/*      $NetBSD: ulfs_dirhash.c,v 1.19 2022/08/07 02:33:47 simonb Exp $ */
/*  from NetBSD: ufs_dirhash.c,v 1.37 2014/12/20 00:28:05 christos Exp  */

/*
 * 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.
 *
 * $FreeBSD: src/sys/ufs/ufs/ufs_dirhash.c,v 1.3.2.8 2004/12/08 11:54:13 dwmalone Exp $
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: ulfs_dirhash.c,v 1.19 2022/08/07 02:33:47 simonb Exp $");

/*
 * This implements a hash-based lookup scheme for ULFS directories.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/kmem.h>
#include <sys/types.h>
#include <sys/hash.h>
#include <sys/proc.h>
#include <sys/buf.h>
#include <sys/vnode.h>
#include <sys/mount.h>
#include <sys/pool.h>
#include <sys/sysctl.h>
#include <sys/atomic.h>

#include <ufs/lfs/lfs.h>
#include <ufs/lfs/lfs_accessors.h>
#include <ufs/lfs/ulfs_inode.h>
#include <ufs/lfs/ulfs_dirhash.h>
#include <ufs/lfs/ulfsmount.h>
#include <ufs/lfs/ulfs_bswap.h>
#include <ufs/lfs/ulfs_extern.h>

/*
 * Defaults for dirhash cache sizes:
 *  - use up to 1/64th of system memory.
 *  - disable dirhash (set the cache size to 0 bytes) if the
 *    calculated value of hash is less than 2MB.
 *  - cap maximum size of the dirhash cache at 32MB.
 */
#define DIRHASH_DEFAULT_DIVIDER 64
#define MIN_DEFAULT_DIRHASH_MEM (2 * 1024 * 1024)
#define MAX_DEFAULT_DIRHASH_MEM (32 * 1024 * 1024)


#define WRAPINCR(val, limit)    (((val) + 1 == (limit)) ? 0 : ((val) + 1))
#define WRAPDECR(val, limit)    (((val) == 0) ? ((limit) - 1) : ((val) - 1))
#define OFSFMT(ip)              ((ip)->i_lfs->um_maxsymlinklen <= 0)
#define BLKFREE2IDX(n)          ((n) > DH_NFSTATS ? DH_NFSTATS : (n))

static u_int ulfs_dirhashminblks = 5;
static u_int ulfs_dirhashmaxmem = 0;
static u_int ulfs_dirhashmem;
static u_int ulfs_dirhashcheck = 0;

static int ulfsdirhash_hash(struct dirhash *dh, const char *name, int namelen);
static void ulfsdirhash_adjfree(struct dirhash *dh, doff_t offset, int diff,
           int dirblksiz);
static void ulfsdirhash_delslot(struct dirhash *dh, int slot);
static int ulfsdirhash_findslot(struct dirhash *dh, const char *name,
           int namelen, doff_t offset);
static doff_t ulfsdirhash_getprev(struct lfs *fs, LFS_DIRHEADER *dp,
           doff_t offset, int dirblksiz);
static int ulfsdirhash_recycle(int wanted);

static pool_cache_t ulfsdirhashblk_cache;
static pool_cache_t ulfsdirhash_cache;

#define DIRHASHLIST_LOCK()              mutex_enter(&ulfsdirhash_lock)
#define DIRHASHLIST_UNLOCK()            mutex_exit(&ulfsdirhash_lock)
#define DIRHASH_LOCK(dh)                mutex_enter(&(dh)->dh_lock)
#define DIRHASH_UNLOCK(dh)              mutex_exit(&(dh)->dh_lock)
#define DIRHASH_BLKALLOC()              \
    pool_cache_get(ulfsdirhashblk_cache, PR_NOWAIT)
#define DIRHASH_BLKFREE(ptr)            \
    pool_cache_put(ulfsdirhashblk_cache, ptr)

/* Dirhash list; recently-used entries are near the tail. */
static TAILQ_HEAD(, dirhash) ulfsdirhash_list;

/* Protects: ulfsdirhash_list, `dh_list' field, ulfs_dirhashmem. */
static kmutex_t ulfsdirhash_lock;

static struct sysctllog *ulfsdirhash_sysctl_log;

/*
 * Locking order:
 *      ulfsdirhash_lock
 *      dh_lock
 *
 * The dh_lock mutex should be acquired either via the inode lock, or via
 * ulfsdirhash_lock. Only the owner of the inode may free the associated
 * dirhash, but anything can steal its memory and set dh_hash to NULL.
 */

/*
 * 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
ulfsdirhash_build(struct inode *ip)
{
        struct lfs *fs = ip->i_lfs;
        struct dirhash *dh;
        struct buf *bp = NULL;
        LFS_DIRHEADER *ep;
        struct vnode *vp;
        doff_t bmask, pos;
        int dirblocks, i, j, memreqd, nblocks, narrays, nslots, slot;
        int dirblksiz = ip->i_lfs->um_dirblksiz;

        /* Check if we can/should use dirhash. */
        if (ip->i_dirhash == NULL) {
                if (ulfs_dirhashmaxmem == 0 ||
                    ip->i_size < (ulfs_dirhashminblks * dirblksiz) ||
                    OFSFMT(ip))
                        return (-1);
        } else {
                /* Hash exists, but sysctls could have changed. */
                if (ip->i_size < (ulfs_dirhashminblks * dirblksiz) ||
                    ulfs_dirhashmem > ulfs_dirhashmaxmem) {
                        ulfsdirhash_free(ip);
                        return (-1);
                }
                /* Check if hash exists and is intact (note: unlocked read). */
                if (ip->i_dirhash->dh_hash != NULL)
                        return (0);
                /* Free the old, recycled hash and build a new one. */
                ulfsdirhash_free(ip);
        }

        /* Don't hash removed directories. */
        if (ip->i_nlink == 0)
                return (-1);

        vp = ip->i_vnode;
        /* Allocate 50% more entries than this dir size could ever need. */
        KASSERT(ip->i_size >= dirblksiz);
        nslots = ip->i_size / LFS_DIRECTSIZ(fs, 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);

        while (atomic_add_int_nv(&ulfs_dirhashmem, memreqd) >
            ulfs_dirhashmaxmem) {
                atomic_add_int(&ulfs_dirhashmem, -memreqd);
                if (memreqd > ulfs_dirhashmaxmem / 2)
                        return (-1);
                /* Try to free some space. */
                if (ulfsdirhash_recycle(memreqd) != 0)
                        return (-1);
                else
                        DIRHASHLIST_UNLOCK();
        }

        /*
         * Use non-blocking mallocs so that we will revert to a linear
         * lookup on failure rather than potentially blocking forever.
         */
        dh = pool_cache_get(ulfsdirhash_cache, PR_NOWAIT);
        if (dh == NULL) {
                atomic_add_int(&ulfs_dirhashmem, -memreqd);
                return (-1);
        }
        memset(dh, 0, sizeof(*dh));
        mutex_init(&dh->dh_lock, MUTEX_DEFAULT, IPL_NONE);
        DIRHASH_LOCK(dh);
        dh->dh_hashsz = narrays * sizeof(dh->dh_hash[0]);
        dh->dh_hash = kmem_zalloc(dh->dh_hashsz, KM_NOSLEEP);
        dh->dh_blkfreesz = nblocks * sizeof(dh->dh_blkfree[0]);
        dh->dh_blkfree = kmem_zalloc(dh->dh_blkfreesz, KM_NOSLEEP);
        if (dh->dh_hash == NULL || 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;
        }

        /* Initialise the hash table and block statistics. */
        dh->dh_narrays = narrays;
        dh->dh_hlen = nslots;
        dh->dh_nblk = nblocks;
        dh->dh_dirblks = dirblocks;
        for (i = 0; i < dirblocks; i++)
                dh->dh_blkfree[i] = dirblksiz / DIRALIGN;
        for (i = 0; i < DH_NFSTATS; i++)
                dh->dh_firstfree[i] = -1;
        dh->dh_firstfree[DH_NFSTATS] = 0;
        dh->dh_seqopt = 0;
        dh->dh_seqoff = 0;
        dh->dh_score = DH_SCOREINIT;
        ip->i_dirhash = dh;

        bmask = VFSTOULFS(vp->v_mount)->um_mountp->mnt_stat.f_iosize - 1;
        pos = 0;
        while (pos < ip->i_size) {
                preempt_point();

                /* If necessary, get the next directory block. */
                if ((pos & bmask) == 0) {
                        if (bp != NULL)
                                brelse(bp, 0);
                        if (ulfs_blkatoff(vp, (off_t)pos, NULL, &bp, false) != 0)
                                goto fail;
                }

                /* Add this entry to the hash. */
                ep = (LFS_DIRHEADER *)((char *)bp->b_data + (pos & bmask));
                if (lfs_dir_getreclen(fs, ep) == 0 || lfs_dir_getreclen(fs, ep) >
                    dirblksiz - (pos & (dirblksiz - 1))) {
                        /* Corrupted directory. */
                        brelse(bp, 0);
                        goto fail;
                }
                if (lfs_dir_getino(fs, ep) != 0) {
                        /* Add the entry (simplified ulfsdirhash_add). */
                        slot = ulfsdirhash_hash(dh, lfs_dir_nameptr(fs, ep),
                                                lfs_dir_getnamlen(fs, ep));
                        while (DH_ENTRY(dh, slot) != DIRHASH_EMPTY)
                                slot = WRAPINCR(slot, dh->dh_hlen);
                        dh->dh_hused++;
                        DH_ENTRY(dh, slot) = pos;
                        ulfsdirhash_adjfree(dh, pos, -LFS_DIRSIZ(fs, ep),
                            dirblksiz);
                }
                pos += lfs_dir_getreclen(fs, ep);
        }

        if (bp != NULL)
                brelse(bp, 0);
        DIRHASHLIST_LOCK();
        TAILQ_INSERT_TAIL(&ulfsdirhash_list, dh, dh_list);
        dh->dh_onlist = 1;
        DIRHASH_UNLOCK(dh);
        DIRHASHLIST_UNLOCK();
        return (0);

fail:
        ip->i_dirhash = NULL;
        DIRHASH_UNLOCK(dh);
        if (dh->dh_hash != NULL) {
                for (i = 0; i < narrays; i++)
                        if (dh->dh_hash[i] != NULL)
                                DIRHASH_BLKFREE(dh->dh_hash[i]);
                kmem_free(dh->dh_hash, dh->dh_hashsz);
        }
        if (dh->dh_blkfree != NULL)
                kmem_free(dh->dh_blkfree, dh->dh_blkfreesz);
        mutex_destroy(&dh->dh_lock);
        pool_cache_put(ulfsdirhash_cache, dh);
        atomic_add_int(&ulfs_dirhashmem, -memreqd);
        return (-1);
}

/*
 * Free any hash table associated with inode 'ip'.
 */
void
ulfsdirhash_free(struct inode *ip)
{
        struct dirhash *dh;
        int i, mem;

        if ((dh = ip->i_dirhash) == NULL)
                return;

        ip->i_dirhash = NULL;

        if (dh->dh_onlist) {
                DIRHASHLIST_LOCK();
                if (dh->dh_onlist)
                        TAILQ_REMOVE(&ulfsdirhash_list, dh, dh_list);
                DIRHASHLIST_UNLOCK();
        }

        /* The dirhash pointed to by 'dh' is exclusively ours now. */
        mem = sizeof(*dh);
        if (dh->dh_hash != NULL) {
                for (i = 0; i < dh->dh_narrays; i++)
                        DIRHASH_BLKFREE(dh->dh_hash[i]);
                kmem_free(dh->dh_hash, dh->dh_hashsz);
                kmem_free(dh->dh_blkfree, dh->dh_blkfreesz);
                mem += dh->dh_hashsz;
                mem += dh->dh_narrays * DH_NBLKOFF * sizeof(**dh->dh_hash);
                mem += dh->dh_nblk * sizeof(*dh->dh_blkfree);
        }
        mutex_destroy(&dh->dh_lock);
        pool_cache_put(ulfsdirhash_cache, dh);

        atomic_add_int(&ulfs_dirhashmem, -mem);
}

/*
 * 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).
 */
int
ulfsdirhash_lookup(struct inode *ip, const char *name, int namelen, doff_t *offp,
    struct buf **bpp, doff_t *prevoffp)
{
        struct lfs *fs = ip->i_lfs;
        struct dirhash *dh, *dh_next;
        LFS_DIRHEADER *dp;
        struct vnode *vp;
        struct buf *bp;
        doff_t blkoff, bmask, offset, prevoff;
        int i, slot;
        int dirblksiz = ip->i_lfs->um_dirblksiz;

        if ((dh = ip->i_dirhash) == NULL)
                return (EJUSTRETURN);

        /*
         * Move this dirhash towards the end of the list if it has a
         * score higher than the next entry, and acquire the dh_lock.
         * Optimise the case where it's already the last by performing
         * an unlocked read of the TAILQ_NEXT pointer.
         *
         * In both cases, end up holding just dh_lock.
         */
        if (TAILQ_NEXT(dh, dh_list) != NULL) {
                DIRHASHLIST_LOCK();
                DIRHASH_LOCK(dh);
                /*
                 * 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->dh_hash != NULL &&
                    (dh_next = TAILQ_NEXT(dh, dh_list)) != NULL &&
                    dh->dh_score >= dh_next->dh_score) {
                        KASSERT(dh->dh_onlist);
                        TAILQ_REMOVE(&ulfsdirhash_list, dh, dh_list);
                        TAILQ_INSERT_AFTER(&ulfsdirhash_list, dh_next, dh,
                            dh_list);
                }
                DIRHASHLIST_UNLOCK();
        } else {
                /* Already the last, though that could change as we wait. */
                DIRHASH_LOCK(dh);
        }
        if (dh->dh_hash == NULL) {
                DIRHASH_UNLOCK(dh);
                ulfsdirhash_free(ip);
                return (EJUSTRETURN);
        }

        /* Update the score. */
        if (dh->dh_score < DH_SCOREMAX)
                dh->dh_score++;

        vp = ip->i_vnode;
        bmask = VFSTOULFS(vp->v_mount)->um_mountp->mnt_stat.f_iosize - 1;
        blkoff = -1;
        bp = NULL;
restart:
        slot = ulfsdirhash_hash(dh, name, namelen);

        if (dh->dh_seqopt) {
                /*
                 * Sequential access optimisation. dh_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 == dh->dh_seqoff)
                                break;
                if (offset == dh->dh_seqoff) {
                        /*
                         * We found an entry with the expected offset. This
                         * is probably the entry we want, but if not, the
                         * code below will turn off seqoff and retry.
                         */
                        slot = i;
                } else
                        dh->dh_seqopt = 0;
        }

        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("ulfsdirhash_lookup: bad offset in hash array");
                if ((offset & ~bmask) != blkoff) {
                        if (bp != NULL)
                                brelse(bp, 0);
                        blkoff = offset & ~bmask;
                        if (ulfs_blkatoff(vp, (off_t)blkoff,
                            NULL, &bp, false) != 0) {
                                DIRHASH_UNLOCK(dh);
                                return (EJUSTRETURN);
                        }
                }
                dp = (LFS_DIRHEADER *)((char *)bp->b_data + (offset & bmask));
                if (lfs_dir_getreclen(fs, dp) == 0 || lfs_dir_getreclen(fs, dp) >
                    dirblksiz - (offset & (dirblksiz - 1))) {
                        /* Corrupted directory. */
                        DIRHASH_UNLOCK(dh);
                        brelse(bp, 0);
                        return (EJUSTRETURN);
                }
                if (lfs_dir_getnamlen(fs, dp) == namelen &&
                    memcmp(lfs_dir_nameptr(fs, dp), name, namelen) == 0) {
                        /* Found. Get the prev offset if needed. */
                        if (prevoffp != NULL) {
                                if (offset & (dirblksiz - 1)) {
                                        prevoff = ulfsdirhash_getprev(fs, dp,
                                            offset, dirblksiz);
                                        if (prevoff == -1) {
                                                brelse(bp, 0);
                                                return (EJUSTRETURN);
                                        }
                                } else
                                        prevoff = offset;
                                *prevoffp = prevoff;
                        }

                        /* Check for sequential access, and update offset. */
                        if (dh->dh_seqopt == 0 && dh->dh_seqoff == offset)
                                dh->dh_seqopt = 1;
                        dh->dh_seqoff = offset + LFS_DIRSIZ(fs, dp);
                        DIRHASH_UNLOCK(dh);

                        *bpp = bp;
                        *offp = offset;
                        return (0);
                }

                if (dh->dh_hash == NULL) {
                        DIRHASH_UNLOCK(dh);
                        if (bp != NULL)
                                brelse(bp, 0);
                        ulfsdirhash_free(ip);
                        return (EJUSTRETURN);
                }
                /*
                 * When the name doesn't match in the seqopt case, go back
                 * and search normally.
                 */
                if (dh->dh_seqopt) {
                        dh->dh_seqopt = 0;
                        goto restart;
                }
        }
        DIRHASH_UNLOCK(dh);
        if (bp != NULL)
                brelse(bp, 0);
        return (ENOENT);
}

/*
 * 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
ulfsdirhash_findfree(struct inode *ip, int slotneeded, int *slotsize)
{
        struct lfs *fs = ip->i_lfs;
        LFS_DIRHEADER *dp;
        struct dirhash *dh;
        struct buf *bp;
        doff_t pos, slotstart;
        int dirblock, error, freebytes, i;
        int dirblksiz = ip->i_lfs->um_dirblksiz;

        if ((dh = ip->i_dirhash) == NULL)
                return (-1);

        DIRHASH_LOCK(dh);
        if (dh->dh_hash == NULL) {
                DIRHASH_UNLOCK(dh);
                ulfsdirhash_free(ip);
                return (-1);
        }

        /* 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) {
                DIRHASH_UNLOCK(dh);
                return (-1);
        }

        KASSERT(dirblock < dh->dh_nblk &&
            dh->dh_blkfree[dirblock] >= howmany(slotneeded, DIRALIGN));
        pos = dirblock * dirblksiz;
        error = ulfs_blkatoff(ip->i_vnode, (off_t)pos, (void *)&dp, &bp, false);
        if (error) {
                DIRHASH_UNLOCK(dh);
                return (-1);
        }
        /* Find the first entry with free space. */
        for (i = 0; i < dirblksiz; ) {
                if (lfs_dir_getreclen(fs, dp) == 0) {
                        DIRHASH_UNLOCK(dh);
                        brelse(bp, 0);
                        return (-1);
                }
                if (lfs_dir_getino(fs, dp) == 0 || lfs_dir_getreclen(fs, dp) > LFS_DIRSIZ(fs, dp))
                        break;
                i += lfs_dir_getreclen(fs, dp);
                dp = LFS_NEXTDIR(fs, dp);
        }
        if (i > dirblksiz) {
                DIRHASH_UNLOCK(dh);
                brelse(bp, 0);
                return (-1);
        }
        slotstart = pos + i;

        /* Find the range of entries needed to get enough space */
        freebytes = 0;
        while (i < dirblksiz && freebytes < slotneeded) {
                freebytes += lfs_dir_getreclen(fs, dp);
                if (lfs_dir_getino(fs, dp) != 0)
                        freebytes -= LFS_DIRSIZ(fs, dp);
                if (lfs_dir_getreclen(fs, dp) == 0) {
                        DIRHASH_UNLOCK(dh);
                        brelse(bp, 0);
                        return (-1);
                }
                i += lfs_dir_getreclen(fs, dp);
                dp = LFS_NEXTDIR(fs, dp);
        }
        if (i > dirblksiz) {
                DIRHASH_UNLOCK(dh);
                brelse(bp, 0);
                return (-1);
        }
        if (freebytes < slotneeded)
                panic("ulfsdirhash_findfree: free mismatch");
        DIRHASH_UNLOCK(dh);
        brelse(bp, 0);
        *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
ulfsdirhash_enduseful(struct inode *ip)
{
        struct dirhash *dh;
        int i;
        int dirblksiz = ip->i_lfs->um_dirblksiz;

        if ((dh = ip->i_dirhash) == NULL)
                return (-1);

        DIRHASH_LOCK(dh);
        if (dh->dh_hash == NULL) {
                DIRHASH_UNLOCK(dh);
                ulfsdirhash_free(ip);
                return (-1);
        }

        if (dh->dh_blkfree[dh->dh_dirblks - 1] != dirblksiz / DIRALIGN) {
                DIRHASH_UNLOCK(dh);
                return (-1);
        }

        for (i = dh->dh_dirblks - 1; i >= 0; i--)
                if (dh->dh_blkfree[i] != dirblksiz / DIRALIGN)
                        break;
        DIRHASH_UNLOCK(dh);
        return ((doff_t)(i + 1) * dirblksiz);
}

/*
 * Insert information into the hash about a new directory entry. dirp
 * points to a struct lfs_direct containing the entry, and offset specifies
 * the offset of this entry.
 */
void
ulfsdirhash_add(struct inode *ip, LFS_DIRHEADER *dirp, doff_t offset)
{
        struct lfs *fs = ip->i_lfs;
        struct dirhash *dh;
        int slot;
        int dirblksiz = ip->i_lfs->um_dirblksiz;

        if ((dh = ip->i_dirhash) == NULL)
                return;

        DIRHASH_LOCK(dh);
        if (dh->dh_hash == NULL) {
                DIRHASH_UNLOCK(dh);
                ulfsdirhash_free(ip);
                return;
        }

        KASSERT(offset < dh->dh_dirblks * dirblksiz);
        /*
         * 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) {
                DIRHASH_UNLOCK(dh);
                ulfsdirhash_free(ip);
                return;
        }

        /* Find a free hash slot (empty or deleted), and add the entry. */
        slot = ulfsdirhash_hash(dh, lfs_dir_nameptr(fs, dirp),
                                lfs_dir_getnamlen(fs, dirp));
        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 the per-block summary info. */
        ulfsdirhash_adjfree(dh, offset, -LFS_DIRSIZ(fs, dirp), dirblksiz);
        DIRHASH_UNLOCK(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
ulfsdirhash_remove(struct inode *ip, LFS_DIRHEADER *dirp, doff_t offset)
{
        struct lfs *fs = ip->i_lfs;
        struct dirhash *dh;
        int slot;
        int dirblksiz = ip->i_lfs->um_dirblksiz;

        if ((dh = ip->i_dirhash) == NULL)
                return;

        DIRHASH_LOCK(dh);
        if (dh->dh_hash == NULL) {
                DIRHASH_UNLOCK(dh);
                ulfsdirhash_free(ip);
                return;
        }

        KASSERT(offset < dh->dh_dirblks * dirblksiz);
        /* Find the entry */
        slot = ulfsdirhash_findslot(dh, lfs_dir_nameptr(fs, dirp),
                                    lfs_dir_getnamlen(fs, dirp), offset);

        /* Remove the hash entry. */
        ulfsdirhash_delslot(dh, slot);

        /* Update the per-block summary info. */
        ulfsdirhash_adjfree(dh, offset, LFS_DIRSIZ(fs, dirp), dirblksiz);
        DIRHASH_UNLOCK(dh);
}

/*
 * Change the offset associated with a directory entry in the hash. Used
 * when compacting directory blocks.
 */
void
ulfsdirhash_move(struct inode *ip, LFS_DIRHEADER *dirp, doff_t oldoff,
    doff_t newoff)
{
        struct lfs *fs = ip->i_lfs;
        struct dirhash *dh;
        int slot;

        if ((dh = ip->i_dirhash) == NULL)
                return;
        DIRHASH_LOCK(dh);
        if (dh->dh_hash == NULL) {
                DIRHASH_UNLOCK(dh);
                ulfsdirhash_free(ip);
                return;
        }

        KASSERT(oldoff < dh->dh_dirblks * ip->i_lfs->um_dirblksiz &&
            newoff < dh->dh_dirblks * ip->i_lfs->um_dirblksiz);
        /* Find the entry, and update the offset. */
        slot = ulfsdirhash_findslot(dh, lfs_dir_nameptr(fs, dirp),
                                    lfs_dir_getnamlen(fs, dirp), oldoff);
        DH_ENTRY(dh, slot) = newoff;
        DIRHASH_UNLOCK(dh);
}

/*
 * Inform dirhash that the directory has grown by one block that
 * begins at offset (i.e. the new length is offset + DIRBLKSIZ).
 */
void
ulfsdirhash_newblk(struct inode *ip, doff_t offset)
{
        struct dirhash *dh;
        int block;
        int dirblksiz = ip->i_lfs->um_dirblksiz;

        if ((dh = ip->i_dirhash) == NULL)
                return;
        DIRHASH_LOCK(dh);
        if (dh->dh_hash == NULL) {
                DIRHASH_UNLOCK(dh);
                ulfsdirhash_free(ip);
                return;
        }

        KASSERT(offset == dh->dh_dirblks * dirblksiz);
        block = offset / dirblksiz;
        if (block >= dh->dh_nblk) {
                /* Out of space; must rebuild. */
                DIRHASH_UNLOCK(dh);
                ulfsdirhash_free(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;
        DIRHASH_UNLOCK(dh);
}

/*
 * Inform dirhash that the directory is being truncated.
 */
void
ulfsdirhash_dirtrunc(struct inode *ip, doff_t offset)
{
        struct dirhash *dh;
        int block, i;
        int dirblksiz = ip->i_lfs->um_dirblksiz;

        if ((dh = ip->i_dirhash) == NULL)
                return;

        DIRHASH_LOCK(dh);
        if (dh->dh_hash == NULL) {
                DIRHASH_UNLOCK(dh);
                ulfsdirhash_free(ip);
                return;
        }

        KASSERT(offset <= dh->dh_dirblks * dirblksiz);
        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
         * ulfsdirhash_build) then free it, and let the caller rebuild
         * if necessary.
         */
        if (block < dh->dh_nblk / 8 && dh->dh_narrays > 1) {
                DIRHASH_UNLOCK(dh);
                ulfsdirhash_free(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("ulfsdirhash_dirtrunc: blocks in use");
        for (i = 0; i < DH_NFSTATS; i++)
                if (dh->dh_firstfree[i] >= block)
                        panic("ulfsdirhash_dirtrunc: first free corrupt");
        dh->dh_dirblks = block;
        DIRHASH_UNLOCK(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, `sbuf' 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
ulfsdirhash_checkblock(struct inode *ip, char *sbuf, doff_t offset)
{
        struct lfs *fs = ip->i_lfs;
        struct dirhash *dh;
        LFS_DIRHEADER *dp;
        int block, ffslot, i, nfree;
        int dirblksiz = ip->i_lfs->um_dirblksiz;

        if (!ulfs_dirhashcheck)
                return;
        if ((dh = ip->i_dirhash) == NULL)
                return;

        DIRHASH_LOCK(dh);
        if (dh->dh_hash == NULL) {
                DIRHASH_UNLOCK(dh);
                ulfsdirhash_free(ip);
                return;
        }

        block = offset / dirblksiz;
        if ((offset & (dirblksiz - 1)) != 0 || block >= dh->dh_dirblks)
                panic("ulfsdirhash_checkblock: bad offset");

        nfree = 0;
        for (i = 0; i < dirblksiz; i += lfs_dir_getreclen(fs, dp)) {
                dp = (LFS_DIRHEADER *)(sbuf + i);
                if (lfs_dir_getreclen(fs, dp) == 0 || i + lfs_dir_getreclen(fs, dp) > dirblksiz)
                        panic("ulfsdirhash_checkblock: bad dir");

                if (lfs_dir_getino(fs, dp) == 0) {
#if 0
                        /*
                         * XXX entries with d_ino == 0 should only occur
                         * at the start of a DIRBLKSIZ block. However the
                         * ulfs code is tolerant of such entries at other
                         * offsets, and fsck does not fix them.
                         */
                        if (i != 0)
                                panic("ulfsdirhash_checkblock: bad dir inode");
#endif
                        nfree += lfs_dir_getreclen(fs, dp);
                        continue;
                }

                /* Check that the entry exists (will panic if it doesn't). */
                ulfsdirhash_findslot(dh, lfs_dir_nameptr(fs, dp),
                                     lfs_dir_getnamlen(fs, dp),
                                     offset + i);

                nfree += lfs_dir_getreclen(fs, dp) - LFS_DIRSIZ(fs, dp);
        }
        if (i != dirblksiz)
                panic("ulfsdirhash_checkblock: bad dir end");

        if (dh->dh_blkfree[block] * DIRALIGN != nfree)
                panic("ulfsdirhash_checkblock: bad free count");

        ffslot = BLKFREE2IDX(nfree / DIRALIGN);
        for (i = 0; i <= DH_NFSTATS; i++)
                if (dh->dh_firstfree[i] == block && i != ffslot)
                        panic("ulfsdirhash_checkblock: bad first-free");
        if (dh->dh_firstfree[ffslot] == -1)
                panic("ulfsdirhash_checkblock: missing first-free entry");
        DIRHASH_UNLOCK(dh);
}

/*
 * Hash the specified filename into a dirhash slot.
 */
static int
ulfsdirhash_hash(struct dirhash *dh, const 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 = hash32_buf(name, namelen, HASH32_BUF_INIT);
        hash = hash32_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 ulfsdirhash_build() where exclusive access can be assumed.
 */
static void
ulfsdirhash_adjfree(struct dirhash *dh, doff_t offset, int diff, int dirblksiz)
{
        int block, i, nfidx, ofidx;

        KASSERT(mutex_owned(&dh->dh_lock));

        /* Update the per-block summary info. */
        block = offset / dirblksiz;
        KASSERT(block < dh->dh_nblk && block < dh->dh_dirblks);
        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
ulfsdirhash_findslot(struct dirhash *dh, const char *name, int namelen,
    doff_t offset)
{
        int slot;

        KASSERT(mutex_owned(&dh->dh_lock));

        /* Find the entry. */
        KASSERT(dh->dh_hused < dh->dh_hlen);
        slot = ulfsdirhash_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("ulfsdirhash_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
ulfsdirhash_delslot(struct dirhash *dh, int slot)
{
        int i;

        KASSERT(mutex_owned(&dh->dh_lock));

        /* 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);
        }
}

/*
 * 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
ulfsdirhash_getprev(struct lfs *fs, LFS_DIRHEADER *dirp,
                doff_t offset, int dirblksiz)
{
        LFS_DIRHEADER *dp;
        char *blkbuf;
        doff_t blkoff, prevoff;
        int entrypos, i;
        unsigned reclen;

        blkoff = offset & ~(dirblksiz - 1);     /* 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 += reclen) {
                dp = (LFS_DIRHEADER *)(blkbuf + i);
                reclen = lfs_dir_getreclen(fs, dp);
                if (reclen == 0 || i + reclen > entrypos)
                        return (-1);    /* Corrupted directory. */
                prevoff = blkoff + i;
        }
        return (prevoff);
}

/*
 * Try to free up `wanted' bytes by stealing memory from existing
 * dirhashes. Returns zero with list locked if successful.
 */
static int
ulfsdirhash_recycle(int wanted)
{
        struct dirhash *dh;
        doff_t **hash;
        u_int8_t *blkfree;
        int i, mem, narrays;
        size_t hashsz, blkfreesz;

        DIRHASHLIST_LOCK();
        while (wanted + ulfs_dirhashmem > ulfs_dirhashmaxmem) {
                /* Find a dirhash, and lock it. */
                if ((dh = TAILQ_FIRST(&ulfsdirhash_list)) == NULL) {
                        DIRHASHLIST_UNLOCK();
                        return (-1);
                }
                DIRHASH_LOCK(dh);
                KASSERT(dh->dh_hash != NULL);

                /* Decrement the score; only recycle if it becomes zero. */
                if (--dh->dh_score > 0) {
                        DIRHASH_UNLOCK(dh);
                        DIRHASHLIST_UNLOCK();
                        return (-1);
                }

                /* Remove it from the list and detach its memory. */
                TAILQ_REMOVE(&ulfsdirhash_list, dh, dh_list);
                dh->dh_onlist = 0;
                hash = dh->dh_hash;
                hashsz = dh->dh_hashsz;
                dh->dh_hash = NULL;
                blkfree = dh->dh_blkfree;
                blkfreesz = dh->dh_blkfreesz;
                dh->dh_blkfree = NULL;
                narrays = dh->dh_narrays;
                mem = narrays * sizeof(*dh->dh_hash) +
                    narrays * DH_NBLKOFF * sizeof(**dh->dh_hash) +
                    dh->dh_nblk * sizeof(*dh->dh_blkfree);

                /* Unlock everything, free the detached memory. */
                DIRHASH_UNLOCK(dh);
                DIRHASHLIST_UNLOCK();

                for (i = 0; i < narrays; i++)
                        DIRHASH_BLKFREE(hash[i]);
                kmem_free(hash, hashsz);
                kmem_free(blkfree, blkfreesz);

                /* Account for the returned memory, and repeat if necessary. */
                DIRHASHLIST_LOCK();
                atomic_add_int(&ulfs_dirhashmem, -mem);
        }
        /* Success. */
        return (0);
}

static void
ulfsdirhash_sysctl_init(void)
{
        const struct sysctlnode *rnode, *cnode;

        sysctl_createv(&ulfsdirhash_sysctl_log, 0, NULL, &rnode,
                       CTLFLAG_PERMANENT,
                       CTLTYPE_NODE, "ulfs",
                       SYSCTL_DESCR("ulfs"),
                       NULL, 0, NULL, 0,
                       CTL_VFS, CTL_CREATE, CTL_EOL);

        sysctl_createv(&ulfsdirhash_sysctl_log, 0, &rnode, &rnode,
                       CTLFLAG_PERMANENT,
                       CTLTYPE_NODE, "dirhash",
                       SYSCTL_DESCR("dirhash"),
                       NULL, 0, NULL, 0,
                       CTL_CREATE, CTL_EOL);

        sysctl_createv(&ulfsdirhash_sysctl_log, 0, &rnode, &cnode,
                       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                       CTLTYPE_INT, "minblocks",
                       SYSCTL_DESCR("minimum hashed directory size in blocks"),
                       NULL, 0, &ulfs_dirhashminblks, 0,
                       CTL_CREATE, CTL_EOL);

        sysctl_createv(&ulfsdirhash_sysctl_log, 0, &rnode, &cnode,
                       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                       CTLTYPE_INT, "maxmem",
                       SYSCTL_DESCR("maximum dirhash memory usage"),
                       NULL, 0, &ulfs_dirhashmaxmem, 0,
                       CTL_CREATE, CTL_EOL);

        sysctl_createv(&ulfsdirhash_sysctl_log, 0, &rnode, &cnode,
                       CTLFLAG_PERMANENT|CTLFLAG_READONLY,
                       CTLTYPE_INT, "memused",
                       SYSCTL_DESCR("current dirhash memory usage"),
                       NULL, 0, &ulfs_dirhashmem, 0,
                       CTL_CREATE, CTL_EOL);

        sysctl_createv(&ulfsdirhash_sysctl_log, 0, &rnode, &cnode,
                       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                       CTLTYPE_INT, "docheck",
                       SYSCTL_DESCR("enable extra sanity checks"),
                       NULL, 0, &ulfs_dirhashcheck, 0,
                       CTL_CREATE, CTL_EOL);
}

void
ulfsdirhash_init(void)
{

        /*
         * Only initialise defaults for the dirhash size if it hasn't
         * hasn't been set.
         */
        if (ulfs_dirhashmaxmem == 0) {
                /* Use 64-bit math to avoid overflows. */
                uint64_t physmem_bytes, hash_bytes;

                physmem_bytes = ctob((uint64_t)physmem);
                hash_bytes = physmem_bytes / DIRHASH_DEFAULT_DIVIDER;

                if (hash_bytes < MIN_DEFAULT_DIRHASH_MEM)
                        hash_bytes = 0;

                if (hash_bytes > MAX_DEFAULT_DIRHASH_MEM)
                        hash_bytes = MAX_DEFAULT_DIRHASH_MEM;

                ulfs_dirhashmaxmem = (u_int)hash_bytes;
        }

        mutex_init(&ulfsdirhash_lock, MUTEX_DEFAULT, IPL_NONE);
        ulfsdirhashblk_cache = pool_cache_init(DH_NBLKOFF * sizeof(daddr_t), 0,
            0, 0, "dirhashblk", NULL, IPL_NONE, NULL, NULL, NULL);
        ulfsdirhash_cache = pool_cache_init(sizeof(struct dirhash), 0,
            0, 0, "dirhash", NULL, IPL_NONE, NULL, NULL, NULL);
        TAILQ_INIT(&ulfsdirhash_list);
        ulfsdirhash_sysctl_init();
}

void
ulfsdirhash_done(void)
{

        KASSERT(TAILQ_EMPTY(&ulfsdirhash_list));
        pool_cache_destroy(ulfsdirhashblk_cache);
        pool_cache_destroy(ulfsdirhash_cache);
        mutex_destroy(&ulfsdirhash_lock);
        sysctl_teardown(&ulfsdirhash_sysctl_log);
}