MFC r213197, r213198:

[FreeBSD/stable/8.git] / sys / cddl / contrib / opensolaris / uts / common / fs / 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 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#include <sys/zfs_context.h>
#include <sys/spa.h>
#include <sys/spa_impl.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.h>
#include <sys/dmu_tx.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:
 */

/*
 * This global ZIL switch affects all pools
 */
int zil_disable = 0;    /* disable intent logging */
SYSCTL_DECL(_vfs_zfs);
TUNABLE_INT("vfs.zfs.zil_disable", &zil_disable);
SYSCTL_INT(_vfs_zfs, OID_AUTO, zil_disable, CTLFLAG_RW, &zil_disable, 0,
    "Disable ZFS Intent Log (ZIL)");

/*
 * 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.
 */
boolean_t zfs_nocacheflush = B_FALSE;
TUNABLE_INT("vfs.zfs.cache_flush_disable", &zfs_nocacheflush);
SYSCTL_INT(_vfs_zfs, OID_AUTO, cache_flush_disable, CTLFLAG_RDTUN,
    &zfs_nocacheflush, 0, "Disable cache flush");

static kmem_cache_t *zil_lwb_cache;

static int
zil_dva_compare(const void *x1, const void *x2)
{
        const dva_t *dva1 = x1;
        const dva_t *dva2 = x2;

        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_dva_tree_init(avl_tree_t *t)
{
        avl_create(t, zil_dva_compare, sizeof (zil_dva_node_t),
            offsetof(zil_dva_node_t, zn_node));
}

static void
zil_dva_tree_fini(avl_tree_t *t)
{
        zil_dva_node_t *zn;
        void *cookie = NULL;

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

        avl_destroy(t);
}

static int
zil_dva_tree_add(avl_tree_t *t, dva_t *dva)
{
        zil_dva_node_t *zn;
        avl_index_t where;

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

        zn = kmem_alloc(sizeof (zil_dva_node_t), KM_SLEEP);
        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, make sure it's valid, and byteswap it if necessary.
 */
static int
zil_read_log_block(zilog_t *zilog, const blkptr_t *bp, arc_buf_t **abufpp)
{
        blkptr_t blk = *bp;
        zbookmark_t zb;
        uint32_t aflags = ARC_WAIT;
        int error;

        zb.zb_objset = bp->blk_cksum.zc_word[ZIL_ZC_OBJSET];
        zb.zb_object = 0;
        zb.zb_level = -1;
        zb.zb_blkid = bp->blk_cksum.zc_word[ZIL_ZC_SEQ];

        *abufpp = NULL;

        /*
         * We shouldn't be doing any scrubbing while we're doing log
         * replay, it's OK to not lock.
         */
        error = arc_read_nolock(NULL, zilog->zl_spa, &blk,
            arc_getbuf_func, abufpp, ZIO_PRIORITY_SYNC_READ, ZIO_FLAG_CANFAIL |
            ZIO_FLAG_SPECULATIVE | ZIO_FLAG_SCRUB, &aflags, &zb);

        if (error == 0) {
                char *data = (*abufpp)->b_data;
                uint64_t blksz = BP_GET_LSIZE(bp);
                zil_trailer_t *ztp = (zil_trailer_t *)(data + blksz) - 1;
                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 (bcmp(&cksum, &ztp->zit_next_blk.blk_cksum,
                    sizeof (cksum)) || BP_IS_HOLE(&ztp->zit_next_blk) ||
                    (ztp->zit_nused > (blksz - sizeof (zil_trailer_t)))) {
                        error = ECKSUM;
                }

                if (error) {
                        VERIFY(arc_buf_remove_ref(*abufpp, abufpp) == 1);
                        *abufpp = NULL;
                }
        }

        dprintf("error %d on %llu:%llu\n", error, zb.zb_objset, zb.zb_blkid);

        return (error);
}

/*
 * Parse the intent log, and call parse_func for each valid record within.
 * Return the highest sequence number.
 */
uint64_t
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;
        uint64_t claim_seq = zh->zh_claim_seq;
        uint64_t seq = 0;
        uint64_t max_seq = 0;
        blkptr_t blk = zh->zh_log;
        arc_buf_t *abuf;
        char *lrbuf, *lrp;
        zil_trailer_t *ztp;
        int reclen, error;

        if (BP_IS_HOLE(&blk))
                return (max_seq);

        /*
         * 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.
         */
        zil_dva_tree_init(&zilog->zl_dva_tree);
        for (;;) {
                seq = blk.blk_cksum.zc_word[ZIL_ZC_SEQ];

                if (claim_seq != 0 && seq > claim_seq)
                        break;

                ASSERT(max_seq < seq);
                max_seq = seq;

                error = zil_read_log_block(zilog, &blk, &abuf);

                if (parse_blk_func != NULL)
                        parse_blk_func(zilog, &blk, arg, txg);

                if (error)
                        break;

                lrbuf = abuf->b_data;
                ztp = (zil_trailer_t *)(lrbuf + BP_GET_LSIZE(&blk)) - 1;
                blk = ztp->zit_next_blk;

                if (parse_lr_func == NULL) {
                        VERIFY(arc_buf_remove_ref(abuf, &abuf) == 1);
                        continue;
                }

                for (lrp = lrbuf; lrp < lrbuf + ztp->zit_nused; lrp += reclen) {
                        lr_t *lr = (lr_t *)lrp;
                        reclen = lr->lrc_reclen;
                        ASSERT3U(reclen, >=, sizeof (lr_t));
                        parse_lr_func(zilog, lr, arg, txg);
                }
                VERIFY(arc_buf_remove_ref(abuf, &abuf) == 1);
        }
        zil_dva_tree_fini(&zilog->zl_dva_tree);

        return (max_seq);
}

/* ARGSUSED */
static void
zil_claim_log_block(zilog_t *zilog, blkptr_t *bp, void *tx, uint64_t first_txg)
{
        spa_t *spa = zilog->zl_spa;
        int err;

        /*
         * Claim log block if not already committed and not already claimed.
         */
        if (bp->blk_birth >= first_txg &&
            zil_dva_tree_add(&zilog->zl_dva_tree, BP_IDENTITY(bp)) == 0) {
                err = zio_wait(zio_claim(NULL, spa, first_txg, bp, NULL, NULL,
                    ZIO_FLAG_MUSTSUCCEED));
                ASSERT(err == 0);
        }
}

static void
zil_claim_log_record(zilog_t *zilog, lr_t *lrc, void *tx, uint64_t first_txg)
{
        if (lrc->lrc_txtype == TX_WRITE) {
                lr_write_t *lr = (lr_write_t *)lrc;
                zil_claim_log_block(zilog, &lr->lr_blkptr, tx, first_txg);
        }
}

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

static void
zil_free_log_record(zilog_t *zilog, lr_t *lrc, void *tx, uint64_t claim_txg)
{
        /*
         * If we previously claimed it, we need to free it.
         */
        if (claim_txg != 0 && lrc->lrc_txtype == TX_WRITE) {
                lr_write_t *lr = (lr_write_t *)lrc;
                blkptr_t *bp = &lr->lr_blkptr;
                if (bp->blk_birth >= claim_txg &&
                    !zil_dva_tree_add(&zilog->zl_dva_tree, BP_IDENTITY(bp))) {
                        (void) arc_free(NULL, zilog->zl_spa,
                            dmu_tx_get_txg(tx), bp, NULL, NULL, ARC_WAIT);
                }
        }
}

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

        /*
         * 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;

        /*
         * If we don't already have an initial log block or we have one
         * but it's the wrong endianness then allocate one.
         */
        if (BP_IS_HOLE(&blk) || BP_SHOULD_BYTESWAP(&blk)) {
                tx = dmu_tx_create(zilog->zl_os);
                (void) dmu_tx_assign(tx, TXG_WAIT);
                dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
                txg = dmu_tx_get_txg(tx);

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

                error = zio_alloc_blk(zilog->zl_spa, ZIL_MIN_BLKSZ, &blk,
                    NULL, txg);

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

        /*
         * Allocate a log write buffer (lwb) for the first log block.
         */
        if (error == 0) {
                lwb = kmem_cache_alloc(zil_lwb_cache, KM_SLEEP);
                lwb->lwb_zilog = zilog;
                lwb->lwb_blk = blk;
                lwb->lwb_nused = 0;
                lwb->lwb_sz = BP_GET_LSIZE(&lwb->lwb_blk);
                lwb->lwb_buf = zio_buf_alloc(lwb->lwb_sz);
                lwb->lwb_max_txg = txg;
                lwb->lwb_zio = NULL;

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

        /*
         * 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);
}

/*
 * 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);

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

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

        mutex_enter(&zilog->zl_lock);

        /*
         * It is possible for the ZIL to get the previously mounted zilog
         * structure of the same dataset if quickly remounted and the dbuf
         * eviction has not completed. In this case we can see a non
         * empty lwb list and keep_first will be set. We fix this by
         * clearing the keep_first. This will be slower but it's very rare.
         */
        if (!list_is_empty(&zilog->zl_lwb_list) && keep_first)
                keep_first = B_FALSE;

        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);
                ASSERT(!keep_first);
                while ((lwb = list_head(&zilog->zl_lwb_list)) != NULL) {
                        list_remove(&zilog->zl_lwb_list, lwb);
                        if (lwb->lwb_buf != NULL)
                                zio_buf_free(lwb->lwb_buf, lwb->lwb_sz);
                        zio_free_blk(zilog->zl_spa, &lwb->lwb_blk, txg);
                        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);
}

/*
 * return true if the initial log block is not valid
 */
static boolean_t
zil_empty(zilog_t *zilog)
{
        const zil_header_t *zh = zilog->zl_header;
        arc_buf_t *abuf = NULL;

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

        if (zil_read_log_block(zilog, &zh->zh_log, &abuf) != 0)
                return (B_TRUE);

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

int
zil_claim(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_open(osname, DMU_OST_ANY, DS_MODE_USER, &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 (zilog->zl_spa->spa_log_state == SPA_LOG_CLEAR) {
                if (!BP_IS_HOLE(&zh->zh_log))
                        zio_free_blk(zilog->zl_spa, &zh->zh_log, first_txg);
                BP_ZERO(&zh->zh_log);
                dsl_dataset_dirty(dmu_objset_ds(os), tx);
        }

        /*
         * Record here whether the zil has any records to replay.
         * If the header block pointer is null or the block points
         * to the stubby then we know there are no valid log records.
         * We use the header to store this state as the the zilog gets
         * freed later in dmu_objset_close().
         * The flags (and the rest of the header fields) are cleared in
         * zil_sync() as a result of a zil_destroy(), after replaying the log.
         *
         * Note, the intent log can be empty but still need the
         * stubby to be claimed.
         */
        if (!zil_empty(zilog)) {
                zh->zh_flags |= ZIL_REPLAY_NEEDED;
                dsl_dataset_dirty(dmu_objset_ds(os), tx);
        }

        /*
         * 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)) {
                zh->zh_claim_txg = first_txg;
                zh->zh_claim_seq = zil_parse(zilog, zil_claim_log_block,
                    zil_claim_log_record, tx, first_txg);
                dsl_dataset_dirty(dmu_objset_ds(os), tx);
        }

        ASSERT3U(first_txg, ==, (spa_last_synced_txg(zilog->zl_spa) + 1));
        dmu_objset_close(os);
        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.
 */
/* ARGSUSED */
int
zil_check_log_chain(char *osname, void *txarg)
{
        zilog_t *zilog;
        zil_header_t *zh;
        blkptr_t blk;
        arc_buf_t *abuf;
        objset_t *os;
        char *lrbuf;
        zil_trailer_t *ztp;
        int error;

        error = dmu_objset_open(osname, DMU_OST_ANY, DS_MODE_USER, &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);
        blk = zh->zh_log;
        if (BP_IS_HOLE(&blk)) {
                dmu_objset_close(os);
                return (0); /* no chain */
        }

        for (;;) {
                error = zil_read_log_block(zilog, &blk, &abuf);
                if (error)
                        break;
                lrbuf = abuf->b_data;
                ztp = (zil_trailer_t *)(lrbuf + BP_GET_LSIZE(&blk)) - 1;
                blk = ztp->zit_next_blk;
                VERIFY(arc_buf_remove_ref(abuf, &abuf) == 1);
        }
        dmu_objset_close(os);
        if (error == ECKSUM)
                return (0); /* normal end of chain */
        return (error);
}

static int
zil_vdev_compare(const void *x1, const void *x2)
{
        uint64_t v1 = ((zil_vdev_node_t *)x1)->zv_vdev;
        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, 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_SLEEP);
                        zv->zv_vdev = zvsearch.zv_vdev;
                        avl_insert(t, zv, where);
                }
        }
        mutex_exit(&zilog->zl_vdev_lock);
}

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;

        ASSERT(BP_GET_COMPRESS(zio->io_bp) == ZIO_COMPRESS_OFF);
        ASSERT(BP_GET_CHECKSUM(zio->io_bp) == ZIO_CHECKSUM_ZILOG);
        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_buf = NULL;
        if (zio->io_error)
                zilog->zl_log_error = B_TRUE;

        /*
         * 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. We still have the
         * zl_lock to ensure zil_sync doesn't kmem free the lwb.
         */
        txg_rele_to_sync(&lwb->lwb_txgh);
        mutex_exit(&zilog->zl_lock);
}

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

        zb.zb_objset = lwb->lwb_blk.blk_cksum.zc_word[ZIL_ZC_OBJSET];
        zb.zb_object = 0;
        zb.zb_level = -1;
        zb.zb_blkid = 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);
        }
        if (lwb->lwb_zio == NULL) {
                lwb->lwb_zio = zio_rewrite(zilog->zl_root_zio, zilog->zl_spa,
                    0, &lwb->lwb_blk, lwb->lwb_buf, lwb->lwb_sz,
                    zil_lwb_write_done, lwb, ZIO_PRIORITY_LOG_WRITE,
                    ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE, &zb);
        }
}

/*
 * 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;
        zil_trailer_t *ztp = (zil_trailer_t *)(lwb->lwb_buf + lwb->lwb_sz) - 1;
        spa_t *spa = zilog->zl_spa;
        blkptr_t *bp = &ztp->zit_next_blk;
        uint64_t txg;
        uint64_t zil_blksz;
        int error;

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

        /*
         * 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 txg_rele_to_sync() until zil_lwb_write_done().
         */
        txg = txg_hold_open(zilog->zl_dmu_pool, &lwb->lwb_txgh);
        txg_rele_to_quiesce(&lwb->lwb_txgh);

        /*
         * Pick a ZIL blocksize. We request a size that is the
         * maximum of the previous used size, the current used size and
         * the amount waiting in the queue.
         */
        zil_blksz = MAX(zilog->zl_prev_used,
            zilog->zl_cur_used + sizeof (*ztp));
        zil_blksz = MAX(zil_blksz, zilog->zl_itx_list_sz + sizeof (*ztp));
        zil_blksz = P2ROUNDUP_TYPED(zil_blksz, ZIL_MIN_BLKSZ, uint64_t);
        if (zil_blksz > ZIL_MAX_BLKSZ)
                zil_blksz = ZIL_MAX_BLKSZ;

        BP_ZERO(bp);
        /* pass the old blkptr in order to spread log blocks across devs */
        error = zio_alloc_blk(spa, zil_blksz, bp, &lwb->lwb_blk, txg);
        if (error) {
                dmu_tx_t *tx = dmu_tx_create_assigned(zilog->zl_dmu_pool, txg);

                /*
                 * We dirty the dataset to ensure that zil_sync() will
                 * be called to remove this lwb from our zl_lwb_list.
                 * Failing to do so, may leave an lwb with a NULL lwb_buf
                 * hanging around on the zl_lwb_list.
                 */
                dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
                dmu_tx_commit(tx);

                /*
                 * Since we've just experienced an allocation failure so we
                 * terminate the current lwb and send it on its way.
                 */
                ztp->zit_pad = 0;
                ztp->zit_nused = lwb->lwb_nused;
                ztp->zit_bt.zbt_cksum = lwb->lwb_blk.blk_cksum;
                zio_nowait(lwb->lwb_zio);

                /*
                 * By returning NULL the caller will call tx_wait_synced()
                 */
                return (NULL);
        }

        ASSERT3U(bp->blk_birth, ==, txg);
        ztp->zit_pad = 0;
        ztp->zit_nused = lwb->lwb_nused;
        ztp->zit_bt.zbt_cksum = lwb->lwb_blk.blk_cksum;
        bp->blk_cksum = lwb->lwb_blk.blk_cksum;
        bp->blk_cksum.zc_word[ZIL_ZC_SEQ]++;

        /*
         * Allocate a new log write buffer (lwb).
         */
        nlwb = kmem_cache_alloc(zil_lwb_cache, KM_SLEEP);

        nlwb->lwb_zilog = zilog;
        nlwb->lwb_blk = *bp;
        nlwb->lwb_nused = 0;
        nlwb->lwb_sz = BP_GET_LSIZE(&nlwb->lwb_blk);
        nlwb->lwb_buf = zio_buf_alloc(nlwb->lwb_sz);
        nlwb->lwb_max_txg = txg;
        nlwb->lwb_zio = NULL;

        /*
         * Put new lwb at the end of the log chain
         */
        mutex_enter(&zilog->zl_lock);
        list_insert_tail(&zilog->zl_lwb_list, nlwb);
        mutex_exit(&zilog->zl_lock);

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

        /*
         * kick off the write for the old log block
         */
        dprintf_bp(&lwb->lwb_blk, "lwb %p txg %llu: ", lwb, txg);
        ASSERT(lwb->lwb_zio);
        zio_nowait(lwb->lwb_zio);

        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 *lr = (lr_write_t *)lrc;
        uint64_t txg = lrc->lrc_txg;
        uint64_t reclen = lrc->lrc_reclen;
        uint64_t dlen;

        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(
                    lr->lr_length, sizeof (uint64_t), uint64_t);
        else
                dlen = 0;

        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 > ZIL_BLK_DATA_SZ(lwb)) {
                lwb = zil_lwb_write_start(zilog, lwb);
                if (lwb == NULL)
                        return (NULL);
                zil_lwb_write_init(zilog, lwb);
                ASSERT(lwb->lwb_nused == 0);
                if (reclen + dlen > ZIL_BLK_DATA_SZ(lwb)) {
                        txg_wait_synced(zilog->zl_dmu_pool, txg);
                        return (lwb);
                }
        }

        /*
         * Update the lrc_seq, to be log record sequence number. See zil.h
         * Then copy the record to the log buffer.
         */
        lrc->lrc_seq = ++zilog->zl_lr_seq; /* we are single threaded */
        bcopy(lrc, lwb->lwb_buf + lwb->lwb_nused, reclen);

        /*
         * 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) {
                        char *dbuf;
                        int error;

                        /* alignment is guaranteed */
                        lr = (lr_write_t *)(lwb->lwb_buf + lwb->lwb_nused);
                        if (dlen) {
                                ASSERT(itx->itx_wr_state == WR_NEED_COPY);
                                dbuf = lwb->lwb_buf + lwb->lwb_nused + reclen;
                                lr->lr_common.lrc_reclen += dlen;
                        } else {
                                ASSERT(itx->itx_wr_state == WR_INDIRECT);
                                dbuf = NULL;
                        }
                        error = zilog->zl_get_data(
                            itx->itx_private, lr, dbuf, lwb->lwb_zio);
                        if (error) {
                                ASSERT(error == ENOENT || error == EEXIST ||
                                    error == EALREADY);
                                return (lwb);
                        }
                }
        }

        lwb->lwb_nused += reclen + dlen;
        lwb->lwb_max_txg = MAX(lwb->lwb_max_txg, txg);
        ASSERT3U(lwb->lwb_nused, <=, ZIL_BLK_DATA_SZ(lwb));
        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_SLEEP);
        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 */

        return (itx);
}

uint64_t
zil_itx_assign(zilog_t *zilog, itx_t *itx, dmu_tx_t *tx)
{
        uint64_t seq;

        ASSERT(itx->itx_lr.lrc_seq == 0);

        mutex_enter(&zilog->zl_lock);
        list_insert_tail(&zilog->zl_itx_list, itx);
        zilog->zl_itx_list_sz += itx->itx_sod;
        itx->itx_lr.lrc_txg = dmu_tx_get_txg(tx);
        itx->itx_lr.lrc_seq = seq = ++zilog->zl_itx_seq;
        mutex_exit(&zilog->zl_lock);

        return (seq);
}

/*
 * Free up all in-memory intent log transactions that have now been synced.
 */
static void
zil_itx_clean(zilog_t *zilog)
{
        uint64_t synced_txg = spa_last_synced_txg(zilog->zl_spa);
        uint64_t freeze_txg = spa_freeze_txg(zilog->zl_spa);
        list_t clean_list;
        itx_t *itx;

        list_create(&clean_list, sizeof (itx_t), offsetof(itx_t, itx_node));

        mutex_enter(&zilog->zl_lock);
        /* wait for a log writer to finish walking list */
        while (zilog->zl_writer) {
                cv_wait(&zilog->zl_cv_writer, &zilog->zl_lock);
        }

        /*
         * Move the sync'd log transactions to a separate list so we can call
         * kmem_free without holding the zl_lock.
         *
         * There is no need to set zl_writer as we don't drop zl_lock here
         */
        while ((itx = list_head(&zilog->zl_itx_list)) != NULL &&
            itx->itx_lr.lrc_txg <= MIN(synced_txg, freeze_txg)) {
                list_remove(&zilog->zl_itx_list, itx);
                zilog->zl_itx_list_sz -= itx->itx_sod;
                list_insert_tail(&clean_list, itx);
        }
        cv_broadcast(&zilog->zl_cv_writer);
        mutex_exit(&zilog->zl_lock);

        /* destroy sync'd log transactions */
        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);
}

/*
 * 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)
{
        itx_t *itx;

        mutex_enter(&zilog->zl_lock);
        itx = list_head(&zilog->zl_itx_list);
        if ((itx != NULL) &&
            (itx->itx_lr.lrc_txg <= spa_last_synced_txg(zilog->zl_spa))) {
                (void) taskq_dispatch(zilog->zl_clean_taskq,
                    (task_func_t *)zil_itx_clean, zilog, TQ_SLEEP);
        }
        mutex_exit(&zilog->zl_lock);
}

static void
zil_commit_writer(zilog_t *zilog, uint64_t seq, uint64_t foid)
{
        uint64_t txg;
        uint64_t commit_seq = 0;
        itx_t *itx, *itx_next = (itx_t *)-1;
        lwb_t *lwb;
        spa_t *spa;

        zilog->zl_writer = B_TRUE;
        ASSERT(zilog->zl_root_zio == NULL);
        spa = zilog->zl_spa;

        if (zilog->zl_suspend) {
                lwb = NULL;
        } else {
                lwb = list_tail(&zilog->zl_lwb_list);
                if (lwb == NULL) {
                        /*
                         * Return if there's nothing to flush before we
                         * dirty the fs by calling zil_create()
                         */
                        if (list_is_empty(&zilog->zl_itx_list)) {
                                zilog->zl_writer = B_FALSE;
                                return;
                        }
                        mutex_exit(&zilog->zl_lock);
                        zil_create(zilog);
                        mutex_enter(&zilog->zl_lock);
                        lwb = list_tail(&zilog->zl_lwb_list);
                }
        }

        /* Loop through in-memory log transactions filling log blocks. */
        DTRACE_PROBE1(zil__cw1, zilog_t *, zilog);
        for (;;) {
                /*
                 * Find the next itx to push:
                 * Push all transactions related to specified foid and all
                 * other transactions except TX_WRITE, TX_TRUNCATE,
                 * TX_SETATTR and TX_ACL for all other files.
                 */
                if (itx_next != (itx_t *)-1)
                        itx = itx_next;
                else
                        itx = list_head(&zilog->zl_itx_list);
                for (; itx != NULL; itx = list_next(&zilog->zl_itx_list, itx)) {
                        if (foid == 0) /* push all foids? */
                                break;
                        if (itx->itx_sync) /* push all O_[D]SYNC */
                                break;
                        switch (itx->itx_lr.lrc_txtype) {
                        case TX_SETATTR:
                        case TX_WRITE:
                        case TX_TRUNCATE:
                        case TX_ACL:
                                /* lr_foid is same offset for these records */
                                if (((lr_write_t *)&itx->itx_lr)->lr_foid
                                    != foid) {
                                        continue; /* skip this record */
                                }
                        }
                        break;
                }
                if (itx == NULL)
                        break;

                if ((itx->itx_lr.lrc_seq > seq) &&
                    ((lwb == NULL) || (lwb->lwb_nused == 0) ||
                    (lwb->lwb_nused + itx->itx_sod > ZIL_BLK_DATA_SZ(lwb)))) {
                        break;
                }

                /*
                 * Save the next pointer.  Even though we soon drop
                 * zl_lock all threads that may change the list
                 * (another writer or zil_itx_clean) can't do so until
                 * they have zl_writer.
                 */
                itx_next = list_next(&zilog->zl_itx_list, itx);
                list_remove(&zilog->zl_itx_list, itx);
                zilog->zl_itx_list_sz -= itx->itx_sod;
                mutex_exit(&zilog->zl_lock);
                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);
                kmem_free(itx, offsetof(itx_t, itx_lr)
                    + itx->itx_lr.lrc_reclen);
                mutex_enter(&zilog->zl_lock);
        }
        DTRACE_PROBE1(zil__cw2, zilog_t *, zilog);
        /* determine commit sequence number */
        itx = list_head(&zilog->zl_itx_list);
        if (itx)
                commit_seq = itx->itx_lr.lrc_seq;
        else
                commit_seq = zilog->zl_itx_seq;
        mutex_exit(&zilog->zl_lock);

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

        zilog->zl_prev_used = zilog->zl_cur_used;
        zilog->zl_cur_used = 0;

        /*
         * Wait if necessary for the log blocks to be on stable storage.
         */
        if (zilog->zl_root_zio) {
                DTRACE_PROBE1(zil__cw3, zilog_t *, zilog);
                (void) zio_wait(zilog->zl_root_zio);
                zilog->zl_root_zio = NULL;
                DTRACE_PROBE1(zil__cw4, zilog_t *, zilog);
                zil_flush_vdevs(zilog);
        }

        if (zilog->zl_log_error || lwb == NULL) {
                zilog->zl_log_error = 0;
                txg_wait_synced(zilog->zl_dmu_pool, 0);
        }

        mutex_enter(&zilog->zl_lock);
        zilog->zl_writer = B_FALSE;

        ASSERT3U(commit_seq, >=, zilog->zl_commit_seq);
        zilog->zl_commit_seq = commit_seq;
}

/*
 * Push zfs transactions to stable storage up to the supplied sequence number.
 * If foid is 0 push out all transactions, otherwise push only those
 * for that file or might have been used to create that file.
 */
void
zil_commit(zilog_t *zilog, uint64_t seq, uint64_t foid)
{
        if (zilog == NULL || seq == 0)
                return;

        mutex_enter(&zilog->zl_lock);

        seq = MIN(seq, zilog->zl_itx_seq);      /* cap seq at largest itx seq */

        while (zilog->zl_writer) {
                cv_wait(&zilog->zl_cv_writer, &zilog->zl_lock);
                if (seq < zilog->zl_commit_seq) {
                        mutex_exit(&zilog->zl_lock);
                        return;
                }
        }
        zil_commit_writer(zilog, seq, foid); /* drops zl_lock */
        /* wake up others waiting on the commit */
        cv_broadcast(&zilog->zl_cv_writer);
        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;
        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);

        zh->zh_replay_seq = zilog->zl_replayed_seq[txg & TXG_MASK];

        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;
                list_remove(&zilog->zl_lwb_list, lwb);
                zio_free_blk(spa, &lwb->lwb_blk, txg);
                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);
        }
        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);
}

void
zil_fini(void)
{
        kmem_cache_destroy(zil_lwb_cache);
}

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

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

        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;

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

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

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

        return (zilog);
}

void
zil_free(zilog_t *zilog)
{
        lwb_t *lwb;

        zilog->zl_stop_sync = 1;

        while ((lwb = list_head(&zilog->zl_lwb_list)) != NULL) {
                list_remove(&zilog->zl_lwb_list, lwb);
                if (lwb->lwb_buf != NULL)
                        zio_buf_free(lwb->lwb_buf, lwb->lwb_sz);
                kmem_cache_free(zil_lwb_cache, lwb);
        }
        list_destroy(&zilog->zl_lwb_list);

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

        ASSERT(list_head(&zilog->zl_itx_list) == NULL);
        list_destroy(&zilog->zl_itx_list);
        mutex_destroy(&zilog->zl_lock);

        cv_destroy(&zilog->zl_cv_writer);
        cv_destroy(&zilog->zl_cv_suspend);

        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);

        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)
{
        /*
         * If the log isn't already committed, mark the objset dirty
         * (so zil_sync() will be called) and wait for that txg to sync.
         */
        if (!zil_is_committed(zilog)) {
                uint64_t txg;
                dmu_tx_t *tx = dmu_tx_create(zilog->zl_os);
                (void) dmu_tx_assign(tx, TXG_WAIT);
                dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
                txg = dmu_tx_get_txg(tx);
                dmu_tx_commit(tx);
                txg_wait_synced(zilog->zl_dmu_pool, txg);
        }

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

        zil_itx_clean(zilog);
        ASSERT(list_head(&zilog->zl_itx_list) == NULL);
}

/*
 * 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, UINT64_MAX, 0);

        /*
         * Wait for any in-flight log writes to complete.
         */
        mutex_enter(&zilog->zl_lock);
        while (zilog->zl_writer)
                cv_wait(&zilog->zl_cv_writer, &zilog->zl_lock);
        mutex_exit(&zilog->zl_lock);

        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);
}

/*
 * Read in the data for the dmu_sync()ed block, and change the log
 * record to write this whole block.
 */
void
zil_get_replay_data(zilog_t *zilog, lr_write_t *lr)
{
        blkptr_t *wbp = &lr->lr_blkptr;
        char *wbuf = (char *)(lr + 1); /* data follows lr_write_t */
        uint64_t blksz;

        if (BP_IS_HOLE(wbp)) {  /* compressed to a hole */
                blksz = BP_GET_LSIZE(&lr->lr_blkptr);
                /*
                 * If the blksz is zero then we must be replaying a log
                 * from an version prior to setting the blksize of null blocks.
                 * So we just zero the actual write size reqeusted.
                 */
                if (blksz == 0) {
                        bzero(wbuf, lr->lr_length);
                        return;
                }
                bzero(wbuf, blksz);
        } else {
                /*
                 * A subsequent write may have overwritten this block, in which
                 * case wbp may have been been freed and reallocated, and our
                 * read of wbp may fail with a checksum error.  We can safely
                 * ignore this because the later write will provide the
                 * correct data.
                 */
                zbookmark_t zb;

                zb.zb_objset = dmu_objset_id(zilog->zl_os);
                zb.zb_object = lr->lr_foid;
                zb.zb_level = 0;
                zb.zb_blkid = -1; /* unknown */

                blksz = BP_GET_LSIZE(&lr->lr_blkptr);
                (void) zio_wait(zio_read(NULL, zilog->zl_spa, wbp, wbuf, blksz,
                    NULL, NULL, ZIO_PRIORITY_SYNC_READ,
                    ZIO_FLAG_CANFAIL | ZIO_FLAG_SPECULATIVE, &zb));
        }
        lr->lr_offset -= lr->lr_offset % blksz;
        lr->lr_length = blksz;
}

typedef struct zil_replay_arg {
        objset_t        *zr_os;
        zil_replay_func_t **zr_replay;
        void            *zr_arg;
        boolean_t       zr_byteswap;
        char            *zr_lrbuf;
} zil_replay_arg_t;

static void
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;
        char *name;
        int pass, error;

        if (!zilog->zl_replay)                  /* giving up */
                return;

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

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

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

        if (txtype == 0 || txtype >= TX_MAX_TYPE) {
                error = EINVAL;
                goto bad;
        }

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

        /*
         * 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 data 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_lrbuf, 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.
         */
        for (pass = 1; pass <= 2; pass++) {
                zilog->zl_replaying_seq = lr->lrc_seq;
                /* Only byteswap (if needed) on the 1st pass.  */
                error = zr->zr_replay[txtype](zr->zr_arg, zr->zr_lrbuf,
                    zr->zr_byteswap && pass == 1);

                if (!error)
                        return;

                /*
                 * 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.
                 */
                if (pass == 1)
                        txg_wait_synced(spa_get_dsl(zilog->zl_spa), 0);
        }

bad:
        ASSERT(error);
        name = kmem_alloc(MAXNAMELEN, KM_SLEEP);
        dmu_objset_name(zr->zr_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)txtype,
            (lr->lrc_txtype & TX_CI) ? "CI" : "");
        zilog->zl_replay = B_FALSE;
        kmem_free(name, MAXNAMELEN);
}

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

/*
 * 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;
        }
        //printf("ZFS: Replaying ZIL on %s...\n", os->os->os_spa->spa_name);

        zr.zr_os = os;
        zr.zr_replay = replay_func;
        zr.zr_arg = arg;
        zr.zr_byteswap = BP_SHOULD_BYTESWAP(&zh->zh_log);
        zr.zr_lrbuf = kmem_alloc(2 * SPA_MAXBLOCKSIZE, KM_SLEEP);

        /*
         * 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 = LBOLT;
        ASSERT(zilog->zl_replay_blks == 0);
        (void) zil_parse(zilog, zil_incr_blks, zil_replay_log_record, &zr,
            zh->zh_claim_txg);
        kmem_free(zr.zr_lrbuf, 2 * SPA_MAXBLOCKSIZE);

        zil_destroy(zilog, B_FALSE);
        txg_wait_synced(zilog->zl_dmu_pool, zilog->zl_destroy_txg);
        zilog->zl_replay = B_FALSE;
        //printf("ZFS: Replay of ZIL on %s finished.\n", os->os->os_spa->spa_name);
}

/*
 * Report whether all transactions are committed
 */
int
zil_is_committed(zilog_t *zilog)
{
        lwb_t *lwb;
        int ret;

        mutex_enter(&zilog->zl_lock);
        while (zilog->zl_writer)
                cv_wait(&zilog->zl_cv_writer, &zilog->zl_lock);

        /* recent unpushed intent log transactions? */
        if (!list_is_empty(&zilog->zl_itx_list)) {
                ret = B_FALSE;
                goto out;
        }

        /* intent log never used? */
        lwb = list_head(&zilog->zl_lwb_list);
        if (lwb == NULL) {
                ret = B_TRUE;
                goto out;
        }

        /*
         * more than 1 log buffer means zil_sync() hasn't yet freed
         * entries after a txg has committed
         */
        if (list_next(&zilog->zl_lwb_list, lwb)) {
                ret = B_FALSE;
                goto out;
        }

        ASSERT(zil_empty(zilog));
        ret = B_TRUE;
out:
        cv_broadcast(&zilog->zl_cv_writer);
        mutex_exit(&zilog->zl_lock);
        return (ret);
}

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

        error = dmu_objset_open(osname, DMU_OST_ANY, DS_MODE_USER, &os);
        if (error)
                return (error);

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