Add FASTWRITE algorithm for synchronous writes.

[zfs.git] / module / zfs / zil.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) 2011 by Delphix. All rights reserved.
 */

/* Portions Copyright 2010 Robert Milkowski */

#include <sys/zfs_context.h>
#include <sys/spa.h>
#include <sys/dmu.h>
#include <sys/zap.h>
#include <sys/arc.h>
#include <sys/stat.h>
#include <sys/resource.h>
#include <sys/zil.h>
#include <sys/zil_impl.h>
#include <sys/dsl_dataset.h>
#include <sys/vdev_impl.h>
#include <sys/dmu_tx.h>
#include <sys/dsl_pool.h>
#include <sys/metaslab.h>

/*
 * The zfs intent log (ZIL) saves transaction records of system calls
 * that change the file system in memory with enough information
 * to be able to replay them. These are stored in memory until
 * either the DMU transaction group (txg) commits them to the stable pool
 * and they can be discarded, or they are flushed to the stable log
 * (also in the pool) due to a fsync, O_DSYNC or other synchronous
 * requirement. In the event of a panic or power fail then those log
 * records (transactions) are replayed.
 *
 * There is one ZIL per file system. Its on-disk (pool) format consists
 * of 3 parts:
 *
 *      - ZIL header
 *      - ZIL blocks
 *      - ZIL records
 *
 * A log record holds a system call transaction. Log blocks can
 * hold many log records and the blocks are chained together.
 * Each ZIL block contains a block pointer (blkptr_t) to the next
 * ZIL block in the chain. The ZIL header points to the first
 * block in the chain. Note there is not a fixed place in the pool
 * to hold blocks. They are dynamically allocated and freed as
 * needed from the blocks available. Figure X shows the ZIL structure:
 */

/*
 * See zil.h for more information about these fields.
 */
zil_stats_t zil_stats = {
        { "zil_commit_count",              KSTAT_DATA_UINT64 },
        { "zil_commit_writer_count",       KSTAT_DATA_UINT64 },
        { "zil_itx_count",                 KSTAT_DATA_UINT64 },
        { "zil_itx_indirect_count",        KSTAT_DATA_UINT64 },
        { "zil_itx_indirect_bytes",        KSTAT_DATA_UINT64 },
        { "zil_itx_copied_count",          KSTAT_DATA_UINT64 },
        { "zil_itx_copied_bytes",          KSTAT_DATA_UINT64 },
        { "zil_itx_needcopy_count",        KSTAT_DATA_UINT64 },
        { "zil_itx_needcopy_bytes",        KSTAT_DATA_UINT64 },
        { "zil_itx_metaslab_normal_count", KSTAT_DATA_UINT64 },
        { "zil_itx_metaslab_normal_bytes", KSTAT_DATA_UINT64 },
        { "zil_itx_metaslab_slog_count",   KSTAT_DATA_UINT64 },
        { "zil_itx_metaslab_slog_bytes",   KSTAT_DATA_UINT64 },
};

static kstat_t *zil_ksp;

/*
 * This global ZIL switch affects all pools
 */
int zil_replay_disable = 0;    /* disable intent logging replay */

/*
 * Tunable parameter for debugging or performance analysis.  Setting
 * zfs_nocacheflush will cause corruption on power loss if a volatile
 * out-of-order write cache is enabled.
 */
int zfs_nocacheflush = 0;

static kmem_cache_t *zil_lwb_cache;

static void zil_async_to_sync(zilog_t *zilog, uint64_t foid);

#define LWB_EMPTY(lwb) ((BP_GET_LSIZE(&lwb->lwb_blk) - \
    sizeof (zil_chain_t)) == (lwb->lwb_sz - lwb->lwb_nused))


/*
 * ziltest is by and large an ugly hack, but very useful in
 * checking replay without tedious work.
 * When running ziltest we want to keep all itx's and so maintain
 * a single list in the zl_itxg[] that uses a high txg: ZILTEST_TXG
 * We subtract TXG_CONCURRENT_STATES to allow for common code.
 */
#define ZILTEST_TXG (UINT64_MAX - TXG_CONCURRENT_STATES)

static int
zil_bp_compare(const void *x1, const void *x2)
{
        const dva_t *dva1 = &((zil_bp_node_t *)x1)->zn_dva;
        const dva_t *dva2 = &((zil_bp_node_t *)x2)->zn_dva;

        if (DVA_GET_VDEV(dva1) < DVA_GET_VDEV(dva2))
                return (-1);
        if (DVA_GET_VDEV(dva1) > DVA_GET_VDEV(dva2))
                return (1);

        if (DVA_GET_OFFSET(dva1) < DVA_GET_OFFSET(dva2))
                return (-1);
        if (DVA_GET_OFFSET(dva1) > DVA_GET_OFFSET(dva2))
                return (1);

        return (0);
}

static void
zil_bp_tree_init(zilog_t *zilog)
{
        avl_create(&zilog->zl_bp_tree, zil_bp_compare,
            sizeof (zil_bp_node_t), offsetof(zil_bp_node_t, zn_node));
}

static void
zil_bp_tree_fini(zilog_t *zilog)
{
        avl_tree_t *t = &zilog->zl_bp_tree;
        zil_bp_node_t *zn;
        void *cookie = NULL;

        while ((zn = avl_destroy_nodes(t, &cookie)) != NULL)
                kmem_free(zn, sizeof (zil_bp_node_t));

        avl_destroy(t);
}

int
zil_bp_tree_add(zilog_t *zilog, const blkptr_t *bp)
{
        avl_tree_t *t = &zilog->zl_bp_tree;
        const dva_t *dva = BP_IDENTITY(bp);
        zil_bp_node_t *zn;
        avl_index_t where;

        if (avl_find(t, dva, &where) != NULL)
                return (EEXIST);

        zn = kmem_alloc(sizeof (zil_bp_node_t), KM_PUSHPAGE);
        zn->zn_dva = *dva;
        avl_insert(t, zn, where);

        return (0);
}

static zil_header_t *
zil_header_in_syncing_context(zilog_t *zilog)
{
        return ((zil_header_t *)zilog->zl_header);
}

static void
zil_init_log_chain(zilog_t *zilog, blkptr_t *bp)
{
        zio_cksum_t *zc = &bp->blk_cksum;

        zc->zc_word[ZIL_ZC_GUID_0] = spa_get_random(-1ULL);
        zc->zc_word[ZIL_ZC_GUID_1] = spa_get_random(-1ULL);
        zc->zc_word[ZIL_ZC_OBJSET] = dmu_objset_id(zilog->zl_os);
        zc->zc_word[ZIL_ZC_SEQ] = 1ULL;
}

/*
 * Read a log block and make sure it's valid.
 */
static int
zil_read_log_block(zilog_t *zilog, const blkptr_t *bp, blkptr_t *nbp, void *dst,
    char **end)
{
        enum zio_flag zio_flags = ZIO_FLAG_CANFAIL;
        uint32_t aflags = ARC_WAIT;
        arc_buf_t *abuf = NULL;
        zbookmark_t zb;
        int error;

        if (zilog->zl_header->zh_claim_txg == 0)
                zio_flags |= ZIO_FLAG_SPECULATIVE | ZIO_FLAG_SCRUB;

        if (!(zilog->zl_header->zh_flags & ZIL_CLAIM_LR_SEQ_VALID))
                zio_flags |= ZIO_FLAG_SPECULATIVE;

        SET_BOOKMARK(&zb, bp->blk_cksum.zc_word[ZIL_ZC_OBJSET],
            ZB_ZIL_OBJECT, ZB_ZIL_LEVEL, bp->blk_cksum.zc_word[ZIL_ZC_SEQ]);

        error = dsl_read_nolock(NULL, zilog->zl_spa, bp, arc_getbuf_func, &abuf,
            ZIO_PRIORITY_SYNC_READ, zio_flags, &aflags, &zb);

        if (error == 0) {
                zio_cksum_t cksum = bp->blk_cksum;

                /*
                 * Validate the checksummed log block.
                 *
                 * Sequence numbers should be... sequential.  The checksum
                 * verifier for the next block should be bp's checksum plus 1.
                 *
                 * Also check the log chain linkage and size used.
                 */
                cksum.zc_word[ZIL_ZC_SEQ]++;

                if (BP_GET_CHECKSUM(bp) == ZIO_CHECKSUM_ZILOG2) {
                        zil_chain_t *zilc = abuf->b_data;
                        char *lr = (char *)(zilc + 1);
                        uint64_t len = zilc->zc_nused - sizeof (zil_chain_t);

                        if (bcmp(&cksum, &zilc->zc_next_blk.blk_cksum,
                            sizeof (cksum)) || BP_IS_HOLE(&zilc->zc_next_blk)) {
                                error = ECKSUM;
                        } else {
                                bcopy(lr, dst, len);
                                *end = (char *)dst + len;
                                *nbp = zilc->zc_next_blk;
                        }
                } else {
                        char *lr = abuf->b_data;
                        uint64_t size = BP_GET_LSIZE(bp);
                        zil_chain_t *zilc = (zil_chain_t *)(lr + size) - 1;

                        if (bcmp(&cksum, &zilc->zc_next_blk.blk_cksum,
                            sizeof (cksum)) || BP_IS_HOLE(&zilc->zc_next_blk) ||
                            (zilc->zc_nused > (size - sizeof (*zilc)))) {
                                error = ECKSUM;
                        } else {
                                bcopy(lr, dst, zilc->zc_nused);
                                *end = (char *)dst + zilc->zc_nused;
                                *nbp = zilc->zc_next_blk;
                        }
                }

                VERIFY(arc_buf_remove_ref(abuf, &abuf) == 1);
        }

        return (error);
}

/*
 * Read a TX_WRITE log data block.
 */
static int
zil_read_log_data(zilog_t *zilog, const lr_write_t *lr, void *wbuf)
{
        enum zio_flag zio_flags = ZIO_FLAG_CANFAIL;
        const blkptr_t *bp = &lr->lr_blkptr;
        uint32_t aflags = ARC_WAIT;
        arc_buf_t *abuf = NULL;
        zbookmark_t zb;
        int error;

        if (BP_IS_HOLE(bp)) {
                if (wbuf != NULL)
                        bzero(wbuf, MAX(BP_GET_LSIZE(bp), lr->lr_length));
                return (0);
        }

        if (zilog->zl_header->zh_claim_txg == 0)
                zio_flags |= ZIO_FLAG_SPECULATIVE | ZIO_FLAG_SCRUB;

        SET_BOOKMARK(&zb, dmu_objset_id(zilog->zl_os), lr->lr_foid,
            ZB_ZIL_LEVEL, lr->lr_offset / BP_GET_LSIZE(bp));

        error = arc_read_nolock(NULL, zilog->zl_spa, bp, arc_getbuf_func, &abuf,
            ZIO_PRIORITY_SYNC_READ, zio_flags, &aflags, &zb);

        if (error == 0) {
                if (wbuf != NULL)
                        bcopy(abuf->b_data, wbuf, arc_buf_size(abuf));
                (void) arc_buf_remove_ref(abuf, &abuf);
        }

        return (error);
}

/*
 * Parse the intent log, and call parse_func for each valid record within.
 */
int
zil_parse(zilog_t *zilog, zil_parse_blk_func_t *parse_blk_func,
    zil_parse_lr_func_t *parse_lr_func, void *arg, uint64_t txg)
{
        const zil_header_t *zh = zilog->zl_header;
        boolean_t claimed = !!zh->zh_claim_txg;
        uint64_t claim_blk_seq = claimed ? zh->zh_claim_blk_seq : UINT64_MAX;
        uint64_t claim_lr_seq = claimed ? zh->zh_claim_lr_seq : UINT64_MAX;
        uint64_t max_blk_seq = 0;
        uint64_t max_lr_seq = 0;
        uint64_t blk_count = 0;
        uint64_t lr_count = 0;
        blkptr_t blk, next_blk;
        char *lrbuf, *lrp;
        int error = 0;

        bzero(&next_blk, sizeof(blkptr_t));

        /*
         * Old logs didn't record the maximum zh_claim_lr_seq.
         */
        if (!(zh->zh_flags & ZIL_CLAIM_LR_SEQ_VALID))
                claim_lr_seq = UINT64_MAX;

        /*
         * Starting at the block pointed to by zh_log we read the log chain.
         * For each block in the chain we strongly check that block to
         * ensure its validity.  We stop when an invalid block is found.
         * For each block pointer in the chain we call parse_blk_func().
         * For each record in each valid block we call parse_lr_func().
         * If the log has been claimed, stop if we encounter a sequence
         * number greater than the highest claimed sequence number.
         */
        lrbuf = zio_buf_alloc(SPA_MAXBLOCKSIZE);
        zil_bp_tree_init(zilog);

        for (blk = zh->zh_log; !BP_IS_HOLE(&blk); blk = next_blk) {
                uint64_t blk_seq = blk.blk_cksum.zc_word[ZIL_ZC_SEQ];
                int reclen;
                char *end = NULL;

                if (blk_seq > claim_blk_seq)
                        break;
                if ((error = parse_blk_func(zilog, &blk, arg, txg)) != 0)
                        break;
                ASSERT3U(max_blk_seq, <, blk_seq);
                max_blk_seq = blk_seq;
                blk_count++;

                if (max_lr_seq == claim_lr_seq && max_blk_seq == claim_blk_seq)
                        break;

                error = zil_read_log_block(zilog, &blk, &next_blk, lrbuf, &end);
                if (error)
                        break;

                for (lrp = lrbuf; lrp < end; lrp += reclen) {
                        lr_t *lr = (lr_t *)lrp;
                        reclen = lr->lrc_reclen;
                        ASSERT3U(reclen, >=, sizeof (lr_t));
                        if (lr->lrc_seq > claim_lr_seq)
                                goto done;
                        if ((error = parse_lr_func(zilog, lr, arg, txg)) != 0)
                                goto done;
                        ASSERT3U(max_lr_seq, <, lr->lrc_seq);
                        max_lr_seq = lr->lrc_seq;
                        lr_count++;
                }
        }
done:
        zilog->zl_parse_error = error;
        zilog->zl_parse_blk_seq = max_blk_seq;
        zilog->zl_parse_lr_seq = max_lr_seq;
        zilog->zl_parse_blk_count = blk_count;
        zilog->zl_parse_lr_count = lr_count;

        ASSERT(!claimed || !(zh->zh_flags & ZIL_CLAIM_LR_SEQ_VALID) ||
            (max_blk_seq == claim_blk_seq && max_lr_seq == claim_lr_seq));

        zil_bp_tree_fini(zilog);
        zio_buf_free(lrbuf, SPA_MAXBLOCKSIZE);

        return (error);
}

static int
zil_claim_log_block(zilog_t *zilog, blkptr_t *bp, void *tx, uint64_t first_txg)
{
        /*
         * Claim log block if not already committed and not already claimed.
         * If tx == NULL, just verify that the block is claimable.
         */
        if (bp->blk_birth < first_txg || zil_bp_tree_add(zilog, bp) != 0)
                return (0);

        return (zio_wait(zio_claim(NULL, zilog->zl_spa,
            tx == NULL ? 0 : first_txg, bp, spa_claim_notify, NULL,
            ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE | ZIO_FLAG_SCRUB)));
}

static int
zil_claim_log_record(zilog_t *zilog, lr_t *lrc, void *tx, uint64_t first_txg)
{
        lr_write_t *lr = (lr_write_t *)lrc;
        int error;

        if (lrc->lrc_txtype != TX_WRITE)
                return (0);

        /*
         * If the block is not readable, don't claim it.  This can happen
         * in normal operation when a log block is written to disk before
         * some of the dmu_sync() blocks it points to.  In this case, the
         * transaction cannot have been committed to anyone (we would have
         * waited for all writes to be stable first), so it is semantically
         * correct to declare this the end of the log.
         */
        if (lr->lr_blkptr.blk_birth >= first_txg &&
            (error = zil_read_log_data(zilog, lr, NULL)) != 0)
                return (error);
        return (zil_claim_log_block(zilog, &lr->lr_blkptr, tx, first_txg));
}

/* ARGSUSED */
static int
zil_free_log_block(zilog_t *zilog, blkptr_t *bp, void *tx, uint64_t claim_txg)
{
        zio_free_zil(zilog->zl_spa, dmu_tx_get_txg(tx), bp);

        return (0);
}

static int
zil_free_log_record(zilog_t *zilog, lr_t *lrc, void *tx, uint64_t claim_txg)
{
        lr_write_t *lr = (lr_write_t *)lrc;
        blkptr_t *bp = &lr->lr_blkptr;

        /*
         * If we previously claimed it, we need to free it.
         */
        if (claim_txg != 0 && lrc->lrc_txtype == TX_WRITE &&
            bp->blk_birth >= claim_txg && zil_bp_tree_add(zilog, bp) == 0)
                zio_free(zilog->zl_spa, dmu_tx_get_txg(tx), bp);

        return (0);
}

static lwb_t *
zil_alloc_lwb(zilog_t *zilog, blkptr_t *bp, uint64_t txg, boolean_t fastwrite)
{
        lwb_t *lwb;

        lwb = kmem_cache_alloc(zil_lwb_cache, KM_PUSHPAGE);
        lwb->lwb_zilog = zilog;
        lwb->lwb_blk = *bp;
        lwb->lwb_fastwrite = fastwrite;
        lwb->lwb_buf = zio_buf_alloc(BP_GET_LSIZE(bp));
        lwb->lwb_max_txg = txg;
        lwb->lwb_zio = NULL;
        lwb->lwb_tx = NULL;
        if (BP_GET_CHECKSUM(bp) == ZIO_CHECKSUM_ZILOG2) {
                lwb->lwb_nused = sizeof (zil_chain_t);
                lwb->lwb_sz = BP_GET_LSIZE(bp);
        } else {
                lwb->lwb_nused = 0;
                lwb->lwb_sz = BP_GET_LSIZE(bp) - sizeof (zil_chain_t);
        }

        mutex_enter(&zilog->zl_lock);
        list_insert_tail(&zilog->zl_lwb_list, lwb);
        mutex_exit(&zilog->zl_lock);

        return (lwb);
}

/*
 * Create an on-disk intent log.
 */
static lwb_t *
zil_create(zilog_t *zilog)
{
        const zil_header_t *zh = zilog->zl_header;
        lwb_t *lwb = NULL;
        uint64_t txg = 0;
        dmu_tx_t *tx = NULL;
        blkptr_t blk;
        int error = 0;
        boolean_t fastwrite = FALSE;

        /*
         * Wait for any previous destroy to complete.
         */
        txg_wait_synced(zilog->zl_dmu_pool, zilog->zl_destroy_txg);

        ASSERT(zh->zh_claim_txg == 0);
        ASSERT(zh->zh_replay_seq == 0);

        blk = zh->zh_log;

        /*
         * Allocate an initial log block if:
         *    - there isn't one already
         *    - the existing block is the wrong endianess
         */
        if (BP_IS_HOLE(&blk) || BP_SHOULD_BYTESWAP(&blk)) {
                tx = dmu_tx_create(zilog->zl_os);
                VERIFY(dmu_tx_assign(tx, TXG_WAIT) == 0);
                dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
                txg = dmu_tx_get_txg(tx);

                if (!BP_IS_HOLE(&blk)) {
                        zio_free_zil(zilog->zl_spa, txg, &blk);
                        BP_ZERO(&blk);
                }

                error = zio_alloc_zil(zilog->zl_spa, txg, &blk,
                    ZIL_MIN_BLKSZ, zilog->zl_logbias == ZFS_LOGBIAS_LATENCY);
                fastwrite = TRUE;

                if (error == 0)
                        zil_init_log_chain(zilog, &blk);
        }

        /*
         * Allocate a log write buffer (lwb) for the first log block.
         */
        if (error == 0)
                lwb = zil_alloc_lwb(zilog, &blk, txg, fastwrite);

        /*
         * If we just allocated the first log block, commit our transaction
         * and wait for zil_sync() to stuff the block poiner into zh_log.
         * (zh is part of the MOS, so we cannot modify it in open context.)
         */
        if (tx != NULL) {
                dmu_tx_commit(tx);
                txg_wait_synced(zilog->zl_dmu_pool, txg);
        }

        ASSERT(bcmp(&blk, &zh->zh_log, sizeof (blk)) == 0);

        return (lwb);
}

/*
 * In one tx, free all log blocks and clear the log header.
 * If keep_first is set, then we're replaying a log with no content.
 * We want to keep the first block, however, so that the first
 * synchronous transaction doesn't require a txg_wait_synced()
 * in zil_create().  We don't need to txg_wait_synced() here either
 * when keep_first is set, because both zil_create() and zil_destroy()
 * will wait for any in-progress destroys to complete.
 */
void
zil_destroy(zilog_t *zilog, boolean_t keep_first)
{
        const zil_header_t *zh = zilog->zl_header;
        lwb_t *lwb;
        dmu_tx_t *tx;
        uint64_t txg;

        /*
         * Wait for any previous destroy to complete.
         */
        txg_wait_synced(zilog->zl_dmu_pool, zilog->zl_destroy_txg);

        zilog->zl_old_header = *zh;             /* debugging aid */

        if (BP_IS_HOLE(&zh->zh_log))
                return;

        tx = dmu_tx_create(zilog->zl_os);
        VERIFY(dmu_tx_assign(tx, TXG_WAIT) == 0);
        dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
        txg = dmu_tx_get_txg(tx);

        mutex_enter(&zilog->zl_lock);

        ASSERT3U(zilog->zl_destroy_txg, <, txg);
        zilog->zl_destroy_txg = txg;
        zilog->zl_keep_first = keep_first;

        if (!list_is_empty(&zilog->zl_lwb_list)) {
                ASSERT(zh->zh_claim_txg == 0);
                VERIFY(!keep_first);
                while ((lwb = list_head(&zilog->zl_lwb_list)) != NULL) {
                        ASSERT(lwb->lwb_zio == NULL);
                        if (lwb->lwb_fastwrite)
                                metaslab_fastwrite_unmark(zilog->zl_spa,
                                    &lwb->lwb_blk);
                        list_remove(&zilog->zl_lwb_list, lwb);
                        if (lwb->lwb_buf != NULL)
                                zio_buf_free(lwb->lwb_buf, lwb->lwb_sz);
                        zio_free_zil(zilog->zl_spa, txg, &lwb->lwb_blk);
                        kmem_cache_free(zil_lwb_cache, lwb);
                }
        } else if (!keep_first) {
                (void) zil_parse(zilog, zil_free_log_block,
                    zil_free_log_record, tx, zh->zh_claim_txg);
        }
        mutex_exit(&zilog->zl_lock);

        dmu_tx_commit(tx);
}

int
zil_claim(const char *osname, void *txarg)
{
        dmu_tx_t *tx = txarg;
        uint64_t first_txg = dmu_tx_get_txg(tx);
        zilog_t *zilog;
        zil_header_t *zh;
        objset_t *os;
        int error;

        error = dmu_objset_hold(osname, FTAG, &os);
        if (error) {
                cmn_err(CE_WARN, "can't open objset for %s", osname);
                return (0);
        }

        zilog = dmu_objset_zil(os);
        zh = zil_header_in_syncing_context(zilog);

        if (spa_get_log_state(zilog->zl_spa) == SPA_LOG_CLEAR) {
                if (!BP_IS_HOLE(&zh->zh_log))
                        zio_free_zil(zilog->zl_spa, first_txg, &zh->zh_log);
                BP_ZERO(&zh->zh_log);
                dsl_dataset_dirty(dmu_objset_ds(os), tx);
                dmu_objset_rele(os, FTAG);
                return (0);
        }

        /*
         * Claim all log blocks if we haven't already done so, and remember
         * the highest claimed sequence number.  This ensures that if we can
         * read only part of the log now (e.g. due to a missing device),
         * but we can read the entire log later, we will not try to replay
         * or destroy beyond the last block we successfully claimed.
         */
        ASSERT3U(zh->zh_claim_txg, <=, first_txg);
        if (zh->zh_claim_txg == 0 && !BP_IS_HOLE(&zh->zh_log)) {
                (void) zil_parse(zilog, zil_claim_log_block,
                    zil_claim_log_record, tx, first_txg);
                zh->zh_claim_txg = first_txg;
                zh->zh_claim_blk_seq = zilog->zl_parse_blk_seq;
                zh->zh_claim_lr_seq = zilog->zl_parse_lr_seq;
                if (zilog->zl_parse_lr_count || zilog->zl_parse_blk_count > 1)
                        zh->zh_flags |= ZIL_REPLAY_NEEDED;
                zh->zh_flags |= ZIL_CLAIM_LR_SEQ_VALID;
                dsl_dataset_dirty(dmu_objset_ds(os), tx);
        }

        ASSERT3U(first_txg, ==, (spa_last_synced_txg(zilog->zl_spa) + 1));
        dmu_objset_rele(os, FTAG);
        return (0);
}

/*
 * Check the log by walking the log chain.
 * Checksum errors are ok as they indicate the end of the chain.
 * Any other error (no device or read failure) returns an error.
 */
int
zil_check_log_chain(const char *osname, void *tx)
{
        zilog_t *zilog;
        objset_t *os;
        blkptr_t *bp;
        int error;

        ASSERT(tx == NULL);

        error = dmu_objset_hold(osname, FTAG, &os);
        if (error) {
                cmn_err(CE_WARN, "can't open objset for %s", osname);
                return (0);
        }

        zilog = dmu_objset_zil(os);
        bp = (blkptr_t *)&zilog->zl_header->zh_log;

        /*
         * Check the first block and determine if it's on a log device
         * which may have been removed or faulted prior to loading this
         * pool.  If so, there's no point in checking the rest of the log
         * as its content should have already been synced to the pool.
         */
        if (!BP_IS_HOLE(bp)) {
                vdev_t *vd;
                boolean_t valid = B_TRUE;

                spa_config_enter(os->os_spa, SCL_STATE, FTAG, RW_READER);
                vd = vdev_lookup_top(os->os_spa, DVA_GET_VDEV(&bp->blk_dva[0]));
                if (vd->vdev_islog && vdev_is_dead(vd))
                        valid = vdev_log_state_valid(vd);
                spa_config_exit(os->os_spa, SCL_STATE, FTAG);

                if (!valid) {
                        dmu_objset_rele(os, FTAG);
                        return (0);
                }
        }

        /*
         * Because tx == NULL, zil_claim_log_block() will not actually claim
         * any blocks, but just determine whether it is possible to do so.
         * In addition to checking the log chain, zil_claim_log_block()
         * will invoke zio_claim() with a done func of spa_claim_notify(),
         * which will update spa_max_claim_txg.  See spa_load() for details.
         */
        error = zil_parse(zilog, zil_claim_log_block, zil_claim_log_record, tx,
            zilog->zl_header->zh_claim_txg ? -1ULL : spa_first_txg(os->os_spa));

        dmu_objset_rele(os, FTAG);

        return ((error == ECKSUM || error == ENOENT) ? 0 : error);
}

static int
zil_vdev_compare(const void *x1, const void *x2)
{
        const uint64_t v1 = ((zil_vdev_node_t *)x1)->zv_vdev;
        const uint64_t v2 = ((zil_vdev_node_t *)x2)->zv_vdev;

        if (v1 < v2)
                return (-1);
        if (v1 > v2)
                return (1);

        return (0);
}

void
zil_add_block(zilog_t *zilog, const blkptr_t *bp)
{
        avl_tree_t *t = &zilog->zl_vdev_tree;
        avl_index_t where;
        zil_vdev_node_t *zv, zvsearch;
        int ndvas = BP_GET_NDVAS(bp);
        int i;

        if (zfs_nocacheflush)
                return;

        ASSERT(zilog->zl_writer);

        /*
         * Even though we're zl_writer, we still need a lock because the
         * zl_get_data() callbacks may have dmu_sync() done callbacks
         * that will run concurrently.
         */
        mutex_enter(&zilog->zl_vdev_lock);
        for (i = 0; i < ndvas; i++) {
                zvsearch.zv_vdev = DVA_GET_VDEV(&bp->blk_dva[i]);
                if (avl_find(t, &zvsearch, &where) == NULL) {
                        zv = kmem_alloc(sizeof (*zv), KM_PUSHPAGE);
                        zv->zv_vdev = zvsearch.zv_vdev;
                        avl_insert(t, zv, where);
                }
        }
        mutex_exit(&zilog->zl_vdev_lock);
}

static void
zil_flush_vdevs(zilog_t *zilog)
{
        spa_t *spa = zilog->zl_spa;
        avl_tree_t *t = &zilog->zl_vdev_tree;
        void *cookie = NULL;
        zil_vdev_node_t *zv;
        zio_t *zio;

        ASSERT(zilog->zl_writer);

        /*
         * We don't need zl_vdev_lock here because we're the zl_writer,
         * and all zl_get_data() callbacks are done.
         */
        if (avl_numnodes(t) == 0)
                return;

        spa_config_enter(spa, SCL_STATE, FTAG, RW_READER);

        zio = zio_root(spa, NULL, NULL, ZIO_FLAG_CANFAIL);

        while ((zv = avl_destroy_nodes(t, &cookie)) != NULL) {
                vdev_t *vd = vdev_lookup_top(spa, zv->zv_vdev);
                if (vd != NULL)
                        zio_flush(zio, vd);
                kmem_free(zv, sizeof (*zv));
        }

        /*
         * Wait for all the flushes to complete.  Not all devices actually
         * support the DKIOCFLUSHWRITECACHE ioctl, so it's OK if it fails.
         */
        (void) zio_wait(zio);

        spa_config_exit(spa, SCL_STATE, FTAG);
}

/*
 * Function called when a log block write completes
 */
static void
zil_lwb_write_done(zio_t *zio)
{
        lwb_t *lwb = zio->io_private;
        zilog_t *zilog = lwb->lwb_zilog;
        dmu_tx_t *tx = lwb->lwb_tx;

        ASSERT(BP_GET_COMPRESS(zio->io_bp) == ZIO_COMPRESS_OFF);
        ASSERT(BP_GET_TYPE(zio->io_bp) == DMU_OT_INTENT_LOG);
        ASSERT(BP_GET_LEVEL(zio->io_bp) == 0);
        ASSERT(BP_GET_BYTEORDER(zio->io_bp) == ZFS_HOST_BYTEORDER);
        ASSERT(!BP_IS_GANG(zio->io_bp));
        ASSERT(!BP_IS_HOLE(zio->io_bp));
        ASSERT(zio->io_bp->blk_fill == 0);

        /*
         * Ensure the lwb buffer pointer is cleared before releasing
         * the txg. If we have had an allocation failure and
         * the txg is waiting to sync then we want want zil_sync()
         * to remove the lwb so that it's not picked up as the next new
         * one in zil_commit_writer(). zil_sync() will only remove
         * the lwb if lwb_buf is null.
         */
        zio_buf_free(lwb->lwb_buf, lwb->lwb_sz);
        mutex_enter(&zilog->zl_lock);
        lwb->lwb_zio = NULL;
        lwb->lwb_fastwrite = FALSE;
        lwb->lwb_buf = NULL;
        lwb->lwb_tx = NULL;
        mutex_exit(&zilog->zl_lock);

        /*
         * Now that we've written this log block, we have a stable pointer
         * to the next block in the chain, so it's OK to let the txg in
         * which we allocated the next block sync.
         */
        dmu_tx_commit(tx);
}

/*
 * Initialize the io for a log block.
 */
static void
zil_lwb_write_init(zilog_t *zilog, lwb_t *lwb)
{
        zbookmark_t zb;

        SET_BOOKMARK(&zb, lwb->lwb_blk.blk_cksum.zc_word[ZIL_ZC_OBJSET],
            ZB_ZIL_OBJECT, ZB_ZIL_LEVEL,
            lwb->lwb_blk.blk_cksum.zc_word[ZIL_ZC_SEQ]);

        if (zilog->zl_root_zio == NULL) {
                zilog->zl_root_zio = zio_root(zilog->zl_spa, NULL, NULL,
                    ZIO_FLAG_CANFAIL);
        }

        /* Lock so zil_sync() doesn't fastwrite_unmark after zio is created */
        mutex_enter(&zilog->zl_lock);
        if (lwb->lwb_zio == NULL) {
                if (!lwb->lwb_fastwrite) {
                        metaslab_fastwrite_mark(zilog->zl_spa, &lwb->lwb_blk);
                        lwb->lwb_fastwrite = 1;
                }
                lwb->lwb_zio = zio_rewrite(zilog->zl_root_zio, zilog->zl_spa,
                    0, &lwb->lwb_blk, lwb->lwb_buf, BP_GET_LSIZE(&lwb->lwb_blk),
                    zil_lwb_write_done, lwb, ZIO_PRIORITY_LOG_WRITE,
                    ZIO_FLAG_CANFAIL | ZIO_FLAG_DONT_PROPAGATE |
                    ZIO_FLAG_FASTWRITE, &zb);
        }
        mutex_exit(&zilog->zl_lock);
}

/*
 * Define a limited set of intent log block sizes.
 * These must be a multiple of 4KB. Note only the amount used (again
 * aligned to 4KB) actually gets written. However, we can't always just
 * allocate SPA_MAXBLOCKSIZE as the slog space could be exhausted.
 */
uint64_t zil_block_buckets[] = {
    4096,               /* non TX_WRITE */
    8192+4096,          /* data base */
    32*1024 + 4096,     /* NFS writes */
    UINT64_MAX
};

/*
 * Use the slog as long as the logbias is 'latency' and the current commit size
 * is less than the limit or the total list size is less than 2X the limit.
 * Limit checking is disabled by setting zil_slog_limit to UINT64_MAX.
 */
unsigned long zil_slog_limit = 1024 * 1024;
#define USE_SLOG(zilog) (((zilog)->zl_logbias == ZFS_LOGBIAS_LATENCY) && \
        (((zilog)->zl_cur_used < zil_slog_limit) || \
        ((zilog)->zl_itx_list_sz < (zil_slog_limit << 1))))

/*
 * Start a log block write and advance to the next log block.
 * Calls are serialized.
 */
static lwb_t *
zil_lwb_write_start(zilog_t *zilog, lwb_t *lwb)
{
        lwb_t *nlwb = NULL;
        zil_chain_t *zilc;
        spa_t *spa = zilog->zl_spa;
        blkptr_t *bp;
        dmu_tx_t *tx;
        uint64_t txg;
        uint64_t zil_blksz, wsz;
        int i, error;
        boolean_t use_slog;

        if (BP_GET_CHECKSUM(&lwb->lwb_blk) == ZIO_CHECKSUM_ZILOG2) {
                zilc = (zil_chain_t *)lwb->lwb_buf;
                bp = &zilc->zc_next_blk;
        } else {
                zilc = (zil_chain_t *)(lwb->lwb_buf + lwb->lwb_sz);
                bp = &zilc->zc_next_blk;
        }

        ASSERT(lwb->lwb_nused <= lwb->lwb_sz);

        /*
         * Allocate the next block and save its address in this block
         * before writing it in order to establish the log chain.
         * Note that if the allocation of nlwb synced before we wrote
         * the block that points at it (lwb), we'd leak it if we crashed.
         * Therefore, we don't do dmu_tx_commit() until zil_lwb_write_done().
         * We dirty the dataset to ensure that zil_sync() will be called
         * to clean up in the event of allocation failure or I/O failure.
         */
        tx = dmu_tx_create(zilog->zl_os);
        VERIFY(dmu_tx_assign(tx, TXG_WAIT) == 0);
        dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
        txg = dmu_tx_get_txg(tx);

        lwb->lwb_tx = tx;

        /*
         * Log blocks are pre-allocated. Here we select the size of the next
         * block, based on size used in the last block.
         * - first find the smallest bucket that will fit the block from a
         *   limited set of block sizes. This is because it's faster to write
         *   blocks allocated from the same metaslab as they are adjacent or
         *   close.
         * - next find the maximum from the new suggested size and an array of
         *   previous sizes. This lessens a picket fence effect of wrongly
         *   guesssing the size if we have a stream of say 2k, 64k, 2k, 64k
         *   requests.
         *
         * Note we only write what is used, but we can't just allocate
         * the maximum block size because we can exhaust the available
         * pool log space.
         */
        zil_blksz = zilog->zl_cur_used + sizeof (zil_chain_t);
        for (i = 0; zil_blksz > zil_block_buckets[i]; i++)
                continue;
        zil_blksz = zil_block_buckets[i];
        if (zil_blksz == UINT64_MAX)
                zil_blksz = SPA_MAXBLOCKSIZE;
        zilog->zl_prev_blks[zilog->zl_prev_rotor] = zil_blksz;
        for (i = 0; i < ZIL_PREV_BLKS; i++)
                zil_blksz = MAX(zil_blksz, zilog->zl_prev_blks[i]);
        zilog->zl_prev_rotor = (zilog->zl_prev_rotor + 1) & (ZIL_PREV_BLKS - 1);

        BP_ZERO(bp);
        use_slog = USE_SLOG(zilog);
        error = zio_alloc_zil(spa, txg, bp, zil_blksz, USE_SLOG(zilog));
        if (use_slog)
        {
                ZIL_STAT_BUMP(zil_itx_metaslab_slog_count);
                ZIL_STAT_INCR(zil_itx_metaslab_slog_bytes, lwb->lwb_nused);
        }
        else
        {
                ZIL_STAT_BUMP(zil_itx_metaslab_normal_count);
                ZIL_STAT_INCR(zil_itx_metaslab_normal_bytes, lwb->lwb_nused);
        }
        if (!error) {
                ASSERT3U(bp->blk_birth, ==, txg);
                bp->blk_cksum = lwb->lwb_blk.blk_cksum;
                bp->blk_cksum.zc_word[ZIL_ZC_SEQ]++;

                /*
                 * Allocate a new log write buffer (lwb).
                 */
                nlwb = zil_alloc_lwb(zilog, bp, txg, TRUE);

                /* Record the block for later vdev flushing */
                zil_add_block(zilog, &lwb->lwb_blk);
        }

        if (BP_GET_CHECKSUM(&lwb->lwb_blk) == ZIO_CHECKSUM_ZILOG2) {
                /* For Slim ZIL only write what is used. */
                wsz = P2ROUNDUP_TYPED(lwb->lwb_nused, ZIL_MIN_BLKSZ, uint64_t);
                ASSERT3U(wsz, <=, lwb->lwb_sz);
                zio_shrink(lwb->lwb_zio, wsz);

        } else {
                wsz = lwb->lwb_sz;
        }

        zilc->zc_pad = 0;
        zilc->zc_nused = lwb->lwb_nused;
        zilc->zc_eck.zec_cksum = lwb->lwb_blk.blk_cksum;

        /*
         * clear unused data for security
         */
        bzero(lwb->lwb_buf + lwb->lwb_nused, wsz - lwb->lwb_nused);

        zio_nowait(lwb->lwb_zio); /* Kick off the write for the old log block */

        /*
         * If there was an allocation failure then nlwb will be null which
         * forces a txg_wait_synced().
         */
        return (nlwb);
}

static lwb_t *
zil_lwb_commit(zilog_t *zilog, itx_t *itx, lwb_t *lwb)
{
        lr_t *lrc = &itx->itx_lr; /* common log record */
        lr_write_t *lrw = (lr_write_t *)lrc;
        char *lr_buf;
        uint64_t txg = lrc->lrc_txg;
        uint64_t reclen = lrc->lrc_reclen;
        uint64_t dlen = 0;

        if (lwb == NULL)
                return (NULL);

        ASSERT(lwb->lwb_buf != NULL);

        if (lrc->lrc_txtype == TX_WRITE && itx->itx_wr_state == WR_NEED_COPY)
                dlen = P2ROUNDUP_TYPED(
                    lrw->lr_length, sizeof (uint64_t), uint64_t);

        zilog->zl_cur_used += (reclen + dlen);

        zil_lwb_write_init(zilog, lwb);

        /*
         * If this record won't fit in the current log block, start a new one.
         */
        if (lwb->lwb_nused + reclen + dlen > lwb->lwb_sz) {
                lwb = zil_lwb_write_start(zilog, lwb);
                if (lwb == NULL)
                        return (NULL);
                zil_lwb_write_init(zilog, lwb);
                ASSERT(LWB_EMPTY(lwb));
                if (lwb->lwb_nused + reclen + dlen > lwb->lwb_sz) {
                        txg_wait_synced(zilog->zl_dmu_pool, txg);
                        return (lwb);
                }
        }

        lr_buf = lwb->lwb_buf + lwb->lwb_nused;
        bcopy(lrc, lr_buf, reclen);
        lrc = (lr_t *)lr_buf;
        lrw = (lr_write_t *)lrc;

        ZIL_STAT_BUMP(zil_itx_count);

        /*
         * If it's a write, fetch the data or get its blkptr as appropriate.
         */
        if (lrc->lrc_txtype == TX_WRITE) {
                if (txg > spa_freeze_txg(zilog->zl_spa))
                        txg_wait_synced(zilog->zl_dmu_pool, txg);
                if (itx->itx_wr_state == WR_COPIED) {
                        ZIL_STAT_BUMP(zil_itx_copied_count);
                        ZIL_STAT_INCR(zil_itx_copied_bytes, lrw->lr_length);
                } else {
                        char *dbuf;
                        int error;

                        if (dlen) {
                                ASSERT(itx->itx_wr_state == WR_NEED_COPY);
                                dbuf = lr_buf + reclen;
                                lrw->lr_common.lrc_reclen += dlen;
                                ZIL_STAT_BUMP(zil_itx_needcopy_count);
                                ZIL_STAT_INCR(zil_itx_needcopy_bytes, lrw->lr_length);
                        } else {
                                ASSERT(itx->itx_wr_state == WR_INDIRECT);
                                dbuf = NULL;
                                ZIL_STAT_BUMP(zil_itx_indirect_count);
                                ZIL_STAT_INCR(zil_itx_indirect_bytes, lrw->lr_length);
                        }
                        error = zilog->zl_get_data(
                            itx->itx_private, lrw, dbuf, lwb->lwb_zio);
                        if (error == EIO) {
                                txg_wait_synced(zilog->zl_dmu_pool, txg);
                                return (lwb);
                        }
                        if (error) {
                                ASSERT(error == ENOENT || error == EEXIST ||
                                    error == EALREADY);
                                return (lwb);
                        }
                }
        }

        /*
         * We're actually making an entry, so update lrc_seq to be the
         * log record sequence number.  Note that this is generally not
         * equal to the itx sequence number because not all transactions
         * are synchronous, and sometimes spa_sync() gets there first.
         */
        lrc->lrc_seq = ++zilog->zl_lr_seq; /* we are single threaded */
        lwb->lwb_nused += reclen + dlen;
        lwb->lwb_max_txg = MAX(lwb->lwb_max_txg, txg);
        ASSERT3U(lwb->lwb_nused, <=, lwb->lwb_sz);
        ASSERT3U(P2PHASE(lwb->lwb_nused, sizeof (uint64_t)), ==, 0);

        return (lwb);
}

itx_t *
zil_itx_create(uint64_t txtype, size_t lrsize)
{
        itx_t *itx;

        lrsize = P2ROUNDUP_TYPED(lrsize, sizeof (uint64_t), size_t);

        itx = kmem_alloc(offsetof(itx_t, itx_lr) + lrsize,
            KM_PUSHPAGE | KM_NODEBUG);
        itx->itx_lr.lrc_txtype = txtype;
        itx->itx_lr.lrc_reclen = lrsize;
        itx->itx_sod = lrsize; /* if write & WR_NEED_COPY will be increased */
        itx->itx_lr.lrc_seq = 0;        /* defensive */
        itx->itx_sync = B_TRUE;         /* default is synchronous */

        return (itx);
}

void
zil_itx_destroy(itx_t *itx)
{
        kmem_free(itx, offsetof(itx_t, itx_lr) + itx->itx_lr.lrc_reclen);
}

/*
 * Free up the sync and async itxs. The itxs_t has already been detached
 * so no locks are needed.
 */
static void
zil_itxg_clean(itxs_t *itxs)
{
        itx_t *itx;
        list_t *list;
        avl_tree_t *t;
        void *cookie;
        itx_async_node_t *ian;

        list = &itxs->i_sync_list;
        while ((itx = list_head(list)) != NULL) {
                list_remove(list, itx);
                kmem_free(itx, offsetof(itx_t, itx_lr) +
                    itx->itx_lr.lrc_reclen);
        }

        cookie = NULL;
        t = &itxs->i_async_tree;
        while ((ian = avl_destroy_nodes(t, &cookie)) != NULL) {
                list = &ian->ia_list;
                while ((itx = list_head(list)) != NULL) {
                        list_remove(list, itx);
                        kmem_free(itx, offsetof(itx_t, itx_lr) +
                            itx->itx_lr.lrc_reclen);
                }
                list_destroy(list);
                kmem_free(ian, sizeof (itx_async_node_t));
        }
        avl_destroy(t);

        kmem_free(itxs, sizeof (itxs_t));
}

static int
zil_aitx_compare(const void *x1, const void *x2)
{
        const uint64_t o1 = ((itx_async_node_t *)x1)->ia_foid;
        const uint64_t o2 = ((itx_async_node_t *)x2)->ia_foid;

        if (o1 < o2)
                return (-1);
        if (o1 > o2)
                return (1);

        return (0);
}

/*
 * Remove all async itx with the given oid.
 */
static void
zil_remove_async(zilog_t *zilog, uint64_t oid)
{
        uint64_t otxg, txg;
        itx_async_node_t *ian;
        avl_tree_t *t;
        avl_index_t where;
        list_t clean_list;
        itx_t *itx;

        ASSERT(oid != 0);
        list_create(&clean_list, sizeof (itx_t), offsetof(itx_t, itx_node));

        if (spa_freeze_txg(zilog->zl_spa) != UINT64_MAX) /* ziltest support */
                otxg = ZILTEST_TXG;
        else
                otxg = spa_last_synced_txg(zilog->zl_spa) + 1;

        for (txg = otxg; txg < (otxg + TXG_CONCURRENT_STATES); txg++) {
                itxg_t *itxg = &zilog->zl_itxg[txg & TXG_MASK];

                mutex_enter(&itxg->itxg_lock);
                if (itxg->itxg_txg != txg) {
                        mutex_exit(&itxg->itxg_lock);
                        continue;
                }

                /*
                 * Locate the object node and append its list.
                 */
                t = &itxg->itxg_itxs->i_async_tree;
                ian = avl_find(t, &oid, &where);
                if (ian != NULL)
                        list_move_tail(&clean_list, &ian->ia_list);
                mutex_exit(&itxg->itxg_lock);
        }
        while ((itx = list_head(&clean_list)) != NULL) {
                list_remove(&clean_list, itx);
                kmem_free(itx, offsetof(itx_t, itx_lr) +
                    itx->itx_lr.lrc_reclen);
        }
        list_destroy(&clean_list);
}

void
zil_itx_assign(zilog_t *zilog, itx_t *itx, dmu_tx_t *tx)
{
        uint64_t txg;
        itxg_t *itxg;
        itxs_t *itxs, *clean = NULL;

        /*
         * Object ids can be re-instantiated in the next txg so
         * remove any async transactions to avoid future leaks.
         * This can happen if a fsync occurs on the re-instantiated
         * object for a WR_INDIRECT or WR_NEED_COPY write, which gets
         * the new file data and flushes a write record for the old object.
         */
        if ((itx->itx_lr.lrc_txtype & ~TX_CI) == TX_REMOVE)
                zil_remove_async(zilog, itx->itx_oid);

        /*
         * Ensure the data of a renamed file is committed before the rename.
         */
        if ((itx->itx_lr.lrc_txtype & ~TX_CI) == TX_RENAME)
                zil_async_to_sync(zilog, itx->itx_oid);

        if (spa_freeze_txg(zilog->zl_spa) !=  UINT64_MAX)
                txg = ZILTEST_TXG;
        else
                txg = dmu_tx_get_txg(tx);

        itxg = &zilog->zl_itxg[txg & TXG_MASK];
        mutex_enter(&itxg->itxg_lock);
        itxs = itxg->itxg_itxs;
        if (itxg->itxg_txg != txg) {
                if (itxs != NULL) {
                        /*
                         * The zil_clean callback hasn't got around to cleaning
                         * this itxg. Save the itxs for release below.
                         * This should be rare.
                         */
                        atomic_add_64(&zilog->zl_itx_list_sz, -itxg->itxg_sod);
                        itxg->itxg_sod = 0;
                        clean = itxg->itxg_itxs;
                }
                ASSERT(itxg->itxg_sod == 0);
                itxg->itxg_txg = txg;
                itxs = itxg->itxg_itxs = kmem_zalloc(sizeof (itxs_t), KM_PUSHPAGE);

                list_create(&itxs->i_sync_list, sizeof (itx_t),
                    offsetof(itx_t, itx_node));
                avl_create(&itxs->i_async_tree, zil_aitx_compare,
                    sizeof (itx_async_node_t),
                    offsetof(itx_async_node_t, ia_node));
        }
        if (itx->itx_sync) {
                list_insert_tail(&itxs->i_sync_list, itx);
                atomic_add_64(&zilog->zl_itx_list_sz, itx->itx_sod);
                itxg->itxg_sod += itx->itx_sod;
        } else {
                avl_tree_t *t = &itxs->i_async_tree;
                uint64_t foid = ((lr_ooo_t *)&itx->itx_lr)->lr_foid;
                itx_async_node_t *ian;
                avl_index_t where;

                ian = avl_find(t, &foid, &where);
                if (ian == NULL) {
                        ian = kmem_alloc(sizeof (itx_async_node_t), KM_PUSHPAGE);
                        list_create(&ian->ia_list, sizeof (itx_t),
                            offsetof(itx_t, itx_node));
                        ian->ia_foid = foid;
                        avl_insert(t, ian, where);
                }
                list_insert_tail(&ian->ia_list, itx);
        }

        itx->itx_lr.lrc_txg = dmu_tx_get_txg(tx);
        mutex_exit(&itxg->itxg_lock);

        /* Release the old itxs now we've dropped the lock */
        if (clean != NULL)
                zil_itxg_clean(clean);
}

/*
 * If there are any in-memory intent log transactions which have now been
 * synced then start up a taskq to free them.
 */
void
zil_clean(zilog_t *zilog, uint64_t synced_txg)
{
        itxg_t *itxg = &zilog->zl_itxg[synced_txg & TXG_MASK];
        itxs_t *clean_me;

        mutex_enter(&itxg->itxg_lock);
        if (itxg->itxg_itxs == NULL || itxg->itxg_txg == ZILTEST_TXG) {
                mutex_exit(&itxg->itxg_lock);
                return;
        }
        ASSERT3U(itxg->itxg_txg, <=, synced_txg);
        ASSERT(itxg->itxg_txg != 0);
        ASSERT(zilog->zl_clean_taskq != NULL);
        atomic_add_64(&zilog->zl_itx_list_sz, -itxg->itxg_sod);
        itxg->itxg_sod = 0;
        clean_me = itxg->itxg_itxs;
        itxg->itxg_itxs = NULL;
        itxg->itxg_txg = 0;
        mutex_exit(&itxg->itxg_lock);
        /*
         * Preferably start a task queue to free up the old itxs but
         * if taskq_dispatch can't allocate resources to do that then
         * free it in-line. This should be rare. Note, using TQ_SLEEP
         * created a bad performance problem.
         */
        if (taskq_dispatch(zilog->zl_clean_taskq,
            (void (*)(void *))zil_itxg_clean, clean_me, TQ_NOSLEEP) == 0)
                zil_itxg_clean(clean_me);
}

/*
 * Get the list of itxs to commit into zl_itx_commit_list.
 */
static void
zil_get_commit_list(zilog_t *zilog)
{
        uint64_t otxg, txg;
        list_t *commit_list = &zilog->zl_itx_commit_list;
        uint64_t push_sod = 0;

        if (spa_freeze_txg(zilog->zl_spa) != UINT64_MAX) /* ziltest support */
                otxg = ZILTEST_TXG;
        else
                otxg = spa_last_synced_txg(zilog->zl_spa) + 1;

        for (txg = otxg; txg < (otxg + TXG_CONCURRENT_STATES); txg++) {
                itxg_t *itxg = &zilog->zl_itxg[txg & TXG_MASK];

                mutex_enter(&itxg->itxg_lock);
                if (itxg->itxg_txg != txg) {
                        mutex_exit(&itxg->itxg_lock);
                        continue;
                }

                list_move_tail(commit_list, &itxg->itxg_itxs->i_sync_list);
                push_sod += itxg->itxg_sod;
                itxg->itxg_sod = 0;

                mutex_exit(&itxg->itxg_lock);
        }
        atomic_add_64(&zilog->zl_itx_list_sz, -push_sod);
}

/*
 * Move the async itxs for a specified object to commit into sync lists.
 */
static void
zil_async_to_sync(zilog_t *zilog, uint64_t foid)
{
        uint64_t otxg, txg;
        itx_async_node_t *ian;
        avl_tree_t *t;
        avl_index_t where;

        if (spa_freeze_txg(zilog->zl_spa) != UINT64_MAX) /* ziltest support */
                otxg = ZILTEST_TXG;
        else
                otxg = spa_last_synced_txg(zilog->zl_spa) + 1;

        for (txg = otxg; txg < (otxg + TXG_CONCURRENT_STATES); txg++) {
                itxg_t *itxg = &zilog->zl_itxg[txg & TXG_MASK];

                mutex_enter(&itxg->itxg_lock);
                if (itxg->itxg_txg != txg) {
                        mutex_exit(&itxg->itxg_lock);
                        continue;
                }

                /*
                 * If a foid is specified then find that node and append its
                 * list. Otherwise walk the tree appending all the lists
                 * to the sync list. We add to the end rather than the
                 * beginning to ensure the create has happened.
                 */
                t = &itxg->itxg_itxs->i_async_tree;
                if (foid != 0) {
                        ian = avl_find(t, &foid, &where);
                        if (ian != NULL) {
                                list_move_tail(&itxg->itxg_itxs->i_sync_list,
                                    &ian->ia_list);
                        }
                } else {
                        void *cookie = NULL;

                        while ((ian = avl_destroy_nodes(t, &cookie)) != NULL) {
                                list_move_tail(&itxg->itxg_itxs->i_sync_list,
                                    &ian->ia_list);
                                list_destroy(&ian->ia_list);
                                kmem_free(ian, sizeof (itx_async_node_t));
                        }
                }
                mutex_exit(&itxg->itxg_lock);
        }
}

static void
zil_commit_writer(zilog_t *zilog)
{
        uint64_t txg;
        itx_t *itx;
        lwb_t *lwb;
        spa_t *spa = zilog->zl_spa;
        int error = 0;

        ASSERT(zilog->zl_root_zio == NULL);

        mutex_exit(&zilog->zl_lock);

        zil_get_commit_list(zilog);

        /*
         * Return if there's nothing to commit before we dirty the fs by
         * calling zil_create().
         */
        if (list_head(&zilog->zl_itx_commit_list) == NULL) {
                mutex_enter(&zilog->zl_lock);
                return;
        }

        if (zilog->zl_suspend) {
                lwb = NULL;
        } else {
                lwb = list_tail(&zilog->zl_lwb_list);
                if (lwb == NULL)
                        lwb = zil_create(zilog);
        }

        DTRACE_PROBE1(zil__cw1, zilog_t *, zilog);
        while ((itx = list_head(&zilog->zl_itx_commit_list))) {
                txg = itx->itx_lr.lrc_txg;
                ASSERT(txg);

                if (txg > spa_last_synced_txg(spa) || txg > spa_freeze_txg(spa))
                        lwb = zil_lwb_commit(zilog, itx, lwb);
                list_remove(&zilog->zl_itx_commit_list, itx);
                kmem_free(itx, offsetof(itx_t, itx_lr)
                    + itx->itx_lr.lrc_reclen);
        }
        DTRACE_PROBE1(zil__cw2, zilog_t *, zilog);

        /* write the last block out */
        if (lwb != NULL && lwb->lwb_zio != NULL)
                lwb = zil_lwb_write_start(zilog, lwb);

        zilog->zl_cur_used = 0;

        /*
         * Wait if necessary for the log blocks to be on stable storage.
         */
        if (zilog->zl_root_zio) {
                error = zio_wait(zilog->zl_root_zio);
                zilog->zl_root_zio = NULL;
                zil_flush_vdevs(zilog);
        }

        if (error || lwb == NULL)
                txg_wait_synced(zilog->zl_dmu_pool, 0);

        mutex_enter(&zilog->zl_lock);

        /*
         * Remember the highest committed log sequence number for ztest.
         * We only update this value when all the log writes succeeded,
         * because ztest wants to ASSERT that it got the whole log chain.
         */
        if (error == 0 && lwb != NULL)
                zilog->zl_commit_lr_seq = zilog->zl_lr_seq;
}

/*
 * Commit zfs transactions to stable storage.
 * If foid is 0 push out all transactions, otherwise push only those
 * for that object or might reference that object.
 *
 * itxs are committed in batches. In a heavily stressed zil there will be
 * a commit writer thread who is writing out a bunch of itxs to the log
 * for a set of committing threads (cthreads) in the same batch as the writer.
 * Those cthreads are all waiting on the same cv for that batch.
 *
 * There will also be a different and growing batch of threads that are
 * waiting to commit (qthreads). When the committing batch completes
 * a transition occurs such that the cthreads exit and the qthreads become
 * cthreads. One of the new cthreads becomes the writer thread for the
 * batch. Any new threads arriving become new qthreads.
 *
 * Only 2 condition variables are needed and there's no transition
 * between the two cvs needed. They just flip-flop between qthreads
 * and cthreads.
 *
 * Using this scheme we can efficiently wakeup up only those threads
 * that have been committed.
 */
void
zil_commit(zilog_t *zilog, uint64_t foid)
{
        uint64_t mybatch;

        if (zilog->zl_sync == ZFS_SYNC_DISABLED)
                return;

        ZIL_STAT_BUMP(zil_commit_count);

        /* move the async itxs for the foid to the sync queues */
        zil_async_to_sync(zilog, foid);

        mutex_enter(&zilog->zl_lock);
        mybatch = zilog->zl_next_batch;
        while (zilog->zl_writer) {
                cv_wait(&zilog->zl_cv_batch[mybatch & 1], &zilog->zl_lock);
                if (mybatch <= zilog->zl_com_batch) {
                        mutex_exit(&zilog->zl_lock);
                        return;
                }
        }

        zilog->zl_next_batch++;
        zilog->zl_writer = B_TRUE;
        ZIL_STAT_BUMP(zil_commit_writer_count);
        zil_commit_writer(zilog);
        zilog->zl_com_batch = mybatch;
        zilog->zl_writer = B_FALSE;

        /* wake up one thread to become the next writer */
        cv_signal(&zilog->zl_cv_batch[(mybatch+1) & 1]);

        /* wake up all threads waiting for this batch to be committed */
        cv_broadcast(&zilog->zl_cv_batch[mybatch & 1]);

        mutex_exit(&zilog->zl_lock);
}

/*
 * Called in syncing context to free committed log blocks and update log header.
 */
void
zil_sync(zilog_t *zilog, dmu_tx_t *tx)
{
        zil_header_t *zh = zil_header_in_syncing_context(zilog);
        uint64_t txg = dmu_tx_get_txg(tx);
        spa_t *spa = zilog->zl_spa;
        uint64_t *replayed_seq = &zilog->zl_replayed_seq[txg & TXG_MASK];
        lwb_t *lwb;

        /*
         * We don't zero out zl_destroy_txg, so make sure we don't try
         * to destroy it twice.
         */
        if (spa_sync_pass(spa) != 1)
                return;

        mutex_enter(&zilog->zl_lock);

        ASSERT(zilog->zl_stop_sync == 0);

        if (*replayed_seq != 0) {
                ASSERT(zh->zh_replay_seq < *replayed_seq);
                zh->zh_replay_seq = *replayed_seq;
                *replayed_seq = 0;
        }

        if (zilog->zl_destroy_txg == txg) {
                blkptr_t blk = zh->zh_log;

                ASSERT(list_head(&zilog->zl_lwb_list) == NULL);

                bzero(zh, sizeof (zil_header_t));
                bzero(zilog->zl_replayed_seq, sizeof (zilog->zl_replayed_seq));

                if (zilog->zl_keep_first) {
                        /*
                         * If this block was part of log chain that couldn't
                         * be claimed because a device was missing during
                         * zil_claim(), but that device later returns,
                         * then this block could erroneously appear valid.
                         * To guard against this, assign a new GUID to the new
                         * log chain so it doesn't matter what blk points to.
                         */
                        zil_init_log_chain(zilog, &blk);
                        zh->zh_log = blk;
                }
        }

        while ((lwb = list_head(&zilog->zl_lwb_list)) != NULL) {
                zh->zh_log = lwb->lwb_blk;
                if (lwb->lwb_buf != NULL || lwb->lwb_max_txg > txg)
                        break;

                ASSERT(lwb->lwb_zio == NULL);

                list_remove(&zilog->zl_lwb_list, lwb);
                zio_free_zil(spa, txg, &lwb->lwb_blk);
                kmem_cache_free(zil_lwb_cache, lwb);

                /*
                 * If we don't have anything left in the lwb list then
                 * we've had an allocation failure and we need to zero
                 * out the zil_header blkptr so that we don't end
                 * up freeing the same block twice.
                 */
                if (list_head(&zilog->zl_lwb_list) == NULL)
                        BP_ZERO(&zh->zh_log);
        }

        /*
         * Remove fastwrite on any blocks that have been pre-allocated for
         * the next commit. This prevents fastwrite counter pollution by
         * unused, long-lived LWBs.
         */
        for (; lwb != NULL; lwb = list_next(&zilog->zl_lwb_list, lwb)) {
                if (lwb->lwb_fastwrite && !lwb->lwb_zio) {
                        metaslab_fastwrite_unmark(zilog->zl_spa, &lwb->lwb_blk);
                        lwb->lwb_fastwrite = 0;
                }
        }

        mutex_exit(&zilog->zl_lock);
}

void
zil_init(void)
{
        zil_lwb_cache = kmem_cache_create("zil_lwb_cache",
            sizeof (struct lwb), 0, NULL, NULL, NULL, NULL, NULL, 0);

        zil_ksp = kstat_create("zfs", 0, "zil", "misc",
            KSTAT_TYPE_NAMED, sizeof(zil_stats) / sizeof(kstat_named_t),
            KSTAT_FLAG_VIRTUAL);

        if (zil_ksp != NULL) {
                zil_ksp->ks_data = &zil_stats;
                kstat_install(zil_ksp);
        }
}

void
zil_fini(void)
{
        kmem_cache_destroy(zil_lwb_cache);

        if (zil_ksp != NULL) {
                kstat_delete(zil_ksp);
                zil_ksp = NULL;
        }
}

void
zil_set_sync(zilog_t *zilog, uint64_t sync)
{
        zilog->zl_sync = sync;
}

void
zil_set_logbias(zilog_t *zilog, uint64_t logbias)
{
        zilog->zl_logbias = logbias;
}

zilog_t *
zil_alloc(objset_t *os, zil_header_t *zh_phys)
{
        zilog_t *zilog;
        int i;

        zilog = kmem_zalloc(sizeof (zilog_t), KM_PUSHPAGE);

        zilog->zl_header = zh_phys;
        zilog->zl_os = os;
        zilog->zl_spa = dmu_objset_spa(os);
        zilog->zl_dmu_pool = dmu_objset_pool(os);
        zilog->zl_destroy_txg = TXG_INITIAL - 1;
        zilog->zl_logbias = dmu_objset_logbias(os);
        zilog->zl_sync = dmu_objset_syncprop(os);
        zilog->zl_next_batch = 1;

        mutex_init(&zilog->zl_lock, NULL, MUTEX_DEFAULT, NULL);

        for (i = 0; i < TXG_SIZE; i++) {
                mutex_init(&zilog->zl_itxg[i].itxg_lock, NULL,
                    MUTEX_DEFAULT, NULL);
        }

        list_create(&zilog->zl_lwb_list, sizeof (lwb_t),
            offsetof(lwb_t, lwb_node));

        list_create(&zilog->zl_itx_commit_list, sizeof (itx_t),
            offsetof(itx_t, itx_node));

        mutex_init(&zilog->zl_vdev_lock, NULL, MUTEX_DEFAULT, NULL);

        avl_create(&zilog->zl_vdev_tree, zil_vdev_compare,
            sizeof (zil_vdev_node_t), offsetof(zil_vdev_node_t, zv_node));

        cv_init(&zilog->zl_cv_writer, NULL, CV_DEFAULT, NULL);
        cv_init(&zilog->zl_cv_suspend, NULL, CV_DEFAULT, NULL);
        cv_init(&zilog->zl_cv_batch[0], NULL, CV_DEFAULT, NULL);
        cv_init(&zilog->zl_cv_batch[1], NULL, CV_DEFAULT, NULL);

        return (zilog);
}

void
zil_free(zilog_t *zilog)
{
        int i;

        zilog->zl_stop_sync = 1;

        ASSERT(list_is_empty(&zilog->zl_lwb_list));
        list_destroy(&zilog->zl_lwb_list);

        avl_destroy(&zilog->zl_vdev_tree);
        mutex_destroy(&zilog->zl_vdev_lock);

        ASSERT(list_is_empty(&zilog->zl_itx_commit_list));
        list_destroy(&zilog->zl_itx_commit_list);

        for (i = 0; i < TXG_SIZE; i++) {
                /*
                 * It's possible for an itx to be generated that doesn't dirty
                 * a txg (e.g. ztest TX_TRUNCATE). So there's no zil_clean()
                 * callback to remove the entry. We remove those here.
                 *
                 * Also free up the ziltest itxs.
                 */
                if (zilog->zl_itxg[i].itxg_itxs)
                        zil_itxg_clean(zilog->zl_itxg[i].itxg_itxs);
                mutex_destroy(&zilog->zl_itxg[i].itxg_lock);
        }

        mutex_destroy(&zilog->zl_lock);

        cv_destroy(&zilog->zl_cv_writer);
        cv_destroy(&zilog->zl_cv_suspend);
        cv_destroy(&zilog->zl_cv_batch[0]);
        cv_destroy(&zilog->zl_cv_batch[1]);

        kmem_free(zilog, sizeof (zilog_t));
}

/*
 * Open an intent log.
 */
zilog_t *
zil_open(objset_t *os, zil_get_data_t *get_data)
{
        zilog_t *zilog = dmu_objset_zil(os);

        ASSERT(zilog->zl_clean_taskq == NULL);
        ASSERT(zilog->zl_get_data == NULL);
        ASSERT(list_is_empty(&zilog->zl_lwb_list));

        zilog->zl_get_data = get_data;
        zilog->zl_clean_taskq = taskq_create("zil_clean", 1, minclsyspri,
            2, 2, TASKQ_PREPOPULATE);

        return (zilog);
}

/*
 * Close an intent log.
 */
void
zil_close(zilog_t *zilog)
{
        lwb_t *lwb;
        uint64_t txg = 0;

        zil_commit(zilog, 0); /* commit all itx */

        /*
         * The lwb_max_txg for the stubby lwb will reflect the last activity
         * for the zil.  After a txg_wait_synced() on the txg we know all the
         * callbacks have occurred that may clean the zil.  Only then can we
         * destroy the zl_clean_taskq.
         */
        mutex_enter(&zilog->zl_lock);
        lwb = list_tail(&zilog->zl_lwb_list);
        if (lwb != NULL)
                txg = lwb->lwb_max_txg;
        mutex_exit(&zilog->zl_lock);
        if (txg)
                txg_wait_synced(zilog->zl_dmu_pool, txg);

        taskq_destroy(zilog->zl_clean_taskq);
        zilog->zl_clean_taskq = NULL;
        zilog->zl_get_data = NULL;

        /*
         * We should have only one LWB left on the list; remove it now.
         */
        mutex_enter(&zilog->zl_lock);
        lwb = list_head(&zilog->zl_lwb_list);
        if (lwb != NULL) {
                ASSERT(lwb == list_tail(&zilog->zl_lwb_list));
                ASSERT(lwb->lwb_zio == NULL);
                if (lwb->lwb_fastwrite)
                        metaslab_fastwrite_unmark(zilog->zl_spa, &lwb->lwb_blk);
                list_remove(&zilog->zl_lwb_list, lwb);
                zio_buf_free(lwb->lwb_buf, lwb->lwb_sz);
                kmem_cache_free(zil_lwb_cache, lwb);
        }
        mutex_exit(&zilog->zl_lock);
}

/*
 * Suspend an intent log.  While in suspended mode, we still honor
 * synchronous semantics, but we rely on txg_wait_synced() to do it.
 * We suspend the log briefly when taking a snapshot so that the snapshot
 * contains all the data it's supposed to, and has an empty intent log.
 */
int
zil_suspend(zilog_t *zilog)
{
        const zil_header_t *zh = zilog->zl_header;

        mutex_enter(&zilog->zl_lock);
        if (zh->zh_flags & ZIL_REPLAY_NEEDED) {         /* unplayed log */
                mutex_exit(&zilog->zl_lock);
                return (EBUSY);
        }
        if (zilog->zl_suspend++ != 0) {
                /*
                 * Someone else already began a suspend.
                 * Just wait for them to finish.
                 */
                while (zilog->zl_suspending)
                        cv_wait(&zilog->zl_cv_suspend, &zilog->zl_lock);
                mutex_exit(&zilog->zl_lock);
                return (0);
        }
        zilog->zl_suspending = B_TRUE;
        mutex_exit(&zilog->zl_lock);

        zil_commit(zilog, 0);

        zil_destroy(zilog, B_FALSE);

        mutex_enter(&zilog->zl_lock);
        zilog->zl_suspending = B_FALSE;
        cv_broadcast(&zilog->zl_cv_suspend);
        mutex_exit(&zilog->zl_lock);

        return (0);
}

void
zil_resume(zilog_t *zilog)
{
        mutex_enter(&zilog->zl_lock);
        ASSERT(zilog->zl_suspend != 0);
        zilog->zl_suspend--;
        mutex_exit(&zilog->zl_lock);
}

typedef struct zil_replay_arg {
        zil_replay_func_t **zr_replay;
        void            *zr_arg;
        boolean_t       zr_byteswap;
        char            *zr_lr;
} zil_replay_arg_t;

static int
zil_replay_error(zilog_t *zilog, lr_t *lr, int error)
{
        char name[MAXNAMELEN];

        zilog->zl_replaying_seq--;      /* didn't actually replay this one */

        dmu_objset_name(zilog->zl_os, name);

        cmn_err(CE_WARN, "ZFS replay transaction error %d, "
            "dataset %s, seq 0x%llx, txtype %llu %s\n", error, name,
            (u_longlong_t)lr->lrc_seq,
            (u_longlong_t)(lr->lrc_txtype & ~TX_CI),
            (lr->lrc_txtype & TX_CI) ? "CI" : "");

        return (error);
}

static int
zil_replay_log_record(zilog_t *zilog, lr_t *lr, void *zra, uint64_t claim_txg)
{
        zil_replay_arg_t *zr = zra;
        const zil_header_t *zh = zilog->zl_header;
        uint64_t reclen = lr->lrc_reclen;
        uint64_t txtype = lr->lrc_txtype;
        int error = 0;

        zilog->zl_replaying_seq = lr->lrc_seq;

        if (lr->lrc_seq <= zh->zh_replay_seq)   /* already replayed */
                return (0);

        if (lr->lrc_txg < claim_txg)            /* already committed */
                return (0);

        /* Strip case-insensitive bit, still present in log record */
        txtype &= ~TX_CI;

        if (txtype == 0 || txtype >= TX_MAX_TYPE)
                return (zil_replay_error(zilog, lr, EINVAL));

        /*
         * If this record type can be logged out of order, the object
         * (lr_foid) may no longer exist.  That's legitimate, not an error.
         */
        if (TX_OOO(txtype)) {
                error = dmu_object_info(zilog->zl_os,
                    ((lr_ooo_t *)lr)->lr_foid, NULL);
                if (error == ENOENT || error == EEXIST)
                        return (0);
        }

        /*
         * Make a copy of the data so we can revise and extend it.
         */
        bcopy(lr, zr->zr_lr, reclen);

        /*
         * If this is a TX_WRITE with a blkptr, suck in the data.
         */
        if (txtype == TX_WRITE && reclen == sizeof (lr_write_t)) {
                error = zil_read_log_data(zilog, (lr_write_t *)lr,
                    zr->zr_lr + reclen);
                if (error)
                        return (zil_replay_error(zilog, lr, error));
        }

        /*
         * The log block containing this lr may have been byteswapped
         * so that we can easily examine common fields like lrc_txtype.
         * However, the log is a mix of different record types, and only the
         * replay vectors know how to byteswap their records.  Therefore, if
         * the lr was byteswapped, undo it before invoking the replay vector.
         */
        if (zr->zr_byteswap)
                byteswap_uint64_array(zr->zr_lr, reclen);

        /*
         * We must now do two things atomically: replay this log record,
         * and update the log header sequence number to reflect the fact that
         * we did so. At the end of each replay function the sequence number
         * is updated if we are in replay mode.
         */
        error = zr->zr_replay[txtype](zr->zr_arg, zr->zr_lr, zr->zr_byteswap);
        if (error) {
                /*
                 * The DMU's dnode layer doesn't see removes until the txg
                 * commits, so a subsequent claim can spuriously fail with
                 * EEXIST. So if we receive any error we try syncing out
                 * any removes then retry the transaction.  Note that we
                 * specify B_FALSE for byteswap now, so we don't do it twice.
                 */
                txg_wait_synced(spa_get_dsl(zilog->zl_spa), 0);
                error = zr->zr_replay[txtype](zr->zr_arg, zr->zr_lr, B_FALSE);
                if (error)
                        return (zil_replay_error(zilog, lr, error));
        }
        return (0);
}

/* ARGSUSED */
static int
zil_incr_blks(zilog_t *zilog, blkptr_t *bp, void *arg, uint64_t claim_txg)
{
        zilog->zl_replay_blks++;

        return (0);
}

/*
 * If this dataset has a non-empty intent log, replay it and destroy it.
 */
void
zil_replay(objset_t *os, void *arg, zil_replay_func_t *replay_func[TX_MAX_TYPE])
{
        zilog_t *zilog = dmu_objset_zil(os);
        const zil_header_t *zh = zilog->zl_header;
        zil_replay_arg_t zr;

        if ((zh->zh_flags & ZIL_REPLAY_NEEDED) == 0) {
                zil_destroy(zilog, B_TRUE);
                return;
        }

        zr.zr_replay = replay_func;
        zr.zr_arg = arg;
        zr.zr_byteswap = BP_SHOULD_BYTESWAP(&zh->zh_log);
        zr.zr_lr = vmem_alloc(2 * SPA_MAXBLOCKSIZE, KM_PUSHPAGE);

        /*
         * Wait for in-progress removes to sync before starting replay.
         */
        txg_wait_synced(zilog->zl_dmu_pool, 0);

        zilog->zl_replay = B_TRUE;
        zilog->zl_replay_time = ddi_get_lbolt();
        ASSERT(zilog->zl_replay_blks == 0);
        (void) zil_parse(zilog, zil_incr_blks, zil_replay_log_record, &zr,
            zh->zh_claim_txg);
        vmem_free(zr.zr_lr, 2 * SPA_MAXBLOCKSIZE);

        zil_destroy(zilog, B_FALSE);
        txg_wait_synced(zilog->zl_dmu_pool, zilog->zl_destroy_txg);
        zilog->zl_replay = B_FALSE;
}

boolean_t
zil_replaying(zilog_t *zilog, dmu_tx_t *tx)
{
        if (zilog->zl_sync == ZFS_SYNC_DISABLED)
                return (B_TRUE);

        if (zilog->zl_replay) {
                dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
                zilog->zl_replayed_seq[dmu_tx_get_txg(tx) & TXG_MASK] =
                    zilog->zl_replaying_seq;
                return (B_TRUE);
        }

        return (B_FALSE);
}

/* ARGSUSED */
int
zil_vdev_offline(const char *osname, void *arg)
{
        objset_t *os;
        zilog_t *zilog;
        int error;

        error = dmu_objset_hold(osname, FTAG, &os);
        if (error)
                return (error);

        zilog = dmu_objset_zil(os);
        if (zil_suspend(zilog) != 0)
                error = EEXIST;
        else
                zil_resume(zilog);
        dmu_objset_rele(os, FTAG);
        return (error);
}

#if defined(_KERNEL) && defined(HAVE_SPL)
module_param(zil_replay_disable, int, 0644);
MODULE_PARM_DESC(zil_replay_disable, "Disable intent logging replay");

module_param(zfs_nocacheflush, int, 0644);
MODULE_PARM_DESC(zfs_nocacheflush, "Disable cache flushes");

module_param(zil_slog_limit, ulong, 0644);
MODULE_PARM_DESC(zil_slog_limit, "Max commit bytes to separate log device");
#endif