view usr/src/uts/common/fs/zfs/dmu_send.c @ 14008:0a1a841641da

3645 dmu_send_impl: possibilty of pool hold leak 3692 Panic on zfs receive of a recursive deduplicated stream Reviewed by: Adam Leventhal <ahl@delphix.com> Reviewed by: Christopher Siden <christopher.siden@delphix.com> Reviewed by: Dan McDonald <danmcd@nexenta.com> Approved by: Richard Lowe <richlowe@richlowe.net>
author Matthew Ahrens <mahrens@delphix.com>
date Wed, 10 Apr 2013 13:54:56 -0800
parents d7059eb1884c
children 3ca4e9e72fe7
line wrap: on
line source

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright 2011 Nexenta Systems, Inc. All rights reserved.
 * Copyright (c) 2013 by Delphix. All rights reserved.
 * Copyright (c) 2012, Joyent, Inc. All rights reserved.
 */

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

/* Set this tunable to TRUE to replace corrupt data with 0x2f5baddb10c */
int zfs_send_corrupt_data = B_FALSE;

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

static int
dump_bytes(dmu_sendarg_t *dsp, void *buf, int len)
{
	dsl_dataset_t *ds = dsp->dsa_os->os_dsl_dataset;
	ssize_t resid; /* have to get resid to get detailed errno */
	ASSERT0(len % 8);

	fletcher_4_incremental_native(buf, len, &dsp->dsa_zc);
	dsp->dsa_err = vn_rdwr(UIO_WRITE, dsp->dsa_vp,
	    (caddr_t)buf, len,
	    0, UIO_SYSSPACE, FAPPEND, RLIM64_INFINITY, CRED(), &resid);

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

	return (dsp->dsa_err);
}

static int
dump_free(dmu_sendarg_t *dsp, uint64_t object, uint64_t offset,
    uint64_t length)
{
	struct drr_free *drrf = &(dsp->dsa_drr->drr_u.drr_free);

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

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

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

	return (0);
}

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


	/*
	 * If there is any kind of pending aggregation (currently either
	 * a grouping of free objects or free blocks), push it out to
	 * the stream, since aggregation can't be done across operations
	 * of different types.
	 */
	if (dsp->dsa_pending_op != PENDING_NONE) {
		if (dump_bytes(dsp, dsp->dsa_drr,
		    sizeof (dmu_replay_record_t)) != 0)
			return (SET_ERROR(EINTR));
		dsp->dsa_pending_op = PENDING_NONE;
	}
	/* write a DATA record */
	bzero(dsp->dsa_drr, sizeof (dmu_replay_record_t));
	dsp->dsa_drr->drr_type = DRR_WRITE;
	drrw->drr_object = object;
	drrw->drr_type = type;
	drrw->drr_offset = offset;
	drrw->drr_length = blksz;
	drrw->drr_toguid = dsp->dsa_toguid;
	drrw->drr_checksumtype = BP_GET_CHECKSUM(bp);
	if (zio_checksum_table[drrw->drr_checksumtype].ci_dedup)
		drrw->drr_checksumflags |= DRR_CHECKSUM_DEDUP;
	DDK_SET_LSIZE(&drrw->drr_key, BP_GET_LSIZE(bp));
	DDK_SET_PSIZE(&drrw->drr_key, BP_GET_PSIZE(bp));
	DDK_SET_COMPRESS(&drrw->drr_key, BP_GET_COMPRESS(bp));
	drrw->drr_key.ddk_cksum = bp->blk_cksum;

	if (dump_bytes(dsp, dsp->dsa_drr, sizeof (dmu_replay_record_t)) != 0)
		return (SET_ERROR(EINTR));
	if (dump_bytes(dsp, data, blksz) != 0)
		return (SET_ERROR(EINTR));
	return (0);
}

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

	if (dsp->dsa_pending_op != PENDING_NONE) {
		if (dump_bytes(dsp, dsp->dsa_drr,
		    sizeof (dmu_replay_record_t)) != 0)
			return (SET_ERROR(EINTR));
		dsp->dsa_pending_op = PENDING_NONE;
	}

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

	if (dump_bytes(dsp, dsp->dsa_drr, sizeof (dmu_replay_record_t)))
		return (SET_ERROR(EINTR));
	if (dump_bytes(dsp, data, blksz))
		return (SET_ERROR(EINTR));
	return (0);
}

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

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

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

	dsp->dsa_pending_op = PENDING_FREEOBJECTS;

	return (0);
}

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

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

	if (dsp->dsa_pending_op != PENDING_NONE) {
		if (dump_bytes(dsp, dsp->dsa_drr,
		    sizeof (dmu_replay_record_t)) != 0)
			return (SET_ERROR(EINTR));
		dsp->dsa_pending_op = PENDING_NONE;
	}

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

	if (dump_bytes(dsp, dsp->dsa_drr, sizeof (dmu_replay_record_t)) != 0)
		return (SET_ERROR(EINTR));

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

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

#define	BP_SPAN(dnp, level) \
	(((uint64_t)dnp->dn_datablkszsec) << (SPA_MINBLOCKSHIFT + \
	(level) * (dnp->dn_indblkshift - SPA_BLKPTRSHIFT)))

/* ARGSUSED */
static int
backup_cb(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
    const zbookmark_t *zb, const dnode_phys_t *dnp, void *arg)
{
	dmu_sendarg_t *dsp = arg;
	dmu_object_type_t type = bp ? BP_GET_TYPE(bp) : DMU_OT_NONE;
	int err = 0;

	if (issig(JUSTLOOKING) && issig(FORREAL))
		return (SET_ERROR(EINTR));

	if (zb->zb_object != DMU_META_DNODE_OBJECT &&
	    DMU_OBJECT_IS_SPECIAL(zb->zb_object)) {
		return (0);
	} else if (bp == NULL && zb->zb_object == DMU_META_DNODE_OBJECT) {
		uint64_t span = BP_SPAN(dnp, zb->zb_level);
		uint64_t dnobj = (zb->zb_blkid * span) >> DNODE_SHIFT;
		err = dump_freeobjects(dsp, dnobj, span >> DNODE_SHIFT);
	} else if (bp == NULL) {
		uint64_t span = BP_SPAN(dnp, zb->zb_level);
		err = dump_free(dsp, zb->zb_object, zb->zb_blkid * span, span);
	} else if (zb->zb_level > 0 || type == DMU_OT_OBJSET) {
		return (0);
	} else if (type == DMU_OT_DNODE) {
		dnode_phys_t *blk;
		int i;
		int blksz = BP_GET_LSIZE(bp);
		uint32_t aflags = ARC_WAIT;
		arc_buf_t *abuf;

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

		blk = abuf->b_data;
		for (i = 0; i < blksz >> DNODE_SHIFT; i++) {
			uint64_t dnobj = (zb->zb_blkid <<
			    (DNODE_BLOCK_SHIFT - DNODE_SHIFT)) + i;
			err = dump_dnode(dsp, dnobj, blk+i);
			if (err != 0)
				break;
		}
		(void) arc_buf_remove_ref(abuf, &abuf);
	} else if (type == DMU_OT_SA) {
		uint32_t aflags = ARC_WAIT;
		arc_buf_t *abuf;
		int blksz = BP_GET_LSIZE(bp);

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

		err = dump_spill(dsp, zb->zb_object, blksz, abuf->b_data);
		(void) arc_buf_remove_ref(abuf, &abuf);
	} else { /* it's a level-0 block of a regular object */
		uint32_t aflags = ARC_WAIT;
		arc_buf_t *abuf;
		int blksz = BP_GET_LSIZE(bp);

		if (arc_read(NULL, spa, bp, arc_getbuf_func, &abuf,
		    ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL,
		    &aflags, zb) != 0) {
			if (zfs_send_corrupt_data) {
				/* Send a block filled with 0x"zfs badd bloc" */
				abuf = arc_buf_alloc(spa, blksz, &abuf,
				    ARC_BUFC_DATA);
				uint64_t *ptr;
				for (ptr = abuf->b_data;
				    (char *)ptr < (char *)abuf->b_data + blksz;
				    ptr++)
					*ptr = 0x2f5baddb10c;
			} else {
				return (SET_ERROR(EIO));
			}
		}

		err = dump_data(dsp, type, zb->zb_object, zb->zb_blkid * blksz,
		    blksz, bp, abuf->b_data);
		(void) arc_buf_remove_ref(abuf, &abuf);
	}

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

/*
 * Releases dp, ds, and fromds, using the specified tag.
 */
static int
dmu_send_impl(void *tag, dsl_pool_t *dp, dsl_dataset_t *ds,
    dsl_dataset_t *fromds, int outfd, vnode_t *vp, offset_t *off)
{
	objset_t *os;
	dmu_replay_record_t *drr;
	dmu_sendarg_t *dsp;
	int err;
	uint64_t fromtxg = 0;

	if (fromds != NULL && !dsl_dataset_is_before(ds, fromds)) {
		dsl_dataset_rele(fromds, tag);
		dsl_dataset_rele(ds, tag);
		dsl_pool_rele(dp, tag);
		return (SET_ERROR(EXDEV));
	}

	err = dmu_objset_from_ds(ds, &os);
	if (err != 0) {
		if (fromds != NULL)
			dsl_dataset_rele(fromds, tag);
		dsl_dataset_rele(ds, tag);
		dsl_pool_rele(dp, tag);
		return (err);
	}

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

#ifdef _KERNEL
	if (dmu_objset_type(os) == DMU_OST_ZFS) {
		uint64_t version;
		if (zfs_get_zplprop(os, ZFS_PROP_VERSION, &version) != 0) {
			kmem_free(drr, sizeof (dmu_replay_record_t));
			if (fromds != NULL)
				dsl_dataset_rele(fromds, tag);
			dsl_dataset_rele(ds, tag);
			dsl_pool_rele(dp, tag);
			return (SET_ERROR(EINVAL));
		}
		if (version >= ZPL_VERSION_SA) {
			DMU_SET_FEATUREFLAGS(
			    drr->drr_u.drr_begin.drr_versioninfo,
			    DMU_BACKUP_FEATURE_SA_SPILL);
		}
	}
#endif

	drr->drr_u.drr_begin.drr_creation_time =
	    ds->ds_phys->ds_creation_time;
	drr->drr_u.drr_begin.drr_type = dmu_objset_type(os);
	if (fromds != NULL && ds->ds_dir != fromds->ds_dir)
		drr->drr_u.drr_begin.drr_flags |= DRR_FLAG_CLONE;
	drr->drr_u.drr_begin.drr_toguid = ds->ds_phys->ds_guid;
	if (ds->ds_phys->ds_flags & DS_FLAG_CI_DATASET)
		drr->drr_u.drr_begin.drr_flags |= DRR_FLAG_CI_DATA;

	if (fromds != NULL)
		drr->drr_u.drr_begin.drr_fromguid = fromds->ds_phys->ds_guid;
	dsl_dataset_name(ds, drr->drr_u.drr_begin.drr_toname);

	if (fromds != NULL) {
		fromtxg = fromds->ds_phys->ds_creation_txg;
		dsl_dataset_rele(fromds, tag);
		fromds = NULL;
	}

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

	dsp->dsa_drr = drr;
	dsp->dsa_vp = vp;
	dsp->dsa_outfd = outfd;
	dsp->dsa_proc = curproc;
	dsp->dsa_os = os;
	dsp->dsa_off = off;
	dsp->dsa_toguid = ds->ds_phys->ds_guid;
	ZIO_SET_CHECKSUM(&dsp->dsa_zc, 0, 0, 0, 0);
	dsp->dsa_pending_op = PENDING_NONE;

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

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

	if (dump_bytes(dsp, drr, sizeof (dmu_replay_record_t)) != 0) {
		err = dsp->dsa_err;
		goto out;
	}

	err = traverse_dataset(ds, fromtxg, TRAVERSE_PRE | TRAVERSE_PREFETCH,
	    backup_cb, dsp);

	if (dsp->dsa_pending_op != PENDING_NONE)
		if (dump_bytes(dsp, drr, sizeof (dmu_replay_record_t)) != 0)
			err = SET_ERROR(EINTR);

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

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

	if (dump_bytes(dsp, drr, sizeof (dmu_replay_record_t)) != 0) {
		err = dsp->dsa_err;
		goto out;
	}

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

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

	dsl_dataset_long_rele(ds, FTAG);
	dsl_dataset_rele(ds, tag);

	return (err);
}

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

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

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

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

	return (dmu_send_impl(FTAG, dp, ds, fromds, outfd, vp, off));
}

int
dmu_send(const char *tosnap, const char *fromsnap,
    int outfd, vnode_t *vp, offset_t *off)
{
	dsl_pool_t *dp;
	dsl_dataset_t *ds;
	dsl_dataset_t *fromds = NULL;
	int err;

	if (strchr(tosnap, '@') == NULL)
		return (SET_ERROR(EINVAL));
	if (fromsnap != NULL && strchr(fromsnap, '@') == NULL)
		return (SET_ERROR(EINVAL));

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

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

	if (fromsnap != NULL) {
		err = dsl_dataset_hold(dp, fromsnap, FTAG, &fromds);
		if (err != 0) {
			dsl_dataset_rele(ds, FTAG);
			dsl_pool_rele(dp, FTAG);
			return (err);
		}
	}
	return (dmu_send_impl(FTAG, dp, ds, fromds, outfd, vp, off));
}

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

	ASSERT(dsl_pool_config_held(dp));

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

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

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

	/*
	 * Assume that space (both on-disk and in-stream) is dominated by
	 * data.  We will adjust for indirect blocks and the copies property,
	 * but ignore per-object space used (eg, dnodes and DRR_OBJECT records).
	 */

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

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

	*sizep = size;

	return (0);
}

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

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

	/* must not have any changes since most recent snapshot */
	if (!drba->drba_cookie->drc_force &&
	    dsl_dataset_modified_since_lastsnap(ds))
		return (SET_ERROR(ETXTBSY));

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

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

	if (fromguid != 0) {
		/* if incremental, most recent snapshot must match fromguid */
		if (ds->ds_prev == NULL)
			return (SET_ERROR(ENODEV));

		/*
		 * most recent snapshot must match fromguid, or there are no
		 * changes since the fromguid one
		 */
		if (ds->ds_prev->ds_phys->ds_guid != fromguid) {
			uint64_t birth = ds->ds_prev->ds_phys->ds_bp.blk_birth;
			uint64_t obj = ds->ds_prev->ds_phys->ds_prev_snap_obj;
			while (obj != 0) {
				dsl_dataset_t *snap;
				error = dsl_dataset_hold_obj(dp, obj, FTAG,
				    &snap);
				if (error != 0)
					return (SET_ERROR(ENODEV));
				if (snap->ds_phys->ds_creation_txg < birth) {
					dsl_dataset_rele(snap, FTAG);
					return (SET_ERROR(ENODEV));
				}
				if (snap->ds_phys->ds_guid == fromguid) {
					dsl_dataset_rele(snap, FTAG);
					break; /* it's ok */
				}
				obj = snap->ds_phys->ds_prev_snap_obj;
				dsl_dataset_rele(snap, FTAG);
			}
			if (obj == 0)
				return (SET_ERROR(ENODEV));
		}
	} else {
		/* if full, most recent snapshot must be $ORIGIN */
		if (ds->ds_phys->ds_prev_snap_txg >= TXG_INITIAL)
			return (SET_ERROR(ENODEV));
	}

	return (0);

}

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

	/* already checked */
	ASSERT3U(drrb->drr_magic, ==, DMU_BACKUP_MAGIC);

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

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

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

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

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

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

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

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

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

	crflags = (drrb->drr_flags & DRR_FLAG_CI_DATA) ?
	    DS_FLAG_CI_DATASET : 0;

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

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

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

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

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

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

	drba->drba_cookie->drc_ds = newds;

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

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

	bzero(drc, sizeof (dmu_recv_cookie_t));
	drc->drc_drrb = drrb;
	drc->drc_tosnap = tosnap;
	drc->drc_tofs = tofs;
	drc->drc_force = force;

	if (drrb->drr_magic == BSWAP_64(DMU_BACKUP_MAGIC))
		drc->drc_byteswap = B_TRUE;
	else if (drrb->drr_magic != DMU_BACKUP_MAGIC)
		return (SET_ERROR(EINVAL));

	drr = kmem_zalloc(sizeof (dmu_replay_record_t), KM_SLEEP);
	drr->drr_type = DRR_BEGIN;
	drr->drr_u.drr_begin = *drc->drc_drrb;
	if (drc->drc_byteswap) {
		fletcher_4_incremental_byteswap(drr,
		    sizeof (dmu_replay_record_t), &drc->drc_cksum);
	} else {
		fletcher_4_incremental_native(drr,
		    sizeof (dmu_replay_record_t), &drc->drc_cksum);
	}
	kmem_free(drr, sizeof (dmu_replay_record_t));

	if (drc->drc_byteswap) {
		drrb->drr_magic = BSWAP_64(drrb->drr_magic);
		drrb->drr_versioninfo = BSWAP_64(drrb->drr_versioninfo);
		drrb->drr_creation_time = BSWAP_64(drrb->drr_creation_time);
		drrb->drr_type = BSWAP_32(drrb->drr_type);
		drrb->drr_toguid = BSWAP_64(drrb->drr_toguid);
		drrb->drr_fromguid = BSWAP_64(drrb->drr_fromguid);
	}

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

	return (dsl_sync_task(tofs, dmu_recv_begin_check, dmu_recv_begin_sync,
	    &drba, 5));
}

struct restorearg {
	int err;
	boolean_t byteswap;
	vnode_t *vp;
	char *buf;
	uint64_t voff;
	int bufsize; /* amount of memory allocated for buf */
	zio_cksum_t cksum;
	avl_tree_t *guid_to_ds_map;
};

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

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

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

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

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

static void *
restore_read(struct restorearg *ra, int len)
{
	void *rv;
	int done = 0;

	/* some things will require 8-byte alignment, so everything must */
	ASSERT0(len % 8);

	while (done < len) {
		ssize_t resid;

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

		if (resid == len - done)
			ra->err = SET_ERROR(EINVAL);
		ra->voff += len - done - resid;
		done = len - resid;
		if (ra->err != 0)
			return (NULL);
	}

	ASSERT3U(done, ==, len);
	rv = ra->buf;
	if (ra->byteswap)
		fletcher_4_incremental_byteswap(rv, len, &ra->cksum);
	else
		fletcher_4_incremental_native(rv, len, &ra->cksum);
	return (rv);
}

static void
backup_byteswap(dmu_replay_record_t *drr)
{
#define	DO64(X) (drr->drr_u.X = BSWAP_64(drr->drr_u.X))
#define	DO32(X) (drr->drr_u.X = BSWAP_32(drr->drr_u.X))
	drr->drr_type = BSWAP_32(drr->drr_type);
	drr->drr_payloadlen = BSWAP_32(drr->drr_payloadlen);
	switch (drr->drr_type) {
	case DRR_BEGIN:
		DO64(drr_begin.drr_magic);
		DO64(drr_begin.drr_versioninfo);
		DO64(drr_begin.drr_creation_time);
		DO32(drr_begin.drr_type);
		DO32(drr_begin.drr_flags);
		DO64(drr_begin.drr_toguid);
		DO64(drr_begin.drr_fromguid);
		break;
	case DRR_OBJECT:
		DO64(drr_object.drr_object);
		/* DO64(drr_object.drr_allocation_txg); */
		DO32(drr_object.drr_type);
		DO32(drr_object.drr_bonustype);
		DO32(drr_object.drr_blksz);
		DO32(drr_object.drr_bonuslen);
		DO64(drr_object.drr_toguid);
		break;
	case DRR_FREEOBJECTS:
		DO64(drr_freeobjects.drr_firstobj);
		DO64(drr_freeobjects.drr_numobjs);
		DO64(drr_freeobjects.drr_toguid);
		break;
	case DRR_WRITE:
		DO64(drr_write.drr_object);
		DO32(drr_write.drr_type);
		DO64(drr_write.drr_offset);
		DO64(drr_write.drr_length);
		DO64(drr_write.drr_toguid);
		DO64(drr_write.drr_key.ddk_cksum.zc_word[0]);
		DO64(drr_write.drr_key.ddk_cksum.zc_word[1]);
		DO64(drr_write.drr_key.ddk_cksum.zc_word[2]);
		DO64(drr_write.drr_key.ddk_cksum.zc_word[3]);
		DO64(drr_write.drr_key.ddk_prop);
		break;
	case DRR_WRITE_BYREF:
		DO64(drr_write_byref.drr_object);
		DO64(drr_write_byref.drr_offset);
		DO64(drr_write_byref.drr_length);
		DO64(drr_write_byref.drr_toguid);
		DO64(drr_write_byref.drr_refguid);
		DO64(drr_write_byref.drr_refobject);
		DO64(drr_write_byref.drr_refoffset);
		DO64(drr_write_byref.drr_key.ddk_cksum.zc_word[0]);
		DO64(drr_write_byref.drr_key.ddk_cksum.zc_word[1]);
		DO64(drr_write_byref.drr_key.ddk_cksum.zc_word[2]);
		DO64(drr_write_byref.drr_key.ddk_cksum.zc_word[3]);
		DO64(drr_write_byref.drr_key.ddk_prop);
		break;
	case DRR_FREE:
		DO64(drr_free.drr_object);
		DO64(drr_free.drr_offset);
		DO64(drr_free.drr_length);
		DO64(drr_free.drr_toguid);
		break;
	case DRR_SPILL:
		DO64(drr_spill.drr_object);
		DO64(drr_spill.drr_length);
		DO64(drr_spill.drr_toguid);
		break;
	case DRR_END:
		DO64(drr_end.drr_checksum.zc_word[0]);
		DO64(drr_end.drr_checksum.zc_word[1]);
		DO64(drr_end.drr_checksum.zc_word[2]);
		DO64(drr_end.drr_checksum.zc_word[3]);
		DO64(drr_end.drr_toguid);
		break;
	}
#undef DO64
#undef DO32
}

static int
restore_object(struct restorearg *ra, objset_t *os, struct drr_object *drro)
{
	int err;
	dmu_tx_t *tx;
	void *data = NULL;

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

	err = dmu_object_info(os, drro->drr_object, NULL);

	if (err != 0 && err != ENOENT)
		return (SET_ERROR(EINVAL));

	if (drro->drr_bonuslen) {
		data = restore_read(ra, P2ROUNDUP(drro->drr_bonuslen, 8));
		if (ra->err != 0)
			return (ra->err);
	}

	if (err == ENOENT) {
		/* currently free, want to be allocated */
		tx = dmu_tx_create(os);
		dmu_tx_hold_bonus(tx, DMU_NEW_OBJECT);
		err = dmu_tx_assign(tx, TXG_WAIT);
		if (err != 0) {
			dmu_tx_abort(tx);
			return (err);
		}
		err = dmu_object_claim(os, drro->drr_object,
		    drro->drr_type, drro->drr_blksz,
		    drro->drr_bonustype, drro->drr_bonuslen, tx);
		dmu_tx_commit(tx);
	} else {
		/* currently allocated, want to be allocated */
		err = dmu_object_reclaim(os, drro->drr_object,
		    drro->drr_type, drro->drr_blksz,
		    drro->drr_bonustype, drro->drr_bonuslen);
	}
	if (err != 0) {
		return (SET_ERROR(EINVAL));
	}

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

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

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

		VERIFY(0 == dmu_bonus_hold(os, drro->drr_object, FTAG, &db));
		dmu_buf_will_dirty(db, tx);

		ASSERT3U(db->db_size, >=, drro->drr_bonuslen);
		bcopy(data, db->db_data, drro->drr_bonuslen);
		if (ra->byteswap) {
			dmu_object_byteswap_t byteswap =
			    DMU_OT_BYTESWAP(drro->drr_bonustype);
			dmu_ot_byteswap[byteswap].ob_func(db->db_data,
			    drro->drr_bonuslen);
		}
		dmu_buf_rele(db, FTAG);
	}
	dmu_tx_commit(tx);
	return (0);
}

/* ARGSUSED */
static int
restore_freeobjects(struct restorearg *ra, objset_t *os,
    struct drr_freeobjects *drrfo)
{
	uint64_t obj;

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

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

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

		err = dmu_free_object(os, obj);
		if (err != 0)
			return (err);
	}
	return (0);
}

static int
restore_write(struct restorearg *ra, objset_t *os,
    struct drr_write *drrw)
{
	dmu_tx_t *tx;
	void *data;
	int err;

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

	data = restore_read(ra, drrw->drr_length);
	if (data == NULL)
		return (ra->err);

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

	tx = dmu_tx_create(os);

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

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

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

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

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

	tx = dmu_tx_create(os);

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

static int
restore_spill(struct restorearg *ra, objset_t *os, struct drr_spill *drrs)
{
	dmu_tx_t *tx;
	void *data;
	dmu_buf_t *db, *db_spill;
	int err;

	if (drrs->drr_length < SPA_MINBLOCKSIZE ||
	    drrs->drr_length > SPA_MAXBLOCKSIZE)
		return (SET_ERROR(EINVAL));

	data = restore_read(ra, drrs->drr_length);
	if (data == NULL)
		return (ra->err);

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

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

	tx = dmu_tx_create(os);

	dmu_tx_hold_spill(tx, db->db_object);

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

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

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

	dmu_tx_commit(tx);
	return (0);
}

/* ARGSUSED */
static int
restore_free(struct restorearg *ra, objset_t *os,
    struct drr_free *drrf)
{
	int err;

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

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

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

/* used to destroy the drc_ds on error */
static void
dmu_recv_cleanup_ds(dmu_recv_cookie_t *drc)
{
	char name[MAXNAMELEN];
	dsl_dataset_name(drc->drc_ds, name);
	dsl_dataset_disown(drc->drc_ds, dmu_recv_tag);
	(void) dsl_destroy_head(name);
}

/*
 * NB: callers *must* call dmu_recv_end() if this succeeds.
 */
int
dmu_recv_stream(dmu_recv_cookie_t *drc, vnode_t *vp, offset_t *voffp,
    int cleanup_fd, uint64_t *action_handlep)
{
	struct restorearg ra = { 0 };
	dmu_replay_record_t *drr;
	objset_t *os;
	zio_cksum_t pcksum;
	int featureflags;

	ra.byteswap = drc->drc_byteswap;
	ra.cksum = drc->drc_cksum;
	ra.vp = vp;
	ra.voff = *voffp;
	ra.bufsize = 1<<20;
	ra.buf = kmem_alloc(ra.bufsize, KM_SLEEP);

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

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

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

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

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

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

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

		drc->drc_guid_to_ds_map = ra.guid_to_ds_map;
	}

	/*
	 * Read records and process them.
	 */
	pcksum = ra.cksum;
	while (ra.err == 0 &&
	    NULL != (drr = restore_read(&ra, sizeof (*drr)))) {
		if (issig(JUSTLOOKING) && issig(FORREAL)) {
			ra.err = SET_ERROR(EINTR);
			goto out;
		}

		if (ra.byteswap)
			backup_byteswap(drr);

		switch (drr->drr_type) {
		case DRR_OBJECT:
		{
			/*
			 * We need to make a copy of the record header,
			 * because restore_{object,write} may need to
			 * restore_read(), which will invalidate drr.
			 */
			struct drr_object drro = drr->drr_u.drr_object;
			ra.err = restore_object(&ra, os, &drro);
			break;
		}
		case DRR_FREEOBJECTS:
		{
			struct drr_freeobjects drrfo =
			    drr->drr_u.drr_freeobjects;
			ra.err = restore_freeobjects(&ra, os, &drrfo);
			break;
		}
		case DRR_WRITE:
		{
			struct drr_write drrw = drr->drr_u.drr_write;
			ra.err = restore_write(&ra, os, &drrw);
			break;
		}
		case DRR_WRITE_BYREF:
		{
			struct drr_write_byref drrwbr =
			    drr->drr_u.drr_write_byref;
			ra.err = restore_write_byref(&ra, os, &drrwbr);
			break;
		}
		case DRR_FREE:
		{
			struct drr_free drrf = drr->drr_u.drr_free;
			ra.err = restore_free(&ra, os, &drrf);
			break;
		}
		case DRR_END:
		{
			struct drr_end drre = drr->drr_u.drr_end;
			/*
			 * We compare against the *previous* checksum
			 * value, because the stored checksum is of
			 * everything before the DRR_END record.
			 */
			if (!ZIO_CHECKSUM_EQUAL(drre.drr_checksum, pcksum))
				ra.err = SET_ERROR(ECKSUM);
			goto out;
		}
		case DRR_SPILL:
		{
			struct drr_spill drrs = drr->drr_u.drr_spill;
			ra.err = restore_spill(&ra, os, &drrs);
			break;
		}
		default:
			ra.err = SET_ERROR(EINVAL);
			goto out;
		}
		pcksum = ra.cksum;
	}
	ASSERT(ra.err != 0);

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

	if (ra.err != 0) {
		/*
		 * destroy what we created, so we don't leave it in the
		 * inconsistent restoring state.
		 */
		dmu_recv_cleanup_ds(drc);
	}

	kmem_free(ra.buf, ra.bufsize);
	*voffp = ra.voff;
	return (ra.err);
}

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

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

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

		error = dsl_dataset_hold(dp, drc->drc_tofs, FTAG, &origin_head);
		if (error != 0)
			return (error);
		error = dsl_dataset_clone_swap_check_impl(drc->drc_ds,
		    origin_head, drc->drc_force);
		if (error != 0) {
			dsl_dataset_rele(origin_head, FTAG);
			return (error);
		}
		error = dsl_dataset_snapshot_check_impl(origin_head,
		    drc->drc_tosnap, tx);
		dsl_dataset_rele(origin_head, FTAG);
		if (error != 0)
			return (error);

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

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

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

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

		VERIFY0(dsl_dataset_hold(dp, drc->drc_tofs, FTAG,
		    &origin_head));
		dsl_dataset_clone_swap_sync_impl(drc->drc_ds,
		    origin_head, tx);
		dsl_dataset_snapshot_sync_impl(origin_head,
		    drc->drc_tosnap, tx);

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

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

		dsl_dataset_rele(origin_head, FTAG);
		dsl_destroy_head_sync_impl(drc->drc_ds, tx);
	} else {
		dsl_dataset_t *ds = drc->drc_ds;

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

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

		dmu_buf_will_dirty(ds->ds_dbuf, tx);
		ds->ds_phys->ds_flags &= ~DS_FLAG_INCONSISTENT;
	}
	drc->drc_newsnapobj = drc->drc_ds->ds_phys->ds_prev_snap_obj;
	/*
	 * Release the hold from dmu_recv_begin.  This must be done before
	 * we return to open context, so that when we free the dataset's dnode,
	 * we can evict its bonus buffer.
	 */
	dsl_dataset_disown(drc->drc_ds, dmu_recv_tag);
	drc->drc_ds = NULL;
}

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

	ASSERT(guid_map != NULL);

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

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

static int dmu_recv_end_modified_blocks = 3;

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

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

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

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

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

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

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

int
dmu_recv_end(dmu_recv_cookie_t *drc)
{
	if (drc->drc_newfs)
		return (dmu_recv_new_end(drc));
	else
		return (dmu_recv_existing_end(drc));
}