libxfs/xfs_rmap_btree.c

   1 /*
   2  * Copyright (c) 2014 Red Hat, Inc.
   3  * All Rights Reserved.
   4  *
   5  * This program is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU General Public License as
   7  * published by the Free Software Foundation.
   8  *
   9  * This program is distributed in the hope that it would be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write the Free Software Foundation,
  16  * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  17  */
  18 #include "libxfs_priv.h"
  19 #include "xfs_fs.h"
  20 #include "xfs_shared.h"
  21 #include "xfs_format.h"
  22 #include "xfs_log_format.h"
  23 #include "xfs_trans_resv.h"
  24 #include "xfs_bit.h"
  25 #include "xfs_sb.h"
  26 #include "xfs_mount.h"
  27 #include "xfs_defer.h"
  28 #include "xfs_inode.h"
  29 #include "xfs_trans.h"
  30 #include "xfs_alloc.h"
  31 #include "xfs_btree.h"
  32 #include "xfs_rmap.h"
  33 #include "xfs_rmap_btree.h"
  34 #include "xfs_trace.h"
  35 #include "xfs_cksum.h"
  36 #include "xfs_ag_resv.h"
  37
  38 /*
  39  * Reverse map btree.
  40  *
  41  * This is a per-ag tree used to track the owner(s) of a given extent. With
  42  * reflink it is possible for there to be multiple owners, which is a departure
  43  * from classic XFS. Owner records for data extents are inserted when the
  44  * extent is mapped and removed when an extent is unmapped.  Owner records for
  45  * all other block types (i.e. metadata) are inserted when an extent is
  46  * allocated and removed when an extent is freed. There can only be one owner
  47  * of a metadata extent, usually an inode or some other metadata structure like
  48  * an AG btree.
  49  *
  50  * The rmap btree is part of the free space management, so blocks for the tree
  51  * are sourced from the agfl. Hence we need transaction reservation support for
  52  * this tree so that the freelist is always large enough. This also impacts on
  53  * the minimum space we need to leave free in the AG.
  54  *
  55  * The tree is ordered by [ag block, owner, offset]. This is a large key size,
  56  * but it is the only way to enforce unique keys when a block can be owned by
  57  * multiple files at any offset. There's no need to order/search by extent
  58  * size for online updating/management of the tree. It is intended that most
  59  * reverse lookups will be to find the owner(s) of a particular block, or to
  60  * try to recover tree and file data from corrupt primary metadata.
  61  */
  62
  63 static struct xfs_btree_cur *
  64 xfs_rmapbt_dup_cursor(
  65         struct xfs_btree_cur    *cur)
  66 {
  67         return xfs_rmapbt_init_cursor(cur->bc_mp, cur->bc_tp,
  68                         cur->bc_private.a.agbp, cur->bc_private.a.agno);
  69 }
  70
  71 STATIC void
  72 xfs_rmapbt_set_root(
  73         struct xfs_btree_cur    *cur,
  74         union xfs_btree_ptr     *ptr,
  75         int                     inc)
  76 {
  77         struct xfs_buf          *agbp = cur->bc_private.a.agbp;
  78         struct xfs_agf          *agf = XFS_BUF_TO_AGF(agbp);
  79         xfs_agnumber_t          seqno = be32_to_cpu(agf->agf_seqno);
  80         int                     btnum = cur->bc_btnum;
  81         struct xfs_perag        *pag = xfs_perag_get(cur->bc_mp, seqno);
  82
  83         ASSERT(ptr->s != 0);
  84
  85         agf->agf_roots[btnum] = ptr->s;
  86         be32_add_cpu(&agf->agf_levels[btnum], inc);
  87         pag->pagf_levels[btnum] += inc;
  88         xfs_perag_put(pag);
  89
  90         xfs_alloc_log_agf(cur->bc_tp, agbp, XFS_AGF_ROOTS | XFS_AGF_LEVELS);
  91 }
  92
  93 STATIC int
  94 xfs_rmapbt_alloc_block(
  95         struct xfs_btree_cur    *cur,
  96         union xfs_btree_ptr     *start,
  97         union xfs_btree_ptr     *new,
  98         int                     *stat)
  99 {
 100         struct xfs_buf          *agbp = cur->bc_private.a.agbp;
 101         struct xfs_agf          *agf = XFS_BUF_TO_AGF(agbp);
 102         int                     error;
 103         xfs_agblock_t           bno;
 104
 105         XFS_BTREE_TRACE_CURSOR(cur, XBT_ENTRY);
 106
 107         /* Allocate the new block from the freelist. If we can't, give up.  */
 108         error = xfs_alloc_get_freelist(cur->bc_tp, cur->bc_private.a.agbp,
 109                                        &bno, 1);
 110         if (error) {
 111                 XFS_BTREE_TRACE_CURSOR(cur, XBT_ERROR);
 112                 return error;
 113         }
 114
 115         trace_xfs_rmapbt_alloc_block(cur->bc_mp, cur->bc_private.a.agno,
 116                         bno, 1);
 117         if (bno == NULLAGBLOCK) {
 118                 XFS_BTREE_TRACE_CURSOR(cur, XBT_EXIT);
 119                 *stat = 0;
 120                 return 0;
 121         }
 122
 123         xfs_extent_busy_reuse(cur->bc_mp, cur->bc_private.a.agno, bno, 1,
 124                         false);
 125
 126         xfs_trans_agbtree_delta(cur->bc_tp, 1);
 127         new->s = cpu_to_be32(bno);
 128         be32_add_cpu(&agf->agf_rmap_blocks, 1);
 129         xfs_alloc_log_agf(cur->bc_tp, agbp, XFS_AGF_RMAP_BLOCKS);
 130
 131         XFS_BTREE_TRACE_CURSOR(cur, XBT_EXIT);
 132         *stat = 1;
 133         return 0;
 134 }
 135
 136 STATIC int
 137 xfs_rmapbt_free_block(
 138         struct xfs_btree_cur    *cur,
 139         struct xfs_buf          *bp)
 140 {
 141         struct xfs_buf          *agbp = cur->bc_private.a.agbp;
 142         struct xfs_agf          *agf = XFS_BUF_TO_AGF(agbp);
 143         xfs_agblock_t           bno;
 144         int                     error;
 145
 146         bno = xfs_daddr_to_agbno(cur->bc_mp, XFS_BUF_ADDR(bp));
 147         trace_xfs_rmapbt_free_block(cur->bc_mp, cur->bc_private.a.agno,
 148                         bno, 1);
 149         be32_add_cpu(&agf->agf_rmap_blocks, -1);
 150         xfs_alloc_log_agf(cur->bc_tp, agbp, XFS_AGF_RMAP_BLOCKS);
 151         error = xfs_alloc_put_freelist(cur->bc_tp, agbp, NULL, bno, 1);
 152         if (error)
 153                 return error;
 154
 155         xfs_extent_busy_insert(cur->bc_tp, be32_to_cpu(agf->agf_seqno), bno, 1,
 156                               XFS_EXTENT_BUSY_SKIP_DISCARD);
 157         xfs_trans_agbtree_delta(cur->bc_tp, -1);
 158
 159         return 0;
 160 }
 161
 162 STATIC int
 163 xfs_rmapbt_get_minrecs(
 164         struct xfs_btree_cur    *cur,
 165         int                     level)
 166 {
 167         return cur->bc_mp->m_rmap_mnr[level != 0];
 168 }
 169
 170 STATIC int
 171 xfs_rmapbt_get_maxrecs(
 172         struct xfs_btree_cur    *cur,
 173         int                     level)
 174 {
 175         return cur->bc_mp->m_rmap_mxr[level != 0];
 176 }
 177
 178 STATIC void
 179 xfs_rmapbt_init_key_from_rec(
 180         union xfs_btree_key     *key,
 181         union xfs_btree_rec     *rec)
 182 {
 183         key->rmap.rm_startblock = rec->rmap.rm_startblock;
 184         key->rmap.rm_owner = rec->rmap.rm_owner;
 185         key->rmap.rm_offset = rec->rmap.rm_offset;
 186 }
 187
 188 /*
 189  * The high key for a reverse mapping record can be computed by shifting
 190  * the startblock and offset to the highest value that would still map
 191  * to that record.  In practice this means that we add blockcount-1 to
 192  * the startblock for all records, and if the record is for a data/attr
 193  * fork mapping, we add blockcount-1 to the offset too.
 194  */
 195 STATIC void
 196 xfs_rmapbt_init_high_key_from_rec(
 197         union xfs_btree_key     *key,
 198         union xfs_btree_rec     *rec)
 199 {
 200         uint64_t                off;
 201         int                     adj;
 202
 203         adj = be32_to_cpu(rec->rmap.rm_blockcount) - 1;
 204
 205         key->rmap.rm_startblock = rec->rmap.rm_startblock;
 206         be32_add_cpu(&key->rmap.rm_startblock, adj);
 207         key->rmap.rm_owner = rec->rmap.rm_owner;
 208         key->rmap.rm_offset = rec->rmap.rm_offset;
 209         if (XFS_RMAP_NON_INODE_OWNER(be64_to_cpu(rec->rmap.rm_owner)) ||
 210             XFS_RMAP_IS_BMBT_BLOCK(be64_to_cpu(rec->rmap.rm_offset)))
 211                 return;
 212         off = be64_to_cpu(key->rmap.rm_offset);
 213         off = (XFS_RMAP_OFF(off) + adj) | (off & ~XFS_RMAP_OFF_MASK);
 214         key->rmap.rm_offset = cpu_to_be64(off);
 215 }
 216
 217 STATIC void
 218 xfs_rmapbt_init_rec_from_cur(
 219         struct xfs_btree_cur    *cur,
 220         union xfs_btree_rec     *rec)
 221 {
 222         rec->rmap.rm_startblock = cpu_to_be32(cur->bc_rec.r.rm_startblock);
 223         rec->rmap.rm_blockcount = cpu_to_be32(cur->bc_rec.r.rm_blockcount);
 224         rec->rmap.rm_owner = cpu_to_be64(cur->bc_rec.r.rm_owner);
 225         rec->rmap.rm_offset = cpu_to_be64(
 226                         xfs_rmap_irec_offset_pack(&cur->bc_rec.r));
 227 }
 228
 229 STATIC void
 230 xfs_rmapbt_init_ptr_from_cur(
 231         struct xfs_btree_cur    *cur,
 232         union xfs_btree_ptr     *ptr)
 233 {
 234         struct xfs_agf          *agf = XFS_BUF_TO_AGF(cur->bc_private.a.agbp);
 235
 236         ASSERT(cur->bc_private.a.agno == be32_to_cpu(agf->agf_seqno));
 237         ASSERT(agf->agf_roots[cur->bc_btnum] != 0);
 238
 239         ptr->s = agf->agf_roots[cur->bc_btnum];
 240 }
 241
 242 STATIC int64_t
 243 xfs_rmapbt_key_diff(
 244         struct xfs_btree_cur    *cur,
 245         union xfs_btree_key     *key)
 246 {
 247         struct xfs_rmap_irec    *rec = &cur->bc_rec.r;
 248         struct xfs_rmap_key     *kp = &key->rmap;
 249         __u64                   x, y;
 250         int64_t                 d;
 251
 252         d = (int64_t)be32_to_cpu(kp->rm_startblock) - rec->rm_startblock;
 253         if (d)
 254                 return d;
 255
 256         x = be64_to_cpu(kp->rm_owner);
 257         y = rec->rm_owner;
 258         if (x > y)
 259                 return 1;
 260         else if (y > x)
 261                 return -1;
 262
 263         x = XFS_RMAP_OFF(be64_to_cpu(kp->rm_offset));
 264         y = rec->rm_offset;
 265         if (x > y)
 266                 return 1;
 267         else if (y > x)
 268                 return -1;
 269         return 0;
 270 }
 271
 272 STATIC int64_t
 273 xfs_rmapbt_diff_two_keys(
 274         struct xfs_btree_cur    *cur,
 275         union xfs_btree_key     *k1,
 276         union xfs_btree_key     *k2)
 277 {
 278         struct xfs_rmap_key     *kp1 = &k1->rmap;
 279         struct xfs_rmap_key     *kp2 = &k2->rmap;
 280         int64_t                 d;
 281         __u64                   x, y;
 282
 283         d = (int64_t)be32_to_cpu(kp1->rm_startblock) -
 284                        be32_to_cpu(kp2->rm_startblock);
 285         if (d)
 286                 return d;
 287
 288         x = be64_to_cpu(kp1->rm_owner);
 289         y = be64_to_cpu(kp2->rm_owner);
 290         if (x > y)
 291                 return 1;
 292         else if (y > x)
 293                 return -1;
 294
 295         x = XFS_RMAP_OFF(be64_to_cpu(kp1->rm_offset));
 296         y = XFS_RMAP_OFF(be64_to_cpu(kp2->rm_offset));
 297         if (x > y)
 298                 return 1;
 299         else if (y > x)
 300                 return -1;
 301         return 0;
 302 }
 303
 304 static bool
 305 xfs_rmapbt_verify(
 306         struct xfs_buf          *bp)
 307 {
 308         struct xfs_mount        *mp = bp->b_target->bt_mount;
 309         struct xfs_btree_block  *block = XFS_BUF_TO_BLOCK(bp);
 310         struct xfs_perag        *pag = bp->b_pag;
 311         unsigned int            level;
 312
 313         /*
 314          * magic number and level verification
 315          *
 316          * During growfs operations, we can't verify the exact level or owner as
 317          * the perag is not fully initialised and hence not attached to the
 318          * buffer.  In this case, check against the maximum tree depth.
 319          *
 320          * Similarly, during log recovery we will have a perag structure
 321          * attached, but the agf information will not yet have been initialised
 322          * from the on disk AGF. Again, we can only check against maximum limits
 323          * in this case.
 324          */
 325         if (block->bb_magic != cpu_to_be32(XFS_RMAP_CRC_MAGIC))
 326                 return false;
 327
 328         if (!xfs_sb_version_hasrmapbt(&mp->m_sb))
 329                 return false;
 330         if (!xfs_btree_sblock_v5hdr_verify(bp))
 331                 return false;
 332
 333         level = be16_to_cpu(block->bb_level);
 334         if (pag && pag->pagf_init) {
 335                 if (level >= pag->pagf_levels[XFS_BTNUM_RMAPi])
 336                         return false;
 337         } else if (level >= mp->m_rmap_maxlevels)
 338                 return false;
 339
 340         return xfs_btree_sblock_verify(bp, mp->m_rmap_mxr[level != 0]);
 341 }
 342
 343 static void
 344 xfs_rmapbt_read_verify(
 345         struct xfs_buf  *bp)
 346 {
 347         if (!xfs_btree_sblock_verify_crc(bp))
 348                 xfs_buf_ioerror(bp, -EFSBADCRC);
 349         else if (!xfs_rmapbt_verify(bp))
 350                 xfs_buf_ioerror(bp, -EFSCORRUPTED);
 351
 352         if (bp->b_error) {
 353                 trace_xfs_btree_corrupt(bp, _RET_IP_);
 354                 xfs_verifier_error(bp);
 355         }
 356 }
 357
 358 static void
 359 xfs_rmapbt_write_verify(
 360         struct xfs_buf  *bp)
 361 {
 362         if (!xfs_rmapbt_verify(bp)) {
 363                 trace_xfs_btree_corrupt(bp, _RET_IP_);
 364                 xfs_buf_ioerror(bp, -EFSCORRUPTED);
 365                 xfs_verifier_error(bp);
 366                 return;
 367         }
 368         xfs_btree_sblock_calc_crc(bp);
 369
 370 }
 371
 372 const struct xfs_buf_ops xfs_rmapbt_buf_ops = {
 373         .name                   = "xfs_rmapbt",
 374         .verify_read            = xfs_rmapbt_read_verify,
 375         .verify_write           = xfs_rmapbt_write_verify,
 376 };
 377
 378 STATIC int
 379 xfs_rmapbt_keys_inorder(
 380         struct xfs_btree_cur    *cur,
 381         union xfs_btree_key     *k1,
 382         union xfs_btree_key     *k2)
 383 {
 384         uint32_t                x;
 385         uint32_t                y;
 386         uint64_t                a;
 387         uint64_t                b;
 388
 389         x = be32_to_cpu(k1->rmap.rm_startblock);
 390         y = be32_to_cpu(k2->rmap.rm_startblock);
 391         if (x < y)
 392                 return 1;
 393         else if (x > y)
 394                 return 0;
 395         a = be64_to_cpu(k1->rmap.rm_owner);
 396         b = be64_to_cpu(k2->rmap.rm_owner);
 397         if (a < b)
 398                 return 1;
 399         else if (a > b)
 400                 return 0;
 401         a = XFS_RMAP_OFF(be64_to_cpu(k1->rmap.rm_offset));
 402         b = XFS_RMAP_OFF(be64_to_cpu(k2->rmap.rm_offset));
 403         if (a <= b)
 404                 return 1;
 405         return 0;
 406 }
 407
 408 STATIC int
 409 xfs_rmapbt_recs_inorder(
 410         struct xfs_btree_cur    *cur,
 411         union xfs_btree_rec     *r1,
 412         union xfs_btree_rec     *r2)
 413 {
 414         uint32_t                x;
 415         uint32_t                y;
 416         uint64_t                a;
 417         uint64_t                b;
 418
 419         x = be32_to_cpu(r1->rmap.rm_startblock);
 420         y = be32_to_cpu(r2->rmap.rm_startblock);
 421         if (x < y)
 422                 return 1;
 423         else if (x > y)
 424                 return 0;
 425         a = be64_to_cpu(r1->rmap.rm_owner);
 426         b = be64_to_cpu(r2->rmap.rm_owner);
 427         if (a < b)
 428                 return 1;
 429         else if (a > b)
 430                 return 0;
 431         a = XFS_RMAP_OFF(be64_to_cpu(r1->rmap.rm_offset));
 432         b = XFS_RMAP_OFF(be64_to_cpu(r2->rmap.rm_offset));
 433         if (a <= b)
 434                 return 1;
 435         return 0;
 436 }
 437
 438 static const struct xfs_btree_ops xfs_rmapbt_ops = {
 439         .rec_len                = sizeof(struct xfs_rmap_rec),
 440         .key_len                = 2 * sizeof(struct xfs_rmap_key),
 441
 442         .dup_cursor             = xfs_rmapbt_dup_cursor,
 443         .set_root               = xfs_rmapbt_set_root,
 444         .alloc_block            = xfs_rmapbt_alloc_block,
 445         .free_block             = xfs_rmapbt_free_block,
 446         .get_minrecs            = xfs_rmapbt_get_minrecs,
 447         .get_maxrecs            = xfs_rmapbt_get_maxrecs,
 448         .init_key_from_rec      = xfs_rmapbt_init_key_from_rec,
 449         .init_high_key_from_rec = xfs_rmapbt_init_high_key_from_rec,
 450         .init_rec_from_cur      = xfs_rmapbt_init_rec_from_cur,
 451         .init_ptr_from_cur      = xfs_rmapbt_init_ptr_from_cur,
 452         .key_diff               = xfs_rmapbt_key_diff,
 453         .buf_ops                = &xfs_rmapbt_buf_ops,
 454         .diff_two_keys          = xfs_rmapbt_diff_two_keys,
 455         .keys_inorder           = xfs_rmapbt_keys_inorder,
 456         .recs_inorder           = xfs_rmapbt_recs_inorder,
 457 };
 458
 459 /*
 460  * Allocate a new allocation btree cursor.
 461  */
 462 struct xfs_btree_cur *
 463 xfs_rmapbt_init_cursor(
 464         struct xfs_mount        *mp,
 465         struct xfs_trans        *tp,
 466         struct xfs_buf          *agbp,
 467         xfs_agnumber_t          agno)
 468 {
 469         struct xfs_agf          *agf = XFS_BUF_TO_AGF(agbp);
 470         struct xfs_btree_cur    *cur;
 471
 472         cur = kmem_zone_zalloc(xfs_btree_cur_zone, KM_NOFS);
 473         cur->bc_tp = tp;
 474         cur->bc_mp = mp;
 475         /* Overlapping btree; 2 keys per pointer. */
 476         cur->bc_btnum = XFS_BTNUM_RMAP;
 477         cur->bc_flags = XFS_BTREE_CRC_BLOCKS | XFS_BTREE_OVERLAPPING;
 478         cur->bc_blocklog = mp->m_sb.sb_blocklog;
 479         cur->bc_ops = &xfs_rmapbt_ops;
 480         cur->bc_nlevels = be32_to_cpu(agf->agf_levels[XFS_BTNUM_RMAP]);
 481         cur->bc_statoff = XFS_STATS_CALC_INDEX(xs_rmap_2);
 482
 483         cur->bc_private.a.agbp = agbp;
 484         cur->bc_private.a.agno = agno;
 485
 486         return cur;
 487 }
 488
 489 /*
 490  * Calculate number of records in an rmap btree block.
 491  */
 492 int
 493 xfs_rmapbt_maxrecs(
 494         struct xfs_mount        *mp,
 495         int                     blocklen,
 496         int                     leaf)
 497 {
 498         blocklen -= XFS_RMAP_BLOCK_LEN;
 499
 500         if (leaf)
 501                 return blocklen / sizeof(struct xfs_rmap_rec);
 502         return blocklen /
 503                 (2 * sizeof(struct xfs_rmap_key) + sizeof(xfs_rmap_ptr_t));
 504 }
 505
 506 /* Compute the maximum height of an rmap btree. */
 507 void
 508 xfs_rmapbt_compute_maxlevels(
 509         struct xfs_mount                *mp)
 510 {
 511         /*
 512          * On a non-reflink filesystem, the maximum number of rmap
 513          * records is the number of blocks in the AG, hence the max
 514          * rmapbt height is log_$maxrecs($agblocks).  However, with
 515          * reflink each AG block can have up to 2^32 (per the refcount
 516          * record format) owners, which means that theoretically we
 517          * could face up to 2^64 rmap records.
 518          *
 519          * That effectively means that the max rmapbt height must be
 520          * XFS_BTREE_MAXLEVELS.  "Fortunately" we'll run out of AG
 521          * blocks to feed the rmapbt long before the rmapbt reaches
 522          * maximum height.  The reflink code uses ag_resv_critical to
 523          * disallow reflinking when less than 10% of the per-AG metadata
 524          * block reservation since the fallback is a regular file copy.
 525          */
 526         if (xfs_sb_version_hasreflink(&mp->m_sb))
 527                 mp->m_rmap_maxlevels = XFS_BTREE_MAXLEVELS;
 528         else
 529                 mp->m_rmap_maxlevels = xfs_btree_compute_maxlevels(mp,
 530                                 mp->m_rmap_mnr, mp->m_sb.sb_agblocks);
 531 }
 532
 533 /* Calculate the refcount btree size for some records. */
 534 xfs_extlen_t
 535 xfs_rmapbt_calc_size(
 536         struct xfs_mount        *mp,
 537         unsigned long long      len)
 538 {
 539         return xfs_btree_calc_size(mp, mp->m_rmap_mnr, len);
 540 }
 541
 542 /*
 543  * Calculate the maximum refcount btree size.
 544  */
 545 xfs_extlen_t
 546 xfs_rmapbt_max_size(
 547         struct xfs_mount        *mp,
 548         xfs_agblock_t           agblocks)
 549 {
 550         /* Bail out if we're uninitialized, which can happen in mkfs. */
 551         if (mp->m_rmap_mxr[0] == 0)
 552                 return 0;
 553
 554         return xfs_rmapbt_calc_size(mp, agblocks);
 555 }
 556
 557 /*
 558  * Figure out how many blocks to reserve and how many are used by this btree.
 559  */
 560 int
 561 xfs_rmapbt_calc_reserves(
 562         struct xfs_mount        *mp,
 563         xfs_agnumber_t          agno,
 564         xfs_extlen_t            *ask,
 565         xfs_extlen_t            *used)
 566 {
 567         struct xfs_buf          *agbp;
 568         struct xfs_agf          *agf;
 569         xfs_agblock_t           agblocks;
 570         xfs_extlen_t            tree_len;
 571         int                     error;
 572
 573         if (!xfs_sb_version_hasrmapbt(&mp->m_sb))
 574                 return 0;
 575
 576         error = xfs_alloc_read_agf(mp, NULL, agno, 0, &agbp);
 577         if (error)
 578                 return error;
 579
 580         agf = XFS_BUF_TO_AGF(agbp);
 581         agblocks = be32_to_cpu(agf->agf_length);
 582         tree_len = be32_to_cpu(agf->agf_rmap_blocks);
 583         xfs_buf_relse(agbp);
 584
 585         /* Reserve 1% of the AG or enough for 1 block per record. */
 586         *ask += max(agblocks / 100, xfs_rmapbt_max_size(mp, agblocks));
 587         *used += tree_len;
 588
 589         return error;
 590 }