FreeBSD/Linux Kernel Cross Reference
sys/ufs/ufs/ufs_dirhash.c

     /*-
      * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
      *
      * Copyright (c) 2001, 2002 Ian Dowse.  All rights reserved.
      *
      * 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.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     */
    
    /*
     * This implements a hash-based lookup scheme for UFS directories.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include "opt_ufs.h"
    
    #ifdef UFS_DIRHASH
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/kernel.h>
    #include <sys/lock.h>
    #include <sys/mutex.h>
    #include <sys/malloc.h>
    #include <sys/fnv_hash.h>
    #include <sys/proc.h>
    #include <sys/bio.h>
    #include <sys/buf.h>
    #include <sys/vnode.h>
    #include <sys/mount.h>
    #include <sys/refcount.h>
    #include <sys/sysctl.h>
    #include <sys/sx.h>
    #include <sys/eventhandler.h>
    #include <sys/time.h>
    #include <vm/uma.h>
    
    #include <ufs/ufs/quota.h>
    #include <ufs/ufs/inode.h>
    #include <ufs/ufs/dir.h>
    #include <ufs/ufs/dirhash.h>
    #include <ufs/ufs/extattr.h>
    #include <ufs/ufs/ufsmount.h>
    #include <ufs/ufs/ufs_extern.h>
    
    #define WRAPINCR(val, limit)    (((val) + 1 == (limit)) ? 0 : ((val) + 1))
    #define WRAPDECR(val, limit)    (((val) == 0) ? ((limit) - 1) : ((val) - 1))
    #define BLKFREE2IDX(n)          ((n) > DH_NFSTATS ? DH_NFSTATS : (n))
    
    static MALLOC_DEFINE(M_DIRHASH, "ufs_dirhash", "UFS directory hash tables");
    
    static int ufs_mindirhashsize = DIRBLKSIZ * 5;
    SYSCTL_INT(_vfs_ufs, OID_AUTO, dirhash_minsize, CTLFLAG_RW,
        &ufs_mindirhashsize,
        0, "minimum directory size in bytes for which to use hashed lookup");
    static int ufs_dirhashmaxmem = 2 * 1024 * 1024; /* NOTE: initial value. It is
                                                       tuned in ufsdirhash_init() */
    SYSCTL_INT(_vfs_ufs, OID_AUTO, dirhash_maxmem, CTLFLAG_RW, &ufs_dirhashmaxmem,
        0, "maximum allowed dirhash memory usage");
    static int ufs_dirhashmem;
    SYSCTL_INT(_vfs_ufs, OID_AUTO, dirhash_mem, CTLFLAG_RD, &ufs_dirhashmem,
        0, "current dirhash memory usage");
    static int ufs_dirhashcheck = 0;
    SYSCTL_INT(_vfs_ufs, OID_AUTO, dirhash_docheck, CTLFLAG_RW, &ufs_dirhashcheck,
        0, "enable extra sanity tests");
    static int ufs_dirhashlowmemcount = 0;
    SYSCTL_INT(_vfs_ufs, OID_AUTO, dirhash_lowmemcount, CTLFLAG_RD, 
        &ufs_dirhashlowmemcount, 0, "number of times low memory hook called");
    static int ufs_dirhashreclaimpercent = 10;
    static int ufsdirhash_set_reclaimpercent(SYSCTL_HANDLER_ARGS);
    SYSCTL_PROC(_vfs_ufs, OID_AUTO, dirhash_reclaimpercent,
        CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
        0, 0, ufsdirhash_set_reclaimpercent, "I",
        "set percentage of dirhash cache to be removed in low VM events");
    
    static int ufsdirhash_hash(struct dirhash *dh, char *name, int namelen);
    static void ufsdirhash_adjfree(struct dirhash *dh, doff_t offset, int diff);
    static void ufsdirhash_delslot(struct dirhash *dh, int slot);
    static int ufsdirhash_findslot(struct dirhash *dh, char *name, int namelen,
              doff_t offset);
   static doff_t ufsdirhash_getprev(struct direct *dp, doff_t offset);
   static int ufsdirhash_recycle(int wanted);
   static void ufsdirhash_lowmem(void);
   static void ufsdirhash_free_locked(struct inode *ip);
   
   static uma_zone_t       ufsdirhash_zone;
   
   #define DIRHASHLIST_LOCK()              mtx_lock(&ufsdirhash_mtx)
   #define DIRHASHLIST_UNLOCK()            mtx_unlock(&ufsdirhash_mtx)
   #define DIRHASH_BLKALLOC()              uma_zalloc(ufsdirhash_zone, M_NOWAIT)
   #define DIRHASH_BLKFREE(ptr)            uma_zfree(ufsdirhash_zone, (ptr))
   #define DIRHASH_ASSERT_LOCKED(dh)                                       \
       sx_assert(&(dh)->dh_lock, SA_LOCKED)
   
   /* Dirhash list; recently-used entries are near the tail. */
   static TAILQ_HEAD(, dirhash) ufsdirhash_list;
   
   /* Protects: ufsdirhash_list, `dh_list' field, ufs_dirhashmem. */
   static struct mtx       ufsdirhash_mtx;
   
   /*
    * Locking:
    *
    * The relationship between inode and dirhash is protected either by an
    * exclusive vnode lock or the vnode interlock where a shared vnode lock
    * may be used.  The dirhash_mtx is acquired after the dirhash lock.  To
    * handle teardown races, code wishing to lock the dirhash for an inode
    * when using a shared vnode lock must obtain a private reference on the
    * dirhash while holding the vnode interlock.  They can drop it once they
    * have obtained the dirhash lock and verified that the dirhash wasn't
    * recycled while they waited for the dirhash lock.
    *
    * ufsdirhash_build() acquires a shared lock on the dirhash when it is
    * successful.  This lock is released after a call to ufsdirhash_lookup().
    *
    * Functions requiring exclusive access use ufsdirhash_acquire() which may
    * free a dirhash structure that was recycled by ufsdirhash_recycle().
    *
    * The dirhash lock may be held across io operations.
    *
    * WITNESS reports a lock order reversal between the "bufwait" lock
    * and the "dirhash" lock.  However, this specific reversal will not
    * cause a deadlock.  To get a deadlock, one would have to lock a
    * buffer followed by the dirhash while a second thread locked a
    * buffer while holding the dirhash lock.  The second order can happen
    * under a shared or exclusive vnode lock for the associated directory
    * in lookup().  The first order, however, can only happen under an
    * exclusive vnode lock (e.g. unlink(), rename(), etc.).  Thus, for
    * a thread to be doing a "bufwait" -> "dirhash" order, it has to hold
    * an exclusive vnode lock.  That exclusive vnode lock will prevent
    * any other threads from doing a "dirhash" -> "bufwait" order.
    */
   
   static void
   ufsdirhash_hold(struct dirhash *dh)
   {
   
           refcount_acquire(&dh->dh_refcount);
   }
   
   static void
   ufsdirhash_drop(struct dirhash *dh)
   {
   
           if (refcount_release(&dh->dh_refcount)) {
                   sx_destroy(&dh->dh_lock);
                   free(dh, M_DIRHASH);
           }
   }
   
   /*
    * Release the lock on a dirhash.
    */
   static void
   ufsdirhash_release(struct dirhash *dh)
   {
   
           sx_unlock(&dh->dh_lock);
   }
   
   /*
    * Either acquire an existing hash locked shared or create a new hash and
    * return it exclusively locked.  May return NULL if the allocation fails.
    *
    * The vnode interlock is used to protect the i_dirhash pointer from
    * simultaneous access while only a shared vnode lock is held.
    */
   static struct dirhash *
   ufsdirhash_create(struct inode *ip)
   {
           struct dirhash *ndh;
           struct dirhash *dh;
           struct vnode *vp;
           bool excl;
   
           ndh = dh = NULL;
           vp = ip->i_vnode;
           excl = false;
           for (;;) {
                   /* Racy check for i_dirhash to prefetch a dirhash structure. */
                   if (ip->i_dirhash == NULL && ndh == NULL) {
                           ndh = malloc(sizeof *dh, M_DIRHASH,
                               M_NOWAIT | M_ZERO);
                           if (ndh == NULL)
                                   return (NULL);
                           refcount_init(&ndh->dh_refcount, 1);
   
                           /*
                            * The DUPOK is to prevent warnings from the
                            * sx_slock() a few lines down which is safe
                            * since the duplicate lock in that case is
                            * the one for this dirhash we are creating
                            * now which has no external references until
                            * after this function returns.
                            */
                           sx_init_flags(&ndh->dh_lock, "dirhash", SX_DUPOK);
                           sx_xlock(&ndh->dh_lock);
                   }
                   /*
                    * Check i_dirhash.  If it's NULL just try to use a
                    * preallocated structure.  If none exists loop and try again.
                    */
                   VI_LOCK(vp);
                   dh = ip->i_dirhash;
                   if (dh == NULL) {
                           ip->i_dirhash = ndh;
                           VI_UNLOCK(vp);
                           if (ndh == NULL)
                                   continue;
                           return (ndh);
                   }
                   ufsdirhash_hold(dh);
                   VI_UNLOCK(vp);
   
                   /* Acquire a lock on existing hashes. */
                   if (excl)
                           sx_xlock(&dh->dh_lock);
                   else
                           sx_slock(&dh->dh_lock);
   
                   /* The hash could've been recycled while we were waiting. */
                   VI_LOCK(vp);
                   if (ip->i_dirhash != dh) {
                           VI_UNLOCK(vp);
                           ufsdirhash_release(dh);
                           ufsdirhash_drop(dh);
                           continue;
                   }
                   VI_UNLOCK(vp);
                   ufsdirhash_drop(dh);
   
                   /* If the hash is still valid we've succeeded. */
                   if (dh->dh_hash != NULL)
                           break;
                   /*
                    * If the hash is NULL it has been recycled.  Try to upgrade
                    * so we can recreate it.  If we fail the upgrade, drop our
                    * lock and try again.
                    */
                   if (excl || sx_try_upgrade(&dh->dh_lock))
                           break;
                   sx_sunlock(&dh->dh_lock);
                   excl = true;
           }
           /* Free the preallocated structure if it was not necessary. */
           if (ndh) {
                   ufsdirhash_release(ndh);
                   ufsdirhash_drop(ndh);
           }
           return (dh);
   }
   
   /*
    * Acquire an exclusive lock on an existing hash.  Requires an exclusive
    * vnode lock to protect the i_dirhash pointer.  hashes that have been
    * recycled are reclaimed here and NULL is returned.
    */
   static struct dirhash *
   ufsdirhash_acquire(struct inode *ip)
   {
           struct dirhash *dh;
   
           ASSERT_VOP_ELOCKED(ip->i_vnode, __FUNCTION__);
   
           dh = ip->i_dirhash;
           if (dh == NULL)
                   return (NULL);
           sx_xlock(&dh->dh_lock);
           if (dh->dh_hash != NULL)
                   return (dh);
           ufsdirhash_free_locked(ip);
           return (NULL);
   }
   
   /*
    * Acquire exclusively and free the hash pointed to by ip.  Works with a
    * shared or exclusive vnode lock.
    */
   void
   ufsdirhash_free(struct inode *ip)
   {
           struct dirhash *dh;
           struct vnode *vp;
   
           vp = ip->i_vnode;
           for (;;) {
                   /* Grab a reference on this inode's dirhash if it has one. */
                   VI_LOCK(vp);
                   dh = ip->i_dirhash;
                   if (dh == NULL) {
                           VI_UNLOCK(vp);
                           return;
                   }
                   ufsdirhash_hold(dh);
                   VI_UNLOCK(vp);
   
                   /* Exclusively lock the dirhash. */
                   sx_xlock(&dh->dh_lock);
   
                   /* If this dirhash still belongs to this inode, then free it. */
                   VI_LOCK(vp);
                   if (ip->i_dirhash == dh) {
                           VI_UNLOCK(vp);
                           ufsdirhash_drop(dh);
                           break;
                   }
                   VI_UNLOCK(vp);
   
                   /*
                    * This inode's dirhash has changed while we were
                    * waiting for the dirhash lock, so try again.
                    */
                   ufsdirhash_release(dh);
                   ufsdirhash_drop(dh);
           }
           ufsdirhash_free_locked(ip);
   }
   
   /*
    * Attempt to build up a hash table for the directory contents in
    * inode 'ip'. Returns 0 on success, or -1 of the operation failed.
    */
   int
   ufsdirhash_build(struct inode *ip)
   {
           struct dirhash *dh;
           struct buf *bp = NULL;
           struct direct *ep;
           struct vnode *vp;
           doff_t bmask, pos;
           u_int dirblocks, i, narrays, nblocks, nslots;
           int j, memreqd, slot;
   
           /* Take care of a decreased sysctl value. */
           while (ufs_dirhashmem > ufs_dirhashmaxmem) {
                   if (ufsdirhash_recycle(0) != 0)
                           return (-1);
                   /* Recycled enough memory, so unlock the list. */
                   DIRHASHLIST_UNLOCK();
           }
   
           /* Check if we can/should use dirhash. */
           if (ip->i_size < ufs_mindirhashsize || OFSFMT(ip->i_vnode) ||
               ip->i_effnlink == 0) {
                   if (ip->i_dirhash)
                           ufsdirhash_free(ip);
                   return (-1);
           }
           dh = ufsdirhash_create(ip);
           if (dh == NULL)
                   return (-1);
           if (dh->dh_hash != NULL)
                   return (0);
   
           vp = ip->i_vnode;
           /* Allocate 50% more entries than this dir size could ever need. */
           KASSERT(ip->i_size >= DIRBLKSIZ, ("ufsdirhash_build size"));
           nslots = ip->i_size / DIRECTSIZ(1);
           nslots = (nslots * 3 + 1) / 2;
           narrays = howmany(nslots, DH_NBLKOFF);
           nslots = narrays * DH_NBLKOFF;
           dirblocks = howmany(ip->i_size, DIRBLKSIZ);
           nblocks = (dirblocks * 3 + 1) / 2;
           memreqd = sizeof(*dh) + narrays * sizeof(*dh->dh_hash) +
               narrays * DH_NBLKOFF * sizeof(**dh->dh_hash) +
               nblocks * sizeof(*dh->dh_blkfree);
           DIRHASHLIST_LOCK();
           if (memreqd + ufs_dirhashmem > ufs_dirhashmaxmem) {
                   DIRHASHLIST_UNLOCK();
                   if (memreqd > ufs_dirhashmaxmem / 2)
                           goto fail;
                   /* Try to free some space. */
                   if (ufsdirhash_recycle(memreqd) != 0)
                           goto fail;
                   /* Enough was freed, and list has been locked. */
           }
           ufs_dirhashmem += memreqd;
           DIRHASHLIST_UNLOCK();
   
           /* Initialise the hash table and block statistics. */
           dh->dh_memreq = memreqd;
           dh->dh_narrays = narrays;
           dh->dh_hlen = nslots;
           dh->dh_nblk = nblocks;
           dh->dh_dirblks = dirblocks;
           for (i = 0; i < DH_NFSTATS; i++)
                   dh->dh_firstfree[i] = -1;
           dh->dh_firstfree[DH_NFSTATS] = 0;
           dh->dh_hused = 0;
           dh->dh_seqoff = -1;
           dh->dh_score = DH_SCOREINIT;
           dh->dh_lastused = time_second;
   
           /*
            * Use non-blocking mallocs so that we will revert to a linear
            * lookup on failure rather than potentially blocking forever.
            */
           dh->dh_hash = malloc(narrays * sizeof(dh->dh_hash[0]),
               M_DIRHASH, M_NOWAIT | M_ZERO);
           if (dh->dh_hash == NULL)
                   goto fail;
           dh->dh_blkfree = malloc(nblocks * sizeof(dh->dh_blkfree[0]),
               M_DIRHASH, M_NOWAIT);
           if (dh->dh_blkfree == NULL)
                   goto fail;
           for (i = 0; i < narrays; i++) {
                   if ((dh->dh_hash[i] = DIRHASH_BLKALLOC()) == NULL)
                           goto fail;
                   for (j = 0; j < DH_NBLKOFF; j++)
                           dh->dh_hash[i][j] = DIRHASH_EMPTY;
           }
           for (i = 0; i < dirblocks; i++)
                   dh->dh_blkfree[i] = DIRBLKSIZ / DIRALIGN;
           bmask = vp->v_mount->mnt_stat.f_iosize - 1;
           pos = 0;
           while (pos < ip->i_size) {
                   /* If necessary, get the next directory block. */
                   if ((pos & bmask) == 0) {
                           if (bp != NULL)
                                   brelse(bp);
                           if (UFS_BLKATOFF(vp, (off_t)pos, NULL, &bp) != 0)
                                   goto fail;
                   }
   
                   /* Add this entry to the hash. */
                   ep = (struct direct *)((char *)bp->b_data + (pos & bmask));
                   if (ep->d_reclen == 0 || ep->d_reclen >
                       DIRBLKSIZ - (pos & (DIRBLKSIZ - 1))) {
                           /* Corrupted directory. */
                           brelse(bp);
                           goto fail;
                   }
                   if (ep->d_ino != 0) {
                           /* Add the entry (simplified ufsdirhash_add). */
                           slot = ufsdirhash_hash(dh, ep->d_name, ep->d_namlen);
                           while (DH_ENTRY(dh, slot) != DIRHASH_EMPTY)
                                   slot = WRAPINCR(slot, dh->dh_hlen);
                           dh->dh_hused++;
                           DH_ENTRY(dh, slot) = pos;
                           ufsdirhash_adjfree(dh, pos, -DIRSIZ(0, ep));
                   }
                   pos += ep->d_reclen;
           }
   
           if (bp != NULL)
                   brelse(bp);
           DIRHASHLIST_LOCK();
           TAILQ_INSERT_TAIL(&ufsdirhash_list, dh, dh_list);
           dh->dh_onlist = 1;
           DIRHASHLIST_UNLOCK();
           sx_downgrade(&dh->dh_lock);
           return (0);
   
   fail:
           ufsdirhash_free_locked(ip);
           return (-1);
   }
   
   /*
    * Free any hash table associated with inode 'ip'.
    */
   static void
   ufsdirhash_free_locked(struct inode *ip)
   {
           struct dirhash *dh;
           struct vnode *vp;
           int i;
   
           DIRHASH_ASSERT_LOCKED(ip->i_dirhash);
   
           /*
            * Clear the pointer in the inode to prevent new threads from
            * finding the dead structure.
            */
           vp = ip->i_vnode;
           VI_LOCK(vp);
           dh = ip->i_dirhash;
           ip->i_dirhash = NULL;
           VI_UNLOCK(vp);
   
           /*
            * Remove the hash from the list since we are going to free its
            * memory.
            */
           DIRHASHLIST_LOCK();
           if (dh->dh_onlist)
                   TAILQ_REMOVE(&ufsdirhash_list, dh, dh_list);
           ufs_dirhashmem -= dh->dh_memreq;
           DIRHASHLIST_UNLOCK();
   
           /*
            * At this point, any waiters for the lock should hold their
            * own reference on the dirhash structure.  They will drop
            * that reference once they grab the vnode interlock and see
            * that ip->i_dirhash is NULL.
            */
           sx_xunlock(&dh->dh_lock);
   
           /*
            * Handle partially recycled as well as fully constructed hashes.
            */
           if (dh->dh_hash != NULL) {
                   for (i = 0; i < dh->dh_narrays; i++)
                           if (dh->dh_hash[i] != NULL)
                                   DIRHASH_BLKFREE(dh->dh_hash[i]);
                   free(dh->dh_hash, M_DIRHASH);
                   if (dh->dh_blkfree != NULL)
                           free(dh->dh_blkfree, M_DIRHASH);
           }
   
           /*
            * Drop the inode's reference to the data structure.
            */
           ufsdirhash_drop(dh);
   }
   
   /*
    * Find the offset of the specified name within the given inode.
    * Returns 0 on success, ENOENT if the entry does not exist, or
    * EJUSTRETURN if the caller should revert to a linear search.
    *
    * If successful, the directory offset is stored in *offp, and a
    * pointer to a struct buf containing the entry is stored in *bpp. If
    * prevoffp is non-NULL, the offset of the previous entry within
    * the DIRBLKSIZ-sized block is stored in *prevoffp (if the entry
    * is the first in a block, the start of the block is used).
    *
    * Must be called with the hash locked.  Returns with the hash unlocked.
    */
   int
   ufsdirhash_lookup(struct inode *ip, char *name, int namelen, doff_t *offp,
       struct buf **bpp, doff_t *prevoffp)
   {
           struct dirhash *dh, *dh_next;
           struct direct *dp;
           struct vnode *vp;
           struct buf *bp;
           doff_t blkoff, bmask, offset, prevoff, seqoff;
           int i, slot;
           int error;
   
           dh = ip->i_dirhash;
           KASSERT(dh != NULL && dh->dh_hash != NULL,
               ("ufsdirhash_lookup: Invalid dirhash %p\n", dh));
           DIRHASH_ASSERT_LOCKED(dh);
           /*
            * Move this dirhash towards the end of the list if it has a
            * score higher than the next entry, and acquire the dh_lock.
            */
           DIRHASHLIST_LOCK();
           if (TAILQ_NEXT(dh, dh_list) != NULL) {
                   /*
                    * If the new score will be greater than that of the next
                    * entry, then move this entry past it. With both mutexes
                    * held, dh_next won't go away, but its dh_score could
                    * change; that's not important since it is just a hint.
                    */
                   if ((dh_next = TAILQ_NEXT(dh, dh_list)) != NULL &&
                       dh->dh_score >= dh_next->dh_score) {
                           KASSERT(dh->dh_onlist, ("dirhash: not on list"));
                           TAILQ_REMOVE(&ufsdirhash_list, dh, dh_list);
                           TAILQ_INSERT_AFTER(&ufsdirhash_list, dh_next, dh,
                               dh_list);
                   }
           }
           /* Update the score. */
           if (dh->dh_score < DH_SCOREMAX)
                   dh->dh_score++;
   
           /* Update last used time. */
           dh->dh_lastused = time_second;
           DIRHASHLIST_UNLOCK();
   
           vp = ip->i_vnode;
           bmask = vp->v_mount->mnt_stat.f_iosize - 1;
           blkoff = -1;
           bp = NULL;
           seqoff = dh->dh_seqoff;
   restart:
           slot = ufsdirhash_hash(dh, name, namelen);
   
           if (seqoff != -1) {
                   /*
                    * Sequential access optimisation. seqoff contains the
                    * offset of the directory entry immediately following
                    * the last entry that was looked up. Check if this offset
                    * appears in the hash chain for the name we are looking for.
                    */
                   for (i = slot; (offset = DH_ENTRY(dh, i)) != DIRHASH_EMPTY;
                       i = WRAPINCR(i, dh->dh_hlen))
                           if (offset == seqoff)
                                   break;
                   if (offset == seqoff) {
                           /*
                            * We found an entry with the expected offset. This
                            * is probably the entry we want, but if not, the
                            * code below will retry.
                            */ 
                           slot = i;
                   } else
                           seqoff = -1;
           }
   
           for (; (offset = DH_ENTRY(dh, slot)) != DIRHASH_EMPTY;
               slot = WRAPINCR(slot, dh->dh_hlen)) {
                   if (offset == DIRHASH_DEL)
                           continue;
                   if (offset < 0 || offset >= ip->i_size)
                           panic("ufsdirhash_lookup: bad offset in hash array");
                   if ((offset & ~bmask) != blkoff) {
                           if (bp != NULL)
                                   brelse(bp);
                           blkoff = offset & ~bmask;
                           if (UFS_BLKATOFF(vp, (off_t)blkoff, NULL, &bp) != 0) {
                                   error = EJUSTRETURN;
                                   goto fail;
                           }
                   }
                   KASSERT(bp != NULL, ("no buffer allocated"));
                   dp = (struct direct *)(bp->b_data + (offset & bmask));
                   if (dp->d_reclen == 0 || dp->d_reclen >
                       DIRBLKSIZ - (offset & (DIRBLKSIZ - 1))) {
                           /* Corrupted directory. */
                           error = EJUSTRETURN;
                           goto fail;
                   }
                   if (dp->d_namlen == namelen &&
                       bcmp(dp->d_name, name, namelen) == 0) {
                           /* Found. Get the prev offset if needed. */
                           if (prevoffp != NULL) {
                                   if (offset & (DIRBLKSIZ - 1)) {
                                           prevoff = ufsdirhash_getprev(dp,
                                               offset);
                                           if (prevoff == -1) {
                                                   error = EJUSTRETURN;
                                                   goto fail;
                                           }
                                   } else
                                           prevoff = offset;
                                   *prevoffp = prevoff;
                           }
   
                           /* Update offset. */
                           dh->dh_seqoff = offset + DIRSIZ(0, dp);
                           *bpp = bp;
                           *offp = offset;
                           ufsdirhash_release(dh);
                           return (0);
                   }
   
                   /*
                    * When the name doesn't match in the sequential
                    * optimization case, go back and search normally.
                    */
                   if (seqoff != -1) {
                           seqoff = -1;
                           goto restart;
                   }
           }
           error = ENOENT;
   fail:
           ufsdirhash_release(dh);
           if (bp != NULL)
                   brelse(bp);
           return (error);
   }
   
   /*
    * Find a directory block with room for 'slotneeded' bytes. Returns
    * the offset of the directory entry that begins the free space.
    * This will either be the offset of an existing entry that has free
    * space at the end, or the offset of an entry with d_ino == 0 at
    * the start of a DIRBLKSIZ block.
    *
    * To use the space, the caller may need to compact existing entries in
    * the directory. The total number of bytes in all of the entries involved
    * in the compaction is stored in *slotsize. In other words, all of
    * the entries that must be compacted are exactly contained in the
    * region beginning at the returned offset and spanning *slotsize bytes.
    *
    * Returns -1 if no space was found, indicating that the directory
    * must be extended.
    */
   doff_t
   ufsdirhash_findfree(struct inode *ip, int slotneeded, int *slotsize)
   {
           struct direct *dp;
           struct dirhash *dh;
           struct buf *bp;
           doff_t pos, slotstart;
           int dirblock, error, freebytes, i;
   
           dh = ip->i_dirhash;
           KASSERT(dh != NULL && dh->dh_hash != NULL,
               ("ufsdirhash_findfree: Invalid dirhash %p\n", dh));
           DIRHASH_ASSERT_LOCKED(dh);
   
           /* Find a directory block with the desired free space. */
           dirblock = -1;
           for (i = howmany(slotneeded, DIRALIGN); i <= DH_NFSTATS; i++)
                   if ((dirblock = dh->dh_firstfree[i]) != -1)
                           break;
           if (dirblock == -1)
                   return (-1);
   
           KASSERT(dirblock < dh->dh_nblk &&
               dh->dh_blkfree[dirblock] >= howmany(slotneeded, DIRALIGN),
               ("ufsdirhash_findfree: bad stats"));
           pos = dirblock * DIRBLKSIZ;
           error = UFS_BLKATOFF(ip->i_vnode, (off_t)pos, (char **)&dp, &bp);
           if (error)
                   return (-1);
   
           /* Find the first entry with free space. */
           for (i = 0; i < DIRBLKSIZ; ) {
                   if (dp->d_reclen == 0) {
                           brelse(bp);
                           return (-1);
                   }
                   if (dp->d_ino == 0 || dp->d_reclen > DIRSIZ(0, dp))
                           break;
                   i += dp->d_reclen;
                   dp = (struct direct *)((char *)dp + dp->d_reclen);
           }
           if (i > DIRBLKSIZ) {
                   brelse(bp);
                   return (-1);
           }
           slotstart = pos + i;
   
           /* Find the range of entries needed to get enough space */
           freebytes = 0;
           while (i < DIRBLKSIZ && freebytes < slotneeded) {
                   freebytes += dp->d_reclen;
                   if (dp->d_ino != 0)
                           freebytes -= DIRSIZ(0, dp);
                   if (dp->d_reclen == 0) {
                           brelse(bp);
                           return (-1);
                   }
                   i += dp->d_reclen;
                   dp = (struct direct *)((char *)dp + dp->d_reclen);
           }
           if (i > DIRBLKSIZ) {
                   brelse(bp);
                   return (-1);
           }
           if (freebytes < slotneeded)
                   panic("ufsdirhash_findfree: free mismatch");
           brelse(bp);
           *slotsize = pos + i - slotstart;
           return (slotstart);
   }
   
   /*
    * Return the start of the unused space at the end of a directory, or
    * -1 if there are no trailing unused blocks.
    */
   doff_t
   ufsdirhash_enduseful(struct inode *ip)
   {
   
           struct dirhash *dh;
           int i;
   
           dh = ip->i_dirhash;
           DIRHASH_ASSERT_LOCKED(dh);
           KASSERT(dh != NULL && dh->dh_hash != NULL,
               ("ufsdirhash_enduseful: Invalid dirhash %p\n", dh));
   
           if (dh->dh_blkfree[dh->dh_dirblks - 1] != DIRBLKSIZ / DIRALIGN)
                   return (-1);
   
           for (i = dh->dh_dirblks - 1; i >= 0; i--)
                   if (dh->dh_blkfree[i] != DIRBLKSIZ / DIRALIGN)
                           break;
   
           return ((doff_t)(i + 1) * DIRBLKSIZ);
   }
   
   /*
    * Insert information into the hash about a new directory entry. dirp
    * points to a struct direct containing the entry, and offset specifies
    * the offset of this entry.
    */
   void
   ufsdirhash_add(struct inode *ip, struct direct *dirp, doff_t offset)
   {
           struct dirhash *dh;
           int slot;
   
           if ((dh = ufsdirhash_acquire(ip)) == NULL)
                   return;
   
           KASSERT(offset < dh->dh_dirblks * DIRBLKSIZ,
               ("ufsdirhash_add: bad offset"));
           /*
            * Normal hash usage is < 66%. If the usage gets too high then
            * remove the hash entirely and let it be rebuilt later.
            */
           if (dh->dh_hused >= (dh->dh_hlen * 3) / 4) {
                   ufsdirhash_free_locked(ip);
                   return;
           }
   
           /* Find a free hash slot (empty or deleted), and add the entry. */
           slot = ufsdirhash_hash(dh, dirp->d_name, dirp->d_namlen);
           while (DH_ENTRY(dh, slot) >= 0)
                   slot = WRAPINCR(slot, dh->dh_hlen);
           if (DH_ENTRY(dh, slot) == DIRHASH_EMPTY)
                   dh->dh_hused++;
           DH_ENTRY(dh, slot) = offset;
   
           /* Update last used time. */
           dh->dh_lastused = time_second;
   
           /* Update the per-block summary info. */
           ufsdirhash_adjfree(dh, offset, -DIRSIZ(0, dirp));
           ufsdirhash_release(dh);
   }
   
   /*
    * Remove the specified directory entry from the hash. The entry to remove
    * is defined by the name in `dirp', which must exist at the specified
    * `offset' within the directory.
    */
   void
   ufsdirhash_remove(struct inode *ip, struct direct *dirp, doff_t offset)
   {
           struct dirhash *dh;
           int slot;
   
           if ((dh = ufsdirhash_acquire(ip)) == NULL)
                   return;
   
           KASSERT(offset < dh->dh_dirblks * DIRBLKSIZ,
               ("ufsdirhash_remove: bad offset"));
           /* Find the entry */
           slot = ufsdirhash_findslot(dh, dirp->d_name, dirp->d_namlen, offset);
   
           /* Remove the hash entry. */
           ufsdirhash_delslot(dh, slot);
   
           /* Update the per-block summary info. */
           ufsdirhash_adjfree(dh, offset, DIRSIZ(0, dirp));
           ufsdirhash_release(dh);
   }
   
   /*
    * Change the offset associated with a directory entry in the hash. Used
    * when compacting directory blocks.
    */
   void
   ufsdirhash_move(struct inode *ip, struct direct *dirp, doff_t oldoff,
       doff_t newoff)
   {
           struct dirhash *dh;
           int slot;
   
           if ((dh = ufsdirhash_acquire(ip)) == NULL)
                   return;
   
           KASSERT(oldoff < dh->dh_dirblks * DIRBLKSIZ &&
               newoff < dh->dh_dirblks * DIRBLKSIZ,
               ("ufsdirhash_move: bad offset"));
           /* Find the entry, and update the offset. */
           slot = ufsdirhash_findslot(dh, dirp->d_name, dirp->d_namlen, oldoff);
           DH_ENTRY(dh, slot) = newoff;
           ufsdirhash_release(dh);
   }
   
   /*
    * Inform dirhash that the directory has grown by one block that
    * begins at offset (i.e. the new length is offset + DIRBLKSIZ).
    */
   void
   ufsdirhash_newblk(struct inode *ip, doff_t offset)
   {
           struct dirhash *dh;
           int block;
   
           if ((dh = ufsdirhash_acquire(ip)) == NULL)
                   return;
   
           KASSERT(offset == dh->dh_dirblks * DIRBLKSIZ,
               ("ufsdirhash_newblk: bad offset"));
           block = offset / DIRBLKSIZ;
           if (block >= dh->dh_nblk) {
                   /* Out of space; must rebuild. */
                   ufsdirhash_free_locked(ip);
                   return;
           }
           dh->dh_dirblks = block + 1;
   
           /* Account for the new free block. */
           dh->dh_blkfree[block] = DIRBLKSIZ / DIRALIGN;
           if (dh->dh_firstfree[DH_NFSTATS] == -1)
                   dh->dh_firstfree[DH_NFSTATS] = block;
           ufsdirhash_release(dh);
   }
   
   /*
    * Inform dirhash that the directory is being truncated.
    */
   void
   ufsdirhash_dirtrunc(struct inode *ip, doff_t offset)
   {
           struct dirhash *dh;
           int block, i;
   
           if ((dh = ufsdirhash_acquire(ip)) == NULL)
                   return;
   
           KASSERT(offset <= dh->dh_dirblks * DIRBLKSIZ,
               ("ufsdirhash_dirtrunc: bad offset"));
           block = howmany(offset, DIRBLKSIZ);
           /*
            * If the directory shrinks to less than 1/8 of dh_nblk blocks
            * (about 20% of its original size due to the 50% extra added in
            * ufsdirhash_build) then free it, and let the caller rebuild
            * if necessary.
            */
           if (block < dh->dh_nblk / 8 && dh->dh_narrays > 1) {
                   ufsdirhash_free_locked(ip);
                   return;
           }
   
           /*
            * Remove any `first free' information pertaining to the
            * truncated blocks. All blocks we're removing should be
            * completely unused.
            */
           if (dh->dh_firstfree[DH_NFSTATS] >= block)
                   dh->dh_firstfree[DH_NFSTATS] = -1;
           for (i = block; i < dh->dh_dirblks; i++)
                   if (dh->dh_blkfree[i] != DIRBLKSIZ / DIRALIGN)
                           panic("ufsdirhash_dirtrunc: blocks in use");
           for (i = 0; i < DH_NFSTATS; i++)
                   if (dh->dh_firstfree[i] >= block)
                           panic("ufsdirhash_dirtrunc: first free corrupt");
           dh->dh_dirblks = block;
           ufsdirhash_release(dh);
   }
   
   /*
    * Debugging function to check that the dirhash information about
    * a directory block matches its actual contents. Panics if a mismatch
    * is detected.
    *
    * On entry, `buf' should point to the start of an in-core
    * DIRBLKSIZ-sized directory block, and `offset' should contain the
    * offset from the start of the directory of that block.
    */
   void
   ufsdirhash_checkblock(struct inode *ip, char *buf, doff_t offset)
   {
           struct dirhash *dh;
           struct direct *dp;
           int block, ffslot, i, nfree;
   
           if (!ufs_dirhashcheck)
                   return;
           if ((dh = ufsdirhash_acquire(ip)) == NULL)
                   return;
   
           block = offset / DIRBLKSIZ;
           if ((offset & (DIRBLKSIZ - 1)) != 0 || block >= dh->dh_dirblks)
                   panic("ufsdirhash_checkblock: bad offset");
   
           nfree = 0;
           for (i = 0; i < DIRBLKSIZ; i += dp->d_reclen) {
                   dp = (struct direct *)(buf + i);
                   if (dp->d_reclen == 0 || i + dp->d_reclen > DIRBLKSIZ)
                           panic("ufsdirhash_checkblock: bad dir");
   
                   if (dp->d_ino == 0) {
   #if 0
                           /*
                            * XXX entries with d_ino == 0 should only occur
                           * at the start of a DIRBLKSIZ block. However the
                           * ufs code is tolerant of such entries at other
                           * offsets, and fsck does not fix them.
                           */
                          if (i != 0)
                                  panic("ufsdirhash_checkblock: bad dir inode");
  #endif
                          nfree += dp->d_reclen;
                          continue;
                  }
  
                  /* Check that the entry exists (will panic if it doesn't). */
                  ufsdirhash_findslot(dh, dp->d_name, dp->d_namlen, offset + i);
  
                  nfree += dp->d_reclen - DIRSIZ(0, dp);
          }
          if (i != DIRBLKSIZ)
                  panic("ufsdirhash_checkblock: bad dir end");
  
          if (dh->dh_blkfree[block] * DIRALIGN != nfree)
                  panic("ufsdirhash_checkblock: bad free count");
  
          ffslot = BLKFREE2IDX(nfree / DIRALIGN);
          for (i = 0; i <= DH_NFSTATS; i++)
                  if (dh->dh_firstfree[i] == block && i != ffslot)
                          panic("ufsdirhash_checkblock: bad first-free");
          if (dh->dh_firstfree[ffslot] == -1)
                  panic("ufsdirhash_checkblock: missing first-free entry");
          ufsdirhash_release(dh);
  }
  
  /*
   * Hash the specified filename into a dirhash slot.
   */
  static int
  ufsdirhash_hash(struct dirhash *dh, char *name, int namelen)
  {
          u_int32_t hash;
  
          /*
           * We hash the name and then some other bit of data that is
           * invariant over the dirhash's lifetime. Otherwise names
           * differing only in the last byte are placed close to one
           * another in the table, which is bad for linear probing.
           */
          hash = fnv_32_buf(name, namelen, FNV1_32_INIT);
          hash = fnv_32_buf(&dh, sizeof(dh), hash);
          return (hash % dh->dh_hlen);
  }
  
  /*
   * Adjust the number of free bytes in the block containing `offset'
   * by the value specified by `diff'.
   *
   * The caller must ensure we have exclusive access to `dh'; normally
   * that means that dh_lock should be held, but this is also called
   * from ufsdirhash_build() where exclusive access can be assumed.
   */
  static void
  ufsdirhash_adjfree(struct dirhash *dh, doff_t offset, int diff)
  {
          int block, i, nfidx, ofidx;
  
          /* Update the per-block summary info. */
          block = offset / DIRBLKSIZ;
          KASSERT(block < dh->dh_nblk && block < dh->dh_dirblks,
               ("dirhash bad offset"));
          ofidx = BLKFREE2IDX(dh->dh_blkfree[block]);
          dh->dh_blkfree[block] = (int)dh->dh_blkfree[block] + (diff / DIRALIGN);
          nfidx = BLKFREE2IDX(dh->dh_blkfree[block]);
  
          /* Update the `first free' list if necessary. */
          if (ofidx != nfidx) {
                  /* If removing, scan forward for the next block. */
                  if (dh->dh_firstfree[ofidx] == block) {
                          for (i = block + 1; i < dh->dh_dirblks; i++)
                                  if (BLKFREE2IDX(dh->dh_blkfree[i]) == ofidx)
                                          break;
                          dh->dh_firstfree[ofidx] = (i < dh->dh_dirblks) ? i : -1;
                  }
  
                  /* Make this the new `first free' if necessary */
                  if (dh->dh_firstfree[nfidx] > block ||
                      dh->dh_firstfree[nfidx] == -1)
                          dh->dh_firstfree[nfidx] = block;
          }
  }
  
  /*
   * Find the specified name which should have the specified offset.
   * Returns a slot number, and panics on failure.
   *
   * `dh' must be locked on entry and remains so on return.
   */
  static int
  ufsdirhash_findslot(struct dirhash *dh, char *name, int namelen, doff_t offset)
  {
          int slot;
  
          DIRHASH_ASSERT_LOCKED(dh);
  
          /* Find the entry. */
          KASSERT(dh->dh_hused < dh->dh_hlen, ("dirhash find full"));
          slot = ufsdirhash_hash(dh, name, namelen);
          while (DH_ENTRY(dh, slot) != offset &&
              DH_ENTRY(dh, slot) != DIRHASH_EMPTY)
                  slot = WRAPINCR(slot, dh->dh_hlen);
          if (DH_ENTRY(dh, slot) != offset)
                  panic("ufsdirhash_findslot: '%.*s' not found", namelen, name);
  
          return (slot);
  }
  
  /*
   * Remove the entry corresponding to the specified slot from the hash array.
   *
   * `dh' must be locked on entry and remains so on return.
   */
  static void
  ufsdirhash_delslot(struct dirhash *dh, int slot)
  {
          int i;
  
          DIRHASH_ASSERT_LOCKED(dh);
  
          /* Mark the entry as deleted. */
          DH_ENTRY(dh, slot) = DIRHASH_DEL;
  
          /* If this is the end of a chain of DIRHASH_DEL slots, remove them. */
          for (i = slot; DH_ENTRY(dh, i) == DIRHASH_DEL; )
                  i = WRAPINCR(i, dh->dh_hlen);
          if (DH_ENTRY(dh, i) == DIRHASH_EMPTY) {
                  i = WRAPDECR(i, dh->dh_hlen);
                  while (DH_ENTRY(dh, i) == DIRHASH_DEL) {
                          DH_ENTRY(dh, i) = DIRHASH_EMPTY;
                          dh->dh_hused--;
                          i = WRAPDECR(i, dh->dh_hlen);
                  }
                  KASSERT(dh->dh_hused >= 0, ("ufsdirhash_delslot neg hlen"));
          }
  }
  
  /*
   * Given a directory entry and its offset, find the offset of the
   * previous entry in the same DIRBLKSIZ-sized block. Returns an
   * offset, or -1 if there is no previous entry in the block or some
   * other problem occurred.
   */
  static doff_t
  ufsdirhash_getprev(struct direct *dirp, doff_t offset)
  {
          struct direct *dp;
          char *blkbuf;
          doff_t blkoff, prevoff;
          int entrypos, i;
  
          blkoff = rounddown2(offset, DIRBLKSIZ); /* offset of start of block */
          entrypos = offset & (DIRBLKSIZ - 1);    /* entry relative to block */
          blkbuf = (char *)dirp - entrypos;
          prevoff = blkoff;
  
          /* If `offset' is the start of a block, there is no previous entry. */
          if (entrypos == 0)
                  return (-1);
  
          /* Scan from the start of the block until we get to the entry. */
          for (i = 0; i < entrypos; i += dp->d_reclen) {
                  dp = (struct direct *)(blkbuf + i);
                  if (dp->d_reclen == 0 || i + dp->d_reclen > entrypos)
                          return (-1);    /* Corrupted directory. */
                  prevoff = blkoff + i;
          }
          return (prevoff);
  }
  
  /*
   * Delete the given dirhash and reclaim its memory. Assumes that 
   * ufsdirhash_list is locked, and leaves it locked. Also assumes 
   * that dh is locked. Returns the amount of memory freed.
   */
  static int
  ufsdirhash_destroy(struct dirhash *dh)
  {
          doff_t **hash;
          u_int8_t *blkfree;
          int i, mem, narrays;
  
          KASSERT(dh->dh_hash != NULL, ("dirhash: NULL hash on list"));
  
          /* Remove it from the list and detach its memory. */
          TAILQ_REMOVE(&ufsdirhash_list, dh, dh_list);
          dh->dh_onlist = 0;
          hash = dh->dh_hash;
          dh->dh_hash = NULL;
          blkfree = dh->dh_blkfree;
          dh->dh_blkfree = NULL;
          narrays = dh->dh_narrays;
          mem = dh->dh_memreq;
          dh->dh_memreq = 0;
  
          /* Unlock dirhash and free the detached memory. */
          ufsdirhash_release(dh);
          for (i = 0; i < narrays; i++)
                  DIRHASH_BLKFREE(hash[i]);
          free(hash, M_DIRHASH);
          free(blkfree, M_DIRHASH);
  
          /* Account for the returned memory. */
          ufs_dirhashmem -= mem;
  
          return (mem);
  }
  
  /*
   * Try to free up `wanted' bytes by stealing memory from existing
   * dirhashes. Returns zero with list locked if successful.
   */
  static int
  ufsdirhash_recycle(int wanted)
  {
          struct dirhash *dh;
  
          DIRHASHLIST_LOCK();
          dh = TAILQ_FIRST(&ufsdirhash_list);
          while (wanted + ufs_dirhashmem > ufs_dirhashmaxmem) {
                  /* Decrement the score; only recycle if it becomes zero. */
                  if (dh == NULL || --dh->dh_score > 0) {
                          DIRHASHLIST_UNLOCK();
                          return (-1);
                  }
                  /*
                   * If we can't lock it it's in use and we don't want to
                   * recycle it anyway.
                   */
                  if (!sx_try_xlock(&dh->dh_lock)) {
                          dh = TAILQ_NEXT(dh, dh_list);
                          continue;
                  }
  
                  ufsdirhash_destroy(dh);
  
                  /* Repeat if necessary. */
                  dh = TAILQ_FIRST(&ufsdirhash_list);
          }
          /* Success; return with list locked. */
          return (0);
  }
  
  /*
   * Callback that frees some dirhashes when the system is low on virtual memory.
   */
  static void
  ufsdirhash_lowmem(void)
  {
          struct dirhash *dh, *dh_temp;
          int memfreed, memwanted;
  
          ufs_dirhashlowmemcount++;
          memfreed = 0;
          memwanted = ufs_dirhashmem * ufs_dirhashreclaimpercent / 100;
  
          DIRHASHLIST_LOCK();
  
          /*
           * Reclaim up to memwanted from the oldest dirhashes. This will allow
           * us to make some progress when the system is running out of memory
           * without compromising the dinamicity of maximum age. If the situation
           * does not improve lowmem will be eventually retriggered and free some
           * other entry in the cache. The entries on the head of the list should
           * be the oldest. If during list traversal we can't get a lock on the
           * dirhash, it will be skipped.
           */
          TAILQ_FOREACH_SAFE(dh, &ufsdirhash_list, dh_list, dh_temp) {
                  if (sx_try_xlock(&dh->dh_lock))
                          memfreed += ufsdirhash_destroy(dh);
                  if (memfreed >= memwanted)
                          break;
          }
          DIRHASHLIST_UNLOCK();
  }
  
  static int
  ufsdirhash_set_reclaimpercent(SYSCTL_HANDLER_ARGS)
  {
          int error, v;
  
          v = ufs_dirhashreclaimpercent;
          error = sysctl_handle_int(oidp, &v, v, req);
          if (error)
                  return (error);
          if (req->newptr == NULL)
                  return (error);
          if (v == ufs_dirhashreclaimpercent)
                  return (0);
  
          /* Refuse invalid percentages */
          if (v < 0 || v > 100)
                  return (EINVAL);
          ufs_dirhashreclaimpercent = v;
          return (0);
  }
  
  void
  ufsdirhash_init(void)
  {
          ufs_dirhashmaxmem = lmax(roundup(hibufspace / 64, PAGE_SIZE),
              2 * 1024 * 1024);
  
          ufsdirhash_zone = uma_zcreate("DIRHASH", DH_NBLKOFF * sizeof(doff_t),
              NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
          mtx_init(&ufsdirhash_mtx, "dirhash list", NULL, MTX_DEF);
          TAILQ_INIT(&ufsdirhash_list);
  
          /* Register a callback function to handle low memory signals */
          EVENTHANDLER_REGISTER(vm_lowmem, ufsdirhash_lowmem, NULL, 
              EVENTHANDLER_PRI_FIRST);
  }
  
  void
  ufsdirhash_uninit(void)
  {
          KASSERT(TAILQ_EMPTY(&ufsdirhash_list), ("ufsdirhash_uninit"));
          uma_zdestroy(ufsdirhash_zone);
          mtx_destroy(&ufsdirhash_mtx);
  }
  
  #endif /* UFS_DIRHASH */

Cache object: efcf97592dc2c27990ca5f688dba7ce3