Allow dsl_deadlist_open() return errors

[zfs.git] / module / zfs / bpobj.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 (c) 2011, 2018 by Delphix. All rights reserved.
 * Copyright (c) 2017 Datto Inc.
 */

#include <sys/bpobj.h>
#include <sys/zfs_context.h>
#include <sys/zfs_refcount.h>
#include <sys/dsl_pool.h>
#include <sys/zfeature.h>
#include <sys/zap.h>

/*
 * Return an empty bpobj, preferably the empty dummy one (dp_empty_bpobj).
 */
uint64_t
bpobj_alloc_empty(objset_t *os, int blocksize, dmu_tx_t *tx)
{
        spa_t *spa = dmu_objset_spa(os);
        dsl_pool_t *dp = dmu_objset_pool(os);

        if (spa_feature_is_enabled(spa, SPA_FEATURE_EMPTY_BPOBJ)) {
                if (!spa_feature_is_active(spa, SPA_FEATURE_EMPTY_BPOBJ)) {
                        ASSERT0(dp->dp_empty_bpobj);
                        dp->dp_empty_bpobj =
                            bpobj_alloc(os, SPA_OLD_MAXBLOCKSIZE, tx);
                        VERIFY(zap_add(os,
                            DMU_POOL_DIRECTORY_OBJECT,
                            DMU_POOL_EMPTY_BPOBJ, sizeof (uint64_t), 1,
                            &dp->dp_empty_bpobj, tx) == 0);
                }
                spa_feature_incr(spa, SPA_FEATURE_EMPTY_BPOBJ, tx);
                ASSERT(dp->dp_empty_bpobj != 0);
                return (dp->dp_empty_bpobj);
        } else {
                return (bpobj_alloc(os, blocksize, tx));
        }
}

void
bpobj_decr_empty(objset_t *os, dmu_tx_t *tx)
{
        dsl_pool_t *dp = dmu_objset_pool(os);

        spa_feature_decr(dmu_objset_spa(os), SPA_FEATURE_EMPTY_BPOBJ, tx);
        if (!spa_feature_is_active(dmu_objset_spa(os),
            SPA_FEATURE_EMPTY_BPOBJ)) {
                VERIFY3U(0, ==, zap_remove(dp->dp_meta_objset,
                    DMU_POOL_DIRECTORY_OBJECT,
                    DMU_POOL_EMPTY_BPOBJ, tx));
                VERIFY3U(0, ==, dmu_object_free(os, dp->dp_empty_bpobj, tx));
                dp->dp_empty_bpobj = 0;
        }
}

uint64_t
bpobj_alloc(objset_t *os, int blocksize, dmu_tx_t *tx)
{
        int size;

        if (spa_version(dmu_objset_spa(os)) < SPA_VERSION_BPOBJ_ACCOUNT)
                size = BPOBJ_SIZE_V0;
        else if (spa_version(dmu_objset_spa(os)) < SPA_VERSION_DEADLISTS)
                size = BPOBJ_SIZE_V1;
        else if (!spa_feature_is_active(dmu_objset_spa(os),
            SPA_FEATURE_LIVELIST))
                size = BPOBJ_SIZE_V2;
        else
                size = sizeof (bpobj_phys_t);

        return (dmu_object_alloc(os, DMU_OT_BPOBJ, blocksize,
            DMU_OT_BPOBJ_HDR, size, tx));
}

void
bpobj_free(objset_t *os, uint64_t obj, dmu_tx_t *tx)
{
        int64_t i;
        bpobj_t bpo;
        dmu_object_info_t doi;
        int epb;
        dmu_buf_t *dbuf = NULL;

        ASSERT(obj != dmu_objset_pool(os)->dp_empty_bpobj);
        VERIFY3U(0, ==, bpobj_open(&bpo, os, obj));

        mutex_enter(&bpo.bpo_lock);

        if (!bpo.bpo_havesubobj || bpo.bpo_phys->bpo_subobjs == 0)
                goto out;

        VERIFY3U(0, ==, dmu_object_info(os, bpo.bpo_phys->bpo_subobjs, &doi));
        epb = doi.doi_data_block_size / sizeof (uint64_t);

        for (i = bpo.bpo_phys->bpo_num_subobjs - 1; i >= 0; i--) {
                uint64_t *objarray;
                uint64_t offset, blkoff;

                offset = i * sizeof (uint64_t);
                blkoff = P2PHASE(i, epb);

                if (dbuf == NULL || dbuf->db_offset > offset) {
                        if (dbuf)
                                dmu_buf_rele(dbuf, FTAG);
                        VERIFY3U(0, ==, dmu_buf_hold(os,
                            bpo.bpo_phys->bpo_subobjs, offset, FTAG, &dbuf, 0));
                }

                ASSERT3U(offset, >=, dbuf->db_offset);
                ASSERT3U(offset, <, dbuf->db_offset + dbuf->db_size);

                objarray = dbuf->db_data;
                bpobj_free(os, objarray[blkoff], tx);
        }
        if (dbuf) {
                dmu_buf_rele(dbuf, FTAG);
                dbuf = NULL;
        }
        VERIFY3U(0, ==, dmu_object_free(os, bpo.bpo_phys->bpo_subobjs, tx));

out:
        mutex_exit(&bpo.bpo_lock);
        bpobj_close(&bpo);

        VERIFY3U(0, ==, dmu_object_free(os, obj, tx));
}

int
bpobj_open(bpobj_t *bpo, objset_t *os, uint64_t object)
{
        dmu_object_info_t doi;
        int err;

        err = dmu_object_info(os, object, &doi);
        if (err)
                return (err);

        memset(bpo, 0, sizeof (*bpo));
        mutex_init(&bpo->bpo_lock, NULL, MUTEX_DEFAULT, NULL);

        ASSERT(bpo->bpo_dbuf == NULL);
        ASSERT(bpo->bpo_phys == NULL);
        ASSERT(object != 0);
        ASSERT3U(doi.doi_type, ==, DMU_OT_BPOBJ);
        ASSERT3U(doi.doi_bonus_type, ==, DMU_OT_BPOBJ_HDR);

        err = dmu_bonus_hold(os, object, bpo, &bpo->bpo_dbuf);
        if (err)
                return (err);

        bpo->bpo_os = os;
        bpo->bpo_object = object;
        bpo->bpo_epb = doi.doi_data_block_size >> SPA_BLKPTRSHIFT;
        bpo->bpo_havecomp = (doi.doi_bonus_size > BPOBJ_SIZE_V0);
        bpo->bpo_havesubobj = (doi.doi_bonus_size > BPOBJ_SIZE_V1);
        bpo->bpo_havefreed = (doi.doi_bonus_size > BPOBJ_SIZE_V2);
        bpo->bpo_phys = bpo->bpo_dbuf->db_data;
        return (0);
}

boolean_t
bpobj_is_open(const bpobj_t *bpo)
{
        return (bpo->bpo_object != 0);
}

void
bpobj_close(bpobj_t *bpo)
{
        /* Lame workaround for closing a bpobj that was never opened. */
        if (bpo->bpo_object == 0)
                return;

        dmu_buf_rele(bpo->bpo_dbuf, bpo);
        if (bpo->bpo_cached_dbuf != NULL)
                dmu_buf_rele(bpo->bpo_cached_dbuf, bpo);
        bpo->bpo_dbuf = NULL;
        bpo->bpo_phys = NULL;
        bpo->bpo_cached_dbuf = NULL;
        bpo->bpo_object = 0;

        mutex_destroy(&bpo->bpo_lock);
}

static boolean_t
bpobj_is_empty_impl(bpobj_t *bpo)
{
        ASSERT(MUTEX_HELD(&bpo->bpo_lock));
        return (bpo->bpo_phys->bpo_num_blkptrs == 0 &&
            (!bpo->bpo_havesubobj || bpo->bpo_phys->bpo_num_subobjs == 0));
}

boolean_t
bpobj_is_empty(bpobj_t *bpo)
{
        mutex_enter(&bpo->bpo_lock);
        boolean_t is_empty = bpobj_is_empty_impl(bpo);
        mutex_exit(&bpo->bpo_lock);
        return (is_empty);
}

/*
 * A recursive iteration of the bpobjs would be nice here but we run the risk
 * of overflowing function stack space.  Instead, find each subobj and add it
 * to the head of our list so it can be scanned for subjobjs.  Like a
 * recursive implementation, the "deepest" subobjs will be freed first.
 * When a subobj is found to have no additional subojs, free it.
 */
typedef struct bpobj_info {
        bpobj_t *bpi_bpo;
        /*
         * This object is a subobj of bpi_parent,
         * at bpi_index in its subobj array.
         */
        struct bpobj_info *bpi_parent;
        uint64_t bpi_index;
        /* How many of our subobj's are left to process. */
        uint64_t bpi_unprocessed_subobjs;
        /* True after having visited this bpo's directly referenced BPs. */
        boolean_t bpi_visited;
        list_node_t bpi_node;
} bpobj_info_t;

static bpobj_info_t *
bpi_alloc(bpobj_t *bpo, bpobj_info_t *parent, uint64_t index)
{
        bpobj_info_t *bpi = kmem_zalloc(sizeof (bpobj_info_t), KM_SLEEP);
        bpi->bpi_bpo = bpo;
        bpi->bpi_parent = parent;
        bpi->bpi_index = index;
        if (bpo->bpo_havesubobj && bpo->bpo_phys->bpo_subobjs != 0) {
                bpi->bpi_unprocessed_subobjs = bpo->bpo_phys->bpo_num_subobjs;
        }
        return (bpi);
}

/*
 * Update bpobj and all of its parents with new space accounting.
 */
static void
propagate_space_reduction(bpobj_info_t *bpi, int64_t freed,
    int64_t comp_freed, int64_t uncomp_freed, dmu_tx_t *tx)
{

        for (; bpi != NULL; bpi = bpi->bpi_parent) {
                bpobj_t *p = bpi->bpi_bpo;
                ASSERT(dmu_buf_is_dirty(p->bpo_dbuf, tx));
                p->bpo_phys->bpo_bytes -= freed;
                ASSERT3S(p->bpo_phys->bpo_bytes, >=, 0);
                if (p->bpo_havecomp) {
                        p->bpo_phys->bpo_comp -= comp_freed;
                        p->bpo_phys->bpo_uncomp -= uncomp_freed;
                }
        }
}

static int
bpobj_iterate_blkptrs(bpobj_info_t *bpi, bpobj_itor_t func, void *arg,
    int64_t start, dmu_tx_t *tx, boolean_t free)
{
        int err = 0;
        int64_t freed = 0, comp_freed = 0, uncomp_freed = 0;
        dmu_buf_t *dbuf = NULL;
        bpobj_t *bpo = bpi->bpi_bpo;

        int64_t i = bpo->bpo_phys->bpo_num_blkptrs - 1;
        uint64_t pe = P2ALIGN_TYPED(i, bpo->bpo_epb, uint64_t) *
            sizeof (blkptr_t);
        uint64_t ps = start * sizeof (blkptr_t);
        uint64_t pb = MAX((pe > dmu_prefetch_max) ? pe - dmu_prefetch_max : 0,
            ps);
        if (pe > pb) {
                dmu_prefetch(bpo->bpo_os, bpo->bpo_object, 0, pb, pe - pb,
                    ZIO_PRIORITY_ASYNC_READ);
        }
        for (; i >= start; i--) {
                uint64_t offset = i * sizeof (blkptr_t);
                uint64_t blkoff = P2PHASE(i, bpo->bpo_epb);

                if (dbuf == NULL || dbuf->db_offset > offset) {
                        if (dbuf)
                                dmu_buf_rele(dbuf, FTAG);
                        err = dmu_buf_hold(bpo->bpo_os, bpo->bpo_object,
                            offset, FTAG, &dbuf, DMU_READ_NO_PREFETCH);
                        if (err)
                                break;
                        pe = pb;
                        pb = MAX((dbuf->db_offset > dmu_prefetch_max) ?
                            dbuf->db_offset - dmu_prefetch_max : 0, ps);
                        if (pe > pb) {
                                dmu_prefetch(bpo->bpo_os, bpo->bpo_object, 0,
                                    pb, pe - pb, ZIO_PRIORITY_ASYNC_READ);
                        }
                }

                ASSERT3U(offset, >=, dbuf->db_offset);
                ASSERT3U(offset, <, dbuf->db_offset + dbuf->db_size);

                blkptr_t *bparray = dbuf->db_data;
                blkptr_t *bp = &bparray[blkoff];

                boolean_t bp_freed = BP_GET_FREE(bp);
                err = func(arg, bp, bp_freed, tx);
                if (err)
                        break;

                if (free) {
                        int sign = bp_freed ? -1 : +1;
                        spa_t *spa = dmu_objset_spa(bpo->bpo_os);
                        freed += sign * bp_get_dsize_sync(spa, bp);
                        comp_freed += sign * BP_GET_PSIZE(bp);
                        uncomp_freed += sign * BP_GET_UCSIZE(bp);
                        ASSERT(dmu_buf_is_dirty(bpo->bpo_dbuf, tx));
                        bpo->bpo_phys->bpo_num_blkptrs--;
                        ASSERT3S(bpo->bpo_phys->bpo_num_blkptrs, >=, 0);
                        if (bp_freed) {
                                ASSERT(bpo->bpo_havefreed);
                                bpo->bpo_phys->bpo_num_freed--;
                                ASSERT3S(bpo->bpo_phys->bpo_num_freed, >=, 0);
                        }
                }
        }
        if (free) {
                propagate_space_reduction(bpi, freed, comp_freed,
                    uncomp_freed, tx);
                VERIFY0(dmu_free_range(bpo->bpo_os,
                    bpo->bpo_object,
                    bpo->bpo_phys->bpo_num_blkptrs * sizeof (blkptr_t),
                    DMU_OBJECT_END, tx));
        }
        if (dbuf) {
                dmu_buf_rele(dbuf, FTAG);
                dbuf = NULL;
        }
        return (err);
}

/*
 * Given an initial bpo, start by freeing the BPs that are directly referenced
 * by that bpo. If the bpo has subobjs, read in its last subobj and push the
 * subobj to our stack. By popping items off our stack, eventually we will
 * encounter a bpo that has no subobjs.  We can free its bpobj_info_t, and if
 * requested also free the now-empty bpo from disk and decrement
 * its parent's subobj count. We continue popping each subobj from our stack,
 * visiting its last subobj until they too have no more subobjs, and so on.
 */
static int
bpobj_iterate_impl(bpobj_t *initial_bpo, bpobj_itor_t func, void *arg,
    dmu_tx_t *tx, boolean_t free, uint64_t *bpobj_size)
{
        list_t stack;
        bpobj_info_t *bpi;
        int err = 0;

        /*
         * Create a "stack" for us to work with without worrying about
         * stack overflows. Initialize it with the initial_bpo.
         */
        list_create(&stack, sizeof (bpobj_info_t),
            offsetof(bpobj_info_t, bpi_node));
        mutex_enter(&initial_bpo->bpo_lock);

        if (bpobj_size != NULL)
                *bpobj_size = initial_bpo->bpo_phys->bpo_num_blkptrs;

        list_insert_head(&stack, bpi_alloc(initial_bpo, NULL, 0));

        while ((bpi = list_head(&stack)) != NULL) {
                bpobj_t *bpo = bpi->bpi_bpo;

                ASSERT3P(bpo, !=, NULL);
                ASSERT(MUTEX_HELD(&bpo->bpo_lock));
                ASSERT(bpobj_is_open(bpo));

                if (free)
                        dmu_buf_will_dirty(bpo->bpo_dbuf, tx);

                if (bpi->bpi_visited == B_FALSE) {
                        err = bpobj_iterate_blkptrs(bpi, func, arg, 0, tx,
                            free);
                        bpi->bpi_visited = B_TRUE;
                        if (err != 0)
                                break;
                }
                /*
                 * We've finished with this bpo's directly-referenced BP's and
                 * it has no more unprocessed subobjs. We can free its
                 * bpobj_info_t (unless it is the topmost, initial_bpo).
                 * If we are freeing from disk, we can also do that.
                 */
                if (bpi->bpi_unprocessed_subobjs == 0) {
                        /*
                         * If there are no entries, there should
                         * be no bytes.
                         */
                        if (bpobj_is_empty_impl(bpo)) {
                                ASSERT0(bpo->bpo_phys->bpo_bytes);
                                ASSERT0(bpo->bpo_phys->bpo_comp);
                                ASSERT0(bpo->bpo_phys->bpo_uncomp);
                        }

                        /* The initial_bpo has no parent and is not closed. */
                        if (bpi->bpi_parent != NULL) {
                                if (free) {
                                        bpobj_t *p = bpi->bpi_parent->bpi_bpo;

                                        ASSERT0(bpo->bpo_phys->bpo_num_blkptrs);
                                        ASSERT3U(p->bpo_phys->bpo_num_subobjs,
                                            >, 0);
                                        ASSERT3U(bpi->bpi_index, ==,
                                            p->bpo_phys->bpo_num_subobjs - 1);
                                        ASSERT(dmu_buf_is_dirty(bpo->bpo_dbuf,
                                            tx));

                                        p->bpo_phys->bpo_num_subobjs--;

                                        VERIFY0(dmu_free_range(p->bpo_os,
                                            p->bpo_phys->bpo_subobjs,
                                            bpi->bpi_index * sizeof (uint64_t),
                                            sizeof (uint64_t), tx));

                                        /* eliminate the empty subobj list */
                                        if (bpo->bpo_havesubobj &&
                                            bpo->bpo_phys->bpo_subobjs != 0) {
                                                ASSERT0(bpo->bpo_phys->
                                                    bpo_num_subobjs);
                                                err = dmu_object_free(
                                                    bpo->bpo_os,
                                                    bpo->bpo_phys->bpo_subobjs,
                                                    tx);
                                                if (err)
                                                        break;
                                                bpo->bpo_phys->bpo_subobjs = 0;
                                        }
                                        err = dmu_object_free(p->bpo_os,
                                            bpo->bpo_object, tx);
                                        if (err)
                                                break;
                                }

                                mutex_exit(&bpo->bpo_lock);
                                bpobj_close(bpo);
                                kmem_free(bpo, sizeof (bpobj_t));
                        } else {
                                mutex_exit(&bpo->bpo_lock);
                        }

                        /*
                         * Finished processing this bpo. Unlock, and free
                         * our "stack" info.
                         */
                        list_remove_head(&stack);
                        kmem_free(bpi, sizeof (bpobj_info_t));
                } else {
                        /*
                         * We have unprocessed subobjs. Process the next one.
                         */
                        ASSERT(bpo->bpo_havecomp);
                        ASSERT3P(bpobj_size, ==, NULL);

                        /* Add the last subobj to stack. */
                        int64_t i = bpi->bpi_unprocessed_subobjs - 1;
                        uint64_t offset = i * sizeof (uint64_t);

                        uint64_t subobj;
                        err = dmu_read(bpo->bpo_os, bpo->bpo_phys->bpo_subobjs,
                            offset, sizeof (uint64_t), &subobj,
                            DMU_READ_NO_PREFETCH);
                        if (err)
                                break;

                        bpobj_t *subbpo = kmem_alloc(sizeof (bpobj_t),
                            KM_SLEEP);
                        err = bpobj_open(subbpo, bpo->bpo_os, subobj);
                        if (err) {
                                kmem_free(subbpo, sizeof (bpobj_t));
                                break;
                        }

                        if (subbpo->bpo_havesubobj &&
                            subbpo->bpo_phys->bpo_subobjs != 0) {
                                dmu_prefetch(subbpo->bpo_os,
                                    subbpo->bpo_phys->bpo_subobjs, 0, 0, 0,
                                    ZIO_PRIORITY_ASYNC_READ);
                        }

                        list_insert_head(&stack, bpi_alloc(subbpo, bpi, i));
                        mutex_enter(&subbpo->bpo_lock);
                        bpi->bpi_unprocessed_subobjs--;
                }
        }
        /*
         * Cleanup anything left on the "stack" after we left the loop.
         * Every bpo on the stack is locked so we must remember to undo
         * that now (in LIFO order).
         */
        while ((bpi = list_remove_head(&stack)) != NULL) {
                bpobj_t *bpo = bpi->bpi_bpo;
                ASSERT(err != 0);
                ASSERT3P(bpo, !=, NULL);

                mutex_exit(&bpo->bpo_lock);

                /* do not free the initial_bpo */
                if (bpi->bpi_parent != NULL) {
                        bpobj_close(bpi->bpi_bpo);
                        kmem_free(bpi->bpi_bpo, sizeof (bpobj_t));
                }
                kmem_free(bpi, sizeof (bpobj_info_t));
        }

        list_destroy(&stack);

        return (err);
}

/*
 * Iterate and remove the entries.  If func returns nonzero, iteration
 * will stop and that entry will not be removed.
 */
int
bpobj_iterate(bpobj_t *bpo, bpobj_itor_t func, void *arg, dmu_tx_t *tx)
{
        return (bpobj_iterate_impl(bpo, func, arg, tx, B_TRUE, NULL));
}

/*
 * Iterate the entries.  If func returns nonzero, iteration will stop.
 *
 * If there are no subobjs:
 *
 * *bpobj_size can be used to return the number of block pointers in the
 * bpobj.  Note that this may be different from the number of block pointers
 * that are iterated over, if iteration is terminated early (e.g. by the func
 * returning nonzero).
 *
 * If there are concurrent (or subsequent) modifications to the bpobj then the
 * returned *bpobj_size can be passed as "start" to
 * livelist_bpobj_iterate_from_nofree() to iterate the newly added entries.
 */
int
bpobj_iterate_nofree(bpobj_t *bpo, bpobj_itor_t func, void *arg,
    uint64_t *bpobj_size)
{
        return (bpobj_iterate_impl(bpo, func, arg, NULL, B_FALSE, bpobj_size));
}

/*
 * Iterate over the blkptrs in the bpobj beginning at index start. If func
 * returns nonzero, iteration will stop. This is a livelist specific function
 * since it assumes that there are no subobjs present.
 */
int
livelist_bpobj_iterate_from_nofree(bpobj_t *bpo, bpobj_itor_t func, void *arg,
    int64_t start)
{
        if (bpo->bpo_havesubobj)
                VERIFY0(bpo->bpo_phys->bpo_subobjs);
        bpobj_info_t *bpi = bpi_alloc(bpo, NULL, 0);
        int err = bpobj_iterate_blkptrs(bpi, func, arg, start, NULL, B_FALSE);
        kmem_free(bpi, sizeof (bpobj_info_t));
        return (err);
}

/*
 * Logically add subobj's contents to the parent bpobj.
 *
 * In the most general case, this is accomplished in constant time by adding
 * a reference to subobj.  This case is used when enqueuing a large subobj:
 * +--------------+                        +--------------+
 * | bpobj        |----------------------->| subobj list  |
 * +----+----+----+----+----+              +-----+-----+--+--+
 * | bp | bp | bp | bp | bp |              | obj | obj | obj |
 * +----+----+----+----+----+              +-----+-----+-----+
 *
 * +--------------+                        +--------------+
 * | sub-bpobj    |----------------------> | subsubobj    |
 * +----+----+----+----+---------+----+    +-----+-----+--+--------+-----+
 * | bp | bp | bp | bp |   ...   | bp |    | obj | obj |    ...    | obj |
 * +----+----+----+----+---------+----+    +-----+-----+-----------+-----+
 *
 * Result: sub-bpobj added to parent's subobj list.
 * +--------------+                        +--------------+
 * | bpobj        |----------------------->| subobj list  |
 * +----+----+----+----+----+              +-----+-----+--+--+-----+
 * | bp | bp | bp | bp | bp |              | obj | obj | obj | OBJ |
 * +----+----+----+----+----+              +-----+-----+-----+--|--+
 *                                                              |
 *       /-----------------------------------------------------/
 *       v
 * +--------------+                        +--------------+
 * | sub-bpobj    |----------------------> | subsubobj    |
 * +----+----+----+----+---------+----+    +-----+-----+--+--------+-----+
 * | bp | bp | bp | bp |   ...   | bp |    | obj | obj |    ...    | obj |
 * +----+----+----+----+---------+----+    +-----+-----+-----------+-----+
 *
 *
 * In a common case, the subobj is small: its bp's and its list of subobj's
 * are each stored in a single block.  In this case we copy the subobj's
 * contents to the parent:
 * +--------------+                        +--------------+
 * | bpobj        |----------------------->| subobj list  |
 * +----+----+----+----+----+              +-----+-----+--+--+
 * | bp | bp | bp | bp | bp |              | obj | obj | obj |
 * +----+----+----+----+----+              +-----+-----+-----+
 *                          ^                                ^
 * +--------------+         |              +--------------+  |
 * | sub-bpobj    |---------^------------> | subsubobj    |  ^
 * +----+----+----+         |              +-----+-----+--+  |
 * | BP | BP |-->-->-->-->-/               | OBJ | OBJ |-->-/
 * +----+----+                             +-----+-----+
 *
 * Result: subobj destroyed, contents copied to parent:
 * +--------------+                        +--------------+
 * | bpobj        |----------------------->| subobj list  |
 * +----+----+----+----+----+----+----+    +-----+-----+--+--+-----+-----+
 * | bp | bp | bp | bp | bp | BP | BP |    | obj | obj | obj | OBJ | OBJ |
 * +----+----+----+----+----+----+----+    +-----+-----+-----+-----+-----+
 *
 *
 * If the subobj has many BP's but few subobj's, we can copy the sub-subobj's
 * but retain the sub-bpobj:
 * +--------------+                        +--------------+
 * | bpobj        |----------------------->| subobj list  |
 * +----+----+----+----+----+              +-----+-----+--+--+
 * | bp | bp | bp | bp | bp |              | obj | obj | obj |
 * +----+----+----+----+----+              +-----+-----+-----+
 *                                                           ^
 * +--------------+                        +--------------+  |
 * | sub-bpobj    |----------------------> | subsubobj    |  ^
 * +----+----+----+----+---------+----+    +-----+-----+--+  |
 * | bp | bp | bp | bp |   ...   | bp |    | OBJ | OBJ |-->-/
 * +----+----+----+----+---------+----+    +-----+-----+
 *
 * Result: sub-sub-bpobjs and subobj added to parent's subobj list.
 * +--------------+                     +--------------+
 * | bpobj        |-------------------->| subobj list  |
 * +----+----+----+----+----+           +-----+-----+--+--+-----+-----+------+
 * | bp | bp | bp | bp | bp |           | obj | obj | obj | OBJ | OBJ | OBJ* |
 * +----+----+----+----+----+           +-----+-----+-----+-----+-----+--|---+
 *                                                                       |
 *       /--------------------------------------------------------------/
 *       v
 * +--------------+
 * | sub-bpobj    |
 * +----+----+----+----+---------+----+
 * | bp | bp | bp | bp |   ...   | bp |
 * +----+----+----+----+---------+----+
 */
void
bpobj_enqueue_subobj(bpobj_t *bpo, uint64_t subobj, dmu_tx_t *tx)
{
        bpobj_t subbpo;
        uint64_t used, comp, uncomp, subsubobjs;
        boolean_t copy_subsub = B_TRUE;
        boolean_t copy_bps = B_TRUE;

        ASSERT(bpobj_is_open(bpo));
        ASSERT(subobj != 0);
        ASSERT(bpo->bpo_havesubobj);
        ASSERT(bpo->bpo_havecomp);
        ASSERT(bpo->bpo_object != dmu_objset_pool(bpo->bpo_os)->dp_empty_bpobj);

        if (subobj == dmu_objset_pool(bpo->bpo_os)->dp_empty_bpobj) {
                bpobj_decr_empty(bpo->bpo_os, tx);
                return;
        }

        VERIFY3U(0, ==, bpobj_open(&subbpo, bpo->bpo_os, subobj));
        if (bpobj_is_empty(&subbpo)) {
                /* No point in having an empty subobj. */
                bpobj_close(&subbpo);
                bpobj_free(bpo->bpo_os, subobj, tx);
                return;
        }
        VERIFY3U(0, ==, bpobj_space(&subbpo, &used, &comp, &uncomp));

        mutex_enter(&bpo->bpo_lock);
        dmu_buf_will_dirty(bpo->bpo_dbuf, tx);

        dmu_object_info_t doi;

        if (bpo->bpo_phys->bpo_subobjs != 0) {
                ASSERT0(dmu_object_info(bpo->bpo_os, bpo->bpo_phys->bpo_subobjs,
                    &doi));
                ASSERT3U(doi.doi_type, ==, DMU_OT_BPOBJ_SUBOBJ);
        }

        /*
         * If subobj has only one block of subobjs, then move subobj's
         * subobjs to bpo's subobj list directly.  This reduces recursion in
         * bpobj_iterate due to nested subobjs.
         */
        subsubobjs = subbpo.bpo_phys->bpo_subobjs;
        if (subsubobjs != 0) {
                VERIFY0(dmu_object_info(bpo->bpo_os, subsubobjs, &doi));
                if (doi.doi_max_offset > doi.doi_data_block_size) {
                        copy_subsub = B_FALSE;
                }
        }

        /*
         * If, in addition to having only one block of subobj's, subobj has
         * only one block of bp's, then move subobj's bp's to bpo's bp list
         * directly. This reduces recursion in bpobj_iterate due to nested
         * subobjs.
         */
        VERIFY3U(0, ==, dmu_object_info(bpo->bpo_os, subobj, &doi));
        if (doi.doi_max_offset > doi.doi_data_block_size || !copy_subsub) {
                copy_bps = B_FALSE;
        }

        if (copy_subsub && subsubobjs != 0) {
                dmu_buf_t *subdb;
                uint64_t numsubsub = subbpo.bpo_phys->bpo_num_subobjs;

                VERIFY0(dmu_buf_hold(bpo->bpo_os, subsubobjs,
                    0, FTAG, &subdb, 0));
                /*
                 * Make sure that we are not asking dmu_write()
                 * to write more data than we have in our buffer.
                 */
                VERIFY3U(subdb->db_size, >=,
                    numsubsub * sizeof (subobj));
                if (bpo->bpo_phys->bpo_subobjs == 0) {
                        bpo->bpo_phys->bpo_subobjs =
                            dmu_object_alloc(bpo->bpo_os,
                            DMU_OT_BPOBJ_SUBOBJ, SPA_OLD_MAXBLOCKSIZE,
                            DMU_OT_NONE, 0, tx);
                }
                dmu_write(bpo->bpo_os, bpo->bpo_phys->bpo_subobjs,
                    bpo->bpo_phys->bpo_num_subobjs * sizeof (subobj),
                    numsubsub * sizeof (subobj), subdb->db_data, tx);
                dmu_buf_rele(subdb, FTAG);
                bpo->bpo_phys->bpo_num_subobjs += numsubsub;

                dmu_buf_will_dirty(subbpo.bpo_dbuf, tx);
                subbpo.bpo_phys->bpo_subobjs = 0;
                VERIFY0(dmu_object_free(bpo->bpo_os, subsubobjs, tx));
        }

        if (copy_bps) {
                dmu_buf_t *bps;
                uint64_t numbps = subbpo.bpo_phys->bpo_num_blkptrs;

                ASSERT(copy_subsub);
                VERIFY0(dmu_buf_hold(bpo->bpo_os, subobj,
                    0, FTAG, &bps, 0));

                /*
                 * Make sure that we are not asking dmu_write()
                 * to write more data than we have in our buffer.
                 */
                VERIFY3U(bps->db_size, >=, numbps * sizeof (blkptr_t));
                dmu_write(bpo->bpo_os, bpo->bpo_object,
                    bpo->bpo_phys->bpo_num_blkptrs * sizeof (blkptr_t),
                    numbps * sizeof (blkptr_t),
                    bps->db_data, tx);
                dmu_buf_rele(bps, FTAG);
                bpo->bpo_phys->bpo_num_blkptrs += numbps;

                bpobj_close(&subbpo);
                VERIFY0(dmu_object_free(bpo->bpo_os, subobj, tx));
        } else {
                bpobj_close(&subbpo);
                if (bpo->bpo_phys->bpo_subobjs == 0) {
                        bpo->bpo_phys->bpo_subobjs =
                            dmu_object_alloc(bpo->bpo_os,
                            DMU_OT_BPOBJ_SUBOBJ, SPA_OLD_MAXBLOCKSIZE,
                            DMU_OT_NONE, 0, tx);
                }

                dmu_write(bpo->bpo_os, bpo->bpo_phys->bpo_subobjs,
                    bpo->bpo_phys->bpo_num_subobjs * sizeof (subobj),
                    sizeof (subobj), &subobj, tx);
                bpo->bpo_phys->bpo_num_subobjs++;
        }

        bpo->bpo_phys->bpo_bytes += used;
        bpo->bpo_phys->bpo_comp += comp;
        bpo->bpo_phys->bpo_uncomp += uncomp;
        mutex_exit(&bpo->bpo_lock);

}

/*
 * Prefetch metadata required for bpobj_enqueue_subobj().
 */
void
bpobj_prefetch_subobj(bpobj_t *bpo, uint64_t subobj)
{
        dmu_object_info_t doi;
        bpobj_t subbpo;
        uint64_t subsubobjs;
        boolean_t copy_subsub = B_TRUE;
        boolean_t copy_bps = B_TRUE;

        ASSERT(bpobj_is_open(bpo));
        ASSERT(subobj != 0);

        if (subobj == dmu_objset_pool(bpo->bpo_os)->dp_empty_bpobj)
                return;

        if (bpobj_open(&subbpo, bpo->bpo_os, subobj) != 0)
                return;
        if (bpobj_is_empty(&subbpo)) {
                bpobj_close(&subbpo);
                return;
        }
        subsubobjs = subbpo.bpo_phys->bpo_subobjs;
        bpobj_close(&subbpo);

        if (subsubobjs != 0) {
                if (dmu_object_info(bpo->bpo_os, subsubobjs, &doi) != 0)
                        return;
                if (doi.doi_max_offset > doi.doi_data_block_size)
                        copy_subsub = B_FALSE;
        }

        if (dmu_object_info(bpo->bpo_os, subobj, &doi) != 0)
                return;
        if (doi.doi_max_offset > doi.doi_data_block_size || !copy_subsub)
                copy_bps = B_FALSE;

        if (copy_subsub && subsubobjs != 0) {
                if (bpo->bpo_phys->bpo_subobjs) {
                        dmu_prefetch(bpo->bpo_os, bpo->bpo_phys->bpo_subobjs, 0,
                            bpo->bpo_phys->bpo_num_subobjs * sizeof (subobj), 1,
                            ZIO_PRIORITY_ASYNC_READ);
                }
                dmu_prefetch(bpo->bpo_os, subsubobjs, 0, 0, 1,
                    ZIO_PRIORITY_ASYNC_READ);
        }

        if (copy_bps) {
                dmu_prefetch(bpo->bpo_os, bpo->bpo_object, 0,
                    bpo->bpo_phys->bpo_num_blkptrs * sizeof (blkptr_t), 1,
                    ZIO_PRIORITY_ASYNC_READ);
                dmu_prefetch(bpo->bpo_os, subobj, 0, 0, 1,
                    ZIO_PRIORITY_ASYNC_READ);
        } else if (bpo->bpo_phys->bpo_subobjs) {
                dmu_prefetch(bpo->bpo_os, bpo->bpo_phys->bpo_subobjs, 0,
                    bpo->bpo_phys->bpo_num_subobjs * sizeof (subobj), 1,
                    ZIO_PRIORITY_ASYNC_READ);
        }
}

void
bpobj_enqueue(bpobj_t *bpo, const blkptr_t *bp, boolean_t bp_freed,
    dmu_tx_t *tx)
{
        blkptr_t stored_bp = *bp;
        uint64_t offset;
        int blkoff;
        blkptr_t *bparray;

        ASSERT(bpobj_is_open(bpo));
        ASSERT(!BP_IS_HOLE(bp));
        ASSERT(bpo->bpo_object != dmu_objset_pool(bpo->bpo_os)->dp_empty_bpobj);

        if (BP_IS_EMBEDDED(bp)) {
                /*
                 * The bpobj will compress better without the payload.
                 *
                 * Note that we store EMBEDDED bp's because they have an
                 * uncompressed size, which must be accounted for.  An
                 * alternative would be to add their size to bpo_uncomp
                 * without storing the bp, but that would create additional
                 * complications: bpo_uncomp would be inconsistent with the
                 * set of BP's stored, and bpobj_iterate() wouldn't visit
                 * all the space accounted for in the bpobj.
                 */
                memset(&stored_bp, 0, sizeof (stored_bp));
                stored_bp.blk_prop = bp->blk_prop;
                BP_SET_LOGICAL_BIRTH(&stored_bp, BP_GET_LOGICAL_BIRTH(bp));
        } else if (!BP_GET_DEDUP(bp)) {
                /* The bpobj will compress better without the checksum */
                memset(&stored_bp.blk_cksum, 0, sizeof (stored_bp.blk_cksum));
        }

        stored_bp.blk_fill = 0;
        BP_SET_FREE(&stored_bp, bp_freed);

        mutex_enter(&bpo->bpo_lock);

        offset = bpo->bpo_phys->bpo_num_blkptrs * sizeof (stored_bp);
        blkoff = P2PHASE(bpo->bpo_phys->bpo_num_blkptrs, bpo->bpo_epb);

        if (bpo->bpo_cached_dbuf == NULL ||
            offset < bpo->bpo_cached_dbuf->db_offset ||
            offset >= bpo->bpo_cached_dbuf->db_offset +
            bpo->bpo_cached_dbuf->db_size) {
                if (bpo->bpo_cached_dbuf)
                        dmu_buf_rele(bpo->bpo_cached_dbuf, bpo);
                VERIFY3U(0, ==, dmu_buf_hold(bpo->bpo_os, bpo->bpo_object,
                    offset, bpo, &bpo->bpo_cached_dbuf, 0));
                ASSERT3P(bpo->bpo_cached_dbuf, !=, NULL);
        }

        dmu_buf_will_dirty(bpo->bpo_cached_dbuf, tx);
        bparray = bpo->bpo_cached_dbuf->db_data;
        bparray[blkoff] = stored_bp;

        dmu_buf_will_dirty(bpo->bpo_dbuf, tx);
        bpo->bpo_phys->bpo_num_blkptrs++;
        int sign = bp_freed ? -1 : +1;
        bpo->bpo_phys->bpo_bytes += sign *
            bp_get_dsize_sync(dmu_objset_spa(bpo->bpo_os), bp);
        if (bpo->bpo_havecomp) {
                bpo->bpo_phys->bpo_comp += sign * BP_GET_PSIZE(bp);
                bpo->bpo_phys->bpo_uncomp += sign * BP_GET_UCSIZE(bp);
        }
        if (bp_freed) {
                ASSERT(bpo->bpo_havefreed);
                bpo->bpo_phys->bpo_num_freed++;
        }
        mutex_exit(&bpo->bpo_lock);
}

struct space_range_arg {
        spa_t *spa;
        uint64_t mintxg;
        uint64_t maxtxg;
        uint64_t used;
        uint64_t comp;
        uint64_t uncomp;
};

static int
space_range_cb(void *arg, const blkptr_t *bp, boolean_t bp_freed, dmu_tx_t *tx)
{
        (void) bp_freed, (void) tx;
        struct space_range_arg *sra = arg;

        if (BP_GET_LOGICAL_BIRTH(bp) > sra->mintxg &&
            BP_GET_LOGICAL_BIRTH(bp) <= sra->maxtxg) {
                if (dsl_pool_sync_context(spa_get_dsl(sra->spa)))
                        sra->used += bp_get_dsize_sync(sra->spa, bp);
                else
                        sra->used += bp_get_dsize(sra->spa, bp);
                sra->comp += BP_GET_PSIZE(bp);
                sra->uncomp += BP_GET_UCSIZE(bp);
        }
        return (0);
}

int
bpobj_space(bpobj_t *bpo, uint64_t *usedp, uint64_t *compp, uint64_t *uncompp)
{
        ASSERT(bpobj_is_open(bpo));
        mutex_enter(&bpo->bpo_lock);

        *usedp = bpo->bpo_phys->bpo_bytes;
        if (bpo->bpo_havecomp) {
                *compp = bpo->bpo_phys->bpo_comp;
                *uncompp = bpo->bpo_phys->bpo_uncomp;
                mutex_exit(&bpo->bpo_lock);
                return (0);
        } else {
                mutex_exit(&bpo->bpo_lock);
                return (bpobj_space_range(bpo, 0, UINT64_MAX,
                    usedp, compp, uncompp));
        }
}

/*
 * Return the amount of space in the bpobj which is:
 * mintxg < logical birth <= maxtxg
 */
int
bpobj_space_range(bpobj_t *bpo, uint64_t mintxg, uint64_t maxtxg,
    uint64_t *usedp, uint64_t *compp, uint64_t *uncompp)
{
        struct space_range_arg sra = { 0 };
        int err;

        ASSERT(bpobj_is_open(bpo));

        /*
         * As an optimization, if they want the whole txg range, just
         * get bpo_bytes rather than iterating over the bps.
         */
        if (mintxg < TXG_INITIAL && maxtxg == UINT64_MAX && bpo->bpo_havecomp)
                return (bpobj_space(bpo, usedp, compp, uncompp));

        sra.spa = dmu_objset_spa(bpo->bpo_os);
        sra.mintxg = mintxg;
        sra.maxtxg = maxtxg;

        err = bpobj_iterate_nofree(bpo, space_range_cb, &sra, NULL);
        *usedp = sra.used;
        *compp = sra.comp;
        *uncompp = sra.uncomp;
        return (err);
}

/*
 * A bpobj_itor_t to append blkptrs to a bplist. Note that while blkptrs in a
 * bpobj are designated as free or allocated that information is not preserved
 * in bplists.
 */
int
bplist_append_cb(void *arg, const blkptr_t *bp, boolean_t bp_freed,
    dmu_tx_t *tx)
{
        (void) bp_freed, (void) tx;
        bplist_t *bpl = arg;
        bplist_append(bpl, bp);
        return (0);
}