Optimize RAIDZ expansion

[zfs.git] / module / 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 https://opensource.org/licenses/CDDL-1.0.
 * 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, 2018 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) 2016 Actifio, Inc. All rights reserved.
 * Copyright (c) 2019, 2024, Klara, Inc.
 * Copyright (c) 2019, Allan Jude
 */

#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/spa_impl.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/dmu_recv.h>
#include <sys/dsl_destroy.h>
#include <sys/blkptr.h>
#include <sys/dsl_bookmark.h>
#include <sys/zfeature.h>
#include <sys/bqueue.h>
#include <sys/zvol.h>
#include <sys/policy.h>
#include <sys/objlist.h>
#ifdef _KERNEL
#include <sys/zfs_vfsops.h>
#endif

/* Set this tunable to TRUE to replace corrupt data with 0x2f5baddb10c */
static int zfs_send_corrupt_data = B_FALSE;
/*
 * This tunable controls the amount of data (measured in bytes) that will be
 * prefetched by zfs send.  If the main thread is blocking on reads that haven't
 * completed, this variable might need to be increased.  If instead the main
 * thread is issuing new reads because the prefetches have fallen out of the
 * cache, this may need to be decreased.
 */
static uint_t zfs_send_queue_length = SPA_MAXBLOCKSIZE;
/*
 * This tunable controls the length of the queues that zfs send worker threads
 * use to communicate.  If the send_main_thread is blocking on these queues,
 * this variable may need to be increased.  If there is a significant slowdown
 * at the start of a send as these threads consume all the available IO
 * resources, this variable may need to be decreased.
 */
static uint_t zfs_send_no_prefetch_queue_length = 1024 * 1024;
/*
 * These tunables control the fill fraction of the queues by zfs send.  The fill
 * fraction controls the frequency with which threads have to be cv_signaled.
 * If a lot of cpu time is being spent on cv_signal, then these should be tuned
 * down.  If the queues empty before the signalled thread can catch up, then
 * these should be tuned up.
 */
static uint_t zfs_send_queue_ff = 20;
static uint_t zfs_send_no_prefetch_queue_ff = 20;

/*
 * Use this to override the recordsize calculation for fast zfs send estimates.
 */
static uint_t zfs_override_estimate_recordsize = 0;

/* Set this tunable to FALSE to disable setting of DRR_FLAG_FREERECORDS */
static const boolean_t zfs_send_set_freerecords_bit = B_TRUE;

/* Set this tunable to FALSE is disable sending unmodified spill blocks. */
static int zfs_send_unmodified_spill_blocks = B_TRUE;

static inline boolean_t
overflow_multiply(uint64_t a, uint64_t b, uint64_t *c)
{
        uint64_t temp = a * b;
        if (b != 0 && temp / b != a)
                return (B_FALSE);
        *c = temp;
        return (B_TRUE);
}

struct send_thread_arg {
        bqueue_t        q;
        objset_t        *os;            /* Objset 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;
        uint64_t        *num_blocks_visited;
};

struct redact_list_thread_arg {
        boolean_t               cancel;
        bqueue_t                q;
        zbookmark_phys_t        resume;
        redaction_list_t        *rl;
        boolean_t               mark_redact;
        int                     error_code;
        uint64_t                *num_blocks_visited;
};

struct send_merge_thread_arg {
        bqueue_t                        q;
        objset_t                        *os;
        struct redact_list_thread_arg   *from_arg;
        struct send_thread_arg          *to_arg;
        struct redact_list_thread_arg   *redact_arg;
        int                             error;
        boolean_t                       cancel;
};

struct send_range {
        boolean_t               eos_marker; /* Marks the end of the stream */
        uint64_t                object;
        uint64_t                start_blkid;
        uint64_t                end_blkid;
        bqueue_node_t           ln;
        enum type {DATA, HOLE, OBJECT, OBJECT_RANGE, REDACT,
            PREVIOUSLY_REDACTED} type;
        union {
                struct srd {
                        dmu_object_type_t       obj_type;
                        uint32_t                datablksz; // logical size
                        uint32_t                datasz; // payload size
                        blkptr_t                bp;
                        arc_buf_t               *abuf;
                        abd_t                   *abd;
                        kmutex_t                lock;
                        kcondvar_t              cv;
                        boolean_t               io_outstanding;
                        boolean_t               io_compressed;
                        int                     io_err;
                } data;
                struct srh {
                        uint32_t                datablksz;
                } hole;
                struct sro {
                        /*
                         * This is a pointer because embedding it in the
                         * struct causes these structures to be massively larger
                         * for all range types; this makes the code much less
                         * memory efficient.
                         */
                        dnode_phys_t            *dnp;
                        blkptr_t                bp;
                        /* Piggyback unmodified spill block */
                        struct send_range       *spill_range;
                } object;
                struct srr {
                        uint32_t                datablksz;
                } redact;
                struct sror {
                        blkptr_t                bp;
                } object_range;
        } sru;
};

/*
 * The list of data whose inclusion in a send stream can be pending from
 * one call to backup_cb to another.  Multiple calls to dump_free(),
 * dump_freeobjects(), and dump_redact() can be aggregated into a single
 * DRR_FREE, DRR_FREEOBJECTS, or DRR_REDACT replay record.
 */
typedef enum {
        PENDING_NONE,
        PENDING_FREE,
        PENDING_FREEOBJECTS,
        PENDING_REDACT
} dmu_pendop_t;

typedef struct dmu_send_cookie {
        dmu_replay_record_t *dsc_drr;
        dmu_send_outparams_t *dsc_dso;
        offset_t *dsc_off;
        objset_t *dsc_os;
        zio_cksum_t dsc_zc;
        uint64_t dsc_toguid;
        uint64_t dsc_fromtxg;
        int dsc_err;
        dmu_pendop_t dsc_pending_op;
        uint64_t dsc_featureflags;
        uint64_t dsc_last_data_object;
        uint64_t dsc_last_data_offset;
        uint64_t dsc_resume_object;
        uint64_t dsc_resume_offset;
        boolean_t dsc_sent_begin;
        boolean_t dsc_sent_end;
} dmu_send_cookie_t;

static int do_dump(dmu_send_cookie_t *dscp, struct send_range *range);

static void
range_free(struct send_range *range)
{
        if (range->type == OBJECT) {
                size_t size = sizeof (dnode_phys_t) *
                    (range->sru.object.dnp->dn_extra_slots + 1);
                kmem_free(range->sru.object.dnp, size);
                if (range->sru.object.spill_range)
                        range_free(range->sru.object.spill_range);
        } else if (range->type == DATA) {
                mutex_enter(&range->sru.data.lock);
                while (range->sru.data.io_outstanding)
                        cv_wait(&range->sru.data.cv, &range->sru.data.lock);
                if (range->sru.data.abd != NULL)
                        abd_free(range->sru.data.abd);
                if (range->sru.data.abuf != NULL) {
                        arc_buf_destroy(range->sru.data.abuf,
                            &range->sru.data.abuf);
                }
                mutex_exit(&range->sru.data.lock);

                cv_destroy(&range->sru.data.cv);
                mutex_destroy(&range->sru.data.lock);
        }
        kmem_free(range, sizeof (*range));
}

/*
 * 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_send_cookie_t *dscp, void *payload, int payload_len)
{
        dmu_send_outparams_t *dso = dscp->dsc_dso;
        ASSERT3U(offsetof(dmu_replay_record_t, drr_u.drr_checksum.drr_checksum),
            ==, sizeof (dmu_replay_record_t) - sizeof (zio_cksum_t));
        (void) fletcher_4_incremental_native(dscp->dsc_drr,
            offsetof(dmu_replay_record_t, drr_u.drr_checksum.drr_checksum),
            &dscp->dsc_zc);
        if (dscp->dsc_drr->drr_type == DRR_BEGIN) {
                dscp->dsc_sent_begin = B_TRUE;
        } else {
                ASSERT(ZIO_CHECKSUM_IS_ZERO(&dscp->dsc_drr->drr_u.
                    drr_checksum.drr_checksum));
                dscp->dsc_drr->drr_u.drr_checksum.drr_checksum = dscp->dsc_zc;
        }
        if (dscp->dsc_drr->drr_type == DRR_END) {
                dscp->dsc_sent_end = B_TRUE;
        }
        (void) fletcher_4_incremental_native(&dscp->dsc_drr->
            drr_u.drr_checksum.drr_checksum,
            sizeof (zio_cksum_t), &dscp->dsc_zc);
        *dscp->dsc_off += sizeof (dmu_replay_record_t);
        dscp->dsc_err = dso->dso_outfunc(dscp->dsc_os, dscp->dsc_drr,
            sizeof (dmu_replay_record_t), dso->dso_arg);
        if (dscp->dsc_err != 0)
                return (SET_ERROR(EINTR));
        if (payload_len != 0) {
                *dscp->dsc_off += payload_len;
                /*
                 * payload is null when dso_dryrun == B_TRUE (i.e. when we're
                 * doing a send size calculation)
                 */
                if (payload != NULL) {
                        (void) fletcher_4_incremental_native(
                            payload, payload_len, &dscp->dsc_zc);
                }

                /*
                 * 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).
                 *
                 * Raw sends cannot be received on old software, and so can
                 * bypass this assertion.
                 */

                ASSERT((payload_len % 8 == 0) ||
                    (dscp->dsc_featureflags & DMU_BACKUP_FEATURE_RAW));

                dscp->dsc_err = dso->dso_outfunc(dscp->dsc_os, payload,
                    payload_len, dso->dso_arg);
                if (dscp->dsc_err != 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_send_cookie_t *dscp, uint64_t object, uint64_t offset,
    uint64_t length)
{
        struct drr_free *drrf = &(dscp->dsc_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 > dscp->dsc_last_data_object ||
            (object == dscp->dsc_last_data_object &&
            offset > dscp->dsc_last_data_offset));

        /*
         * 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 (dscp->dsc_pending_op != PENDING_NONE &&
            dscp->dsc_pending_op != PENDING_FREE) {
                if (dump_record(dscp, NULL, 0) != 0)
                        return (SET_ERROR(EINTR));
                dscp->dsc_pending_op = PENDING_NONE;
        }

        if (dscp->dsc_pending_op == PENDING_FREE) {
                /*
                 * 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) {
                        if (offset + length < offset || length == UINT64_MAX)
                                drrf->drr_length = UINT64_MAX;
                        else
                                drrf->drr_length += length;
                        return (0);
                } else {
                        /* not a continuation.  Push out pending record */
                        if (dump_record(dscp, NULL, 0) != 0)
                                return (SET_ERROR(EINTR));
                        dscp->dsc_pending_op = PENDING_NONE;
                }
        }
        /* create a FREE record and make it pending */
        memset(dscp->dsc_drr, 0, sizeof (dmu_replay_record_t));
        dscp->dsc_drr->drr_type = DRR_FREE;
        drrf->drr_object = object;
        drrf->drr_offset = offset;
        if (offset + length < offset)
                drrf->drr_length = DMU_OBJECT_END;
        else
                drrf->drr_length = length;
        drrf->drr_toguid = dscp->dsc_toguid;
        if (length == DMU_OBJECT_END) {
                if (dump_record(dscp, NULL, 0) != 0)
                        return (SET_ERROR(EINTR));
        } else {
                dscp->dsc_pending_op = PENDING_FREE;
        }

        return (0);
}

/*
 * Fill in the drr_redact struct, or perform aggregation if the previous record
 * is also a redaction record, and the two are adjacent.
 */
static int
dump_redact(dmu_send_cookie_t *dscp, uint64_t object, uint64_t offset,
    uint64_t length)
{
        struct drr_redact *drrr = &dscp->dsc_drr->drr_u.drr_redact;

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

        if (dscp->dsc_pending_op == PENDING_REDACT) {
                /*
                 * Check to see whether this redacted block can be aggregated
                 * with pending one.
                 */
                if (drrr->drr_object == object && drrr->drr_offset +
                    drrr->drr_length == offset) {
                        drrr->drr_length += length;
                        return (0);
                } else {
                        /* not a continuation.  Push out pending record */
                        if (dump_record(dscp, NULL, 0) != 0)
                                return (SET_ERROR(EINTR));
                        dscp->dsc_pending_op = PENDING_NONE;
                }
        }
        /* create a REDACT record and make it pending */
        memset(dscp->dsc_drr, 0, sizeof (dmu_replay_record_t));
        dscp->dsc_drr->drr_type = DRR_REDACT;
        drrr->drr_object = object;
        drrr->drr_offset = offset;
        drrr->drr_length = length;
        drrr->drr_toguid = dscp->dsc_toguid;
        dscp->dsc_pending_op = PENDING_REDACT;

        return (0);
}

static int
dmu_dump_write(dmu_send_cookie_t *dscp, dmu_object_type_t type, uint64_t object,
    uint64_t offset, int lsize, int psize, const blkptr_t *bp,
    boolean_t io_compressed, void *data)
{
        uint64_t payload_size;
        boolean_t raw = (dscp->dsc_featureflags & DMU_BACKUP_FEATURE_RAW);
        struct drr_write *drrw = &(dscp->dsc_drr->drr_u.drr_write);

        /*
         * We send data in increasing object, offset order.
         * See comment in dump_free() for details.
         */
        ASSERT(object > dscp->dsc_last_data_object ||
            (object == dscp->dsc_last_data_object &&
            offset > dscp->dsc_last_data_offset));
        dscp->dsc_last_data_object = object;
        dscp->dsc_last_data_offset = offset + lsize - 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 (dscp->dsc_pending_op != PENDING_NONE) {
                if (dump_record(dscp, NULL, 0) != 0)
                        return (SET_ERROR(EINTR));
                dscp->dsc_pending_op = PENDING_NONE;
        }
        /* write a WRITE record */
        memset(dscp->dsc_drr, 0, sizeof (dmu_replay_record_t));
        dscp->dsc_drr->drr_type = DRR_WRITE;
        drrw->drr_object = object;
        drrw->drr_type = type;
        drrw->drr_offset = offset;
        drrw->drr_toguid = dscp->dsc_toguid;
        drrw->drr_logical_size = lsize;

        /* only set the compression fields if the buf is compressed or raw */
        boolean_t compressed =
            (bp != NULL ? BP_GET_COMPRESS(bp) != ZIO_COMPRESS_OFF &&
            io_compressed : lsize != psize);
        if (raw || compressed) {
                ASSERT(bp != NULL);
                ASSERT(raw || dscp->dsc_featureflags &
                    DMU_BACKUP_FEATURE_COMPRESSED);
                ASSERT(!BP_IS_EMBEDDED(bp));
                ASSERT3S(psize, >, 0);

                if (raw) {
                        ASSERT(BP_IS_PROTECTED(bp));

                        /*
                         * This is a raw protected block so we need to pass
                         * along everything the receiving side will need to
                         * interpret this block, including the byteswap, salt,
                         * IV, and MAC.
                         */
                        if (BP_SHOULD_BYTESWAP(bp))
                                drrw->drr_flags |= DRR_RAW_BYTESWAP;
                        zio_crypt_decode_params_bp(bp, drrw->drr_salt,
                            drrw->drr_iv);
                        zio_crypt_decode_mac_bp(bp, drrw->drr_mac);
                } else {
                        /* this is a compressed block */
                        ASSERT(dscp->dsc_featureflags &
                            DMU_BACKUP_FEATURE_COMPRESSED);
                        ASSERT(!BP_SHOULD_BYTESWAP(bp));
                        ASSERT(!DMU_OT_IS_METADATA(BP_GET_TYPE(bp)));
                        ASSERT3U(BP_GET_COMPRESS(bp), !=, ZIO_COMPRESS_OFF);
                        ASSERT3S(lsize, >=, psize);
                }

                /* set fields common to compressed and raw sends */
                drrw->drr_compressiontype = BP_GET_COMPRESS(bp);
                drrw->drr_compressed_size = psize;
                payload_size = drrw->drr_compressed_size;
        } else {
                payload_size = drrw->drr_logical_size;
        }

        if (bp == NULL || BP_IS_EMBEDDED(bp) || (BP_IS_PROTECTED(bp) && !raw)) {
                /*
                 * There's no pre-computed checksum for partial-block writes,
                 * embedded BP's, or encrypted BP's that are being sent as
                 * plaintext, so (like fletcher4-checksummed 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_flags |= 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));
                DDK_SET_CRYPT(&drrw->drr_key, BP_IS_PROTECTED(bp));
                drrw->drr_key.ddk_cksum = bp->blk_cksum;
        }

        if (dump_record(dscp, data, payload_size) != 0)
                return (SET_ERROR(EINTR));
        return (0);
}

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

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

        ASSERT(BP_IS_EMBEDDED(bp));

        memset(dscp->dsc_drr, 0, sizeof (dmu_replay_record_t));
        dscp->dsc_drr->drr_type = DRR_WRITE_EMBEDDED;
        drrw->drr_object = object;
        drrw->drr_offset = offset;
        drrw->drr_length = blksz;
        drrw->drr_toguid = dscp->dsc_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);

        uint32_t psize = drrw->drr_psize;
        uint32_t rsize = P2ROUNDUP(psize, 8);

        if (psize != rsize)
                memset(buf + psize, 0, rsize - psize);

        if (dump_record(dscp, buf, rsize) != 0)
                return (SET_ERROR(EINTR));
        return (0);
}

static int
dump_spill(dmu_send_cookie_t *dscp, const blkptr_t *bp, uint64_t object,
    void *data)
{
        struct drr_spill *drrs = &(dscp->dsc_drr->drr_u.drr_spill);
        uint64_t blksz = BP_GET_LSIZE(bp);
        uint64_t payload_size = blksz;

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

        /* write a SPILL record */
        memset(dscp->dsc_drr, 0, sizeof (dmu_replay_record_t));
        dscp->dsc_drr->drr_type = DRR_SPILL;
        drrs->drr_object = object;
        drrs->drr_length = blksz;
        drrs->drr_toguid = dscp->dsc_toguid;

        /* See comment in piggyback_unmodified_spill() for full details */
        if (zfs_send_unmodified_spill_blocks &&
            (BP_GET_LOGICAL_BIRTH(bp) <= dscp->dsc_fromtxg)) {
                drrs->drr_flags |= DRR_SPILL_UNMODIFIED;
        }

        /* handle raw send fields */
        if (dscp->dsc_featureflags & DMU_BACKUP_FEATURE_RAW) {
                ASSERT(BP_IS_PROTECTED(bp));

                if (BP_SHOULD_BYTESWAP(bp))
                        drrs->drr_flags |= DRR_RAW_BYTESWAP;
                drrs->drr_compressiontype = BP_GET_COMPRESS(bp);
                drrs->drr_compressed_size = BP_GET_PSIZE(bp);
                zio_crypt_decode_params_bp(bp, drrs->drr_salt, drrs->drr_iv);
                zio_crypt_decode_mac_bp(bp, drrs->drr_mac);
                payload_size = drrs->drr_compressed_size;
        }

        if (dump_record(dscp, data, payload_size) != 0)
                return (SET_ERROR(EINTR));
        return (0);
}

static int
dump_freeobjects(dmu_send_cookie_t *dscp, uint64_t firstobj, uint64_t numobjs)
{
        struct drr_freeobjects *drrfo = &(dscp->dsc_drr->drr_u.drr_freeobjects);
        uint64_t maxobj = DNODES_PER_BLOCK *
            (DMU_META_DNODE(dscp->dsc_os)->dn_maxblkid + 1);

        /*
         * ZoL < 0.7 does not handle large FREEOBJECTS records correctly,
         * leading to zfs recv never completing. to avoid this issue, don't
         * send FREEOBJECTS records for object IDs which cannot exist on the
         * receiving side.
         */
        if (maxobj > 0) {
                if (maxobj <= firstobj)
                        return (0);

                if (maxobj < firstobj + numobjs)
                        numobjs = maxobj - firstobj;
        }

        /*
         * 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 (dscp->dsc_pending_op != PENDING_NONE &&
            dscp->dsc_pending_op != PENDING_FREEOBJECTS) {
                if (dump_record(dscp, NULL, 0) != 0)
                        return (SET_ERROR(EINTR));
                dscp->dsc_pending_op = PENDING_NONE;
        }

        if (dscp->dsc_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(dscp, NULL, 0) != 0)
                                return (SET_ERROR(EINTR));
                        dscp->dsc_pending_op = PENDING_NONE;
                }
        }

        /* write a FREEOBJECTS record */
        memset(dscp->dsc_drr, 0, sizeof (dmu_replay_record_t));
        dscp->dsc_drr->drr_type = DRR_FREEOBJECTS;
        drrfo->drr_firstobj = firstobj;
        drrfo->drr_numobjs = numobjs;
        drrfo->drr_toguid = dscp->dsc_toguid;

        dscp->dsc_pending_op = PENDING_FREEOBJECTS;

        return (0);
}

static int
dump_dnode(dmu_send_cookie_t *dscp, const blkptr_t *bp, uint64_t object,
    dnode_phys_t *dnp)
{
        struct drr_object *drro = &(dscp->dsc_drr->drr_u.drr_object);
        int bonuslen;

        if (object < dscp->dsc_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(dscp->dsc_resume_object - object, <,
                    1 << (DNODE_BLOCK_SHIFT - DNODE_SHIFT));
                return (0);
        }

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

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

        /* write an OBJECT record */
        memset(dscp->dsc_drr, 0, sizeof (dmu_replay_record_t));
        dscp->dsc_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_dn_slots = dnp->dn_extra_slots + 1;
        drro->drr_checksumtype = dnp->dn_checksum;
        drro->drr_compress = dnp->dn_compress;
        drro->drr_toguid = dscp->dsc_toguid;

        if (!(dscp->dsc_featureflags & DMU_BACKUP_FEATURE_LARGE_BLOCKS) &&
            drro->drr_blksz > SPA_OLD_MAXBLOCKSIZE)
                drro->drr_blksz = SPA_OLD_MAXBLOCKSIZE;

        bonuslen = P2ROUNDUP(dnp->dn_bonuslen, 8);

        if ((dscp->dsc_featureflags & DMU_BACKUP_FEATURE_RAW)) {
                ASSERT(BP_IS_ENCRYPTED(bp));

                if (BP_SHOULD_BYTESWAP(bp))
                        drro->drr_flags |= DRR_RAW_BYTESWAP;

                /* needed for reconstructing dnp on recv side */
                drro->drr_maxblkid = dnp->dn_maxblkid;
                drro->drr_indblkshift = dnp->dn_indblkshift;
                drro->drr_nlevels = dnp->dn_nlevels;
                drro->drr_nblkptr = dnp->dn_nblkptr;

                /*
                 * Since we encrypt the entire bonus area, the (raw) part
                 * beyond the bonuslen is actually nonzero, so we need
                 * to send it.
                 */
                if (bonuslen != 0) {
                        if (drro->drr_bonuslen > DN_MAX_BONUS_LEN(dnp))
                                return (SET_ERROR(EINVAL));
                        drro->drr_raw_bonuslen = DN_MAX_BONUS_LEN(dnp);
                        bonuslen = drro->drr_raw_bonuslen;
                }
        }

        /*
         * DRR_OBJECT_SPILL is set for every dnode which references a
         * spill block.  This allows the receiving pool to definitively
         * determine when a spill block should be kept or freed.
         */
        if (dnp->dn_flags & DNODE_FLAG_SPILL_BLKPTR)
                drro->drr_flags |= DRR_OBJECT_SPILL;

        if (dump_record(dscp, DN_BONUS(dnp), bonuslen) != 0)
                return (SET_ERROR(EINTR));

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

        if (dscp->dsc_err != 0)
                return (SET_ERROR(EINTR));

        return (0);
}

static int
dump_object_range(dmu_send_cookie_t *dscp, const blkptr_t *bp,
    uint64_t firstobj, uint64_t numslots)
{
        struct drr_object_range *drror =
            &(dscp->dsc_drr->drr_u.drr_object_range);

        /* we only use this record type for raw sends */
        ASSERT(BP_IS_PROTECTED(bp));
        ASSERT(dscp->dsc_featureflags & DMU_BACKUP_FEATURE_RAW);
        ASSERT3U(BP_GET_COMPRESS(bp), ==, ZIO_COMPRESS_OFF);
        ASSERT3U(BP_GET_TYPE(bp), ==, DMU_OT_DNODE);
        ASSERT0(BP_GET_LEVEL(bp));

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

        memset(dscp->dsc_drr, 0, sizeof (dmu_replay_record_t));
        dscp->dsc_drr->drr_type = DRR_OBJECT_RANGE;
        drror->drr_firstobj = firstobj;
        drror->drr_numslots = numslots;
        drror->drr_toguid = dscp->dsc_toguid;
        if (BP_SHOULD_BYTESWAP(bp))
                drror->drr_flags |= DRR_RAW_BYTESWAP;
        zio_crypt_decode_params_bp(bp, drror->drr_salt, drror->drr_iv);
        zio_crypt_decode_mac_bp(bp, drror->drr_mac);

        if (dump_record(dscp, NULL, 0) != 0)
                return (SET_ERROR(EINTR));
        return (0);
}

static boolean_t
send_do_embed(const blkptr_t *bp, uint64_t featureflags)
{
        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 &&
            !(featureflags & DMU_BACKUP_FEATURE_LZ4)))
                return (B_FALSE);

        /*
         * If we have not set the ZSTD feature flag, we can't send ZSTD
         * compressed embedded blocks, as the receiver may not support them.
         */
        if ((BP_GET_COMPRESS(bp) == ZIO_COMPRESS_ZSTD &&
            !(featureflags & DMU_BACKUP_FEATURE_ZSTD)))
                return (B_FALSE);

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

/*
 * This function actually handles figuring out what kind of record needs to be
 * dumped, and calling the appropriate helper function.  In most cases,
 * the data has already been read by send_reader_thread().
 */
static int
do_dump(dmu_send_cookie_t *dscp, struct send_range *range)
{
        int err = 0;
        switch (range->type) {
        case OBJECT:
                err = dump_dnode(dscp, &range->sru.object.bp, range->object,
                    range->sru.object.dnp);
                /* Dump piggybacked unmodified spill block */
                if (!err && range->sru.object.spill_range)
                        err = do_dump(dscp, range->sru.object.spill_range);
                return (err);
        case OBJECT_RANGE: {
                ASSERT3U(range->start_blkid + 1, ==, range->end_blkid);
                if (!(dscp->dsc_featureflags & DMU_BACKUP_FEATURE_RAW)) {
                        return (0);
                }
                uint64_t epb = BP_GET_LSIZE(&range->sru.object_range.bp) >>
                    DNODE_SHIFT;
                uint64_t firstobj = range->start_blkid * epb;
                err = dump_object_range(dscp, &range->sru.object_range.bp,
                    firstobj, epb);
                break;
        }
        case REDACT: {
                struct srr *srrp = &range->sru.redact;
                err = dump_redact(dscp, range->object, range->start_blkid *
                    srrp->datablksz, (range->end_blkid - range->start_blkid) *
                    srrp->datablksz);
                return (err);
        }
        case DATA: {
                struct srd *srdp = &range->sru.data;
                blkptr_t *bp = &srdp->bp;
                spa_t *spa =
                    dmu_objset_spa(dscp->dsc_os);

                ASSERT3U(srdp->datablksz, ==, BP_GET_LSIZE(bp));
                ASSERT3U(range->start_blkid + 1, ==, range->end_blkid);

                if (send_do_embed(bp, dscp->dsc_featureflags)) {
                        err = dump_write_embedded(dscp, range->object,
                            range->start_blkid * srdp->datablksz,
                            srdp->datablksz, bp);
                        return (err);
                }
                ASSERT(range->object > dscp->dsc_resume_object ||
                    (range->object == dscp->dsc_resume_object &&
                    (range->start_blkid == DMU_SPILL_BLKID ||
                    range->start_blkid * srdp->datablksz >=
                    dscp->dsc_resume_offset)));
                /* it's a level-0 block of a regular object */

                mutex_enter(&srdp->lock);
                while (srdp->io_outstanding)
                        cv_wait(&srdp->cv, &srdp->lock);
                err = srdp->io_err;
                mutex_exit(&srdp->lock);

                if (err != 0) {
                        if (zfs_send_corrupt_data &&
                            !dscp->dsc_dso->dso_dryrun) {
                                /*
                                 * Send a block filled with 0x"zfs badd bloc"
                                 */
                                srdp->abuf = arc_alloc_buf(spa, &srdp->abuf,
                                    ARC_BUFC_DATA, srdp->datablksz);
                                uint64_t *ptr;
                                for (ptr = srdp->abuf->b_data;
                                    (char *)ptr < (char *)srdp->abuf->b_data +
                                    srdp->datablksz; ptr++)
                                        *ptr = 0x2f5baddb10cULL;
                        } else {
                                return (SET_ERROR(EIO));
                        }
                }

                ASSERT(dscp->dsc_dso->dso_dryrun ||
                    srdp->abuf != NULL || srdp->abd != NULL);

                char *data = NULL;
                if (srdp->abd != NULL) {
                        data = abd_to_buf(srdp->abd);
                        ASSERT3P(srdp->abuf, ==, NULL);
                } else if (srdp->abuf != NULL) {
                        data = srdp->abuf->b_data;
                }

                if (BP_GET_TYPE(bp) == DMU_OT_SA) {
                        ASSERT3U(range->start_blkid, ==, DMU_SPILL_BLKID);
                        err = dump_spill(dscp, bp, range->object, data);
                        return (err);
                }

                uint64_t offset = range->start_blkid * srdp->datablksz;

                /*
                 * If we have large blocks stored on disk but the send flags
                 * don't allow us to send large blocks, we split the data from
                 * the arc buf into chunks.
                 */
                if (srdp->datablksz > SPA_OLD_MAXBLOCKSIZE &&
                    !(dscp->dsc_featureflags &
                    DMU_BACKUP_FEATURE_LARGE_BLOCKS)) {
                        while (srdp->datablksz > 0 && err == 0) {
                                int n = MIN(srdp->datablksz,
                                    SPA_OLD_MAXBLOCKSIZE);
                                err = dmu_dump_write(dscp, srdp->obj_type,
                                    range->object, offset, n, n, NULL, B_FALSE,
                                    data);
                                offset += n;
                                /*
                                 * When doing dry run, data==NULL is used as a
                                 * sentinel value by
                                 * dmu_dump_write()->dump_record().
                                 */
                                if (data != NULL)
                                        data += n;
                                srdp->datablksz -= n;
                        }
                } else {
                        err = dmu_dump_write(dscp, srdp->obj_type,
                            range->object, offset,
                            srdp->datablksz, srdp->datasz, bp,
                            srdp->io_compressed, data);
                }
                return (err);
        }
        case HOLE: {
                struct srh *srhp = &range->sru.hole;
                if (range->object == DMU_META_DNODE_OBJECT) {
                        uint32_t span = srhp->datablksz >> DNODE_SHIFT;
                        uint64_t first_obj = range->start_blkid * span;
                        uint64_t numobj = range->end_blkid * span - first_obj;
                        return (dump_freeobjects(dscp, first_obj, numobj));
                }
                uint64_t offset = 0;

                /*
                 * If this multiply overflows, we don't need to send this block.
                 * Even if it has a birth time, it can never not be a hole, so
                 * we don't need to send records for it.
                 */
                if (!overflow_multiply(range->start_blkid, srhp->datablksz,
                    &offset)) {
                        return (0);
                }
                uint64_t len = 0;

                if (!overflow_multiply(range->end_blkid, srhp->datablksz, &len))
                        len = UINT64_MAX;
                len = len - offset;
                return (dump_free(dscp, range->object, offset, len));
        }
        default:
                panic("Invalid range type in do_dump: %d", range->type);
        }
        return (err);
}

static struct send_range *
range_alloc(enum type type, uint64_t object, uint64_t start_blkid,
    uint64_t end_blkid, boolean_t eos)
{
        struct send_range *range = kmem_alloc(sizeof (*range), KM_SLEEP);
        range->type = type;
        range->object = object;
        range->start_blkid = start_blkid;
        range->end_blkid = end_blkid;
        range->eos_marker = eos;
        if (type == DATA) {
                range->sru.data.abd = NULL;
                range->sru.data.abuf = NULL;
                mutex_init(&range->sru.data.lock, NULL, MUTEX_DEFAULT, NULL);
                cv_init(&range->sru.data.cv, NULL, CV_DEFAULT, NULL);
                range->sru.data.io_outstanding = 0;
                range->sru.data.io_err = 0;
                range->sru.data.io_compressed = B_FALSE;
        } else if (type == OBJECT) {
                range->sru.object.spill_range = NULL;
        }
        return (range);
}

/*
 * This is the callback function to traverse_dataset that acts as a worker
 * thread for dmu_send_impl.
 */
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)
{
        (void) zilog;
        struct send_thread_arg *sta = arg;
        struct send_range *record;

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

        /*
         * All bps of an encrypted os should have the encryption bit set.
         * If this is not true it indicates tampering and we report an error.
         */
        if (sta->os->os_encrypted &&
            !BP_IS_HOLE(bp) && !BP_USES_CRYPT(bp)) {
                spa_log_error(spa, zb, BP_GET_LOGICAL_BIRTH(bp));
                return (SET_ERROR(EIO));
        }

        if (sta->cancel)
                return (SET_ERROR(EINTR));
        if (zb->zb_object != DMU_META_DNODE_OBJECT &&
            DMU_OBJECT_IS_SPECIAL(zb->zb_object))
                return (0);
        atomic_inc_64(sta->num_blocks_visited);

        if (zb->zb_level == ZB_DNODE_LEVEL) {
                if (zb->zb_object == DMU_META_DNODE_OBJECT)
                        return (0);
                record = range_alloc(OBJECT, zb->zb_object, 0, 0, B_FALSE);
                record->sru.object.bp = *bp;
                size_t size  = sizeof (*dnp) * (dnp->dn_extra_slots + 1);
                record->sru.object.dnp = kmem_alloc(size, KM_SLEEP);
                memcpy(record->sru.object.dnp, dnp, size);
                bqueue_enqueue(&sta->q, record, sizeof (*record));
                return (0);
        }
        if (zb->zb_level == 0 && zb->zb_object == DMU_META_DNODE_OBJECT &&
            !BP_IS_HOLE(bp)) {
                record = range_alloc(OBJECT_RANGE, 0, zb->zb_blkid,
                    zb->zb_blkid + 1, B_FALSE);
                record->sru.object_range.bp = *bp;
                bqueue_enqueue(&sta->q, record, sizeof (*record));
                return (0);
        }
        if (zb->zb_level < 0 || (zb->zb_level > 0 && !BP_IS_HOLE(bp)))
                return (0);
        if (zb->zb_object == DMU_META_DNODE_OBJECT && !BP_IS_HOLE(bp))
                return (0);

        uint64_t span = bp_span_in_blocks(dnp->dn_indblkshift, zb->zb_level);
        uint64_t start;

        /*
         * If this multiply overflows, we don't need to send this block.
         * Even if it has a birth time, it can never not be a hole, so
         * we don't need to send records for it.
         */
        if (!overflow_multiply(span, zb->zb_blkid, &start) || (!(zb->zb_blkid ==
            DMU_SPILL_BLKID || DMU_OT_IS_METADATA(dnp->dn_type)) &&
            span * zb->zb_blkid > dnp->dn_maxblkid)) {
                ASSERT(BP_IS_HOLE(bp));
                return (0);
        }

        if (zb->zb_blkid == DMU_SPILL_BLKID)
                ASSERT3U(BP_GET_TYPE(bp), ==, DMU_OT_SA);

        enum type record_type = DATA;
        if (BP_IS_HOLE(bp))
                record_type = HOLE;
        else if (BP_IS_REDACTED(bp))
                record_type = REDACT;
        else
                record_type = DATA;

        record = range_alloc(record_type, zb->zb_object, start,
            (start + span < start ? 0 : start + span), B_FALSE);

        uint64_t datablksz = (zb->zb_blkid == DMU_SPILL_BLKID ?
            BP_GET_LSIZE(bp) : dnp->dn_datablkszsec << SPA_MINBLOCKSHIFT);

        if (BP_IS_HOLE(bp)) {
                record->sru.hole.datablksz = datablksz;
        } else if (BP_IS_REDACTED(bp)) {
                record->sru.redact.datablksz = datablksz;
        } else {
                record->sru.data.datablksz = datablksz;
                record->sru.data.obj_type = dnp->dn_type;
                record->sru.data.bp = *bp;
        }

        bqueue_enqueue(&sta->q, record, sizeof (*record));
        return (0);
}

struct redact_list_cb_arg {
        uint64_t *num_blocks_visited;
        bqueue_t *q;
        boolean_t *cancel;
        boolean_t mark_redact;
};

static int
redact_list_cb(redact_block_phys_t *rb, void *arg)
{
        struct redact_list_cb_arg *rlcap = arg;

        atomic_inc_64(rlcap->num_blocks_visited);
        if (*rlcap->cancel)
                return (-1);

        struct send_range *data = range_alloc(REDACT, rb->rbp_object,
            rb->rbp_blkid, rb->rbp_blkid + redact_block_get_count(rb), B_FALSE);
        ASSERT3U(data->end_blkid, >, rb->rbp_blkid);
        if (rlcap->mark_redact) {
                data->type = REDACT;
                data->sru.redact.datablksz = redact_block_get_size(rb);
        } else {
                data->type = PREVIOUSLY_REDACTED;
        }
        bqueue_enqueue(rlcap->q, data, sizeof (*data));

        return (0);
}

/*
 * 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.
 */
static __attribute__((noreturn)) void
send_traverse_thread(void *arg)
{
        struct send_thread_arg *st_arg = arg;
        int err = 0;
        struct send_range *data;
        fstrans_cookie_t cookie = spl_fstrans_mark();

        err = traverse_dataset_resume(st_arg->os->os_dsl_dataset,
            st_arg->fromtxg, &st_arg->resume,
            st_arg->flags, send_cb, st_arg);

        if (err != EINTR)
                st_arg->error_code = err;
        data = range_alloc(DATA, 0, 0, 0, B_TRUE);
        bqueue_enqueue_flush(&st_arg->q, data, sizeof (*data));
        spl_fstrans_unmark(cookie);
        thread_exit();
}

/*
 * Utility function that causes End of Stream records to compare after of all
 * others, so that other threads' comparison logic can stay simple.
 */
static int __attribute__((unused))
send_range_after(const struct send_range *from, const struct send_range *to)
{
        if (from->eos_marker == B_TRUE)
                return (1);
        if (to->eos_marker == B_TRUE)
                return (-1);

        uint64_t from_obj = from->object;
        uint64_t from_end_obj = from->object + 1;
        uint64_t to_obj = to->object;
        uint64_t to_end_obj = to->object + 1;
        if (from_obj == 0) {
                ASSERT(from->type == HOLE || from->type == OBJECT_RANGE);
                from_obj = from->start_blkid << DNODES_PER_BLOCK_SHIFT;
                from_end_obj = from->end_blkid << DNODES_PER_BLOCK_SHIFT;
        }
        if (to_obj == 0) {
                ASSERT(to->type == HOLE || to->type == OBJECT_RANGE);
                to_obj = to->start_blkid << DNODES_PER_BLOCK_SHIFT;
                to_end_obj = to->end_blkid << DNODES_PER_BLOCK_SHIFT;
        }

        if (from_end_obj <= to_obj)
                return (-1);
        if (from_obj >= to_end_obj)
                return (1);
        int64_t cmp = TREE_CMP(to->type == OBJECT_RANGE, from->type ==
            OBJECT_RANGE);
        if (unlikely(cmp))
                return (cmp);
        cmp = TREE_CMP(to->type == OBJECT, from->type == OBJECT);
        if (unlikely(cmp))
                return (cmp);
        if (from->end_blkid <= to->start_blkid)
                return (-1);
        if (from->start_blkid >= to->end_blkid)
                return (1);
        return (0);
}

/*
 * Pop the new data off the queue, check that the records we receive are in
 * the right order, but do not free the old data.  This is used so that the
 * records can be sent on to the main thread without copying the data.
 */
static struct send_range *
get_next_range_nofree(bqueue_t *bq, struct send_range *prev)
{
        struct send_range *next = bqueue_dequeue(bq);
        ASSERT3S(send_range_after(prev, next), ==, -1);
        return (next);
}

/*
 * Pop the new data off the queue, check that the records we receive are in
 * the right order, and free the old data.
 */
static struct send_range *
get_next_range(bqueue_t *bq, struct send_range *prev)
{
        struct send_range *next = get_next_range_nofree(bq, prev);
        range_free(prev);
        return (next);
}

static __attribute__((noreturn)) void
redact_list_thread(void *arg)
{
        struct redact_list_thread_arg *rlt_arg = arg;
        struct send_range *record;
        fstrans_cookie_t cookie = spl_fstrans_mark();
        if (rlt_arg->rl != NULL) {
                struct redact_list_cb_arg rlcba = {0};
                rlcba.cancel = &rlt_arg->cancel;
                rlcba.q = &rlt_arg->q;
                rlcba.num_blocks_visited = rlt_arg->num_blocks_visited;
                rlcba.mark_redact = rlt_arg->mark_redact;
                int err = dsl_redaction_list_traverse(rlt_arg->rl,
                    &rlt_arg->resume, redact_list_cb, &rlcba);
                if (err != EINTR)
                        rlt_arg->error_code = err;
        }
        record = range_alloc(DATA, 0, 0, 0, B_TRUE);
        bqueue_enqueue_flush(&rlt_arg->q, record, sizeof (*record));
        spl_fstrans_unmark(cookie);

        thread_exit();
}

/*
 * Compare the start point of the two provided ranges. End of stream ranges
 * compare last, objects compare before any data or hole inside that object and
 * multi-object holes that start at the same object.
 */
static int
send_range_start_compare(struct send_range *r1, struct send_range *r2)
{
        uint64_t r1_objequiv = r1->object;
        uint64_t r1_l0equiv = r1->start_blkid;
        uint64_t r2_objequiv = r2->object;
        uint64_t r2_l0equiv = r2->start_blkid;
        int64_t cmp = TREE_CMP(r1->eos_marker, r2->eos_marker);
        if (unlikely(cmp))
                return (cmp);
        if (r1->object == 0) {
                r1_objequiv = r1->start_blkid * DNODES_PER_BLOCK;
                r1_l0equiv = 0;
        }
        if (r2->object == 0) {
                r2_objequiv = r2->start_blkid * DNODES_PER_BLOCK;
                r2_l0equiv = 0;
        }

        cmp = TREE_CMP(r1_objequiv, r2_objequiv);
        if (likely(cmp))
                return (cmp);
        cmp = TREE_CMP(r2->type == OBJECT_RANGE, r1->type == OBJECT_RANGE);
        if (unlikely(cmp))
                return (cmp);
        cmp = TREE_CMP(r2->type == OBJECT, r1->type == OBJECT);
        if (unlikely(cmp))
                return (cmp);

        return (TREE_CMP(r1_l0equiv, r2_l0equiv));
}

enum q_idx {
        REDACT_IDX = 0,
        TO_IDX,
        FROM_IDX,
        NUM_THREADS
};

/*
 * This function returns the next range the send_merge_thread should operate on.
 * The inputs are two arrays; the first one stores the range at the front of the
 * queues stored in the second one.  The ranges are sorted in descending
 * priority order; the metadata from earlier ranges overrules metadata from
 * later ranges.  out_mask is used to return which threads the ranges came from;
 * bit i is set if ranges[i] started at the same place as the returned range.
 *
 * This code is not hardcoded to compare a specific number of threads; it could
 * be used with any number, just by changing the q_idx enum.
 *
 * The "next range" is the one with the earliest start; if two starts are equal,
 * the highest-priority range is the next to operate on.  If a higher-priority
 * range starts in the middle of the first range, then the first range will be
 * truncated to end where the higher-priority range starts, and we will operate
 * on that one next time.   In this way, we make sure that each block covered by
 * some range gets covered by a returned range, and each block covered is
 * returned using the metadata of the highest-priority range it appears in.
 *
 * For example, if the three ranges at the front of the queues were [2,4),
 * [3,5), and [1,3), then the ranges returned would be [1,2) with the metadata
 * from the third range, [2,4) with the metadata from the first range, and then
 * [4,5) with the metadata from the second.
 */
static struct send_range *
find_next_range(struct send_range **ranges, bqueue_t **qs, uint64_t *out_mask)
{
        int idx = 0; // index of the range with the earliest start
        int i;
        uint64_t bmask = 0;
        for (i = 1; i < NUM_THREADS; i++) {
                if (send_range_start_compare(ranges[i], ranges[idx]) < 0)
                        idx = i;
        }
        if (ranges[idx]->eos_marker) {
                struct send_range *ret = range_alloc(DATA, 0, 0, 0, B_TRUE);
                *out_mask = 0;
                return (ret);
        }
        /*
         * Find all the ranges that start at that same point.
         */
        for (i = 0; i < NUM_THREADS; i++) {
                if (send_range_start_compare(ranges[i], ranges[idx]) == 0)
                        bmask |= 1 << i;
        }
        *out_mask = bmask;
        /*
         * OBJECT_RANGE records only come from the TO thread, and should always
         * be treated as overlapping with nothing and sent on immediately.  They
         * are only used in raw sends, and are never redacted.
         */
        if (ranges[idx]->type == OBJECT_RANGE) {
                ASSERT3U(idx, ==, TO_IDX);
                ASSERT3U(*out_mask, ==, 1 << TO_IDX);
                struct send_range *ret = ranges[idx];
                ranges[idx] = get_next_range_nofree(qs[idx], ranges[idx]);
                return (ret);
        }
        /*
         * Find the first start or end point after the start of the first range.
         */
        uint64_t first_change = ranges[idx]->end_blkid;
        for (i = 0; i < NUM_THREADS; i++) {
                if (i == idx || ranges[i]->eos_marker ||
                    ranges[i]->object > ranges[idx]->object ||
                    ranges[i]->object == DMU_META_DNODE_OBJECT)
                        continue;
                ASSERT3U(ranges[i]->object, ==, ranges[idx]->object);
                if (first_change > ranges[i]->start_blkid &&
                    (bmask & (1 << i)) == 0)
                        first_change = ranges[i]->start_blkid;
                else if (first_change > ranges[i]->end_blkid)
                        first_change = ranges[i]->end_blkid;
        }
        /*
         * Update all ranges to no longer overlap with the range we're
         * returning. All such ranges must start at the same place as the range
         * being returned, and end at or after first_change. Thus we update
         * their start to first_change. If that makes them size 0, then free
         * them and pull a new range from that thread.
         */
        for (i = 0; i < NUM_THREADS; i++) {
                if (i == idx || (bmask & (1 << i)) == 0)
                        continue;
                ASSERT3U(first_change, >, ranges[i]->start_blkid);
                ranges[i]->start_blkid = first_change;
                ASSERT3U(ranges[i]->start_blkid, <=, ranges[i]->end_blkid);
                if (ranges[i]->start_blkid == ranges[i]->end_blkid)
                        ranges[i] = get_next_range(qs[i], ranges[i]);
        }
        /*
         * Short-circuit the simple case; if the range doesn't overlap with
         * anything else, or it only overlaps with things that start at the same
         * place and are longer, send it on.
         */
        if (first_change == ranges[idx]->end_blkid) {
                struct send_range *ret = ranges[idx];
                ranges[idx] = get_next_range_nofree(qs[idx], ranges[idx]);
                return (ret);
        }

        /*
         * Otherwise, return a truncated copy of ranges[idx] and move the start
         * of ranges[idx] back to first_change.
         */
        struct send_range *ret = kmem_alloc(sizeof (*ret), KM_SLEEP);
        *ret = *ranges[idx];
        ret->end_blkid = first_change;
        ranges[idx]->start_blkid = first_change;
        return (ret);
}

#define FROM_AND_REDACT_BITS ((1 << REDACT_IDX) | (1 << FROM_IDX))

/*
 * Merge the results from the from thread and the to thread, and then hand the
 * records off to send_prefetch_thread to prefetch them.  If this is not a
 * send from a redaction bookmark, the from thread will push an end of stream
 * record and stop, and we'll just send everything that was changed in the
 * to_ds since the ancestor's creation txg. If it is, then since
 * traverse_dataset has a canonical order, we can compare each change as
 * they're pulled off the queues.  That will give us a stream that is
 * appropriately sorted, and covers all records.  In addition, we pull the
 * data from the redact_list_thread and use that to determine which blocks
 * should be redacted.
 */
static __attribute__((noreturn)) void
send_merge_thread(void *arg)
{
        struct send_merge_thread_arg *smt_arg = arg;
        struct send_range *front_ranges[NUM_THREADS];
        bqueue_t *queues[NUM_THREADS];
        int err = 0;
        fstrans_cookie_t cookie = spl_fstrans_mark();

        if (smt_arg->redact_arg == NULL) {
                front_ranges[REDACT_IDX] =
                    kmem_zalloc(sizeof (struct send_range), KM_SLEEP);
                front_ranges[REDACT_IDX]->eos_marker = B_TRUE;
                front_ranges[REDACT_IDX]->type = REDACT;
                queues[REDACT_IDX] = NULL;
        } else {
                front_ranges[REDACT_IDX] =
                    bqueue_dequeue(&smt_arg->redact_arg->q);
                queues[REDACT_IDX] = &smt_arg->redact_arg->q;
        }
        front_ranges[TO_IDX] = bqueue_dequeue(&smt_arg->to_arg->q);
        queues[TO_IDX] = &smt_arg->to_arg->q;
        front_ranges[FROM_IDX] = bqueue_dequeue(&smt_arg->from_arg->q);
        queues[FROM_IDX] = &smt_arg->from_arg->q;
        uint64_t mask = 0;
        struct send_range *range;
        for (range = find_next_range(front_ranges, queues, &mask);
            !range->eos_marker && err == 0 && !smt_arg->cancel;
            range = find_next_range(front_ranges, queues, &mask)) {
                /*
                 * If the range in question was in both the from redact bookmark
                 * and the bookmark we're using to redact, then don't send it.
                 * It's already redacted on the receiving system, so a redaction
                 * record would be redundant.
                 */
                if ((mask & FROM_AND_REDACT_BITS) == FROM_AND_REDACT_BITS) {
                        ASSERT3U(range->type, ==, REDACT);
                        range_free(range);
                        continue;
                }
                bqueue_enqueue(&smt_arg->q, range, sizeof (*range));

                if (smt_arg->to_arg->error_code != 0) {
                        err = smt_arg->to_arg->error_code;
                } else if (smt_arg->from_arg->error_code != 0) {
                        err = smt_arg->from_arg->error_code;
                } else if (smt_arg->redact_arg != NULL &&
                    smt_arg->redact_arg->error_code != 0) {
                        err = smt_arg->redact_arg->error_code;
                }
        }
        if (smt_arg->cancel && err == 0)
                err = SET_ERROR(EINTR);
        smt_arg->error = err;
        if (smt_arg->error != 0) {
                smt_arg->to_arg->cancel = B_TRUE;
                smt_arg->from_arg->cancel = B_TRUE;
                if (smt_arg->redact_arg != NULL)
                        smt_arg->redact_arg->cancel = B_TRUE;
        }
        for (int i = 0; i < NUM_THREADS; i++) {
                while (!front_ranges[i]->eos_marker) {
                        front_ranges[i] = get_next_range(queues[i],
                            front_ranges[i]);
                }
                range_free(front_ranges[i]);
        }
        range->eos_marker = B_TRUE;
        bqueue_enqueue_flush(&smt_arg->q, range, 1);
        spl_fstrans_unmark(cookie);
        thread_exit();
}

struct send_reader_thread_arg {
        struct send_merge_thread_arg *smta;
        bqueue_t q;
        boolean_t cancel;
        boolean_t issue_reads;
        uint64_t featureflags;
        int error;
};

static void
dmu_send_read_done(zio_t *zio)
{
        struct send_range *range = zio->io_private;

        mutex_enter(&range->sru.data.lock);
        if (zio->io_error != 0) {
                abd_free(range->sru.data.abd);
                range->sru.data.abd = NULL;
                range->sru.data.io_err = zio->io_error;
        }

        ASSERT(range->sru.data.io_outstanding);
        range->sru.data.io_outstanding = B_FALSE;
        cv_broadcast(&range->sru.data.cv);
        mutex_exit(&range->sru.data.lock);
}

static void
issue_data_read(struct send_reader_thread_arg *srta, struct send_range *range)
{
        struct srd *srdp = &range->sru.data;
        blkptr_t *bp = &srdp->bp;
        objset_t *os = srta->smta->os;

        ASSERT3U(range->type, ==, DATA);
        ASSERT3U(range->start_blkid + 1, ==, range->end_blkid);
        /*
         * If we have large blocks stored on disk but
         * the send flags don't allow us to send large
         * blocks, we split the data from the arc buf
         * into chunks.
         */
        boolean_t split_large_blocks =
            srdp->datablksz > SPA_OLD_MAXBLOCKSIZE &&
            !(srta->featureflags & DMU_BACKUP_FEATURE_LARGE_BLOCKS);
        /*
         * We should only request compressed data from the ARC if all
         * the following are true:
         *  - stream compression was requested
         *  - we aren't splitting large blocks into smaller chunks
         *  - the data won't need to be byteswapped before sending
         *  - this isn't an embedded block
         *  - this isn't metadata (if receiving on a different endian
         *    system it can be byteswapped more easily)
         */
        boolean_t request_compressed =
            (srta->featureflags & DMU_BACKUP_FEATURE_COMPRESSED) &&
            !split_large_blocks && !BP_SHOULD_BYTESWAP(bp) &&
            !BP_IS_EMBEDDED(bp) && !DMU_OT_IS_METADATA(BP_GET_TYPE(bp));

        zio_flag_t zioflags = ZIO_FLAG_CANFAIL;

        if (srta->featureflags & DMU_BACKUP_FEATURE_RAW) {
                zioflags |= ZIO_FLAG_RAW;
                srdp->io_compressed = B_TRUE;
        } else if (request_compressed) {
                zioflags |= ZIO_FLAG_RAW_COMPRESS;
                srdp->io_compressed = B_TRUE;
        }

        srdp->datasz = (zioflags & ZIO_FLAG_RAW_COMPRESS) ?
            BP_GET_PSIZE(bp) : BP_GET_LSIZE(bp);

        if (!srta->issue_reads)
                return;
        if (BP_IS_REDACTED(bp))
                return;
        if (send_do_embed(bp, srta->featureflags))
                return;

        zbookmark_phys_t zb = {
            .zb_objset = dmu_objset_id(os),
            .zb_object = range->object,
            .zb_level = 0,
            .zb_blkid = range->start_blkid,
        };

        arc_flags_t aflags = ARC_FLAG_CACHED_ONLY;

        int arc_err = arc_read(NULL, os->os_spa, bp,
            arc_getbuf_func, &srdp->abuf, ZIO_PRIORITY_ASYNC_READ,
            zioflags, &aflags, &zb);
        /*
         * If the data is not already cached in the ARC, we read directly
         * from zio.  This avoids the performance overhead of adding a new
         * entry to the ARC, and we also avoid polluting the ARC cache with
         * data that is not likely to be used in the future.
         */
        if (arc_err != 0) {
                srdp->abd = abd_alloc_linear(srdp->datasz, B_FALSE);
                srdp->io_outstanding = B_TRUE;
                zio_nowait(zio_read(NULL, os->os_spa, bp, srdp->abd,
                    srdp->datasz, dmu_send_read_done, range,
                    ZIO_PRIORITY_ASYNC_READ, zioflags, &zb));
        }
}

/*
 * Create a new record with the given values.
 */
static void
enqueue_range(struct send_reader_thread_arg *srta, bqueue_t *q, dnode_t *dn,
    uint64_t blkid, uint64_t count, const blkptr_t *bp, uint32_t datablksz)
{
        enum type range_type = (bp == NULL || BP_IS_HOLE(bp) ? HOLE :
            (BP_IS_REDACTED(bp) ? REDACT : DATA));

        struct send_range *range = range_alloc(range_type, dn->dn_object,
            blkid, blkid + count, B_FALSE);

        if (blkid == DMU_SPILL_BLKID) {
                ASSERT3P(bp, !=, NULL);
                ASSERT3U(BP_GET_TYPE(bp), ==, DMU_OT_SA);
        }

        switch (range_type) {
        case HOLE:
                range->sru.hole.datablksz = datablksz;
                break;
        case DATA:
                ASSERT3U(count, ==, 1);
                range->sru.data.datablksz = datablksz;
                range->sru.data.obj_type = dn->dn_type;
                range->sru.data.bp = *bp;
                issue_data_read(srta, range);
                break;
        case REDACT:
                range->sru.redact.datablksz = datablksz;
                break;
        default:
                break;
        }
        bqueue_enqueue(q, range, datablksz);
}

/*
 * Send DRR_SPILL records for unmodified spill blocks.  This is useful
 * because changing certain attributes of the object (e.g. blocksize)
 * can cause old versions of ZFS to incorrectly remove a spill block.
 * Including these records in the stream forces an up to date version
 * to always be written ensuring they're never lost.  Current versions
 * of the code which understand the DRR_FLAG_SPILL_BLOCK feature can
 * ignore these unmodified spill blocks.
 *
 * We piggyback the spill_range to dnode range instead of enqueueing it
 * so send_range_after won't complain.
 */
static uint64_t
piggyback_unmodified_spill(struct send_reader_thread_arg *srta,
    struct send_range *range)
{
        ASSERT3U(range->type, ==, OBJECT);

        dnode_phys_t *dnp = range->sru.object.dnp;
        uint64_t fromtxg = srta->smta->to_arg->fromtxg;

        if (!zfs_send_unmodified_spill_blocks ||
            !(dnp->dn_flags & DNODE_FLAG_SPILL_BLKPTR) ||
            !(BP_GET_LOGICAL_BIRTH(DN_SPILL_BLKPTR(dnp)) <= fromtxg))
                return (0);

        blkptr_t *bp = DN_SPILL_BLKPTR(dnp);
        struct send_range *spill_range = range_alloc(DATA, range->object,
            DMU_SPILL_BLKID, DMU_SPILL_BLKID+1, B_FALSE);
        spill_range->sru.data.bp = *bp;
        spill_range->sru.data.obj_type = dnp->dn_type;
        spill_range->sru.data.datablksz = BP_GET_LSIZE(bp);

        issue_data_read(srta, spill_range);
        range->sru.object.spill_range = spill_range;

        return (BP_GET_LSIZE(bp));
}

/*
 * This thread is responsible for two things: First, it retrieves the correct
 * blkptr in the to ds if we need to send the data because of something from
 * the from thread.  As a result of this, we're the first ones to discover that
 * some indirect blocks can be discarded because they're not holes. Second,
 * it issues prefetches for the data we need to send.
 */
static __attribute__((noreturn)) void
send_reader_thread(void *arg)
{
        struct send_reader_thread_arg *srta = arg;
        struct send_merge_thread_arg *smta = srta->smta;
        bqueue_t *inq = &smta->q;
        bqueue_t *outq = &srta->q;
        objset_t *os = smta->os;
        fstrans_cookie_t cookie = spl_fstrans_mark();
        struct send_range *range = bqueue_dequeue(inq);
        int err = 0;

        /*
         * If the record we're analyzing is from a redaction bookmark from the
         * fromds, then we need to know whether or not it exists in the tods so
         * we know whether to create records for it or not. If it does, we need
         * the datablksz so we can generate an appropriate record for it.
         * Finally, if it isn't redacted, we need the blkptr so that we can send
         * a WRITE record containing the actual data.
         */
        uint64_t last_obj = UINT64_MAX;
        uint64_t last_obj_exists = B_TRUE;
        while (!range->eos_marker && !srta->cancel && smta->error == 0 &&
            err == 0) {
                uint64_t spill = 0;
                switch (range->type) {
                case DATA:
                        issue_data_read(srta, range);
                        bqueue_enqueue(outq, range, range->sru.data.datablksz);
                        range = get_next_range_nofree(inq, range);
                        break;
                case OBJECT:
                        spill = piggyback_unmodified_spill(srta, range);
                        zfs_fallthrough;
                case HOLE:
                case OBJECT_RANGE:
                case REDACT: // Redacted blocks must exist
                        bqueue_enqueue(outq, range, sizeof (*range) + spill);
                        range = get_next_range_nofree(inq, range);
                        break;
                case PREVIOUSLY_REDACTED: {
                        /*
                         * This entry came from the "from bookmark" when
                         * sending from a bookmark that has a redaction
                         * list.  We need to check if this object/blkid
                         * exists in the target ("to") dataset, and if
                         * not then we drop this entry.  We also need
                         * to fill in the block pointer so that we know
                         * what to prefetch.
                         *
                         * To accomplish the above, we first cache whether or
                         * not the last object we examined exists.  If it
                         * doesn't, we can drop this record. If it does, we hold
                         * the dnode and use it to call dbuf_dnode_findbp. We do
                         * this instead of dbuf_bookmark_findbp because we will
                         * often operate on large ranges, and holding the dnode
                         * once is more efficient.
                         */
                        boolean_t object_exists = B_TRUE;
                        /*
                         * If the data is redacted, we only care if it exists,
                         * so that we don't send records for objects that have
                         * been deleted.
                         */
                        dnode_t *dn;
                        if (range->object == last_obj && !last_obj_exists) {
                                /*
                                 * If we're still examining the same object as
                                 * previously, and it doesn't exist, we don't
                                 * need to call dbuf_bookmark_findbp.
                                 */
                                object_exists = B_FALSE;
                        } else {
                                err = dnode_hold(os, range->object, FTAG, &dn);
                                if (err == ENOENT) {
                                        object_exists = B_FALSE;
                                        err = 0;
                                }
                                last_obj = range->object;
                                last_obj_exists = object_exists;
                        }

                        if (err != 0) {
                                break;
                        } else if (!object_exists) {
                                /*
                                 * The block was modified, but doesn't
                                 * exist in the to dataset; if it was
                                 * deleted in the to dataset, then we'll
                                 * visit the hole bp for it at some point.
                                 */
                                range = get_next_range(inq, range);
                                continue;
                        }
                        uint64_t file_max =
                            MIN(dn->dn_maxblkid, range->end_blkid);
                        /*
                         * The object exists, so we need to try to find the
                         * blkptr for each block in the range we're processing.
                         */
                        rw_enter(&dn->dn_struct_rwlock, RW_READER);
                        for (uint64_t blkid = range->start_blkid;
                            blkid < file_max; blkid++) {
                                blkptr_t bp;
                                uint32_t datablksz =
                                    dn->dn_phys->dn_datablkszsec <<
                                    SPA_MINBLOCKSHIFT;
                                uint64_t offset = blkid * datablksz;
                                /*
                                 * This call finds the next non-hole block in
                                 * the object. This is to prevent a
                                 * performance problem where we're unredacting
                                 * a large hole. Using dnode_next_offset to
                                 * skip over the large hole avoids iterating
                                 * over every block in it.
                                 */
                                err = dnode_next_offset(dn, DNODE_FIND_HAVELOCK,
                                    &offset, 1, 1, 0);
                                if (err == ESRCH) {
                                        offset = UINT64_MAX;
                                        err = 0;
                                } else if (err != 0) {
                                        break;
                                }
                                if (offset != blkid * datablksz) {
                                        /*
                                         * if there is a hole from here
                                         * (blkid) to offset
                                         */
                                        offset = MIN(offset, file_max *
                                            datablksz);
                                        uint64_t nblks = (offset / datablksz) -
                                            blkid;
                                        enqueue_range(srta, outq, dn, blkid,
                                            nblks, NULL, datablksz);
                                        blkid += nblks;
                                }
                                if (blkid >= file_max)
                                        break;
                                err = dbuf_dnode_findbp(dn, 0, blkid, &bp,
                                    NULL, NULL);
                                if (err != 0)
                                        break;
                                ASSERT(!BP_IS_HOLE(&bp));
                                enqueue_range(srta, outq, dn, blkid, 1, &bp,
                                    datablksz);
                        }
                        rw_exit(&dn->dn_struct_rwlock);
                        dnode_rele(dn, FTAG);
                        range = get_next_range(inq, range);
                }
                }
        }
        if (srta->cancel || err != 0) {
                smta->cancel = B_TRUE;
                srta->error = err;
        } else if (smta->error != 0) {
                srta->error = smta->error;
        }
        while (!range->eos_marker)
                range = get_next_range(inq, range);

        bqueue_enqueue_flush(outq, range, 1);
        spl_fstrans_unmark(cookie);
        thread_exit();
}

#define NUM_SNAPS_NOT_REDACTED UINT64_MAX

struct dmu_send_params {
        /* Pool args */
        const void *tag; // Tag dp was held with, will be used to release dp.
        dsl_pool_t *dp;
        /* To snapshot args */
        const char *tosnap;
        dsl_dataset_t *to_ds;
        /* From snapshot args */
        zfs_bookmark_phys_t ancestor_zb;
        uint64_t *fromredactsnaps;
        /* NUM_SNAPS_NOT_REDACTED if not sending from redaction bookmark */
        uint64_t numfromredactsnaps;
        /* Stream params */
        boolean_t is_clone;
        boolean_t embedok;
        boolean_t large_block_ok;
        boolean_t compressok;
        boolean_t rawok;
        boolean_t savedok;
        uint64_t resumeobj;
        uint64_t resumeoff;
        uint64_t saved_guid;
        zfs_bookmark_phys_t *redactbook;
        /* Stream output params */
        dmu_send_outparams_t *dso;

        /* Stream progress params */
        offset_t *off;
        int outfd;
        char saved_toname[MAXNAMELEN];
};

static int
setup_featureflags(struct dmu_send_params *dspp, objset_t *os,
    uint64_t *featureflags)
{
        dsl_dataset_t *to_ds = dspp->to_ds;
        dsl_pool_t *dp = dspp->dp;

        if (dmu_objset_type(os) == DMU_OST_ZFS) {
                uint64_t version;
                if (zfs_get_zplprop(os, ZFS_PROP_VERSION, &version) != 0)
                        return (SET_ERROR(EINVAL));

                if (version >= ZPL_VERSION_SA)
                        *featureflags |= DMU_BACKUP_FEATURE_SA_SPILL;
        }

        /* raw sends imply large_block_ok */
        if ((dspp->rawok || dspp->large_block_ok) &&
            dsl_dataset_feature_is_active(to_ds, SPA_FEATURE_LARGE_BLOCKS)) {
                *featureflags |= DMU_BACKUP_FEATURE_LARGE_BLOCKS;
        }

        /* encrypted datasets will not have embedded blocks */
        if ((dspp->embedok || dspp->rawok) && !os->os_encrypted &&
            spa_feature_is_active(dp->dp_spa, SPA_FEATURE_EMBEDDED_DATA)) {
                *featureflags |= DMU_BACKUP_FEATURE_EMBED_DATA;
        }

        /* raw send implies compressok */
        if (dspp->compressok || dspp->rawok)
                *featureflags |= DMU_BACKUP_FEATURE_COMPRESSED;

        if (dspp->rawok && os->os_encrypted)
                *featureflags |= DMU_BACKUP_FEATURE_RAW;

        if ((*featureflags &
            (DMU_BACKUP_FEATURE_EMBED_DATA | DMU_BACKUP_FEATURE_COMPRESSED |
            DMU_BACKUP_FEATURE_RAW)) != 0 &&
            spa_feature_is_active(dp->dp_spa, SPA_FEATURE_LZ4_COMPRESS)) {
                *featureflags |= DMU_BACKUP_FEATURE_LZ4;
        }

        /*
         * We specifically do not include DMU_BACKUP_FEATURE_EMBED_DATA here to
         * allow sending ZSTD compressed datasets to a receiver that does not
         * support ZSTD
         */
        if ((*featureflags &
            (DMU_BACKUP_FEATURE_COMPRESSED | DMU_BACKUP_FEATURE_RAW)) != 0 &&
            dsl_dataset_feature_is_active(to_ds, SPA_FEATURE_ZSTD_COMPRESS)) {
                *featureflags |= DMU_BACKUP_FEATURE_ZSTD;
        }

        if (dspp->resumeobj != 0 || dspp->resumeoff != 0) {
                *featureflags |= DMU_BACKUP_FEATURE_RESUMING;
        }

        if (dspp->redactbook != NULL) {
                *featureflags |= DMU_BACKUP_FEATURE_REDACTED;
        }

        if (dsl_dataset_feature_is_active(to_ds, SPA_FEATURE_LARGE_DNODE)) {
                *featureflags |= DMU_BACKUP_FEATURE_LARGE_DNODE;
        }

        if (dsl_dataset_feature_is_active(to_ds, SPA_FEATURE_LONGNAME)) {
                *featureflags |= DMU_BACKUP_FEATURE_LONGNAME;
        }

        if (dsl_dataset_feature_is_active(to_ds, SPA_FEATURE_LARGE_MICROZAP)) {
                /*
                 * We must never split a large microzap block, so we can only
                 * send large microzaps if LARGE_BLOCKS is already enabled.
                 */
                if (!(*featureflags & DMU_BACKUP_FEATURE_LARGE_BLOCKS))
                        return (SET_ERROR(ZFS_ERR_STREAM_LARGE_MICROZAP));
                *featureflags |= DMU_BACKUP_FEATURE_LARGE_MICROZAP;
        }

        return (0);
}

static dmu_replay_record_t *
create_begin_record(struct dmu_send_params *dspp, objset_t *os,
    uint64_t featureflags)
{
        dmu_replay_record_t *drr = kmem_zalloc(sizeof (dmu_replay_record_t),
            KM_SLEEP);
        drr->drr_type = DRR_BEGIN;

        struct drr_begin *drrb = &drr->drr_u.drr_begin;
        dsl_dataset_t *to_ds = dspp->to_ds;

        drrb->drr_magic = DMU_BACKUP_MAGIC;
        drrb->drr_creation_time = dsl_dataset_phys(to_ds)->ds_creation_time;
        drrb->drr_type = dmu_objset_type(os);
        drrb->drr_toguid = dsl_dataset_phys(to_ds)->ds_guid;
        drrb->drr_fromguid = dspp->ancestor_zb.zbm_guid;

        DMU_SET_STREAM_HDRTYPE(drrb->drr_versioninfo, DMU_SUBSTREAM);
        DMU_SET_FEATUREFLAGS(drrb->drr_versioninfo, featureflags);

        if (dspp->is_clone)
                drrb->drr_flags |= DRR_FLAG_CLONE;
        if (dsl_dataset_phys(dspp->to_ds)->ds_flags & DS_FLAG_CI_DATASET)
                drrb->drr_flags |= DRR_FLAG_CI_DATA;
        if (zfs_send_set_freerecords_bit)
                drrb->drr_flags |= DRR_FLAG_FREERECORDS;
        drr->drr_u.drr_begin.drr_flags |= DRR_FLAG_SPILL_BLOCK;

        if (dspp->savedok) {
                drrb->drr_toguid = dspp->saved_guid;
                strlcpy(drrb->drr_toname, dspp->saved_toname,
                    sizeof (drrb->drr_toname));
        } else {
                dsl_dataset_name(to_ds, drrb->drr_toname);
                if (!to_ds->ds_is_snapshot) {
                        (void) strlcat(drrb->drr_toname, "@--head--",
                            sizeof (drrb->drr_toname));
                }
        }
        return (drr);
}

static void
setup_to_thread(struct send_thread_arg *to_arg, objset_t *to_os,
    dmu_sendstatus_t *dssp, uint64_t fromtxg, boolean_t rawok)
{
        VERIFY0(bqueue_init(&to_arg->q, zfs_send_no_prefetch_queue_ff,
            MAX(zfs_send_no_prefetch_queue_length, 2 * zfs_max_recordsize),
            offsetof(struct send_range, ln)));
        to_arg->error_code = 0;
        to_arg->cancel = B_FALSE;
        to_arg->os = to_os;
        to_arg->fromtxg = fromtxg;
        to_arg->flags = TRAVERSE_PRE | TRAVERSE_PREFETCH_METADATA;
        if (rawok)
                to_arg->flags |= TRAVERSE_NO_DECRYPT;
        if (zfs_send_corrupt_data)
                to_arg->flags |= TRAVERSE_HARD;
        to_arg->num_blocks_visited = &dssp->dss_blocks;
        (void) thread_create(NULL, 0, send_traverse_thread, to_arg, 0,
            curproc, TS_RUN, minclsyspri);
}

static void
setup_from_thread(struct redact_list_thread_arg *from_arg,
    redaction_list_t *from_rl, dmu_sendstatus_t *dssp)
{
        VERIFY0(bqueue_init(&from_arg->q, zfs_send_no_prefetch_queue_ff,
            MAX(zfs_send_no_prefetch_queue_length, 2 * zfs_max_recordsize),
            offsetof(struct send_range, ln)));
        from_arg->error_code = 0;
        from_arg->cancel = B_FALSE;
        from_arg->rl = from_rl;
        from_arg->mark_redact = B_FALSE;
        from_arg->num_blocks_visited = &dssp->dss_blocks;
        /*
         * If from_ds is null, send_traverse_thread just returns success and
         * enqueues an eos marker.
         */
        (void) thread_create(NULL, 0, redact_list_thread, from_arg, 0,
            curproc, TS_RUN, minclsyspri);
}

static void
setup_redact_list_thread(struct redact_list_thread_arg *rlt_arg,
    struct dmu_send_params *dspp, redaction_list_t *rl, dmu_sendstatus_t *dssp)
{
        if (dspp->redactbook == NULL)
                return;

        rlt_arg->cancel = B_FALSE;
        VERIFY0(bqueue_init(&rlt_arg->q, zfs_send_no_prefetch_queue_ff,
            MAX(zfs_send_no_prefetch_queue_length, 2 * zfs_max_recordsize),
            offsetof(struct send_range, ln)));
        rlt_arg->error_code = 0;
        rlt_arg->mark_redact = B_TRUE;
        rlt_arg->rl = rl;
        rlt_arg->num_blocks_visited = &dssp->dss_blocks;

        (void) thread_create(NULL, 0, redact_list_thread, rlt_arg, 0,
            curproc, TS_RUN, minclsyspri);
}

static void
setup_merge_thread(struct send_merge_thread_arg *smt_arg,
    struct dmu_send_params *dspp, struct redact_list_thread_arg *from_arg,
    struct send_thread_arg *to_arg, struct redact_list_thread_arg *rlt_arg,
    objset_t *os)
{
        VERIFY0(bqueue_init(&smt_arg->q, zfs_send_no_prefetch_queue_ff,
            MAX(zfs_send_no_prefetch_queue_length, 2 * zfs_max_recordsize),
            offsetof(struct send_range, ln)));
        smt_arg->cancel = B_FALSE;
        smt_arg->error = 0;
        smt_arg->from_arg = from_arg;
        smt_arg->to_arg = to_arg;
        if (dspp->redactbook != NULL)
                smt_arg->redact_arg = rlt_arg;

        smt_arg->os = os;
        (void) thread_create(NULL, 0, send_merge_thread, smt_arg, 0, curproc,
            TS_RUN, minclsyspri);
}

static void
setup_reader_thread(struct send_reader_thread_arg *srt_arg,
    struct dmu_send_params *dspp, struct send_merge_thread_arg *smt_arg,
    uint64_t featureflags)
{
        VERIFY0(bqueue_init(&srt_arg->q, zfs_send_queue_ff,
            MAX(zfs_send_queue_length, 2 * zfs_max_recordsize),
            offsetof(struct send_range, ln)));
        srt_arg->smta = smt_arg;
        srt_arg->issue_reads = !dspp->dso->dso_dryrun;
        srt_arg->featureflags = featureflags;
        (void) thread_create(NULL, 0, send_reader_thread, srt_arg, 0,
            curproc, TS_RUN, minclsyspri);
}

static int
setup_resume_points(struct dmu_send_params *dspp,
    struct send_thread_arg *to_arg, struct redact_list_thread_arg *from_arg,
    struct redact_list_thread_arg *rlt_arg,
    struct send_merge_thread_arg *smt_arg, boolean_t resuming, objset_t *os,
    redaction_list_t *redact_rl, nvlist_t *nvl)
{
        (void) smt_arg;
        dsl_dataset_t *to_ds = dspp->to_ds;
        int err = 0;

        uint64_t obj = 0;
        uint64_t blkid = 0;
        if (resuming) {
                obj = dspp->resumeobj;
                dmu_object_info_t to_doi;
                err = dmu_object_info(os, obj, &to_doi);
                if (err != 0)
                        return (err);

                blkid = dspp->resumeoff / to_doi.doi_data_block_size;
        }
        /*
         * If we're resuming a redacted send, we can skip to the appropriate
         * point in the redaction bookmark by binary searching through it.
         */
        if (redact_rl != NULL) {
                SET_BOOKMARK(&rlt_arg->resume, to_ds->ds_object, obj, 0, blkid);
        }

        SET_BOOKMARK(&to_arg->resume, to_ds->ds_object, obj, 0, blkid);
        if (nvlist_exists(nvl, BEGINNV_REDACT_FROM_SNAPS)) {
                uint64_t objset = dspp->ancestor_zb.zbm_redaction_obj;
                /*
                 * Note: If the resume point is in an object whose
                 * blocksize is different in the from vs to snapshots,
                 * we will have divided by the "wrong" blocksize.
                 * However, in this case fromsnap's send_cb() will
                 * detect that the blocksize has changed and therefore
                 * ignore this object.
                 *
                 * If we're resuming a send from a redaction bookmark,
                 * we still cannot accidentally suggest blocks behind
                 * the to_ds.  In addition, we know that any blocks in
                 * the object in the to_ds will have to be sent, since
                 * the size changed.  Therefore, we can't cause any harm
                 * this way either.
                 */
                SET_BOOKMARK(&from_arg->resume, objset, obj, 0, blkid);
        }
        if (resuming) {
                fnvlist_add_uint64(nvl, BEGINNV_RESUME_OBJECT, dspp->resumeobj);
                fnvlist_add_uint64(nvl, BEGINNV_RESUME_OFFSET, dspp->resumeoff);
        }
        return (0);
}

static dmu_sendstatus_t *
setup_send_progress(struct dmu_send_params *dspp)
{
        dmu_sendstatus_t *dssp = kmem_zalloc(sizeof (*dssp), KM_SLEEP);
        dssp->dss_outfd = dspp->outfd;
        dssp->dss_off = dspp->off;
        dssp->dss_proc = curproc;
        mutex_enter(&dspp->to_ds->ds_sendstream_lock);
        list_insert_head(&dspp->to_ds->ds_sendstreams, dssp);
        mutex_exit(&dspp->to_ds->ds_sendstream_lock);
        return (dssp);
}

/*
 * Actually do the bulk of the work in a zfs send.
 *
 * The idea is that we want to do a send from ancestor_zb to to_ds.  We also
 * want to not send any data that has been modified by all the datasets in
 * redactsnaparr, and store the list of blocks that are redacted in this way in
 * a bookmark named redactbook, created on the to_ds.  We do this by creating
 * several worker threads, whose function is described below.
 *
 * There are three cases.
 * The first case is a redacted zfs send.  In this case there are 5 threads.
 * The first thread is the to_ds traversal thread: it calls dataset_traverse on
 * the to_ds and finds all the blocks that have changed since ancestor_zb (if
 * it's a full send, that's all blocks in the dataset).  It then sends those
 * blocks on to the send merge thread. The redact list thread takes the data
 * from the redaction bookmark and sends those blocks on to the send merge
 * thread.  The send merge thread takes the data from the to_ds traversal
 * thread, and combines it with the redaction records from the redact list
 * thread.  If a block appears in both the to_ds's data and the redaction data,
 * the send merge thread will mark it as redacted and send it on to the prefetch
 * thread.  Otherwise, the send merge thread will send the block on to the
 * prefetch thread unchanged. The prefetch thread will issue prefetch reads for
 * any data that isn't redacted, and then send the data on to the main thread.
 * The main thread behaves the same as in a normal send case, issuing demand
 * reads for data blocks and sending out records over the network
 *
 * The graphic below diagrams the flow of data in the case of a redacted zfs
 * send.  Each box represents a thread, and each line represents the flow of
 * data.
 *
 *             Records from the |
 *           redaction bookmark |
 * +--------------------+       |  +---------------------------+
 * |                    |       v  | Send Merge Thread         |
 * | Redact List Thread +----------> Apply redaction marks to  |
 * |                    |          | records as specified by   |
 * +--------------------+          | redaction ranges          |
 *                                 +----^---------------+------+
 *                                      |               | Merged data
 *                                      |               |
 *                                      |  +------------v--------+
 *                                      |  | Prefetch Thread     |
 * +--------------------+               |  | Issues prefetch     |
 * | to_ds Traversal    |               |  | reads of data blocks|
 * | Thread (finds      +---------------+  +------------+--------+
 * | candidate blocks)  |  Blocks modified              | Prefetched data
 * +--------------------+  by to_ds since               |
 *                         ancestor_zb     +------------v----+
 *                                         | Main Thread     |  File Descriptor
 *                                         | Sends data over +->(to zfs receive)
 *                                         | wire            |
 *                                         +-----------------+
 *
 * The second case is an incremental send from a redaction bookmark.  The to_ds
 * traversal thread and the main thread behave the same as in the redacted
 * send case.  The new thread is the from bookmark traversal thread.  It
 * iterates over the redaction list in the redaction bookmark, and enqueues
 * records for each block that was redacted in the original send.  The send
 * merge thread now has to merge the data from the two threads.  For details
 * about that process, see the header comment of send_merge_thread().  Any data
 * it decides to send on will be prefetched by the prefetch thread.  Note that
 * you can perform a redacted send from a redaction bookmark; in that case,
 * the data flow behaves very similarly to the flow in the redacted send case,
 * except with the addition of the bookmark traversal thread iterating over the
 * redaction bookmark.  The send_merge_thread also has to take on the
 * responsibility of merging the redact list thread's records, the bookmark
 * traversal thread's records, and the to_ds records.
 *
 * +---------------------+
 * |                     |
 * | Redact List Thread  +--------------+
 * |                     |              |
 * +---------------------+              |
 *        Blocks in redaction list      | Ranges modified by every secure snap
 *        of from bookmark              | (or EOS if not readcted)
 *                                      |
 * +---------------------+   |     +----v----------------------+
 * | bookmark Traversal  |   v     | Send Merge Thread         |
 * | Thread (finds       +---------> Merges bookmark, rlt, and |
 * | candidate blocks)   |         | to_ds send records        |
 * +---------------------+         +----^---------------+------+
 *                                      |               | Merged data
 *                                      |  +------------v--------+
 *                                      |  | Prefetch Thread     |
 * +--------------------+               |  | Issues prefetch     |
 * | to_ds Traversal    |               |  | reads of data blocks|
 * | Thread (finds      +---------------+  +------------+--------+
 * | candidate blocks)  |  Blocks modified              | Prefetched data
 * +--------------------+  by to_ds since  +------------v----+
 *                         ancestor_zb     | Main Thread     |  File Descriptor
 *                                         | Sends data over +->(to zfs receive)
 *                                         | wire            |
 *                                         +-----------------+
 *
 * The final case is a simple zfs full or incremental send.  The to_ds traversal
 * thread behaves the same as always. The redact list thread is never started.
 * The send merge thread takes all the blocks that the to_ds traversal thread
 * sends it, prefetches the data, and sends the blocks on to the main thread.
 * The main thread sends the data over the wire.
 *
 * To keep performance acceptable, we want to prefetch the data in the worker
 * threads.  While the to_ds thread could simply use the TRAVERSE_PREFETCH
 * feature built into traverse_dataset, the combining and deletion of records
 * due to redaction and sends from redaction bookmarks mean that we could
 * issue many unnecessary prefetches.  As a result, we only prefetch data
 * after we've determined that the record is not going to be redacted.  To
 * prevent the prefetching from getting too far ahead of the main thread, the
 * blocking queues that are used for communication are capped not by the
 * number of entries in the queue, but by the sum of the size of the
 * prefetches associated with them.  The limit on the amount of data that the
 * thread can prefetch beyond what the main thread has reached is controlled
 * by the global variable zfs_send_queue_length.  In addition, to prevent poor
 * performance in the beginning of a send, we also limit the distance ahead
 * that the traversal threads can be.  That distance is controlled by the
 * zfs_send_no_prefetch_queue_length tunable.
 *
 * Note: Releases dp using the specified tag.
 */
static int
dmu_send_impl(struct dmu_send_params *dspp)
{
        objset_t *os;
        dmu_replay_record_t *drr;
        dmu_sendstatus_t *dssp;
        dmu_send_cookie_t dsc = {0};
        int err;
        uint64_t fromtxg = dspp->ancestor_zb.zbm_creation_txg;
        uint64_t featureflags = 0;
        struct redact_list_thread_arg *from_arg;
        struct send_thread_arg *to_arg;
        struct redact_list_thread_arg *rlt_arg;
        struct send_merge_thread_arg *smt_arg;
        struct send_reader_thread_arg *srt_arg;
        struct send_range *range;
        redaction_list_t *from_rl = NULL;
        redaction_list_t *redact_rl = NULL;
        boolean_t resuming = (dspp->resumeobj != 0 || dspp->resumeoff != 0);
        boolean_t book_resuming = resuming;

        dsl_dataset_t *to_ds = dspp->to_ds;
        zfs_bookmark_phys_t *ancestor_zb = &dspp->ancestor_zb;
        dsl_pool_t *dp = dspp->dp;
        const void *tag = dspp->tag;

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

        /*
         * If this is a non-raw send of an encrypted ds, we can ensure that
         * the objset_phys_t is authenticated. This is safe because this is
         * either a snapshot or we have owned the dataset, ensuring that
         * it can't be modified.
         */
        if (!dspp->rawok && os->os_encrypted &&
            arc_is_unauthenticated(os->os_phys_buf)) {
                zbookmark_phys_t zb;

                SET_BOOKMARK(&zb, to_ds->ds_object, ZB_ROOT_OBJECT,
                    ZB_ROOT_LEVEL, ZB_ROOT_BLKID);
                err = arc_untransform(os->os_phys_buf, os->os_spa,
                    &zb, B_FALSE);
                if (err != 0) {
                        dsl_pool_rele(dp, tag);
                        return (err);
                }

                ASSERT0(arc_is_unauthenticated(os->os_phys_buf));
        }

        if ((err = setup_featureflags(dspp, os, &featureflags)) != 0) {
                dsl_pool_rele(dp, tag);
                return (err);
        }

        /*
         * If we're doing a redacted send, hold the bookmark's redaction list.
         */
        if (dspp->redactbook != NULL) {
                err = dsl_redaction_list_hold_obj(dp,
                    dspp->redactbook->zbm_redaction_obj, FTAG,
                    &redact_rl);
                if (err != 0) {
                        dsl_pool_rele(dp, tag);
                        return (SET_ERROR(EINVAL));
                }
                dsl_redaction_list_long_hold(dp, redact_rl, FTAG);
        }

        /*
         * If we're sending from a redaction bookmark, hold the redaction list
         * so that we can consider sending the redacted blocks.
         */
        if (ancestor_zb->zbm_redaction_obj != 0) {
                err = dsl_redaction_list_hold_obj(dp,
                    ancestor_zb->zbm_redaction_obj, FTAG, &from_rl);
                if (err != 0) {
                        if (redact_rl != NULL) {
                                dsl_redaction_list_long_rele(redact_rl, FTAG);
                                dsl_redaction_list_rele(redact_rl, FTAG);
                        }
                        dsl_pool_rele(dp, tag);
                        return (SET_ERROR(EINVAL));
                }
                dsl_redaction_list_long_hold(dp, from_rl, FTAG);
        }

        dsl_dataset_long_hold(to_ds, FTAG);

        from_arg = kmem_zalloc(sizeof (*from_arg), KM_SLEEP);
        to_arg = kmem_zalloc(sizeof (*to_arg), KM_SLEEP);
        rlt_arg = kmem_zalloc(sizeof (*rlt_arg), KM_SLEEP);
        smt_arg = kmem_zalloc(sizeof (*smt_arg), KM_SLEEP);
        srt_arg = kmem_zalloc(sizeof (*srt_arg), KM_SLEEP);

        drr = create_begin_record(dspp, os, featureflags);
        dssp = setup_send_progress(dspp);

        dsc.dsc_drr = drr;
        dsc.dsc_dso = dspp->dso;
        dsc.dsc_os = os;
        dsc.dsc_off = dspp->off;
        dsc.dsc_toguid = dsl_dataset_phys(to_ds)->ds_guid;
        dsc.dsc_fromtxg = fromtxg;
        dsc.dsc_pending_op = PENDING_NONE;
        dsc.dsc_featureflags = featureflags;
        dsc.dsc_resume_object = dspp->resumeobj;
        dsc.dsc_resume_offset = dspp->resumeoff;

        dsl_pool_rele(dp, tag);

        void *payload = NULL;
        size_t payload_len = 0;
        nvlist_t *nvl = fnvlist_alloc();

        /*
         * If we're doing a redacted send, we include the snapshots we're
         * redacted with respect to so that the target system knows what send
         * streams can be correctly received on top of this dataset. If we're
         * instead sending a redacted dataset, we include the snapshots that the
         * dataset was created with respect to.
         */
        if (dspp->redactbook != NULL) {
                fnvlist_add_uint64_array(nvl, BEGINNV_REDACT_SNAPS,
                    redact_rl->rl_phys->rlp_snaps,
                    redact_rl->rl_phys->rlp_num_snaps);
        } else if (dsl_dataset_feature_is_active(to_ds,
            SPA_FEATURE_REDACTED_DATASETS)) {
                uint64_t *tods_guids;
                uint64_t length;
                VERIFY(dsl_dataset_get_uint64_array_feature(to_ds,
                    SPA_FEATURE_REDACTED_DATASETS, &length, &tods_guids));
                fnvlist_add_uint64_array(nvl, BEGINNV_REDACT_SNAPS, tods_guids,
                    length);
        }

        /*
         * If we're sending from a redaction bookmark, then we should retrieve
         * the guids of that bookmark so we can send them over the wire.
         */
        if (from_rl != NULL) {
                fnvlist_add_uint64_array(nvl, BEGINNV_REDACT_FROM_SNAPS,
                    from_rl->rl_phys->rlp_snaps,
                    from_rl->rl_phys->rlp_num_snaps);
        }

        /*
         * If the snapshot we're sending from is redacted, include the redaction
         * list in the stream.
         */
        if (dspp->numfromredactsnaps != NUM_SNAPS_NOT_REDACTED) {
                ASSERT3P(from_rl, ==, NULL);
                fnvlist_add_uint64_array(nvl, BEGINNV_REDACT_FROM_SNAPS,
                    dspp->fromredactsnaps, (uint_t)dspp->numfromredactsnaps);
                if (dspp->numfromredactsnaps > 0) {
                        kmem_free(dspp->fromredactsnaps,
                            dspp->numfromredactsnaps * sizeof (uint64_t));
                        dspp->fromredactsnaps = NULL;
                }
        }

        if (resuming || book_resuming) {
                err = setup_resume_points(dspp, to_arg, from_arg,
                    rlt_arg, smt_arg, resuming, os, redact_rl, nvl);
                if (err != 0)
                        goto out;
        }

        if (featureflags & DMU_BACKUP_FEATURE_RAW) {
                uint64_t ivset_guid = ancestor_zb->zbm_ivset_guid;
                nvlist_t *keynvl = NULL;
                ASSERT(os->os_encrypted);

                err = dsl_crypto_populate_key_nvlist(os, ivset_guid,
                    &keynvl);
                if (err != 0) {
                        fnvlist_free(nvl);
                        goto out;
                }

                fnvlist_add_nvlist(nvl, "crypt_keydata", keynvl);
                fnvlist_free(keynvl);
        }

        if (!nvlist_empty(nvl)) {
                payload = fnvlist_pack(nvl, &payload_len);
                drr->drr_payloadlen = payload_len;
        }

        fnvlist_free(nvl);
        err = dump_record(&dsc, payload, payload_len);
        fnvlist_pack_free(payload, payload_len);
        if (err != 0) {
                err = dsc.dsc_err;
                goto out;
        }

        setup_to_thread(to_arg, os, dssp, fromtxg, dspp->rawok);
        setup_from_thread(from_arg, from_rl, dssp);
        setup_redact_list_thread(rlt_arg, dspp, redact_rl, dssp);
        setup_merge_thread(smt_arg, dspp, from_arg, to_arg, rlt_arg, os);
        setup_reader_thread(srt_arg, dspp, smt_arg, featureflags);

        range = bqueue_dequeue(&srt_arg->q);
        while (err == 0 && !range->eos_marker) {
                err = do_dump(&dsc, range);
                range = get_next_range(&srt_arg->q, range);
                if (issig())
                        err = SET_ERROR(EINTR);
        }

        /*
         * If we hit an error or are interrupted, cancel our worker threads and
         * clear the queue of any pending records.  The threads will pass the
         * cancel up the tree of worker threads, and each one will clean up any
         * pending records before exiting.
         */
        if (err != 0) {
                srt_arg->cancel = B_TRUE;
                while (!range->eos_marker) {
                        range = get_next_range(&srt_arg->q, range);
                }
        }
        range_free(range);

        bqueue_destroy(&srt_arg->q);
        bqueue_destroy(&smt_arg->q);
        if (dspp->redactbook != NULL)
                bqueue_destroy(&rlt_arg->q);
        bqueue_destroy(&to_arg->q);
        bqueue_destroy(&from_arg->q);

        if (err == 0 && srt_arg->error != 0)
                err = srt_arg->error;

        if (err != 0)
                goto out;

        if (dsc.dsc_pending_op != PENDING_NONE)
                if (dump_record(&dsc, NULL, 0) != 0)
                        err = SET_ERROR(EINTR);

        if (err != 0) {
                if (err == EINTR && dsc.dsc_err != 0)
                        err = dsc.dsc_err;
                goto out;
        }

        /*
         * Send the DRR_END record if this is not a saved stream.
         * Otherwise, the omitted DRR_END record will signal to
         * the receive side that the stream is incomplete.
         */
        if (!dspp->savedok) {
                memset(drr, 0, sizeof (dmu_replay_record_t));
                drr->drr_type = DRR_END;
                drr->drr_u.drr_end.drr_checksum = dsc.dsc_zc;
                drr->drr_u.drr_end.drr_toguid = dsc.dsc_toguid;

                if (dump_record(&dsc, NULL, 0) != 0)
                        err = dsc.dsc_err;
        }
out:
        mutex_enter(&to_ds->ds_sendstream_lock);
        list_remove(&to_ds->ds_sendstreams, dssp);
        mutex_exit(&to_ds->ds_sendstream_lock);

        VERIFY(err != 0 || (dsc.dsc_sent_begin &&
            (dsc.dsc_sent_end || dspp->savedok)));

        kmem_free(drr, sizeof (dmu_replay_record_t));
        kmem_free(dssp, sizeof (dmu_sendstatus_t));
        kmem_free(from_arg, sizeof (*from_arg));
        kmem_free(to_arg, sizeof (*to_arg));
        kmem_free(rlt_arg, sizeof (*rlt_arg));
        kmem_free(smt_arg, sizeof (*smt_arg));
        kmem_free(srt_arg, sizeof (*srt_arg));

        dsl_dataset_long_rele(to_ds, FTAG);
        if (from_rl != NULL) {
                dsl_redaction_list_long_rele(from_rl, FTAG);
                dsl_redaction_list_rele(from_rl, FTAG);
        }
        if (redact_rl != NULL) {
                dsl_redaction_list_long_rele(redact_rl, FTAG);
                dsl_redaction_list_rele(redact_rl, FTAG);
        }

        return (err);
}

int
dmu_send_obj(const char *pool, uint64_t tosnap, uint64_t fromsnap,
    boolean_t embedok, boolean_t large_block_ok, boolean_t compressok,
    boolean_t rawok, boolean_t savedok, int outfd, offset_t *off,
    dmu_send_outparams_t *dsop)
{
        int err;
        dsl_dataset_t *fromds;
        ds_hold_flags_t dsflags;
        struct dmu_send_params dspp = {0};
        dspp.embedok = embedok;
        dspp.large_block_ok = large_block_ok;
        dspp.compressok = compressok;
        dspp.outfd = outfd;
        dspp.off = off;
        dspp.dso = dsop;
        dspp.tag = FTAG;
        dspp.rawok = rawok;
        dspp.savedok = savedok;

        dsflags = (rawok) ? DS_HOLD_FLAG_NONE : DS_HOLD_FLAG_DECRYPT;
        err = dsl_pool_hold(pool, FTAG, &dspp.dp);
        if (err != 0)
                return (err);

        err = dsl_dataset_hold_obj_flags(dspp.dp, tosnap, dsflags, FTAG,
            &dspp.to_ds);
        if (err != 0) {
                dsl_pool_rele(dspp.dp, FTAG);
                return (err);
        }

        if (fromsnap != 0) {
                err = dsl_dataset_hold_obj_flags(dspp.dp, fromsnap, dsflags,
                    FTAG, &fromds);
                if (err != 0) {
                        dsl_dataset_rele_flags(dspp.to_ds, dsflags, FTAG);
                        dsl_pool_rele(dspp.dp, FTAG);
                        return (err);
                }
                dspp.ancestor_zb.zbm_guid = dsl_dataset_phys(fromds)->ds_guid;
                dspp.ancestor_zb.zbm_creation_txg =
                    dsl_dataset_phys(fromds)->ds_creation_txg;
                dspp.ancestor_zb.zbm_creation_time =
                    dsl_dataset_phys(fromds)->ds_creation_time;

                if (dsl_dataset_is_zapified(fromds)) {
                        (void) zap_lookup(dspp.dp->dp_meta_objset,
                            fromds->ds_object, DS_FIELD_IVSET_GUID, 8, 1,
                            &dspp.ancestor_zb.zbm_ivset_guid);
                }

                /* See dmu_send for the reasons behind this. */
                uint64_t *fromredact;

                if (!dsl_dataset_get_uint64_array_feature(fromds,
                    SPA_FEATURE_REDACTED_DATASETS,
                    &dspp.numfromredactsnaps,
                    &fromredact)) {
                        dspp.numfromredactsnaps = NUM_SNAPS_NOT_REDACTED;
                } else if (dspp.numfromredactsnaps > 0) {
                        uint64_t size = dspp.numfromredactsnaps *
                            sizeof (uint64_t);
                        dspp.fromredactsnaps = kmem_zalloc(size, KM_SLEEP);
                        memcpy(dspp.fromredactsnaps, fromredact, size);
                }

                boolean_t is_before =
                    dsl_dataset_is_before(dspp.to_ds, fromds, 0);
                dspp.is_clone = (dspp.to_ds->ds_dir !=
                    fromds->ds_dir);
                dsl_dataset_rele(fromds, FTAG);
                if (!is_before) {
                        dsl_pool_rele(dspp.dp, FTAG);
                        err = SET_ERROR(EXDEV);
                } else {
                        err = dmu_send_impl(&dspp);
                }
        } else {
                dspp.numfromredactsnaps = NUM_SNAPS_NOT_REDACTED;
                err = dmu_send_impl(&dspp);
        }
        if (dspp.fromredactsnaps)
                kmem_free(dspp.fromredactsnaps,
                    dspp.numfromredactsnaps * sizeof (uint64_t));

        dsl_dataset_rele(dspp.to_ds, FTAG);
        return (err);
}

int
dmu_send(const char *tosnap, const char *fromsnap, boolean_t embedok,
    boolean_t large_block_ok, boolean_t compressok, boolean_t rawok,
    boolean_t savedok, uint64_t resumeobj, uint64_t resumeoff,
    const char *redactbook, int outfd, offset_t *off,
    dmu_send_outparams_t *dsop)
{
        int err = 0;
        ds_hold_flags_t dsflags;
        boolean_t owned = B_FALSE;
        dsl_dataset_t *fromds = NULL;
        zfs_bookmark_phys_t book = {0};
        struct dmu_send_params dspp = {0};

        dsflags = (rawok) ? DS_HOLD_FLAG_NONE : DS_HOLD_FLAG_DECRYPT;
        dspp.tosnap = tosnap;
        dspp.embedok = embedok;
        dspp.large_block_ok = large_block_ok;
        dspp.compressok = compressok;
        dspp.outfd = outfd;
        dspp.off = off;
        dspp.dso = dsop;
        dspp.tag = FTAG;
        dspp.resumeobj = resumeobj;
        dspp.resumeoff = resumeoff;
        dspp.rawok = rawok;
        dspp.savedok = savedok;

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

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

        if (strchr(tosnap, '@') == NULL && spa_writeable(dspp.dp->dp_spa)) {
                /*
                 * We are sending a filesystem or volume.  Ensure
                 * that it doesn't change by owning the dataset.
                 */

                if (savedok) {
                        /*
                         * We are looking for the dataset that represents the
                         * partially received send stream. If this stream was
                         * received as a new snapshot of an existing dataset,
                         * this will be saved in a hidden clone named
                         * "<pool>/<dataset>/%recv". Otherwise, the stream
                         * will be saved in the live dataset itself. In
                         * either case we need to use dsl_dataset_own_force()
                         * because the stream is marked as inconsistent,
                         * which would normally make it unavailable to be
                         * owned.
                         */
                        char *name = kmem_asprintf("%s/%s", tosnap,
                            recv_clone_name);
                        err = dsl_dataset_own_force(dspp.dp, name, dsflags,
                            FTAG, &dspp.to_ds);
                        if (err == ENOENT) {
                                err = dsl_dataset_own_force(dspp.dp, tosnap,
                                    dsflags, FTAG, &dspp.to_ds);
                        }

                        if (err == 0) {
                                owned = B_TRUE;
                                err = zap_lookup(dspp.dp->dp_meta_objset,
                                    dspp.to_ds->ds_object,
                                    DS_FIELD_RESUME_TOGUID, 8, 1,
                                    &dspp.saved_guid);
                        }

                        if (err == 0) {
                                err = zap_lookup(dspp.dp->dp_meta_objset,
                                    dspp.to_ds->ds_object,
                                    DS_FIELD_RESUME_TONAME, 1,
                                    sizeof (dspp.saved_toname),
                                    dspp.saved_toname);
                        }
                        /* Only disown if there was an error in the lookups */
                        if (owned && (err != 0))
                                dsl_dataset_disown(dspp.to_ds, dsflags, FTAG);

                        kmem_strfree(name);
                } else {
                        err = dsl_dataset_own(dspp.dp, tosnap, dsflags,
                            FTAG, &dspp.to_ds);
                        if (err == 0)
                                owned = B_TRUE;
                }
        } else {
                err = dsl_dataset_hold_flags(dspp.dp, tosnap, dsflags, FTAG,
                    &dspp.to_ds);
        }

        if (err != 0) {
                /* Note: dsl dataset is not owned at this point */
                dsl_pool_rele(dspp.dp, FTAG);
                return (err);
        }

        if (redactbook != NULL) {
                char path[ZFS_MAX_DATASET_NAME_LEN];
                (void) strlcpy(path, tosnap, sizeof (path));
                char *at = strchr(path, '@');
                if (at == NULL) {
                        err = EINVAL;
                } else {
                        (void) snprintf(at, sizeof (path) - (at - path), "#%s",
                            redactbook);
                        err = dsl_bookmark_lookup(dspp.dp, path,
                            NULL, &book);
                        dspp.redactbook = &book;
                }
        }

        if (err != 0) {
                dsl_pool_rele(dspp.dp, FTAG);
                if (owned)
                        dsl_dataset_disown(dspp.to_ds, dsflags, FTAG);
                else
                        dsl_dataset_rele_flags(dspp.to_ds, dsflags, FTAG);
                return (err);
        }

        if (fromsnap != NULL) {
                zfs_bookmark_phys_t *zb = &dspp.ancestor_zb;
                int fsnamelen;
                if (strpbrk(tosnap, "@#") != NULL)
                        fsnamelen = strpbrk(tosnap, "@#") - tosnap;
                else
                        fsnamelen = strlen(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] != '#')) {
                        dspp.is_clone = B_TRUE;
                }

                if (strchr(fromsnap, '@') != NULL) {
                        err = dsl_dataset_hold(dspp.dp, fromsnap, FTAG,
                            &fromds);

                        if (err != 0) {
                                ASSERT3P(fromds, ==, NULL);
                        } else {
                                /*
                                 * We need to make a deep copy of the redact
                                 * snapshots of the from snapshot, because the
                                 * array will be freed when we evict from_ds.
                                 */
                                uint64_t *fromredact;
                                if (!dsl_dataset_get_uint64_array_feature(
                                    fromds, SPA_FEATURE_REDACTED_DATASETS,
                                    &dspp.numfromredactsnaps,
                                    &fromredact)) {
                                        dspp.numfromredactsnaps =
                                            NUM_SNAPS_NOT_REDACTED;
                                } else if (dspp.numfromredactsnaps > 0) {
                                        uint64_t size =
                                            dspp.numfromredactsnaps *
                                            sizeof (uint64_t);
                                        dspp.fromredactsnaps = kmem_zalloc(size,
                                            KM_SLEEP);
                                        memcpy(dspp.fromredactsnaps, fromredact,
                                            size);
                                }
                                if (!dsl_dataset_is_before(dspp.to_ds, fromds,
                                    0)) {
                                        err = SET_ERROR(EXDEV);
                                } else {
                                        zb->zbm_creation_txg =
                                            dsl_dataset_phys(fromds)->
                                            ds_creation_txg;
                                        zb->zbm_creation_time =
                                            dsl_dataset_phys(fromds)->
                                            ds_creation_time;
                                        zb->zbm_guid =
                                            dsl_dataset_phys(fromds)->ds_guid;
                                        zb->zbm_redaction_obj = 0;

                                        if (dsl_dataset_is_zapified(fromds)) {
                                                (void) zap_lookup(
                                                    dspp.dp->dp_meta_objset,
                                                    fromds->ds_object,
                                                    DS_FIELD_IVSET_GUID, 8, 1,
                                                    &zb->zbm_ivset_guid);
                                        }
                                }
                                dsl_dataset_rele(fromds, FTAG);
                        }
                } else {
                        dspp.numfromredactsnaps = NUM_SNAPS_NOT_REDACTED;
                        err = dsl_bookmark_lookup(dspp.dp, fromsnap, dspp.to_ds,
                            zb);
                        if (err == EXDEV && zb->zbm_redaction_obj != 0 &&
                            zb->zbm_guid ==
                            dsl_dataset_phys(dspp.to_ds)->ds_guid)
                                err = 0;
                }

                if (err == 0) {
                        /* dmu_send_impl will call dsl_pool_rele for us. */
                        err = dmu_send_impl(&dspp);
                } else {
                        if (dspp.fromredactsnaps)
                                kmem_free(dspp.fromredactsnaps,
                                    dspp.numfromredactsnaps *
                                    sizeof (uint64_t));
                        dsl_pool_rele(dspp.dp, FTAG);
                }
        } else {
                dspp.numfromredactsnaps = NUM_SNAPS_NOT_REDACTED;
                err = dmu_send_impl(&dspp);
        }
        if (owned)
                dsl_dataset_disown(dspp.to_ds, dsflags, FTAG);
        else
                dsl_dataset_rele_flags(dspp.to_ds, dsflags, FTAG);
        return (err);
}

static int
dmu_adjust_send_estimate_for_indirects(dsl_dataset_t *ds, uint64_t uncompressed,
    uint64_t compressed, boolean_t stream_compressed, uint64_t *sizep)
{
        int err = 0;
        uint64_t size;
        /*
         * 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).
         */

        uint64_t recordsize;
        uint64_t record_count;
        objset_t *os;
        VERIFY0(dmu_objset_from_ds(ds, &os));

        /* Assume all (uncompressed) blocks are recordsize. */
        if (zfs_override_estimate_recordsize != 0) {
                recordsize = zfs_override_estimate_recordsize;
        } else if (os->os_phys->os_type == DMU_OST_ZVOL) {
                err = dsl_prop_get_int_ds(ds,
                    zfs_prop_to_name(ZFS_PROP_VOLBLOCKSIZE), &recordsize);
        } else {
                err = dsl_prop_get_int_ds(ds,
                    zfs_prop_to_name(ZFS_PROP_RECORDSIZE), &recordsize);
        }
        if (err != 0)
                return (err);
        record_count = uncompressed / recordsize;

        /*
         * If we're estimating a send size for a compressed stream, use the
         * compressed data size to estimate the stream size. Otherwise, use the
         * uncompressed data size.
         */
        size = stream_compressed ? compressed : uncompressed;

        /*
         * Subtract out approximate space used by indirect blocks.
         * Assume most space is used by data blocks (non-indirect, non-dnode).
         * Assume no ditto blocks or internal fragmentation.
         *
         * Therefore, space used by indirect blocks is sizeof(blkptr_t) per
         * block.
         */
        size -= record_count * sizeof (blkptr_t);

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

        *sizep = size;

        return (0);
}

int
dmu_send_estimate_fast(dsl_dataset_t *origds, dsl_dataset_t *fromds,
    zfs_bookmark_phys_t *frombook, boolean_t stream_compressed,
    boolean_t saved, uint64_t *sizep)
{
        int err;
        dsl_dataset_t *ds = origds;
        uint64_t uncomp, comp;

        ASSERT(dsl_pool_config_held(origds->ds_dir->dd_pool));
        ASSERT(fromds == NULL || frombook == NULL);

        /*
         * If this is a saved send we may actually be sending
         * from the %recv clone used for resuming.
         */
        if (saved) {
                objset_t *mos = origds->ds_dir->dd_pool->dp_meta_objset;
                uint64_t guid;
                char dsname[ZFS_MAX_DATASET_NAME_LEN + 6];

                dsl_dataset_name(origds, dsname);
                (void) strcat(dsname, "/");
                (void) strlcat(dsname, recv_clone_name, sizeof (dsname));

                err = dsl_dataset_hold(origds->ds_dir->dd_pool,
                    dsname, FTAG, &ds);
                if (err != ENOENT && err != 0) {
                        return (err);
                } else if (err == ENOENT) {
                        ds = origds;
                }

                /* check that this dataset has partially received data */
                err = zap_lookup(mos, ds->ds_object,
                    DS_FIELD_RESUME_TOGUID, 8, 1, &guid);
                if (err != 0) {
                        err = SET_ERROR(err == ENOENT ? EINVAL : err);
                        goto out;
                }

                err = zap_lookup(mos, ds->ds_object,
                    DS_FIELD_RESUME_TONAME, 1, sizeof (dsname), dsname);
                if (err != 0) {
                        err = SET_ERROR(err == ENOENT ? EINVAL : err);
                        goto out;
                }
        }

        /* tosnap must be a snapshot or the target of a saved send */
        if (!ds->ds_is_snapshot && ds == origds)
                return (SET_ERROR(EINVAL));

        if (fromds != NULL) {
                uint64_t used;
                if (!fromds->ds_is_snapshot) {
                        err = SET_ERROR(EINVAL);
                        goto out;
                }

                if (!dsl_dataset_is_before(ds, fromds, 0)) {
                        err = SET_ERROR(EXDEV);
                        goto out;
                }

                err = dsl_dataset_space_written(fromds, ds, &used, &comp,
                    &uncomp);
                if (err != 0)
                        goto out;
        } else if (frombook != NULL) {
                uint64_t used;
                err = dsl_dataset_space_written_bookmark(frombook, ds, &used,
                    &comp, &uncomp);
                if (err != 0)
                        goto out;
        } else {
                uncomp = dsl_dataset_phys(ds)->ds_uncompressed_bytes;
                comp = dsl_dataset_phys(ds)->ds_compressed_bytes;
        }

        err = dmu_adjust_send_estimate_for_indirects(ds, uncomp, comp,
            stream_compressed, sizep);
        /*
         * Add the size of the BEGIN and END records to the estimate.
         */
        *sizep += 2 * sizeof (dmu_replay_record_t);

out:
        if (ds != origds)
                dsl_dataset_rele(ds, FTAG);
        return (err);
}

ZFS_MODULE_PARAM(zfs_send, zfs_send_, corrupt_data, INT, ZMOD_RW,
        "Allow sending corrupt data");

ZFS_MODULE_PARAM(zfs_send, zfs_send_, queue_length, UINT, ZMOD_RW,
        "Maximum send queue length");

ZFS_MODULE_PARAM(zfs_send, zfs_send_, unmodified_spill_blocks, INT, ZMOD_RW,
        "Send unmodified spill blocks");

ZFS_MODULE_PARAM(zfs_send, zfs_send_, no_prefetch_queue_length, UINT, ZMOD_RW,
        "Maximum send queue length for non-prefetch queues");

ZFS_MODULE_PARAM(zfs_send, zfs_send_, queue_ff, UINT, ZMOD_RW,
        "Send queue fill fraction");

ZFS_MODULE_PARAM(zfs_send, zfs_send_, no_prefetch_queue_ff, UINT, ZMOD_RW,
        "Send queue fill fraction for non-prefetch queues");

ZFS_MODULE_PARAM(zfs_send, zfs_, override_estimate_recordsize, UINT, ZMOD_RW,
        "Override block size estimate with fixed size");