fs/zfs/dmu.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#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_pool.h>
#include <sys/dsl_synctask.h>
#include <sys/dsl_prop.h>
#include <sys/dmu_zfetch.h>
#include <sys/zfs_ioctl.h>
#include <sys/zap.h>
#include <sys/zio_checksum.h>
#ifdef _KERNEL
#include <sys/vmsystm.h>
#include <sys/zfs_znode.h>
#endif

const dmu_object_type_info_t dmu_ot[DMU_OT_NUMTYPES] = {
	{	byteswap_uint8_array,	TRUE,	"unallocated"		},
	{	zap_byteswap,		TRUE,	"object directory"	},
	{	byteswap_uint64_array,	TRUE,	"object array"		},
	{	byteswap_uint8_array,	TRUE,	"packed nvlist"		},
	{	byteswap_uint64_array,	TRUE,	"packed nvlist size"	},
	{	byteswap_uint64_array,	TRUE,	"bplist"		},
	{	byteswap_uint64_array,	TRUE,	"bplist header"		},
	{	byteswap_uint64_array,	TRUE,	"SPA space map header"	},
	{	byteswap_uint64_array,	TRUE,	"SPA space map"		},
	{	byteswap_uint64_array,	TRUE,	"ZIL intent log"	},
	{	dnode_buf_byteswap,	TRUE,	"DMU dnode"		},
	{	dmu_objset_byteswap,	TRUE,	"DMU objset"		},
	{	byteswap_uint64_array,	TRUE,	"DSL directory"		},
	{	zap_byteswap,		TRUE,	"DSL directory child map"},
	{	zap_byteswap,		TRUE,	"DSL dataset snap map"	},
	{	zap_byteswap,		TRUE,	"DSL props"		},
	{	byteswap_uint64_array,	TRUE,	"DSL dataset"		},
	{	zfs_znode_byteswap,	TRUE,	"ZFS znode"		},
	{	zfs_oldacl_byteswap,	TRUE,	"ZFS V0 ACL"		},
	{	byteswap_uint8_array,	FALSE,	"ZFS plain file"	},
	{	zap_byteswap,		TRUE,	"ZFS directory"		},
	{	zap_byteswap,		TRUE,	"ZFS master node"	},
	{	zap_byteswap,		TRUE,	"ZFS delete queue"	},
	{	byteswap_uint8_array,	FALSE,	"zvol object"		},
	{	zap_byteswap,		TRUE,	"zvol prop"		},
	{	byteswap_uint8_array,	FALSE,	"other uint8[]"		},
	{	byteswap_uint64_array,	FALSE,	"other uint64[]"	},
	{	zap_byteswap,		TRUE,	"other ZAP"		},
	{	zap_byteswap,		TRUE,	"persistent error log"	},
	{	byteswap_uint8_array,	TRUE,	"SPA history"		},
	{	byteswap_uint64_array,	TRUE,	"SPA history offsets"	},
	{	zap_byteswap,		TRUE,	"Pool properties"	},
	{	zap_byteswap,		TRUE,	"DSL permissions"	},
	{	zfs_acl_byteswap,	TRUE,	"ZFS ACL"		},
	{	byteswap_uint8_array,	TRUE,	"ZFS SYSACL"		},
	{	byteswap_uint8_array,	TRUE,	"FUID table"		},
	{	byteswap_uint64_array,	TRUE,	"FUID table size"	},
	{	zap_byteswap,		TRUE,	"DSL dataset next clones"},
	{	zap_byteswap,		TRUE,	"scrub work queue"	},
};

int
dmu_buf_hold(objset_t *os, uint64_t object, uint64_t offset,
    void *tag, dmu_buf_t **dbp)
{
	dnode_t *dn;
	uint64_t blkid;
	dmu_buf_impl_t *db;
	int err;

	err = dnode_hold(os->os, object, FTAG, &dn);
	if (err)
		return (err);
	blkid = dbuf_whichblock(dn, offset);
	rw_enter(&dn->dn_struct_rwlock, RW_READER);
	db = dbuf_hold(dn, blkid, tag);
	rw_exit(&dn->dn_struct_rwlock);
	if (db == NULL) {
		err = EIO;
	} else {
		err = dbuf_read(db, NULL, DB_RF_CANFAIL);
		if (err) {
			dbuf_rele(db, tag);
			db = NULL;
		}
	}

	dnode_rele(dn, FTAG);
	*dbp = &db->db;
	return (err);
}

int
dmu_bonus_max(void)
{
	return (DN_MAX_BONUSLEN);
}

int
dmu_set_bonus(dmu_buf_t *db, int newsize, dmu_tx_t *tx)
{
	dnode_t *dn = ((dmu_buf_impl_t *)db)->db_dnode;

	if (dn->dn_bonus != (dmu_buf_impl_t *)db)
		return (EINVAL);
	if (newsize < 0 || newsize > db->db_size)
		return (EINVAL);
	dnode_setbonuslen(dn, newsize, tx);
	return (0);
}

/*
 * returns ENOENT, EIO, or 0.
 */
int
dmu_bonus_hold(objset_t *os, uint64_t object, void *tag, dmu_buf_t **dbp)
{
	dnode_t *dn;
	dmu_buf_impl_t *db;
	int error;

	error = dnode_hold(os->os, object, FTAG, &dn);
	if (error)
		return (error);

	rw_enter(&dn->dn_struct_rwlock, RW_READER);
	if (dn->dn_bonus == NULL) {
		rw_exit(&dn->dn_struct_rwlock);
		rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
		if (dn->dn_bonus == NULL)
			dbuf_create_bonus(dn);
	}
	db = dn->dn_bonus;
	rw_exit(&dn->dn_struct_rwlock);

	/* as long as the bonus buf is held, the dnode will be held */
	if (refcount_add(&db->db_holds, tag) == 1)
		VERIFY(dnode_add_ref(dn, db));

	dnode_rele(dn, FTAG);

	VERIFY(0 == dbuf_read(db, NULL, DB_RF_MUST_SUCCEED));

	*dbp = &db->db;
	return (0);
}

/*
 * Note: longer-term, we should modify all of the dmu_buf_*() interfaces
 * to take a held dnode rather than <os, object> -- the lookup is wasteful,
 * and can induce severe lock contention when writing to several files
 * whose dnodes are in the same block.
 */
static int
dmu_buf_hold_array_by_dnode(dnode_t *dn, uint64_t offset,
    uint64_t length, int read, void *tag, int *numbufsp, dmu_buf_t ***dbpp)
{
	dsl_pool_t *dp = NULL;
	dmu_buf_t **dbp;
	uint64_t blkid, nblks, i;
	uint32_t flags;
	int err;
	zio_t *zio;
	hrtime_t start;

	ASSERT(length <= DMU_MAX_ACCESS);

	flags = DB_RF_CANFAIL | DB_RF_NEVERWAIT;
	if (length > zfetch_array_rd_sz)
		flags |= DB_RF_NOPREFETCH;

	rw_enter(&dn->dn_struct_rwlock, RW_READER);
	if (dn->dn_datablkshift) {
		int blkshift = dn->dn_datablkshift;
		nblks = (P2ROUNDUP(offset+length, 1ULL<<blkshift) -
		    P2ALIGN(offset, 1ULL<<blkshift)) >> blkshift;
	} else {
		if (offset + length > dn->dn_datablksz) {
			zfs_panic_recover("zfs: accessing past end of object "
			    "%llx/%llx (size=%u access=%llu+%llu)",
			    (longlong_t)dn->dn_objset->
			    os_dsl_dataset->ds_object,
			    (longlong_t)dn->dn_object, dn->dn_datablksz,
			    (longlong_t)offset, (longlong_t)length);
			return (EIO);
		}
		nblks = 1;
	}
	dbp = kmem_zalloc(sizeof (dmu_buf_t *) * nblks, KM_SLEEP);

	if (dn->dn_objset->os_dsl_dataset)
		dp = dn->dn_objset->os_dsl_dataset->ds_dir->dd_pool;
	if (dp && dsl_pool_sync_context(dp))
		start = gethrtime();
	zio = zio_root(dn->dn_objset->os_spa, NULL, NULL, ZIO_FLAG_CANFAIL);
	blkid = dbuf_whichblock(dn, offset);
	for (i = 0; i < nblks; i++) {
		dmu_buf_impl_t *db = dbuf_hold(dn, blkid+i, tag);
		if (db == NULL) {
			rw_exit(&dn->dn_struct_rwlock);
			dmu_buf_rele_array(dbp, nblks, tag);
			zio_nowait(zio);
			return (EIO);
		}
		/* initiate async i/o */
		if (read) {
			rw_exit(&dn->dn_struct_rwlock);
			(void) dbuf_read(db, zio, flags);
			rw_enter(&dn->dn_struct_rwlock, RW_READER);
		}
		dbp[i] = &db->db;
	}
	rw_exit(&dn->dn_struct_rwlock);

	/* wait for async i/o */
	err = zio_wait(zio);
	/* track read overhead when we are in sync context */
	if (dp && dsl_pool_sync_context(dp))
		dp->dp_read_overhead += gethrtime() - start;
	if (err) {
		dmu_buf_rele_array(dbp, nblks, tag);
		return (err);
	}

	/* wait for other io to complete */
	if (read) {
		for (i = 0; i < nblks; i++) {
			dmu_buf_impl_t *db = (dmu_buf_impl_t *)dbp[i];
			mutex_enter(&db->db_mtx);
			while (db->db_state == DB_READ ||
			    db->db_state == DB_FILL)
				cv_wait(&db->db_changed, &db->db_mtx);
			if (db->db_state == DB_UNCACHED)
				err = EIO;
			mutex_exit(&db->db_mtx);
			if (err) {
				dmu_buf_rele_array(dbp, nblks, tag);
				return (err);
			}
		}
	}

	*numbufsp = nblks;
	*dbpp = dbp;
	return (0);
}

static int
dmu_buf_hold_array(objset_t *os, uint64_t object, uint64_t offset,
    uint64_t length, int read, void *tag, int *numbufsp, dmu_buf_t ***dbpp)
{
	dnode_t *dn;
	int err;

	err = dnode_hold(os->os, object, FTAG, &dn);
	if (err)
		return (err);

	err = dmu_buf_hold_array_by_dnode(dn, offset, length, read, tag,
	    numbufsp, dbpp);

	dnode_rele(dn, FTAG);

	return (err);
}

int
dmu_buf_hold_array_by_bonus(dmu_buf_t *db, uint64_t offset,
    uint64_t length, int read, void *tag, int *numbufsp, dmu_buf_t ***dbpp)
{
	dnode_t *dn = ((dmu_buf_impl_t *)db)->db_dnode;
	int err;

	err = dmu_buf_hold_array_by_dnode(dn, offset, length, read, tag,
	    numbufsp, dbpp);

	return (err);
}

void
dmu_buf_rele_array(dmu_buf_t **dbp_fake, int numbufs, void *tag)
{
	int i;
	dmu_buf_impl_t **dbp = (dmu_buf_impl_t **)dbp_fake;

	if (numbufs == 0)
		return;

	for (i = 0; i < numbufs; i++) {
		if (dbp[i])
			dbuf_rele(dbp[i], tag);
	}

	kmem_free(dbp, sizeof (dmu_buf_t *) * numbufs);
}

void
dmu_prefetch(objset_t *os, uint64_t object, uint64_t offset, uint64_t len)
{
	dnode_t *dn;
	uint64_t blkid;
	int nblks, i, err;

	if (zfs_prefetch_disable)
		return;

	if (len == 0) {  /* they're interested in the bonus buffer */
		dn = os->os->os_meta_dnode;

		if (object == 0 || object >= DN_MAX_OBJECT)
			return;

		rw_enter(&dn->dn_struct_rwlock, RW_READER);
		blkid = dbuf_whichblock(dn, object * sizeof (dnode_phys_t));
		dbuf_prefetch(dn, blkid);
		rw_exit(&dn->dn_struct_rwlock);
		return;
	}

	/*
	 * XXX - Note, if the dnode for the requested object is not
	 * already cached, we will do a *synchronous* read in the
	 * dnode_hold() call.  The same is true for any indirects.
	 */
	err = dnode_hold(os->os, object, FTAG, &dn);
	if (err != 0)
		return;

	rw_enter(&dn->dn_struct_rwlock, RW_READER);
	if (dn->dn_datablkshift) {
		int blkshift = dn->dn_datablkshift;
		nblks = (P2ROUNDUP(offset+len, 1<<blkshift) -
		    P2ALIGN(offset, 1<<blkshift)) >> blkshift;
	} else {
		nblks = (offset < dn->dn_datablksz);
	}

	if (nblks != 0) {
		blkid = dbuf_whichblock(dn, offset);
		for (i = 0; i < nblks; i++)
			dbuf_prefetch(dn, blkid+i);
	}

	rw_exit(&dn->dn_struct_rwlock);

	dnode_rele(dn, FTAG);
}

static int
get_next_chunk(dnode_t *dn, uint64_t *offset, uint64_t limit)
{
	uint64_t len = *offset - limit;
	uint64_t chunk_len = dn->dn_datablksz * DMU_MAX_DELETEBLKCNT;
	uint64_t subchunk =
	    dn->dn_datablksz * EPB(dn->dn_indblkshift, SPA_BLKPTRSHIFT);

	ASSERT(limit <= *offset);

	if (len <= chunk_len) {
		*offset = limit;
		return (0);
	}

	ASSERT(ISP2(subchunk));

	while (*offset > limit) {
		uint64_t initial_offset = P2ROUNDUP(*offset, subchunk);
		uint64_t delta;
		int err;

		/* skip over allocated data */
		err = dnode_next_offset(dn,
		    DNODE_FIND_HOLE|DNODE_FIND_BACKWARDS, offset, 1, 1, 0);
		if (err == ESRCH)
			*offset = limit;
		else if (err)
			return (err);

		ASSERT3U(*offset, <=, initial_offset);
		*offset = P2ALIGN(*offset, subchunk);
		delta = initial_offset - *offset;
		if (delta >= chunk_len) {
			*offset += delta - chunk_len;
			return (0);
		}
		chunk_len -= delta;

		/* skip over unallocated data */
		err = dnode_next_offset(dn,
		    DNODE_FIND_BACKWARDS, offset, 1, 1, 0);
		if (err == ESRCH)
			*offset = limit;
		else if (err)
			return (err);

		if (*offset < limit)
			*offset = limit;
		ASSERT3U(*offset, <, initial_offset);
	}
	return (0);
}

static int
dmu_free_long_range_impl(objset_t *os, dnode_t *dn, uint64_t offset,
    uint64_t length, boolean_t free_dnode)
{
	dmu_tx_t *tx;
	uint64_t object_size, start, end, len;
	boolean_t trunc = (length == DMU_OBJECT_END);
	int align, err;

	align = 1 << dn->dn_datablkshift;
	ASSERT(align > 0);
	object_size = align == 1 ? dn->dn_datablksz :
	    (dn->dn_maxblkid + 1) << dn->dn_datablkshift;

	if (trunc || (end = offset + length) > object_size)
		end = object_size;
	if (end <= offset)
		return (0);
	length = end - offset;

	while (length) {
		start = end;
		err = get_next_chunk(dn, &start, offset);
		if (err)
			return (err);
		len = trunc ? DMU_OBJECT_END : end - start;

		tx = dmu_tx_create(os);
		dmu_tx_hold_free(tx, dn->dn_object, start, len);
		err = dmu_tx_assign(tx, TXG_WAIT);
		if (err) {
			dmu_tx_abort(tx);
			return (err);
		}

		dnode_free_range(dn, start, trunc ? -1 : len, tx);

		if (start == 0 && free_dnode) {
			ASSERT(trunc);
			dnode_free(dn, tx);
		}

		length -= end - start;

		dmu_tx_commit(tx);
		end = start;
	}
	return (0);
}

int
dmu_free_long_range(objset_t *os, uint64_t object,
    uint64_t offset, uint64_t length)
{
	dnode_t *dn;
	int err;

	err = dnode_hold(os->os, object, FTAG, &dn);
	if (err != 0)
		return (err);
	err = dmu_free_long_range_impl(os, dn, offset, length, FALSE);
	dnode_rele(dn, FTAG);
	return (err);
}

int
dmu_free_object(objset_t *os, uint64_t object)
{
	dnode_t *dn;
	dmu_tx_t *tx;
	int err;

	err = dnode_hold_impl(os->os, object, DNODE_MUST_BE_ALLOCATED,
	    FTAG, &dn);
	if (err != 0)
		return (err);
	if (dn->dn_nlevels == 1) {
		tx = dmu_tx_create(os);
		dmu_tx_hold_bonus(tx, object);
		dmu_tx_hold_free(tx, dn->dn_object, 0, DMU_OBJECT_END);
		err = dmu_tx_assign(tx, TXG_WAIT);
		if (err == 0) {
			dnode_free_range(dn, 0, DMU_OBJECT_END, tx);
			dnode_free(dn, tx);
			dmu_tx_commit(tx);
		} else {
			dmu_tx_abort(tx);
		}
	} else {
		err = dmu_free_long_range_impl(os, dn, 0, DMU_OBJECT_END, TRUE);
	}
	dnode_rele(dn, FTAG);
	return (err);
}

int
dmu_free_range(objset_t *os, uint64_t object, uint64_t offset,
    uint64_t size, dmu_tx_t *tx)
{
	dnode_t *dn;
	int err = dnode_hold(os->os, object, FTAG, &dn);
	if (err)
		return (err);
	ASSERT(offset < UINT64_MAX);
	ASSERT(size == -1ULL || size <= UINT64_MAX - offset);
	dnode_free_range(dn, offset, size, tx);
	dnode_rele(dn, FTAG);
	return (0);
}

int
dmu_read(objset_t *os, uint64_t object, uint64_t offset, uint64_t size,
    void *buf)
{
	dnode_t *dn;
	dmu_buf_t **dbp;
	int numbufs, i, err;

	err = dnode_hold(os->os, object, FTAG, &dn);
	if (err)
		return (err);

	/*
	 * Deal with odd block sizes, where there can't be data past the first
	 * block.  If we ever do the tail block optimization, we will need to
	 * handle that here as well.
	 */
	if (dn->dn_datablkshift == 0) {
		int newsz = offset > dn->dn_datablksz ? 0 :
		    MIN(size, dn->dn_datablksz - offset);
		bzero((char *)buf + newsz, size - newsz);
		size = newsz;
	}

	while (size > 0) {
		uint64_t mylen = MIN(size, DMU_MAX_ACCESS / 2);

		/*
		 * NB: we could do this block-at-a-time, but it's nice
		 * to be reading in parallel.
		 */
		err = dmu_buf_hold_array_by_dnode(dn, offset, mylen,
		    TRUE, FTAG, &numbufs, &dbp);
		if (err)
			break;

		for (i = 0; i < numbufs; i++) {
			int tocpy;
			int bufoff;
			dmu_buf_t *db = dbp[i];

			ASSERT(size > 0);

			bufoff = offset - db->db_offset;
			tocpy = (int)MIN(db->db_size - bufoff, size);

			bcopy((char *)db->db_data + bufoff, buf, tocpy);

			offset += tocpy;
			size -= tocpy;
			buf = (char *)buf + tocpy;
		}
		dmu_buf_rele_array(dbp, numbufs, FTAG);
	}
	dnode_rele(dn, FTAG);
	return (err);
}

void
dmu_write(objset_t *os, uint64_t object, uint64_t offset, uint64_t size,
    const void *buf, dmu_tx_t *tx)
{
	dmu_buf_t **dbp;
	int numbufs, i;

	if (size == 0)
		return;

	VERIFY(0 == dmu_buf_hold_array(os, object, offset, size,
	    FALSE, FTAG, &numbufs, &dbp));

	for (i = 0; i < numbufs; i++) {
		int tocpy;
		int bufoff;
		dmu_buf_t *db = dbp[i];

		ASSERT(size > 0);

		bufoff = offset - db->db_offset;
		tocpy = (int)MIN(db->db_size - bufoff, size);

		ASSERT(i == 0 || i == numbufs-1 || tocpy == db->db_size);

		if (tocpy == db->db_size)
			dmu_buf_will_fill(db, tx);
		else
			dmu_buf_will_dirty(db, tx);

		bcopy(buf, (char *)db->db_data + bufoff, tocpy);

		if (tocpy == db->db_size)
			dmu_buf_fill_done(db, tx);

		offset += tocpy;
		size -= tocpy;
		buf = (char *)buf + tocpy;
	}
	dmu_buf_rele_array(dbp, numbufs, FTAG);
}

#ifdef _KERNEL
int
dmu_read_uio(objset_t *os, uint64_t object, uio_t *uio, uint64_t size)
{
	dmu_buf_t **dbp;
	int numbufs, i, err;

	/*
	 * NB: we could do this block-at-a-time, but it's nice
	 * to be reading in parallel.
	 */
	err = dmu_buf_hold_array(os, object, uio->uio_loffset, size, TRUE, FTAG,
	    &numbufs, &dbp);
	if (err)
		return (err);

	for (i = 0; i < numbufs; i++) {
		int tocpy;
		int bufoff;
		dmu_buf_t *db = dbp[i];

		ASSERT(size > 0);

		bufoff = uio->uio_loffset - db->db_offset;
		tocpy = (int)MIN(db->db_size - bufoff, size);

		err = uiomove((char *)db->db_data + bufoff, tocpy,
		    UIO_READ, uio);
		if (err)
			break;

		size -= tocpy;
	}
	dmu_buf_rele_array(dbp, numbufs, FTAG);

	return (err);
}

int
dmu_write_uio(objset_t *os, uint64_t object, uio_t *uio, uint64_t size,
    dmu_tx_t *tx)
{
	dmu_buf_t **dbp;
	int numbufs, i;
	int err = 0;

	if (size == 0)
		return (0);

	err = dmu_buf_hold_array(os, object, uio->uio_loffset, size,
	    FALSE, FTAG, &numbufs, &dbp);
	if (err)
		return (err);

	for (i = 0; i < numbufs; i++) {
		int tocpy;
		int bufoff;
		dmu_buf_t *db = dbp[i];

		ASSERT(size > 0);

		bufoff = uio->uio_loffset - db->db_offset;
		tocpy = (int)MIN(db->db_size - bufoff, size);

		ASSERT(i == 0 || i == numbufs-1 || tocpy == db->db_size);

		if (tocpy == db->db_size)
			dmu_buf_will_fill(db, tx);
		else
			dmu_buf_will_dirty(db, tx);

		/*
		 * XXX uiomove could block forever (eg. nfs-backed
		 * pages).  There needs to be a uiolockdown() function
		 * to lock the pages in memory, so that uiomove won't
		 * block.
		 */
		err = uiomove((char *)db->db_data + bufoff, tocpy,
		    UIO_WRITE, uio);

		if (tocpy == db->db_size)
			dmu_buf_fill_done(db, tx);

		if (err)
			break;

		size -= tocpy;
	}
	dmu_buf_rele_array(dbp, numbufs, FTAG);
	return (err);
}

int
dmu_write_pages(objset_t *os, uint64_t object, uint64_t offset, uint64_t size,
    page_t *pp, dmu_tx_t *tx)
{
	dmu_buf_t **dbp;
	int numbufs, i;
	int err;

	if (size == 0)
		return (0);

	err = dmu_buf_hold_array(os, object, offset, size,
	    FALSE, FTAG, &numbufs, &dbp);
	if (err)
		return (err);

	for (i = 0; i < numbufs; i++) {
		int tocpy, copied, thiscpy;
		int bufoff;
		dmu_buf_t *db = dbp[i];
		caddr_t va;

		ASSERT(size > 0);
		ASSERT3U(db->db_size, >=, PAGESIZE);

		bufoff = offset - db->db_offset;
		tocpy = (int)MIN(db->db_size - bufoff, size);

		ASSERT(i == 0 || i == numbufs-1 || tocpy == db->db_size);

		if (tocpy == db->db_size)
			dmu_buf_will_fill(db, tx);
		else
			dmu_buf_will_dirty(db, tx);

		for (copied = 0; copied < tocpy; copied += PAGESIZE) {
			ASSERT3U(pp->p_offset, ==, db->db_offset + bufoff);
			thiscpy = MIN(PAGESIZE, tocpy - copied);
			va = zfs_map_page(pp, S_READ);
			bcopy(va, (char *)db->db_data + bufoff, thiscpy);
			zfs_unmap_page(pp, va);
			pp = pp->p_next;
			bufoff += PAGESIZE;
		}

		if (tocpy == db->db_size)
			dmu_buf_fill_done(db, tx);

		if (err)
			break;

		offset += tocpy;
		size -= tocpy;
	}
	dmu_buf_rele_array(dbp, numbufs, FTAG);
	return (err);
}
#endif

typedef struct {
	dbuf_dirty_record_t	*dr;
	dmu_sync_cb_t		*done;
	void			*arg;
} dmu_sync_arg_t;

/* ARGSUSED */
static void
dmu_sync_ready(zio_t *zio, arc_buf_t *buf, void *varg)
{
	blkptr_t *bp = zio->io_bp;

	if (!BP_IS_HOLE(bp)) {
		dmu_sync_arg_t *in = varg;
		dbuf_dirty_record_t *dr = in->dr;
		dmu_buf_impl_t *db = dr->dr_dbuf;
		ASSERT(BP_GET_TYPE(bp) == db->db_dnode->dn_type);
		ASSERT(BP_GET_LEVEL(bp) == 0);
		bp->blk_fill = 1;
	}
}

/* ARGSUSED */
static void
dmu_sync_done(zio_t *zio, arc_buf_t *buf, void *varg)
{
	dmu_sync_arg_t *in = varg;
	dbuf_dirty_record_t *dr = in->dr;
	dmu_buf_impl_t *db = dr->dr_dbuf;
	dmu_sync_cb_t *done = in->done;

	mutex_enter(&db->db_mtx);
	ASSERT(dr->dt.dl.dr_override_state == DR_IN_DMU_SYNC);
	dr->dt.dl.dr_overridden_by = *zio->io_bp; /* structure assignment */
	dr->dt.dl.dr_override_state = DR_OVERRIDDEN;
	cv_broadcast(&db->db_changed);
	mutex_exit(&db->db_mtx);

	if (done)
		done(&(db->db), in->arg);

	kmem_free(in, sizeof (dmu_sync_arg_t));
}

/*
 * Intent log support: sync the block associated with db to disk.
 * N.B. and XXX: the caller is responsible for making sure that the
 * data isn't changing while dmu_sync() is writing it.
 *
 * Return values:
 *
 *	EEXIST: this txg has already been synced, so there's nothing to to.
 *		The caller should not log the write.
 *
 *	ENOENT: the block was dbuf_free_range()'d, so there's nothing to do.
 *		The caller should not log the write.
 *
 *	EALREADY: this block is already in the process of being synced.
 *		The caller should track its progress (somehow).
 *
 *	EINPROGRESS: the IO has been initiated.
 *		The caller should log this blkptr in the callback.
 *
 *	0: completed.  Sets *bp to the blkptr just written.
 *		The caller should log this blkptr immediately.
 */
int
dmu_sync(zio_t *pio, dmu_buf_t *db_fake,
    blkptr_t *bp, uint64_t txg, dmu_sync_cb_t *done, void *arg)
{
	dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
	objset_impl_t *os = db->db_objset;
	dsl_pool_t *dp = os->os_dsl_dataset->ds_dir->dd_pool;
	tx_state_t *tx = &dp->dp_tx;
	dbuf_dirty_record_t *dr;
	dmu_sync_arg_t *in;
	zbookmark_t zb;
	writeprops_t wp = { 0 };
	zio_t *zio;
	int err;

	ASSERT(BP_IS_HOLE(bp));
	ASSERT(txg != 0);

	dprintf("dmu_sync txg=%llu, s,o,q %llu %llu %llu\n",
	    txg, tx->tx_synced_txg, tx->tx_open_txg, tx->tx_quiesced_txg);

	/*
	 * XXX - would be nice if we could do this without suspending...
	 */
	txg_suspend(dp);

	/*
	 * If this txg already synced, there's nothing to do.
	 */
	if (txg <= tx->tx_synced_txg) {
		txg_resume(dp);
		/*
		 * If we're running ziltest, we need the blkptr regardless.
		 */
		if (txg > spa_freeze_txg(dp->dp_spa)) {
			/* if db_blkptr == NULL, this was an empty write */
			if (db->db_blkptr)
				*bp = *db->db_blkptr; /* structure assignment */
			return (0);
		}
		return (EEXIST);
	}

	mutex_enter(&db->db_mtx);

	if (txg == tx->tx_syncing_txg) {
		while (db->db_data_pending) {
			/*
			 * IO is in-progress.  Wait for it to finish.
			 * XXX - would be nice to be able to somehow "attach"
			 * this zio to the parent zio passed in.
			 */
			cv_wait(&db->db_changed, &db->db_mtx);
			if (!db->db_data_pending &&
			    db->db_blkptr && BP_IS_HOLE(db->db_blkptr)) {
				/*
				 * IO was compressed away
				 */
				*bp = *db->db_blkptr; /* structure assignment */
				mutex_exit(&db->db_mtx);
				txg_resume(dp);
				return (0);
			}
			ASSERT(db->db_data_pending ||
			    (db->db_blkptr && db->db_blkptr->blk_birth == txg));
		}

		if (db->db_blkptr && db->db_blkptr->blk_birth == txg) {
			/*
			 * IO is already completed.
			 */
			*bp = *db->db_blkptr; /* structure assignment */
			mutex_exit(&db->db_mtx);
			txg_resume(dp);
			return (0);
		}
	}

	dr = db->db_last_dirty;
	while (dr && dr->dr_txg > txg)
		dr = dr->dr_next;
	if (dr == NULL || dr->dr_txg < txg) {
		/*
		 * This dbuf isn't dirty, must have been free_range'd.
		 * There's no need to log writes to freed blocks, so we're done.
		 */
		mutex_exit(&db->db_mtx);
		txg_resume(dp);
		return (ENOENT);
	}

	ASSERT(dr->dr_txg == txg);
	if (dr->dt.dl.dr_override_state == DR_IN_DMU_SYNC) {
		/*
		 * We have already issued a sync write for this buffer.
		 */
		mutex_exit(&db->db_mtx);
		txg_resume(dp);
		return (EALREADY);
	} else if (dr->dt.dl.dr_override_state == DR_OVERRIDDEN) {
		/*
		 * This buffer has already been synced.  It could not
		 * have been dirtied since, or we would have cleared the state.
		 */
		*bp = dr->dt.dl.dr_overridden_by; /* structure assignment */
		mutex_exit(&db->db_mtx);
		txg_resume(dp);
		return (0);
	}

	dr->dt.dl.dr_override_state = DR_IN_DMU_SYNC;
	in = kmem_alloc(sizeof (dmu_sync_arg_t), KM_SLEEP);
	in->dr = dr;
	in->done = done;
	in->arg = arg;
	mutex_exit(&db->db_mtx);
	txg_resume(dp);

	zb.zb_objset =