2);
           }
           return(0);
   }
   
   /*
    * Unmount a file system.
    *
    * Note: unmount takes a path to the vnode mounted on as argument,
    * not special file (as before).
    *
    * umount_args(char *path, int flags)
    *
    * MPALMOSTSAFE
    */
   int
   sys_unmount(struct unmount_args *uap)
   {
           struct thread *td = curthread;
           struct proc *p __debugvar = td->td_proc;
           struct mount *mp = NULL;
           struct nlookupdata nd;
           int error;
   
           KKASSERT(p);
           get_mplock();
           if (td->td_ucred->cr_prison != NULL) {
                   error = EPERM;
                   goto done;
           }
           if (usermount == 0 && (error = priv_check(td, PRIV_ROOT)))
                   goto done;
   
           error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
           if (error == 0)
                   error = nlookup(&nd);
           if (error)
                   goto out;
   
           mp = nd.nl_nch.mount;
   
           /*
            * Only root, or the user that did the original mount is
            * permitted to unmount this filesystem.
            */
           if ((mp->mnt_stat.f_owner != td->td_ucred->cr_uid) &&
               (error = priv_check(td, PRIV_ROOT)))
                   goto out;
   
           /*
            * Don't allow unmounting the root file system.
            */
           if (mp->mnt_flag & MNT_ROOTFS) {
                   error = EINVAL;
                   goto out;
           }
   
           /*
            * Must be the root of the filesystem
            */
           if (nd.nl_nch.ncp != mp->mnt_ncmountpt.ncp) {
                   error = EINVAL;
                   goto out;
           }
   
   out:
           nlookup_done(&nd);
           if (error == 0)
                   error = dounmount(mp, uap->flags);
   done:
           rel_mplock();
           return (error);
   }
   
   /*
    * Do the actual file system unmount.
    */
   static int
   dounmount_interlock(struct mount *mp)
   {
           if (mp->mnt_kern_flag & MNTK_UNMOUNT)
                   return (EBUSY);
           mp->mnt_kern_flag |= MNTK_UNMOUNT;
           return(0);
   }
   
   static int
   unmount_allproc_cb(struct proc *p, void *arg)
   {
           struct mount *mp;
   
           if (p->p_textnch.ncp == NULL)
                   return 0;
   
           mp = (struct mount *)arg;
           if (p->p_textnch.mount == mp)
                   cache_drop(&p->p_textnch);
   
           return 0;
   }
   
   int
   dounmount(struct mount *mp, int flags)
   {
           struct namecache *ncp;
           struct nchandle nch;
           struct vnode *vp;
           int error;
           int async_flag;
           int lflags;
           int freeok = 1;
           int retry;
   
           lwkt_gettoken(&mp->mnt_token);
           /*
            * Exclusive access for unmounting purposes
            */
           if ((error = mountlist_interlock(dounmount_interlock, mp)) != 0)
                   goto out;
   
           /*
            * Allow filesystems to detect that a forced unmount is in progress.
            */
           if (flags & MNT_FORCE)
                   mp->mnt_kern_flag |= MNTK_UNMOUNTF;
           lflags = LK_EXCLUSIVE | ((flags & MNT_FORCE) ? 0 : LK_TIMELOCK);
           error = lockmgr(&mp->mnt_lock, lflags);
           if (error) {
                   mp->mnt_kern_flag &= ~(MNTK_UNMOUNT | MNTK_UNMOUNTF);
                   if (mp->mnt_kern_flag & MNTK_MWAIT) {
                           mp->mnt_kern_flag &= ~MNTK_MWAIT;
                           wakeup(mp);
                   }
                   goto out;
           }
   
           if (mp->mnt_flag & MNT_EXPUBLIC)
                   vfs_setpublicfs(NULL, NULL, NULL);
   
           vfs_msync(mp, MNT_WAIT);
           async_flag = mp->mnt_flag & MNT_ASYNC;
           mp->mnt_flag &=~ MNT_ASYNC;
   
           /*
            * If this filesystem isn't aliasing other filesystems,
            * try to invalidate any remaining namecache entries and
            * check the count afterwords.
            */
           if ((mp->mnt_kern_flag & MNTK_NCALIASED) == 0) {
                   cache_lock(&mp->mnt_ncmountpt);
                   cache_inval(&mp->mnt_ncmountpt, CINV_DESTROY|CINV_CHILDREN);
                   cache_unlock(&mp->mnt_ncmountpt);
   
                   if ((ncp = mp->mnt_ncmountpt.ncp) != NULL &&
                       (ncp->nc_refs != 1 || TAILQ_FIRST(&ncp->nc_list))) {
                           allproc_scan(&unmount_allproc_cb, mp);
                   }
   
                   if ((ncp = mp->mnt_ncmountpt.ncp) != NULL &&
                       (ncp->nc_refs != 1 || TAILQ_FIRST(&ncp->nc_list))) {
   
                           if ((flags & MNT_FORCE) == 0) {
                                   error = EBUSY;
                                   mount_warning(mp, "Cannot unmount: "
                                                     "%d namecache "
                                                     "references still "
                                                     "present",
                                                     ncp->nc_refs - 1);
                           } else {
                                   mount_warning(mp, "Forced unmount: "
                                                     "%d namecache "
                                                     "references still "
                                                     "present",
                                                     ncp->nc_refs - 1);
                                   freeok = 0;
                           }
                   }
           }
   
           /*
            * Decomission our special mnt_syncer vnode.  This also stops
            * the vnlru code.  If we are unable to unmount we recommission
            * the vnode.
            *
            * Then sync the filesystem.
            */
           if ((vp = mp->mnt_syncer) != NULL) {
                   mp->mnt_syncer = NULL;
                   atomic_set_int(&vp->v_refcnt, VREF_FINALIZE);
                   vrele(vp);
           }
           if ((mp->mnt_flag & MNT_RDONLY) == 0)
                   VFS_SYNC(mp, MNT_WAIT);
   
           /*
            * nchandle records ref the mount structure.  Expect a count of 1
            * (our mount->mnt_ncmountpt).
            *
            * Scans can get temporary refs on a mountpoint (thought really
            * heavy duty stuff like cache_findmount() do not).
            */
           for (retry = 0; retry < 10 && mp->mnt_refs != 1; ++retry) {
                   cache_unmounting(mp);
                   tsleep(&mp->mnt_refs, 0, "mntbsy", hz / 10 + 1);
           }
           if (mp->mnt_refs != 1) {
                   if ((flags & MNT_FORCE) == 0) {
                           mount_warning(mp, "Cannot unmount: "
                                             "%d mount refs still present",
                                             mp->mnt_refs);
                           error = EBUSY;
                   } else {
                           mount_warning(mp, "Forced unmount: "
                                             "%d mount refs still present",
                                             mp->mnt_refs);
                           freeok = 0;
                   }
           }
   
           /*
            * So far so good, sync the filesystem once more and
            * call the VFS unmount code if the sync succeeds.
            */
           if (error == 0) {
                   if (((mp->mnt_flag & MNT_RDONLY) ||
                        (error = VFS_SYNC(mp, MNT_WAIT)) == 0) ||
                       (flags & MNT_FORCE)) {
                           error = VFS_UNMOUNT(mp, flags);
                   }
           }
   
           /*
            * If an error occurred we can still recover, restoring the
            * syncer vnode and misc flags.
            */
           if (error) {
                   if (mp->mnt_syncer == NULL)
                           vfs_allocate_syncvnode(mp);
                   mp->mnt_kern_flag &= ~(MNTK_UNMOUNT | MNTK_UNMOUNTF);
                   mp->mnt_flag |= async_flag;
                   lockmgr(&mp->mnt_lock, LK_RELEASE);
                   if (mp->mnt_kern_flag & MNTK_MWAIT) {
                           mp->mnt_kern_flag &= ~MNTK_MWAIT;
                           wakeup(mp);
                   }
                   goto out;
           }
           /*
            * Clean up any journals still associated with the mount after
            * filesystem activity has ceased.
            */
           journal_remove_all_journals(mp, 
               ((flags & MNT_FORCE) ? MC_JOURNAL_STOP_IMM : 0));
   
           mountlist_remove(mp);
   
           /*
            * Remove any installed vnode ops here so the individual VFSs don't
            * have to.
            */
           vfs_rm_vnodeops(mp, NULL, &mp->mnt_vn_coherency_ops);
           vfs_rm_vnodeops(mp, NULL, &mp->mnt_vn_journal_ops);
           vfs_rm_vnodeops(mp, NULL, &mp->mnt_vn_norm_ops);
           vfs_rm_vnodeops(mp, NULL, &mp->mnt_vn_spec_ops);
           vfs_rm_vnodeops(mp, NULL, &mp->mnt_vn_fifo_ops);
   
           if (mp->mnt_ncmountpt.ncp != NULL) {
                   nch = mp->mnt_ncmountpt;
                   cache_zero(&mp->mnt_ncmountpt);
                   cache_clrmountpt(&nch);
                   cache_drop(&nch);
           }
           if (mp->mnt_ncmounton.ncp != NULL) {
                   cache_unmounting(mp);
                   nch = mp->mnt_ncmounton;
                   cache_zero(&mp->mnt_ncmounton);
                   cache_clrmountpt(&nch);
                   cache_drop(&nch);
           }
   
           mp->mnt_vfc->vfc_refcount--;
           if (!TAILQ_EMPTY(&mp->mnt_nvnodelist))
                   panic("unmount: dangling vnode");
           lockmgr(&mp->mnt_lock, LK_RELEASE);
           if (mp->mnt_kern_flag & MNTK_MWAIT) {
                   mp->mnt_kern_flag &= ~MNTK_MWAIT;
                   wakeup(mp);
           }
   
           /*
            * If we reach here and freeok != 0 we must free the mount.
            * If refs > 1 cycle and wait, just in case someone tried
            * to busy the mount after we decided to do the unmount.
            */
           if (freeok) {
                   while (mp->mnt_refs > 1) {
                           cache_unmounting(mp);
                           wakeup(mp);
                           tsleep(&mp->mnt_refs, 0, "umntrwait", hz / 10 + 1);
                   }
                   lwkt_reltoken(&mp->mnt_token);
                   kfree(mp, M_MOUNT);
                   mp = NULL;
           }
           error = 0;
   out:
           if (mp)
                   lwkt_reltoken(&mp->mnt_token);
           return (error);
   }
   
   static
   void
   mount_warning(struct mount *mp, const char *ctl, ...)
   {
           char *ptr;
           char *buf;
           __va_list va;
   
           __va_start(va, ctl);
           if (cache_fullpath(NULL, &mp->mnt_ncmounton, NULL,
                              &ptr, &buf, 0) == 0) {
                   kprintf("unmount(%s): ", ptr);
                   kvprintf(ctl, va);
                   kprintf("\n");
                   kfree(buf, M_TEMP);
           } else {
                   kprintf("unmount(%p", mp);
                   if (mp->mnt_ncmounton.ncp && mp->mnt_ncmounton.ncp->nc_name)
                           kprintf(",%s", mp->mnt_ncmounton.ncp->nc_name);
                   kprintf("): ");
                   kvprintf(ctl, va);
                   kprintf("\n");
           }
           __va_end(va);
   }
   
   /*
    * Shim cache_fullpath() to handle the case where a process is chrooted into
    * a subdirectory of a mount.  In this case if the root mount matches the
    * process root directory's mount we have to specify the process's root
    * directory instead of the mount point, because the mount point might
    * be above the root directory.
    */
   static
   int
   mount_path(struct proc *p, struct mount *mp, char **rb, char **fb)
   {
           struct nchandle *nch;
   
           if (p && p->p_fd->fd_nrdir.mount == mp)
                   nch = &p->p_fd->fd_nrdir;
           else
                   nch = &mp->mnt_ncmountpt;
           return(cache_fullpath(p, nch, NULL, rb, fb, 0));
   }
   
   /*
    * Sync each mounted filesystem.
    */
   
   #ifdef DEBUG
   static int syncprt = 0;
   SYSCTL_INT(_debug, OID_AUTO, syncprt, CTLFLAG_RW, &syncprt, 0, "");
   #endif /* DEBUG */
   
   static int sync_callback(struct mount *mp, void *data);
   
   int
   sys_sync(struct sync_args *uap)
   {
           mountlist_scan(sync_callback, NULL, MNTSCAN_FORWARD);
           return (0);
   }
   
   static
   int
   sync_callback(struct mount *mp, void *data __unused)
   {
           int asyncflag;
   
           if ((mp->mnt_flag & MNT_RDONLY) == 0) {
                   asyncflag = mp->mnt_flag & MNT_ASYNC;
                   mp->mnt_flag &= ~MNT_ASYNC;
                   vfs_msync(mp, MNT_NOWAIT);
                   VFS_SYNC(mp, MNT_NOWAIT);
                   mp->mnt_flag |= asyncflag;
           }
           return(0);
   }
   
   /* XXX PRISON: could be per prison flag */
   static int prison_quotas;
   #if 0
   SYSCTL_INT(_kern_prison, OID_AUTO, quotas, CTLFLAG_RW, &prison_quotas, 0, "");
   #endif
   
   /*
    *  quotactl_args(char *path, int fcmd, int uid, caddr_t arg)
    *
    * Change filesystem quotas.
    *
    * MPALMOSTSAFE
    */
   int
   sys_quotactl(struct quotactl_args *uap)
   {
           struct nlookupdata nd;
           struct thread *td;
           struct mount *mp;
           int error;
   
           get_mplock();
           td = curthread;
           if (td->td_ucred->cr_prison && !prison_quotas) {
                   error = EPERM;
                   goto done;
           }
   
           error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
           if (error == 0)
                   error = nlookup(&nd);
           if (error == 0) {
                   mp = nd.nl_nch.mount;
                   error = VFS_QUOTACTL(mp, uap->cmd, uap->uid,
                                       uap->arg, nd.nl_cred);
           }
           nlookup_done(&nd);
   done:
           rel_mplock();
           return (error);
   }
   
   /*
    * mountctl(char *path, int op, int fd, const void *ctl, int ctllen,
    *              void *buf, int buflen)
    *
    * This function operates on a mount point and executes the specified
    * operation using the specified control data, and possibly returns data.
    *
    * The actual number of bytes stored in the result buffer is returned, 0
    * if none, otherwise an error is returned.
   *
   * MPALMOSTSAFE
   */
  int
  sys_mountctl(struct mountctl_args *uap)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct file *fp;
          void *ctl = NULL;
          void *buf = NULL;
          char *path = NULL;
          int error;
  
          /*
           * Sanity and permissions checks.  We must be root.
           */
          KKASSERT(p);
          if (td->td_ucred->cr_prison != NULL)
                  return (EPERM);
          if ((uap->op != MOUNTCTL_MOUNTFLAGS) &&
              (error = priv_check(td, PRIV_ROOT)) != 0)
                  return (error);
  
          /*
           * Argument length checks
           */
          if (uap->ctllen < 0 || uap->ctllen > 1024)
                  return (EINVAL);
          if (uap->buflen < 0 || uap->buflen > 16 * 1024)
                  return (EINVAL);
          if (uap->path == NULL)
                  return (EINVAL);
  
          /*
           * Allocate the necessary buffers and copyin data
           */
          path = objcache_get(namei_oc, M_WAITOK);
          error = copyinstr(uap->path, path, MAXPATHLEN, NULL);
          if (error)
                  goto done;
  
          if (uap->ctllen) {
                  ctl = kmalloc(uap->ctllen + 1, M_TEMP, M_WAITOK|M_ZERO);
                  error = copyin(uap->ctl, ctl, uap->ctllen);
                  if (error)
                          goto done;
          }
          if (uap->buflen)
                  buf = kmalloc(uap->buflen + 1, M_TEMP, M_WAITOK|M_ZERO);
  
          /*
           * Validate the descriptor
           */
          if (uap->fd >= 0) {
                  fp = holdfp(p->p_fd, uap->fd, -1);
                  if (fp == NULL) {
                          error = EBADF;
                          goto done;
                  }
          } else {
                  fp = NULL;
          }
  
          /*
           * Execute the internal kernel function and clean up.
           */
          get_mplock();
          error = kern_mountctl(path, uap->op, fp, ctl, uap->ctllen, buf, uap->buflen, &uap->sysmsg_result);
          rel_mplock();
          if (fp)
                  fdrop(fp);
          if (error == 0 && uap->sysmsg_result > 0)
                  error = copyout(buf, uap->buf, uap->sysmsg_result);
  done:
          if (path)
                  objcache_put(namei_oc, path);
          if (ctl)
                  kfree(ctl, M_TEMP);
          if (buf)
                  kfree(buf, M_TEMP);
          return (error);
  }
  
  /*
   * Execute a mount control operation by resolving the path to a mount point
   * and calling vop_mountctl().  
   *
   * Use the mount point from the nch instead of the vnode so nullfs mounts
   * can properly spike the VOP.
   */
  int
  kern_mountctl(const char *path, int op, struct file *fp, 
                  const void *ctl, int ctllen, 
                  void *buf, int buflen, int *res)
  {
          struct vnode *vp;
          struct mount *mp;
          struct nlookupdata nd;
          int error;
  
          *res = 0;
          vp = NULL;
          error = nlookup_init(&nd, path, UIO_SYSSPACE, NLC_FOLLOW);
          if (error == 0)
                  error = nlookup(&nd);
          if (error == 0)
                  error = cache_vget(&nd.nl_nch, nd.nl_cred, LK_EXCLUSIVE, &vp);
          mp = nd.nl_nch.mount;
          nlookup_done(&nd);
          if (error)
                  return (error);
          vn_unlock(vp);
  
          /*
           * Must be the root of the filesystem
           */
          if ((vp->v_flag & (VROOT|VPFSROOT)) == 0) {
                  vrele(vp);
                  return (EINVAL);
          }
          error = vop_mountctl(mp->mnt_vn_use_ops, vp, op, fp, ctl, ctllen,
                               buf, buflen, res);
          vrele(vp);
          return (error);
  }
  
  int
  kern_statfs(struct nlookupdata *nd, struct statfs *buf)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct mount *mp;
          struct statfs *sp;
          char *fullpath, *freepath;
          int error;
  
          if ((error = nlookup(nd)) != 0)
                  return (error);
          mp = nd->nl_nch.mount;
          sp = &mp->mnt_stat;
          if ((error = VFS_STATFS(mp, sp, nd->nl_cred)) != 0)
                  return (error);
  
          error = mount_path(p, mp, &fullpath, &freepath);
          if (error)
                  return(error);
          bzero(sp->f_mntonname, sizeof(sp->f_mntonname));
          strlcpy(sp->f_mntonname, fullpath, sizeof(sp->f_mntonname));
          kfree(freepath, M_TEMP);
  
          sp->f_flags = mp->mnt_flag & MNT_VISFLAGMASK;
          bcopy(sp, buf, sizeof(*buf));
          /* Only root should have access to the fsid's. */
          if (priv_check(td, PRIV_ROOT))
                  buf->f_fsid.val[0] = buf->f_fsid.val[1] = 0;
          return (0);
  }
  
  /*
   * statfs_args(char *path, struct statfs *buf)
   *
   * Get filesystem statistics.
   */
  int
  sys_statfs(struct statfs_args *uap)
  {
          struct nlookupdata nd;
          struct statfs buf;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
          if (error == 0)
                  error = kern_statfs(&nd, &buf);
          nlookup_done(&nd);
          if (error == 0)
                  error = copyout(&buf, uap->buf, sizeof(*uap->buf));
          return (error);
  }
  
  int
  kern_fstatfs(int fd, struct statfs *buf)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct file *fp;
          struct mount *mp;
          struct statfs *sp;
          char *fullpath, *freepath;
          int error;
  
          KKASSERT(p);
          if ((error = holdvnode(p->p_fd, fd, &fp)) != 0)
                  return (error);
  
          /*
           * Try to use mount info from any overlays rather than the
           * mount info for the underlying vnode, otherwise we will
           * fail when operating on null-mounted paths inside a chroot.
           */
          if ((mp = fp->f_nchandle.mount) == NULL)
                  mp = ((struct vnode *)fp->f_data)->v_mount;
          if (mp == NULL) {
                  error = EBADF;
                  goto done;
          }
          if (fp->f_cred == NULL) {
                  error = EINVAL;
                  goto done;
          }
          sp = &mp->mnt_stat;
          if ((error = VFS_STATFS(mp, sp, fp->f_cred)) != 0)
                  goto done;
  
          if ((error = mount_path(p, mp, &fullpath, &freepath)) != 0)
                  goto done;
          bzero(sp->f_mntonname, sizeof(sp->f_mntonname));
          strlcpy(sp->f_mntonname, fullpath, sizeof(sp->f_mntonname));
          kfree(freepath, M_TEMP);
  
          sp->f_flags = mp->mnt_flag & MNT_VISFLAGMASK;
          bcopy(sp, buf, sizeof(*buf));
  
          /* Only root should have access to the fsid's. */
          if (priv_check(td, PRIV_ROOT))
                  buf->f_fsid.val[0] = buf->f_fsid.val[1] = 0;
          error = 0;
  done:
          fdrop(fp);
          return (error);
  }
  
  /*
   * fstatfs_args(int fd, struct statfs *buf)
   *
   * Get filesystem statistics.
   */
  int
  sys_fstatfs(struct fstatfs_args *uap)
  {
          struct statfs buf;
          int error;
  
          error = kern_fstatfs(uap->fd, &buf);
  
          if (error == 0)
                  error = copyout(&buf, uap->buf, sizeof(*uap->buf));
          return (error);
  }
  
  int
  kern_statvfs(struct nlookupdata *nd, struct statvfs *buf)
  {
          struct mount *mp;
          struct statvfs *sp;
          int error;
  
          if ((error = nlookup(nd)) != 0)
                  return (error);
          mp = nd->nl_nch.mount;
          sp = &mp->mnt_vstat;
          if ((error = VFS_STATVFS(mp, sp, nd->nl_cred)) != 0)
                  return (error);
  
          sp->f_flag = 0;
          if (mp->mnt_flag & MNT_RDONLY)
                  sp->f_flag |= ST_RDONLY;
          if (mp->mnt_flag & MNT_NOSUID)
                  sp->f_flag |= ST_NOSUID;
          bcopy(sp, buf, sizeof(*buf));
          return (0);
  }
  
  /*
   * statfs_args(char *path, struct statfs *buf)
   *
   * Get filesystem statistics.
   */
  int
  sys_statvfs(struct statvfs_args *uap)
  {
          struct nlookupdata nd;
          struct statvfs buf;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
          if (error == 0)
                  error = kern_statvfs(&nd, &buf);
          nlookup_done(&nd);
          if (error == 0)
                  error = copyout(&buf, uap->buf, sizeof(*uap->buf));
          return (error);
  }
  
  int
  kern_fstatvfs(int fd, struct statvfs *buf)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct file *fp;
          struct mount *mp;
          struct statvfs *sp;
          int error;
  
          KKASSERT(p);
          if ((error = holdvnode(p->p_fd, fd, &fp)) != 0)
                  return (error);
          if ((mp = fp->f_nchandle.mount) == NULL)
                  mp = ((struct vnode *)fp->f_data)->v_mount;
          if (mp == NULL) {
                  error = EBADF;
                  goto done;
          }
          if (fp->f_cred == NULL) {
                  error = EINVAL;
                  goto done;
          }
          sp = &mp->mnt_vstat;
          if ((error = VFS_STATVFS(mp, sp, fp->f_cred)) != 0)
                  goto done;
  
          sp->f_flag = 0;
          if (mp->mnt_flag & MNT_RDONLY)
                  sp->f_flag |= ST_RDONLY;
          if (mp->mnt_flag & MNT_NOSUID)
                  sp->f_flag |= ST_NOSUID;
  
          bcopy(sp, buf, sizeof(*buf));
          error = 0;
  done:
          fdrop(fp);
          return (error);
  }
  
  /*
   * fstatfs_args(int fd, struct statfs *buf)
   *
   * Get filesystem statistics.
   */
  int
  sys_fstatvfs(struct fstatvfs_args *uap)
  {
          struct statvfs buf;
          int error;
  
          error = kern_fstatvfs(uap->fd, &buf);
  
          if (error == 0)
                  error = copyout(&buf, uap->buf, sizeof(*uap->buf));
          return (error);
  }
  
  /*
   * getfsstat_args(struct statfs *buf, long bufsize, int flags)
   *
   * Get statistics on all filesystems.
   */
  
  struct getfsstat_info {
          struct statfs *sfsp;
          long count;
          long maxcount;
          int error;
          int flags;
          struct thread *td;
  };
  
  static int getfsstat_callback(struct mount *, void *);
  
  int
  sys_getfsstat(struct getfsstat_args *uap)
  {
          struct thread *td = curthread;
          struct getfsstat_info info;
  
          bzero(&info, sizeof(info));
  
          info.maxcount = uap->bufsize / sizeof(struct statfs);
          info.sfsp = uap->buf;
          info.count = 0;
          info.flags = uap->flags;
          info.td = td;
  
          mountlist_scan(getfsstat_callback, &info, MNTSCAN_FORWARD);
          if (info.sfsp && info.count > info.maxcount)
                  uap->sysmsg_result = info.maxcount;
          else
                  uap->sysmsg_result = info.count;
          return (info.error);
  }
  
  static int
  getfsstat_callback(struct mount *mp, void *data)
  {
          struct getfsstat_info *info = data;
          struct statfs *sp;
          char *freepath;
          char *fullpath;
          int error;
  
          if (info->sfsp && info->count < info->maxcount) {
                  if (info->td->td_proc &&
                      !chroot_visible_mnt(mp, info->td->td_proc)) {
                          return(0);
                  }
                  sp = &mp->mnt_stat;
  
                  /*
                   * If MNT_NOWAIT or MNT_LAZY is specified, do not
                   * refresh the fsstat cache. MNT_NOWAIT or MNT_LAZY
                   * overrides MNT_WAIT.
                   */
                  if (((info->flags & (MNT_LAZY|MNT_NOWAIT)) == 0 ||
                      (info->flags & MNT_WAIT)) &&
                      (error = VFS_STATFS(mp, sp, info->td->td_ucred))) {
                          return(0);
                  }
                  sp->f_flags = mp->mnt_flag & MNT_VISFLAGMASK;
  
                  error = mount_path(info->td->td_proc, mp, &fullpath, &freepath);
                  if (error) {
                          info->error = error;
                          return(-1);
                  }
                  bzero(sp->f_mntonname, sizeof(sp->f_mntonname));
                  strlcpy(sp->f_mntonname, fullpath, sizeof(sp->f_mntonname));
                  kfree(freepath, M_TEMP);
  
                  error = copyout(sp, info->sfsp, sizeof(*sp));
                  if (error) {
                          info->error = error;
                          return (-1);
                  }
                  ++info->sfsp;
          }
          info->count++;
          return(0);
  }
  
  /*
   * getvfsstat_args(struct statfs *buf, struct statvfs *vbuf,
                     long bufsize, int flags)
   *
   * Get statistics on all filesystems.
   */
  
  struct getvfsstat_info {
          struct statfs *sfsp;
          struct statvfs *vsfsp;
          long count;
          long maxcount;
          int error;
          int flags;
          struct thread *td;
  };
  
  static int getvfsstat_callback(struct mount *, void *);
  
  int
  sys_getvfsstat(struct getvfsstat_args *uap)
  {
          struct thread *td = curthread;
          struct getvfsstat_info info;
  
          bzero(&info, sizeof(info));
  
          info.maxcount = uap->vbufsize / sizeof(struct statvfs);
          info.sfsp = uap->buf;
          info.vsfsp = uap->vbuf;
          info.count = 0;
          info.flags = uap->flags;
          info.td = td;
  
          mountlist_scan(getvfsstat_callback, &info, MNTSCAN_FORWARD);
          if (info.vsfsp && info.count > info.maxcount)
                  uap->sysmsg_result = info.maxcount;
          else
                  uap->sysmsg_result = info.count;
          return (info.error);
  }
  
  static int
  getvfsstat_callback(struct mount *mp, void *data)
  {
          struct getvfsstat_info *info = data;
          struct statfs *sp;
          struct statvfs *vsp;
          char *freepath;
          char *fullpath;
          int error;
  
          if (info->vsfsp && info->count < info->maxcount) {
                  if (info->td->td_proc &&
                      !chroot_visible_mnt(mp, info->td->td_proc)) {
                          return(0);
                  }
                  sp = &mp->mnt_stat;
                  vsp = &mp->mnt_vstat;
  
                  /*
                   * If MNT_NOWAIT or MNT_LAZY is specified, do not
                   * refresh the fsstat cache. MNT_NOWAIT or MNT_LAZY
                   * overrides MNT_WAIT.
                   */
                  if (((info->flags & (MNT_LAZY|MNT_NOWAIT)) == 0 ||
                      (info->flags & MNT_WAIT)) &&
                      (error = VFS_STATFS(mp, sp, info->td->td_ucred))) {
                          return(0);
                  }
                  sp->f_flags = mp->mnt_flag & MNT_VISFLAGMASK;
  
                  if (((info->flags & (MNT_LAZY|MNT_NOWAIT)) == 0 ||
                      (info->flags & MNT_WAIT)) &&
                      (error = VFS_STATVFS(mp, vsp, info->td->td_ucred))) {
                          return(0);
                  }
                  vsp->f_flag = 0;
                  if (mp->mnt_flag & MNT_RDONLY)
                          vsp->f_flag |= ST_RDONLY;
                  if (mp->mnt_flag & MNT_NOSUID)
                          vsp->f_flag |= ST_NOSUID;
  
                  error = mount_path(info->td->td_proc, mp, &fullpath, &freepath);
                  if (error) {
                          info->error = error;
                          return(-1);
                  }
                  bzero(sp->f_mntonname, sizeof(sp->f_mntonname));
                  strlcpy(sp->f_mntonname, fullpath, sizeof(sp->f_mntonname));
                  kfree(freepath, M_TEMP);
  
                  error = copyout(sp, info->sfsp, sizeof(*sp));
                  if (error == 0)
                          error = copyout(vsp, info->vsfsp, sizeof(*vsp));
                  if (error) {
                          info->error = error;
                          return (-1);
                  }
                  ++info->sfsp;
                  ++info->vsfsp;
          }
          info->count++;
          return(0);
  }
  
  
  /*
   * fchdir_args(int fd)
   *
   * Change current working directory to a given file descriptor.
   */
  int
  sys_fchdir(struct fchdir_args *uap)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct filedesc *fdp = p->p_fd;
          struct vnode *vp, *ovp;
          struct mount *mp;
          struct file *fp;
          struct nchandle nch, onch, tnch;
          int error;
  
          if ((error = holdvnode(fdp, uap->fd, &fp)) != 0)
                  return (error);
          lwkt_gettoken(&p->p_token);
          vp = (struct vnode *)fp->f_data;
          vref(vp);
          vn_lock(vp, LK_SHARED | LK_RETRY);
          if (fp->f_nchandle.ncp == NULL)
                  error = ENOTDIR;
          else
                  error = checkvp_chdir(vp, td);
          if (error) {
                  vput(vp);
                  goto done;
          }
          cache_copy(&fp->f_nchandle, &nch);
  
          /*
           * If the ncp has become a mount point, traverse through
           * the mount point.
           */
  
          while (!error && (nch.ncp->nc_flag & NCF_ISMOUNTPT) &&
                 (mp = cache_findmount(&nch)) != NULL
          ) {
                  error = nlookup_mp(mp, &tnch);
                  if (error == 0) {
                          cache_unlock(&tnch);    /* leave ref intact */
                          vput(vp);
                          vp = tnch.ncp->nc_vp;
                          error = vget(vp, LK_SHARED);
                          KKASSERT(error == 0);
                          cache_drop(&nch);
                          nch = tnch;
                  }
                  cache_dropmount(mp);
          }
          if (error == 0) {
                  ovp = fdp->fd_cdir;
                  onch = fdp->fd_ncdir;
                  vn_unlock(vp);          /* leave ref intact */
                  fdp->fd_cdir = vp;
                  fdp->fd_ncdir = nch;
                  cache_drop(&onch);
                  vrele(ovp);
          } else {
                  cache_drop(&nch);
                  vput(vp);
          }
          fdrop(fp);
  done:
          lwkt_reltoken(&p->p_token);
          return (error);
  }
  
  int
  kern_chdir(struct nlookupdata *nd)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct filedesc *fdp = p->p_fd;
          struct vnode *vp, *ovp;
          struct nchandle onch;
          int error;
  
          nd->nl_flags |= NLC_SHAREDLOCK;
          if ((error = nlookup(nd)) != 0)
                  return (error);
          if ((vp = nd->nl_nch.ncp->nc_vp) == NULL)
                  return (ENOENT);
          if ((error = vget(vp, LK_SHARED)) != 0)
                  return (error);
  
          lwkt_gettoken(&p->p_token);
          error = checkvp_chdir(vp, td);
          vn_unlock(vp);
          if (error == 0) {
                  ovp = fdp->fd_cdir;
                  onch = fdp->fd_ncdir;
                  cache_unlock(&nd->nl_nch);      /* leave reference intact */
                  fdp->fd_ncdir = nd->nl_nch;
                  fdp->fd_cdir = vp;
                  cache_drop(&onch);
                  vrele(ovp);
                  cache_zero(&nd->nl_nch);
          } else {
                  vrele(vp);
          }
          lwkt_reltoken(&p->p_token);
          return (error);
  }
  
  /*
   * chdir_args(char *path)
   *
   * Change current working directory (``.'').
   */
  int
  sys_chdir(struct chdir_args *uap)
  {
          struct nlookupdata nd;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
          if (error == 0)
                  error = kern_chdir(&nd);
          nlookup_done(&nd);
          return (error);
  }
  
  /*
   * Helper function for raised chroot(2) security function:  Refuse if
   * any filedescriptors are open directories.
   */
  static int
  chroot_refuse_vdir_fds(struct filedesc *fdp)
  {
          struct vnode *vp;
          struct file *fp;
          int error;
          int fd;
  
          for (fd = 0; fd < fdp->fd_nfiles ; fd++) {
                  if ((error = holdvnode(fdp, fd, &fp)) != 0)
                          continue;
                  vp = (struct vnode *)fp->f_data;
                  if (vp->v_type != VDIR) {
                          fdrop(fp);
                          continue;
                  }
                  fdrop(fp);
                  return(EPERM);
          }
          return (0);
  }
  
  /*
   * This sysctl determines if we will allow a process to chroot(2) if it
   * has a directory open:
   *      0: disallowed for all processes.
   *      1: allowed for processes that were not already chroot(2)'ed.
   *      2: allowed for all processes.
   */
  
  static int chroot_allow_open_directories = 1;
  
  SYSCTL_INT(_kern, OID_AUTO, chroot_allow_open_directories, CTLFLAG_RW,
       &chroot_allow_open_directories, 0, "");
  
  /*
   * chroot to the specified namecache entry.  We obtain the vp from the
   * namecache data.  The passed ncp must be locked and referenced and will
   * remain locked and referenced on return.
   */
  int
  kern_chroot(struct nchandle *nch)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct filedesc *fdp = p->p_fd;
          struct vnode *vp;
          int error;
  
          /*
           * Only privileged user can chroot
           */
          error = priv_check_cred(td->td_ucred, PRIV_VFS_CHROOT, 0);
          if (error)
                  return (error);
  
          /*
           * Disallow open directory descriptors (fchdir() breakouts).
           */
          if (chroot_allow_open_directories == 0 ||
             (chroot_allow_open_directories == 1 && fdp->fd_rdir != rootvnode)) {
                  if ((error = chroot_refuse_vdir_fds(fdp)) != 0)
                          return (error);
          }
          if ((vp = nch->ncp->nc_vp) == NULL)
                  return (ENOENT);
  
          if ((error = vget(vp, LK_SHARED)) != 0)
                  return (error);
  
          /*
           * Check the validity of vp as a directory to change to and 
           * associate it with rdir/jdir.
           */
          error = checkvp_chdir(vp, td);
          vn_unlock(vp);                  /* leave reference intact */
          if (error == 0) {
                  vrele(fdp->fd_rdir);
                  fdp->fd_rdir = vp;      /* reference inherited by fd_rdir */
                  cache_drop(&fdp->fd_nrdir);
                  cache_copy(nch, &fdp->fd_nrdir);
                  if (fdp->fd_jdir == NULL) {
                          fdp->fd_jdir = vp;
                          vref(fdp->fd_jdir);
                          cache_copy(nch, &fdp->fd_njdir);
                  }
          } else {
                  vrele(vp);
          }
          return (error);
  }
  
  /*
   * chroot_args(char *path)
   *
   * Change notion of root (``/'') directory.
   */
  int
  sys_chroot(struct chroot_args *uap)
  {
          struct thread *td __debugvar = curthread;
          struct nlookupdata nd;
          int error;
  
          KKASSERT(td->td_proc);
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
          if (error == 0) {
                  nd.nl_flags |= NLC_EXEC;
                  error = nlookup(&nd);
                  if (error == 0)
                          error = kern_chroot(&nd.nl_nch);
          }
          nlookup_done(&nd);
          return(error);
  }
  
  int
  sys_chroot_kernel(struct chroot_kernel_args *uap)
  {
          struct thread *td = curthread;
          struct nlookupdata nd;
          struct nchandle *nch;
          struct vnode *vp;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
          if (error)
                  goto error_nond;
  
          error = nlookup(&nd);
          if (error)
                  goto error_out;
  
          nch = &nd.nl_nch;
  
          error = priv_check_cred(td->td_ucred, PRIV_VFS_CHROOT, 0);
          if (error)
                  goto error_out;
  
          if ((vp = nch->ncp->nc_vp) == NULL) {
                  error = ENOENT;
                  goto error_out;
          }
  
          if ((error = cache_vref(nch, nd.nl_cred, &vp)) != 0)
                  goto error_out;
  
          kprintf("chroot_kernel: set new rootnch/rootvnode to %s\n", uap->path);
          get_mplock();
          vfs_cache_setroot(vp, cache_hold(nch));
          rel_mplock();
  
  error_out:
          nlookup_done(&nd);
  error_nond:
          return(error);
  }
  
  /*
   * Common routine for chroot and chdir.  Given a locked, referenced vnode,
   * determine whether it is legal to chdir to the vnode.  The vnode's state
   * is not changed by this call.
   */
  int
  checkvp_chdir(struct vnode *vp, struct thread *td)
  {
          int error;
  
          if (vp->v_type != VDIR)
                  error = ENOTDIR;
          else
                  error = VOP_EACCESS(vp, VEXEC, td->td_ucred);
          return (error);
  }
  
  int
  kern_open(struct nlookupdata *nd, int oflags, int mode, int *res)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct lwp *lp = td->td_lwp;
          struct filedesc *fdp = p->p_fd;
          int cmode, flags;
          struct file *nfp;
          struct file *fp;
          struct vnode *vp;
          int type, indx, error = 0;
          struct flock lf;
  
          if ((oflags & O_ACCMODE) == O_ACCMODE)
                  return (EINVAL);
          flags = FFLAGS(oflags);
          error = falloc(lp, &nfp, NULL);
          if (error)
                  return (error);
          fp = nfp;
          cmode = ((mode &~ fdp->fd_cmask) & ALLPERMS) & ~S_ISTXT;
  
          /*
           * XXX p_dupfd is a real mess.  It allows a device to return a
           * file descriptor to be duplicated rather then doing the open
           * itself.
           */
          lp->lwp_dupfd = -1;
  
          /*
           * Call vn_open() to do the lookup and assign the vnode to the 
           * file pointer.  vn_open() does not change the ref count on fp
           * and the vnode, on success, will be inherited by the file pointer
           * and unlocked.
           *
           * Request a shared lock on the vnode if possible.
           */
          nd->nl_flags |= NLC_LOCKVP;
          if ((flags & (O_CREAT|O_TRUNC)) == 0)
                  nd->nl_flags |= NLC_SHAREDLOCK;
  
          error = vn_open(nd, fp, flags, cmode);
          nlookup_done(nd);
  
          if (error) {
                  /*
                   * handle special fdopen() case.  bleh.  dupfdopen() is
                   * responsible for dropping the old contents of ofiles[indx]
                   * if it succeeds.
                   *
                   * Note that fsetfd() will add a ref to fp which represents
                   * the fd_files[] assignment.  We must still drop our
                   * reference.
                   */
                  if ((error == ENODEV || error == ENXIO) && lp->lwp_dupfd >= 0) {
                          if (fdalloc(p, 0, &indx) == 0) {
                                  error = dupfdopen(fdp, indx, lp->lwp_dupfd, flags, error);
                                  if (error == 0) {
                                          *res = indx;
                                          fdrop(fp);      /* our ref */
                                          return (0);
                                  }
                                  fsetfd(fdp, NULL, indx);
                          }
                  }
                  fdrop(fp);      /* our ref */
                  if (error == ERESTART)
                          error = EINTR;
                  return (error);
          }
  
          /*
           * ref the vnode for ourselves so it can't be ripped out from under
           * is.  XXX need an ND flag to request that the vnode be returned
           * anyway.
           *
           * Reserve a file descriptor but do not assign it until the open
           * succeeds.
           */
          vp = (struct vnode *)fp->f_data;
          vref(vp);
          if ((error = fdalloc(p, 0, &indx)) != 0) {
                  fdrop(fp);
                  vrele(vp);
                  return (error);
          }
  
          /*
           * If no error occurs the vp will have been assigned to the file
           * pointer.
           */
          lp->lwp_dupfd = 0;
  
          if (flags & (O_EXLOCK | O_SHLOCK)) {
                  lf.l_whence = SEEK_SET;
                  lf.l_start = 0;
                  lf.l_len = 0;
                  if (flags & O_EXLOCK)
                          lf.l_type = F_WRLCK;
                  else
                          lf.l_type = F_RDLCK;
                  if (flags & FNONBLOCK)
                          type = 0;
                  else
                          type = F_WAIT;
  
                  if ((error = VOP_ADVLOCK(vp, (caddr_t)fp, F_SETLK, &lf, type)) != 0) {
                          /*
                           * lock request failed.  Clean up the reserved
                           * descriptor.
                           */
                          vrele(vp);
                          fsetfd(fdp, NULL, indx);
                          fdrop(fp);
                          return (error);
                  }
                  fp->f_flag |= FHASLOCK;
          }
  #if 0
          /*
           * Assert that all regular file vnodes were created with a object.
           */
          KASSERT(vp->v_type != VREG || vp->v_object != NULL,
                  ("open: regular file has no backing object after vn_open"));
  #endif
  
          vrele(vp);
  
          /*
           * release our private reference, leaving the one associated with the
           * descriptor table intact.
           */
          fsetfd(fdp, fp, indx);
          fdrop(fp);
          *res = indx;
          if (oflags & O_CLOEXEC)
                  error = fsetfdflags(fdp, *res, UF_EXCLOSE);
          return (error);
  }
  
  /*
   * open_args(char *path, int flags, int mode)
   *
   * Check permissions, allocate an open file structure,
   * and call the device open routine if any.
   */
  int
  sys_open(struct open_args *uap)
  {
          struct nlookupdata nd;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, 0);
          if (error == 0) {
                  error = kern_open(&nd, uap->flags,
                                      uap->mode, &uap->sysmsg_result);
          }
          nlookup_done(&nd);
          return (error);
  }
  
  /*
   * openat_args(int fd, char *path, int flags, int mode)
   */
  int
  sys_openat(struct openat_args *uap)
  {
          struct nlookupdata nd;
          int error;
          struct file *fp;
  
          error = nlookup_init_at(&nd, &fp, uap->fd, uap->path, UIO_USERSPACE, 0);
          if (error == 0) {
                  error = kern_open(&nd, uap->flags, uap->mode, 
                                          &uap->sysmsg_result);
          }
          nlookup_done_at(&nd, fp);
          return (error);
  }
  
  int
  kern_mknod(struct nlookupdata *nd, int mode, int rmajor, int rminor)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct vnode *vp;
          struct vattr vattr;
          int error;
          int whiteout = 0;
  
          KKASSERT(p);
  
          VATTR_NULL(&vattr);
          vattr.va_mode = (mode & ALLPERMS) &~ p->p_fd->fd_cmask;
          vattr.va_rmajor = rmajor;
          vattr.va_rminor = rminor;
  
          switch (mode & S_IFMT) {
          case S_IFMT:    /* used by badsect to flag bad sectors */
                  error = priv_check_cred(td->td_ucred, PRIV_VFS_MKNOD_BAD, 0);
                  vattr.va_type = VBAD;
                  break;
          case S_IFCHR:
                  error = priv_check(td, PRIV_VFS_MKNOD_DEV);
                  vattr.va_type = VCHR;
                  break;
          case S_IFBLK:
                  error = priv_check(td, PRIV_VFS_MKNOD_DEV);
                  vattr.va_type = VBLK;
                  break;
          case S_IFWHT:
                  error = priv_check_cred(td->td_ucred, PRIV_VFS_MKNOD_WHT, 0);
                  whiteout = 1;
                  break;
          case S_IFDIR:   /* special directories support for HAMMER */
                  error = priv_check_cred(td->td_ucred, PRIV_VFS_MKNOD_DIR, 0);
                  vattr.va_type = VDIR;
                  break;
          default:
                  error = EINVAL;
                  break;
          }
  
          if (error)
                  return (error);
  
          bwillinode(1);
          nd->nl_flags |= NLC_CREATE | NLC_REFDVP;
          if ((error = nlookup(nd)) != 0)
                  return (error);
          if (nd->nl_nch.ncp->nc_vp)
                  return (EEXIST);
          if ((error = ncp_writechk(&nd->nl_nch)) != 0)
                  return (error);
  
          if (whiteout) {
                  error = VOP_NWHITEOUT(&nd->nl_nch, nd->nl_dvp,
                                        nd->nl_cred, NAMEI_CREATE);
          } else {
                  vp = NULL;
                  error = VOP_NMKNOD(&nd->nl_nch, nd->nl_dvp,
                                     &vp, nd->nl_cred, &vattr);
                  if (error == 0)
                          vput(vp);
          }
          return (error);
  }
  
  /*
   * mknod_args(char *path, int mode, int dev)
   *
   * Create a special file.
   */
  int
  sys_mknod(struct mknod_args *uap)
  {
          struct nlookupdata nd;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, 0);
          if (error == 0) {
                  error = kern_mknod(&nd, uap->mode,
                                     umajor(uap->dev), uminor(uap->dev));
          }
          nlookup_done(&nd);
          return (error);
  }
  
  /*
   * mknodat_args(int fd, char *path, mode_t mode, dev_t dev)
   *
   * Create a special file.  The path is relative to the directory associated
   * with fd.
   */
  int
  sys_mknodat(struct mknodat_args *uap)
  {
          struct nlookupdata nd;
          struct file *fp;
          int error;
  
          error = nlookup_init_at(&nd, &fp, uap->fd, uap->path, UIO_USERSPACE, 0);
          if (error == 0) {
                  error = kern_mknod(&nd, uap->mode,
                                     umajor(uap->dev), uminor(uap->dev));
          }
          nlookup_done_at(&nd, fp);
          return (error);
  }
  
  int
  kern_mkfifo(struct nlookupdata *nd, int mode)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct vattr vattr;
          struct vnode *vp;
          int error;
  
          bwillinode(1);
  
          nd->nl_flags |= NLC_CREATE | NLC_REFDVP;
          if ((error = nlookup(nd)) != 0)
                  return (error);
          if (nd->nl_nch.ncp->nc_vp)
                  return (EEXIST);
          if ((error = ncp_writechk(&nd->nl_nch)) != 0)
                  return (error);
  
          VATTR_NULL(&vattr);
          vattr.va_type = VFIFO;
          vattr.va_mode = (mode & ALLPERMS) &~ p->p_fd->fd_cmask;
          vp = NULL;
          error = VOP_NMKNOD(&nd->nl_nch, nd->nl_dvp, &vp, nd->nl_cred, &vattr);
          if (error == 0)
                  vput(vp);
          return (error);
  }
  
  /*
   * mkfifo_args(char *path, int mode)
   *
   * Create a named pipe.
   */
  int
  sys_mkfifo(struct mkfifo_args *uap)
  {
          struct nlookupdata nd;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, 0);
          if (error == 0)
                  error = kern_mkfifo(&nd, uap->mode);
          nlookup_done(&nd);
          return (error);
  }
  
  /*
   * mkfifoat_args(int fd, char *path, mode_t mode)
   *
   * Create a named pipe.  The path is relative to the directory associated
   * with fd.
   */
  int
  sys_mkfifoat(struct mkfifoat_args *uap)
  {
          struct nlookupdata nd;
          struct file *fp;
          int error;
  
          error = nlookup_init_at(&nd, &fp, uap->fd, uap->path, UIO_USERSPACE, 0);
          if (error == 0)
                  error = kern_mkfifo(&nd, uap->mode);
          nlookup_done_at(&nd, fp);
          return (error);
  }
  
  static int hardlink_check_uid = 0;
  SYSCTL_INT(_security, OID_AUTO, hardlink_check_uid, CTLFLAG_RW,
      &hardlink_check_uid, 0, 
      "Unprivileged processes cannot create hard links to files owned by other "
      "users");
  static int hardlink_check_gid = 0;
  SYSCTL_INT(_security, OID_AUTO, hardlink_check_gid, CTLFLAG_RW,
      &hardlink_check_gid, 0,
      "Unprivileged processes cannot create hard links to files owned by other "
      "groups");
  
  static int
  can_hardlink(struct vnode *vp, struct thread *td, struct ucred *cred)
  {
          struct vattr va;
          int error;
  
          /*
           * Shortcut if disabled
           */
          if (hardlink_check_uid == 0 && hardlink_check_gid == 0)
                  return (0);
  
          /*
           * Privileged user can always hardlink
           */
          if (priv_check_cred(cred, PRIV_VFS_LINK, 0) == 0)
                  return (0);
  
          /*
           * Otherwise only if the originating file is owned by the
           * same user or group.  Note that any group is allowed if
           * the file is owned by the caller.
           */
          error = VOP_GETATTR(vp, &va);
          if (error != 0)
                  return (error);
          
          if (hardlink_check_uid) {
                  if (cred->cr_uid != va.va_uid)
                          return (EPERM);
          }
          
          if (hardlink_check_gid) {
                  if (cred->cr_uid != va.va_uid && !groupmember(va.va_gid, cred))
                          return (EPERM);
          }
  
          return (0);
  }
  
  int
  kern_link(struct nlookupdata *nd, struct nlookupdata *linknd)
  {
          struct thread *td = curthread;
          struct vnode *vp;
          int error;
  
          /*
           * Lookup the source and obtained a locked vnode.
           *
           * You may only hardlink a file which you have write permission
           * on or which you own.
           *
           * XXX relookup on vget failure / race ?
           */
          bwillinode(1);
          nd->nl_flags |= NLC_WRITE | NLC_OWN | NLC_HLINK;
          if ((error = nlookup(nd)) != 0)
                  return (error);
          vp = nd->nl_nch.ncp->nc_vp;
          KKASSERT(vp != NULL);
          if (vp->v_type == VDIR)
                  return (EPERM);         /* POSIX */
          if ((error = ncp_writechk(&nd->nl_nch)) != 0)
                  return (error);
          if ((error = vget(vp, LK_EXCLUSIVE)) != 0)
                  return (error);
  
          /*
           * Unlock the source so we can lookup the target without deadlocking
           * (XXX vp is locked already, possible other deadlock?).  The target
           * must not exist.
           */
          KKASSERT(nd->nl_flags & NLC_NCPISLOCKED);
          nd->nl_flags &= ~NLC_NCPISLOCKED;
          cache_unlock(&nd->nl_nch);
          vn_unlock(vp);
  
          linknd->nl_flags |= NLC_CREATE | NLC_REFDVP;
          if ((error = nlookup(linknd)) != 0) {
                  vrele(vp);
                  return (error);
          }
          if (linknd->nl_nch.ncp->nc_vp) {
                  vrele(vp);
                  return (EEXIST);
          }
          error = vn_lock(vp, LK_EXCLUSIVE | LK_RETRY | LK_FAILRECLAIM);
          if (error) {
                  vrele(vp);
                  return (error);
          }
  
          /*
           * Finally run the new API VOP.
           */
          error = can_hardlink(vp, td, td->td_ucred);
          if (error == 0) {
                  error = VOP_NLINK(&linknd->nl_nch, linknd->nl_dvp,
                                    vp, linknd->nl_cred);
          }
          vput(vp);
          return (error);
  }
  
  /*
   * link_args(char *path, char *link)
   *
   * Make a hard file link.
   */
  int
  sys_link(struct link_args *uap)
  {
          struct nlookupdata nd, linknd;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
          if (error == 0) {
                  error = nlookup_init(&linknd, uap->link, UIO_USERSPACE, 0);
                  if (error == 0)
                          error = kern_link(&nd, &linknd);
                  nlookup_done(&linknd);
          }
          nlookup_done(&nd);
          return (error);
  }
  
  /*
   * linkat_args(int fd1, char *path1, int fd2, char *path2, int flags)
   *
   * Make a hard file link. The path1 argument is relative to the directory
   * associated with fd1, and similarly the path2 argument is relative to
   * the directory associated with fd2.
   */
  int
  sys_linkat(struct linkat_args *uap)
  {
          struct nlookupdata nd, linknd;
          struct file *fp1, *fp2;
          int error;
  
          error = nlookup_init_at(&nd, &fp1, uap->fd1, uap->path1, UIO_USERSPACE,
              (uap->flags & AT_SYMLINK_FOLLOW) ? NLC_FOLLOW : 0);
          if (error == 0) {
                  error = nlookup_init_at(&linknd, &fp2, uap->fd2,
                      uap->path2, UIO_USERSPACE, 0);
                  if (error == 0)
                          error = kern_link(&nd, &linknd);
                  nlookup_done_at(&linknd, fp2);
          }
          nlookup_done_at(&nd, fp1);
          return (error);
  }
  
  int
  kern_symlink(struct nlookupdata *nd, char *path, int mode)
  {
          struct vattr vattr;
          struct vnode *vp;
          struct vnode *dvp;
          int error;
  
          bwillinode(1);
          nd->nl_flags |= NLC_CREATE | NLC_REFDVP;
          if ((error = nlookup(nd)) != 0)
                  return (error);
          if (nd->nl_nch.ncp->nc_vp)
                  return (EEXIST);
          if ((error = ncp_writechk(&nd->nl_nch)) != 0)
                  return (error);
          dvp = nd->nl_dvp;
          VATTR_NULL(&vattr);
          vattr.va_mode = mode;
          error = VOP_NSYMLINK(&nd->nl_nch, dvp, &vp, nd->nl_cred, &vattr, path);
          if (error == 0)
                  vput(vp);
          return (error);
  }
  
  /*
   * symlink(char *path, char *link)
   *
   * Make a symbolic link.
   */
  int
  sys_symlink(struct symlink_args *uap)
  {
          struct thread *td = curthread;
          struct nlookupdata nd;
          char *path;
          int error;
          int mode;
  
          path = objcache_get(namei_oc, M_WAITOK);
          error = copyinstr(uap->path, path, MAXPATHLEN, NULL);
          if (error == 0) {
                  error = nlookup_init(&nd, uap->link, UIO_USERSPACE, 0);
                  if (error == 0) {
                          mode = ACCESSPERMS & ~td->td_proc->p_fd->fd_cmask;
                          error = kern_symlink(&nd, path, mode);
                  }
                  nlookup_done(&nd);
          }
          objcache_put(namei_oc, path);
          return (error);
  }
  
  /*
   * symlinkat_args(char *path1, int fd, char *path2)
   *
   * Make a symbolic link.  The path2 argument is relative to the directory
   * associated with fd.
   */
  int
  sys_symlinkat(struct symlinkat_args *uap)
  {
          struct thread *td = curthread;
          struct nlookupdata nd;
          struct file *fp;
          char *path1;
          int error;
          int mode;
  
          path1 = objcache_get(namei_oc, M_WAITOK);
          error = copyinstr(uap->path1, path1, MAXPATHLEN, NULL);
          if (error == 0) {
                  error = nlookup_init_at(&nd, &fp, uap->fd, uap->path2,
                      UIO_USERSPACE, 0);
                  if (error == 0) {
                          mode = ACCESSPERMS & ~td->td_proc->p_fd->fd_cmask;
                          error = kern_symlink(&nd, path1, mode);
                  }
                  nlookup_done_at(&nd, fp);
          }
          objcache_put(namei_oc, path1);
          return (error);
  }
  
  /*
   * undelete_args(char *path)
   *
   * Delete a whiteout from the filesystem.
   */
  int
  sys_undelete(struct undelete_args *uap)
  {
          struct nlookupdata nd;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, 0);
          bwillinode(1);
          nd.nl_flags |= NLC_DELETE | NLC_REFDVP;
          if (error == 0)
                  error = nlookup(&nd);
          if (error == 0)
                  error = ncp_writechk(&nd.nl_nch);
          if (error == 0) {
                  error = VOP_NWHITEOUT(&nd.nl_nch, nd.nl_dvp, nd.nl_cred,
                                        NAMEI_DELETE);
          }
          nlookup_done(&nd);
          return (error);
  }
  
  int
  kern_unlink(struct nlookupdata *nd)
  {
          int error;
  
          bwillinode(1);
          nd->nl_flags |= NLC_DELETE | NLC_REFDVP;
          if ((error = nlookup(nd)) != 0)
                  return (error);
          if ((error = ncp_writechk(&nd->nl_nch)) != 0)
                  return (error);
          error = VOP_NREMOVE(&nd->nl_nch, nd->nl_dvp, nd->nl_cred);
          return (error);
  }
  
  /*
   * unlink_args(char *path)
   *
   * Delete a name from the filesystem.
   */
  int
  sys_unlink(struct unlink_args *uap)
  {
          struct nlookupdata nd;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, 0);
          if (error == 0)
                  error = kern_unlink(&nd);
          nlookup_done(&nd);
          return (error);
  }
  
  
  /*
   * unlinkat_args(int fd, char *path, int flags)
   *
   * Delete the file or directory entry pointed to by fd/path.
   */
  int
  sys_unlinkat(struct unlinkat_args *uap)
  {
          struct nlookupdata nd;
          struct file *fp;
          int error;
  
          if (uap->flags & ~AT_REMOVEDIR)
                  return (EINVAL);
  
          error = nlookup_init_at(&nd, &fp, uap->fd, uap->path, UIO_USERSPACE, 0);
          if (error == 0) {
                  if (uap->flags & AT_REMOVEDIR)
                          error = kern_rmdir(&nd);
                  else
                          error = kern_unlink(&nd);
          }
          nlookup_done_at(&nd, fp);
          return (error);
  }
  
  int
  kern_lseek(int fd, off_t offset, int whence, off_t *res)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct file *fp;
          struct vnode *vp;
          struct vattr vattr;
          off_t new_offset;
          int error;
  
          fp = holdfp(p->p_fd, fd, -1);
          if (fp == NULL)
                  return (EBADF);
          if (fp->f_type != DTYPE_VNODE) {
                  error = ESPIPE;
                  goto done;
          }
          vp = (struct vnode *)fp->f_data;
  
          switch (whence) {
          case L_INCR:
                  spin_lock(&fp->f_spin);
                  new_offset = fp->f_offset + offset;
                  error = 0;
                  break;
          case L_XTND:
                  error = VOP_GETATTR(vp, &vattr);
                  spin_lock(&fp->f_spin);
                  new_offset = offset + vattr.va_size;
                  break;
          case L_SET:
                  new_offset = offset;
                  error = 0;
                  spin_lock(&fp->f_spin);
                  break;
          default:
                  new_offset = 0;
                  error = EINVAL;
                  spin_lock(&fp->f_spin);
                  break;
          }
  
          /*
           * Validate the seek position.  Negative offsets are not allowed
           * for regular files or directories.
           *
           * Normally we would also not want to allow negative offsets for
           * character and block-special devices.  However kvm addresses
           * on 64 bit architectures might appear to be negative and must
           * be allowed.
           */
          if (error == 0) {
                  if (new_offset < 0 &&
                      (vp->v_type == VREG || vp->v_type == VDIR)) {
                          error = EINVAL;
                  } else {
                          fp->f_offset = new_offset;
                  }
          }
          *res = fp->f_offset;
          spin_unlock(&fp->f_spin);
  done:
          fdrop(fp);
          return (error);
  }
  
  /*
   * lseek_args(int fd, int pad, off_t offset, int whence)
   *
   * Reposition read/write file offset.
   */
  int
  sys_lseek(struct lseek_args *uap)
  {
          int error;
  
          error = kern_lseek(uap->fd, uap->offset, uap->whence,
                             &uap->sysmsg_offset);
  
          return (error);
  }
  
  /*
   * Check if current process can access given file.  amode is a bitmask of *_OK
   * access bits.  flags is a bitmask of AT_* flags.
   */
  int
  kern_access(struct nlookupdata *nd, int amode, int flags)
  {
          struct vnode *vp;
          int error, mode;
  
          if (flags & ~AT_EACCESS)
                  return (EINVAL);
          nd->nl_flags |= NLC_SHAREDLOCK;
          if ((error = nlookup(nd)) != 0)
                  return (error);
  retry:
          error = cache_vget(&nd->nl_nch, nd->nl_cred, LK_SHARED, &vp);
          if (error)
                  return (error);
  
          /* Flags == 0 means only check for existence. */
          if (amode) {
                  mode = 0;
                  if (amode & R_OK)
                          mode |= VREAD;
                  if (amode & W_OK)
                          mode |= VWRITE;
                  if (amode & X_OK)
                          mode |= VEXEC;
                  if ((mode & VWRITE) == 0 || 
                      (error = vn_writechk(vp, &nd->nl_nch)) == 0)
                          error = VOP_ACCESS_FLAGS(vp, mode, flags, nd->nl_cred);
  
                  /*
                   * If the file handle is stale we have to re-resolve the
                   * entry with the ncp held exclusively.  This is a hack
                   * at the moment.
                   */
                  if (error == ESTALE) {
                          vput(vp);
                          cache_unlock(&nd->nl_nch);
                          cache_lock(&nd->nl_nch);
                          cache_setunresolved(&nd->nl_nch);
                          error = cache_resolve(&nd->nl_nch, nd->nl_cred);
                          if (error == 0) {
                                  vp = NULL;
                                  goto retry;
                          }
                          return(error);
                  }
          }
          vput(vp);
          return (error);
  }
  
  /*
   * access_args(char *path, int flags)
   *
   * Check access permissions.
   */
  int
  sys_access(struct access_args *uap)
  {
          struct nlookupdata nd;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
          if (error == 0)
                  error = kern_access(&nd, uap->flags, 0);
          nlookup_done(&nd);
          return (error);
  }
  
  
  /*
   * eaccess_args(char *path, int flags)
   *
   * Check access permissions.
   */
  int
  sys_eaccess(struct eaccess_args *uap)
  {
          struct nlookupdata nd;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
          if (error == 0)
                  error = kern_access(&nd, uap->flags, AT_EACCESS);
          nlookup_done(&nd);
          return (error);
  }
  
  
  /*
   * faccessat_args(int fd, char *path, int amode, int flags)
   *
   * Check access permissions.
   */
  int
  sys_faccessat(struct faccessat_args *uap)
  {
          struct nlookupdata nd;
          struct file *fp;
          int error;
  
          error = nlookup_init_at(&nd, &fp, uap->fd, uap->path, UIO_USERSPACE, 
                                  NLC_FOLLOW);
          if (error == 0)
                  error = kern_access(&nd, uap->amode, uap->flags);
          nlookup_done_at(&nd, fp);
          return (error);
  }
  
  int
  kern_stat(struct nlookupdata *nd, struct stat *st)
  {
          int error;
          struct vnode *vp;
  
          nd->nl_flags |= NLC_SHAREDLOCK;
          if ((error = nlookup(nd)) != 0)
                  return (error);
  again:
          if ((vp = nd->nl_nch.ncp->nc_vp) == NULL)
                  return (ENOENT);
  
          if ((error = vget(vp, LK_SHARED)) != 0)
                  return (error);
          error = vn_stat(vp, st, nd->nl_cred);
  
          /*
           * If the file handle is stale we have to re-resolve the
           * entry with the ncp held exclusively.  This is a hack
           * at the moment.
           */
          if (error == ESTALE) {
                  vput(vp);
                  cache_unlock(&nd->nl_nch);
                  cache_lock(&nd->nl_nch);
                  cache_setunresolved(&nd->nl_nch);
                  error = cache_resolve(&nd->nl_nch, nd->nl_cred);
                  if (error == 0)
                          goto again;
          } else {
                  vput(vp);
          }
          return (error);
  }
  
  /*
   * stat_args(char *path, struct stat *ub)
   *
   * Get file status; this version follows links.
   */
  int
  sys_stat(struct stat_args *uap)
  {
          struct nlookupdata nd;
          struct stat st;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
          if (error == 0) {
                  error = kern_stat(&nd, &st);
                  if (error == 0)
                          error = copyout(&st, uap->ub, sizeof(*uap->ub));
          }
          nlookup_done(&nd);
          return (error);
  }
  
  /*
   * lstat_args(char *path, struct stat *ub)
   *
   * Get file status; this version does not follow links.
   */
  int
  sys_lstat(struct lstat_args *uap)
  {
          struct nlookupdata nd;
          struct stat st;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, 0);
          if (error == 0) {
                  error = kern_stat(&nd, &st);
                  if (error == 0)
                          error = copyout(&st, uap->ub, sizeof(*uap->ub));
          }
          nlookup_done(&nd);
          return (error);
  }
  
  /*
   * fstatat_args(int fd, char *path, struct stat *sb, int flags)
   *
   * Get status of file pointed to by fd/path.
   */
  int
  sys_fstatat(struct fstatat_args *uap)
  {
          struct nlookupdata nd;
          struct stat st;
          int error;
          int flags;
          struct file *fp;
  
          if (uap->flags & ~AT_SYMLINK_NOFOLLOW)
                  return (EINVAL);
  
          flags = (uap->flags & AT_SYMLINK_NOFOLLOW) ? 0 : NLC_FOLLOW;
  
          error = nlookup_init_at(&nd, &fp, uap->fd, uap->path, 
                                  UIO_USERSPACE, flags);
          if (error == 0) {
                  error = kern_stat(&nd, &st);
                  if (error == 0)
                          error = copyout(&st, uap->sb, sizeof(*uap->sb));
          }
          nlookup_done_at(&nd, fp);
          return (error);
  }
  
  static int
  kern_pathconf(char *path, int name, int flags, register_t *sysmsg_regp)
  {
          struct nlookupdata nd;
          struct vnode *vp;
          int error;
  
          vp = NULL;
          error = nlookup_init(&nd, path, UIO_USERSPACE, flags);
          if (error == 0)
                  error = nlookup(&nd);
          if (error == 0)
                  error = cache_vget(&nd.nl_nch, nd.nl_cred, LK_EXCLUSIVE, &vp);
          nlookup_done(&nd);
          if (error == 0) {
                  error = VOP_PATHCONF(vp, name, sysmsg_regp);
                  vput(vp);
          }
          return (error);
  }
  
  /*
   * pathconf_Args(char *path, int name)
   *
   * Get configurable pathname variables.
   */
  int
  sys_pathconf(struct pathconf_args *uap)
  {
          return (kern_pathconf(uap->path, uap->name, NLC_FOLLOW,
                  &uap->sysmsg_reg));
  }
  
  /*
   * lpathconf_Args(char *path, int name)
   *
   * Get configurable pathname variables, but don't follow symlinks.
   */
  int
  sys_lpathconf(struct lpathconf_args *uap)
  {
          return (kern_pathconf(uap->path, uap->name, 0, &uap->sysmsg_reg));
  }
  
  /*
   * XXX: daver
   * kern_readlink isn't properly split yet.  There is a copyin burried
   * in VOP_READLINK().
   */
  int
  kern_readlink(struct nlookupdata *nd, char *buf, int count, int *res)
  {
          struct thread *td = curthread;
          struct vnode *vp;
          struct iovec aiov;
          struct uio auio;
          int error;
  
          nd->nl_flags |= NLC_SHAREDLOCK;
          if ((error = nlookup(nd)) != 0)
                  return (error);
          error = cache_vget(&nd->nl_nch, nd->nl_cred, LK_SHARED, &vp);
          if (error)
                  return (error);
          if (vp->v_type != VLNK) {
                  error = EINVAL;
          } else {
                  aiov.iov_base = buf;
                  aiov.iov_len = count;
                  auio.uio_iov = &aiov;
                  auio.uio_iovcnt = 1;
                  auio.uio_offset = 0;
                  auio.uio_rw = UIO_READ;
                  auio.uio_segflg = UIO_USERSPACE;
                  auio.uio_td = td;
                  auio.uio_resid = count;
                  error = VOP_READLINK(vp, &auio, td->td_ucred);
          }
          vput(vp);
          *res = count - auio.uio_resid;
          return (error);
  }
  
  /*
   * readlink_args(char *path, char *buf, int count)
   *
   * Return target name of a symbolic link.
   */
  int
  sys_readlink(struct readlink_args *uap)
  {
          struct nlookupdata nd;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, 0);
          if (error == 0) {
                  error = kern_readlink(&nd, uap->buf, uap->count,
                                          &uap->sysmsg_result);
          }
          nlookup_done(&nd);
          return (error);
  }
  
  /*
   * readlinkat_args(int fd, char *path, char *buf, size_t bufsize)
   *
   * Return target name of a symbolic link.  The path is relative to the
   * directory associated with fd.
   */
  int
  sys_readlinkat(struct readlinkat_args *uap)
  {
          struct nlookupdata nd;
          struct file *fp;
          int error;
  
          error = nlookup_init_at(&nd, &fp, uap->fd, uap->path, UIO_USERSPACE, 0);
          if (error == 0) {
                  error = kern_readlink(&nd, uap->buf, uap->bufsize,
                                          &uap->sysmsg_result);
          }
          nlookup_done_at(&nd, fp);
          return (error);
  }
  
  static int
  setfflags(struct vnode *vp, int flags)
  {
          struct thread *td = curthread;
          int error;
          struct vattr vattr;
  
          /*
           * Prevent non-root users from setting flags on devices.  When
           * a device is reused, users can retain ownership of the device
           * if they are allowed to set flags and programs assume that
           * chown can't fail when done as root.
           */
          if ((vp->v_type == VCHR || vp->v_type == VBLK) && 
              ((error = priv_check_cred(td->td_ucred, PRIV_VFS_CHFLAGS_DEV, 0)) != 0))
                  return (error);
  
          /*
           * note: vget is required for any operation that might mod the vnode
           * so VINACTIVE is properly cleared.
           */
          if ((error = vget(vp, LK_EXCLUSIVE)) == 0) {
                  VATTR_NULL(&vattr);
                  vattr.va_flags = flags;
                  error = VOP_SETATTR(vp, &vattr, td->td_ucred);
                  vput(vp);
          }
          return (error);
  }
  
  /*
   * chflags(char *path, int flags)
   *
   * Change flags of a file given a path name.
   */
  int
  sys_chflags(struct chflags_args *uap)
  {
          struct nlookupdata nd;
          struct vnode *vp;
          int error;
  
          vp = NULL;
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
          if (error == 0)
                  error = nlookup(&nd);
          if (error == 0)
                  error = ncp_writechk(&nd.nl_nch);
          if (error == 0)
                  error = cache_vref(&nd.nl_nch, nd.nl_cred, &vp);
          nlookup_done(&nd);
          if (error == 0) {
                  error = setfflags(vp, uap->flags);
                  vrele(vp);
          }
          return (error);
  }
  
  /*
   * lchflags(char *path, int flags)
   *
   * Change flags of a file given a path name, but don't follow symlinks.
   */
  int
  sys_lchflags(struct lchflags_args *uap)
  {
          struct nlookupdata nd;
          struct vnode *vp;
          int error;
  
          vp = NULL;
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, 0);
          if (error == 0)
                  error = nlookup(&nd);
          if (error == 0)
                  error = ncp_writechk(&nd.nl_nch);
          if (error == 0)
                  error = cache_vref(&nd.nl_nch, nd.nl_cred, &vp);
          nlookup_done(&nd);
          if (error == 0) {
                  error = setfflags(vp, uap->flags);
                  vrele(vp);
          }
          return (error);
  }
  
  /*
   * fchflags_args(int fd, int flags)
   *
   * Change flags of a file given a file descriptor.
   */
  int
  sys_fchflags(struct fchflags_args *uap)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct file *fp;
          int error;
  
          if ((error = holdvnode(p->p_fd, uap->fd, &fp)) != 0)
                  return (error);
          if (fp->f_nchandle.ncp)
                  error = ncp_writechk(&fp->f_nchandle);
          if (error == 0)
                  error = setfflags((struct vnode *) fp->f_data, uap->flags);
          fdrop(fp);
          return (error);
  }
  
  static int
  setfmode(struct vnode *vp, int mode)
  {
          struct thread *td = curthread;
          int error;
          struct vattr vattr;
  
          /*
           * note: vget is required for any operation that might mod the vnode
           * so VINACTIVE is properly cleared.
           */
          if ((error = vget(vp, LK_EXCLUSIVE)) == 0) {
                  VATTR_NULL(&vattr);
                  vattr.va_mode = mode & ALLPERMS;
                  error = VOP_SETATTR(vp, &vattr, td->td_ucred);
                  vput(vp);
          }
          return error;
  }
  
  int
  kern_chmod(struct nlookupdata *nd, int mode)
  {
          struct vnode *vp;
          int error;
  
          if ((error = nlookup(nd)) != 0)
                  return (error);
          if ((error = cache_vref(&nd->nl_nch, nd->nl_cred, &vp)) != 0)
                  return (error);
          if ((error = ncp_writechk(&nd->nl_nch)) == 0)
                  error = setfmode(vp, mode);
          vrele(vp);
          return (error);
  }
  
  /*
   * chmod_args(char *path, int mode)
   *
   * Change mode of a file given path name.
   */
  int
  sys_chmod(struct chmod_args *uap)
  {
          struct nlookupdata nd;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
          if (error == 0)
                  error = kern_chmod(&nd, uap->mode);
          nlookup_done(&nd);
          return (error);
  }
  
  /*
   * lchmod_args(char *path, int mode)
   *
   * Change mode of a file given path name (don't follow links.)
   */
  int
  sys_lchmod(struct lchmod_args *uap)
  {
          struct nlookupdata nd;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, 0);
          if (error == 0)
                  error = kern_chmod(&nd, uap->mode);
          nlookup_done(&nd);
          return (error);
  }
  
  /*
   * fchmod_args(int fd, int mode)
   *
   * Change mode of a file given a file descriptor.
   */
  int
  sys_fchmod(struct fchmod_args *uap)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct file *fp;
          int error;
  
          if ((error = holdvnode(p->p_fd, uap->fd, &fp)) != 0)
                  return (error);
          if (fp->f_nchandle.ncp)
                  error = ncp_writechk(&fp->f_nchandle);
          if (error == 0)
                  error = setfmode((struct vnode *)fp->f_data, uap->mode);
          fdrop(fp);
          return (error);
  }
  
  /*
   * fchmodat_args(char *path, int mode)
   *
   * Change mode of a file pointed to by fd/path.
   */
  int
  sys_fchmodat(struct fchmodat_args *uap)
  {
          struct nlookupdata nd;
          struct file *fp;
          int error;
          int flags;
  
          if (uap->flags & ~AT_SYMLINK_NOFOLLOW)
                  return (EINVAL);
          flags = (uap->flags & AT_SYMLINK_NOFOLLOW) ? 0 : NLC_FOLLOW;
  
          error = nlookup_init_at(&nd, &fp, uap->fd, uap->path, 
                                  UIO_USERSPACE, flags);
          if (error == 0)
                  error = kern_chmod(&nd, uap->mode);
          nlookup_done_at(&nd, fp);
          return (error);
  }
  
  static int
  setfown(struct mount *mp, struct vnode *vp, uid_t uid, gid_t gid)
  {
          struct thread *td = curthread;
          int error;
          struct vattr vattr;
          uid_t o_uid;
          gid_t o_gid;
          uint64_t size;
  
          /*
           * note: vget is required for any operation that might mod the vnode
           * so VINACTIVE is properly cleared.
           */
          if ((error = vget(vp, LK_EXCLUSIVE)) == 0) {
                  if ((error = VOP_GETATTR(vp, &vattr)) != 0)
                          return error;
                  o_uid = vattr.va_uid;
                  o_gid = vattr.va_gid;
                  size = vattr.va_size;
  
                  VATTR_NULL(&vattr);
                  vattr.va_uid = uid;
                  vattr.va_gid = gid;
                  error = VOP_SETATTR(vp, &vattr, td->td_ucred);
                  vput(vp);
          }
  
          if (error == 0) {
                  if (uid == -1)
                          uid = o_uid;
                  if (gid == -1)
                          gid = o_gid;
                  VFS_ACCOUNT(mp, o_uid, o_gid, -size);
                  VFS_ACCOUNT(mp,   uid,   gid,  size);
          }
  
          return error;
  }
  
  int
  kern_chown(struct nlookupdata *nd, int uid, int gid)
  {
          struct vnode *vp;
          int error;
  
          if ((error = nlookup(nd)) != 0)
                  return (error);
          if ((error = cache_vref(&nd->nl_nch, nd->nl_cred, &vp)) != 0)
                  return (error);
          if ((error = ncp_writechk(&nd->nl_nch)) == 0)
                  error = setfown(nd->nl_nch.mount, vp, uid, gid);
          vrele(vp);
          return (error);
  }
  
  /*
   * chown(char *path, int uid, int gid)
   *
   * Set ownership given a path name.
   */
  int
  sys_chown(struct chown_args *uap)
  {
          struct nlookupdata nd;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
          if (error == 0)
                  error = kern_chown(&nd, uap->uid, uap->gid);
          nlookup_done(&nd);
          return (error);
  }
  
  /*
   * lchown_args(char *path, int uid, int gid)
   *
   * Set ownership given a path name, do not cross symlinks.
   */
  int
  sys_lchown(struct lchown_args *uap)
  {
          struct nlookupdata nd;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, 0);
          if (error == 0)
                  error = kern_chown(&nd, uap->uid, uap->gid);
          nlookup_done(&nd);
          return (error);
  }
  
  /*
   * fchown_args(int fd, int uid, int gid)
   *
   * Set ownership given a file descriptor.
   */
  int
  sys_fchown(struct fchown_args *uap)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct file *fp;
          int error;
  
          if ((error = holdvnode(p->p_fd, uap->fd, &fp)) != 0)
                  return (error);
          if (fp->f_nchandle.ncp)
                  error = ncp_writechk(&fp->f_nchandle);
          if (error == 0)
                  error = setfown(p->p_fd->fd_ncdir.mount,
                          (struct vnode *)fp->f_data, uap->uid, uap->gid);
          fdrop(fp);
          return (error);
  }
  
  /*
   * fchownat(int fd, char *path, int uid, int gid, int flags)
   *
   * Set ownership of file pointed to by fd/path.
   */
  int
  sys_fchownat(struct fchownat_args *uap)
  {
          struct nlookupdata nd;
          struct file *fp;
          int error;
          int flags;
  
          if (uap->flags & ~AT_SYMLINK_NOFOLLOW)
                  return (EINVAL);
          flags = (uap->flags & AT_SYMLINK_NOFOLLOW) ? 0 : NLC_FOLLOW;
  
          error = nlookup_init_at(&nd, &fp, uap->fd, uap->path, 
                                  UIO_USERSPACE, flags);
          if (error == 0)
                  error = kern_chown(&nd, uap->uid, uap->gid);
          nlookup_done_at(&nd, fp);
          return (error);
  }
  
  
  static int
  getutimes(const struct timeval *tvp, struct timespec *tsp)
  {
          struct timeval tv[2];
  
          if (tvp == NULL) {
                  microtime(&tv[0]);
                  TIMEVAL_TO_TIMESPEC(&tv[0], &tsp[0]);
                  tsp[1] = tsp[0];
          } else {
                  TIMEVAL_TO_TIMESPEC(&tvp[0], &tsp[0]);
                  TIMEVAL_TO_TIMESPEC(&tvp[1], &tsp[1]);
          }
          return 0;
  }
  
  static int
  setutimes(struct vnode *vp, struct vattr *vattr,
            const struct timespec *ts, int nullflag)
  {
          struct thread *td = curthread;
          int error;
  
          VATTR_NULL(vattr);
          vattr->va_atime = ts[0];
          vattr->va_mtime = ts[1];
          if (nullflag)
                  vattr->va_vaflags |= VA_UTIMES_NULL;
          error = VOP_SETATTR(vp, vattr, td->td_ucred);
  
          return error;
  }
  
  int
  kern_utimes(struct nlookupdata *nd, struct timeval *tptr)
  {
          struct timespec ts[2];
          struct vnode *vp;
          struct vattr vattr;
          int error;
  
          if ((error = getutimes(tptr, ts)) != 0)
                  return (error);
  
          /*
           * NOTE: utimes() succeeds for the owner even if the file
           * is not user-writable.
           */
          nd->nl_flags |= NLC_OWN | NLC_WRITE;
  
          if ((error = nlookup(nd)) != 0)
                  return (error);
          if ((error = ncp_writechk(&nd->nl_nch)) != 0)
                  return (error);
          if ((error = cache_vref(&nd->nl_nch, nd->nl_cred, &vp)) != 0)
                  return (error);
  
          /*
           * note: vget is required for any operation that might mod the vnode
           * so VINACTIVE is properly cleared.
           */
          if ((error = vn_writechk(vp, &nd->nl_nch)) == 0) {
                  error = vget(vp, LK_EXCLUSIVE);
                  if (error == 0) {
                          error = setutimes(vp, &vattr, ts, (tptr == NULL));
                          vput(vp);
                  }
          }
          vrele(vp);
          return (error);
  }
  
  /*
   * utimes_args(char *path, struct timeval *tptr)
   *
   * Set the access and modification times of a file.
   */
  int
  sys_utimes(struct utimes_args *uap)
  {
          struct timeval tv[2];
          struct nlookupdata nd;
          int error;
  
          if (uap->tptr) {
                  error = copyin(uap->tptr, tv, sizeof(tv));
                  if (error)
                          return (error);
          }
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
          if (error == 0)
                  error = kern_utimes(&nd, uap->tptr ? tv : NULL);
          nlookup_done(&nd);
          return (error);
  }
  
  /*
   * lutimes_args(char *path, struct timeval *tptr)
   *
   * Set the access and modification times of a file.
   */
  int
  sys_lutimes(struct lutimes_args *uap)
  {
          struct timeval tv[2];
          struct nlookupdata nd;
          int error;
  
          if (uap->tptr) {
                  error = copyin(uap->tptr, tv, sizeof(tv));
                  if (error)
                          return (error);
          }
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, 0);
          if (error == 0)
                  error = kern_utimes(&nd, uap->tptr ? tv : NULL);
          nlookup_done(&nd);
          return (error);
  }
  
  /*
   * Set utimes on a file descriptor.  The creds used to open the
   * file are used to determine whether the operation is allowed
   * or not.
   */
  int
  kern_futimes(int fd, struct timeval *tptr)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct timespec ts[2];
          struct file *fp;
          struct vnode *vp;
          struct vattr vattr;
          int error;
  
          error = getutimes(tptr, ts);
          if (error)
                  return (error);
          if ((error = holdvnode(p->p_fd, fd, &fp)) != 0)
                  return (error);
          if (fp->f_nchandle.ncp)
                  error = ncp_writechk(&fp->f_nchandle);
          if (error == 0) {
                  vp = fp->f_data;
                  error = vget(vp, LK_EXCLUSIVE);
                  if (error == 0) {
                          error = VOP_GETATTR(vp, &vattr);
                          if (error == 0) {
                                  error = naccess_va(&vattr, NLC_OWN | NLC_WRITE,
                                                     fp->f_cred);
                          }
                          if (error == 0) {
                                  error = setutimes(vp, &vattr, ts,
                                                    (tptr == NULL));
                          }
                          vput(vp);
                  }
          }
          fdrop(fp);
          return (error);
  }
  
  /*
   * futimes_args(int fd, struct timeval *tptr)
   *
   * Set the access and modification times of a file.
   */
  int
  sys_futimes(struct futimes_args *uap)
  {
          struct timeval tv[2];
          int error;
  
          if (uap->tptr) {
                  error = copyin(uap->tptr, tv, sizeof(tv));
                  if (error)
                          return (error);
          }
          error = kern_futimes(uap->fd, uap->tptr ? tv : NULL);
  
          return (error);
  }
  
  int
  kern_truncate(struct nlookupdata *nd, off_t length)
  {
          struct vnode *vp;
          struct vattr vattr;
          int error;
          uid_t uid = 0;
          gid_t gid = 0;
          uint64_t old_size = 0;
  
          if (length < 0)
                  return(EINVAL);
          nd->nl_flags |= NLC_WRITE | NLC_TRUNCATE;
          if ((error = nlookup(nd)) != 0)
                  return (error);
          if ((error = ncp_writechk(&nd->nl_nch)) != 0)
                  return (error);
          if ((error = cache_vref(&nd->nl_nch, nd->nl_cred, &vp)) != 0)
                  return (error);
          error = vn_lock(vp, LK_EXCLUSIVE | LK_RETRY | LK_FAILRECLAIM);
          if (error) {
                  vrele(vp);
                  return (error);
          }
          if (vp->v_type == VDIR) {
                  error = EISDIR;
                  goto done;
          }
          if (vfs_quota_enabled) {
                  error = VOP_GETATTR(vp, &vattr);
                  KASSERT(error == 0, ("kern_truncate(): VOP_GETATTR didn't return 0"));
                  uid = vattr.va_uid;
                  gid = vattr.va_gid;
                  old_size = vattr.va_size;
          }
  
          if ((error = vn_writechk(vp, &nd->nl_nch)) == 0) {
                  VATTR_NULL(&vattr);
                  vattr.va_size = length;
                  error = VOP_SETATTR(vp, &vattr, nd->nl_cred);
                  VFS_ACCOUNT(nd->nl_nch.mount, uid, gid, length - old_size);
          }
  done:
          vput(vp);
          return (error);
  }
  
  /*
   * truncate(char *path, int pad, off_t length)
   *
   * Truncate a file given its path name.
   */
  int
  sys_truncate(struct truncate_args *uap)
  {
          struct nlookupdata nd;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
          if (error == 0)
                  error = kern_truncate(&nd, uap->length);
          nlookup_done(&nd);
          return error;
  }
  
  int
  kern_ftruncate(int fd, off_t length)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct vattr vattr;
          struct vnode *vp;
          struct file *fp;
          int error;
          uid_t uid = 0;
          gid_t gid = 0;
          uint64_t old_size = 0;
          struct mount *mp;
  
          if (length < 0)
                  return(EINVAL);
          if ((error = holdvnode(p->p_fd, fd, &fp)) != 0)
                  return (error);
          if (fp->f_nchandle.ncp) {
                  error = ncp_writechk(&fp->f_nchandle);
                  if (error)
                          goto done;
          }
          if ((fp->f_flag & FWRITE) == 0) {
                  error = EINVAL;
                  goto done;
          }
          if (fp->f_flag & FAPPENDONLY) { /* inode was set s/uapnd */
                  error = EINVAL;
                  goto done;
          }
          vp = (struct vnode *)fp->f_data;
          vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
          if (vp->v_type == VDIR) {
                  error = EISDIR;
                  goto done;
          }
  
          if (vfs_quota_enabled) {
                  error = VOP_GETATTR(vp, &vattr);
                  KASSERT(error == 0, ("kern_ftruncate(): VOP_GETATTR didn't return 0"));
                  uid = vattr.va_uid;
                  gid = vattr.va_gid;
                  old_size = vattr.va_size;
          }
  
          if ((error = vn_writechk(vp, NULL)) == 0) {
                  VATTR_NULL(&vattr);
                  vattr.va_size = length;
                  error = VOP_SETATTR(vp, &vattr, fp->f_cred);
                  mp = vq_vptomp(vp);
                  VFS_ACCOUNT(mp, uid, gid, length - old_size);
          }
          vn_unlock(vp);
  done:
          fdrop(fp);
          return (error);
  }
  
  /*
   * ftruncate_args(int fd, int pad, off_t length)
   *
   * Truncate a file given a file descriptor.
   */
  int
  sys_ftruncate(struct ftruncate_args *uap)
  {
          int error;
  
          error = kern_ftruncate(uap->fd, uap->length);
  
          return (error);
  }
  
  /*
   * fsync(int fd)
   *
   * Sync an open file.
   */
  int
  sys_fsync(struct fsync_args *uap)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct vnode *vp;
          struct file *fp;
          vm_object_t obj;
          int error;
  
          if ((error = holdvnode(p->p_fd, uap->fd, &fp)) != 0)
                  return (error);
          vp = (struct vnode *)fp->f_data;
          vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
          if ((obj = vp->v_object) != NULL) {
                  if (vp->v_mount == NULL ||
                      (vp->v_mount->mnt_kern_flag & MNTK_NOMSYNC) == 0) {
                          vm_object_page_clean(obj, 0, 0, 0);
                  }
          }
          error = VOP_FSYNC(vp, MNT_WAIT, VOP_FSYNC_SYSCALL);
          if (error == 0 && vp->v_mount)
                  error = buf_fsync(vp);
          vn_unlock(vp);
          fdrop(fp);
  
          return (error);
  }
  
  int
  kern_rename(struct nlookupdata *fromnd, struct nlookupdata *tond)
  {
          struct nchandle fnchd;
          struct nchandle tnchd;
          struct namecache *ncp;
          struct vnode *fdvp;
          struct vnode *tdvp;
          struct mount *mp;
          int error;
  
          bwillinode(1);
          fromnd->nl_flags |= NLC_REFDVP | NLC_RENAME_SRC;
          if ((error = nlookup(fromnd)) != 0)
                  return (error);
          if ((fnchd.ncp = fromnd->nl_nch.ncp->nc_parent) == NULL)
                  return (ENOENT);
          fnchd.mount = fromnd->nl_nch.mount;
          cache_hold(&fnchd);
  
          /*
           * unlock the source nch so we can lookup the target nch without
           * deadlocking.  The target may or may not exist so we do not check
           * for a target vp like kern_mkdir() and other creation functions do.
           *
           * The source and target directories are ref'd and rechecked after
           * everything is relocked to determine if the source or target file
           * has been renamed.
           */
          KKASSERT(fromnd->nl_flags & NLC_NCPISLOCKED);
          fromnd->nl_flags &= ~NLC_NCPISLOCKED;
          cache_unlock(&fromnd->nl_nch);
  
          tond->nl_flags |= NLC_RENAME_DST | NLC_REFDVP;
          if ((error = nlookup(tond)) != 0) {
                  cache_drop(&fnchd);
                  return (error);
          }
          if ((tnchd.ncp = tond->nl_nch.ncp->nc_parent) == NULL) {
                  cache_drop(&fnchd);
                  return (ENOENT);
          }
          tnchd.mount = tond->nl_nch.mount;
          cache_hold(&tnchd);
  
          /*
           * If the source and target are the same there is nothing to do
           */
          if (fromnd->nl_nch.ncp == tond->nl_nch.ncp) {
                  cache_drop(&fnchd);
                  cache_drop(&tnchd);
                  return (0);
          }
  
          /*
           * Mount points cannot be renamed or overwritten
           */
          if ((fromnd->nl_nch.ncp->nc_flag | tond->nl_nch.ncp->nc_flag) &
              NCF_ISMOUNTPT
          ) {
                  cache_drop(&fnchd);
                  cache_drop(&tnchd);
                  return (EINVAL);
          }
  
          /*
           * Relock the source ncp.  cache_relock() will deal with any
           * deadlocks against the already-locked tond and will also
           * make sure both are resolved.
           *
           * NOTE AFTER RELOCKING: The source or target ncp may have become
           * invalid while they were unlocked, nc_vp and nc_mount could
           * be NULL.
           */
          cache_relock(&fromnd->nl_nch, fromnd->nl_cred,
                       &tond->nl_nch, tond->nl_cred);
          fromnd->nl_flags |= NLC_NCPISLOCKED;
  
          /*
           * If either fromnd or tond are marked destroyed a ripout occured
           * out from under us and we must retry.
           */
          if ((fromnd->nl_nch.ncp->nc_flag & (NCF_DESTROYED | NCF_UNRESOLVED)) ||
              fromnd->nl_nch.ncp->nc_vp == NULL ||
              (tond->nl_nch.ncp->nc_flag & NCF_DESTROYED)) {
                  kprintf("kern_rename: retry due to ripout on: "
                          "\"%s\" -> \"%s\"\n",
                          fromnd->nl_nch.ncp->nc_name,
                          tond->nl_nch.ncp->nc_name);
                  cache_drop(&fnchd);
                  cache_drop(&tnchd);
                  return (EAGAIN);
          }
  
          /*
           * make sure the parent directories linkages are the same
           */
          if (fnchd.ncp != fromnd->nl_nch.ncp->nc_parent ||
              tnchd.ncp != tond->nl_nch.ncp->nc_parent) {
                  cache_drop(&fnchd);
                  cache_drop(&tnchd);
                  return (ENOENT);
          }
  
          /*
           * Both the source and target must be within the same filesystem and
           * in the same filesystem as their parent directories within the
           * namecache topology.
           *
           * NOTE: fromnd's nc_mount or nc_vp could be NULL.
           */
          mp = fnchd.mount;
          if (mp != tnchd.mount || mp != fromnd->nl_nch.mount ||
              mp != tond->nl_nch.mount) {
                  cache_drop(&fnchd);
                  cache_drop(&tnchd);
                  return (EXDEV);
          }
  
          /*
           * Make sure the mount point is writable
           */
          if ((error = ncp_writechk(&tond->nl_nch)) != 0) {
                  cache_drop(&fnchd);
                  cache_drop(&tnchd);
                  return (error);
          }
  
          /*
           * If the target exists and either the source or target is a directory,
           * then both must be directories.
           *
           * Due to relocking of the source, fromnd->nl_nch.ncp->nc_vp might h
           * have become NULL.
           */
          if (tond->nl_nch.ncp->nc_vp) {
                  if (fromnd->nl_nch.ncp->nc_vp == NULL) {
                          error = ENOENT;
                  } else if (fromnd->nl_nch.ncp->nc_vp->v_type == VDIR) {
                          if (tond->nl_nch.ncp->nc_vp->v_type != VDIR)
                                  error = ENOTDIR;
                  } else if (tond->nl_nch.ncp->nc_vp->v_type == VDIR) {
                          error = EISDIR;
                  }
          }
  
          /*
           * You cannot rename a source into itself or a subdirectory of itself.
           * We check this by travsersing the target directory upwards looking
           * for a match against the source.
           *
           * XXX MPSAFE
           */
          if (error == 0) {
                  for (ncp = tnchd.ncp; ncp; ncp = ncp->nc_parent) {
                          if (fromnd->nl_nch.ncp == ncp) {
                                  error = EINVAL;
                                  break;
                          }
                  }
          }
  
          cache_drop(&fnchd);
          cache_drop(&tnchd);
  
          /*
           * Even though the namespaces are different, they may still represent
           * hardlinks to the same file.  The filesystem might have a hard time
           * with this so we issue a NREMOVE of the source instead of a NRENAME
           * when we detect the situation.
           */
          if (error == 0) {
                  fdvp = fromnd->nl_dvp;
                  tdvp = tond->nl_dvp;
                  if (fdvp == NULL || tdvp == NULL) {
                          error = EPERM;
                  } else if (fromnd->nl_nch.ncp->nc_vp == tond->nl_nch.ncp->nc_vp) {
                          error = VOP_NREMOVE(&fromnd->nl_nch, fdvp,
                                              fromnd->nl_cred);
                  } else {
                          error = VOP_NRENAME(&fromnd->nl_nch, &tond->nl_nch, 
                                              fdvp, tdvp, tond->nl_cred);
                  }
          }
          return (error);
  }
  
  /*
   * rename_args(char *from, char *to)
   *
   * Rename files.  Source and destination must either both be directories,
   * or both not be directories.  If target is a directory, it must be empty.
   */
  int
  sys_rename(struct rename_args *uap)
  {
          struct nlookupdata fromnd, tond;
          int error;
  
          do {
                  error = nlookup_init(&fromnd, uap->from, UIO_USERSPACE, 0);
                  if (error == 0) {
                          error = nlookup_init(&tond, uap->to, UIO_USERSPACE, 0);
                          if (error == 0)
                                  error = kern_rename(&fromnd, &tond);
                          nlookup_done(&tond);
                  }
                  nlookup_done(&fromnd);
          } while (error == EAGAIN);
          return (error);
  }
  
  /*
   * renameat_args(int oldfd, char *old, int newfd, char *new)
   *
   * Rename files using paths relative to the directories associated with
   * oldfd and newfd.  Source and destination must either both be directories,
   * or both not be directories.  If target is a directory, it must be empty.
   */
  int
  sys_renameat(struct renameat_args *uap)
  {
          struct nlookupdata oldnd, newnd;
          struct file *oldfp, *newfp;
          int error;
  
          do {
                  error = nlookup_init_at(&oldnd, &oldfp,
                                          uap->oldfd, uap->old,
                                          UIO_USERSPACE, 0);
                  if (error == 0) {
                          error = nlookup_init_at(&newnd, &newfp,
                                                  uap->newfd, uap->new,
                                                  UIO_USERSPACE, 0);
                          if (error == 0)
                                  error = kern_rename(&oldnd, &newnd);
                          nlookup_done_at(&newnd, newfp);
                  }
                  nlookup_done_at(&oldnd, oldfp);
          } while (error == EAGAIN);
          return (error);
  }
  
  int
  kern_mkdir(struct nlookupdata *nd, int mode)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct vnode *vp;
          struct vattr vattr;
          int error;
  
          bwillinode(1);
          nd->nl_flags |= NLC_WILLBEDIR | NLC_CREATE | NLC_REFDVP;
          if ((error = nlookup(nd)) != 0)
                  return (error);
  
          if (nd->nl_nch.ncp->nc_vp)
                  return (EEXIST);
          if ((error = ncp_writechk(&nd->nl_nch)) != 0)
                  return (error);
          VATTR_NULL(&vattr);
          vattr.va_type = VDIR;
          vattr.va_mode = (mode & ACCESSPERMS) &~ p->p_fd->fd_cmask;
  
          vp = NULL;
          error = VOP_NMKDIR(&nd->nl_nch, nd->nl_dvp, &vp, td->td_ucred, &vattr);
          if (error == 0)
                  vput(vp);
          return (error);
  }
  
  /*
   * mkdir_args(char *path, int mode)
   *
   * Make a directory file.
   */
  int
  sys_mkdir(struct mkdir_args *uap)
  {
          struct nlookupdata nd;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, 0);
          if (error == 0)
                  error = kern_mkdir(&nd, uap->mode);
          nlookup_done(&nd);
          return (error);
  }
  
  /*
   * mkdirat_args(int fd, char *path, mode_t mode)
   *
   * Make a directory file.  The path is relative to the directory associated
   * with fd.
   */
  int
  sys_mkdirat(struct mkdirat_args *uap)
  {
          struct nlookupdata nd;
          struct file *fp;
          int error;
  
          error = nlookup_init_at(&nd, &fp, uap->fd, uap->path, UIO_USERSPACE, 0);
          if (error == 0)
                  error = kern_mkdir(&nd, uap->mode);
          nlookup_done_at(&nd, fp);
          return (error);
  }
  
  int
  kern_rmdir(struct nlookupdata *nd)
  {
          int error;
  
          bwillinode(1);
          nd->nl_flags |= NLC_DELETE | NLC_REFDVP;
          if ((error = nlookup(nd)) != 0)
                  return (error);
  
          /*
           * Do not allow directories representing mount points to be
           * deleted, even if empty.  Check write perms on mount point
           * in case the vnode is aliased (aka nullfs).
           */
          if (nd->nl_nch.ncp->nc_flag & (NCF_ISMOUNTPT))
                  return (EBUSY);
          if ((error = ncp_writechk(&nd->nl_nch)) != 0)
                  return (error);
          error = VOP_NRMDIR(&nd->nl_nch, nd->nl_dvp, nd->nl_cred);
          return (error);
  }
  
  /*
   * rmdir_args(char *path)
   *
   * Remove a directory file.
   */
  int
  sys_rmdir(struct rmdir_args *uap)
  {
          struct nlookupdata nd;
          int error;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, 0);
          if (error == 0)
                  error = kern_rmdir(&nd);
          nlookup_done(&nd);
          return (error);
  }
  
  int
  kern_getdirentries(int fd, char *buf, u_int count, long *basep, int *res,
                     enum uio_seg direction)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct vnode *vp;
          struct file *fp;
          struct uio auio;
          struct iovec aiov;
          off_t loff;
          int error, eofflag;
  
          if ((error = holdvnode(p->p_fd, fd, &fp)) != 0)
                  return (error);
          if ((fp->f_flag & FREAD) == 0) {
                  error = EBADF;
                  goto done;
          }
          vp = (struct vnode *)fp->f_data;
  unionread:
          if (vp->v_type != VDIR) {
                  error = EINVAL;
                  goto done;
          }
          aiov.iov_base = buf;
          aiov.iov_len = count;
          auio.uio_iov = &aiov;
          auio.uio_iovcnt = 1;
          auio.uio_rw = UIO_READ;
          auio.uio_segflg = direction;
          auio.uio_td = td;
          auio.uio_resid = count;
          loff = auio.uio_offset = fp->f_offset;
          error = VOP_READDIR(vp, &auio, fp->f_cred, &eofflag, NULL, NULL);
          fp->f_offset = auio.uio_offset;
          if (error)
                  goto done;
          if (count == auio.uio_resid) {
                  if (union_dircheckp) {
                          error = union_dircheckp(td, &vp, fp);
                          if (error == -1)
                                  goto unionread;
                          if (error)
                                  goto done;
                  }
  #if 0
                  if ((vp->v_flag & VROOT) &&
                      (vp->v_mount->mnt_flag & MNT_UNION)) {
                          struct vnode *tvp = vp;
                          vp = vp->v_mount->mnt_vnodecovered;
                          vref(vp);
                          fp->f_data = vp;
                          fp->f_offset = 0;
                          vrele(tvp);
                          goto unionread;
                  }
  #endif
          }
  
          /*
           * WARNING!  *basep may not be wide enough to accomodate the
           * seek offset.   XXX should we hack this to return the upper 32 bits
           * for offsets greater then 4G?
           */
          if (basep) {
                  *basep = (long)loff;
          }
          *res = count - auio.uio_resid;
  done:
          fdrop(fp);
          return (error);
  }
  
  /*
   * getdirentries_args(int fd, char *buf, u_int conut, long *basep)
   *
   * Read a block of directory entries in a file system independent format.
   */
  int
  sys_getdirentries(struct getdirentries_args *uap)
  {
          long base;
          int error;
  
          error = kern_getdirentries(uap->fd, uap->buf, uap->count, &base,
                                     &uap->sysmsg_result, UIO_USERSPACE);
  
          if (error == 0 && uap->basep)
                  error = copyout(&base, uap->basep, sizeof(*uap->basep));
          return (error);
  }
  
  /*
   * getdents_args(int fd, char *buf, size_t count)
   */
  int
  sys_getdents(struct getdents_args *uap)
  {
          int error;
  
          error = kern_getdirentries(uap->fd, uap->buf, uap->count, NULL,
                                     &uap->sysmsg_result, UIO_USERSPACE);
  
          return (error);
  }
  
  /*
   * Set the mode mask for creation of filesystem nodes.
   *
   * umask(int newmask)
   */
  int
  sys_umask(struct umask_args *uap)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct filedesc *fdp;
  
          fdp = p->p_fd;
          uap->sysmsg_result = fdp->fd_cmask;
          fdp->fd_cmask = uap->newmask & ALLPERMS;
          return (0);
  }
  
  /*
   * revoke(char *path)
   *
   * Void all references to file by ripping underlying filesystem
   * away from vnode.
   */
  int
  sys_revoke(struct revoke_args *uap)
  {
          struct nlookupdata nd;
          struct vattr vattr;
          struct vnode *vp;
          struct ucred *cred;
          int error;
  
          vp = NULL;
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
          if (error == 0)
                  error = nlookup(&nd);
          if (error == 0)
                  error = cache_vref(&nd.nl_nch, nd.nl_cred, &vp);
          cred = crhold(nd.nl_cred);
          nlookup_done(&nd);
          if (error == 0) {
                  if (error == 0)
                          error = VOP_GETATTR(vp, &vattr);
                  if (error == 0 && cred->cr_uid != vattr.va_uid)
                          error = priv_check_cred(cred, PRIV_VFS_REVOKE, 0);
                  if (error == 0 && (vp->v_type == VCHR || vp->v_type == VBLK)) {
                          if (vcount(vp) > 0)
                                  error = vrevoke(vp, cred);
                  } else if (error == 0) {
                          error = vrevoke(vp, cred);
                  }
                  vrele(vp);
          }
          if (cred)
                  crfree(cred);
          return (error);
  }
  
  /*
   * getfh_args(char *fname, fhandle_t *fhp)
   *
   * Get (NFS) file handle
   *
   * NOTE: We use the fsid of the covering mount, even if it is a nullfs
   * mount.  This allows nullfs mounts to be explicitly exported. 
   *
   * WARNING: nullfs mounts of HAMMER PFS ROOTs are safe.
   *
   *          nullfs mounts of subdirectories are not safe.  That is, it will
   *          work, but you do not really have protection against access to
   *          the related parent directories.
   */
  int
  sys_getfh(struct getfh_args *uap)
  {
          struct thread *td = curthread;
          struct nlookupdata nd;
          fhandle_t fh;
          struct vnode *vp;
          struct mount *mp;
          int error;
  
          /*
           * Must be super user
           */
          if ((error = priv_check(td, PRIV_ROOT)) != 0)
                  return (error);
  
          vp = NULL;
          error = nlookup_init(&nd, uap->fname, UIO_USERSPACE, NLC_FOLLOW);
          if (error == 0)
                  error = nlookup(&nd);
          if (error == 0)
                  error = cache_vget(&nd.nl_nch, nd.nl_cred, LK_EXCLUSIVE, &vp);
          mp = nd.nl_nch.mount;
          nlookup_done(&nd);
          if (error == 0) {
                  bzero(&fh, sizeof(fh));
                  fh.fh_fsid = mp->mnt_stat.f_fsid;
                  error = VFS_VPTOFH(vp, &fh.fh_fid);
                  vput(vp);
                  if (error == 0)
                          error = copyout(&fh, uap->fhp, sizeof(fh));
          }
          return (error);
  }
  
  /*
   * fhopen_args(const struct fhandle *u_fhp, int flags)
   *
   * syscall for the rpc.lockd to use to translate a NFS file handle into
   * an open descriptor.
   *
   * warning: do not remove the priv_check() call or this becomes one giant
   * security hole.
   */
  int
  sys_fhopen(struct fhopen_args *uap)
  {
          struct thread *td = curthread;
          struct filedesc *fdp = td->td_proc->p_fd;
          struct mount *mp;
          struct vnode *vp;
          struct fhandle fhp;
          struct vattr vat;
          struct vattr *vap = &vat;
          struct flock lf;
          int fmode, mode, error = 0, type;
          struct file *nfp; 
          struct file *fp;
          int indx;
  
          /*
           * Must be super user
           */
          error = priv_check(td, PRIV_ROOT);
          if (error)
                  return (error);
  
          fmode = FFLAGS(uap->flags);
  
          /*
           * Why not allow a non-read/write open for our lockd?
           */
          if (((fmode & (FREAD | FWRITE)) == 0) || (fmode & O_CREAT))
                  return (EINVAL);
          error = copyin(uap->u_fhp, &fhp, sizeof(fhp));
          if (error)
                  return(error);
  
          /*
           * Find the mount point
           */
          mp = vfs_getvfs(&fhp.fh_fsid);
          if (mp == NULL) {
                  error = ESTALE;
                  goto  done;
          }
          /* now give me my vnode, it gets returned to me locked */
          error = VFS_FHTOVP(mp, NULL, &fhp.fh_fid, &vp);
          if (error)
                  goto done;
          /*
           * from now on we have to make sure not
           * to forget about the vnode
           * any error that causes an abort must vput(vp) 
           * just set error = err and 'goto bad;'.
           */
  
          /* 
           * from vn_open 
           */
          if (vp->v_type == VLNK) {
                  error = EMLINK;
                  goto bad;
          }
          if (vp->v_type == VSOCK) {
                  error = EOPNOTSUPP;
                  goto bad;
          }
          mode = 0;
          if (fmode & (FWRITE | O_TRUNC)) {
                  if (vp->v_type == VDIR) {
                          error = EISDIR;
                          goto bad;
                  }
                  error = vn_writechk(vp, NULL);
                  if (error)
                          goto bad;
                  mode |= VWRITE;
          }
          if (fmode & FREAD)
                  mode |= VREAD;
          if (mode) {
                  error = VOP_ACCESS(vp, mode, td->td_ucred);
                  if (error)
                          goto bad;
          }
          if (fmode & O_TRUNC) {
                  vn_unlock(vp);                          /* XXX */
                  vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);   /* XXX */
                  VATTR_NULL(vap);
                  vap->va_size = 0;
                  error = VOP_SETATTR(vp, vap, td->td_ucred);
                  if (error)
                          goto bad;
          }
  
          /*
           * VOP_OPEN needs the file pointer so it can potentially override
           * it.
           *
           * WARNING! no f_nchandle will be associated when fhopen()ing a
           * directory.  XXX
           */
          if ((error = falloc(td->td_lwp, &nfp, &indx)) != 0)
                  goto bad;
          fp = nfp;
  
          error = VOP_OPEN(vp, fmode, td->td_ucred, fp);
          if (error) {
                  /*
                   * setting f_ops this way prevents VOP_CLOSE from being
                   * called or fdrop() releasing the vp from v_data.   Since
                   * the VOP_OPEN failed we don't want to VOP_CLOSE.
                   */
                  fp->f_ops = &badfileops;
                  fp->f_data = NULL;
                  goto bad_drop;
          }
  
          /*
           * The fp is given its own reference, we still have our ref and lock.
           *
           * Assert that all regular files must be created with a VM object.
           */
          if (vp->v_type == VREG && vp->v_object == NULL) {
                  kprintf("fhopen: regular file did not have VM object: %p\n", vp);
                  goto bad_drop;
          }
  
          /*
           * The open was successful.  Handle any locking requirements.
           */
          if (fmode & (O_EXLOCK | O_SHLOCK)) {
                  lf.l_whence = SEEK_SET;
                  lf.l_start = 0;
                  lf.l_len = 0;
                  if (fmode & O_EXLOCK)
                          lf.l_type = F_WRLCK;
                  else
                          lf.l_type = F_RDLCK;
                  if (fmode & FNONBLOCK)
                          type = 0;
                  else
                          type = F_WAIT;
                  vn_unlock(vp);
                  if ((error = VOP_ADVLOCK(vp, (caddr_t)fp, F_SETLK, &lf, type)) != 0) {
                          /*
                           * release our private reference.
                           */
                          fsetfd(fdp, NULL, indx);
                          fdrop(fp);
                          vrele(vp);
                          goto done;
                  }
                  vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
                  fp->f_flag |= FHASLOCK;
          }
  
          /*
           * Clean up.  Associate the file pointer with the previously
           * reserved descriptor and return it.
           */
          vput(vp);
          fsetfd(fdp, fp, indx);
          fdrop(fp);
          uap->sysmsg_result = indx;
          if (uap->flags & O_CLOEXEC)
                  error = fsetfdflags(fdp, indx, UF_EXCLOSE);
          return (error);
  
  bad_drop:
          fsetfd(fdp, NULL, indx);
          fdrop(fp);
  bad:
          vput(vp);
  done:
          return (error);
  }
  
  /*
   * fhstat_args(struct fhandle *u_fhp, struct stat *sb)
   */
  int
  sys_fhstat(struct fhstat_args *uap)
  {
          struct thread *td = curthread;
          struct stat sb;
          fhandle_t fh;
          struct mount *mp;
          struct vnode *vp;
          int error;
  
          /*
           * Must be super user
           */
          error = priv_check(td, PRIV_ROOT);
          if (error)
                  return (error);
          
          error = copyin(uap->u_fhp, &fh, sizeof(fhandle_t));
          if (error)
                  return (error);
  
          if ((mp = vfs_getvfs(&fh.fh_fsid)) == NULL)
                  error = ESTALE;
          if (error == 0) {
                  if ((error = VFS_FHTOVP(mp, NULL, &fh.fh_fid, &vp)) == 0) {
                          error = vn_stat(vp, &sb, td->td_ucred);
                          vput(vp);
                  }
          }
          if (error == 0)
                  error = copyout(&sb, uap->sb, sizeof(sb));
          return (error);
  }
  
  /*
   * fhstatfs_args(struct fhandle *u_fhp, struct statfs *buf)
   */
  int
  sys_fhstatfs(struct fhstatfs_args *uap)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct statfs *sp;
          struct mount *mp;
          struct vnode *vp;
          struct statfs sb;
          char *fullpath, *freepath;
          fhandle_t fh;
          int error;
  
          /*
           * Must be super user
           */
          if ((error = priv_check(td, PRIV_ROOT)))
                  return (error);
  
          if ((error = copyin(uap->u_fhp, &fh, sizeof(fhandle_t))) != 0)
                  return (error);
  
          if ((mp = vfs_getvfs(&fh.fh_fsid)) == NULL) {
                  error = ESTALE;
                  goto done;
          }
          if (p != NULL && !chroot_visible_mnt(mp, p)) {
                  error = ESTALE;
                  goto done;
          }
  
          if ((error = VFS_FHTOVP(mp, NULL, &fh.fh_fid, &vp)) != 0)
                  goto done;
          mp = vp->v_mount;
          sp = &mp->mnt_stat;
          vput(vp);
          if ((error = VFS_STATFS(mp, sp, td->td_ucred)) != 0)
                  goto done;
  
          error = mount_path(p, mp, &fullpath, &freepath);
          if (error)
                  goto done;
          bzero(sp->f_mntonname, sizeof(sp->f_mntonname));
          strlcpy(sp->f_mntonname, fullpath, sizeof(sp->f_mntonname));
          kfree(freepath, M_TEMP);
  
          sp->f_flags = mp->mnt_flag & MNT_VISFLAGMASK;
          if (priv_check(td, PRIV_ROOT)) {
                  bcopy(sp, &sb, sizeof(sb));
                  sb.f_fsid.val[0] = sb.f_fsid.val[1] = 0;
                  sp = &sb;
          }
          error = copyout(sp, uap->buf, sizeof(*sp));
  done:
          return (error);
  }
  
  /*
   * fhstatvfs_args(struct fhandle *u_fhp, struct statvfs *buf)
   */
  int
  sys_fhstatvfs(struct fhstatvfs_args *uap)
  {
          struct thread *td = curthread;
          struct proc *p = td->td_proc;
          struct statvfs *sp;
          struct mount *mp;
          struct vnode *vp;
          fhandle_t fh;
          int error;
  
          /*
           * Must be super user
           */
          if ((error = priv_check(td, PRIV_ROOT)))
                  return (error);
  
          if ((error = copyin(uap->u_fhp, &fh, sizeof(fhandle_t))) != 0)
                  return (error);
  
          if ((mp = vfs_getvfs(&fh.fh_fsid)) == NULL) {
                  error = ESTALE;
                  goto done;
          }
          if (p != NULL && !chroot_visible_mnt(mp, p)) {
                  error = ESTALE;
                  goto done;
          }
  
          if ((error = VFS_FHTOVP(mp, NULL, &fh.fh_fid, &vp)))
                  goto done;
          mp = vp->v_mount;
          sp = &mp->mnt_vstat;
          vput(vp);
          if ((error = VFS_STATVFS(mp, sp, td->td_ucred)) != 0)
                  goto done;
  
          sp->f_flag = 0;
          if (mp->mnt_flag & MNT_RDONLY)
                  sp->f_flag |= ST_RDONLY;
          if (mp->mnt_flag & MNT_NOSUID)
                  sp->f_flag |= ST_NOSUID;
          error = copyout(sp, uap->buf, sizeof(*sp));
  done:
          return (error);
  }
  
  
  /*
   * Syscall to push extended attribute configuration information into the
   * VFS.  Accepts a path, which it converts to a mountpoint, as well as
   * a command (int cmd), and attribute name and misc data.  For now, the
   * attribute name is left in userspace for consumption by the VFS_op.
   * It will probably be changed to be copied into sysspace by the
   * syscall in the future, once issues with various consumers of the
   * attribute code have raised their hands.
   *
   * Currently this is used only by UFS Extended Attributes.
   */
  int
  sys_extattrctl(struct extattrctl_args *uap)
  {
          struct nlookupdata nd;
          struct vnode *vp;
          char attrname[EXTATTR_MAXNAMELEN];
          int error;
          size_t size;
  
          attrname[0] = 0;
          vp = NULL;
          error = 0;
  
          if (error == 0 && uap->filename) {
                  error = nlookup_init(&nd, uap->filename, UIO_USERSPACE,
                                       NLC_FOLLOW);
                  if (error == 0)
                          error = nlookup(&nd);
                  if (error == 0)
                          error = cache_vref(&nd.nl_nch, nd.nl_cred, &vp);
                  nlookup_done(&nd);
          }
  
          if (error == 0 && uap->attrname) {
                  error = copyinstr(uap->attrname, attrname, EXTATTR_MAXNAMELEN,
                                    &size);
          }
  
          if (error == 0) {
                  error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
                  if (error == 0)
                          error = nlookup(&nd);
                  if (error == 0)
                          error = ncp_writechk(&nd.nl_nch);
                  if (error == 0) {
                          error = VFS_EXTATTRCTL(nd.nl_nch.mount, uap->cmd, vp,
                                                 uap->attrnamespace,
                                                 uap->attrname, nd.nl_cred);
                  }
                  nlookup_done(&nd);
          }
  
          return (error);
  }
  
  /*
   * Syscall to get a named extended attribute on a file or directory.
   */
  int
  sys_extattr_set_file(struct extattr_set_file_args *uap)
  {
          char attrname[EXTATTR_MAXNAMELEN];
          struct nlookupdata nd;
          struct vnode *vp;
          struct uio auio;
          struct iovec aiov;
          int error;
  
          error = copyin(uap->attrname, attrname, EXTATTR_MAXNAMELEN);
          if (error)
                  return (error);
  
          vp = NULL;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
          if (error == 0)
                  error = nlookup(&nd);
          if (error == 0)
                  error = ncp_writechk(&nd.nl_nch);
          if (error == 0)
                  error = cache_vget(&nd.nl_nch, nd.nl_cred, LK_EXCLUSIVE, &vp);
          if (error) {
                  nlookup_done(&nd);
                  return (error);
          }
  
          bzero(&auio, sizeof(auio));
          aiov.iov_base = uap->data;
          aiov.iov_len = uap->nbytes;
          auio.uio_iov = &aiov;
          auio.uio_iovcnt = 1;
          auio.uio_offset = 0;
          auio.uio_resid = uap->nbytes;
          auio.uio_rw = UIO_WRITE;
          auio.uio_td = curthread;
  
          error = VOP_SETEXTATTR(vp, uap->attrnamespace, attrname,
                                 &auio, nd.nl_cred);
  
          vput(vp);
          nlookup_done(&nd);
          return (error);
  }
  
  /*
   * Syscall to get a named extended attribute on a file or directory.
   */
  int
  sys_extattr_get_file(struct extattr_get_file_args *uap)
  {
          char attrname[EXTATTR_MAXNAMELEN];
          struct nlookupdata nd;
          struct uio auio;
          struct iovec aiov;
          struct vnode *vp;
          int error;
  
          error = copyin(uap->attrname, attrname, EXTATTR_MAXNAMELEN);
          if (error)
                  return (error);
  
          vp = NULL;
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
          if (error == 0)
                  error = nlookup(&nd);
          if (error == 0)
                  error = cache_vget(&nd.nl_nch, nd.nl_cred, LK_SHARED, &vp);
          if (error) {
                  nlookup_done(&nd);
                  return (error);
          }
  
          bzero(&auio, sizeof(auio));
          aiov.iov_base = uap->data;
          aiov.iov_len = uap->nbytes;
          auio.uio_iov = &aiov;
          auio.uio_iovcnt = 1;
          auio.uio_offset = 0;
          auio.uio_resid = uap->nbytes;
          auio.uio_rw = UIO_READ;
          auio.uio_td = curthread;
  
          error = VOP_GETEXTATTR(vp, uap->attrnamespace, attrname,
                                  &auio, nd.nl_cred);
          uap->sysmsg_result = uap->nbytes - auio.uio_resid;
  
          vput(vp);
          nlookup_done(&nd);
          return(error);
  }
  
  /*
   * Syscall to delete a named extended attribute from a file or directory.
   * Accepts attribute name.  The real work happens in VOP_SETEXTATTR().
   */
  int
  sys_extattr_delete_file(struct extattr_delete_file_args *uap)
  {
          char attrname[EXTATTR_MAXNAMELEN];
          struct nlookupdata nd;
          struct vnode *vp;
          int error;
  
          error = copyin(uap->attrname, attrname, EXTATTR_MAXNAMELEN);
          if (error)
                  return(error);
  
          error = nlookup_init(&nd, uap->path, UIO_USERSPACE, NLC_FOLLOW);
          if (error == 0)
                  error = nlookup(&nd);
          if (error == 0)
                  error = ncp_writechk(&nd.nl_nch);
          if (error == 0) {
                  error = cache_vget(&nd.nl_nch, nd.nl_cred, LK_EXCLUSIVE, &vp);
                  if (error == 0) {
                          error = VOP_SETEXTATTR(vp, uap->attrnamespace,
                                                 attrname, NULL, nd.nl_cred);
                          vput(vp);
                  }
          }
          nlookup_done(&nd);
          return(error);
  }
  
  /*
   * Determine if the mount is visible to the process.
   */
  static int
  chroot_visible_mnt(struct mount *mp, struct proc *p)
  {
          struct nchandle nch;
  
          /*
           * Traverse from the mount point upwards.  If we hit the process
           * root then the mount point is visible to the process.
           */
          nch = mp->mnt_ncmountpt;
          while (nch.ncp) {
                  if (nch.mount == p->p_fd->fd_nrdir.mount &&
                      nch.ncp == p->p_fd->fd_nrdir.ncp) {
                          return(1);
                  }
                  if (nch.ncp == nch.mount->mnt_ncmountpt.ncp) {
                          nch = nch.mount->mnt_ncmounton;
                  } else {
                          nch.ncp = nch.ncp->nc_parent;
                  }
          }
  
          /*
           * If the mount point is not visible to the process, but the
           * process root is in a subdirectory of the mount, return
           * TRUE anyway.
           */
          if (p->p_fd->fd_nrdir.mount == mp)
                  return(1);
  
          return(0);
  }