xfs: replace xfs_btree_has_record with a general keyspace scanner

[thirdparty/xfsprogs-dev.git] / libxfs / xfs_rmap_btree.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (c) 2014 Red Hat, Inc.
 * All Rights Reserved.
 */
#include "libxfs_priv.h"
#include "xfs_fs.h"
#include "xfs_shared.h"
#include "xfs_format.h"
#include "xfs_log_format.h"
#include "xfs_trans_resv.h"
#include "xfs_mount.h"
#include "xfs_trans.h"
#include "xfs_alloc.h"
#include "xfs_btree.h"
#include "xfs_btree_staging.h"
#include "xfs_rmap.h"
#include "xfs_rmap_btree.h"
#include "xfs_trace.h"
#include "xfs_ag.h"
#include "xfs_ag_resv.h"

static struct kmem_cache        *xfs_rmapbt_cur_cache;

/*
 * Reverse map btree.
 *
 * This is a per-ag tree used to track the owner(s) of a given extent. With
 * reflink it is possible for there to be multiple owners, which is a departure
 * from classic XFS. Owner records for data extents are inserted when the
 * extent is mapped and removed when an extent is unmapped.  Owner records for
 * all other block types (i.e. metadata) are inserted when an extent is
 * allocated and removed when an extent is freed. There can only be one owner
 * of a metadata extent, usually an inode or some other metadata structure like
 * an AG btree.
 *
 * The rmap btree is part of the free space management, so blocks for the tree
 * are sourced from the agfl. Hence we need transaction reservation support for
 * this tree so that the freelist is always large enough. This also impacts on
 * the minimum space we need to leave free in the AG.
 *
 * The tree is ordered by [ag block, owner, offset]. This is a large key size,
 * but it is the only way to enforce unique keys when a block can be owned by
 * multiple files at any offset. There's no need to order/search by extent
 * size for online updating/management of the tree. It is intended that most
 * reverse lookups will be to find the owner(s) of a particular block, or to
 * try to recover tree and file data from corrupt primary metadata.
 */

static struct xfs_btree_cur *
xfs_rmapbt_dup_cursor(
        struct xfs_btree_cur    *cur)
{
        return xfs_rmapbt_init_cursor(cur->bc_mp, cur->bc_tp,
                                cur->bc_ag.agbp, cur->bc_ag.pag);
}

STATIC void
xfs_rmapbt_set_root(
        struct xfs_btree_cur            *cur,
        const union xfs_btree_ptr       *ptr,
        int                             inc)
{
        struct xfs_buf          *agbp = cur->bc_ag.agbp;
        struct xfs_agf          *agf = agbp->b_addr;
        int                     btnum = cur->bc_btnum;

        ASSERT(ptr->s != 0);

        agf->agf_roots[btnum] = ptr->s;
        be32_add_cpu(&agf->agf_levels[btnum], inc);
        cur->bc_ag.pag->pagf_levels[btnum] += inc;

        xfs_alloc_log_agf(cur->bc_tp, agbp, XFS_AGF_ROOTS | XFS_AGF_LEVELS);
}

STATIC int
xfs_rmapbt_alloc_block(
        struct xfs_btree_cur            *cur,
        const union xfs_btree_ptr       *start,
        union xfs_btree_ptr             *new,
        int                             *stat)
{
        struct xfs_buf          *agbp = cur->bc_ag.agbp;
        struct xfs_agf          *agf = agbp->b_addr;
        struct xfs_perag        *pag = cur->bc_ag.pag;
        int                     error;
        xfs_agblock_t           bno;

        /* Allocate the new block from the freelist. If we can't, give up.  */
        error = xfs_alloc_get_freelist(pag, cur->bc_tp, cur->bc_ag.agbp,
                                       &bno, 1);
        if (error)
                return error;

        trace_xfs_rmapbt_alloc_block(cur->bc_mp, pag->pag_agno, bno, 1);
        if (bno == NULLAGBLOCK) {
                *stat = 0;
                return 0;
        }

        xfs_extent_busy_reuse(cur->bc_mp, pag, bno, 1, false);

        new->s = cpu_to_be32(bno);
        be32_add_cpu(&agf->agf_rmap_blocks, 1);
        xfs_alloc_log_agf(cur->bc_tp, agbp, XFS_AGF_RMAP_BLOCKS);

        xfs_ag_resv_rmapbt_alloc(cur->bc_mp, pag->pag_agno);

        *stat = 1;
        return 0;
}

STATIC int
xfs_rmapbt_free_block(
        struct xfs_btree_cur    *cur,
        struct xfs_buf          *bp)
{
        struct xfs_buf          *agbp = cur->bc_ag.agbp;
        struct xfs_agf          *agf = agbp->b_addr;
        struct xfs_perag        *pag = cur->bc_ag.pag;
        xfs_agblock_t           bno;
        int                     error;

        bno = xfs_daddr_to_agbno(cur->bc_mp, xfs_buf_daddr(bp));
        trace_xfs_rmapbt_free_block(cur->bc_mp, pag->pag_agno,
                        bno, 1);
        be32_add_cpu(&agf->agf_rmap_blocks, -1);
        xfs_alloc_log_agf(cur->bc_tp, agbp, XFS_AGF_RMAP_BLOCKS);
        error = xfs_alloc_put_freelist(pag, cur->bc_tp, agbp, NULL, bno, 1);
        if (error)
                return error;

        xfs_extent_busy_insert(cur->bc_tp, pag, bno, 1,
                              XFS_EXTENT_BUSY_SKIP_DISCARD);

        xfs_ag_resv_free_extent(pag, XFS_AG_RESV_RMAPBT, NULL, 1);
        return 0;
}

STATIC int
xfs_rmapbt_get_minrecs(
        struct xfs_btree_cur    *cur,
        int                     level)
{
        return cur->bc_mp->m_rmap_mnr[level != 0];
}

STATIC int
xfs_rmapbt_get_maxrecs(
        struct xfs_btree_cur    *cur,
        int                     level)
{
        return cur->bc_mp->m_rmap_mxr[level != 0];
}

/*
 * Convert the ondisk record's offset field into the ondisk key's offset field.
 * Fork and bmbt are significant parts of the rmap record key, but written
 * status is merely a record attribute.
 */
static inline __be64 ondisk_rec_offset_to_key(const union xfs_btree_rec *rec)
{
        return rec->rmap.rm_offset & ~cpu_to_be64(XFS_RMAP_OFF_UNWRITTEN);
}

STATIC void
xfs_rmapbt_init_key_from_rec(
        union xfs_btree_key             *key,
        const union xfs_btree_rec       *rec)
{
        key->rmap.rm_startblock = rec->rmap.rm_startblock;
        key->rmap.rm_owner = rec->rmap.rm_owner;
        key->rmap.rm_offset = ondisk_rec_offset_to_key(rec);
}

/*
 * The high key for a reverse mapping record can be computed by shifting
 * the startblock and offset to the highest value that would still map
 * to that record.  In practice this means that we add blockcount-1 to
 * the startblock for all records, and if the record is for a data/attr
 * fork mapping, we add blockcount-1 to the offset too.
 */
STATIC void
xfs_rmapbt_init_high_key_from_rec(
        union xfs_btree_key             *key,
        const union xfs_btree_rec       *rec)
{
        uint64_t                        off;
        int                             adj;

        adj = be32_to_cpu(rec->rmap.rm_blockcount) - 1;

        key->rmap.rm_startblock = rec->rmap.rm_startblock;
        be32_add_cpu(&key->rmap.rm_startblock, adj);
        key->rmap.rm_owner = rec->rmap.rm_owner;
        key->rmap.rm_offset = ondisk_rec_offset_to_key(rec);
        if (XFS_RMAP_NON_INODE_OWNER(be64_to_cpu(rec->rmap.rm_owner)) ||
            XFS_RMAP_IS_BMBT_BLOCK(be64_to_cpu(rec->rmap.rm_offset)))
                return;
        off = be64_to_cpu(key->rmap.rm_offset);
        off = (XFS_RMAP_OFF(off) + adj) | (off & ~XFS_RMAP_OFF_MASK);
        key->rmap.rm_offset = cpu_to_be64(off);
}

STATIC void
xfs_rmapbt_init_rec_from_cur(
        struct xfs_btree_cur    *cur,
        union xfs_btree_rec     *rec)
{
        rec->rmap.rm_startblock = cpu_to_be32(cur->bc_rec.r.rm_startblock);
        rec->rmap.rm_blockcount = cpu_to_be32(cur->bc_rec.r.rm_blockcount);
        rec->rmap.rm_owner = cpu_to_be64(cur->bc_rec.r.rm_owner);
        rec->rmap.rm_offset = cpu_to_be64(
                        xfs_rmap_irec_offset_pack(&cur->bc_rec.r));
}

STATIC void
xfs_rmapbt_init_ptr_from_cur(
        struct xfs_btree_cur    *cur,
        union xfs_btree_ptr     *ptr)
{
        struct xfs_agf          *agf = cur->bc_ag.agbp->b_addr;

        ASSERT(cur->bc_ag.pag->pag_agno == be32_to_cpu(agf->agf_seqno));

        ptr->s = agf->agf_roots[cur->bc_btnum];
}

/*
 * Mask the appropriate parts of the ondisk key field for a key comparison.
 * Fork and bmbt are significant parts of the rmap record key, but written
 * status is merely a record attribute.
 */
static inline uint64_t offset_keymask(uint64_t offset)
{
        return offset & ~XFS_RMAP_OFF_UNWRITTEN;
}

STATIC int64_t
xfs_rmapbt_key_diff(
        struct xfs_btree_cur            *cur,
        const union xfs_btree_key       *key)
{
        struct xfs_rmap_irec            *rec = &cur->bc_rec.r;
        const struct xfs_rmap_key       *kp = &key->rmap;
        __u64                           x, y;
        int64_t                         d;

        d = (int64_t)be32_to_cpu(kp->rm_startblock) - rec->rm_startblock;
        if (d)
                return d;

        x = be64_to_cpu(kp->rm_owner);
        y = rec->rm_owner;
        if (x > y)
                return 1;
        else if (y > x)
                return -1;

        x = offset_keymask(be64_to_cpu(kp->rm_offset));
        y = offset_keymask(xfs_rmap_irec_offset_pack(rec));
        if (x > y)
                return 1;
        else if (y > x)
                return -1;
        return 0;
}

STATIC int64_t
xfs_rmapbt_diff_two_keys(
        struct xfs_btree_cur            *cur,
        const union xfs_btree_key       *k1,
        const union xfs_btree_key       *k2)
{
        const struct xfs_rmap_key       *kp1 = &k1->rmap;
        const struct xfs_rmap_key       *kp2 = &k2->rmap;
        int64_t                         d;
        __u64                           x, y;

        d = (int64_t)be32_to_cpu(kp1->rm_startblock) -
                       be32_to_cpu(kp2->rm_startblock);
        if (d)
                return d;

        x = be64_to_cpu(kp1->rm_owner);
        y = be64_to_cpu(kp2->rm_owner);
        if (x > y)
                return 1;
        else if (y > x)
                return -1;

        x = offset_keymask(be64_to_cpu(kp1->rm_offset));
        y = offset_keymask(be64_to_cpu(kp2->rm_offset));
        if (x > y)
                return 1;
        else if (y > x)
                return -1;
        return 0;
}

static xfs_failaddr_t
xfs_rmapbt_verify(
        struct xfs_buf          *bp)
{
        struct xfs_mount        *mp = bp->b_mount;
        struct xfs_btree_block  *block = XFS_BUF_TO_BLOCK(bp);
        struct xfs_perag        *pag = bp->b_pag;
        xfs_failaddr_t          fa;
        unsigned int            level;

        /*
         * magic number and level verification
         *
         * During growfs operations, we can't verify the exact level or owner as
         * the perag is not fully initialised and hence not attached to the
         * buffer.  In this case, check against the maximum tree depth.
         *
         * Similarly, during log recovery we will have a perag structure
         * attached, but the agf information will not yet have been initialised
         * from the on disk AGF. Again, we can only check against maximum limits
         * in this case.
         */
        if (!xfs_verify_magic(bp, block->bb_magic))
                return __this_address;

        if (!xfs_has_rmapbt(mp))
                return __this_address;
        fa = xfs_btree_sblock_v5hdr_verify(bp);
        if (fa)
                return fa;

        level = be16_to_cpu(block->bb_level);
        if (pag && xfs_perag_initialised_agf(pag)) {
                if (level >= pag->pagf_levels[XFS_BTNUM_RMAPi])
                        return __this_address;
        } else if (level >= mp->m_rmap_maxlevels)
                return __this_address;

        return xfs_btree_sblock_verify(bp, mp->m_rmap_mxr[level != 0]);
}

static void
xfs_rmapbt_read_verify(
        struct xfs_buf  *bp)
{
        xfs_failaddr_t  fa;

        if (!xfs_btree_sblock_verify_crc(bp))
                xfs_verifier_error(bp, -EFSBADCRC, __this_address);
        else {
                fa = xfs_rmapbt_verify(bp);
                if (fa)
                        xfs_verifier_error(bp, -EFSCORRUPTED, fa);
        }

        if (bp->b_error)
                trace_xfs_btree_corrupt(bp, _RET_IP_);
}

static void
xfs_rmapbt_write_verify(
        struct xfs_buf  *bp)
{
        xfs_failaddr_t  fa;

        fa = xfs_rmapbt_verify(bp);
        if (fa) {
                trace_xfs_btree_corrupt(bp, _RET_IP_);
                xfs_verifier_error(bp, -EFSCORRUPTED, fa);
                return;
        }
        xfs_btree_sblock_calc_crc(bp);

}

const struct xfs_buf_ops xfs_rmapbt_buf_ops = {
        .name                   = "xfs_rmapbt",
        .magic                  = { 0, cpu_to_be32(XFS_RMAP_CRC_MAGIC) },
        .verify_read            = xfs_rmapbt_read_verify,
        .verify_write           = xfs_rmapbt_write_verify,
        .verify_struct          = xfs_rmapbt_verify,
};

STATIC int
xfs_rmapbt_keys_inorder(
        struct xfs_btree_cur            *cur,
        const union xfs_btree_key       *k1,
        const union xfs_btree_key       *k2)
{
        uint32_t                x;
        uint32_t                y;
        uint64_t                a;
        uint64_t                b;

        x = be32_to_cpu(k1->rmap.rm_startblock);
        y = be32_to_cpu(k2->rmap.rm_startblock);
        if (x < y)
                return 1;
        else if (x > y)
                return 0;
        a = be64_to_cpu(k1->rmap.rm_owner);
        b = be64_to_cpu(k2->rmap.rm_owner);
        if (a < b)
                return 1;
        else if (a > b)
                return 0;
        a = offset_keymask(be64_to_cpu(k1->rmap.rm_offset));
        b = offset_keymask(be64_to_cpu(k2->rmap.rm_offset));
        if (a <= b)
                return 1;
        return 0;
}

STATIC int
xfs_rmapbt_recs_inorder(
        struct xfs_btree_cur            *cur,
        const union xfs_btree_rec       *r1,
        const union xfs_btree_rec       *r2)
{
        uint32_t                x;
        uint32_t                y;
        uint64_t                a;
        uint64_t                b;

        x = be32_to_cpu(r1->rmap.rm_startblock);
        y = be32_to_cpu(r2->rmap.rm_startblock);
        if (x < y)
                return 1;
        else if (x > y)
                return 0;
        a = be64_to_cpu(r1->rmap.rm_owner);
        b = be64_to_cpu(r2->rmap.rm_owner);
        if (a < b)
                return 1;
        else if (a > b)
                return 0;
        a = offset_keymask(be64_to_cpu(r1->rmap.rm_offset));
        b = offset_keymask(be64_to_cpu(r2->rmap.rm_offset));
        if (a <= b)
                return 1;
        return 0;
}

STATIC enum xbtree_key_contig
xfs_rmapbt_keys_contiguous(
        struct xfs_btree_cur            *cur,
        const union xfs_btree_key       *key1,
        const union xfs_btree_key       *key2)
{
        /*
         * We only support checking contiguity of the physical space component.
         * If any callers ever need more specificity than that, they'll have to
         * implement it here.
         */
        return xbtree_key_contig(be32_to_cpu(key1->rmap.rm_startblock),
                                 be32_to_cpu(key2->rmap.rm_startblock));
}

static const struct xfs_btree_ops xfs_rmapbt_ops = {
        .rec_len                = sizeof(struct xfs_rmap_rec),
        .key_len                = 2 * sizeof(struct xfs_rmap_key),

        .dup_cursor             = xfs_rmapbt_dup_cursor,
        .set_root               = xfs_rmapbt_set_root,
        .alloc_block            = xfs_rmapbt_alloc_block,
        .free_block             = xfs_rmapbt_free_block,
        .get_minrecs            = xfs_rmapbt_get_minrecs,
        .get_maxrecs            = xfs_rmapbt_get_maxrecs,
        .init_key_from_rec      = xfs_rmapbt_init_key_from_rec,
        .init_high_key_from_rec = xfs_rmapbt_init_high_key_from_rec,
        .init_rec_from_cur      = xfs_rmapbt_init_rec_from_cur,
        .init_ptr_from_cur      = xfs_rmapbt_init_ptr_from_cur,
        .key_diff               = xfs_rmapbt_key_diff,
        .buf_ops                = &xfs_rmapbt_buf_ops,
        .diff_two_keys          = xfs_rmapbt_diff_two_keys,
        .keys_inorder           = xfs_rmapbt_keys_inorder,
        .recs_inorder           = xfs_rmapbt_recs_inorder,
        .keys_contiguous        = xfs_rmapbt_keys_contiguous,
};

static struct xfs_btree_cur *
xfs_rmapbt_init_common(
        struct xfs_mount        *mp,
        struct xfs_trans        *tp,
        struct xfs_perag        *pag)
{
        struct xfs_btree_cur    *cur;

        /* Overlapping btree; 2 keys per pointer. */
        cur = xfs_btree_alloc_cursor(mp, tp, XFS_BTNUM_RMAP,
                        mp->m_rmap_maxlevels, xfs_rmapbt_cur_cache);
        cur->bc_flags = XFS_BTREE_CRC_BLOCKS | XFS_BTREE_OVERLAPPING;
        cur->bc_statoff = XFS_STATS_CALC_INDEX(xs_rmap_2);
        cur->bc_ops = &xfs_rmapbt_ops;

        cur->bc_ag.pag = xfs_perag_hold(pag);
        return cur;
}

/* Create a new reverse mapping btree cursor. */
struct xfs_btree_cur *
xfs_rmapbt_init_cursor(
        struct xfs_mount        *mp,
        struct xfs_trans        *tp,
        struct xfs_buf          *agbp,
        struct xfs_perag        *pag)
{
        struct xfs_agf          *agf = agbp->b_addr;
        struct xfs_btree_cur    *cur;

        cur = xfs_rmapbt_init_common(mp, tp, pag);
        cur->bc_nlevels = be32_to_cpu(agf->agf_levels[XFS_BTNUM_RMAP]);
        cur->bc_ag.agbp = agbp;
        return cur;
}

/* Create a new reverse mapping btree cursor with a fake root for staging. */
struct xfs_btree_cur *
xfs_rmapbt_stage_cursor(
        struct xfs_mount        *mp,
        struct xbtree_afakeroot *afake,
        struct xfs_perag        *pag)
{
        struct xfs_btree_cur    *cur;

        cur = xfs_rmapbt_init_common(mp, NULL, pag);
        xfs_btree_stage_afakeroot(cur, afake);
        return cur;
}

/*
 * Install a new reverse mapping btree root.  Caller is responsible for
 * invalidating and freeing the old btree blocks.
 */
void
xfs_rmapbt_commit_staged_btree(
        struct xfs_btree_cur    *cur,
        struct xfs_trans        *tp,
        struct xfs_buf          *agbp)
{
        struct xfs_agf          *agf = agbp->b_addr;
        struct xbtree_afakeroot *afake = cur->bc_ag.afake;

        ASSERT(cur->bc_flags & XFS_BTREE_STAGING);

        agf->agf_roots[cur->bc_btnum] = cpu_to_be32(afake->af_root);
        agf->agf_levels[cur->bc_btnum] = cpu_to_be32(afake->af_levels);
        agf->agf_rmap_blocks = cpu_to_be32(afake->af_blocks);
        xfs_alloc_log_agf(tp, agbp, XFS_AGF_ROOTS | XFS_AGF_LEVELS |
                                    XFS_AGF_RMAP_BLOCKS);
        xfs_btree_commit_afakeroot(cur, tp, agbp, &xfs_rmapbt_ops);
}

/* Calculate number of records in a reverse mapping btree block. */
static inline unsigned int
xfs_rmapbt_block_maxrecs(
        unsigned int            blocklen,
        bool                    leaf)
{
        if (leaf)
                return blocklen / sizeof(struct xfs_rmap_rec);
        return blocklen /
                (2 * sizeof(struct xfs_rmap_key) + sizeof(xfs_rmap_ptr_t));
}

/*
 * Calculate number of records in an rmap btree block.
 */
int
xfs_rmapbt_maxrecs(
        int                     blocklen,
        int                     leaf)
{
        blocklen -= XFS_RMAP_BLOCK_LEN;
        return xfs_rmapbt_block_maxrecs(blocklen, leaf);
}

/* Compute the max possible height for reverse mapping btrees. */
unsigned int
xfs_rmapbt_maxlevels_ondisk(void)
{
        unsigned int            minrecs[2];
        unsigned int            blocklen;

        blocklen = XFS_MIN_CRC_BLOCKSIZE - XFS_BTREE_SBLOCK_CRC_LEN;

        minrecs[0] = xfs_rmapbt_block_maxrecs(blocklen, true) / 2;
        minrecs[1] = xfs_rmapbt_block_maxrecs(blocklen, false) / 2;

        /*
         * Compute the asymptotic maxlevels for an rmapbt on any reflink fs.
         *
         * On a reflink filesystem, each AG block can have up to 2^32 (per the
         * refcount record format) owners, which means that theoretically we
         * could face up to 2^64 rmap records.  However, we're likely to run
         * out of blocks in the AG long before that happens, which means that
         * we must compute the max height based on what the btree will look
         * like if it consumes almost all the blocks in the AG due to maximal
         * sharing factor.
         */
        return xfs_btree_space_to_height(minrecs, XFS_MAX_CRC_AG_BLOCKS);
}

/* Compute the maximum height of an rmap btree. */
void
xfs_rmapbt_compute_maxlevels(
        struct xfs_mount                *mp)
{
        if (!xfs_has_rmapbt(mp)) {
                mp->m_rmap_maxlevels = 0;
                return;
        }

        if (xfs_has_reflink(mp)) {
                /*
                 * Compute the asymptotic maxlevels for an rmap btree on a
                 * filesystem that supports reflink.
                 *
                 * On a reflink filesystem, each AG block can have up to 2^32
                 * (per the refcount record format) owners, which means that
                 * theoretically we could face up to 2^64 rmap records.
                 * However, we're likely to run out of blocks in the AG long
                 * before that happens, which means that we must compute the
                 * max height based on what the btree will look like if it
                 * consumes almost all the blocks in the AG due to maximal
                 * sharing factor.
                 */
                mp->m_rmap_maxlevels = xfs_btree_space_to_height(mp->m_rmap_mnr,
                                mp->m_sb.sb_agblocks);
        } else {
                /*
                 * If there's no block sharing, compute the maximum rmapbt
                 * height assuming one rmap record per AG block.
                 */
                mp->m_rmap_maxlevels = xfs_btree_compute_maxlevels(
                                mp->m_rmap_mnr, mp->m_sb.sb_agblocks);
        }
        ASSERT(mp->m_rmap_maxlevels <= xfs_rmapbt_maxlevels_ondisk());
}

/* Calculate the refcount btree size for some records. */
xfs_extlen_t
xfs_rmapbt_calc_size(
        struct xfs_mount        *mp,
        unsigned long long      len)
{
        return xfs_btree_calc_size(mp->m_rmap_mnr, len);
}

/*
 * Calculate the maximum refcount btree size.
 */
xfs_extlen_t
xfs_rmapbt_max_size(
        struct xfs_mount        *mp,
        xfs_agblock_t           agblocks)
{
        /* Bail out if we're uninitialized, which can happen in mkfs. */
        if (mp->m_rmap_mxr[0] == 0)
                return 0;

        return xfs_rmapbt_calc_size(mp, agblocks);
}

/*
 * Figure out how many blocks to reserve and how many are used by this btree.
 */
int
xfs_rmapbt_calc_reserves(
        struct xfs_mount        *mp,
        struct xfs_trans        *tp,
        struct xfs_perag        *pag,
        xfs_extlen_t            *ask,
        xfs_extlen_t            *used)
{
        struct xfs_buf          *agbp;
        struct xfs_agf          *agf;
        xfs_agblock_t           agblocks;
        xfs_extlen_t            tree_len;
        int                     error;

        if (!xfs_has_rmapbt(mp))
                return 0;

        error = xfs_alloc_read_agf(pag, tp, 0, &agbp);
        if (error)
                return error;

        agf = agbp->b_addr;
        agblocks = be32_to_cpu(agf->agf_length);
        tree_len = be32_to_cpu(agf->agf_rmap_blocks);
        xfs_trans_brelse(tp, agbp);

        /*
         * The log is permanently allocated, so the space it occupies will
         * never be available for the kinds of things that would require btree
         * expansion.  We therefore can pretend the space isn't there.
         */
        if (xfs_ag_contains_log(mp, pag->pag_agno))
                agblocks -= mp->m_sb.sb_logblocks;

        /* Reserve 1% of the AG or enough for 1 block per record. */
        *ask += max(agblocks / 100, xfs_rmapbt_max_size(mp, agblocks));
        *used += tree_len;

        return error;
}

int __init
xfs_rmapbt_init_cur_cache(void)
{
        xfs_rmapbt_cur_cache = kmem_cache_create("xfs_rmapbt_cur",
                        xfs_btree_cur_sizeof(xfs_rmapbt_maxlevels_ondisk()),
                        0, 0, NULL);

        if (!xfs_rmapbt_cur_cache)
                return -ENOMEM;
        return 0;
}

void
xfs_rmapbt_destroy_cur_cache(void)
{
        kmem_cache_destroy(xfs_rmapbt_cur_cache);
        xfs_rmapbt_cur_cache = NULL;
}