8857 zio_remove_child() panic due to already destroyed parent zio

[unleashed.git] / usr / src / uts / common / fs / dnlc.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright (c) 2015, Joyent, Inc.
 * Copyright (c) 2017 by Delphix. All rights reserved.
 */

/*      Copyright (c) 1983, 1984, 1985, 1986, 1987, 1988, 1989 AT&T     */
/*        All Rights Reserved   */

/*
 * University Copyright- Copyright (c) 1982, 1986, 1988
 * The Regents of the University of California
 * All Rights Reserved
 *
 * University Acknowledgment- Portions of this document are derived from
 * software developed by the University of California, Berkeley, and its
 * contributors.
 */

#include <sys/types.h>
#include <sys/systm.h>
#include <sys/param.h>
#include <sys/t_lock.h>
#include <sys/systm.h>
#include <sys/vfs.h>
#include <sys/vnode.h>
#include <sys/dnlc.h>
#include <sys/kmem.h>
#include <sys/cmn_err.h>
#include <sys/vtrace.h>
#include <sys/bitmap.h>
#include <sys/var.h>
#include <sys/sysmacros.h>
#include <sys/kstat.h>
#include <sys/atomic.h>
#include <sys/taskq.h>

/*
 * Directory name lookup cache.
 * Based on code originally done by Robert Elz at Melbourne.
 *
 * Names found by directory scans are retained in a cache
 * for future reference.  Each hash chain is ordered by LRU
 * Cache is indexed by hash value obtained from (vp, name)
 * where the vp refers to the directory containing the name.
 */

/*
 * We want to be able to identify files that are referenced only by the DNLC.
 * When adding a reference from the DNLC, call VN_HOLD_DNLC instead of VN_HOLD,
 * since multiple DNLC references should only be counted once in v_count. The
 * VN_HOLD macro itself is aliased to VN_HOLD_CALLER in this file to help
 * differentiate the behaviors.  (Unfortunately it is not possible to #undef
 * VN_HOLD and retain VN_HOLD_CALLER. Ideally a Makefile rule would grep
 * uncommented C tokens to check that VN_HOLD is referenced only once in this
 * file, to define VN_HOLD_CALLER.)
 */
#define VN_HOLD_CALLER  VN_HOLD
#define VN_HOLD_DNLC(vp)        {       \
        mutex_enter(&(vp)->v_lock);     \
        if ((vp)->v_count_dnlc == 0) {  \
                VN_HOLD_LOCKED(vp);     \
        }                               \
        (vp)->v_count_dnlc++;           \
        mutex_exit(&(vp)->v_lock);      \
}
#define VN_RELE_DNLC(vp)        {       \
        vn_rele_dnlc(vp);               \
}

/*
 * Tunable nc_hashavelen is the average length desired for this chain, from
 * which the size of the nc_hash table is derived at create time.
 */
#define NC_HASHAVELEN_DEFAULT   4
int nc_hashavelen = NC_HASHAVELEN_DEFAULT;

/*
 * NC_MOVETOFRONT is the move-to-front threshold: if the hash lookup
 * depth exceeds this value, we move the looked-up entry to the front of
 * its hash chain.  The idea is to make sure that the most frequently
 * accessed entries are found most quickly (by keeping them near the
 * front of their hash chains).
 */
#define NC_MOVETOFRONT  2

/*
 *
 * DNLC_MAX_RELE is used to size an array on the stack when releasing
 * vnodes. This array is used rather than calling VN_RELE() inline because
 * all dnlc locks must be dropped by that time in order to avoid a
 * possible deadlock. This deadlock occurs when the dnlc holds the last
 * reference to the vnode and so the VOP_INACTIVE vector is called which
 * can in turn call back into the dnlc. A global array was used but had
 * many problems:
 *      1) Actually doesn't have an upper bound on the array size as
 *         entries can be added after starting the purge.
 *      2) The locking scheme causes a hang.
 *      3) Caused serialisation on the global lock.
 *      4) The array was often unnecessarily huge.
 *
 * Note the current value 8 allows up to 4 cache entries (to be purged
 * from each hash chain), before having to cycle around and retry.
 * This ought to be ample given that nc_hashavelen is typically very small.
 */
#define DNLC_MAX_RELE   8 /* must be even */

/*
 * Hash table of name cache entries for fast lookup, dynamically
 * allocated at startup.
 */
nc_hash_t *nc_hash;

/*
 * Rotors. Used to select entries on a round-robin basis.
 */
static nc_hash_t *dnlc_purge_fs1_rotor;
static nc_hash_t *dnlc_free_rotor;

/*
 * # of dnlc entries (uninitialized)
 *
 * the initial value was chosen as being
 * a random string of bits, probably not
 * normally chosen by a systems administrator
 */
int ncsize = -1;
volatile uint32_t dnlc_nentries = 0;    /* current num of name cache entries */
static int nc_hashsz;                   /* size of hash table */
static int nc_hashmask;                 /* size of hash table minus 1 */

/*
 * The dnlc_reduce_cache() taskq queue is activated when there are
 * ncsize name cache entries and if no parameter is provided, it reduces
 * the size down to dnlc_nentries_low_water, which is by default one
 * hundreth less (or 99%) of ncsize.
 *
 * If a parameter is provided to dnlc_reduce_cache(), then we reduce
 * the size down based on ncsize_onepercent - where ncsize_onepercent
 * is 1% of ncsize; however, we never let dnlc_reduce_cache() reduce
 * the size below 3% of ncsize (ncsize_min_percent).
 */
#define DNLC_LOW_WATER_DIVISOR_DEFAULT 100
uint_t dnlc_low_water_divisor = DNLC_LOW_WATER_DIVISOR_DEFAULT;
uint_t dnlc_nentries_low_water;
int dnlc_reduce_idle = 1; /* no locking needed */
uint_t ncsize_onepercent;
uint_t ncsize_min_percent;

/*
 * If dnlc_nentries hits dnlc_max_nentries (twice ncsize)
 * then this means the dnlc_reduce_cache() taskq is failing to
 * keep up. In this case we refuse to add new entries to the dnlc
 * until the taskq catches up.
 */
uint_t dnlc_max_nentries; /* twice ncsize */
uint64_t dnlc_max_nentries_cnt = 0; /* statistic on times we failed */

/*
 * Tunable to define when we should just remove items from
 * the end of the chain.
 */
#define DNLC_LONG_CHAIN 8
uint_t dnlc_long_chain = DNLC_LONG_CHAIN;

/*
 * ncstats has been deprecated, due to the integer size of the counters
 * which can easily overflow in the dnlc.
 * It is maintained (at some expense) for compatability.
 * The preferred interface is the kstat accessible nc_stats below.
 */
struct ncstats ncstats;

struct nc_stats ncs = {
        { "hits",                       KSTAT_DATA_UINT64 },
        { "misses",                     KSTAT_DATA_UINT64 },
        { "negative_cache_hits",        KSTAT_DATA_UINT64 },
        { "enters",                     KSTAT_DATA_UINT64 },
        { "double_enters",              KSTAT_DATA_UINT64 },
        { "purge_total_entries",        KSTAT_DATA_UINT64 },
        { "purge_all",                  KSTAT_DATA_UINT64 },
        { "purge_vp",                   KSTAT_DATA_UINT64 },
        { "purge_vfs",                  KSTAT_DATA_UINT64 },
        { "purge_fs1",                  KSTAT_DATA_UINT64 },
        { "pick_free",                  KSTAT_DATA_UINT64 },
        { "pick_heuristic",             KSTAT_DATA_UINT64 },
        { "pick_last",                  KSTAT_DATA_UINT64 },

        /* directory caching stats */

        { "dir_hits",                   KSTAT_DATA_UINT64 },
        { "dir_misses",                 KSTAT_DATA_UINT64 },
        { "dir_cached_current",         KSTAT_DATA_UINT64 },
        { "dir_entries_cached_current", KSTAT_DATA_UINT64 },
        { "dir_cached_total",           KSTAT_DATA_UINT64 },
        { "dir_start_no_memory",        KSTAT_DATA_UINT64 },
        { "dir_add_no_memory",          KSTAT_DATA_UINT64 },
        { "dir_add_abort",              KSTAT_DATA_UINT64 },
        { "dir_add_max",                KSTAT_DATA_UINT64 },
        { "dir_remove_entry_fail",      KSTAT_DATA_UINT64 },
        { "dir_remove_space_fail",      KSTAT_DATA_UINT64 },
        { "dir_update_fail",            KSTAT_DATA_UINT64 },
        { "dir_fini_purge",             KSTAT_DATA_UINT64 },
        { "dir_reclaim_last",           KSTAT_DATA_UINT64 },
        { "dir_reclaim_any",            KSTAT_DATA_UINT64 },
};

static int doingcache = 1;

vnode_t negative_cache_vnode;

/*
 * Insert entry at the front of the queue
 */
#define nc_inshash(ncp, hp) \
{ \
        (ncp)->hash_next = (hp)->hash_next; \
        (ncp)->hash_prev = (ncache_t *)(hp); \
        (hp)->hash_next->hash_prev = (ncp); \
        (hp)->hash_next = (ncp); \
}

/*
 * Remove entry from hash queue
 */
#define nc_rmhash(ncp) \
{ \
        (ncp)->hash_prev->hash_next = (ncp)->hash_next; \
        (ncp)->hash_next->hash_prev = (ncp)->hash_prev; \
        (ncp)->hash_prev = NULL; \
        (ncp)->hash_next = NULL; \
}

/*
 * Free an entry.
 */
#define dnlc_free(ncp) \
{ \
        kmem_free((ncp), sizeof (ncache_t) + (ncp)->namlen); \
        atomic_dec_32(&dnlc_nentries); \
}


/*
 * Cached directory info.
 * ======================
 */

/*
 * Cached directory free space hash function.
 * Needs the free space handle and the dcp to get the hash table size
 * Returns the hash index.
 */
#define DDFHASH(handle, dcp) ((handle >> 2) & (dcp)->dc_fhash_mask)

/*
 * Cached directory name entry hash function.
 * Uses the name and returns in the input arguments the hash and the name
 * length.
 */
#define DNLC_DIR_HASH(name, hash, namelen)                      \
        {                                                       \
                char Xc;                                        \
                const char *Xcp;                                \
                hash = *name;                                   \
                for (Xcp = (name + 1); (Xc = *Xcp) != 0; Xcp++) \
                        hash = (hash << 4) + hash + Xc;         \
                ASSERT((Xcp - (name)) <= ((1 << NBBY) - 1));    \
                namelen = Xcp - (name);                         \
        }

/* special dircache_t pointer to indicate error should be returned */
/*
 * The anchor directory cache pointer can contain 3 types of values,
 * 1) NULL: No directory cache
 * 2) DC_RET_LOW_MEM (-1): There was a directory cache that found to be
 *    too big or a memory shortage occurred. This value remains in the
 *    pointer until a dnlc_dir_start() which returns the a DNOMEM error.
 *    This is kludgy but efficient and only visible in this source file.
 * 3) A valid cache pointer.
 */
#define DC_RET_LOW_MEM (dircache_t *)1
#define VALID_DIR_CACHE(dcp) ((dircache_t *)(dcp) > DC_RET_LOW_MEM)

/* Tunables */
uint_t dnlc_dir_enable = 1; /* disable caching directories by setting to 0 */
uint_t dnlc_dir_min_size = 40; /* min no of directory entries before caching */
uint_t dnlc_dir_max_size = UINT_MAX; /* ditto maximum */
uint_t dnlc_dir_hash_size_shift = 3; /* 8 entries per hash bucket */
uint_t dnlc_dir_min_reclaim =  350000; /* approx 1MB of dcentrys */
/*
 * dnlc_dir_hash_resize_shift determines when the hash tables
 * get re-adjusted due to growth or shrinkage
 * - currently 2 indicating that there can be at most 4
 * times or at least one quarter the number of entries
 * before hash table readjustment. Note that with
 * dnlc_dir_hash_size_shift above set at 3 this would
 * mean readjustment would occur if the average number
 * of entries went above 32 or below 2
 */
uint_t dnlc_dir_hash_resize_shift = 2; /* readjust rate */

static kmem_cache_t *dnlc_dir_space_cache; /* free space entry cache */
static dchead_t dc_head; /* anchor of cached directories */

/* Prototypes */
static ncache_t *dnlc_get(uchar_t namlen);
static ncache_t *dnlc_search(vnode_t *dp, const char *name, uchar_t namlen,
    int hash);
static void dnlc_dir_reclaim(void *unused);
static void dnlc_dir_abort(dircache_t *dcp);
static void dnlc_dir_adjust_fhash(dircache_t *dcp);
static void dnlc_dir_adjust_nhash(dircache_t *dcp);
static void do_dnlc_reduce_cache(void *);


/*
 * Initialize the directory cache.
 */
void
dnlc_init()
{
        nc_hash_t *hp;
        kstat_t *ksp;
        int i;

        /*
         * Set up the size of the dnlc (ncsize) and its low water mark.
         */
        if (ncsize == -1) {
                /* calculate a reasonable size for the low water */
                dnlc_nentries_low_water = 4 * (v.v_proc + maxusers) + 320;
                ncsize = dnlc_nentries_low_water +
                    (dnlc_nentries_low_water / dnlc_low_water_divisor);
        } else {
                /* don't change the user specified ncsize */
                dnlc_nentries_low_water =
                    ncsize - (ncsize / dnlc_low_water_divisor);
        }
        if (ncsize <= 0) {
                doingcache = 0;
                dnlc_dir_enable = 0; /* also disable directory caching */
                ncsize = 0;
                cmn_err(CE_NOTE, "name cache (dnlc) disabled");
                return;
        }
        dnlc_max_nentries = ncsize * 2;
        ncsize_onepercent = ncsize / 100;
        ncsize_min_percent = ncsize_onepercent * 3;

        /*
         * Initialise the hash table.
         * Compute hash size rounding to the next power of two.
         */
        nc_hashsz = ncsize / nc_hashavelen;
        nc_hashsz = 1 << highbit(nc_hashsz);
        nc_hashmask = nc_hashsz - 1;
        nc_hash = kmem_zalloc(nc_hashsz * sizeof (*nc_hash), KM_SLEEP);
        for (i = 0; i < nc_hashsz; i++) {
                hp = (nc_hash_t *)&nc_hash[i];
                mutex_init(&hp->hash_lock, NULL, MUTEX_DEFAULT, NULL);
                hp->hash_next = (ncache_t *)hp;
                hp->hash_prev = (ncache_t *)hp;
        }

        /*
         * Initialize rotors
         */
        dnlc_free_rotor = dnlc_purge_fs1_rotor = &nc_hash[0];

        /*
         * Set up the directory caching to use kmem_cache_alloc
         * for its free space entries so that we can get a callback
         * when the system is short on memory, to allow us to free
         * up some memory. we don't use the constructor/deconstructor
         * functions.
         */
        dnlc_dir_space_cache = kmem_cache_create("dnlc_space_cache",
            sizeof (dcfree_t), 0, NULL, NULL, dnlc_dir_reclaim, NULL,
            NULL, 0);

        /*
         * Initialise the head of the cached directory structures
         */
        mutex_init(&dc_head.dch_lock, NULL, MUTEX_DEFAULT, NULL);
        dc_head.dch_next = (dircache_t *)&dc_head;
        dc_head.dch_prev = (dircache_t *)&dc_head;

        /*
         * Put a hold on the negative cache vnode so that it never goes away
         * (VOP_INACTIVE isn't called on it).
         */
        vn_reinit(&negative_cache_vnode);

        /*
         * Initialise kstats - both the old compatability raw kind and
         * the more extensive named stats.
         */
        ksp = kstat_create("unix", 0, "ncstats", "misc", KSTAT_TYPE_RAW,
            sizeof (struct ncstats), KSTAT_FLAG_VIRTUAL);
        if (ksp) {
                ksp->ks_data = (void *) &ncstats;
                kstat_install(ksp);
        }
        ksp = kstat_create("unix", 0, "dnlcstats", "misc", KSTAT_TYPE_NAMED,
            sizeof (ncs) / sizeof (kstat_named_t), KSTAT_FLAG_VIRTUAL);
        if (ksp) {
                ksp->ks_data = (void *) &ncs;
                kstat_install(ksp);
        }
}

/*
 * Add a name to the directory cache.
 */
void
dnlc_enter(vnode_t *dp, const char *name, vnode_t *vp)
{
        ncache_t *ncp;
        nc_hash_t *hp;
        uchar_t namlen;
        int hash;

        TRACE_0(TR_FAC_NFS, TR_DNLC_ENTER_START, "dnlc_enter_start:");

        if (!doingcache) {
                TRACE_2(TR_FAC_NFS, TR_DNLC_ENTER_END,
                    "dnlc_enter_end:(%S) %d", "not caching", 0);
                return;
        }

        /*
         * Get a new dnlc entry. Assume the entry won't be in the cache
         * and initialize it now
         */
        DNLCHASH(name, dp, hash, namlen);
        if ((ncp = dnlc_get(namlen)) == NULL)
                return;
        ncp->dp = dp;
        VN_HOLD_DNLC(dp);
        ncp->vp = vp;
        VN_HOLD_DNLC(vp);
        bcopy(name, ncp->name, namlen + 1); /* name and null */
        ncp->hash = hash;
        hp = &nc_hash[hash & nc_hashmask];

        mutex_enter(&hp->hash_lock);
        if (dnlc_search(dp, name, namlen, hash) != NULL) {
                mutex_exit(&hp->hash_lock);
                ncstats.dbl_enters++;
                ncs.ncs_dbl_enters.value.ui64++;
                VN_RELE_DNLC(dp);
                VN_RELE_DNLC(vp);
                dnlc_free(ncp);         /* crfree done here */
                TRACE_2(TR_FAC_NFS, TR_DNLC_ENTER_END,
                    "dnlc_enter_end:(%S) %d", "dbl enter", ncstats.dbl_enters);
                return;
        }
        /*
         * Insert back into the hash chain.
         */
        nc_inshash(ncp, hp);
        mutex_exit(&hp->hash_lock);
        ncstats.enters++;
        ncs.ncs_enters.value.ui64++;
        TRACE_2(TR_FAC_NFS, TR_DNLC_ENTER_END,
            "dnlc_enter_end:(%S) %d", "done", ncstats.enters);
}

/*
 * Add a name to the directory cache.
 *
 * This function is basically identical with
 * dnlc_enter().  The difference is that when the
 * desired dnlc entry is found, the vnode in the
 * ncache is compared with the vnode passed in.
 *
 * If they are not equal then the ncache is
 * updated with the passed in vnode.  Otherwise
 * it just frees up the newly allocated dnlc entry.
 */
void
dnlc_update(vnode_t *dp, const char *name, vnode_t *vp)
{
        ncache_t *ncp;
        ncache_t *tcp;
        vnode_t *tvp;
        nc_hash_t *hp;
        int hash;
        uchar_t namlen;

        TRACE_0(TR_FAC_NFS, TR_DNLC_ENTER_START, "dnlc_update_start:");

        if (!doingcache) {
                TRACE_2(TR_FAC_NFS, TR_DNLC_ENTER_END,
                    "dnlc_update_end:(%S) %d", "not caching", 0);
                return;
        }

        /*
         * Get a new dnlc entry and initialize it now.
         * If we fail to get a new entry, call dnlc_remove() to purge
         * any existing dnlc entry including negative cache (DNLC_NO_VNODE)
         * entry.
         * Failure to clear an existing entry could result in false dnlc
         * lookup (negative/stale entry).
         */
        DNLCHASH(name, dp, hash, namlen);
        if ((ncp = dnlc_get(namlen)) == NULL) {
                dnlc_remove(dp, name);
                return;
        }
        ncp->dp = dp;
        VN_HOLD_DNLC(dp);
        ncp->vp = vp;
        VN_HOLD_DNLC(vp);
        bcopy(name, ncp->name, namlen + 1); /* name and null */
        ncp->hash = hash;
        hp = &nc_hash[hash & nc_hashmask];

        mutex_enter(&hp->hash_lock);
        if ((tcp = dnlc_search(dp, name, namlen, hash)) != NULL) {
                if (tcp->vp != vp) {
                        tvp = tcp->vp;
                        tcp->vp = vp;
                        mutex_exit(&hp->hash_lock);
                        VN_RELE_DNLC(tvp);
                        ncstats.enters++;
                        ncs.ncs_enters.value.ui64++;
                        TRACE_2(TR_FAC_NFS, TR_DNLC_ENTER_END,
                            "dnlc_update_end:(%S) %d", "done", ncstats.enters);
                } else {
                        mutex_exit(&hp->hash_lock);
                        VN_RELE_DNLC(vp);
                        ncstats.dbl_enters++;
                        ncs.ncs_dbl_enters.value.ui64++;
                        TRACE_2(TR_FAC_NFS, TR_DNLC_ENTER_END,
                            "dnlc_update_end:(%S) %d",
                            "dbl enter", ncstats.dbl_enters);
                }
                VN_RELE_DNLC(dp);
                dnlc_free(ncp);         /* crfree done here */
                return;
        }
        /*
         * insert the new entry, since it is not in dnlc yet
         */
        nc_inshash(ncp, hp);
        mutex_exit(&hp->hash_lock);
        ncstats.enters++;
        ncs.ncs_enters.value.ui64++;
        TRACE_2(TR_FAC_NFS, TR_DNLC_ENTER_END,
            "dnlc_update_end:(%S) %d", "done", ncstats.enters);
}

/*
 * Look up a name in the directory name cache.
 *
 * Return a doubly-held vnode if found: one hold so that it may
 * remain in the cache for other users, the other hold so that
 * the cache is not re-cycled and the identity of the vnode is
 * lost before the caller can use the vnode.
 */
vnode_t *
dnlc_lookup(vnode_t *dp, const char *name)
{
        ncache_t *ncp;
        nc_hash_t *hp;
        vnode_t *vp;
        int hash, depth;
        uchar_t namlen;

        TRACE_2(TR_FAC_NFS, TR_DNLC_LOOKUP_START,
            "dnlc_lookup_start:dp %x name %s", dp, name);

        if (!doingcache) {
                TRACE_4(TR_FAC_NFS, TR_DNLC_LOOKUP_END,
                    "dnlc_lookup_end:%S %d vp %x name %s",
                    "not_caching", 0, NULL, name);
                return (NULL);
        }

        DNLCHASH(name, dp, hash, namlen);
        depth = 1;
        hp = &nc_hash[hash & nc_hashmask];
        mutex_enter(&hp->hash_lock);

        for (ncp = hp->hash_next; ncp != (ncache_t *)hp;
            ncp = ncp->hash_next) {
                if (ncp->hash == hash &&        /* fast signature check */
                    ncp->dp == dp &&
                    ncp->namlen == namlen &&
                    bcmp(ncp->name, name, namlen) == 0) {
                        /*
                         * Move this entry to the head of its hash chain
                         * if it's not already close.
                         */
                        if (depth > NC_MOVETOFRONT) {
                                ncache_t *next = ncp->hash_next;
                                ncache_t *prev = ncp->hash_prev;

                                prev->hash_next = next;
                                next->hash_prev = prev;
                                ncp->hash_next = next = hp->hash_next;
                                ncp->hash_prev = (ncache_t *)hp;
                                next->hash_prev = ncp;
                                hp->hash_next = ncp;

                                ncstats.move_to_front++;
                        }

                        /*
                         * Put a hold on the vnode now so its identity
                         * can't change before the caller has a chance to
                         * put a hold on it.
                         */
                        vp = ncp->vp;
                        VN_HOLD_CALLER(vp);
                        mutex_exit(&hp->hash_lock);
                        ncstats.hits++;
                        ncs.ncs_hits.value.ui64++;
                        if (vp == DNLC_NO_VNODE) {
                                ncs.ncs_neg_hits.value.ui64++;
                        }
                        TRACE_4(TR_FAC_NFS, TR_DNLC_LOOKUP_END,
                            "dnlc_lookup_end:%S %d vp %x name %s", "hit",
                            ncstats.hits, vp, name);
                        return (vp);
                }
                depth++;
        }

        mutex_exit(&hp->hash_lock);
        ncstats.misses++;
        ncs.ncs_misses.value.ui64++;
        TRACE_4(TR_FAC_NFS, TR_DNLC_LOOKUP_END,
            "dnlc_lookup_end:%S %d vp %x name %s", "miss", ncstats.misses,
            NULL, name);
        return (NULL);
}

/*
 * Remove an entry in the directory name cache.
 */
void
dnlc_remove(vnode_t *dp, const char *name)
{
        ncache_t *ncp;
        nc_hash_t *hp;
        uchar_t namlen;
        int hash;

        if (!doingcache)
                return;
        DNLCHASH(name, dp, hash, namlen);
        hp = &nc_hash[hash & nc_hashmask];

        mutex_enter(&hp->hash_lock);
        if (ncp = dnlc_search(dp, name, namlen, hash)) {
                /*
                 * Free up the entry
                 */
                nc_rmhash(ncp);
                mutex_exit(&hp->hash_lock);
                VN_RELE_DNLC(ncp->vp);
                VN_RELE_DNLC(ncp->dp);
                dnlc_free(ncp);
                return;
        }
        mutex_exit(&hp->hash_lock);
}

/*
 * Purge the entire cache.
 */
void
dnlc_purge()
{
        nc_hash_t *nch;
        ncache_t *ncp;
        int index;
        int i;
        vnode_t *nc_rele[DNLC_MAX_RELE];

        if (!doingcache)
                return;

        ncstats.purges++;
        ncs.ncs_purge_all.value.ui64++;

        for (nch = nc_hash; nch < &nc_hash[nc_hashsz]; nch++) {
                index = 0;
                mutex_enter(&nch->hash_lock);
                ncp = nch->hash_next;
                while (ncp != (ncache_t *)nch) {
                        ncache_t *np;

                        np = ncp->hash_next;
                        nc_rele[index++] = ncp->vp;
                        nc_rele[index++] = ncp->dp;

                        nc_rmhash(ncp);
                        dnlc_free(ncp);
                        ncp = np;
                        ncs.ncs_purge_total.value.ui64++;
                        if (index == DNLC_MAX_RELE)
                                break;
                }
                mutex_exit(&nch->hash_lock);

                /* Release holds on all the vnodes now that we have no locks */
                for (i = 0; i < index; i++) {
                        VN_RELE_DNLC(nc_rele[i]);
                }
                if (ncp != (ncache_t *)nch) {
                        nch--; /* Do current hash chain again */
                }
        }
}

/*
 * Purge any cache entries referencing a vnode. Exit as soon as the dnlc
 * reference count goes to zero (the caller still holds a reference).
 */
void
dnlc_purge_vp(vnode_t *vp)
{
        nc_hash_t *nch;
        ncache_t *ncp;
        int index;
        vnode_t *nc_rele[DNLC_MAX_RELE];

        ASSERT(vp->v_count > 0);
        if (vp->v_count_dnlc == 0) {
                return;
        }

        if (!doingcache)
                return;

        ncstats.purges++;
        ncs.ncs_purge_vp.value.ui64++;

        for (nch = nc_hash; nch < &nc_hash[nc_hashsz]; nch++) {
                index = 0;
                mutex_enter(&nch->hash_lock);
                ncp = nch->hash_next;
                while (ncp != (ncache_t *)nch) {
                        ncache_t *np;

                        np = ncp->hash_next;
                        if (ncp->dp == vp || ncp->vp == vp) {
                                nc_rele[index++] = ncp->vp;
                                nc_rele[index++] = ncp->dp;
                                nc_rmhash(ncp);
                                dnlc_free(ncp);
                                ncs.ncs_purge_total.value.ui64++;
                                if (index == DNLC_MAX_RELE) {
                                        ncp = np;
                                        break;
                                }
                        }
                        ncp = np;
                }
                mutex_exit(&nch->hash_lock);

                /* Release holds on all the vnodes now that we have no locks */
                while (index) {
                        VN_RELE_DNLC(nc_rele[--index]);
                }

                if (vp->v_count_dnlc == 0) {
                        return;
                }

                if (ncp != (ncache_t *)nch) {
                        nch--; /* Do current hash chain again */
                }
        }
}

/*
 * Purge cache entries referencing a vfsp.  Caller supplies a count
 * of entries to purge; up to that many will be freed.  A count of
 * zero indicates that all such entries should be purged.  Returns
 * the number of entries that were purged.
 */
int
dnlc_purge_vfsp(vfs_t *vfsp, int count)
{
        nc_hash_t *nch;
        ncache_t *ncp;
        int n = 0;
        int index;
        int i;
        vnode_t *nc_rele[DNLC_MAX_RELE];

        if (!doingcache)
                return (0);

        ncstats.purges++;
        ncs.ncs_purge_vfs.value.ui64++;

        for (nch = nc_hash; nch < &nc_hash[nc_hashsz]; nch++) {
                index = 0;
                mutex_enter(&nch->hash_lock);
                ncp = nch->hash_next;
                while (ncp != (ncache_t *)nch) {
                        ncache_t *np;

                        np = ncp->hash_next;
                        ASSERT(ncp->dp != NULL);
                        ASSERT(ncp->vp != NULL);
                        if ((ncp->dp->v_vfsp == vfsp) ||
                            (ncp->vp->v_vfsp == vfsp)) {
                                n++;
                                nc_rele[index++] = ncp->vp;
                                nc_rele[index++] = ncp->dp;
                                nc_rmhash(ncp);
                                dnlc_free(ncp);
                                ncs.ncs_purge_total.value.ui64++;
                                if (index == DNLC_MAX_RELE) {
                                        ncp = np;
                                        break;
                                }
                                if (count != 0 && n >= count) {
                                        break;
                                }
                        }
                        ncp = np;
                }
                mutex_exit(&nch->hash_lock);
                /* Release holds on all the vnodes now that we have no locks */
                for (i = 0; i < index; i++) {
                        VN_RELE_DNLC(nc_rele[i]);
                }
                if (count != 0 && n >= count) {
                        return (n);
                }
                if (ncp != (ncache_t *)nch) {
                        nch--; /* Do current hash chain again */
                }
        }
        return (n);
}

/*
 * Purge 1 entry from the dnlc that is part of the filesystem(s)
 * represented by 'vop'. The purpose of this routine is to allow
 * users of the dnlc to free a vnode that is being held by the dnlc.
 *
 * If we find a vnode that we release which will result in
 * freeing the underlying vnode (count was 1), return 1, 0
 * if no appropriate vnodes found.
 *
 * Note, vop is not the 'right' identifier for a filesystem.
 */
int
dnlc_fs_purge1(vnodeops_t *vop)
{
        nc_hash_t *end;
        nc_hash_t *hp;
        ncache_t *ncp;
        vnode_t *vp;

        if (!doingcache)
                return (0);

        ncs.ncs_purge_fs1.value.ui64++;

        /*
         * Scan the dnlc entries looking for a likely candidate.
         */
        hp = end = dnlc_purge_fs1_rotor;

        do {
                if (++hp == &nc_hash[nc_hashsz])
                        hp = nc_hash;
                dnlc_purge_fs1_rotor = hp;
                if (hp->hash_next == (ncache_t *)hp)
                        continue;
                mutex_enter(&hp->hash_lock);
                for (ncp = hp->hash_prev;
                    ncp != (ncache_t *)hp;
                    ncp = ncp->hash_prev) {
                        vp = ncp->vp;
                        if (!vn_has_cached_data(vp) && (vp->v_count == 1) &&
                            vn_matchops(vp, vop))
                                break;
                }
                if (ncp != (ncache_t *)hp) {
                        nc_rmhash(ncp);
                        mutex_exit(&hp->hash_lock);
                        VN_RELE_DNLC(ncp->dp);
                        VN_RELE_DNLC(vp)
                        dnlc_free(ncp);
                        ncs.ncs_purge_total.value.ui64++;
                        return (1);
                }
                mutex_exit(&hp->hash_lock);
        } while (hp != end);
        return (0);
}

/*
 * Utility routine to search for a cache entry. Return the
 * ncache entry if found, NULL otherwise.
 */
static ncache_t *
dnlc_search(vnode_t *dp, const char *name, uchar_t namlen, int hash)
{
        nc_hash_t *hp;
        ncache_t *ncp;

        hp = &nc_hash[hash & nc_hashmask];

        for (ncp = hp->hash_next; ncp != (ncache_t *)hp; ncp = ncp->hash_next) {
                if (ncp->hash == hash &&
                    ncp->dp == dp &&
                    ncp->namlen == namlen &&
                    bcmp(ncp->name, name, namlen) == 0)
                        return (ncp);
        }
        return (NULL);
}

#if ((1 << NBBY) - 1) < (MAXNAMELEN - 1)
#error ncache_t name length representation is too small
#endif

void
dnlc_reduce_cache(void *reduce_percent)
{
        if (dnlc_reduce_idle && (dnlc_nentries >= ncsize || reduce_percent)) {
                dnlc_reduce_idle = 0;
                if ((taskq_dispatch(system_taskq, do_dnlc_reduce_cache,
                    reduce_percent, TQ_NOSLEEP)) == NULL)
                        dnlc_reduce_idle = 1;
        }
}

/*
 * Get a new name cache entry.
 * If the dnlc_reduce_cache() taskq isn't keeping up with demand, or memory
 * is short then just return NULL. If we're over ncsize then kick off a
 * thread to free some in use entries down to dnlc_nentries_low_water.
 * Caller must initialise all fields except namlen.
 * Component names are defined to be less than MAXNAMELEN
 * which includes a null.
 */
static ncache_t *
dnlc_get(uchar_t namlen)
{
        ncache_t *ncp;

        if (dnlc_nentries > dnlc_max_nentries) {
                dnlc_max_nentries_cnt++; /* keep a statistic */
                return (NULL);
        }
        ncp = kmem_alloc(sizeof (ncache_t) + namlen, KM_NOSLEEP);
        if (ncp == NULL) {
                return (NULL);
        }
        ncp->namlen = namlen;
        atomic_inc_32(&dnlc_nentries);
        dnlc_reduce_cache(NULL);
        return (ncp);
}

/*
 * Taskq routine to free up name cache entries to reduce the
 * cache size to the low water mark if "reduce_percent" is not provided.
 * If "reduce_percent" is provided, reduce cache size by
 * (ncsize_onepercent * reduce_percent).
 */
/*ARGSUSED*/
static void
do_dnlc_reduce_cache(void *reduce_percent)
{
        nc_hash_t *hp = dnlc_free_rotor, *start_hp = hp;
        vnode_t *vp;
        ncache_t *ncp;
        int cnt;
        uint_t low_water = dnlc_nentries_low_water;

        if (reduce_percent) {
                uint_t reduce_cnt;

                /*
                 * Never try to reduce the current number
                 * of cache entries below 3% of ncsize.
                 */
                if (dnlc_nentries <= ncsize_min_percent) {
                        dnlc_reduce_idle = 1;
                        return;
                }
                reduce_cnt = ncsize_onepercent *
                    (uint_t)(uintptr_t)reduce_percent;

                if (reduce_cnt > dnlc_nentries ||
                    dnlc_nentries - reduce_cnt < ncsize_min_percent)
                        low_water = ncsize_min_percent;
                else
                        low_water = dnlc_nentries - reduce_cnt;
        }

        do {
                /*
                 * Find the first non empty hash queue without locking.
                 * Only look at each hash queue once to avoid an infinite loop.
                 */
                do {
                        if (++hp == &nc_hash[nc_hashsz])
                                hp = nc_hash;
                } while (hp->hash_next == (ncache_t *)hp && hp != start_hp);

                /* return if all hash queues are empty. */
                if (hp->hash_next == (ncache_t *)hp) {
                        dnlc_reduce_idle = 1;
                        return;
                }

                mutex_enter(&hp->hash_lock);
                for (cnt = 0, ncp = hp->hash_prev; ncp != (ncache_t *)hp;
                    ncp = ncp->hash_prev, cnt++) {
                        vp = ncp->vp;
                        /*
                         * A name cache entry with a reference count
                         * of one is only referenced by the dnlc.
                         * Also negative cache entries are purged first.
                         */
                        if (!vn_has_cached_data(vp) &&
                            ((vp->v_count == 1) || (vp == DNLC_NO_VNODE))) {
                                ncs.ncs_pick_heur.value.ui64++;
                                goto found;
                        }
                        /*
                         * Remove from the end of the chain if the
                         * chain is too long
                         */
                        if (cnt > dnlc_long_chain) {
                                ncp = hp->hash_prev;
                                ncs.ncs_pick_last.value.ui64++;
                                vp = ncp->vp;
                                goto found;
                        }
                }
                /* check for race and continue */
                if (hp->hash_next == (ncache_t *)hp) {
                        mutex_exit(&hp->hash_lock);
                        continue;
                }

                ncp = hp->hash_prev; /* pick the last one in the hash queue */
                ncs.ncs_pick_last.value.ui64++;
                vp = ncp->vp;
found:
                /*
                 * Remove from hash chain.
                 */
                nc_rmhash(ncp);
                mutex_exit(&hp->hash_lock);
                VN_RELE_DNLC(vp);
                VN_RELE_DNLC(ncp->dp);
                dnlc_free(ncp);
        } while (dnlc_nentries > low_water);

        dnlc_free_rotor = hp;
        dnlc_reduce_idle = 1;
}

/*
 * Directory caching routines
 * ==========================
 *
 * See dnlc.h for details of the interfaces below.
 */

/*
 * Lookup up an entry in a complete or partial directory cache.
 */
dcret_t
dnlc_dir_lookup(dcanchor_t *dcap, const char *name, uint64_t *handle)
{
        dircache_t *dcp;
        dcentry_t *dep;
        int hash;
        int ret;
        uchar_t namlen;

        /*
         * can test without lock as we are only a cache
         */
        if (!VALID_DIR_CACHE(dcap->dca_dircache)) {
                ncs.ncs_dir_misses.value.ui64++;
                return (DNOCACHE);
        }

        if (!dnlc_dir_enable) {
                return (DNOCACHE);
        }

        mutex_enter(&dcap->dca_lock);
        dcp = (dircache_t *)dcap->dca_dircache;
        if (VALID_DIR_CACHE(dcp)) {
                dcp->dc_actime = ddi_get_lbolt64();
                DNLC_DIR_HASH(name, hash, namlen);
                dep = dcp->dc_namehash[hash & dcp->dc_nhash_mask];
                while (dep != NULL) {
                        if ((dep->de_hash == hash) &&
                            (namlen == dep->de_namelen) &&
                            bcmp(dep->de_name, name, namlen) == 0) {
                                *handle = dep->de_handle;
                                mutex_exit(&dcap->dca_lock);
                                ncs.ncs_dir_hits.value.ui64++;
                                return (DFOUND);
                        }
                        dep = dep->de_next;
                }
                if (dcp->dc_complete) {
                        ret = DNOENT;
                } else {
                        ret = DNOCACHE;
                }
                mutex_exit(&dcap->dca_lock);
                return (ret);
        } else {
                mutex_exit(&dcap->dca_lock);
                ncs.ncs_dir_misses.value.ui64++;
                return (DNOCACHE);
        }
}

/*
 * Start a new directory cache. An estimate of the number of
 * entries is provided to as a quick check to ensure the directory
 * is cacheable.
 */
dcret_t
dnlc_dir_start(dcanchor_t *dcap, uint_t num_entries)
{
        dircache_t *dcp;

        if (!dnlc_dir_enable ||
            (num_entries < dnlc_dir_min_size)) {
                return (DNOCACHE);
        }

        if (num_entries > dnlc_dir_max_size) {
                return (DTOOBIG);
        }

        mutex_enter(&dc_head.dch_lock);
        mutex_enter(&dcap->dca_lock);

        if (dcap->dca_dircache == DC_RET_LOW_MEM) {
                dcap->dca_dircache = NULL;
                mutex_exit(&dcap->dca_lock);
                mutex_exit(&dc_head.dch_lock);
                return (DNOMEM);
        }

        /*
         * Check if there's currently a cache.
         * This probably only occurs on a race.
         */
        if (dcap->dca_dircache != NULL) {
                mutex_exit(&dcap->dca_lock);
                mutex_exit(&dc_head.dch_lock);
                return (DNOCACHE);
        }

        /*
         * Allocate the dircache struct, entry and free space hash tables.
         * These tables are initially just one entry but dynamically resize
         * when entries and free space are added or removed.
         */
        if ((dcp = kmem_zalloc(sizeof (dircache_t), KM_NOSLEEP)) == NULL) {
                goto error;
        }
        if ((dcp->dc_namehash = kmem_zalloc(sizeof (dcentry_t *),
            KM_NOSLEEP)) == NULL) {
                goto error;
        }
        if ((dcp->dc_freehash = kmem_zalloc(sizeof (dcfree_t *),
            KM_NOSLEEP)) == NULL) {
                goto error;
        }

        dcp->dc_anchor = dcap; /* set back pointer to anchor */
        dcap->dca_dircache = dcp;

        /* add into head of global chain */
        dcp->dc_next = dc_head.dch_next;
        dcp->dc_prev = (dircache_t *)&dc_head;
        dcp->dc_next->dc_prev = dcp;
        dc_head.dch_next = dcp;

        mutex_exit(&dcap->dca_lock);
        mutex_exit(&dc_head.dch_lock);
        ncs.ncs_cur_dirs.value.ui64++;
        ncs.ncs_dirs_cached.value.ui64++;
        return (DOK);
error:
        if (dcp != NULL) {
                if (dcp->dc_namehash) {
                        kmem_free(dcp->dc_namehash, sizeof (dcentry_t *));
                }
                kmem_free(dcp, sizeof (dircache_t));
        }
        /*
         * Must also kmem_free dcp->dc_freehash if more error cases are added
         */
        mutex_exit(&dcap->dca_lock);
        mutex_exit(&dc_head.dch_lock);
        ncs.ncs_dir_start_nm.value.ui64++;
        return (DNOCACHE);
}

/*
 * Add a directopry entry to a partial or complete directory cache.
 */
dcret_t
dnlc_dir_add_entry(dcanchor_t *dcap, const char *name, uint64_t handle)
{
        dircache_t *dcp;
        dcentry_t **hp, *dep;
        int hash;
        uint_t capacity;
        uchar_t namlen;

        /*
         * Allocate the dcentry struct, including the variable
         * size name. Note, the null terminator is not copied.
         *
         * We do this outside the lock to avoid possible deadlock if
         * dnlc_dir_reclaim() is called as a result of memory shortage.
         */
        DNLC_DIR_HASH(name, hash, namlen);
        dep = kmem_alloc(sizeof (dcentry_t) - 1 + namlen, KM_NOSLEEP);
        if (dep == NULL) {
#ifdef DEBUG
                /*
                 * The kmem allocator generates random failures for
                 * KM_NOSLEEP calls (see KMEM_RANDOM_ALLOCATION_FAILURE)
                 * So try again before we blow away a perfectly good cache.
                 * This is done not to cover an error but purely for
                 * performance running a debug kernel.
                 * This random error only occurs in debug mode.
                 */
                dep = kmem_alloc(sizeof (dcentry_t) - 1 + namlen, KM_NOSLEEP);
                if (dep != NULL)
                        goto ok;
#endif
                ncs.ncs_dir_add_nm.value.ui64++;
                /*
                 * Free a directory cache. This may be the one we are
                 * called with.
                 */
                dnlc_dir_reclaim(NULL);
                dep = kmem_alloc(sizeof (dcentry_t) - 1 + namlen, KM_NOSLEEP);
                if (dep == NULL) {
                        /*
                         * still no memory, better delete this cache
                         */
                        mutex_enter(&dcap->dca_lock);
                        dcp = (dircache_t *)dcap->dca_dircache;
                        if (VALID_DIR_CACHE(dcp)) {
                                dnlc_dir_abort(dcp);
                                dcap->dca_dircache = DC_RET_LOW_MEM;
                        }
                        mutex_exit(&dcap->dca_lock);
                        ncs.ncs_dir_addabort.value.ui64++;
                        return (DNOCACHE);
                }
                /*
                 * fall through as if the 1st kmem_alloc had worked
                 */
        }
#ifdef DEBUG
ok:
#endif
        mutex_enter(&dcap->dca_lock);
        dcp = (dircache_t *)dcap->dca_dircache;
        if (VALID_DIR_CACHE(dcp)) {
                /*
                 * If the total number of entries goes above the max
                 * then free this cache
                 */
                if ((dcp->dc_num_entries + dcp->dc_num_free) >
                    dnlc_dir_max_size) {
                        mutex_exit(&dcap->dca_lock);
                        dnlc_dir_purge(dcap);
                        kmem_free(dep, sizeof (dcentry_t) - 1 + namlen);
                        ncs.ncs_dir_add_max.value.ui64++;
                        return (DTOOBIG);
                }
                dcp->dc_num_entries++;
                capacity = (dcp->dc_nhash_mask + 1) << dnlc_dir_hash_size_shift;
                if (dcp->dc_num_entries >=
                    (capacity << dnlc_dir_hash_resize_shift)) {
                        dnlc_dir_adjust_nhash(dcp);
                }
                hp = &dcp->dc_namehash[hash & dcp->dc_nhash_mask];

                /*
                 * Initialise and chain in new entry
                 */
                dep->de_handle = handle;
                dep->de_hash = hash;
                /*
                 * Note de_namelen is a uchar_t to conserve space
                 * and alignment padding. The max length of any
                 * pathname component is defined as MAXNAMELEN
                 * which is 256 (including the terminating null).
                 * So provided this doesn't change, we don't include the null,
                 * we always use bcmp to compare strings, and we don't
                 * start storing full names, then we are ok.
                 * The space savings is worth it.
                 */
                dep->de_namelen = namlen;
                bcopy(name, dep->de_name, namlen);
                dep->de_next = *hp;
                *hp = dep;
                dcp->dc_actime = ddi_get_lbolt64();
                mutex_exit(&dcap->dca_lock);
                ncs.ncs_dir_num_ents.value.ui64++;
                return (DOK);
        } else {
                mutex_exit(&dcap->dca_lock);
                kmem_free(dep, sizeof (dcentry_t) - 1 + namlen);
                return (DNOCACHE);
        }
}

/*
 * Add free space to a partial or complete directory cache.
 */
dcret_t
dnlc_dir_add_space(dcanchor_t *dcap, uint_t len, uint64_t handle)
{
        dircache_t *dcp;
        dcfree_t *dfp, **hp;
        uint_t capacity;

        /*
         * We kmem_alloc outside the lock to avoid possible deadlock if
         * dnlc_dir_reclaim() is called as a result of memory shortage.
         */
        dfp = kmem_cache_alloc(dnlc_dir_space_cache, KM_NOSLEEP);
        if (dfp == NULL) {
#ifdef DEBUG
                /*
                 * The kmem allocator generates random failures for
                 * KM_NOSLEEP calls (see KMEM_RANDOM_ALLOCATION_FAILURE)
                 * So try again before we blow away a perfectly good cache.
                 * This random error only occurs in debug mode
                 */
                dfp = kmem_cache_alloc(dnlc_dir_space_cache, KM_NOSLEEP);
                if (dfp != NULL)
                        goto ok;
#endif
                ncs.ncs_dir_add_nm.value.ui64++;
                /*
                 * Free a directory cache. This may be the one we are
                 * called with.
                 */
                dnlc_dir_reclaim(NULL);
                dfp = kmem_cache_alloc(dnlc_dir_space_cache, KM_NOSLEEP);
                if (dfp == NULL) {
                        /*
                         * still no memory, better delete this cache
                         */
                        mutex_enter(&dcap->dca_lock);
                        dcp = (dircache_t *)dcap->dca_dircache;
                        if (VALID_DIR_CACHE(dcp)) {
                                dnlc_dir_abort(dcp);
                                dcap->dca_dircache = DC_RET_LOW_MEM;
                        }
                        mutex_exit(&dcap->dca_lock);
                        ncs.ncs_dir_addabort.value.ui64++;
                        return (DNOCACHE);
                }
                /*
                 * fall through as if the 1st kmem_alloc had worked
                 */
        }

#ifdef DEBUG
ok:
#endif
        mutex_enter(&dcap->dca_lock);
        dcp = (dircache_t *)dcap->dca_dircache;
        if (VALID_DIR_CACHE(dcp)) {
                if ((dcp->dc_num_entries + dcp->dc_num_free) >
                    dnlc_dir_max_size) {
                        mutex_exit(&dcap->dca_lock);
                        dnlc_dir_purge(dcap);
                        kmem_cache_free(dnlc_dir_space_cache, dfp);
                        ncs.ncs_dir_add_max.value.ui64++;
                        return (DTOOBIG);
                }
                dcp->dc_num_free++;
                capacity = (dcp->dc_fhash_mask + 1) << dnlc_dir_hash_size_shift;
                if (dcp->dc_num_free >=
                    (capacity << dnlc_dir_hash_resize_shift)) {
                        dnlc_dir_adjust_fhash(dcp);
                }
                /*
                 * Initialise and chain a new entry
                 */
                dfp->df_handle = handle;
                dfp->df_len = len;
                dcp->dc_actime = ddi_get_lbolt64();
                hp = &(dcp->dc_freehash[DDFHASH(handle, dcp)]);
                dfp->df_next = *hp;
                *hp = dfp;
                mutex_exit(&dcap->dca_lock);
                ncs.ncs_dir_num_ents.value.ui64++;
                return (DOK);
        } else {
                mutex_exit(&dcap->dca_lock);
                kmem_cache_free(dnlc_dir_space_cache, dfp);
                return (DNOCACHE);
        }
}

/*
 * Mark a directory cache as complete.
 */
void
dnlc_dir_complete(dcanchor_t *dcap)
{
        dircache_t *dcp;

        mutex_enter(&dcap->dca_lock);
        dcp = (dircache_t *)dcap->dca_dircache;
        if (VALID_DIR_CACHE(dcp)) {
                dcp->dc_complete = B_TRUE;
        }
        mutex_exit(&dcap->dca_lock);
}

/*
 * Internal routine to delete a partial or full directory cache.
 * No additional locking needed.
 */
static void
dnlc_dir_abort(dircache_t *dcp)
{
        dcentry_t *dep, *nhp;
        dcfree_t *fep, *fhp;
        uint_t nhtsize = dcp->dc_nhash_mask + 1; /* name hash table size */
        uint_t fhtsize = dcp->dc_fhash_mask + 1; /* free hash table size */
        uint_t i;

        /*
         * Free up the cached name entries and hash table
         */
        for (i = 0; i < nhtsize; i++) { /* for each hash bucket */
                nhp = dcp->dc_namehash[i];
                while (nhp != NULL) { /* for each chained entry */
                        dep = nhp->de_next;
                        kmem_free(nhp, sizeof (dcentry_t) - 1 +
                            nhp->de_namelen);
                        nhp = dep;
                }
        }
        kmem_free(dcp->dc_namehash, sizeof (dcentry_t *) * nhtsize);

        /*
         * Free up the free space entries and hash table
         */
        for (i = 0; i < fhtsize; i++) { /* for each hash bucket */
                fhp = dcp->dc_freehash[i];
                while (fhp != NULL) { /* for each chained entry */
                        fep = fhp->df_next;
                        kmem_cache_free(dnlc_dir_space_cache, fhp);
                        fhp = fep;
                }
        }
        kmem_free(dcp->dc_freehash, sizeof (dcfree_t *) * fhtsize);

        /*
         * Finally free the directory cache structure itself
         */
        ncs.ncs_dir_num_ents.value.ui64 -= (dcp->dc_num_entries +
            dcp->dc_num_free);
        kmem_free(dcp, sizeof (dircache_t));
        ncs.ncs_cur_dirs.value.ui64--;
}

/*
 * Remove a partial or complete directory cache
 */
void
dnlc_dir_purge(dcanchor_t *dcap)
{
        dircache_t *dcp;

        mutex_enter(&dc_head.dch_lock);
        mutex_enter(&dcap->dca_lock);
        dcp = (dircache_t *)dcap->dca_dircache;
        if (!VALID_DIR_CACHE(dcp)) {
                mutex_exit(&dcap->dca_lock);
                mutex_exit(&dc_head.dch_lock);
                return;
        }
        dcap->dca_dircache = NULL;
        /*
         * Unchain from global list
         */
        dcp->dc_prev->dc_next = dcp->dc_next;
        dcp->dc_next->dc_prev = dcp->dc_prev;
        mutex_exit(&dcap->dca_lock);
        mutex_exit(&dc_head.dch_lock);
        dnlc_dir_abort(dcp);
}

/*
 * Remove an entry from a complete or partial directory cache.
 * Return the handle if it's non null.
 */
dcret_t
dnlc_dir_rem_entry(dcanchor_t *dcap, const char *name, uint64_t *handlep)
{
        dircache_t *dcp;
        dcentry_t **prevpp, *te;
        uint_t capacity;
        int hash;
        int ret;
        uchar_t namlen;

        if (!dnlc_dir_enable) {
                return (DNOCACHE);
        }

        mutex_enter(&dcap->dca_lock);
        dcp = (dircache_t *)dcap->dca_dircache;
        if (VALID_DIR_CACHE(dcp)) {
                dcp->dc_actime = ddi_get_lbolt64();
                if (dcp->dc_nhash_mask > 0) { /* ie not minimum */
                        capacity = (dcp->dc_nhash_mask + 1) <<
                            dnlc_dir_hash_size_shift;
                        if (dcp->dc_num_entries <=
                            (capacity >> dnlc_dir_hash_resize_shift)) {
                                dnlc_dir_adjust_nhash(dcp);
                        }
                }
                DNLC_DIR_HASH(name, hash, namlen);
                prevpp = &dcp->dc_namehash[hash & dcp->dc_nhash_mask];
                while (*prevpp != NULL) {
                        if (((*prevpp)->de_hash == hash) &&
                            (namlen == (*prevpp)->de_namelen) &&
                            bcmp((*prevpp)->de_name, name, namlen) == 0) {
                                if (handlep != NULL) {
                                        *handlep = (*prevpp)->de_handle;
                                }
                                te = *prevpp;
                                *prevpp = (*prevpp)->de_next;
                                kmem_free(te, sizeof (dcentry_t) - 1 +
                                    te->de_namelen);

                                /*
                                 * If the total number of entries
                                 * falls below half the minimum number
                                 * of entries then free this cache.
                                 */
                                if (--dcp->dc_num_entries <
                                    (dnlc_dir_min_size >> 1)) {
                                        mutex_exit(&dcap->dca_lock);
                                        dnlc_dir_purge(dcap);
                                } else {
                                        mutex_exit(&dcap->dca_lock);
                                }
                                ncs.ncs_dir_num_ents.value.ui64--;
                                return (DFOUND);
                        }
                        prevpp = &((*prevpp)->de_next);
                }
                if (dcp->dc_complete) {
                        ncs.ncs_dir_reme_fai.value.ui64++;
                        ret = DNOENT;
                } else {
                        ret = DNOCACHE;
                }
                mutex_exit(&dcap->dca_lock);
                return (ret);
        } else {
                mutex_exit(&dcap->dca_lock);
                return (DNOCACHE);
        }
}


/*
 * Remove free space of at least the given length from a complete
 * or partial directory cache.
 */
dcret_t
dnlc_dir_rem_space_by_len(dcanchor_t *dcap, uint_t len, uint64_t *handlep)
{
        dircache_t *dcp;
        dcfree_t **prevpp, *tfp;
        uint_t fhtsize; /* free hash table size */
        uint_t i;
        uint_t capacity;
        int ret;

        if (!dnlc_dir_enable) {
                return (DNOCACHE);
        }

        mutex_enter(&dcap->dca_lock);
        dcp = (dircache_t *)dcap->dca_dircache;
        if (VALID_DIR_CACHE(dcp)) {
                dcp->dc_actime = ddi_get_lbolt64();
                if (dcp->dc_fhash_mask > 0) { /* ie not minimum */
                        capacity = (dcp->dc_fhash_mask + 1) <<
                            dnlc_dir_hash_size_shift;
                        if (dcp->dc_num_free <=
                            (capacity >> dnlc_dir_hash_resize_shift)) {
                                dnlc_dir_adjust_fhash(dcp);
                        }
                }
                /*
                 * Search for an entry of the appropriate size
                 * on a first fit basis.
                 */
                fhtsize = dcp->dc_fhash_mask + 1;
                for (i = 0; i < fhtsize; i++) { /* for each hash bucket */
                        prevpp = &(dcp->dc_freehash[i]);
                        while (*prevpp != NULL) {
                                if ((*prevpp)->df_len >= len) {
                                        *handlep = (*prevpp)->df_handle;
                                        tfp = *prevpp;
                                        *prevpp = (*prevpp)->df_next;
                                        dcp->dc_num_free--;
                                        mutex_exit(&dcap->dca_lock);
                                        kmem_cache_free(dnlc_dir_space_cache,
                                            tfp);
                                        ncs.ncs_dir_num_ents.value.ui64--;
                                        return (DFOUND);
                                }
                                prevpp = &((*prevpp)->df_next);
                        }
                }
                if (dcp->dc_complete) {
                        ret = DNOENT;
                } else {
                        ret = DNOCACHE;
                }
                mutex_exit(&dcap->dca_lock);
                return (ret);
        } else {
                mutex_exit(&dcap->dca_lock);
                return (DNOCACHE);
        }
}

/*
 * Remove free space with the given handle from a complete or partial
 * directory cache.
 */
dcret_t
dnlc_dir_rem_space_by_handle(dcanchor_t *dcap, uint64_t handle)
{
        dircache_t *dcp;
        dcfree_t **prevpp, *tfp;
        uint_t capacity;
        int ret;

        if (!dnlc_dir_enable) {
                return (DNOCACHE);
        }

        mutex_enter(&dcap->dca_lock);
        dcp = (dircache_t *)dcap->dca_dircache;
        if (VALID_DIR_CACHE(dcp)) {
                dcp->dc_actime = ddi_get_lbolt64();
                if (dcp->dc_fhash_mask > 0) { /* ie not minimum */
                        capacity = (dcp->dc_fhash_mask + 1) <<
                            dnlc_dir_hash_size_shift;
                        if (dcp->dc_num_free <=
                            (capacity >> dnlc_dir_hash_resize_shift)) {
                                dnlc_dir_adjust_fhash(dcp);
                        }
                }

                /*
                 * search for the exact entry
                 */
                prevpp = &(dcp->dc_freehash[DDFHASH(handle, dcp)]);
                while (*prevpp != NULL) {
                        if ((*prevpp)->df_handle == handle) {
                                tfp = *prevpp;
                                *prevpp = (*prevpp)->df_next;
                                dcp->dc_num_free--;
                                mutex_exit(&dcap->dca_lock);
                                kmem_cache_free(dnlc_dir_space_cache, tfp);
                                ncs.ncs_dir_num_ents.value.ui64--;
                                return (DFOUND);
                        }
                        prevpp = &((*prevpp)->df_next);
                }
                if (dcp->dc_complete) {
                        ncs.ncs_dir_rems_fai.value.ui64++;
                        ret = DNOENT;
                } else {
                        ret = DNOCACHE;
                }
                mutex_exit(&dcap->dca_lock);
                return (ret);
        } else {
                mutex_exit(&dcap->dca_lock);
                return (DNOCACHE);
        }
}

/*
 * Update the handle of an directory cache entry.
 */
dcret_t
dnlc_dir_update(dcanchor_t *dcap, const char *name, uint64_t handle)
{
        dircache_t *dcp;
        dcentry_t *dep;
        int hash;
        int ret;
        uchar_t namlen;

        if (!dnlc_dir_enable) {
                return (DNOCACHE);
        }

        mutex_enter(&dcap->dca_lock);
        dcp = (dircache_t *)dcap->dca_dircache;
        if (VALID_DIR_CACHE(dcp)) {
                dcp->dc_actime = ddi_get_lbolt64();
                DNLC_DIR_HASH(name, hash, namlen);
                dep = dcp->dc_namehash[hash & dcp->dc_nhash_mask];
                while (dep != NULL) {
                        if ((dep->de_hash == hash) &&
                            (namlen == dep->de_namelen) &&
                            bcmp(dep->de_name, name, namlen) == 0) {
                                dep->de_handle = handle;
                                mutex_exit(&dcap->dca_lock);
                                return (DFOUND);
                        }
                        dep = dep->de_next;
                }
                if (dcp->dc_complete) {
                        ncs.ncs_dir_upd_fail.value.ui64++;
                        ret = DNOENT;
                } else {
                        ret = DNOCACHE;
                }
                mutex_exit(&dcap->dca_lock);
                return (ret);
        } else {
                mutex_exit(&dcap->dca_lock);
                return (DNOCACHE);
        }
}

void
dnlc_dir_fini(dcanchor_t *dcap)
{
        dircache_t *dcp;

        mutex_enter(&dc_head.dch_lock);
        mutex_enter(&dcap->dca_lock);
        dcp = (dircache_t *)dcap->dca_dircache;
        if (VALID_DIR_CACHE(dcp)) {
                /*
                 * Unchain from global list
                 */
                ncs.ncs_dir_finipurg.value.ui64++;
                dcp->dc_prev->dc_next = dcp->dc_next;
                dcp->dc_next->dc_prev = dcp->dc_prev;
        } else {
                dcp = NULL;
        }
        dcap->dca_dircache = NULL;
        mutex_exit(&dcap->dca_lock);
        mutex_exit(&dc_head.dch_lock);
        mutex_destroy(&dcap->dca_lock);
        if (dcp) {
                dnlc_dir_abort(dcp);
        }
}

/*
 * Reclaim callback for dnlc directory caching.
 * Invoked by the kernel memory allocator when memory gets tight.
 * This is a pretty serious condition and can lead easily lead to system
 * hangs if not enough space is returned.
 *
 * Deciding which directory (or directories) to purge is tricky.
 * Purging everything is an overkill, but purging just the oldest used
 * was found to lead to hangs. The largest cached directories use the
 * most memory, but take the most effort to rebuild, whereas the smaller
 * ones have little value and give back little space. So what to do?
 *
 * The current policy is to continue purging the oldest used directories
 * until at least dnlc_dir_min_reclaim directory entries have been purged.
 */
/*ARGSUSED*/
static void
dnlc_dir_reclaim(void *unused)
{
        dircache_t *dcp, *oldest;
        uint_t dirent_cnt = 0;

        mutex_enter(&dc_head.dch_lock);
        while (dirent_cnt < dnlc_dir_min_reclaim) {
                dcp = dc_head.dch_next;
                oldest = NULL;
                while (dcp != (dircache_t *)&dc_head) {
                        if (oldest == NULL) {
                                oldest = dcp;
                        } else {
                                if (dcp->dc_actime < oldest->dc_actime) {
                                        oldest = dcp;
                                }
                        }
                        dcp = dcp->dc_next;
                }
                if (oldest == NULL) {
                        /* nothing to delete */
                        mutex_exit(&dc_head.dch_lock);
                        return;
                }
                /*
                 * remove from directory chain and purge
                 */
                oldest->dc_prev->dc_next = oldest->dc_next;
                oldest->dc_next->dc_prev = oldest->dc_prev;
                mutex_enter(&oldest->dc_anchor->dca_lock);
                /*
                 * If this was the last entry then it must be too large.
                 * Mark it as such by saving a special dircache_t
                 * pointer (DC_RET_LOW_MEM) in the anchor. The error DNOMEM
                 * will be presented to the caller of dnlc_dir_start()
                 */
                if (oldest->dc_next == oldest->dc_prev) {
                        oldest->dc_anchor->dca_dircache = DC_RET_LOW_MEM;
                        ncs.ncs_dir_rec_last.value.ui64++;
                } else {
                        oldest->dc_anchor->dca_dircache = NULL;
                        ncs.ncs_dir_recl_any.value.ui64++;
                }
                mutex_exit(&oldest->dc_anchor->dca_lock);
                dirent_cnt += oldest->dc_num_entries;
                dnlc_dir_abort(oldest);
        }
        mutex_exit(&dc_head.dch_lock);
}

/*
 * Dynamically grow or shrink the size of the name hash table
 */
static void
dnlc_dir_adjust_nhash(dircache_t *dcp)
{
        dcentry_t **newhash, *dep, **nhp, *tep;
        uint_t newsize;
        uint_t oldsize;
        uint_t newsizemask;
        int i;

        /*
         * Allocate new hash table
         */
        newsize = dcp->dc_num_entries >> dnlc_dir_hash_size_shift;
        newhash = kmem_zalloc(sizeof (dcentry_t *) * newsize, KM_NOSLEEP);
        if (newhash == NULL) {
                /*
                 * System is short on memory just return
                 * Note, the old hash table is still usable.
                 * This return is unlikely to repeatedy occur, because
                 * either some other directory caches will be reclaimed
                 * due to memory shortage, thus freeing memory, or this
                 * directory cahe will be reclaimed.
                 */
                return;
        }
        oldsize = dcp->dc_nhash_mask + 1;
        dcp->dc_nhash_mask = newsizemask = newsize - 1;

        /*
         * Move entries from the old table to the new
         */
        for (i = 0; i < oldsize; i++) { /* for each hash bucket */
                dep = dcp->dc_namehash[i];
                while (dep != NULL) { /* for each chained entry */
                        tep = dep;
                        dep = dep->de_next;
                        nhp = &newhash[tep->de_hash & newsizemask];
                        tep->de_next = *nhp;
                        *nhp = tep;
                }
        }

        /*
         * delete old hash table and set new one in place
         */
        kmem_free(dcp->dc_namehash, sizeof (dcentry_t *) * oldsize);
        dcp->dc_namehash = newhash;
}

/*
 * Dynamically grow or shrink the size of the free space hash table
 */
static void
dnlc_dir_adjust_fhash(dircache_t *dcp)
{
        dcfree_t **newhash, *dfp, **nhp, *tfp;
        uint_t newsize;
        uint_t oldsize;
        int i;

        /*
         * Allocate new hash table
         */
        newsize = dcp->dc_num_free >> dnlc_dir_hash_size_shift;
        newhash = kmem_zalloc(sizeof (dcfree_t *) * newsize, KM_NOSLEEP);
        if (newhash == NULL) {
                /*
                 * System is short on memory just return
                 * Note, the old hash table is still usable.
                 * This return is unlikely to repeatedy occur, because
                 * either some other directory caches will be reclaimed
                 * due to memory shortage, thus freeing memory, or this
                 * directory cahe will be reclaimed.
                 */
                return;
        }
        oldsize = dcp->dc_fhash_mask + 1;
        dcp->dc_fhash_mask = newsize - 1;

        /*
         * Move entries from the old table to the new
         */
        for (i = 0; i < oldsize; i++) { /* for each hash bucket */
                dfp = dcp->dc_freehash[i];
                while (dfp != NULL) { /* for each chained entry */
                        tfp = dfp;
                        dfp = dfp->df_next;
                        nhp = &newhash[DDFHASH(tfp->df_handle, dcp)];
                        tfp->df_next = *nhp;
                        *nhp = tfp;
                }
        }

        /*
         * delete old hash table and set new one in place
         */
        kmem_free(dcp->dc_freehash, sizeof (dcfree_t *) * oldsize);
        dcp->dc_freehash = newhash;
}