sys/vfs/hammer: Rename misleading macro hammer_is_zone2_mapped_index()

[dragonfly.git] / sys / vfs / hammer / hammer_blockmap.c

/*
 * Copyright (c) 2008 The DragonFly Project.  All rights reserved.
 *
 * This code is derived from software contributed to The DragonFly Project
 * by Matthew Dillon <dillon@backplane.com>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name of The DragonFly Project nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific, prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * HAMMER blockmap
 */
#include <vm/vm_page2.h>

#include "hammer.h"

static int hammer_res_rb_compare(hammer_reserve_t res1, hammer_reserve_t res2);
static void hammer_reserve_setdelay_offset(hammer_mount_t hmp,
                                    hammer_off_t base_offset, int zone,
                                    hammer_blockmap_layer2_t layer2);
static void hammer_reserve_setdelay(hammer_mount_t hmp, hammer_reserve_t resv);
static int update_bytes_free(hammer_reserve_t resv, int bytes);
static int hammer_check_volume(hammer_mount_t, hammer_off_t*);
static void hammer_skip_volume(hammer_off_t *offsetp);

/*
 * Reserved big-blocks red-black tree support
 */
RB_GENERATE2(hammer_res_rb_tree, hammer_reserve, rb_node,
             hammer_res_rb_compare, hammer_off_t, zone_offset);

static int
hammer_res_rb_compare(hammer_reserve_t res1, hammer_reserve_t res2)
{
        if (res1->zone_offset < res2->zone_offset)
                return(-1);
        if (res1->zone_offset > res2->zone_offset)
                return(1);
        return(0);
}

/*
 * Allocate bytes from a zone
 */
hammer_off_t
hammer_blockmap_alloc(hammer_transaction_t trans, int zone, int bytes,
                      hammer_off_t hint, int *errorp)
{
        hammer_mount_t hmp;
        hammer_volume_t root_volume;
        hammer_blockmap_t blockmap;
        hammer_blockmap_t freemap;
        hammer_reserve_t resv;
        hammer_blockmap_layer1_t layer1;
        hammer_blockmap_layer2_t layer2;
        hammer_buffer_t buffer1 = NULL;
        hammer_buffer_t buffer2 = NULL;
        hammer_buffer_t buffer3 = NULL;
        hammer_off_t tmp_offset;
        hammer_off_t next_offset;
        hammer_off_t result_offset;
        hammer_off_t layer1_offset;
        hammer_off_t layer2_offset;
        hammer_off_t base_off;
        int loops = 0;
        int offset;             /* offset within big-block */
        int use_hint;

        hmp = trans->hmp;

        /*
         * Deal with alignment and buffer-boundary issues.
         *
         * Be careful, certain primary alignments are used below to allocate
         * new blockmap blocks.
         */
        bytes = HAMMER_DATA_DOALIGN(bytes);
        KKASSERT(bytes > 0 && bytes <= HAMMER_XBUFSIZE);
        KKASSERT(hammer_is_index_record(zone));

        /*
         * Setup
         */
        root_volume = trans->rootvol;
        *errorp = 0;
        blockmap = &hmp->blockmap[zone];
        freemap = &hmp->blockmap[HAMMER_ZONE_FREEMAP_INDEX];
        KKASSERT(HAMMER_ZONE_DECODE(blockmap->next_offset) == zone);

        /*
         * Use the hint if we have one.
         */
        if (hint && HAMMER_ZONE_DECODE(hint) == zone) {
                next_offset = HAMMER_DATA_DOALIGN_WITH(hammer_off_t, hint);
                use_hint = 1;
        } else {
                next_offset = blockmap->next_offset;
                use_hint = 0;
        }
again:

        /*
         * use_hint is turned off if we leave the hinted big-block.
         */
        if (use_hint && ((next_offset ^ hint) & ~HAMMER_HINTBLOCK_MASK64)) {
                next_offset = blockmap->next_offset;
                use_hint = 0;
        }

        /*
         * Check for wrap
         */
        if (next_offset == HAMMER_ZONE_ENCODE(zone + 1, 0)) {
                if (++loops == 2) {
                        hmkprintf(hmp, "No space left for zone %d "
                                "allocation\n", zone);
                        result_offset = 0;
                        *errorp = ENOSPC;
                        goto failed;
                }
                next_offset = HAMMER_ZONE_ENCODE(zone, 0);
        }

        /*
         * The allocation request may not cross a buffer boundary.  Special
         * large allocations must not cross a big-block boundary.
         */
        tmp_offset = next_offset + bytes - 1;
        if (bytes <= HAMMER_BUFSIZE) {
                if ((next_offset ^ tmp_offset) & ~HAMMER_BUFMASK64) {
                        next_offset = tmp_offset & ~HAMMER_BUFMASK64;
                        goto again;
                }
        } else {
                if ((next_offset ^ tmp_offset) & ~HAMMER_BIGBLOCK_MASK64) {
                        next_offset = tmp_offset & ~HAMMER_BIGBLOCK_MASK64;
                        goto again;
                }
        }
        offset = (int)next_offset & HAMMER_BIGBLOCK_MASK;

        /*
         * Dive layer 1.
         */
        layer1_offset = freemap->phys_offset +
                        HAMMER_BLOCKMAP_LAYER1_OFFSET(next_offset);

        layer1 = hammer_bread(hmp, layer1_offset, errorp, &buffer1);
        if (*errorp) {
                result_offset = 0;
                goto failed;
        }

        /*
         * Check CRC.
         */
        if (!hammer_crc_test_layer1(layer1)) {
                hammer_lock_ex(&hmp->blkmap_lock);
                if (!hammer_crc_test_layer1(layer1))
                        hpanic("CRC FAILED: LAYER1");
                hammer_unlock(&hmp->blkmap_lock);
        }

        /*
         * If we are at a big-block boundary and layer1 indicates no
         * free big-blocks, then we cannot allocate a new big-block in
         * layer2, skip to the next layer1 entry.
         */
        if (offset == 0 && layer1->blocks_free == 0) {
                next_offset = HAMMER_ZONE_LAYER1_NEXT_OFFSET(next_offset);
                if (hammer_check_volume(hmp, &next_offset)) {
                        result_offset = 0;
                        goto failed;
                }
                goto again;
        }
        KKASSERT(layer1->phys_offset != HAMMER_BLOCKMAP_UNAVAIL);

        /*
         * Skip the whole volume if it is pointing to a layer2 big-block
         * on a volume that we are currently trying to remove from the
         * file-system. This is used by the volume-del code together with
         * the reblocker to free up a volume.
         */
        if (HAMMER_VOL_DECODE(layer1->phys_offset) == hmp->volume_to_remove) {
                hammer_skip_volume(&next_offset);
                goto again;
        }

        /*
         * Dive layer 2, each entry represents a big-block.
         */
        layer2_offset = layer1->phys_offset +
                        HAMMER_BLOCKMAP_LAYER2_OFFSET(next_offset);
        layer2 = hammer_bread(hmp, layer2_offset, errorp, &buffer2);
        if (*errorp) {
                result_offset = 0;
                goto failed;
        }

        /*
         * Check CRC.  This can race another thread holding the lock
         * and in the middle of modifying layer2.
         */
        if (!hammer_crc_test_layer2(layer2)) {
                hammer_lock_ex(&hmp->blkmap_lock);
                if (!hammer_crc_test_layer2(layer2))
                        hpanic("CRC FAILED: LAYER2");
                hammer_unlock(&hmp->blkmap_lock);
        }

        /*
         * Skip the layer if the zone is owned by someone other then us.
         */
        if (layer2->zone && layer2->zone != zone) {
                next_offset += (HAMMER_BIGBLOCK_SIZE - offset);
                goto again;
        }
        if (offset < layer2->append_off) {
                next_offset += layer2->append_off - offset;
                goto again;
        }

#if 0
        /*
         * If operating in the current non-hint blockmap block, do not
         * allow it to get over-full.  Also drop any active hinting so
         * blockmap->next_offset is updated at the end.
         *
         * We do this for B-Tree and meta-data allocations to provide
         * localization for updates.
         */
        if ((zone == HAMMER_ZONE_BTREE_INDEX ||
             zone == HAMMER_ZONE_META_INDEX) &&
            offset >= HAMMER_BIGBLOCK_OVERFILL &&
            !((next_offset ^ blockmap->next_offset) & ~HAMMER_BIGBLOCK_MASK64)) {
                if (offset >= HAMMER_BIGBLOCK_OVERFILL) {
                        next_offset += (HAMMER_BIGBLOCK_SIZE - offset);
                        use_hint = 0;
                        goto again;
                }
        }
#endif

        /*
         * We need the lock from this point on.  We have to re-check zone
         * ownership after acquiring the lock and also check for reservations.
         */
        hammer_lock_ex(&hmp->blkmap_lock);

        if (layer2->zone && layer2->zone != zone) {
                hammer_unlock(&hmp->blkmap_lock);
                next_offset += (HAMMER_BIGBLOCK_SIZE - offset);
                goto again;
        }
        if (offset < layer2->append_off) {
                hammer_unlock(&hmp->blkmap_lock);
                next_offset += layer2->append_off - offset;
                goto again;
        }

        /*
         * The big-block might be reserved by another zone.  If it is reserved
         * by our zone we may have to move next_offset past the append_off.
         */
        base_off = hammer_xlate_to_zone2(next_offset & ~HAMMER_BIGBLOCK_MASK64);
        resv = RB_LOOKUP(hammer_res_rb_tree, &hmp->rb_resv_root, base_off);
        if (resv) {
                if (resv->zone != zone) {
                        hammer_unlock(&hmp->blkmap_lock);
                        next_offset = HAMMER_ZONE_LAYER2_NEXT_OFFSET(next_offset);
                        goto again;
                }
                if (offset < resv->append_off) {
                        hammer_unlock(&hmp->blkmap_lock);
                        next_offset += resv->append_off - offset;
                        goto again;
                }
                ++resv->refs;
        }

        /*
         * Ok, we can allocate out of this layer2 big-block.  Assume ownership
         * of the layer for real.  At this point we've validated any
         * reservation that might exist and can just ignore resv.
         */
        if (layer2->zone == 0) {
                /*
                 * Assign the big-block to our zone
                 */
                hammer_modify_buffer(trans, buffer1, layer1, sizeof(*layer1));
                --layer1->blocks_free;
                hammer_crc_set_layer1(layer1);
                hammer_modify_buffer_done(buffer1);
                hammer_modify_buffer(trans, buffer2, layer2, sizeof(*layer2));
                layer2->zone = zone;
                KKASSERT(layer2->bytes_free == HAMMER_BIGBLOCK_SIZE);
                KKASSERT(layer2->append_off == 0);
                hammer_modify_volume_field(trans, trans->rootvol,
                                           vol0_stat_freebigblocks);
                --root_volume->ondisk->vol0_stat_freebigblocks;
                hmp->copy_stat_freebigblocks =
                        root_volume->ondisk->vol0_stat_freebigblocks;
                hammer_modify_volume_done(trans->rootvol);
        } else {
                hammer_modify_buffer(trans, buffer2, layer2, sizeof(*layer2));
        }
        KKASSERT(layer2->zone == zone);

        /*
         * NOTE: bytes_free can legally go negative due to de-dup.
         */
        layer2->bytes_free -= bytes;
        KKASSERT(layer2->append_off <= offset);
        layer2->append_off = offset + bytes;
        hammer_crc_set_layer2(layer2);
        hammer_modify_buffer_done(buffer2);

        /*
         * We hold the blockmap lock and should be the only ones
         * capable of modifying resv->append_off.  Track the allocation
         * as appropriate.
         */
        KKASSERT(bytes != 0);
        if (resv) {
                KKASSERT(resv->append_off <= offset);
                resv->append_off = offset + bytes;
                resv->flags &= ~HAMMER_RESF_LAYER2FREE;
                hammer_blockmap_reserve_complete(hmp, resv);
        }

        /*
         * If we are allocating from the base of a new buffer we can avoid
         * a disk read by calling hammer_bnew_ext().
         */
        if ((next_offset & HAMMER_BUFMASK) == 0) {
                hammer_bnew_ext(trans->hmp, next_offset, bytes,
                                errorp, &buffer3);
                if (*errorp) {
                        result_offset = 0;
                        goto failed;
                }
        }
        result_offset = next_offset;

        /*
         * If we weren't supplied with a hint or could not use the hint
         * then we wound up using blockmap->next_offset as the hint and
         * need to save it.
         */
        if (use_hint == 0) {
                hammer_modify_volume_noundo(NULL, root_volume);
                blockmap->next_offset = next_offset + bytes;
                hammer_modify_volume_done(root_volume);
        }
        hammer_unlock(&hmp->blkmap_lock);
failed:

        /*
         * Cleanup
         */
        if (buffer1)
                hammer_rel_buffer(buffer1, 0);
        if (buffer2)
                hammer_rel_buffer(buffer2, 0);
        if (buffer3)
                hammer_rel_buffer(buffer3, 0);

        return(result_offset);
}

/*
 * Frontend function - Reserve bytes in a zone.
 *
 * This code reserves bytes out of a blockmap without committing to any
 * meta-data modifications, allowing the front-end to directly issue disk
 * write I/O for big-blocks of data
 *
 * The backend later finalizes the reservation with hammer_blockmap_finalize()
 * upon committing the related record.
 */
hammer_reserve_t
hammer_blockmap_reserve(hammer_mount_t hmp, int zone, int bytes,
                        hammer_off_t *zone_offp, int *errorp)
{
        hammer_volume_t root_volume;
        hammer_blockmap_t blockmap;
        hammer_blockmap_t freemap;
        hammer_blockmap_layer1_t layer1;
        hammer_blockmap_layer2_t layer2;
        hammer_buffer_t buffer1 = NULL;
        hammer_buffer_t buffer2 = NULL;
        hammer_buffer_t buffer3 = NULL;
        hammer_off_t tmp_offset;
        hammer_off_t next_offset;
        hammer_off_t layer1_offset;
        hammer_off_t layer2_offset;
        hammer_off_t base_off;
        hammer_reserve_t resv;
        hammer_reserve_t resx = NULL;
        int loops = 0;
        int offset;

        /*
         * Setup
         */
        KKASSERT(hammer_is_index_record(zone));
        root_volume = hammer_get_root_volume(hmp, errorp);
        if (*errorp)
                return(NULL);
        blockmap = &hmp->blockmap[zone];
        freemap = &hmp->blockmap[HAMMER_ZONE_FREEMAP_INDEX];
        KKASSERT(HAMMER_ZONE_DECODE(blockmap->next_offset) == zone);

        /*
         * Deal with alignment and buffer-boundary issues.
         *
         * Be careful, certain primary alignments are used below to allocate
         * new blockmap blocks.
         */
        bytes = HAMMER_DATA_DOALIGN(bytes);
        KKASSERT(bytes > 0 && bytes <= HAMMER_XBUFSIZE);

        next_offset = blockmap->next_offset;
again:
        resv = NULL;
        /*
         * Check for wrap
         */
        if (next_offset == HAMMER_ZONE_ENCODE(zone + 1, 0)) {
                if (++loops == 2) {
                        hmkprintf(hmp, "No space left for zone %d "
                                "reservation\n", zone);
                        *errorp = ENOSPC;
                        goto failed;
                }
                next_offset = HAMMER_ZONE_ENCODE(zone, 0);
        }

        /*
         * The allocation request may not cross a buffer boundary.  Special
         * large allocations must not cross a big-block boundary.
         */
        tmp_offset = next_offset + bytes - 1;
        if (bytes <= HAMMER_BUFSIZE) {
                if ((next_offset ^ tmp_offset) & ~HAMMER_BUFMASK64) {
                        next_offset = tmp_offset & ~HAMMER_BUFMASK64;
                        goto again;
                }
        } else {
                if ((next_offset ^ tmp_offset) & ~HAMMER_BIGBLOCK_MASK64) {
                        next_offset = tmp_offset & ~HAMMER_BIGBLOCK_MASK64;
                        goto again;
                }
        }
        offset = (int)next_offset & HAMMER_BIGBLOCK_MASK;

        /*
         * Dive layer 1.
         */
        layer1_offset = freemap->phys_offset +
                        HAMMER_BLOCKMAP_LAYER1_OFFSET(next_offset);
        layer1 = hammer_bread(hmp, layer1_offset, errorp, &buffer1);
        if (*errorp)
                goto failed;

        /*
         * Check CRC.
         */
        if (!hammer_crc_test_layer1(layer1)) {
                hammer_lock_ex(&hmp->blkmap_lock);
                if (!hammer_crc_test_layer1(layer1))
                        hpanic("CRC FAILED: LAYER1");
                hammer_unlock(&hmp->blkmap_lock);
        }

        /*
         * If we are at a big-block boundary and layer1 indicates no
         * free big-blocks, then we cannot allocate a new big-block in
         * layer2, skip to the next layer1 entry.
         */
        if ((next_offset & HAMMER_BIGBLOCK_MASK) == 0 &&
            layer1->blocks_free == 0) {
                next_offset = HAMMER_ZONE_LAYER1_NEXT_OFFSET(next_offset);
                if (hammer_check_volume(hmp, &next_offset))
                        goto failed;
                goto again;
        }
        KKASSERT(layer1->phys_offset != HAMMER_BLOCKMAP_UNAVAIL);

        /*
         * Dive layer 2, each entry represents a big-block.
         */
        layer2_offset = layer1->phys_offset +
                        HAMMER_BLOCKMAP_LAYER2_OFFSET(next_offset);
        layer2 = hammer_bread(hmp, layer2_offset, errorp, &buffer2);
        if (*errorp)
                goto failed;

        /*
         * Check CRC if not allocating into uninitialized space (which we
         * aren't when reserving space).
         */
        if (!hammer_crc_test_layer2(layer2)) {
                hammer_lock_ex(&hmp->blkmap_lock);
                if (!hammer_crc_test_layer2(layer2))
                        hpanic("CRC FAILED: LAYER2");
                hammer_unlock(&hmp->blkmap_lock);
        }

        /*
         * Skip the layer if the zone is owned by someone other then us.
         */
        if (layer2->zone && layer2->zone != zone) {
                next_offset += (HAMMER_BIGBLOCK_SIZE - offset);
                goto again;
        }
        if (offset < layer2->append_off) {
                next_offset += layer2->append_off - offset;
                goto again;
        }

        /*
         * We need the lock from this point on.  We have to re-check zone
         * ownership after acquiring the lock and also check for reservations.
         */
        hammer_lock_ex(&hmp->blkmap_lock);

        if (layer2->zone && layer2->zone != zone) {
                hammer_unlock(&hmp->blkmap_lock);
                next_offset += (HAMMER_BIGBLOCK_SIZE - offset);
                goto again;
        }
        if (offset < layer2->append_off) {
                hammer_unlock(&hmp->blkmap_lock);
                next_offset += layer2->append_off - offset;
                goto again;
        }

        /*
         * The big-block might be reserved by another zone.  If it is reserved
         * by our zone we may have to move next_offset past the append_off.
         */
        base_off = hammer_xlate_to_zone2(next_offset & ~HAMMER_BIGBLOCK_MASK64);
        resv = RB_LOOKUP(hammer_res_rb_tree, &hmp->rb_resv_root, base_off);
        if (resv) {
                if (resv->zone != zone) {
                        hammer_unlock(&hmp->blkmap_lock);
                        next_offset = HAMMER_ZONE_LAYER2_NEXT_OFFSET(next_offset);
                        goto again;
                }
                if (offset < resv->append_off) {
                        hammer_unlock(&hmp->blkmap_lock);
                        next_offset += resv->append_off - offset;
                        goto again;
                }
                ++resv->refs;
        } else {
                resx = kmalloc(sizeof(*resv), hmp->m_misc,
                               M_WAITOK | M_ZERO | M_USE_RESERVE);
                resx->refs = 1;
                resx->zone = zone;
                resx->zone_offset = base_off;
                if (layer2->bytes_free == HAMMER_BIGBLOCK_SIZE)
                        resx->flags |= HAMMER_RESF_LAYER2FREE;
                resv = RB_INSERT(hammer_res_rb_tree, &hmp->rb_resv_root, resx);
                KKASSERT(resv == NULL);
                resv = resx;
                ++hammer_count_reservations;
        }
        resv->append_off = offset + bytes;

        /*
         * If we are not reserving a whole buffer but are at the start of
         * a new block, call hammer_bnew() to avoid a disk read.
         *
         * If we are reserving a whole buffer (or more), the caller will
         * probably use a direct read, so do nothing.
         *
         * If we do not have a whole lot of system memory we really can't
         * afford to block while holding the blkmap_lock!
         */
        if (bytes < HAMMER_BUFSIZE && (next_offset & HAMMER_BUFMASK) == 0) {
                if (!vm_page_count_min(HAMMER_BUFSIZE / PAGE_SIZE)) {
                        hammer_bnew(hmp, next_offset, errorp, &buffer3);
                        if (*errorp)
                                goto failed;
                }
        }

        blockmap->next_offset = next_offset + bytes;
        hammer_unlock(&hmp->blkmap_lock);

failed:
        if (buffer1)
                hammer_rel_buffer(buffer1, 0);
        if (buffer2)
                hammer_rel_buffer(buffer2, 0);
        if (buffer3)
                hammer_rel_buffer(buffer3, 0);
        hammer_rel_volume(root_volume, 0);
        *zone_offp = next_offset;

        return(resv);
}

/*
 * Frontend function - Dedup bytes in a zone.
 *
 * Dedup reservations work exactly the same as normal write reservations
 * except we only adjust bytes_free field and don't touch append offset.
 * Finalization mechanic for dedup reservations is also the same as for
 * normal write ones - the backend finalizes the reservation with
 * hammer_blockmap_finalize().
 */
hammer_reserve_t
hammer_blockmap_reserve_dedup(hammer_mount_t hmp, int zone, int bytes,
                              hammer_off_t zone_offset, int *errorp)
{
        hammer_volume_t root_volume;
        hammer_blockmap_t freemap;
        hammer_blockmap_layer1_t layer1;
        hammer_blockmap_layer2_t layer2;
        hammer_buffer_t buffer1 = NULL;
        hammer_buffer_t buffer2 = NULL;
        hammer_off_t layer1_offset;
        hammer_off_t layer2_offset;
        hammer_off_t base_off;
        hammer_reserve_t resv = NULL;
        hammer_reserve_t resx = NULL;

        /*
         * Setup
         */
        KKASSERT(hammer_is_index_record(zone));
        root_volume = hammer_get_root_volume(hmp, errorp);
        if (*errorp)
                return (NULL);
        freemap = &hmp->blockmap[HAMMER_ZONE_FREEMAP_INDEX];
        KKASSERT(freemap->phys_offset != 0);

        bytes = HAMMER_DATA_DOALIGN(bytes);
        KKASSERT(bytes > 0 && bytes <= HAMMER_XBUFSIZE);

        /*
         * Dive layer 1.
         */
        layer1_offset = freemap->phys_offset +
                        HAMMER_BLOCKMAP_LAYER1_OFFSET(zone_offset);
        layer1 = hammer_bread(hmp, layer1_offset, errorp, &buffer1);
        if (*errorp)
                goto failed;

        /*
         * Check CRC.
         */
        if (!hammer_crc_test_layer1(layer1)) {
                hammer_lock_ex(&hmp->blkmap_lock);
                if (!hammer_crc_test_layer1(layer1))
                        hpanic("CRC FAILED: LAYER1");
                hammer_unlock(&hmp->blkmap_lock);
        }
        KKASSERT(layer1->phys_offset != HAMMER_BLOCKMAP_UNAVAIL);

        /*
         * Dive layer 2, each entry represents a big-block.
         */
        layer2_offset = layer1->phys_offset +
                        HAMMER_BLOCKMAP_LAYER2_OFFSET(zone_offset);
        layer2 = hammer_bread(hmp, layer2_offset, errorp, &buffer2);
        if (*errorp)
                goto failed;

        /*
         * Check CRC.
         */
        if (!hammer_crc_test_layer2(layer2)) {
                hammer_lock_ex(&hmp->blkmap_lock);
                if (!hammer_crc_test_layer2(layer2))
                        hpanic("CRC FAILED: LAYER2");
                hammer_unlock(&hmp->blkmap_lock);
        }

        /*
         * Fail if the zone is owned by someone other than us.
         */
        if (layer2->zone && layer2->zone != zone)
                goto failed;

        /*
         * We need the lock from this point on.  We have to re-check zone
         * ownership after acquiring the lock and also check for reservations.
         */
        hammer_lock_ex(&hmp->blkmap_lock);

        if (layer2->zone && layer2->zone != zone) {
                hammer_unlock(&hmp->blkmap_lock);
                goto failed;
        }

        base_off = hammer_xlate_to_zone2(zone_offset & ~HAMMER_BIGBLOCK_MASK64);
        resv = RB_LOOKUP(hammer_res_rb_tree, &hmp->rb_resv_root, base_off);
        if (resv) {
                if (resv->zone != zone) {
                        hammer_unlock(&hmp->blkmap_lock);
                        resv = NULL;
                        goto failed;
                }
                /*
                 * Due to possible big-block underflow we can't simply
                 * subtract bytes from bytes_free.
                 */
                if (update_bytes_free(resv, bytes) == 0) {
                        hammer_unlock(&hmp->blkmap_lock);
                        resv = NULL;
                        goto failed;
                }
                ++resv->refs;
        } else {
                resx = kmalloc(sizeof(*resv), hmp->m_misc,
                               M_WAITOK | M_ZERO | M_USE_RESERVE);
                resx->refs = 1;
                resx->zone = zone;
                resx->bytes_free = layer2->bytes_free;
                /*
                 * Due to possible big-block underflow we can't simply
                 * subtract bytes from bytes_free.
                 */
                if (update_bytes_free(resx, bytes) == 0) {
                        hammer_unlock(&hmp->blkmap_lock);
                        kfree(resx, hmp->m_misc);
                        goto failed;
                }
                resx->zone_offset = base_off;
                resv = RB_INSERT(hammer_res_rb_tree, &hmp->rb_resv_root, resx);
                KKASSERT(resv == NULL);
                resv = resx;
                ++hammer_count_reservations;
        }

        hammer_unlock(&hmp->blkmap_lock);

failed:
        if (buffer1)
                hammer_rel_buffer(buffer1, 0);
        if (buffer2)
                hammer_rel_buffer(buffer2, 0);
        hammer_rel_volume(root_volume, 0);

        return(resv);
}

static int
update_bytes_free(hammer_reserve_t resv, int bytes)
{
        int32_t temp;

        /*
         * Big-block underflow check
         */
        temp = resv->bytes_free - HAMMER_BIGBLOCK_SIZE * 2;
        cpu_ccfence(); /* XXX do we really need it ? */
        if (temp > resv->bytes_free) {
                hdkprintf("BIGBLOCK UNDERFLOW\n");
                return (0);
        }

        resv->bytes_free -= bytes;
        return (1);
}

/*
 * Dereference a reservation structure.  Upon the final release the
 * underlying big-block is checked and if it is entirely free we delete
 * any related HAMMER buffers to avoid potential conflicts with future
 * reuse of the big-block.
 */
void
hammer_blockmap_reserve_complete(hammer_mount_t hmp, hammer_reserve_t resv)
{
        hammer_off_t base_offset;
        int error;

        KKASSERT(resv->refs > 0);
        KKASSERT(hammer_is_zone_raw_buffer(resv->zone_offset));

        /*
         * Setting append_off to the max prevents any new allocations
         * from occuring while we are trying to dispose of the reservation,
         * allowing us to safely delete any related HAMMER buffers.
         *
         * If we are unable to clean out all related HAMMER buffers we
         * requeue the delay.
         */
        if (resv->refs == 1 && (resv->flags & HAMMER_RESF_LAYER2FREE)) {
                resv->append_off = HAMMER_BIGBLOCK_SIZE;
                base_offset = hammer_xlate_to_zoneX(resv->zone, resv->zone_offset);
                if (!TAILQ_EMPTY(&hmp->dedup_lru_list))
                        hammer_dedup_cache_inval(hmp, base_offset);
                error = hammer_del_buffers(hmp, base_offset,
                                           resv->zone_offset,
                                           HAMMER_BIGBLOCK_SIZE,
                                           1);
                if (hammer_debug_general & 0x20000) {
                        hkprintf("delbgblk %016jx error %d\n",
                                (intmax_t)base_offset, error);
                }
                if (error)
                        hammer_reserve_setdelay(hmp, resv);
        }
        if (--resv->refs == 0) {
                if (hammer_debug_general & 0x20000) {
                        hkprintf("delresvr %016jx zone %02x\n",
                                (intmax_t)resv->zone_offset, resv->zone);
                }
                KKASSERT((resv->flags & HAMMER_RESF_ONDELAY) == 0);
                RB_REMOVE(hammer_res_rb_tree, &hmp->rb_resv_root, resv);
                kfree(resv, hmp->m_misc);
                --hammer_count_reservations;
        }
}

/*
 * Prevent a potentially free big-block from being reused until after
 * the related flushes have completely cycled, otherwise crash recovery
 * could resurrect a data block that was already reused and overwritten.
 *
 * The caller might reset the underlying layer2 entry's append_off to 0, so
 * our covering append_off must be set to max to prevent any reallocation
 * until after the flush delays complete, not to mention proper invalidation
 * of any underlying cached blocks.
 */
static void
hammer_reserve_setdelay_offset(hammer_mount_t hmp, hammer_off_t base_offset,
                        int zone, hammer_blockmap_layer2_t layer2)
{
        hammer_reserve_t resv;

        /*
         * Allocate the reservation if necessary.
         *
         * NOTE: need lock in future around resv lookup/allocation and
         * the setdelay call, currently refs is not bumped until the call.
         */
again:
        resv = RB_LOOKUP(hammer_res_rb_tree, &hmp->rb_resv_root, base_offset);
        if (resv == NULL) {
                resv = kmalloc(sizeof(*resv), hmp->m_misc,
                               M_WAITOK | M_ZERO | M_USE_RESERVE);
                resv->zone = zone;
                resv->zone_offset = base_offset;
                resv->refs = 0;
                resv->append_off = HAMMER_BIGBLOCK_SIZE;

                if (layer2->bytes_free == HAMMER_BIGBLOCK_SIZE)
                        resv->flags |= HAMMER_RESF_LAYER2FREE;
                if (RB_INSERT(hammer_res_rb_tree, &hmp->rb_resv_root, resv)) {
                        kfree(resv, hmp->m_misc);
                        goto again;
                }
                ++hammer_count_reservations;
        } else {
                if (layer2->bytes_free == HAMMER_BIGBLOCK_SIZE)
                        resv->flags |= HAMMER_RESF_LAYER2FREE;
        }
        hammer_reserve_setdelay(hmp, resv);
}

/*
 * Enter the reservation on the on-delay list, or move it if it
 * is already on the list.
 */
static void
hammer_reserve_setdelay(hammer_mount_t hmp, hammer_reserve_t resv)
{
        if (resv->flags & HAMMER_RESF_ONDELAY) {
                TAILQ_REMOVE(&hmp->delay_list, resv, delay_entry);
                resv->flg_no = hmp->flusher.next + 1;
                TAILQ_INSERT_TAIL(&hmp->delay_list, resv, delay_entry);
        } else {
                ++resv->refs;
                ++hmp->rsv_fromdelay;
                resv->flags |= HAMMER_RESF_ONDELAY;
                resv->flg_no = hmp->flusher.next + 1;
                TAILQ_INSERT_TAIL(&hmp->delay_list, resv, delay_entry);
        }
}

/*
 * Reserve has reached its flush point, remove it from the delay list
 * and finish it off.  hammer_blockmap_reserve_complete() inherits
 * the ondelay reference.
 */
void
hammer_reserve_clrdelay(hammer_mount_t hmp, hammer_reserve_t resv)
{
        KKASSERT(resv->flags & HAMMER_RESF_ONDELAY);
        resv->flags &= ~HAMMER_RESF_ONDELAY;
        TAILQ_REMOVE(&hmp->delay_list, resv, delay_entry);
        --hmp->rsv_fromdelay;
        hammer_blockmap_reserve_complete(hmp, resv);
}

/*
 * Backend function - free (offset, bytes) in a zone.
 *
 * XXX error return
 */
void
hammer_blockmap_free(hammer_transaction_t trans,
                     hammer_off_t zone_offset, int bytes)
{
        hammer_mount_t hmp;
        hammer_volume_t root_volume;
        hammer_blockmap_t freemap;
        hammer_blockmap_layer1_t layer1;
        hammer_blockmap_layer2_t layer2;
        hammer_buffer_t buffer1 = NULL;
        hammer_buffer_t buffer2 = NULL;
        hammer_off_t layer1_offset;
        hammer_off_t layer2_offset;
        hammer_off_t base_off;
        int error;
        int zone;

        if (bytes == 0)
                return;
        hmp = trans->hmp;

        /*
         * Alignment
         */
        bytes = HAMMER_DATA_DOALIGN(bytes);
        KKASSERT(bytes <= HAMMER_XBUFSIZE);
        KKASSERT(((zone_offset ^ (zone_offset + (bytes - 1))) &
                  ~HAMMER_BIGBLOCK_MASK64) == 0);

        /*
         * Basic zone validation & locking
         */
        zone = HAMMER_ZONE_DECODE(zone_offset);
        KKASSERT(hammer_is_index_record(zone));
        root_volume = trans->rootvol;
        error = 0;

        freemap = &hmp->blockmap[HAMMER_ZONE_FREEMAP_INDEX];

        /*
         * Dive layer 1.
         */
        layer1_offset = freemap->phys_offset +
                        HAMMER_BLOCKMAP_LAYER1_OFFSET(zone_offset);
        layer1 = hammer_bread(hmp, layer1_offset, &error, &buffer1);
        if (error)
                goto failed;
        KKASSERT(layer1->phys_offset &&
                 layer1->phys_offset != HAMMER_BLOCKMAP_UNAVAIL);
        if (!hammer_crc_test_layer1(layer1)) {
                hammer_lock_ex(&hmp->blkmap_lock);
                if (!hammer_crc_test_layer1(layer1))
                        hpanic("CRC FAILED: LAYER1");
                hammer_unlock(&hmp->blkmap_lock);
        }

        /*
         * Dive layer 2, each entry represents a big-block.
         */
        layer2_offset = layer1->phys_offset +
                        HAMMER_BLOCKMAP_LAYER2_OFFSET(zone_offset);
        layer2 = hammer_bread(hmp, layer2_offset, &error, &buffer2);
        if (error)
                goto failed;
        if (!hammer_crc_test_layer2(layer2)) {
                hammer_lock_ex(&hmp->blkmap_lock);
                if (!hammer_crc_test_layer2(layer2))
                        hpanic("CRC FAILED: LAYER2");
                hammer_unlock(&hmp->blkmap_lock);
        }

        hammer_lock_ex(&hmp->blkmap_lock);

        hammer_modify_buffer(trans, buffer2, layer2, sizeof(*layer2));

        /*
         * Free space previously allocated via blockmap_alloc().
         *
         * NOTE: bytes_free can be and remain negative due to de-dup ops
         *       but can never become larger than HAMMER_BIGBLOCK_SIZE.
         */
        KKASSERT(layer2->zone == zone);
        layer2->bytes_free += bytes;
        KKASSERT(layer2->bytes_free <= HAMMER_BIGBLOCK_SIZE);

        /*
         * If a big-block becomes entirely free we must create a covering
         * reservation to prevent premature reuse.  Note, however, that
         * the big-block and/or reservation may still have an append_off
         * that allows further (non-reused) allocations.
         *
         * Once the reservation has been made we re-check layer2 and if
         * the big-block is still entirely free we reset the layer2 entry.
         * The reservation will prevent premature reuse.
         *
         * NOTE: hammer_buffer's are only invalidated when the reservation
         * is completed, if the layer2 entry is still completely free at
         * that time.  Any allocations from the reservation that may have
         * occured in the mean time, or active references on the reservation
         * from new pending allocations, will prevent the invalidation from
         * occuring.
         */
        if (layer2->bytes_free == HAMMER_BIGBLOCK_SIZE) {
                base_off = hammer_xlate_to_zone2(zone_offset &
                                                ~HAMMER_BIGBLOCK_MASK64);

                hammer_reserve_setdelay_offset(hmp, base_off, zone, layer2);
                if (layer2->bytes_free == HAMMER_BIGBLOCK_SIZE) {
                        layer2->zone = 0;
                        layer2->append_off = 0;
                        hammer_modify_buffer(trans, buffer1,
                                             layer1, sizeof(*layer1));
                        ++layer1->blocks_free;
                        hammer_crc_set_layer1(layer1);
                        hammer_modify_buffer_done(buffer1);
                        hammer_modify_volume_field(trans,
                                        trans->rootvol,
                                        vol0_stat_freebigblocks);
                        ++root_volume->ondisk->vol0_stat_freebigblocks;
                        hmp->copy_stat_freebigblocks =
                           root_volume->ondisk->vol0_stat_freebigblocks;
                        hammer_modify_volume_done(trans->rootvol);
                }
        }
        hammer_crc_set_layer2(layer2);
        hammer_modify_buffer_done(buffer2);
        hammer_unlock(&hmp->blkmap_lock);

failed:
        if (buffer1)
                hammer_rel_buffer(buffer1, 0);
        if (buffer2)
                hammer_rel_buffer(buffer2, 0);
}

int
hammer_blockmap_dedup(hammer_transaction_t trans,
                     hammer_off_t zone_offset, int bytes)
{
        hammer_mount_t hmp;
        hammer_blockmap_t freemap;
        hammer_blockmap_layer1_t layer1;
        hammer_blockmap_layer2_t layer2;
        hammer_buffer_t buffer1 = NULL;
        hammer_buffer_t buffer2 = NULL;
        hammer_off_t layer1_offset;
        hammer_off_t layer2_offset;
        int32_t temp;
        int error;
        int zone __debugvar;

        if (bytes == 0)
                return (0);
        hmp = trans->hmp;

        /*
         * Alignment
         */
        bytes = HAMMER_DATA_DOALIGN(bytes);
        KKASSERT(bytes <= HAMMER_BIGBLOCK_SIZE);
        KKASSERT(((zone_offset ^ (zone_offset + (bytes - 1))) &
                  ~HAMMER_BIGBLOCK_MASK64) == 0);

        /*
         * Basic zone validation & locking
         */
        zone = HAMMER_ZONE_DECODE(zone_offset);
        KKASSERT(hammer_is_index_record(zone));
        error = 0;

        freemap = &hmp->blockmap[HAMMER_ZONE_FREEMAP_INDEX];

        /*
         * Dive layer 1.
         */
        layer1_offset = freemap->phys_offset +
                        HAMMER_BLOCKMAP_LAYER1_OFFSET(zone_offset);
        layer1 = hammer_bread(hmp, layer1_offset, &error, &buffer1);
        if (error)
                goto failed;
        KKASSERT(layer1->phys_offset &&
                 layer1->phys_offset != HAMMER_BLOCKMAP_UNAVAIL);
        if (!hammer_crc_test_layer1(layer1)) {
                hammer_lock_ex(&hmp->blkmap_lock);
                if (!hammer_crc_test_layer1(layer1))
                        hpanic("CRC FAILED: LAYER1");
                hammer_unlock(&hmp->blkmap_lock);
        }

        /*
         * Dive layer 2, each entry represents a big-block.
         */
        layer2_offset = layer1->phys_offset +
                        HAMMER_BLOCKMAP_LAYER2_OFFSET(zone_offset);
        layer2 = hammer_bread(hmp, layer2_offset, &error, &buffer2);
        if (error)
                goto failed;
        if (!hammer_crc_test_layer2(layer2)) {
                hammer_lock_ex(&hmp->blkmap_lock);
                if (!hammer_crc_test_layer2(layer2))
                        hpanic("CRC FAILED: LAYER2");
                hammer_unlock(&hmp->blkmap_lock);
        }

        hammer_lock_ex(&hmp->blkmap_lock);

        hammer_modify_buffer(trans, buffer2, layer2, sizeof(*layer2));

        /*
         * Free space previously allocated via blockmap_alloc().
         *
         * NOTE: bytes_free can be and remain negative due to de-dup ops
         *       but can never become larger than HAMMER_BIGBLOCK_SIZE.
         */
        KKASSERT(layer2->zone == zone);
        temp = layer2->bytes_free - HAMMER_BIGBLOCK_SIZE * 2;
        cpu_ccfence(); /* prevent gcc from optimizing temp out */
        if (temp > layer2->bytes_free) {
                error = ERANGE;
                goto underflow;
        }
        layer2->bytes_free -= bytes;

        KKASSERT(layer2->bytes_free <= HAMMER_BIGBLOCK_SIZE);

        hammer_crc_set_layer2(layer2);
underflow:
        hammer_modify_buffer_done(buffer2);
        hammer_unlock(&hmp->blkmap_lock);

failed:
        if (buffer1)
                hammer_rel_buffer(buffer1, 0);
        if (buffer2)
                hammer_rel_buffer(buffer2, 0);
        return (error);
}

/*
 * Backend function - finalize (offset, bytes) in a zone.
 *
 * Allocate space that was previously reserved by the frontend.
 */
int
hammer_blockmap_finalize(hammer_transaction_t trans,
                         hammer_reserve_t resv,
                         hammer_off_t zone_offset, int bytes)
{
        hammer_mount_t hmp;
        hammer_volume_t root_volume;
        hammer_blockmap_t freemap;
        hammer_blockmap_layer1_t layer1;
        hammer_blockmap_layer2_t layer2;
        hammer_buffer_t buffer1 = NULL;
        hammer_buffer_t buffer2 = NULL;
        hammer_off_t layer1_offset;
        hammer_off_t layer2_offset;
        int error;
        int zone;
        int offset;

        if (bytes == 0)
                return(0);
        hmp = trans->hmp;

        /*
         * Alignment
         */
        bytes = HAMMER_DATA_DOALIGN(bytes);
        KKASSERT(bytes <= HAMMER_XBUFSIZE);

        /*
         * Basic zone validation & locking
         */
        zone = HAMMER_ZONE_DECODE(zone_offset);
        KKASSERT(hammer_is_index_record(zone));
        root_volume = trans->rootvol;
        error = 0;

        freemap = &hmp->blockmap[HAMMER_ZONE_FREEMAP_INDEX];

        /*
         * Dive layer 1.
         */
        layer1_offset = freemap->phys_offset +
                        HAMMER_BLOCKMAP_LAYER1_OFFSET(zone_offset);
        layer1 = hammer_bread(hmp, layer1_offset, &error, &buffer1);
        if (error)
                goto failed;
        KKASSERT(layer1->phys_offset &&
                 layer1->phys_offset != HAMMER_BLOCKMAP_UNAVAIL);
        if (!hammer_crc_test_layer1(layer1)) {
                hammer_lock_ex(&hmp->blkmap_lock);
                if (!hammer_crc_test_layer1(layer1))
                        hpanic("CRC FAILED: LAYER1");
                hammer_unlock(&hmp->blkmap_lock);
        }

        /*
         * Dive layer 2, each entry represents a big-block.
         */
        layer2_offset = layer1->phys_offset +
                        HAMMER_BLOCKMAP_LAYER2_OFFSET(zone_offset);
        layer2 = hammer_bread(hmp, layer2_offset, &error, &buffer2);
        if (error)
                goto failed;
        if (!hammer_crc_test_layer2(layer2)) {
                hammer_lock_ex(&hmp->blkmap_lock);
                if (!hammer_crc_test_layer2(layer2))
                        hpanic("CRC FAILED: LAYER2");
                hammer_unlock(&hmp->blkmap_lock);
        }

        hammer_lock_ex(&hmp->blkmap_lock);

        hammer_modify_buffer(trans, buffer2, layer2, sizeof(*layer2));

        /*
         * Finalize some or all of the space covered by a current
         * reservation.  An allocation in the same layer may have
         * already assigned ownership.
         */
        if (layer2->zone == 0) {
                hammer_modify_buffer(trans, buffer1, layer1, sizeof(*layer1));
                --layer1->blocks_free;
                hammer_crc_set_layer1(layer1);
                hammer_modify_buffer_done(buffer1);
                layer2->zone = zone;
                KKASSERT(layer2->bytes_free == HAMMER_BIGBLOCK_SIZE);
                KKASSERT(layer2->append_off == 0);
                hammer_modify_volume_field(trans,
                                trans->rootvol,
                                vol0_stat_freebigblocks);
                --root_volume->ondisk->vol0_stat_freebigblocks;
                hmp->copy_stat_freebigblocks =
                   root_volume->ondisk->vol0_stat_freebigblocks;
                hammer_modify_volume_done(trans->rootvol);
        }
        if (layer2->zone != zone)
                hdkprintf("layer2 zone mismatch %d %d\n", layer2->zone, zone);
        KKASSERT(layer2->zone == zone);
        KKASSERT(bytes != 0);
        layer2->bytes_free -= bytes;

        if (resv) {
                resv->flags &= ~HAMMER_RESF_LAYER2FREE;
        }

        /*
         * Finalizations can occur out of order, or combined with allocations.
         * append_off must be set to the highest allocated offset.
         */
        offset = ((int)zone_offset & HAMMER_BIGBLOCK_MASK) + bytes;
        if (layer2->append_off < offset)
                layer2->append_off = offset;

        hammer_crc_set_layer2(layer2);
        hammer_modify_buffer_done(buffer2);
        hammer_unlock(&hmp->blkmap_lock);

failed:
        if (buffer1)
                hammer_rel_buffer(buffer1, 0);
        if (buffer2)
                hammer_rel_buffer(buffer2, 0);
        return(error);
}

/*
 * Return the approximate number of free bytes in the big-block
 * containing the specified blockmap offset.
 *
 * WARNING: A negative number can be returned if data de-dup exists,
 *          and the result will also not represent he actual number
 *          of free bytes in this case.
 *
 *          This code is used only by the reblocker.
 */
int
hammer_blockmap_getfree(hammer_mount_t hmp, hammer_off_t zone_offset,
                        int *curp, int *errorp)
{
        hammer_volume_t root_volume;
        hammer_blockmap_t blockmap;
        hammer_blockmap_t freemap;
        hammer_blockmap_layer1_t layer1;
        hammer_blockmap_layer2_t layer2;
        hammer_buffer_t buffer = NULL;
        hammer_off_t layer1_offset;
        hammer_off_t layer2_offset;
        int32_t bytes;
        int zone;

        zone = HAMMER_ZONE_DECODE(zone_offset);
        KKASSERT(hammer_is_index_record(zone));
        root_volume = hammer_get_root_volume(hmp, errorp);
        if (*errorp) {
                *curp = 0;
                return(0);
        }
        blockmap = &hmp->blockmap[zone];
        freemap = &hmp->blockmap[HAMMER_ZONE_FREEMAP_INDEX];

        /*
         * Dive layer 1.
         */
        layer1_offset = freemap->phys_offset +
                        HAMMER_BLOCKMAP_LAYER1_OFFSET(zone_offset);
        layer1 = hammer_bread(hmp, layer1_offset, errorp, &buffer);
        if (*errorp) {
                *curp = 0;
                bytes = 0;
                goto failed;
        }
        KKASSERT(layer1->phys_offset);
        if (!hammer_crc_test_layer1(layer1)) {
                hammer_lock_ex(&hmp->blkmap_lock);
                if (!hammer_crc_test_layer1(layer1))
                        hpanic("CRC FAILED: LAYER1");
                hammer_unlock(&hmp->blkmap_lock);
        }

        /*
         * Dive layer 2, each entry represents a big-block.
         *
         * (reuse buffer, layer1 pointer becomes invalid)
         */
        layer2_offset = layer1->phys_offset +
                        HAMMER_BLOCKMAP_LAYER2_OFFSET(zone_offset);
        layer2 = hammer_bread(hmp, layer2_offset, errorp, &buffer);
        if (*errorp) {
                *curp = 0;
                bytes = 0;
                goto failed;
        }
        if (!hammer_crc_test_layer2(layer2)) {
                hammer_lock_ex(&hmp->blkmap_lock);
                if (!hammer_crc_test_layer2(layer2))
                        hpanic("CRC FAILED: LAYER2");
                hammer_unlock(&hmp->blkmap_lock);
        }
        KKASSERT(layer2->zone == zone);

        bytes = layer2->bytes_free;

        /*
         * *curp becomes 1 only when no error and,
         * next_offset and zone_offset are in the same big-block.
         */
        if ((blockmap->next_offset ^ zone_offset) & ~HAMMER_BIGBLOCK_MASK64)
                *curp = 0;  /* not same */
        else
                *curp = 1;
failed:
        if (buffer)
                hammer_rel_buffer(buffer, 0);
        hammer_rel_volume(root_volume, 0);
        if (hammer_debug_general & 0x4000) {
                hdkprintf("%016jx -> %d\n", (intmax_t)zone_offset, bytes);
        }
        return(bytes);
}


/*
 * Lookup a blockmap offset and verify blockmap layers.
 */
hammer_off_t
hammer_blockmap_lookup_verify(hammer_mount_t hmp, hammer_off_t zone_offset,
                        int *errorp)
{
        hammer_volume_t root_volume;
        hammer_blockmap_t freemap;
        hammer_blockmap_layer1_t layer1;
        hammer_blockmap_layer2_t layer2;
        hammer_buffer_t buffer = NULL;
        hammer_off_t layer1_offset;
        hammer_off_t layer2_offset;
        hammer_off_t result_offset;
        hammer_off_t base_off;
        hammer_reserve_t resv __debugvar;
        int zone;

        /*
         * Calculate the zone-2 offset.
         */
        zone = HAMMER_ZONE_DECODE(zone_offset);
        result_offset = hammer_xlate_to_zone2(zone_offset);

        /*
         * Validate the allocation zone
         */
        root_volume = hammer_get_root_volume(hmp, errorp);
        if (*errorp)
                return(0);
        freemap = &hmp->blockmap[HAMMER_ZONE_FREEMAP_INDEX];
        KKASSERT(freemap->phys_offset != 0);

        /*
         * Dive layer 1.
         */
        layer1_offset = freemap->phys_offset +
                        HAMMER_BLOCKMAP_LAYER1_OFFSET(zone_offset);
        layer1 = hammer_bread(hmp, layer1_offset, errorp, &buffer);
        if (*errorp)
                goto failed;
        KKASSERT(layer1->phys_offset != HAMMER_BLOCKMAP_UNAVAIL);
        if (!hammer_crc_test_layer1(layer1)) {
                hammer_lock_ex(&hmp->blkmap_lock);
                if (!hammer_crc_test_layer1(layer1))
                        hpanic("CRC FAILED: LAYER1");
                hammer_unlock(&hmp->blkmap_lock);
        }

        /*
         * Dive layer 2, each entry represents a big-block.
         */
        layer2_offset = layer1->phys_offset +
                        HAMMER_BLOCKMAP_LAYER2_OFFSET(zone_offset);
        layer2 = hammer_bread(hmp, layer2_offset, errorp, &buffer);

        if (*errorp)
                goto failed;
        if (layer2->zone == 0) {
                base_off = hammer_xlate_to_zone2(zone_offset &
                                                ~HAMMER_BIGBLOCK_MASK64);
                resv = RB_LOOKUP(hammer_res_rb_tree, &hmp->rb_resv_root,
                                 base_off);
                KKASSERT(resv && resv->zone == zone);

        } else if (layer2->zone != zone) {
                hpanic("bad zone %d/%d", layer2->zone, zone);
        }
        if (!hammer_crc_test_layer2(layer2)) {
                hammer_lock_ex(&hmp->blkmap_lock);
                if (!hammer_crc_test_layer2(layer2))
                        hpanic("CRC FAILED: LAYER2");
                hammer_unlock(&hmp->blkmap_lock);
        }

failed:
        if (buffer)
                hammer_rel_buffer(buffer, 0);
        hammer_rel_volume(root_volume, 0);
        if (hammer_debug_general & 0x0800) {
                hdkprintf("%016jx -> %016jx\n",
                        (intmax_t)zone_offset, (intmax_t)result_offset);
        }
        return(result_offset);
}


/*
 * Check space availability
 *
 * MPSAFE - does not require fs_token
 */
int
_hammer_checkspace(hammer_mount_t hmp, int slop, int64_t *resp)
{
        const int in_size = sizeof(struct hammer_inode_data) +
                            sizeof(union hammer_btree_elm);
        const int rec_size = (sizeof(union hammer_btree_elm) * 2);
        int64_t usedbytes;

        usedbytes = hmp->rsv_inodes * in_size +
                    hmp->rsv_recs * rec_size +
                    hmp->rsv_databytes +
                    ((int64_t)hmp->rsv_fromdelay << HAMMER_BIGBLOCK_BITS) +
                    ((int64_t)hammer_limit_dirtybufspace) +
                    (slop << HAMMER_BIGBLOCK_BITS);

        if (resp)
                *resp = usedbytes;

        if (hmp->copy_stat_freebigblocks >=
            (usedbytes >> HAMMER_BIGBLOCK_BITS)) {
                return(0);
        }

        return (ENOSPC);
}

static int
hammer_check_volume(hammer_mount_t hmp, hammer_off_t *offsetp)
{
        hammer_blockmap_t freemap;
        hammer_blockmap_layer1_t layer1;
        hammer_buffer_t buffer1 = NULL;
        hammer_off_t layer1_offset;
        int error = 0;

        freemap = &hmp->blockmap[HAMMER_ZONE_FREEMAP_INDEX];

        layer1_offset = freemap->phys_offset +
                        HAMMER_BLOCKMAP_LAYER1_OFFSET(*offsetp);
        layer1 = hammer_bread(hmp, layer1_offset, &error, &buffer1);
        if (error)
                goto end;

        /*
         * No more physically available space in layer1s
         * of the current volume, go to the next volume.
         */
        if (layer1->phys_offset == HAMMER_BLOCKMAP_UNAVAIL)
                hammer_skip_volume(offsetp);
end:
        if (buffer1)
                hammer_rel_buffer(buffer1, 0);
        return(error);
}

static void
hammer_skip_volume(hammer_off_t *offsetp)
{
        hammer_off_t offset;
        int zone, vol_no;

        offset = *offsetp;
        zone = HAMMER_ZONE_DECODE(offset);
        vol_no = HAMMER_VOL_DECODE(offset) + 1;
        KKASSERT(vol_no <= HAMMER_MAX_VOLUMES);

        if (vol_no == HAMMER_MAX_VOLUMES) {  /* wrap */
                vol_no = 0;
                ++zone;
        }

        *offsetp = HAMMER_ENCODE(zone, vol_no, 0);
}