7054 dmu_tx_hold_t should use refcount_t to track space

[unleashed.git] / usr / src / uts / common / fs / zfs / dmu_send.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 2011 Nexenta Systems, Inc. All rights reserved.
 * Copyright (c) 2011, 2015 by Delphix. All rights reserved.
 * Copyright (c) 2014, Joyent, Inc. All rights reserved.
 * Copyright 2014 HybridCluster. All rights reserved.
 * Copyright 2016 RackTop Systems.
 * Copyright (c) 2014 Integros [integros.com]
 */

#include <sys/dmu.h>
#include <sys/dmu_impl.h>
#include <sys/dmu_tx.h>
#include <sys/dbuf.h>
#include <sys/dnode.h>
#include <sys/zfs_context.h>
#include <sys/dmu_objset.h>
#include <sys/dmu_traverse.h>
#include <sys/dsl_dataset.h>
#include <sys/dsl_dir.h>
#include <sys/dsl_prop.h>
#include <sys/dsl_pool.h>
#include <sys/dsl_synctask.h>
#include <sys/zfs_ioctl.h>
#include <sys/zap.h>
#include <sys/zio_checksum.h>
#include <sys/zfs_znode.h>
#include <zfs_fletcher.h>
#include <sys/avl.h>
#include <sys/ddt.h>
#include <sys/zfs_onexit.h>
#include <sys/dmu_send.h>
#include <sys/dsl_destroy.h>
#include <sys/blkptr.h>
#include <sys/dsl_bookmark.h>
#include <sys/zfeature.h>
#include <sys/bqueue.h>

/* Set this tunable to TRUE to replace corrupt data with 0x2f5baddb10c */
int zfs_send_corrupt_data = B_FALSE;
int zfs_send_queue_length = 16 * 1024 * 1024;
int zfs_recv_queue_length = 16 * 1024 * 1024;
/* Set this tunable to FALSE to disable setting of DRR_FLAG_FREERECORDS */
int zfs_send_set_freerecords_bit = B_TRUE;

static char *dmu_recv_tag = "dmu_recv_tag";
const char *recv_clone_name = "%recv";

#define BP_SPAN(datablkszsec, indblkshift, level) \
        (((uint64_t)datablkszsec) << (SPA_MINBLOCKSHIFT + \
        (level) * (indblkshift - SPA_BLKPTRSHIFT)))

static void byteswap_record(dmu_replay_record_t *drr);

struct send_thread_arg {
        bqueue_t        q;
        dsl_dataset_t   *ds;            /* Dataset to traverse */
        uint64_t        fromtxg;        /* Traverse from this txg */
        int             flags;          /* flags to pass to traverse_dataset */
        int             error_code;
        boolean_t       cancel;
        zbookmark_phys_t resume;
};

struct send_block_record {
        boolean_t               eos_marker; /* Marks the end of the stream */
        blkptr_t                bp;
        zbookmark_phys_t        zb;
        uint8_t                 indblkshift;
        uint16_t                datablkszsec;
        bqueue_node_t           ln;
};

static int
dump_bytes(dmu_sendarg_t *dsp, void *buf, int len)
{
        dsl_dataset_t *ds = dmu_objset_ds(dsp->dsa_os);
        ssize_t resid; /* have to get resid to get detailed errno */

        /*
         * The code does not rely on this (len being a multiple of 8).  We keep
         * this assertion because of the corresponding assertion in
         * receive_read().  Keeping this assertion ensures that we do not
         * inadvertently break backwards compatibility (causing the assertion
         * in receive_read() to trigger on old software).
         *
         * Removing the assertions could be rolled into a new feature that uses
         * data that isn't 8-byte aligned; if the assertions were removed, a
         * feature flag would have to be added.
         */

        ASSERT0(len % 8);

        dsp->dsa_err = vn_rdwr(UIO_WRITE, dsp->dsa_vp,
            (caddr_t)buf, len,
            0, UIO_SYSSPACE, FAPPEND, RLIM64_INFINITY, CRED(), &resid);

        mutex_enter(&ds->ds_sendstream_lock);
        *dsp->dsa_off += len;
        mutex_exit(&ds->ds_sendstream_lock);

        return (dsp->dsa_err);
}

/*
 * For all record types except BEGIN, fill in the checksum (overlaid in
 * drr_u.drr_checksum.drr_checksum).  The checksum verifies everything
 * up to the start of the checksum itself.
 */
static int
dump_record(dmu_sendarg_t *dsp, void *payload, int payload_len)
{
        ASSERT3U(offsetof(dmu_replay_record_t, drr_u.drr_checksum.drr_checksum),
            ==, sizeof (dmu_replay_record_t) - sizeof (zio_cksum_t));
        fletcher_4_incremental_native(dsp->dsa_drr,
            offsetof(dmu_replay_record_t, drr_u.drr_checksum.drr_checksum),
            &dsp->dsa_zc);
        if (dsp->dsa_drr->drr_type != DRR_BEGIN) {
                ASSERT(ZIO_CHECKSUM_IS_ZERO(&dsp->dsa_drr->drr_u.
                    drr_checksum.drr_checksum));
                dsp->dsa_drr->drr_u.drr_checksum.drr_checksum = dsp->dsa_zc;
        }
        fletcher_4_incremental_native(&dsp->dsa_drr->
            drr_u.drr_checksum.drr_checksum,
            sizeof (zio_cksum_t), &dsp->dsa_zc);
        if (dump_bytes(dsp, dsp->dsa_drr, sizeof (dmu_replay_record_t)) != 0)
                return (SET_ERROR(EINTR));
        if (payload_len != 0) {
                fletcher_4_incremental_native(payload, payload_len,
                    &dsp->dsa_zc);
                if (dump_bytes(dsp, payload, payload_len) != 0)
                        return (SET_ERROR(EINTR));
        }
        return (0);
}

/*
 * Fill in the drr_free struct, or perform aggregation if the previous record is
 * also a free record, and the two are adjacent.
 *
 * Note that we send free records even for a full send, because we want to be
 * able to receive a full send as a clone, which requires a list of all the free
 * and freeobject records that were generated on the source.
 */
static int
dump_free(dmu_sendarg_t *dsp, uint64_t object, uint64_t offset,
    uint64_t length)
{
        struct drr_free *drrf = &(dsp->dsa_drr->drr_u.drr_free);

        /*
         * When we receive a free record, dbuf_free_range() assumes
         * that the receiving system doesn't have any dbufs in the range
         * being freed.  This is always true because there is a one-record
         * constraint: we only send one WRITE record for any given
         * object,offset.  We know that the one-record constraint is
         * true because we always send data in increasing order by
         * object,offset.
         *
         * If the increasing-order constraint ever changes, we should find
         * another way to assert that the one-record constraint is still
         * satisfied.
         */
        ASSERT(object > dsp->dsa_last_data_object ||
            (object == dsp->dsa_last_data_object &&
            offset > dsp->dsa_last_data_offset));

        if (length != -1ULL && offset + length < offset)
                length = -1ULL;

        /*
         * If there is a pending op, but it's not PENDING_FREE, push it out,
         * since free block aggregation can only be done for blocks of the
         * same type (i.e., DRR_FREE records can only be aggregated with
         * other DRR_FREE records.  DRR_FREEOBJECTS records can only be
         * aggregated with other DRR_FREEOBJECTS records.
         */
        if (dsp->dsa_pending_op != PENDING_NONE &&
            dsp->dsa_pending_op != PENDING_FREE) {
                if (dump_record(dsp, NULL, 0) != 0)
                        return (SET_ERROR(EINTR));
                dsp->dsa_pending_op = PENDING_NONE;
        }

        if (dsp->dsa_pending_op == PENDING_FREE) {
                /*
                 * There should never be a PENDING_FREE if length is -1
                 * (because dump_dnode is the only place where this
                 * function is called with a -1, and only after flushing
                 * any pending record).
                 */
                ASSERT(length != -1ULL);
                /*
                 * Check to see whether this free block can be aggregated
                 * with pending one.
                 */
                if (drrf->drr_object == object && drrf->drr_offset +
                    drrf->drr_length == offset) {
                        drrf->drr_length += length;
                        return (0);
                } else {
                        /* not a continuation.  Push out pending record */
                        if (dump_record(dsp, NULL, 0) != 0)
                                return (SET_ERROR(EINTR));
                        dsp->dsa_pending_op = PENDING_NONE;
                }
        }
        /* create a FREE record and make it pending */
        bzero(dsp->dsa_drr, sizeof (dmu_replay_record_t));
        dsp->dsa_drr->drr_type = DRR_FREE;
        drrf->drr_object = object;
        drrf->drr_offset = offset;
        drrf->drr_length = length;
        drrf->drr_toguid = dsp->dsa_toguid;
        if (length == -1ULL) {
                if (dump_record(dsp, NULL, 0) != 0)
                        return (SET_ERROR(EINTR));
        } else {
                dsp->dsa_pending_op = PENDING_FREE;
        }

        return (0);
}

static int
dump_write(dmu_sendarg_t *dsp, dmu_object_type_t type,
    uint64_t object, uint64_t offset, int blksz, const blkptr_t *bp, void *data)
{
        struct drr_write *drrw = &(dsp->dsa_drr->drr_u.drr_write);

        /*
         * We send data in increasing object, offset order.
         * See comment in dump_free() for details.
         */
        ASSERT(object > dsp->dsa_last_data_object ||
            (object == dsp->dsa_last_data_object &&
            offset > dsp->dsa_last_data_offset));
        dsp->dsa_last_data_object = object;
        dsp->dsa_last_data_offset = offset + blksz - 1;

        /*
         * If there is any kind of pending aggregation (currently either
         * a grouping of free objects or free blocks), push it out to
         * the stream, since aggregation can't be done across operations
         * of different types.
         */
        if (dsp->dsa_pending_op != PENDING_NONE) {
                if (dump_record(dsp, NULL, 0) != 0)
                        return (SET_ERROR(EINTR));
                dsp->dsa_pending_op = PENDING_NONE;
        }
        /* write a WRITE record */
        bzero(dsp->dsa_drr, sizeof (dmu_replay_record_t));
        dsp->dsa_drr->drr_type = DRR_WRITE;
        drrw->drr_object = object;
        drrw->drr_type = type;
        drrw->drr_offset = offset;
        drrw->drr_length = blksz;
        drrw->drr_toguid = dsp->dsa_toguid;
        if (bp == NULL || BP_IS_EMBEDDED(bp)) {
                /*
                 * There's no pre-computed checksum for partial-block
                 * writes or embedded BP's, so (like
                 * fletcher4-checkummed blocks) userland will have to
                 * compute a dedup-capable checksum itself.
                 */
                drrw->drr_checksumtype = ZIO_CHECKSUM_OFF;
        } else {
                drrw->drr_checksumtype = BP_GET_CHECKSUM(bp);
                if (zio_checksum_table[drrw->drr_checksumtype].ci_flags &
                    ZCHECKSUM_FLAG_DEDUP)
                        drrw->drr_checksumflags |= DRR_CHECKSUM_DEDUP;
                DDK_SET_LSIZE(&drrw->drr_key, BP_GET_LSIZE(bp));
                DDK_SET_PSIZE(&drrw->drr_key, BP_GET_PSIZE(bp));
                DDK_SET_COMPRESS(&drrw->drr_key, BP_GET_COMPRESS(bp));
                drrw->drr_key.ddk_cksum = bp->blk_cksum;
        }

        if (dump_record(dsp, data, blksz) != 0)
                return (SET_ERROR(EINTR));
        return (0);
}

static int
dump_write_embedded(dmu_sendarg_t *dsp, uint64_t object, uint64_t offset,
    int blksz, const blkptr_t *bp)
{
        char buf[BPE_PAYLOAD_SIZE];
        struct drr_write_embedded *drrw =
            &(dsp->dsa_drr->drr_u.drr_write_embedded);

        if (dsp->dsa_pending_op != PENDING_NONE) {
                if (dump_record(dsp, NULL, 0) != 0)
                        return (EINTR);
                dsp->dsa_pending_op = PENDING_NONE;
        }

        ASSERT(BP_IS_EMBEDDED(bp));

        bzero(dsp->dsa_drr, sizeof (dmu_replay_record_t));
        dsp->dsa_drr->drr_type = DRR_WRITE_EMBEDDED;
        drrw->drr_object = object;
        drrw->drr_offset = offset;
        drrw->drr_length = blksz;
        drrw->drr_toguid = dsp->dsa_toguid;
        drrw->drr_compression = BP_GET_COMPRESS(bp);
        drrw->drr_etype = BPE_GET_ETYPE(bp);
        drrw->drr_lsize = BPE_GET_LSIZE(bp);
        drrw->drr_psize = BPE_GET_PSIZE(bp);

        decode_embedded_bp_compressed(bp, buf);

        if (dump_record(dsp, buf, P2ROUNDUP(drrw->drr_psize, 8)) != 0)
                return (EINTR);
        return (0);
}

static int
dump_spill(dmu_sendarg_t *dsp, uint64_t object, int blksz, void *data)
{
        struct drr_spill *drrs = &(dsp->dsa_drr->drr_u.drr_spill);

        if (dsp->dsa_pending_op != PENDING_NONE) {
                if (dump_record(dsp, NULL, 0) != 0)
                        return (SET_ERROR(EINTR));
                dsp->dsa_pending_op = PENDING_NONE;
        }

        /* write a SPILL record */
        bzero(dsp->dsa_drr, sizeof (dmu_replay_record_t));
        dsp->dsa_drr->drr_type = DRR_SPILL;
        drrs->drr_object = object;
        drrs->drr_length = blksz;
        drrs->drr_toguid = dsp->dsa_toguid;

        if (dump_record(dsp, data, blksz) != 0)
                return (SET_ERROR(EINTR));
        return (0);
}

static int
dump_freeobjects(dmu_sendarg_t *dsp, uint64_t firstobj, uint64_t numobjs)
{
        struct drr_freeobjects *drrfo = &(dsp->dsa_drr->drr_u.drr_freeobjects);

        /*
         * If there is a pending op, but it's not PENDING_FREEOBJECTS,
         * push it out, since free block aggregation can only be done for
         * blocks of the same type (i.e., DRR_FREE records can only be
         * aggregated with other DRR_FREE records.  DRR_FREEOBJECTS records
         * can only be aggregated with other DRR_FREEOBJECTS records.
         */
        if (dsp->dsa_pending_op != PENDING_NONE &&
            dsp->dsa_pending_op != PENDING_FREEOBJECTS) {
                if (dump_record(dsp, NULL, 0) != 0)
                        return (SET_ERROR(EINTR));
                dsp->dsa_pending_op = PENDING_NONE;
        }
        if (dsp->dsa_pending_op == PENDING_FREEOBJECTS) {
                /*
                 * See whether this free object array can be aggregated
                 * with pending one
                 */
                if (drrfo->drr_firstobj + drrfo->drr_numobjs == firstobj) {
                        drrfo->drr_numobjs += numobjs;
                        return (0);
                } else {
                        /* can't be aggregated.  Push out pending record */
                        if (dump_record(dsp, NULL, 0) != 0)
                                return (SET_ERROR(EINTR));
                        dsp->dsa_pending_op = PENDING_NONE;
                }
        }

        /* write a FREEOBJECTS record */
        bzero(dsp->dsa_drr, sizeof (dmu_replay_record_t));
        dsp->dsa_drr->drr_type = DRR_FREEOBJECTS;
        drrfo->drr_firstobj = firstobj;
        drrfo->drr_numobjs = numobjs;
        drrfo->drr_toguid = dsp->dsa_toguid;

        dsp->dsa_pending_op = PENDING_FREEOBJECTS;

        return (0);
}

static int
dump_dnode(dmu_sendarg_t *dsp, uint64_t object, dnode_phys_t *dnp)
{
        struct drr_object *drro = &(dsp->dsa_drr->drr_u.drr_object);

        if (object < dsp->dsa_resume_object) {
                /*
                 * Note: when resuming, we will visit all the dnodes in
                 * the block of dnodes that we are resuming from.  In
                 * this case it's unnecessary to send the dnodes prior to
                 * the one we are resuming from.  We should be at most one
                 * block's worth of dnodes behind the resume point.
                 */
                ASSERT3U(dsp->dsa_resume_object - object, <,
                    1 << (DNODE_BLOCK_SHIFT - DNODE_SHIFT));
                return (0);
        }

        if (dnp == NULL || dnp->dn_type == DMU_OT_NONE)
                return (dump_freeobjects(dsp, object, 1));

        if (dsp->dsa_pending_op != PENDING_NONE) {
                if (dump_record(dsp, NULL, 0) != 0)
                        return (SET_ERROR(EINTR));
                dsp->dsa_pending_op = PENDING_NONE;
        }

        /* write an OBJECT record */
        bzero(dsp->dsa_drr, sizeof (dmu_replay_record_t));
        dsp->dsa_drr->drr_type = DRR_OBJECT;
        drro->drr_object = object;
        drro->drr_type = dnp->dn_type;
        drro->drr_bonustype = dnp->dn_bonustype;
        drro->drr_blksz = dnp->dn_datablkszsec << SPA_MINBLOCKSHIFT;
        drro->drr_bonuslen = dnp->dn_bonuslen;
        drro->drr_checksumtype = dnp->dn_checksum;
        drro->drr_compress = dnp->dn_compress;
        drro->drr_toguid = dsp->dsa_toguid;

        if (!(dsp->dsa_featureflags & DMU_BACKUP_FEATURE_LARGE_BLOCKS) &&
            drro->drr_blksz > SPA_OLD_MAXBLOCKSIZE)
                drro->drr_blksz = SPA_OLD_MAXBLOCKSIZE;

        if (dump_record(dsp, DN_BONUS(dnp),
            P2ROUNDUP(dnp->dn_bonuslen, 8)) != 0) {
                return (SET_ERROR(EINTR));
        }

        /* Free anything past the end of the file. */
        if (dump_free(dsp, object, (dnp->dn_maxblkid + 1) *
            (dnp->dn_datablkszsec << SPA_MINBLOCKSHIFT), -1ULL) != 0)
                return (SET_ERROR(EINTR));
        if (dsp->dsa_err != 0)
                return (SET_ERROR(EINTR));
        return (0);
}

static boolean_t
backup_do_embed(dmu_sendarg_t *dsp, const blkptr_t *bp)
{
        if (!BP_IS_EMBEDDED(bp))
                return (B_FALSE);

        /*
         * Compression function must be legacy, or explicitly enabled.
         */
        if ((BP_GET_COMPRESS(bp) >= ZIO_COMPRESS_LEGACY_FUNCTIONS &&
            !(dsp->dsa_featureflags & DMU_BACKUP_FEATURE_EMBED_DATA_LZ4)))
                return (B_FALSE);

        /*
         * Embed type must be explicitly enabled.
         */
        switch (BPE_GET_ETYPE(bp)) {
        case BP_EMBEDDED_TYPE_DATA:
                if (dsp->dsa_featureflags & DMU_BACKUP_FEATURE_EMBED_DATA)
                        return (B_TRUE);
                break;
        default:
                return (B_FALSE);
        }
        return (B_FALSE);
}

/*
 * This is the callback function to traverse_dataset that acts as the worker
 * thread for dmu_send_impl.
 */
/*ARGSUSED*/
static int
send_cb(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
    const zbookmark_phys_t *zb, const struct dnode_phys *dnp, void *arg)
{
        struct send_thread_arg *sta = arg;
        struct send_block_record *record;
        uint64_t record_size;
        int err = 0;

        ASSERT(zb->zb_object == DMU_META_DNODE_OBJECT ||
            zb->zb_object >= sta->resume.zb_object);

        if (sta->cancel)
                return (SET_ERROR(EINTR));

        if (bp == NULL) {
                ASSERT3U(zb->zb_level, ==, ZB_DNODE_LEVEL);
                return (0);
        } else if (zb->zb_level < 0) {
                return (0);
        }

        record = kmem_zalloc(sizeof (struct send_block_record), KM_SLEEP);
        record->eos_marker = B_FALSE;
        record->bp = *bp;
        record->zb = *zb;
        record->indblkshift = dnp->dn_indblkshift;
        record->datablkszsec = dnp->dn_datablkszsec;
        record_size = dnp->dn_datablkszsec << SPA_MINBLOCKSHIFT;
        bqueue_enqueue(&sta->q, record, record_size);

        return (err);
}

/*
 * This function kicks off the traverse_dataset.  It also handles setting the
 * error code of the thread in case something goes wrong, and pushes the End of
 * Stream record when the traverse_dataset call has finished.  If there is no
 * dataset to traverse, the thread immediately pushes End of Stream marker.
 */
static void
send_traverse_thread(void *arg)
{
        struct send_thread_arg *st_arg = arg;
        int err;
        struct send_block_record *data;

        if (st_arg->ds != NULL) {
                err = traverse_dataset_resume(st_arg->ds,
                    st_arg->fromtxg, &st_arg->resume,
                    st_arg->flags, send_cb, st_arg);

                if (err != EINTR)
                        st_arg->error_code = err;
        }
        data = kmem_zalloc(sizeof (*data), KM_SLEEP);
        data->eos_marker = B_TRUE;
        bqueue_enqueue(&st_arg->q, data, 1);
}

/*
 * This function actually handles figuring out what kind of record needs to be
 * dumped, reading the data (which has hopefully been prefetched), and calling
 * the appropriate helper function.
 */
static int
do_dump(dmu_sendarg_t *dsa, struct send_block_record *data)
{
        dsl_dataset_t *ds = dmu_objset_ds(dsa->dsa_os);
        const blkptr_t *bp = &data->bp;
        const zbookmark_phys_t *zb = &data->zb;
        uint8_t indblkshift = data->indblkshift;
        uint16_t dblkszsec = data->datablkszsec;
        spa_t *spa = ds->ds_dir->dd_pool->dp_spa;
        dmu_object_type_t type = bp ? BP_GET_TYPE(bp) : DMU_OT_NONE;
        int err = 0;

        ASSERT3U(zb->zb_level, >=, 0);

        ASSERT(zb->zb_object == DMU_META_DNODE_OBJECT ||
            zb->zb_object >= dsa->dsa_resume_object);

        if (zb->zb_object != DMU_META_DNODE_OBJECT &&
            DMU_OBJECT_IS_SPECIAL(zb->zb_object)) {
                return (0);
        } else if (BP_IS_HOLE(bp) &&
            zb->zb_object == DMU_META_DNODE_OBJECT) {
                uint64_t span = BP_SPAN(dblkszsec, indblkshift, zb->zb_level);
                uint64_t dnobj = (zb->zb_blkid * span) >> DNODE_SHIFT;
                err = dump_freeobjects(dsa, dnobj, span >> DNODE_SHIFT);
        } else if (BP_IS_HOLE(bp)) {
                uint64_t span = BP_SPAN(dblkszsec, indblkshift, zb->zb_level);
                uint64_t offset = zb->zb_blkid * span;
                err = dump_free(dsa, zb->zb_object, offset, span);
        } else if (zb->zb_level > 0 || type == DMU_OT_OBJSET) {
                return (0);
        } else if (type == DMU_OT_DNODE) {
                int blksz = BP_GET_LSIZE(bp);
                arc_flags_t aflags = ARC_FLAG_WAIT;
                arc_buf_t *abuf;

                ASSERT0(zb->zb_level);

                if (arc_read(NULL, spa, bp, arc_getbuf_func, &abuf,
                    ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL,
                    &aflags, zb) != 0)
                        return (SET_ERROR(EIO));

                dnode_phys_t *blk = abuf->b_data;
                uint64_t dnobj = zb->zb_blkid * (blksz >> DNODE_SHIFT);
                for (int i = 0; i < blksz >> DNODE_SHIFT; i++) {
                        err = dump_dnode(dsa, dnobj + i, blk + i);
                        if (err != 0)
                                break;
                }
                (void) arc_buf_remove_ref(abuf, &abuf);
        } else if (type == DMU_OT_SA) {
                arc_flags_t aflags = ARC_FLAG_WAIT;
                arc_buf_t *abuf;
                int blksz = BP_GET_LSIZE(bp);

                if (arc_read(NULL, spa, bp, arc_getbuf_func, &abuf,
                    ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL,
                    &aflags, zb) != 0)
                        return (SET_ERROR(EIO));

                err = dump_spill(dsa, zb->zb_object, blksz, abuf->b_data);
                (void) arc_buf_remove_ref(abuf, &abuf);
        } else if (backup_do_embed(dsa, bp)) {
                /* it's an embedded level-0 block of a regular object */
                int blksz = dblkszsec << SPA_MINBLOCKSHIFT;
                ASSERT0(zb->zb_level);
                err = dump_write_embedded(dsa, zb->zb_object,
                    zb->zb_blkid * blksz, blksz, bp);
        } else {
                /* it's a level-0 block of a regular object */
                arc_flags_t aflags = ARC_FLAG_WAIT;
                arc_buf_t *abuf;
                int blksz = dblkszsec << SPA_MINBLOCKSHIFT;
                uint64_t offset;

                ASSERT0(zb->zb_level);
                ASSERT(zb->zb_object > dsa->dsa_resume_object ||
                    (zb->zb_object == dsa->dsa_resume_object &&
                    zb->zb_blkid * blksz >= dsa->dsa_resume_offset));

                if (arc_read(NULL, spa, bp, arc_getbuf_func, &abuf,
                    ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL,
                    &aflags, zb) != 0) {
                        if (zfs_send_corrupt_data) {
                                /* Send a block filled with 0x"zfs badd bloc" */
                                abuf = arc_buf_alloc(spa, blksz, &abuf,
                                    ARC_BUFC_DATA);
                                uint64_t *ptr;
                                for (ptr = abuf->b_data;
                                    (char *)ptr < (char *)abuf->b_data + blksz;
                                    ptr++)
                                        *ptr = 0x2f5baddb10cULL;
                        } else {
                                return (SET_ERROR(EIO));
                        }
                }

                offset = zb->zb_blkid * blksz;

                if (!(dsa->dsa_featureflags &
                    DMU_BACKUP_FEATURE_LARGE_BLOCKS) &&
                    blksz > SPA_OLD_MAXBLOCKSIZE) {
                        char *buf = abuf->b_data;
                        while (blksz > 0 && err == 0) {
                                int n = MIN(blksz, SPA_OLD_MAXBLOCKSIZE);
                                err = dump_write(dsa, type, zb->zb_object,
                                    offset, n, NULL, buf);
                                offset += n;
                                buf += n;
                                blksz -= n;
                        }
                } else {
                        err = dump_write(dsa, type, zb->zb_object,
                            offset, blksz, bp, abuf->b_data);
                }
                (void) arc_buf_remove_ref(abuf, &abuf);
        }

        ASSERT(err == 0 || err == EINTR);
        return (err);
}

/*
 * Pop the new data off the queue, and free the old data.
 */
static struct send_block_record *
get_next_record(bqueue_t *bq, struct send_block_record *data)
{
        struct send_block_record *tmp = bqueue_dequeue(bq);
        kmem_free(data, sizeof (*data));
        return (tmp);
}

/*
 * Actually do the bulk of the work in a zfs send.
 *
 * Note: Releases dp using the specified tag.
 */
static int
dmu_send_impl(void *tag, dsl_pool_t *dp, dsl_dataset_t *to_ds,
    zfs_bookmark_phys_t *ancestor_zb,
    boolean_t is_clone, boolean_t embedok, boolean_t large_block_ok, int outfd,
    uint64_t resumeobj, uint64_t resumeoff,
    vnode_t *vp, offset_t *off)
{
        objset_t *os;
        dmu_replay_record_t *drr;
        dmu_sendarg_t *dsp;
        int err;
        uint64_t fromtxg = 0;
        uint64_t featureflags = 0;
        struct send_thread_arg to_arg = { 0 };

        err = dmu_objset_from_ds(to_ds, &os);
        if (err != 0) {
                dsl_pool_rele(dp, tag);
                return (err);
        }

        drr = kmem_zalloc(sizeof (dmu_replay_record_t), KM_SLEEP);
        drr->drr_type = DRR_BEGIN;
        drr->drr_u.drr_begin.drr_magic = DMU_BACKUP_MAGIC;
        DMU_SET_STREAM_HDRTYPE(drr->drr_u.drr_begin.drr_versioninfo,
            DMU_SUBSTREAM);

#ifdef _KERNEL
        if (dmu_objset_type(os) == DMU_OST_ZFS) {
                uint64_t version;
                if (zfs_get_zplprop(os, ZFS_PROP_VERSION, &version) != 0) {
                        kmem_free(drr, sizeof (dmu_replay_record_t));
                        dsl_pool_rele(dp, tag);
                        return (SET_ERROR(EINVAL));
                }
                if (version >= ZPL_VERSION_SA) {
                        featureflags |= DMU_BACKUP_FEATURE_SA_SPILL;
                }
        }
#endif

        if (large_block_ok && to_ds->ds_feature_inuse[SPA_FEATURE_LARGE_BLOCKS])
                featureflags |= DMU_BACKUP_FEATURE_LARGE_BLOCKS;
        if (embedok &&
            spa_feature_is_active(dp->dp_spa, SPA_FEATURE_EMBEDDED_DATA)) {
                featureflags |= DMU_BACKUP_FEATURE_EMBED_DATA;
                if (spa_feature_is_active(dp->dp_spa, SPA_FEATURE_LZ4_COMPRESS))
                        featureflags |= DMU_BACKUP_FEATURE_EMBED_DATA_LZ4;
        }

        if (resumeobj != 0 || resumeoff != 0) {
                featureflags |= DMU_BACKUP_FEATURE_RESUMING;
        }

        DMU_SET_FEATUREFLAGS(drr->drr_u.drr_begin.drr_versioninfo,
            featureflags);

        drr->drr_u.drr_begin.drr_creation_time =
            dsl_dataset_phys(to_ds)->ds_creation_time;
        drr->drr_u.drr_begin.drr_type = dmu_objset_type(os);
        if (is_clone)
                drr->drr_u.drr_begin.drr_flags |= DRR_FLAG_CLONE;
        drr->drr_u.drr_begin.drr_toguid = dsl_dataset_phys(to_ds)->ds_guid;
        if (dsl_dataset_phys(to_ds)->ds_flags & DS_FLAG_CI_DATASET)
                drr->drr_u.drr_begin.drr_flags |= DRR_FLAG_CI_DATA;
        if (zfs_send_set_freerecords_bit)
                drr->drr_u.drr_begin.drr_flags |= DRR_FLAG_FREERECORDS;

        if (ancestor_zb != NULL) {
                drr->drr_u.drr_begin.drr_fromguid =
                    ancestor_zb->zbm_guid;
                fromtxg = ancestor_zb->zbm_creation_txg;
        }
        dsl_dataset_name(to_ds, drr->drr_u.drr_begin.drr_toname);
        if (!to_ds->ds_is_snapshot) {
                (void) strlcat(drr->drr_u.drr_begin.drr_toname, "@--head--",
                    sizeof (drr->drr_u.drr_begin.drr_toname));
        }

        dsp = kmem_zalloc(sizeof (dmu_sendarg_t), KM_SLEEP);

        dsp->dsa_drr = drr;
        dsp->dsa_vp = vp;
        dsp->dsa_outfd = outfd;
        dsp->dsa_proc = curproc;
        dsp->dsa_os = os;
        dsp->dsa_off = off;
        dsp->dsa_toguid = dsl_dataset_phys(to_ds)->ds_guid;
        dsp->dsa_pending_op = PENDING_NONE;
        dsp->dsa_featureflags = featureflags;
        dsp->dsa_resume_object = resumeobj;
        dsp->dsa_resume_offset = resumeoff;

        mutex_enter(&to_ds->ds_sendstream_lock);
        list_insert_head(&to_ds->ds_sendstreams, dsp);
        mutex_exit(&to_ds->ds_sendstream_lock);

        dsl_dataset_long_hold(to_ds, FTAG);
        dsl_pool_rele(dp, tag);

        void *payload = NULL;
        size_t payload_len = 0;
        if (resumeobj != 0 || resumeoff != 0) {
                dmu_object_info_t to_doi;
                err = dmu_object_info(os, resumeobj, &to_doi);
                if (err != 0)
                        goto out;
                SET_BOOKMARK(&to_arg.resume, to_ds->ds_object, resumeobj, 0,
                    resumeoff / to_doi.doi_data_block_size);

                nvlist_t *nvl = fnvlist_alloc();
                fnvlist_add_uint64(nvl, "resume_object", resumeobj);
                fnvlist_add_uint64(nvl, "resume_offset", resumeoff);
                payload = fnvlist_pack(nvl, &payload_len);
                drr->drr_payloadlen = payload_len;
                fnvlist_free(nvl);
        }

        err = dump_record(dsp, payload, payload_len);
        fnvlist_pack_free(payload, payload_len);
        if (err != 0) {
                err = dsp->dsa_err;
                goto out;
        }

        err = bqueue_init(&to_arg.q, zfs_send_queue_length,
            offsetof(struct send_block_record, ln));
        to_arg.error_code = 0;
        to_arg.cancel = B_FALSE;
        to_arg.ds = to_ds;
        to_arg.fromtxg = fromtxg;
        to_arg.flags = TRAVERSE_PRE | TRAVERSE_PREFETCH;
        (void) thread_create(NULL, 0, send_traverse_thread, &to_arg, 0, curproc,
            TS_RUN, minclsyspri);

        struct send_block_record *to_data;
        to_data = bqueue_dequeue(&to_arg.q);

        while (!to_data->eos_marker && err == 0) {
                err = do_dump(dsp, to_data);
                to_data = get_next_record(&to_arg.q, to_data);
                if (issig(JUSTLOOKING) && issig(FORREAL))
                        err = EINTR;
        }

        if (err != 0) {
                to_arg.cancel = B_TRUE;
                while (!to_data->eos_marker) {
                        to_data = get_next_record(&to_arg.q, to_data);
                }
        }
        kmem_free(to_data, sizeof (*to_data));

        bqueue_destroy(&to_arg.q);

        if (err == 0 && to_arg.error_code != 0)
                err = to_arg.error_code;

        if (err != 0)
                goto out;

        if (dsp->dsa_pending_op != PENDING_NONE)
                if (dump_record(dsp, NULL, 0) != 0)
                        err = SET_ERROR(EINTR);

        if (err != 0) {
                if (err == EINTR && dsp->dsa_err != 0)
                        err = dsp->dsa_err;
                goto out;
        }

        bzero(drr, sizeof (dmu_replay_record_t));
        drr->drr_type = DRR_END;
        drr->drr_u.drr_end.drr_checksum = dsp->dsa_zc;
        drr->drr_u.drr_end.drr_toguid = dsp->dsa_toguid;

        if (dump_record(dsp, NULL, 0) != 0)
                err = dsp->dsa_err;

out:
        mutex_enter(&to_ds->ds_sendstream_lock);
        list_remove(&to_ds->ds_sendstreams, dsp);
        mutex_exit(&to_ds->ds_sendstream_lock);

        kmem_free(drr, sizeof (dmu_replay_record_t));
        kmem_free(dsp, sizeof (dmu_sendarg_t));

        dsl_dataset_long_rele(to_ds, FTAG);

        return (err);
}

int
dmu_send_obj(const char *pool, uint64_t tosnap, uint64_t fromsnap,
    boolean_t embedok, boolean_t large_block_ok,
    int outfd, vnode_t *vp, offset_t *off)
{
        dsl_pool_t *dp;
        dsl_dataset_t *ds;
        dsl_dataset_t *fromds = NULL;
        int err;

        err = dsl_pool_hold(pool, FTAG, &dp);
        if (err != 0)
                return (err);

        err = dsl_dataset_hold_obj(dp, tosnap, FTAG, &ds);
        if (err != 0) {
                dsl_pool_rele(dp, FTAG);
                return (err);
        }

        if (fromsnap != 0) {
                zfs_bookmark_phys_t zb;
                boolean_t is_clone;

                err = dsl_dataset_hold_obj(dp, fromsnap, FTAG, &fromds);
                if (err != 0) {
                        dsl_dataset_rele(ds, FTAG);
                        dsl_pool_rele(dp, FTAG);
                        return (err);
                }
                if (!dsl_dataset_is_before(ds, fromds, 0))
                        err = SET_ERROR(EXDEV);
                zb.zbm_creation_time =
                    dsl_dataset_phys(fromds)->ds_creation_time;
                zb.zbm_creation_txg = dsl_dataset_phys(fromds)->ds_creation_txg;
                zb.zbm_guid = dsl_dataset_phys(fromds)->ds_guid;
                is_clone = (fromds->ds_dir != ds->ds_dir);
                dsl_dataset_rele(fromds, FTAG);
                err = dmu_send_impl(FTAG, dp, ds, &zb, is_clone,
                    embedok, large_block_ok, outfd, 0, 0, vp, off);
        } else {
                err = dmu_send_impl(FTAG, dp, ds, NULL, B_FALSE,
                    embedok, large_block_ok, outfd, 0, 0, vp, off);
        }
        dsl_dataset_rele(ds, FTAG);
        return (err);
}

int
dmu_send(const char *tosnap, const char *fromsnap, boolean_t embedok,
    boolean_t large_block_ok, int outfd, uint64_t resumeobj, uint64_t resumeoff,
    vnode_t *vp, offset_t *off)
{
        dsl_pool_t *dp;
        dsl_dataset_t *ds;
        int err;
        boolean_t owned = B_FALSE;

        if (fromsnap != NULL && strpbrk(fromsnap, "@#") == NULL)
                return (SET_ERROR(EINVAL));

        err = dsl_pool_hold(tosnap, FTAG, &dp);
        if (err != 0)
                return (err);

        if (strchr(tosnap, '@') == NULL && spa_writeable(dp->dp_spa)) {
                /*
                 * We are sending a filesystem or volume.  Ensure
                 * that it doesn't change by owning the dataset.
                 */
                err = dsl_dataset_own(dp, tosnap, FTAG, &ds);
                owned = B_TRUE;
        } else {
                err = dsl_dataset_hold(dp, tosnap, FTAG, &ds);
        }
        if (err != 0) {
                dsl_pool_rele(dp, FTAG);
                return (err);
        }

        if (fromsnap != NULL) {
                zfs_bookmark_phys_t zb;
                boolean_t is_clone = B_FALSE;
                int fsnamelen = strchr(tosnap, '@') - tosnap;

                /*
                 * If the fromsnap is in a different filesystem, then
                 * mark the send stream as a clone.
                 */
                if (strncmp(tosnap, fromsnap, fsnamelen) != 0 ||
                    (fromsnap[fsnamelen] != '@' &&
                    fromsnap[fsnamelen] != '#')) {
                        is_clone = B_TRUE;
                }

                if (strchr(fromsnap, '@')) {
                        dsl_dataset_t *fromds;
                        err = dsl_dataset_hold(dp, fromsnap, FTAG, &fromds);
                        if (err == 0) {
                                if (!dsl_dataset_is_before(ds, fromds, 0))
                                        err = SET_ERROR(EXDEV);
                                zb.zbm_creation_time =
                                    dsl_dataset_phys(fromds)->ds_creation_time;
                                zb.zbm_creation_txg =
                                    dsl_dataset_phys(fromds)->ds_creation_txg;
                                zb.zbm_guid = dsl_dataset_phys(fromds)->ds_guid;
                                is_clone = (ds->ds_dir != fromds->ds_dir);
                                dsl_dataset_rele(fromds, FTAG);
                        }
                } else {
                        err = dsl_bookmark_lookup(dp, fromsnap, ds, &zb);
                }
                if (err != 0) {
                        dsl_dataset_rele(ds, FTAG);
                        dsl_pool_rele(dp, FTAG);
                        return (err);
                }
                err = dmu_send_impl(FTAG, dp, ds, &zb, is_clone,
                    embedok, large_block_ok,
                    outfd, resumeobj, resumeoff, vp, off);
        } else {
                err = dmu_send_impl(FTAG, dp, ds, NULL, B_FALSE,
                    embedok, large_block_ok,
                    outfd, resumeobj, resumeoff, vp, off);
        }
        if (owned)
                dsl_dataset_disown(ds, FTAG);
        else
                dsl_dataset_rele(ds, FTAG);
        return (err);
}

static int
dmu_adjust_send_estimate_for_indirects(dsl_dataset_t *ds, uint64_t size,
    uint64_t *sizep)
{
        int err;
        /*
         * Assume that space (both on-disk and in-stream) is dominated by
         * data.  We will adjust for indirect blocks and the copies property,
         * but ignore per-object space used (eg, dnodes and DRR_OBJECT records).
         */

        /*
         * Subtract out approximate space used by indirect blocks.
         * Assume most space is used by data blocks (non-indirect, non-dnode).
         * Assume all blocks are recordsize.  Assume ditto blocks and
         * internal fragmentation counter out compression.
         *
         * Therefore, space used by indirect blocks is sizeof(blkptr_t) per
         * block, which we observe in practice.
         */
        uint64_t recordsize;
        err = dsl_prop_get_int_ds(ds, "recordsize", &recordsize);
        if (err != 0)
                return (err);
        size -= size / recordsize * sizeof (blkptr_t);

        /* Add in the space for the record associated with each block. */
        size += size / recordsize * sizeof (dmu_replay_record_t);

        *sizep = size;

        return (0);
}

int
dmu_send_estimate(dsl_dataset_t *ds, dsl_dataset_t *fromds, uint64_t *sizep)
{
        dsl_pool_t *dp = ds->ds_dir->dd_pool;
        int err;
        uint64_t size;

        ASSERT(dsl_pool_config_held(dp));

        /* tosnap must be a snapshot */
        if (!ds->ds_is_snapshot)
                return (SET_ERROR(EINVAL));

        /* fromsnap, if provided, must be a snapshot */
        if (fromds != NULL && !fromds->ds_is_snapshot)
                return (SET_ERROR(EINVAL));

        /*
         * fromsnap must be an earlier snapshot from the same fs as tosnap,
         * or the origin's fs.
         */
        if (fromds != NULL && !dsl_dataset_is_before(ds, fromds, 0))
                return (SET_ERROR(EXDEV));

        /* Get uncompressed size estimate of changed data. */
        if (fromds == NULL) {
                size = dsl_dataset_phys(ds)->ds_uncompressed_bytes;
        } else {
                uint64_t used, comp;
                err = dsl_dataset_space_written(fromds, ds,
                    &used, &comp, &size);
                if (err != 0)
                        return (err);
        }

        err = dmu_adjust_send_estimate_for_indirects(ds, size, sizep);
        return (err);
}

/*
 * Simple callback used to traverse the blocks of a snapshot and sum their
 * uncompressed size
 */
/* ARGSUSED */
static int
dmu_calculate_send_traversal(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
    const zbookmark_phys_t *zb, const dnode_phys_t *dnp, void *arg)
{
        uint64_t *spaceptr = arg;
        if (bp != NULL && !BP_IS_HOLE(bp)) {
                *spaceptr += BP_GET_UCSIZE(bp);
        }
        return (0);
}

/*
 * Given a desination snapshot and a TXG, calculate the approximate size of a
 * send stream sent from that TXG. from_txg may be zero, indicating that the
 * whole snapshot will be sent.
 */
int
dmu_send_estimate_from_txg(dsl_dataset_t *ds, uint64_t from_txg,
    uint64_t *sizep)
{
        dsl_pool_t *dp = ds->ds_dir->dd_pool;
        int err;
        uint64_t size = 0;

        ASSERT(dsl_pool_config_held(dp));

        /* tosnap must be a snapshot */
        if (!dsl_dataset_is_snapshot(ds))
                return (SET_ERROR(EINVAL));

        /* verify that from_txg is before the provided snapshot was taken */
        if (from_txg >= dsl_dataset_phys(ds)->ds_creation_txg) {
                return (SET_ERROR(EXDEV));
        }

        /*
         * traverse the blocks of the snapshot with birth times after
         * from_txg, summing their uncompressed size
         */
        err = traverse_dataset(ds, from_txg, TRAVERSE_POST,
            dmu_calculate_send_traversal, &size);
        if (err)
                return (err);

        err = dmu_adjust_send_estimate_for_indirects(ds, size, sizep);
        return (err);
}

typedef struct dmu_recv_begin_arg {
        const char *drba_origin;
        dmu_recv_cookie_t *drba_cookie;
        cred_t *drba_cred;
        uint64_t drba_snapobj;
} dmu_recv_begin_arg_t;

static int
recv_begin_check_existing_impl(dmu_recv_begin_arg_t *drba, dsl_dataset_t *ds,
    uint64_t fromguid)
{
        uint64_t val;
        int error;
        dsl_pool_t *dp = ds->ds_dir->dd_pool;

        /* temporary clone name must not exist */
        error = zap_lookup(dp->dp_meta_objset,
            dsl_dir_phys(ds->ds_dir)->dd_child_dir_zapobj, recv_clone_name,
            8, 1, &val);
        if (error != ENOENT)
                return (error == 0 ? EBUSY : error);

        /* new snapshot name must not exist */
        error = zap_lookup(dp->dp_meta_objset,
            dsl_dataset_phys(ds)->ds_snapnames_zapobj,
            drba->drba_cookie->drc_tosnap, 8, 1, &val);
        if (error != ENOENT)
                return (error == 0 ? EEXIST : error);

        /*
         * Check snapshot limit before receiving. We'll recheck again at the
         * end, but might as well abort before receiving if we're already over
         * the limit.
         *
         * Note that we do not check the file system limit with
         * dsl_dir_fscount_check because the temporary %clones don't count
         * against that limit.
         */
        error = dsl_fs_ss_limit_check(ds->ds_dir, 1, ZFS_PROP_SNAPSHOT_LIMIT,
            NULL, drba->drba_cred);
        if (error != 0)
                return (error);

        if (fromguid != 0) {
                dsl_dataset_t *snap;
                uint64_t obj = dsl_dataset_phys(ds)->ds_prev_snap_obj;

                /* Find snapshot in this dir that matches fromguid. */
                while (obj != 0) {
                        error = dsl_dataset_hold_obj(dp, obj, FTAG,
                            &snap);
                        if (error != 0)
                                return (SET_ERROR(ENODEV));
                        if (snap->ds_dir != ds->ds_dir) {
                                dsl_dataset_rele(snap, FTAG);
                                return (SET_ERROR(ENODEV));
                        }
                        if (dsl_dataset_phys(snap)->ds_guid == fromguid)
                                break;
                        obj = dsl_dataset_phys(snap)->ds_prev_snap_obj;
                        dsl_dataset_rele(snap, FTAG);
                }
                if (obj == 0)
                        return (SET_ERROR(ENODEV));

                if (drba->drba_cookie->drc_force) {
                        drba->drba_snapobj = obj;
                } else {
                        /*
                         * If we are not forcing, there must be no
                         * changes since fromsnap.
                         */
                        if (dsl_dataset_modified_since_snap(ds, snap)) {
                                dsl_dataset_rele(snap, FTAG);
                                return (SET_ERROR(ETXTBSY));
                        }
                        drba->drba_snapobj = ds->ds_prev->ds_object;
                }

                dsl_dataset_rele(snap, FTAG);
        } else {
                /* if full, then must be forced */
                if (!drba->drba_cookie->drc_force)
                        return (SET_ERROR(EEXIST));
                /* start from $ORIGIN@$ORIGIN, if supported */
                drba->drba_snapobj = dp->dp_origin_snap != NULL ?
                    dp->dp_origin_snap->ds_object : 0;
        }

        return (0);

}

static int
dmu_recv_begin_check(void *arg, dmu_tx_t *tx)
{
        dmu_recv_begin_arg_t *drba = arg;
        dsl_pool_t *dp = dmu_tx_pool(tx);
        struct drr_begin *drrb = drba->drba_cookie->drc_drrb;
        uint64_t fromguid = drrb->drr_fromguid;
        int flags = drrb->drr_flags;
        int error;
        uint64_t featureflags = DMU_GET_FEATUREFLAGS(drrb->drr_versioninfo);
        dsl_dataset_t *ds;
        const char *tofs = drba->drba_cookie->drc_tofs;

        /* already checked */
        ASSERT3U(drrb->drr_magic, ==, DMU_BACKUP_MAGIC);
        ASSERT(!(featureflags & DMU_BACKUP_FEATURE_RESUMING));

        if (DMU_GET_STREAM_HDRTYPE(drrb->drr_versioninfo) ==
            DMU_COMPOUNDSTREAM ||
            drrb->drr_type >= DMU_OST_NUMTYPES ||
            ((flags & DRR_FLAG_CLONE) && drba->drba_origin == NULL))
                return (SET_ERROR(EINVAL));

        /* Verify pool version supports SA if SA_SPILL feature set */
        if ((featureflags & DMU_BACKUP_FEATURE_SA_SPILL) &&
            spa_version(dp->dp_spa) < SPA_VERSION_SA)
                return (SET_ERROR(ENOTSUP));

        if (drba->drba_cookie->drc_resumable &&
            !spa_feature_is_enabled(dp->dp_spa, SPA_FEATURE_EXTENSIBLE_DATASET))
                return (SET_ERROR(ENOTSUP));

        /*
         * The receiving code doesn't know how to translate a WRITE_EMBEDDED
         * record to a plan WRITE record, so the pool must have the
         * EMBEDDED_DATA feature enabled if the stream has WRITE_EMBEDDED
         * records.  Same with WRITE_EMBEDDED records that use LZ4 compression.
         */
        if ((featureflags & DMU_BACKUP_FEATURE_EMBED_DATA) &&
            !spa_feature_is_enabled(dp->dp_spa, SPA_FEATURE_EMBEDDED_DATA))
                return (SET_ERROR(ENOTSUP));
        if ((featureflags & DMU_BACKUP_FEATURE_EMBED_DATA_LZ4) &&
            !spa_feature_is_enabled(dp->dp_spa, SPA_FEATURE_LZ4_COMPRESS))
                return (SET_ERROR(ENOTSUP));

        /*
         * The receiving code doesn't know how to translate large blocks
         * to smaller ones, so the pool must have the LARGE_BLOCKS
         * feature enabled if the stream has LARGE_BLOCKS.
         */
        if ((featureflags & DMU_BACKUP_FEATURE_LARGE_BLOCKS) &&
            !spa_feature_is_enabled(dp->dp_spa, SPA_FEATURE_LARGE_BLOCKS))
                return (SET_ERROR(ENOTSUP));

        error = dsl_dataset_hold(dp, tofs, FTAG, &ds);
        if (error == 0) {
                /* target fs already exists; recv into temp clone */

                /* Can't recv a clone into an existing fs */
                if (flags & DRR_FLAG_CLONE || drba->drba_origin) {
                        dsl_dataset_rele(ds, FTAG);
                        return (SET_ERROR(EINVAL));
                }

                error = recv_begin_check_existing_impl(drba, ds, fromguid);
                dsl_dataset_rele(ds, FTAG);
        } else if (error == ENOENT) {
                /* target fs does not exist; must be a full backup or clone */
                char buf[MAXNAMELEN];

                /*
                 * If it's a non-clone incremental, we are missing the
                 * target fs, so fail the recv.
                 */
                if (fromguid != 0 && !(flags & DRR_FLAG_CLONE ||
                    drba->drba_origin))
                        return (SET_ERROR(ENOENT));

                /*
                 * If we're receiving a full send as a clone, and it doesn't
                 * contain all the necessary free records and freeobject
                 * records, reject it.
                 */
                if (fromguid == 0 && drba->drba_origin &&
                    !(flags & DRR_FLAG_FREERECORDS))
                        return (SET_ERROR(EINVAL));

                /* Open the parent of tofs */
                ASSERT3U(strlen(tofs), <, MAXNAMELEN);
                (void) strlcpy(buf, tofs, strrchr(tofs, '/') - tofs + 1);
                error = dsl_dataset_hold(dp, buf, FTAG, &ds);
                if (error != 0)
                        return (error);

                /*
                 * Check filesystem and snapshot limits before receiving. We'll
                 * recheck snapshot limits again at the end (we create the
                 * filesystems and increment those counts during begin_sync).
                 */
                error = dsl_fs_ss_limit_check(ds->ds_dir, 1,
                    ZFS_PROP_FILESYSTEM_LIMIT, NULL, drba->drba_cred);
                if (error != 0) {
                        dsl_dataset_rele(ds, FTAG);
                        return (error);
                }

                error = dsl_fs_ss_limit_check(ds->ds_dir, 1,
                    ZFS_PROP_SNAPSHOT_LIMIT, NULL, drba->drba_cred);
                if (error != 0) {
                        dsl_dataset_rele(ds, FTAG);
                        return (error);
                }

                if (drba->drba_origin != NULL) {
                        dsl_dataset_t *origin;
                        error = dsl_dataset_hold(dp, drba->drba_origin,
                            FTAG, &origin);
                        if (error != 0) {
                                dsl_dataset_rele(ds, FTAG);
                                return (error);
                        }
                        if (!origin->ds_is_snapshot) {
                                dsl_dataset_rele(origin, FTAG);
                                dsl_dataset_rele(ds, FTAG);
                                return (SET_ERROR(EINVAL));
                        }
                        if (dsl_dataset_phys(origin)->ds_guid != fromguid &&
                            fromguid != 0) {
                                dsl_dataset_rele(origin, FTAG);
                                dsl_dataset_rele(ds, FTAG);
                                return (SET_ERROR(ENODEV));
                        }
                        dsl_dataset_rele(origin, FTAG);
                }
                dsl_dataset_rele(ds, FTAG);
                error = 0;
        }
        return (error);
}

static void
dmu_recv_begin_sync(void *arg, dmu_tx_t *tx)
{
        dmu_recv_begin_arg_t *drba = arg;
        dsl_pool_t *dp = dmu_tx_pool(tx);
        objset_t *mos = dp->dp_meta_objset;
        struct drr_begin *drrb = drba->drba_cookie->drc_drrb;
        const char *tofs = drba->drba_cookie->drc_tofs;
        dsl_dataset_t *ds, *newds;
        uint64_t dsobj;
        int error;
        uint64_t crflags = 0;

        if (drrb->drr_flags & DRR_FLAG_CI_DATA)
                crflags |= DS_FLAG_CI_DATASET;

        error = dsl_dataset_hold(dp, tofs, FTAG, &ds);
        if (error == 0) {
                /* create temporary clone */
                dsl_dataset_t *snap = NULL;
                if (drba->drba_snapobj != 0) {
                        VERIFY0(dsl_dataset_hold_obj(dp,
                            drba->drba_snapobj, FTAG, &snap));
                }
                dsobj = dsl_dataset_create_sync(ds->ds_dir, recv_clone_name,
                    snap, crflags, drba->drba_cred, tx);
                if (drba->drba_snapobj != 0)
                        dsl_dataset_rele(snap, FTAG);
                dsl_dataset_rele(ds, FTAG);
        } else {
                dsl_dir_t *dd;
                const char *tail;
                dsl_dataset_t *origin = NULL;

                VERIFY0(dsl_dir_hold(dp, tofs, FTAG, &dd, &tail));

                if (drba->drba_origin != NULL) {
                        VERIFY0(dsl_dataset_hold(dp, drba->drba_origin,
                            FTAG, &origin));
                }

                /* Create new dataset. */
                dsobj = dsl_dataset_create_sync(dd,
                    strrchr(tofs, '/') + 1,
                    origin, crflags, drba->drba_cred, tx);
                if (origin != NULL)
                        dsl_dataset_rele(origin, FTAG);
                dsl_dir_rele(dd, FTAG);
                drba->drba_cookie->drc_newfs = B_TRUE;
        }
        VERIFY0(dsl_dataset_own_obj(dp, dsobj, dmu_recv_tag, &newds));

        if (drba->drba_cookie->drc_resumable) {
                dsl_dataset_zapify(newds, tx);
                if (drrb->drr_fromguid != 0) {
                        VERIFY0(zap_add(mos, dsobj, DS_FIELD_RESUME_FROMGUID,
                            8, 1, &drrb->drr_fromguid, tx));
                }
                VERIFY0(zap_add(mos, dsobj, DS_FIELD_RESUME_TOGUID,
                    8, 1, &drrb->drr_toguid, tx));
                VERIFY0(zap_add(mos, dsobj, DS_FIELD_RESUME_TONAME,
                    1, strlen(drrb->drr_toname) + 1, drrb->drr_toname, tx));
                uint64_t one = 1;
                uint64_t zero = 0;
                VERIFY0(zap_add(mos, dsobj, DS_FIELD_RESUME_OBJECT,
                    8, 1, &one, tx));
                VERIFY0(zap_add(mos, dsobj, DS_FIELD_RESUME_OFFSET,
                    8, 1, &zero, tx));
                VERIFY0(zap_add(mos, dsobj, DS_FIELD_RESUME_BYTES,
                    8, 1, &zero, tx));
                if (DMU_GET_FEATUREFLAGS(drrb->drr_versioninfo) &
                    DMU_BACKUP_FEATURE_EMBED_DATA) {
                        VERIFY0(zap_add(mos, dsobj, DS_FIELD_RESUME_EMBEDOK,
                            8, 1, &one, tx));
                }
        }

        dmu_buf_will_dirty(newds->ds_dbuf, tx);
        dsl_dataset_phys(newds)->ds_flags |= DS_FLAG_INCONSISTENT;

        /*
         * If we actually created a non-clone, we need to create the
         * objset in our new dataset.
         */
        if (BP_IS_HOLE(dsl_dataset_get_blkptr(newds))) {
                (void) dmu_objset_create_impl(dp->dp_spa,
                    newds, dsl_dataset_get_blkptr(newds), drrb->drr_type, tx);
        }

        drba->drba_cookie->drc_ds = newds;

        spa_history_log_internal_ds(newds, "receive", tx, "");
}

static int
dmu_recv_resume_begin_check(void *arg, dmu_tx_t *tx)
{
        dmu_recv_begin_arg_t *drba = arg;
        dsl_pool_t *dp = dmu_tx_pool(tx);
        struct drr_begin *drrb = drba->drba_cookie->drc_drrb;
        int error;
        uint64_t featureflags = DMU_GET_FEATUREFLAGS(drrb->drr_versioninfo);
        dsl_dataset_t *ds;
        const char *tofs = drba->drba_cookie->drc_tofs;

        /* already checked */
        ASSERT3U(drrb->drr_magic, ==, DMU_BACKUP_MAGIC);
        ASSERT(featureflags & DMU_BACKUP_FEATURE_RESUMING);

        if (DMU_GET_STREAM_HDRTYPE(drrb->drr_versioninfo) ==
            DMU_COMPOUNDSTREAM ||
            drrb->drr_type >= DMU_OST_NUMTYPES)
                return (SET_ERROR(EINVAL));

        /* Verify pool version supports SA if SA_SPILL feature set */
        if ((featureflags & DMU_BACKUP_FEATURE_SA_SPILL) &&
            spa_version(dp->dp_spa) < SPA_VERSION_SA)
                return (SET_ERROR(ENOTSUP));

        /*
         * The receiving code doesn't know how to translate a WRITE_EMBEDDED
         * record to a plain WRITE record, so the pool must have the
         * EMBEDDED_DATA feature enabled if the stream has WRITE_EMBEDDED
         * records.  Same with WRITE_EMBEDDED records that use LZ4 compression.
         */
        if ((featureflags & DMU_BACKUP_FEATURE_EMBED_DATA) &&
            !spa_feature_is_enabled(dp->dp_spa, SPA_FEATURE_EMBEDDED_DATA))
                return (SET_ERROR(ENOTSUP));
        if ((featureflags & DMU_BACKUP_FEATURE_EMBED_DATA_LZ4) &&
            !spa_feature_is_enabled(dp->dp_spa, SPA_FEATURE_LZ4_COMPRESS))
                return (SET_ERROR(ENOTSUP));

        char recvname[ZFS_MAXNAMELEN];

        (void) snprintf(recvname, sizeof (recvname), "%s/%s",
            tofs, recv_clone_name);

        if (dsl_dataset_hold(dp, recvname, FTAG, &ds) != 0) {
                /* %recv does not exist; continue in tofs */
                error = dsl_dataset_hold(dp, tofs, FTAG, &ds);
                if (error != 0)
                        return (error);
        }

        /* check that ds is marked inconsistent */
        if (!DS_IS_INCONSISTENT(ds)) {
                dsl_dataset_rele(ds, FTAG);
                return (SET_ERROR(EINVAL));
        }

        /* check that there is resuming data, and that the toguid matches */
        if (!dsl_dataset_is_zapified(ds)) {
                dsl_dataset_rele(ds, FTAG);
                return (SET_ERROR(EINVAL));
        }
        uint64_t val;
        error = zap_lookup(dp->dp_meta_objset, ds->ds_object,
            DS_FIELD_RESUME_TOGUID, sizeof (val), 1, &val);
        if (error != 0 || drrb->drr_toguid != val) {
                dsl_dataset_rele(ds, FTAG);
                return (SET_ERROR(EINVAL));
        }

        /*
         * Check if the receive is still running.  If so, it will be owned.
         * Note that nothing else can own the dataset (e.g. after the receive
         * fails) because it will be marked inconsistent.
         */
        if (dsl_dataset_has_owner(ds)) {
                dsl_dataset_rele(ds, FTAG);
                return (SET_ERROR(EBUSY));
        }

        /* There should not be any snapshots of this fs yet. */
        if (ds->ds_prev != NULL && ds->ds_prev->ds_dir == ds->ds_dir) {
                dsl_dataset_rele(ds, FTAG);
                return (SET_ERROR(EINVAL));
        }

        /*
         * Note: resume point will be checked when we process the first WRITE
         * record.
         */

        /* check that the origin matches */
        val = 0;
        (void) zap_lookup(dp->dp_meta_objset, ds->ds_object,
            DS_FIELD_RESUME_FROMGUID, sizeof (val), 1, &val);
        if (drrb->drr_fromguid != val) {
                dsl_dataset_rele(ds, FTAG);
                return (SET_ERROR(EINVAL));
        }

        dsl_dataset_rele(ds, FTAG);
        return (0);
}

static void
dmu_recv_resume_begin_sync(void *arg, dmu_tx_t *tx)
{
        dmu_recv_begin_arg_t *drba = arg;
        dsl_pool_t *dp = dmu_tx_pool(tx);
        const char *tofs = drba->drba_cookie->drc_tofs;
        dsl_dataset_t *ds;
        uint64_t dsobj;
        char recvname[ZFS_MAXNAMELEN];

        (void) snprintf(recvname, sizeof (recvname), "%s/%s",
            tofs, recv_clone_name);

        if (dsl_dataset_hold(dp, recvname, FTAG, &ds) != 0) {
                /* %recv does not exist; continue in tofs */
                VERIFY0(dsl_dataset_hold(dp, tofs, FTAG, &ds));
                drba->drba_cookie->drc_newfs = B_TRUE;
        }

        /* clear the inconsistent flag so that we can own it */
        ASSERT(DS_IS_INCONSISTENT(ds));
        dmu_buf_will_dirty(ds->ds_dbuf, tx);
        dsl_dataset_phys(ds)->ds_flags &= ~DS_FLAG_INCONSISTENT;
        dsobj = ds->ds_object;
        dsl_dataset_rele(ds, FTAG);

        VERIFY0(dsl_dataset_own_obj(dp, dsobj, dmu_recv_tag, &ds));

        dmu_buf_will_dirty(ds->ds_dbuf, tx);
        dsl_dataset_phys(ds)->ds_flags |= DS_FLAG_INCONSISTENT;

        ASSERT(!BP_IS_HOLE(dsl_dataset_get_blkptr(ds)));

        drba->drba_cookie->drc_ds = ds;

        spa_history_log_internal_ds(ds, "resume receive", tx, "");
}

/*
 * NB: callers *MUST* call dmu_recv_stream() if dmu_recv_begin()
 * succeeds; otherwise we will leak the holds on the datasets.
 */
int
dmu_recv_begin(char *tofs, char *tosnap, dmu_replay_record_t *drr_begin,
    boolean_t force, boolean_t resumable, char *origin, dmu_recv_cookie_t *drc)
{
        dmu_recv_begin_arg_t drba = { 0 };

        bzero(drc, sizeof (dmu_recv_cookie_t));
        drc->drc_drr_begin = drr_begin;
        drc->drc_drrb = &drr_begin->drr_u.drr_begin;
        drc->drc_tosnap = tosnap;
        drc->drc_tofs = tofs;
        drc->drc_force = force;
        drc->drc_resumable = resumable;
        drc->drc_cred = CRED();

        if (drc->drc_drrb->drr_magic == BSWAP_64(DMU_BACKUP_MAGIC)) {
                drc->drc_byteswap = B_TRUE;
                fletcher_4_incremental_byteswap(drr_begin,
                    sizeof (dmu_replay_record_t), &drc->drc_cksum);
                byteswap_record(drr_begin);
        } else if (drc->drc_drrb->drr_magic == DMU_BACKUP_MAGIC) {
                fletcher_4_incremental_native(drr_begin,
                    sizeof (dmu_replay_record_t), &drc->drc_cksum);
        } else {
                return (SET_ERROR(EINVAL));
        }

        drba.drba_origin = origin;
        drba.drba_cookie = drc;
        drba.drba_cred = CRED();

        if (DMU_GET_FEATUREFLAGS(drc->drc_drrb->drr_versioninfo) &
            DMU_BACKUP_FEATURE_RESUMING) {
                return (dsl_sync_task(tofs,
                    dmu_recv_resume_begin_check, dmu_recv_resume_begin_sync,
                    &drba, 5, ZFS_SPACE_CHECK_NORMAL));
        } else  {
                return (dsl_sync_task(tofs,
                    dmu_recv_begin_check, dmu_recv_begin_sync,
                    &drba, 5, ZFS_SPACE_CHECK_NORMAL));
        }
}

struct receive_record_arg {
        dmu_replay_record_t header;
        void *payload; /* Pointer to a buffer containing the payload */
        /*
         * If the record is a write, pointer to the arc_buf_t containing the
         * payload.
         */
        arc_buf_t *write_buf;
        int payload_size;
        uint64_t bytes_read; /* bytes read from stream when record created */
        boolean_t eos_marker; /* Marks the end of the stream */
        bqueue_node_t node;
};

struct receive_writer_arg {
        objset_t *os;
        boolean_t byteswap;
        bqueue_t q;

        /*
         * These three args are used to signal to the main thread that we're
         * done.
         */
        kmutex_t mutex;
        kcondvar_t cv;
        boolean_t done;

        int err;
        /* A map from guid to dataset to help handle dedup'd streams. */
        avl_tree_t *guid_to_ds_map;
        boolean_t resumable;
        uint64_t last_object, last_offset;
        uint64_t bytes_read; /* bytes read when current record created */
};

struct objlist {
        list_t list; /* List of struct receive_objnode. */
        /*
         * Last object looked up. Used to assert that objects are being looked
         * up in ascending order.
         */
        uint64_t last_lookup;
};

struct receive_objnode {
        list_node_t node;
        uint64_t object;
};

struct receive_arg  {
        objset_t *os;
        vnode_t *vp; /* The vnode to read the stream from */
        uint64_t voff; /* The current offset in the stream */
        uint64_t bytes_read;
        /*
         * A record that has had its payload read in, but hasn't yet been handed
         * off to the worker thread.
         */
        struct receive_record_arg *rrd;
        /* A record that has had its header read in, but not its payload. */
        struct receive_record_arg *next_rrd;
        zio_cksum_t cksum;
        zio_cksum_t prev_cksum;
        int err;
        boolean_t byteswap;
        /* Sorted list of objects not to issue prefetches for. */
        struct objlist ignore_objlist;
};

typedef struct guid_map_entry {
        uint64_t        guid;
        dsl_dataset_t   *gme_ds;
        avl_node_t      avlnode;
} guid_map_entry_t;

static int
guid_compare(const void *arg1, const void *arg2)
{
        const guid_map_entry_t *gmep1 = arg1;
        const guid_map_entry_t *gmep2 = arg2;

        if (gmep1->guid < gmep2->guid)
                return (-1);
        else if (gmep1->guid > gmep2->guid)
                return (1);
        return (0);
}

static void
free_guid_map_onexit(void *arg)
{
        avl_tree_t *ca = arg;
        void *cookie = NULL;
        guid_map_entry_t *gmep;

        while ((gmep = avl_destroy_nodes(ca, &cookie)) != NULL) {
                dsl_dataset_long_rele(gmep->gme_ds, gmep);
                dsl_dataset_rele(gmep->gme_ds, gmep);
                kmem_free(gmep, sizeof (guid_map_entry_t));
        }
        avl_destroy(ca);
        kmem_free(ca, sizeof (avl_tree_t));
}

static int
receive_read(struct receive_arg *ra, int len, void *buf)
{
        int done = 0;

        /*
         * The code doesn't rely on this (lengths being multiples of 8).  See
         * comment in dump_bytes.
         */
        ASSERT0(len % 8);

        while (done < len) {
                ssize_t resid;

                ra->err = vn_rdwr(UIO_READ, ra->vp,
                    (char *)buf + done, len - done,
                    ra->voff, UIO_SYSSPACE, FAPPEND,
                    RLIM64_INFINITY, CRED(), &resid);

                if (resid == len - done) {
                        /*
                         * Note: ECKSUM indicates that the receive
                         * was interrupted and can potentially be resumed.
                         */
                        ra->err = SET_ERROR(ECKSUM);
                }
                ra->voff += len - done - resid;
                done = len - resid;
                if (ra->err != 0)
                        return (ra->err);
        }

        ra->bytes_read += len;

        ASSERT3U(done, ==, len);
        return (0);
}

static void
byteswap_record(dmu_replay_record_t *drr)
{
#define DO64(X) (drr->drr_u.X = BSWAP_64(drr->drr_u.X))
#define DO32(X) (drr->drr_u.X = BSWAP_32(drr->drr_u.X))
        drr->drr_type = BSWAP_32(drr->drr_type);
        drr->drr_payloadlen = BSWAP_32(drr->drr_payloadlen);

        switch (drr->drr_type) {
        case DRR_BEGIN:
                DO64(drr_begin.drr_magic);
                DO64(drr_begin.drr_versioninfo);
                DO64(drr_begin.drr_creation_time);
                DO32(drr_begin.drr_type);
                DO32(drr_begin.drr_flags);
                DO64(drr_begin.drr_toguid);
                DO64(drr_begin.drr_fromguid);
                break;
        case DRR_OBJECT:
                DO64(drr_object.drr_object);
                DO32(drr_object.drr_type);
                DO32(drr_object.drr_bonustype);
                DO32(drr_object.drr_blksz);
                DO32(drr_object.drr_bonuslen);
                DO64(drr_object.drr_toguid);
                break;
        case DRR_FREEOBJECTS:
                DO64(drr_freeobjects.drr_firstobj);
                DO64(drr_freeobjects.drr_numobjs);
                DO64(drr_freeobjects.drr_toguid);
                break;
        case DRR_WRITE:
                DO64(drr_write.drr_object);
                DO32(drr_write.drr_type);
                DO64(drr_write.drr_offset);
                DO64(drr_write.drr_length);
                DO64(drr_write.drr_toguid);
                ZIO_CHECKSUM_BSWAP(&drr->drr_u.drr_write.drr_key.ddk_cksum);
                DO64(drr_write.drr_key.ddk_prop);
                break;
        case DRR_WRITE_BYREF:
                DO64(drr_write_byref.drr_object);
                DO64(drr_write_byref.drr_offset);
                DO64(drr_write_byref.drr_length);
                DO64(drr_write_byref.drr_toguid);
                DO64(drr_write_byref.drr_refguid);
                DO64(drr_write_byref.drr_refobject);
                DO64(drr_write_byref.drr_refoffset);
                ZIO_CHECKSUM_BSWAP(&drr->drr_u.drr_write_byref.
                    drr_key.ddk_cksum);
                DO64(drr_write_byref.drr_key.ddk_prop);
                break;
        case DRR_WRITE_EMBEDDED:
                DO64(drr_write_embedded.drr_object);
                DO64(drr_write_embedded.drr_offset);
                DO64(drr_write_embedded.drr_length);
                DO64(drr_write_embedded.drr_toguid);
                DO32(drr_write_embedded.drr_lsize);
                DO32(drr_write_embedded.drr_psize);
                break;
        case DRR_FREE:
                DO64(drr_free.drr_object);
                DO64(drr_free.drr_offset);
                DO64(drr_free.drr_length);
                DO64(drr_free.drr_toguid);
                break;
        case DRR_SPILL:
                DO64(drr_spill.drr_object);
                DO64(drr_spill.drr_length);
                DO64(drr_spill.drr_toguid);
                break;
        case DRR_END:
                DO64(drr_end.drr_toguid);
                ZIO_CHECKSUM_BSWAP(&drr->drr_u.drr_end.drr_checksum);
                break;
        }

        if (drr->drr_type != DRR_BEGIN) {
                ZIO_CHECKSUM_BSWAP(&drr->drr_u.drr_checksum.drr_checksum);
        }

#undef DO64
#undef DO32
}

static inline uint8_t
deduce_nblkptr(dmu_object_type_t bonus_type, uint64_t bonus_size)
{
        if (bonus_type == DMU_OT_SA) {
                return (1);
        } else {
                return (1 +
                    ((DN_MAX_BONUSLEN - bonus_size) >> SPA_BLKPTRSHIFT));
        }
}

static void
save_resume_state(struct receive_writer_arg *rwa,
    uint64_t object, uint64_t offset, dmu_tx_t *tx)
{
        int txgoff = dmu_tx_get_txg(tx) & TXG_MASK;

        if (!rwa->resumable)
                return;

        /*
         * We use ds_resume_bytes[] != 0 to indicate that we need to
         * update this on disk, so it must not be 0.
         */
        ASSERT(rwa->bytes_read != 0);

        /*
         * We only resume from write records, which have a valid
         * (non-meta-dnode) object number.
         */
        ASSERT(object != 0);

        /*
         * For resuming to work correctly, we must receive records in order,
         * sorted by object,offset.  This is checked by the callers, but
         * assert it here for good measure.
         */
        ASSERT3U(object, >=, rwa->os->os_dsl_dataset->ds_resume_object[txgoff]);
        ASSERT(object != rwa->os->os_dsl_dataset->ds_resume_object[txgoff] ||
            offset >= rwa->os->os_dsl_dataset->ds_resume_offset[txgoff]);
        ASSERT3U(rwa->bytes_read, >=,
            rwa->os->os_dsl_dataset->ds_resume_bytes[txgoff]);

        rwa->os->os_dsl_dataset->ds_resume_object[txgoff] = object;
        rwa->os->os_dsl_dataset->ds_resume_offset[txgoff] = offset;
        rwa->os->os_dsl_dataset->ds_resume_bytes[txgoff] = rwa->bytes_read;
}

static int
receive_object(struct receive_writer_arg *rwa, struct drr_object *drro,
    void *data)
{
        dmu_object_info_t doi;
        dmu_tx_t *tx;
        uint64_t object;
        int err;

        if (drro->drr_type == DMU_OT_NONE ||
            !DMU_OT_IS_VALID(drro->drr_type) ||
            !DMU_OT_IS_VALID(drro->drr_bonustype) ||
            drro->drr_checksumtype >= ZIO_CHECKSUM_FUNCTIONS ||
            drro->drr_compress >= ZIO_COMPRESS_FUNCTIONS ||
            P2PHASE(drro->drr_blksz, SPA_MINBLOCKSIZE) ||
            drro->drr_blksz < SPA_MINBLOCKSIZE ||
            drro->drr_blksz > spa_maxblocksize(dmu_objset_spa(rwa->os)) ||
            drro->drr_bonuslen > DN_MAX_BONUSLEN) {
                return (SET_ERROR(EINVAL));
        }

        err = dmu_object_info(rwa->os, drro->drr_object, &doi);

        if (err != 0 && err != ENOENT)
                return (SET_ERROR(EINVAL));
        object = err == 0 ? drro->drr_object : DMU_NEW_OBJECT;

        /*
         * If we are losing blkptrs or changing the block size this must
         * be a new file instance.  We must clear out the previous file
         * contents before we can change this type of metadata in the dnode.
         */
        if (err == 0) {
                int nblkptr;

                nblkptr = deduce_nblkptr(drro->drr_bonustype,
                    drro->drr_bonuslen);

                if (drro->drr_blksz != doi.doi_data_block_size ||
                    nblkptr < doi.doi_nblkptr) {
                        err = dmu_free_long_range(rwa->os, drro->drr_object,
                            0, DMU_OBJECT_END);
                        if (err != 0)
                                return (SET_ERROR(EINVAL));
                }
        }

        tx = dmu_tx_create(rwa->os);
        dmu_tx_hold_bonus(tx, object);
        err = dmu_tx_assign(tx, TXG_WAIT);
        if (err != 0) {
                dmu_tx_abort(tx);
                return (err);
        }

        if (object == DMU_NEW_OBJECT) {
                /* currently free, want to be allocated */
                err = dmu_object_claim(rwa->os, drro->drr_object,
                    drro->drr_type, drro->drr_blksz,
                    drro->drr_bonustype, drro->drr_bonuslen, tx);
        } else if (drro->drr_type != doi.doi_type ||
            drro->drr_blksz != doi.doi_data_block_size ||
            drro->drr_bonustype != doi.doi_bonus_type ||
            drro->drr_bonuslen != doi.doi_bonus_size) {
                /* currently allocated, but with different properties */
                err = dmu_object_reclaim(rwa->os, drro->drr_object,
                    drro->drr_type, drro->drr_blksz,
                    drro->drr_bonustype, drro->drr_bonuslen, tx);
        }
        if (err != 0) {
                dmu_tx_commit(tx);
                return (SET_ERROR(EINVAL));
        }

        dmu_object_set_checksum(rwa->os, drro->drr_object,
            drro->drr_checksumtype, tx);
        dmu_object_set_compress(rwa->os, drro->drr_object,
            drro->drr_compress, tx);

        if (data != NULL) {
                dmu_buf_t *db;

                VERIFY0(dmu_bonus_hold(rwa->os, drro->drr_object, FTAG, &db));
                dmu_buf_will_dirty(db, tx);

                ASSERT3U(db->db_size, >=, drro->drr_bonuslen);
                bcopy(data, db->db_data, drro->drr_bonuslen);
                if (rwa->byteswap) {
                        dmu_object_byteswap_t byteswap =
                            DMU_OT_BYTESWAP(drro->drr_bonustype);
                        dmu_ot_byteswap[byteswap].ob_func(db->db_data,
                            drro->drr_bonuslen);
                }
                dmu_buf_rele(db, FTAG);
        }
        dmu_tx_commit(tx);

        return (0);
}

/* ARGSUSED */
static int
receive_freeobjects(struct receive_writer_arg *rwa,
    struct drr_freeobjects *drrfo)
{
        uint64_t obj;
        int next_err = 0;

        if (drrfo->drr_firstobj + drrfo->drr_numobjs < drrfo->drr_firstobj)
                return (SET_ERROR(EINVAL));

        for (obj = drrfo->drr_firstobj;
            obj < drrfo->drr_firstobj + drrfo->drr_numobjs && next_err == 0;
            next_err = dmu_object_next(rwa->os, &obj, FALSE, 0)) {
                int err;

                if (dmu_object_info(rwa->os, obj, NULL) != 0)
                        continue;

                err = dmu_free_long_object(rwa->os, obj);
                if (err != 0)
                        return (err);
        }
        if (next_err != ESRCH)
                return (next_err);
        return (0);
}

static int
receive_write(struct receive_writer_arg *rwa, struct drr_write *drrw,
    arc_buf_t *abuf)
{
        dmu_tx_t *tx;
        int err;

        if (drrw->drr_offset + drrw->drr_length < drrw->drr_offset ||
            !DMU_OT_IS_VALID(drrw->drr_type))
                return (SET_ERROR(EINVAL));

        /*
         * For resuming to work, records must be in increasing order
         * by (object, offset).
         */
        if (drrw->drr_object < rwa->last_object ||
            (drrw->drr_object == rwa->last_object &&
            drrw->drr_offset < rwa->last_offset)) {
                return (SET_ERROR(EINVAL));
        }
        rwa->last_object = drrw->drr_object;
        rwa->last_offset = drrw->drr_offset;

        if (dmu_object_info(rwa->os, drrw->drr_object, NULL) != 0)
                return (SET_ERROR(EINVAL));

        tx = dmu_tx_create(rwa->os);

        dmu_tx_hold_write(tx, drrw->drr_object,
            drrw->drr_offset, drrw->drr_length);
        err = dmu_tx_assign(tx, TXG_WAIT);
        if (err != 0) {
                dmu_tx_abort(tx);
                return (err);
        }
        if (rwa->byteswap) {
                dmu_object_byteswap_t byteswap =
                    DMU_OT_BYTESWAP(drrw->drr_type);
                dmu_ot_byteswap[byteswap].ob_func(abuf->b_data,
                    drrw->drr_length);
        }

        dmu_buf_t *bonus;
        if (dmu_bonus_hold(rwa->os, drrw->drr_object, FTAG, &bonus) != 0)
                return (SET_ERROR(EINVAL));
        dmu_assign_arcbuf(bonus, drrw->drr_offset, abuf, tx);

        /*
         * Note: If the receive fails, we want the resume stream to start
         * with the same record that we last successfully received (as opposed
         * to the next record), so that we can verify that we are
         * resuming from the correct location.
         */
        save_resume_state(rwa, drrw->drr_object, drrw->drr_offset, tx);
        dmu_tx_commit(tx);
        dmu_buf_rele(bonus, FTAG);

        return (0);
}

/*
 * Handle a DRR_WRITE_BYREF record.  This record is used in dedup'ed
 * streams to refer to a copy of the data that is already on the
 * system because it came in earlier in the stream.  This function
 * finds the earlier copy of the data, and uses that copy instead of
 * data from the stream to fulfill this write.
 */
static int
receive_write_byref(struct receive_writer_arg *rwa,
    struct drr_write_byref *drrwbr)
{
        dmu_tx_t *tx;
        int err;
        guid_map_entry_t gmesrch;
        guid_map_entry_t *gmep;
        avl_index_t where;
        objset_t *ref_os = NULL;
        dmu_buf_t *dbp;

        if (drrwbr->drr_offset + drrwbr->drr_length < drrwbr->drr_offset)
                return (SET_ERROR(EINVAL));

        /*
         * If the GUID of the referenced dataset is different from the
         * GUID of the target dataset, find the referenced dataset.
         */
        if (drrwbr->drr_toguid != drrwbr->drr_refguid) {
                gmesrch.guid = drrwbr->drr_refguid;
                if ((gmep = avl_find(rwa->guid_to_ds_map, &gmesrch,
                    &where)) == NULL) {
                        return (SET_ERROR(EINVAL));
                }
                if (dmu_objset_from_ds(gmep->gme_ds, &ref_os))
                        return (SET_ERROR(EINVAL));
        } else {
                ref_os = rwa->os;
        }

        err = dmu_buf_hold(ref_os, drrwbr->drr_refobject,
            drrwbr->drr_refoffset, FTAG, &dbp, DMU_READ_PREFETCH);
        if (err != 0)
                return (err);

        tx = dmu_tx_create(rwa->os);

        dmu_tx_hold_write(tx, drrwbr->drr_object,
            drrwbr->drr_offset, drrwbr->drr_length);
        err = dmu_tx_assign(tx, TXG_WAIT);
        if (err != 0) {
                dmu_tx_abort(tx);
                return (err);
        }
        dmu_write(rwa->os, drrwbr->drr_object,
            drrwbr->drr_offset, drrwbr->drr_length, dbp->db_data, tx);
        dmu_buf_rele(dbp, FTAG);

        /* See comment in restore_write. */
        save_resume_state(rwa, drrwbr->drr_object, drrwbr->drr_offset, tx);
        dmu_tx_commit(tx);
        return (0);
}

static int
receive_write_embedded(struct receive_writer_arg *rwa,
    struct drr_write_embedded *drrwe, void *data)
{
        dmu_tx_t *tx;
        int err;

        if (drrwe->drr_offset + drrwe->drr_length < drrwe->drr_offset)
                return (EINVAL);

        if (drrwe->drr_psize > BPE_PAYLOAD_SIZE)
                return (EINVAL);

        if (drrwe->drr_etype >= NUM_BP_EMBEDDED_TYPES)
                return (EINVAL);
        if (drrwe->drr_compression >= ZIO_COMPRESS_FUNCTIONS)
                return (EINVAL);

        tx = dmu_tx_create(rwa->os);

        dmu_tx_hold_write(tx, drrwe->drr_object,
            drrwe->drr_offset, drrwe->drr_length);
        err = dmu_tx_assign(tx, TXG_WAIT);
        if (err != 0) {
                dmu_tx_abort(tx);
                return (err);
        }

        dmu_write_embedded(rwa->os, drrwe->drr_object,
            drrwe->drr_offset, data, drrwe->drr_etype,
            drrwe->drr_compression, drrwe->drr_lsize, drrwe->drr_psize,
            rwa->byteswap ^ ZFS_HOST_BYTEORDER, tx);

        /* See comment in restore_write. */
        save_resume_state(rwa, drrwe->drr_object, drrwe->drr_offset, tx);
        dmu_tx_commit(tx);
        return (0);
}

static int
receive_spill(struct receive_writer_arg *rwa, struct drr_spill *drrs,
    void *data)
{
        dmu_tx_t *tx;
        dmu_buf_t *db, *db_spill;
        int err;

        if (drrs->drr_length < SPA_MINBLOCKSIZE ||
            drrs->drr_length > spa_maxblocksize(dmu_objset_spa(rwa->os)))
                return (SET_ERROR(EINVAL));

        if (dmu_object_info(rwa->os, drrs->drr_object, NULL) != 0)
                return (SET_ERROR(EINVAL));

        VERIFY0(dmu_bonus_hold(rwa->os, drrs->drr_object, FTAG, &db));
        if ((err = dmu_spill_hold_by_bonus(db, FTAG, &db_spill)) != 0) {
                dmu_buf_rele(db, FTAG);
                return (err);
        }

        tx = dmu_tx_create(rwa->os);

        dmu_tx_hold_spill(tx, db->db_object);

        err = dmu_tx_assign(tx, TXG_WAIT);
        if (err != 0) {
                dmu_buf_rele(db, FTAG);
                dmu_buf_rele(db_spill, FTAG);
                dmu_tx_abort(tx);
                return (err);
        }
        dmu_buf_will_dirty(db_spill, tx);

        if (db_spill->db_size < drrs->drr_length)
                VERIFY(0 == dbuf_spill_set_blksz(db_spill,
                    drrs->drr_length, tx));
        bcopy(data, db_spill->db_data, drrs->drr_length);

        dmu_buf_rele(db, FTAG);
        dmu_buf_rele(db_spill, FTAG);

        dmu_tx_commit(tx);
        return (0);
}

/* ARGSUSED */
static int
receive_free(struct receive_writer_arg *rwa, struct drr_free *drrf)
{
        int err;

        if (drrf->drr_length != -1ULL &&
            drrf->drr_offset + drrf->drr_length < drrf->drr_offset)
                return (SET_ERROR(EINVAL));

        if (dmu_object_info(rwa->os, drrf->drr_object, NULL) != 0)
                return (SET_ERROR(EINVAL));

        err = dmu_free_long_range(rwa->os, drrf->drr_object,
            drrf->drr_offset, drrf->drr_length);

        return (err);
}

/* used to destroy the drc_ds on error */
static void
dmu_recv_cleanup_ds(dmu_recv_cookie_t *drc)
{
        if (drc->drc_resumable) {
                /* wait for our resume state to be written to disk */
                txg_wait_synced(drc->drc_ds->ds_dir->dd_pool, 0);
                dsl_dataset_disown(drc->drc_ds, dmu_recv_tag);
        } else {
                char name[MAXNAMELEN];
                dsl_dataset_name(drc->drc_ds, name);
                dsl_dataset_disown(drc->drc_ds, dmu_recv_tag);
                (void) dsl_destroy_head(name);
        }
}

static void
receive_cksum(struct receive_arg *ra, int len, void *buf)
{
        if (ra->byteswap) {
                fletcher_4_incremental_byteswap(buf, len, &ra->cksum);
        } else {
                fletcher_4_incremental_native(buf, len, &ra->cksum);
        }
}

/*
 * Read the payload into a buffer of size len, and update the current record's
 * payload field.
 * Allocate ra->next_rrd and read the next record's header into
 * ra->next_rrd->header.
 * Verify checksum of payload and next record.
 */
static int
receive_read_payload_and_next_header(struct receive_arg *ra, int len, void *buf)
{
        int err;

        if (len != 0) {
                ASSERT3U(len, <=, SPA_MAXBLOCKSIZE);
                err = receive_read(ra, len, buf);
                if (err != 0)
                        return (err);
                receive_cksum(ra, len, buf);

                /* note: rrd is NULL when reading the begin record's payload */
                if (ra->rrd != NULL) {
                        ra->rrd->payload = buf;
                        ra->rrd->payload_size = len;
                        ra->rrd->bytes_read = ra->bytes_read;
                }
        }

        ra->prev_cksum = ra->cksum;

        ra->next_rrd = kmem_zalloc(sizeof (*ra->next_rrd), KM_SLEEP);
        err = receive_read(ra, sizeof (ra->next_rrd->header),
            &ra->next_rrd->header);
        ra->next_rrd->bytes_read = ra->bytes_read;
        if (err != 0) {
                kmem_free(ra->next_rrd, sizeof (*ra->next_rrd));
                ra->next_rrd = NULL;
                return (err);
        }
        if (ra->next_rrd->header.drr_type == DRR_BEGIN) {
                kmem_free(ra->next_rrd, sizeof (*ra->next_rrd));
                ra->next_rrd = NULL;
                return (SET_ERROR(EINVAL));
        }

        /*
         * Note: checksum is of everything up to but not including the
         * checksum itself.
         */
        ASSERT3U(offsetof(dmu_replay_record_t, drr_u.drr_checksum.drr_checksum),
            ==, sizeof (dmu_replay_record_t) - sizeof (zio_cksum_t));
        receive_cksum(ra,
            offsetof(dmu_replay_record_t, drr_u.drr_checksum.drr_checksum),
            &ra->next_rrd->header);

        zio_cksum_t cksum_orig =
            ra->next_rrd->header.drr_u.drr_checksum.drr_checksum;
        zio_cksum_t *cksump =
            &ra->next_rrd->header.drr_u.drr_checksum.drr_checksum;

        if (ra->byteswap)
                byteswap_record(&ra->next_rrd->header);

        if ((!ZIO_CHECKSUM_IS_ZERO(cksump)) &&
            !ZIO_CHECKSUM_EQUAL(ra->cksum, *cksump)) {
                kmem_free(ra->next_rrd, sizeof (*ra->next_rrd));
                ra->next_rrd = NULL;
                return (SET_ERROR(ECKSUM));
        }

        receive_cksum(ra, sizeof (cksum_orig), &cksum_orig);

        return (0);
}

static void
objlist_create(struct objlist *list)
{
        list_create(&list->list, sizeof (struct receive_objnode),
            offsetof(struct receive_objnode, node));
        list->last_lookup = 0;
}

static void
objlist_destroy(struct objlist *list)
{
        for (struct receive_objnode *n = list_remove_head(&list->list);
            n != NULL; n = list_remove_head(&list->list)) {
                kmem_free(n, sizeof (*n));
        }
        list_destroy(&list->list);
}

/*
 * This function looks through the objlist to see if the specified object number
 * is contained in the objlist.  In the process, it will remove all object
 * numbers in the list that are smaller than the specified object number.  Thus,
 * any lookup of an object number smaller than a previously looked up object
 * number will always return false; therefore, all lookups should be done in
 * ascending order.
 */
static boolean_t
objlist_exists(struct objlist *list, uint64_t object)
{
        struct receive_objnode *node = list_head(&list->list);
        ASSERT3U(object, >=, list->last_lookup);
        list->last_lookup = object;
        while (node != NULL && node->object < object) {
                VERIFY3P(node, ==, list_remove_head(&list->list));
                kmem_free(node, sizeof (*node));
                node = list_head(&list->list);
        }
        return (node != NULL && node->object == object);
}

/*
 * The objlist is a list of object numbers stored in ascending order.  However,
 * the insertion of new object numbers does not seek out the correct location to
 * store a new object number; instead, it appends it to the list for simplicity.
 * Thus, any users must take care to only insert new object numbers in ascending
 * order.
 */
static void
objlist_insert(struct objlist *list, uint64_t object)
{
        struct receive_objnode *node = kmem_zalloc(sizeof (*node), KM_SLEEP);
        node->object = object;
#ifdef ZFS_DEBUG
        struct receive_objnode *last_object = list_tail(&list->list);
        uint64_t last_objnum = (last_object != NULL ? last_object->object : 0);
        ASSERT3U(node->object, >, last_objnum);
#endif
        list_insert_tail(&list->list, node);
}

/*
 * Issue the prefetch reads for any necessary indirect blocks.
 *
 * We use the object ignore list to tell us whether or not to issue prefetches
 * for a given object.  We do this for both correctness (in case the blocksize
 * of an object has changed) and performance (if the object doesn't exist, don't
 * needlessly try to issue prefetches).  We also trim the list as we go through
 * the stream to prevent it from growing to an unbounded size.
 *
 * The object numbers within will always be in sorted order, and any write
 * records we see will also be in sorted order, but they're not sorted with
 * respect to each other (i.e. we can get several object records before
 * receiving each object's write records).  As a result, once we've reached a
 * given object number, we can safely remove any reference to lower object
 * numbers in the ignore list. In practice, we receive up to 32 object records
 * before receiving write records, so the list can have up to 32 nodes in it.
 */
/* ARGSUSED */
static void
receive_read_prefetch(struct receive_arg *ra,
    uint64_t object, uint64_t offset, uint64_t length)
{
        if (!objlist_exists(&ra->ignore_objlist, object)) {
                dmu_prefetch(ra->os, object, 1, offset, length,
                    ZIO_PRIORITY_SYNC_READ);
        }
}

/*
 * Read records off the stream, issuing any necessary prefetches.
 */
static int
receive_read_record(struct receive_arg *ra)
{
        int err;

        switch (ra->rrd->header.drr_type) {
        case DRR_OBJECT:
        {
                struct drr_object *drro = &ra->rrd->header.drr_u.drr_object;
                uint32_t size = P2ROUNDUP(drro->drr_bonuslen, 8);
                void *buf = kmem_zalloc(size, KM_SLEEP);
                dmu_object_info_t doi;
                err = receive_read_payload_and_next_header(ra, size, buf);
                if (err != 0) {
                        kmem_free(buf, size);
                        return (err);
                }
                err = dmu_object_info(ra->os, drro->drr_object, &doi);
                /*
                 * See receive_read_prefetch for an explanation why we're
                 * storing this object in the ignore_obj_list.
                 */
                if (err == ENOENT ||
                    (err == 0 && doi.doi_data_block_size != drro->drr_blksz)) {
                        objlist_insert(&ra->ignore_objlist, drro->drr_object);
                        err = 0;
                }
                return (err);
        }
        case DRR_FREEOBJECTS:
        {
                err = receive_read_payload_and_next_header(ra, 0, NULL);
                return (err);
        }
        case DRR_WRITE:
        {
                struct drr_write *drrw = &ra->rrd->header.drr_u.drr_write;
                arc_buf_t *abuf = arc_loan_buf(dmu_objset_spa(ra->os),
                    drrw->drr_length);

                err = receive_read_payload_and_next_header(ra,
                    drrw->drr_length, abuf->b_data);
                if (err != 0) {
                        dmu_return_arcbuf(abuf);
                        return (err);
                }
                ra->rrd->write_buf = abuf;
                receive_read_prefetch(ra, drrw->drr_object, drrw->drr_offset,
                    drrw->drr_length);
                return (err);
        }
        case DRR_WRITE_BYREF:
        {
                struct drr_write_byref *drrwb =
                    &ra->rrd->header.drr_u.drr_write_byref;
                err = receive_read_payload_and_next_header(ra, 0, NULL);
                receive_read_prefetch(ra, drrwb->drr_object, drrwb->drr_offset,
                    drrwb->drr_length);
                return (err);
        }
        case DRR_WRITE_EMBEDDED:
        {
                struct drr_write_embedded *drrwe =
                    &ra->rrd->header.drr_u.drr_write_embedded;
                uint32_t size = P2ROUNDUP(drrwe->drr_psize, 8);
                void *buf = kmem_zalloc(size, KM_SLEEP);

                err = receive_read_payload_and_next_header(ra, size, buf);
                if (err != 0) {
                        kmem_free(buf, size);
                        return (err);
                }

                receive_read_prefetch(ra, drrwe->drr_object, drrwe->drr_offset,
                    drrwe->drr_length);
                return (err);
        }
        case DRR_FREE:
        {
                /*
                 * It might be beneficial to prefetch indirect blocks here, but
                 * we don't really have the data to decide for sure.
                 */
                err = receive_read_payload_and_next_header(ra, 0, NULL);
                return (err);
        }
        case DRR_END:
        {
                struct drr_end *drre = &ra->rrd->header.drr_u.drr_end;
                if (!ZIO_CHECKSUM_EQUAL(ra->prev_cksum, drre->drr_checksum))
                        return (SET_ERROR(ECKSUM));
                return (0);
        }
        case DRR_SPILL:
        {
                struct drr_spill *drrs = &ra->rrd->header.drr_u.drr_spill;
                void *buf = kmem_zalloc(drrs->drr_length, KM_SLEEP);
                err = receive_read_payload_and_next_header(ra, drrs->drr_length,
                    buf);
                if (err != 0)
                        kmem_free(buf, drrs->drr_length);
                return (err);
        }
        default:
                return (SET_ERROR(EINVAL));
        }
}

/*
 * Commit the records to the pool.
 */
static int
receive_process_record(struct receive_writer_arg *rwa,
    struct receive_record_arg *rrd)
{
        int err;

        /* Processing in order, therefore bytes_read should be increasing. */
        ASSERT3U(rrd->bytes_read, >=, rwa->bytes_read);
        rwa->bytes_read = rrd->bytes_read;

        switch (rrd->header.drr_type) {
        case DRR_OBJECT:
        {
                struct drr_object *drro = &rrd->header.drr_u.drr_object;
                err = receive_object(rwa, drro, rrd->payload);
                kmem_free(rrd->payload, rrd->payload_size);
                rrd->payload = NULL;
                return (err);
        }
        case DRR_FREEOBJECTS:
        {
                struct drr_freeobjects *drrfo =
                    &rrd->header.drr_u.drr_freeobjects;
                return (receive_freeobjects(rwa, drrfo));
        }
        case DRR_WRITE:
        {
                struct drr_write *drrw = &rrd->header.drr_u.drr_write;
                err = receive_write(rwa, drrw, rrd->write_buf);
                /* if receive_write() is successful, it consumes the arc_buf */
                if (err != 0)
                        dmu_return_arcbuf(rrd->write_buf);
                rrd->write_buf = NULL;
                rrd->payload = NULL;
                return (err);
        }
        case DRR_WRITE_BYREF:
        {
                struct drr_write_byref *drrwbr =
                    &rrd->header.drr_u.drr_write_byref;
                return (receive_write_byref(rwa, drrwbr));
        }
        case DRR_WRITE_EMBEDDED:
        {
                struct drr_write_embedded *drrwe =
                    &rrd->header.drr_u.drr_write_embedded;
                err = receive_write_embedded(rwa, drrwe, rrd->payload);
                kmem_free(rrd->payload, rrd->payload_size);
                rrd->payload = NULL;
                return (err);
        }
        case DRR_FREE:
        {
                struct drr_free *drrf = &rrd->header.drr_u.drr_free;
                return (receive_free(rwa, drrf));
        }
        case DRR_SPILL:
        {
                struct drr_spill *drrs = &rrd->header.drr_u.drr_spill;
                err = receive_spill(rwa, drrs, rrd->payload);
                kmem_free(rrd->payload, rrd->payload_size);
                rrd->payload = NULL;
                return (err);
        }
        default:
                return (SET_ERROR(EINVAL));
        }
}

/*
 * dmu_recv_stream's worker thread; pull records off the queue, and then call
 * receive_process_record  When we're done, signal the main thread and exit.
 */
static void
receive_writer_thread(void *arg)
{
        struct receive_writer_arg *rwa = arg;
        struct receive_record_arg *rrd;
        for (rrd = bqueue_dequeue(&rwa->q); !rrd->eos_marker;
            rrd = bqueue_dequeue(&rwa->q)) {
                /*
                 * If there's an error, the main thread will stop putting things
                 * on the queue, but we need to clear everything in it before we
                 * can exit.
                 */
                if (rwa->err == 0) {
                        rwa->err = receive_process_record(rwa, rrd);
                } else if (rrd->write_buf != NULL) {
                        dmu_return_arcbuf(rrd->write_buf);
                        rrd->write_buf = NULL;
                        rrd->payload = NULL;
                } else if (rrd->payload != NULL) {
                        kmem_free(rrd->payload, rrd->payload_size);
                        rrd->payload = NULL;
                }
                kmem_free(rrd, sizeof (*rrd));
        }
        kmem_free(rrd, sizeof (*rrd));
        mutex_enter(&rwa->mutex);
        rwa->done = B_TRUE;
        cv_signal(&rwa->cv);
        mutex_exit(&rwa->mutex);
}

static int
resume_check(struct receive_arg *ra, nvlist_t *begin_nvl)
{
        uint64_t val;
        objset_t *mos = dmu_objset_pool(ra->os)->dp_meta_objset;
        uint64_t dsobj = dmu_objset_id(ra->os);
        uint64_t resume_obj, resume_off;

        if (nvlist_lookup_uint64(begin_nvl,
            "resume_object", &resume_obj) != 0 ||
            nvlist_lookup_uint64(begin_nvl,
            "resume_offset", &resume_off) != 0) {
                return (SET_ERROR(EINVAL));
        }
        VERIFY0(zap_lookup(mos, dsobj,
            DS_FIELD_RESUME_OBJECT, sizeof (val), 1, &val));
        if (resume_obj != val)
                return (SET_ERROR(EINVAL));
        VERIFY0(zap_lookup(mos, dsobj,
            DS_FIELD_RESUME_OFFSET, sizeof (val), 1, &val));
        if (resume_off != val)
                return (SET_ERROR(EINVAL));

        return (0);
}

/*
 * Read in the stream's records, one by one, and apply them to the pool.  There
 * are two threads involved; the thread that calls this function will spin up a
 * worker thread, read the records off the stream one by one, and issue
 * prefetches for any necessary indirect blocks.  It will then push the records
 * onto an internal blocking queue.  The worker thread will pull the records off
 * the queue, and actually write the data into the DMU.  This way, the worker
 * thread doesn't have to wait for reads to complete, since everything it needs
 * (the indirect blocks) will be prefetched.
 *
 * NB: callers *must* call dmu_recv_end() if this succeeds.
 */
int
dmu_recv_stream(dmu_recv_cookie_t *drc, vnode_t *vp, offset_t *voffp,
    int cleanup_fd, uint64_t *action_handlep)
{
        int err = 0;
        struct receive_arg ra = { 0 };
        struct receive_writer_arg rwa = { 0 };
        int featureflags;
        nvlist_t *begin_nvl = NULL;

        ra.byteswap = drc->drc_byteswap;
        ra.cksum = drc->drc_cksum;
        ra.vp = vp;
        ra.voff = *voffp;

        if (dsl_dataset_is_zapified(drc->drc_ds)) {
                (void) zap_lookup(drc->drc_ds->ds_dir->dd_pool->dp_meta_objset,
                    drc->drc_ds->ds_object, DS_FIELD_RESUME_BYTES,
                    sizeof (ra.bytes_read), 1, &ra.bytes_read);
        }

        objlist_create(&ra.ignore_objlist);

        /* these were verified in dmu_recv_begin */
        ASSERT3U(DMU_GET_STREAM_HDRTYPE(drc->drc_drrb->drr_versioninfo), ==,
            DMU_SUBSTREAM);
        ASSERT3U(drc->drc_drrb->drr_type, <, DMU_OST_NUMTYPES);

        /*
         * Open the objset we are modifying.
         */
        VERIFY0(dmu_objset_from_ds(drc->drc_ds, &ra.os));

        ASSERT(dsl_dataset_phys(drc->drc_ds)->ds_flags & DS_FLAG_INCONSISTENT);

        featureflags = DMU_GET_FEATUREFLAGS(drc->drc_drrb->drr_versioninfo);

        /* if this stream is dedup'ed, set up the avl tree for guid mapping */
        if (featureflags & DMU_BACKUP_FEATURE_DEDUP) {
                minor_t minor;

                if (cleanup_fd == -1) {
                        ra.err = SET_ERROR(EBADF);
                        goto out;
                }
                ra.err = zfs_onexit_fd_hold(cleanup_fd, &minor);
                if (ra.err != 0) {
                        cleanup_fd = -1;
                        goto out;
                }

                if (*action_handlep == 0) {
                        rwa.guid_to_ds_map =
                            kmem_alloc(sizeof (avl_tree_t), KM_SLEEP);
                        avl_create(rwa.guid_to_ds_map, guid_compare,
                            sizeof (guid_map_entry_t),
                            offsetof(guid_map_entry_t, avlnode));
                        err = zfs_onexit_add_cb(minor,
                            free_guid_map_onexit, rwa.guid_to_ds_map,
                            action_handlep);
                        if (ra.err != 0)
                                goto out;
                } else {
                        err = zfs_onexit_cb_data(minor, *action_handlep,
                            (void **)&rwa.guid_to_ds_map);
                        if (ra.err != 0)
                                goto out;
                }

                drc->drc_guid_to_ds_map = rwa.guid_to_ds_map;
        }

        uint32_t payloadlen = drc->drc_drr_begin->drr_payloadlen;
        void *payload = NULL;
        if (payloadlen != 0)
                payload = kmem_alloc(payloadlen, KM_SLEEP);

        err = receive_read_payload_and_next_header(&ra, payloadlen, payload);
        if (err != 0) {
                if (payloadlen != 0)
                        kmem_free(payload, payloadlen);
                goto out;
        }
        if (payloadlen != 0) {
                err = nvlist_unpack(payload, payloadlen, &begin_nvl, KM_SLEEP);
                kmem_free(payload, payloadlen);
                if (err != 0)
                        goto out;
        }

        if (featureflags & DMU_BACKUP_FEATURE_RESUMING) {
                err = resume_check(&ra, begin_nvl);
                if (err != 0)
                        goto out;
        }

        (void) bqueue_init(&rwa.q, zfs_recv_queue_length,
            offsetof(struct receive_record_arg, node));
        cv_init(&rwa.cv, NULL, CV_DEFAULT, NULL);
        mutex_init(&rwa.mutex, NULL, MUTEX_DEFAULT, NULL);
        rwa.os = ra.os;
        rwa.byteswap = drc->drc_byteswap;
        rwa.resumable = drc->drc_resumable;

        (void) thread_create(NULL, 0, receive_writer_thread, &rwa, 0, curproc,
            TS_RUN, minclsyspri);
        /*
         * We're reading rwa.err without locks, which is safe since we are the
         * only reader, and the worker thread is the only writer.  It's ok if we
         * miss a write for an iteration or two of the loop, since the writer
         * thread will keep freeing records we send it until we send it an eos
         * marker.
         *
         * We can leave this loop in 3 ways:  First, if rwa.err is
         * non-zero.  In that case, the writer thread will free the rrd we just
         * pushed.  Second, if  we're interrupted; in that case, either it's the
         * first loop and ra.rrd was never allocated, or it's later, and ra.rrd
         * has been handed off to the writer thread who will free it.  Finally,
         * if receive_read_record fails or we're at the end of the stream, then
         * we free ra.rrd and exit.
         */
        while (rwa.err == 0) {
                if (issig(JUSTLOOKING) && issig(FORREAL)) {
                        err = SET_ERROR(EINTR);
                        break;
                }

                ASSERT3P(ra.rrd, ==, NULL);
                ra.rrd = ra.next_rrd;
                ra.next_rrd = NULL;
                /* Allocates and loads header into ra.next_rrd */
                err = receive_read_record(&ra);

                if (ra.rrd->header.drr_type == DRR_END || err != 0) {
                        kmem_free(ra.rrd, sizeof (*ra.rrd));
                        ra.rrd = NULL;
                        break;
                }

                bqueue_enqueue(&rwa.q, ra.rrd,
                    sizeof (struct receive_record_arg) + ra.rrd->payload_size);
                ra.rrd = NULL;
        }
        if (ra.next_rrd == NULL)
                ra.next_rrd = kmem_zalloc(sizeof (*ra.next_rrd), KM_SLEEP);
        ra.next_rrd->eos_marker = B_TRUE;
        bqueue_enqueue(&rwa.q, ra.next_rrd, 1);

        mutex_enter(&rwa.mutex);
        while (!rwa.done) {
                cv_wait(&rwa.cv, &rwa.mutex);
        }
        mutex_exit(&rwa.mutex);

        cv_destroy(&rwa.cv);
        mutex_destroy(&rwa.mutex);
        bqueue_destroy(&rwa.q);
        if (err == 0)
                err = rwa.err;

out:
        nvlist_free(begin_nvl);
        if ((featureflags & DMU_BACKUP_FEATURE_DEDUP) && (cleanup_fd != -1))
                zfs_onexit_fd_rele(cleanup_fd);

        if (err != 0) {
                /*
                 * Clean up references. If receive is not resumable,
                 * destroy what we created, so we don't leave it in
                 * the inconsistent state.
                 */
                dmu_recv_cleanup_ds(drc);
        }

        *voffp = ra.voff;
        objlist_destroy(&ra.ignore_objlist);
        return (err);
}

static int
dmu_recv_end_check(void *arg, dmu_tx_t *tx)
{
        dmu_recv_cookie_t *drc = arg;
        dsl_pool_t *dp = dmu_tx_pool(tx);
        int error;

        ASSERT3P(drc->drc_ds->ds_owner, ==, dmu_recv_tag);

        if (!drc->drc_newfs) {
                dsl_dataset_t *origin_head;

                error = dsl_dataset_hold(dp, drc->drc_tofs, FTAG, &origin_head);
                if (error != 0)
                        return (error);
                if (drc->drc_force) {
                        /*
                         * We will destroy any snapshots in tofs (i.e. before
                         * origin_head) that are after the origin (which is
                         * the snap before drc_ds, because drc_ds can not
                         * have any snaps of its own).
                         */
                        uint64_t obj;

                        obj = dsl_dataset_phys(origin_head)->ds_prev_snap_obj;
                        while (obj !=
                            dsl_dataset_phys(drc->drc_ds)->ds_prev_snap_obj) {
                                dsl_dataset_t *snap;
                                error = dsl_dataset_hold_obj(dp, obj, FTAG,
                                    &snap);
                                if (error != 0)
                                        break;
                                if (snap->ds_dir != origin_head->ds_dir)
                                        error = SET_ERROR(EINVAL);
                                if (error == 0)  {
                                        error = dsl_destroy_snapshot_check_impl(
                                            snap, B_FALSE);
                                }
                                obj = dsl_dataset_phys(snap)->ds_prev_snap_obj;
                                dsl_dataset_rele(snap, FTAG);
                                if (error != 0)
                                        break;
                        }
                        if (error != 0) {
                                dsl_dataset_rele(origin_head, FTAG);
                                return (error);
                        }
                }
                error = dsl_dataset_clone_swap_check_impl(drc->drc_ds,
                    origin_head, drc->drc_force, drc->drc_owner, tx);
                if (error != 0) {
                        dsl_dataset_rele(origin_head, FTAG);
                        return (error);
                }
                error = dsl_dataset_snapshot_check_impl(origin_head,
                    drc->drc_tosnap, tx, B_TRUE, 1, drc->drc_cred);
                dsl_dataset_rele(origin_head, FTAG);
                if (error != 0)
                        return (error);

                error = dsl_destroy_head_check_impl(drc->drc_ds, 1);
        } else {
                error = dsl_dataset_snapshot_check_impl(drc->drc_ds,
                    drc->drc_tosnap, tx, B_TRUE, 1, drc->drc_cred);
        }
        return (error);
}

static void
dmu_recv_end_sync(void *arg, dmu_tx_t *tx)
{
        dmu_recv_cookie_t *drc = arg;
        dsl_pool_t *dp = dmu_tx_pool(tx);

        spa_history_log_internal_ds(drc->drc_ds, "finish receiving",
            tx, "snap=%s", drc->drc_tosnap);

        if (!drc->drc_newfs) {
                dsl_dataset_t *origin_head;

                VERIFY0(dsl_dataset_hold(dp, drc->drc_tofs, FTAG,
                    &origin_head));

                if (drc->drc_force) {
                        /*
                         * Destroy any snapshots of drc_tofs (origin_head)
                         * after the origin (the snap before drc_ds).
                         */
                        uint64_t obj;

                        obj = dsl_dataset_phys(origin_head)->ds_prev_snap_obj;
                        while (obj !=
                            dsl_dataset_phys(drc->drc_ds)->ds_prev_snap_obj) {
                                dsl_dataset_t *snap;
                                VERIFY0(dsl_dataset_hold_obj(dp, obj, FTAG,
                                    &snap));
                                ASSERT3P(snap->ds_dir, ==, origin_head->ds_dir);
                                obj = dsl_dataset_phys(snap)->ds_prev_snap_obj;
                                dsl_destroy_snapshot_sync_impl(snap,
                                    B_FALSE, tx);
                                dsl_dataset_rele(snap, FTAG);
                        }
                }
                VERIFY3P(drc->drc_ds->ds_prev, ==,
                    origin_head->ds_prev);

                dsl_dataset_clone_swap_sync_impl(drc->drc_ds,
                    origin_head, tx);
                dsl_dataset_snapshot_sync_impl(origin_head,
                    drc->drc_tosnap, tx);

                /* set snapshot's creation time and guid */
                dmu_buf_will_dirty(origin_head->ds_prev->ds_dbuf, tx);
                dsl_dataset_phys(origin_head->ds_prev)->ds_creation_time =
                    drc->drc_drrb->drr_creation_time;
                dsl_dataset_phys(origin_head->ds_prev)->ds_guid =
                    drc->drc_drrb->drr_toguid;
                dsl_dataset_phys(origin_head->ds_prev)->ds_flags &=
                    ~DS_FLAG_INCONSISTENT;

                dmu_buf_will_dirty(origin_head->ds_dbuf, tx);
                dsl_dataset_phys(origin_head)->ds_flags &=
                    ~DS_FLAG_INCONSISTENT;

                dsl_dataset_rele(origin_head, FTAG);
                dsl_destroy_head_sync_impl(drc->drc_ds, tx);

                if (drc->drc_owner != NULL)
                        VERIFY3P(origin_head->ds_owner, ==, drc->drc_owner);
        } else {
                dsl_dataset_t *ds = drc->drc_ds;

                dsl_dataset_snapshot_sync_impl(ds, drc->drc_tosnap, tx);

                /* set snapshot's creation time and guid */
                dmu_buf_will_dirty(ds->ds_prev->ds_dbuf, tx);
                dsl_dataset_phys(ds->ds_prev)->ds_creation_time =
                    drc->drc_drrb->drr_creation_time;
                dsl_dataset_phys(ds->ds_prev)->ds_guid =
                    drc->drc_drrb->drr_toguid;
                dsl_dataset_phys(ds->ds_prev)->ds_flags &=
                    ~DS_FLAG_INCONSISTENT;

                dmu_buf_will_dirty(ds->ds_dbuf, tx);
                dsl_dataset_phys(ds)->ds_flags &= ~DS_FLAG_INCONSISTENT;
                if (dsl_dataset_has_resume_receive_state(ds)) {
                        (void) zap_remove(dp->dp_meta_objset, ds->ds_object,
                            DS_FIELD_RESUME_FROMGUID, tx);
                        (void) zap_remove(dp->dp_meta_objset, ds->ds_object,
                            DS_FIELD_RESUME_OBJECT, tx);
                        (void) zap_remove(dp->dp_meta_objset, ds->ds_object,
                            DS_FIELD_RESUME_OFFSET, tx);
                        (void) zap_remove(dp->dp_meta_objset, ds->ds_object,
                            DS_FIELD_RESUME_BYTES, tx);
                        (void) zap_remove(dp->dp_meta_objset, ds->ds_object,
                            DS_FIELD_RESUME_TOGUID, tx);
                        (void) zap_remove(dp->dp_meta_objset, ds->ds_object,
                            DS_FIELD_RESUME_TONAME, tx);
                }
        }
        drc->drc_newsnapobj = dsl_dataset_phys(drc->drc_ds)->ds_prev_snap_obj;
        /*
         * Release the hold from dmu_recv_begin.  This must be done before
         * we return to open context, so that when we free the dataset's dnode,
         * we can evict its bonus buffer.
         */
        dsl_dataset_disown(drc->drc_ds, dmu_recv_tag);
        drc->drc_ds = NULL;
}

static int
add_ds_to_guidmap(const char *name, avl_tree_t *guid_map, uint64_t snapobj)
{
        dsl_pool_t *dp;
        dsl_dataset_t *snapds;
        guid_map_entry_t *gmep;
        int err;

        ASSERT(guid_map != NULL);

        err = dsl_pool_hold(name, FTAG, &dp);
        if (err != 0)
                return (err);
        gmep = kmem_alloc(sizeof (*gmep), KM_SLEEP);
        err = dsl_dataset_hold_obj(dp, snapobj, gmep, &snapds);
        if (err == 0) {
                gmep->guid = dsl_dataset_phys(snapds)->ds_guid;
                gmep->gme_ds = snapds;
                avl_add(guid_map, gmep);
                dsl_dataset_long_hold(snapds, gmep);
        } else {
                kmem_free(gmep, sizeof (*gmep));
        }

        dsl_pool_rele(dp, FTAG);
        return (err);
}

static int dmu_recv_end_modified_blocks = 3;

static int
dmu_recv_existing_end(dmu_recv_cookie_t *drc)
{
        int error;
        char name[MAXNAMELEN];

#ifdef _KERNEL
        /*
         * We will be destroying the ds; make sure its origin is unmounted if
         * necessary.
         */
        dsl_dataset_name(drc->drc_ds, name);
        zfs_destroy_unmount_origin(name);
#endif

        error = dsl_sync_task(drc->drc_tofs,
            dmu_recv_end_check, dmu_recv_end_sync, drc,
            dmu_recv_end_modified_blocks, ZFS_SPACE_CHECK_NORMAL);

        if (error != 0)
                dmu_recv_cleanup_ds(drc);
        return (error);
}

static int
dmu_recv_new_end(dmu_recv_cookie_t *drc)
{
        int error;

        error = dsl_sync_task(drc->drc_tofs,
            dmu_recv_end_check, dmu_recv_end_sync, drc,
            dmu_recv_end_modified_blocks, ZFS_SPACE_CHECK_NORMAL);

        if (error != 0) {
                dmu_recv_cleanup_ds(drc);
        } else if (drc->drc_guid_to_ds_map != NULL) {
                (void) add_ds_to_guidmap(drc->drc_tofs,
                    drc->drc_guid_to_ds_map,
                    drc->drc_newsnapobj);
        }
        return (error);
}

int
dmu_recv_end(dmu_recv_cookie_t *drc, void *owner)
{
        drc->drc_owner = owner;

        if (drc->drc_newfs)
                return (dmu_recv_new_end(drc));
        else
                return (dmu_recv_existing_end(drc));
}

/*
 * Return TRUE if this objset is currently being received into.
 */
boolean_t
dmu_objset_is_receiving(objset_t *os)
{
        return (os->os_dsl_dataset != NULL &&
            os->os_dsl_dataset->ds_owner == dmu_recv_tag);
}