fs/btrfs/block-rsv.c

   1 // SPDX-License-Identifier: GPL-2.0
   2
   3 #include "misc.h"
   4 #include "ctree.h"
   5 #include "block-rsv.h"
   6 #include "space-info.h"
   7 #include "transaction.h"
   8 #include "block-group.h"
   9 #include "fs.h"
  10 #include "accessors.h"
  11
  12 /*
  13  * HOW DO BLOCK RESERVES WORK
  14  *
  15  *   Think of block_rsv's as buckets for logically grouped metadata
  16  *   reservations.  Each block_rsv has a ->size and a ->reserved.  ->size is
  17  *   how large we want our block rsv to be, ->reserved is how much space is
  18  *   currently reserved for this block reserve.
  19  *
  20  *   ->failfast exists for the truncate case, and is described below.
  21  *
  22  * NORMAL OPERATION
  23  *
  24  *   -> Reserve
  25  *     Entrance: btrfs_block_rsv_add, btrfs_block_rsv_refill
  26  *
  27  *     We call into btrfs_reserve_metadata_bytes() with our bytes, which is
  28  *     accounted for in space_info->bytes_may_use, and then add the bytes to
  29  *     ->reserved, and ->size in the case of btrfs_block_rsv_add.
  30  *
  31  *     ->size is an over-estimation of how much we may use for a particular
  32  *     operation.
  33  *
  34  *   -> Use
  35  *     Entrance: btrfs_use_block_rsv
  36  *
  37  *     When we do a btrfs_alloc_tree_block() we call into btrfs_use_block_rsv()
  38  *     to determine the appropriate block_rsv to use, and then verify that
  39  *     ->reserved has enough space for our tree block allocation.  Once
  40  *     successful we subtract fs_info->nodesize from ->reserved.
  41  *
  42  *   -> Finish
  43  *     Entrance: btrfs_block_rsv_release
  44  *
  45  *     We are finished with our operation, subtract our individual reservation
  46  *     from ->size, and then subtract ->size from ->reserved and free up the
  47  *     excess if there is any.
  48  *
  49  *     There is some logic here to refill the delayed refs rsv or the global rsv
  50  *     as needed, otherwise the excess is subtracted from
  51  *     space_info->bytes_may_use.
  52  *
  53  * TYPES OF BLOCK RESERVES
  54  *
  55  * BLOCK_RSV_TRANS, BLOCK_RSV_DELOPS, BLOCK_RSV_CHUNK
  56  *   These behave normally, as described above, just within the confines of the
  57  *   lifetime of their particular operation (transaction for the whole trans
  58  *   handle lifetime, for example).
  59  *
  60  * BLOCK_RSV_GLOBAL
  61  *   It is impossible to properly account for all the space that may be required
  62  *   to make our extent tree updates.  This block reserve acts as an overflow
  63  *   buffer in case our delayed refs reserve does not reserve enough space to
  64  *   update the extent tree.
  65  *
  66  *   We can steal from this in some cases as well, notably on evict() or
  67  *   truncate() in order to help users recover from ENOSPC conditions.
  68  *
  69  * BLOCK_RSV_DELALLOC
  70  *   The individual item sizes are determined by the per-inode size
  71  *   calculations, which are described with the delalloc code.  This is pretty
  72  *   straightforward, it's just the calculation of ->size encodes a lot of
  73  *   different items, and thus it gets used when updating inodes, inserting file
  74  *   extents, and inserting checksums.
  75  *
  76  * BLOCK_RSV_DELREFS
  77  *   We keep a running tally of how many delayed refs we have on the system.
  78  *   We assume each one of these delayed refs are going to use a full
  79  *   reservation.  We use the transaction items and pre-reserve space for every
  80  *   operation, and use this reservation to refill any gap between ->size and
  81  *   ->reserved that may exist.
  82  *
  83  *   From there it's straightforward, removing a delayed ref means we remove its
  84  *   count from ->size and free up reservations as necessary.  Since this is
  85  *   the most dynamic block reserve in the system, we will try to refill this
  86  *   block reserve first with any excess returned by any other block reserve.
  87  *
  88  * BLOCK_RSV_EMPTY
  89  *   This is the fallback block reserve to make us try to reserve space if we
  90  *   don't have a specific bucket for this allocation.  It is mostly used for
  91  *   updating the device tree and such, since that is a separate pool we're
  92  *   content to just reserve space from the space_info on demand.
  93  *
  94  * BLOCK_RSV_TEMP
  95  *   This is used by things like truncate and iput.  We will temporarily
  96  *   allocate a block reserve, set it to some size, and then truncate bytes
  97  *   until we have no space left.  With ->failfast set we'll simply return
  98  *   ENOSPC from btrfs_use_block_rsv() to signal that we need to unwind and try
  99  *   to make a new reservation.  This is because these operations are
 100  *   unbounded, so we want to do as much work as we can, and then back off and
 101  *   re-reserve.
 102  */
 103
 104 static u64 block_rsv_release_bytes(struct btrfs_fs_info *fs_info,
 105                                     struct btrfs_block_rsv *block_rsv,
 106                                     struct btrfs_block_rsv *dest, u64 num_bytes,
 107                                     u64 *qgroup_to_release_ret)
 108 {
 109         struct btrfs_space_info *space_info = block_rsv->space_info;
 110         u64 qgroup_to_release = 0;
 111         u64 ret;
 112
 113         spin_lock(&block_rsv->lock);
 114         if (num_bytes == (u64)-1) {
 115                 num_bytes = block_rsv->size;
 116                 qgroup_to_release = block_rsv->qgroup_rsv_size;
 117         }
 118         block_rsv->size -= num_bytes;
 119         if (block_rsv->reserved >= block_rsv->size) {
 120                 num_bytes = block_rsv->reserved - block_rsv->size;
 121                 block_rsv->reserved = block_rsv->size;
 122                 block_rsv->full = true;
 123         } else {
 124                 num_bytes = 0;
 125         }
 126         if (qgroup_to_release_ret &&
 127             block_rsv->qgroup_rsv_reserved >= block_rsv->qgroup_rsv_size) {
 128                 qgroup_to_release = block_rsv->qgroup_rsv_reserved -
 129                                     block_rsv->qgroup_rsv_size;
 130                 block_rsv->qgroup_rsv_reserved = block_rsv->qgroup_rsv_size;
 131         } else {
 132                 qgroup_to_release = 0;
 133         }
 134         spin_unlock(&block_rsv->lock);
 135
 136         ret = num_bytes;
 137         if (num_bytes > 0) {
 138                 if (dest) {
 139                         spin_lock(&dest->lock);
 140                         if (!dest->full) {
 141                                 u64 bytes_to_add;
 142
 143                                 bytes_to_add = dest->size - dest->reserved;
 144                                 bytes_to_add = min(num_bytes, bytes_to_add);
 145                                 dest->reserved += bytes_to_add;
 146                                 if (dest->reserved >= dest->size)
 147                                         dest->full = true;
 148                                 num_bytes -= bytes_to_add;
 149                         }
 150                         spin_unlock(&dest->lock);
 151                 }
 152                 if (num_bytes)
 153                         btrfs_space_info_free_bytes_may_use(fs_info,
 154                                                             space_info,
 155                                                             num_bytes);
 156         }
 157         if (qgroup_to_release_ret)
 158                 *qgroup_to_release_ret = qgroup_to_release;
 159         return ret;
 160 }
 161
 162 int btrfs_block_rsv_migrate(struct btrfs_block_rsv *src,
 163                             struct btrfs_block_rsv *dst, u64 num_bytes,
 164                             bool update_size)
 165 {
 166         int ret;
 167
 168         ret = btrfs_block_rsv_use_bytes(src, num_bytes);
 169         if (ret)
 170                 return ret;
 171
 172         btrfs_block_rsv_add_bytes(dst, num_bytes, update_size);
 173         return 0;
 174 }
 175
 176 void btrfs_init_block_rsv(struct btrfs_block_rsv *rsv, enum btrfs_rsv_type type)
 177 {
 178         memset(rsv, 0, sizeof(*rsv));
 179         spin_lock_init(&rsv->lock);
 180         rsv->type = type;
 181 }
 182
 183 void btrfs_init_metadata_block_rsv(struct btrfs_fs_info *fs_info,
 184                                    struct btrfs_block_rsv *rsv,
 185                                    enum btrfs_rsv_type type)
 186 {
 187         btrfs_init_block_rsv(rsv, type);
 188         rsv->space_info = btrfs_find_space_info(fs_info,
 189                                             BTRFS_BLOCK_GROUP_METADATA);
 190 }
 191
 192 struct btrfs_block_rsv *btrfs_alloc_block_rsv(struct btrfs_fs_info *fs_info,
 193                                               enum btrfs_rsv_type type)
 194 {
 195         struct btrfs_block_rsv *block_rsv;
 196
 197         block_rsv = kmalloc(sizeof(*block_rsv), GFP_NOFS);
 198         if (!block_rsv)
 199                 return NULL;
 200
 201         btrfs_init_metadata_block_rsv(fs_info, block_rsv, type);
 202         return block_rsv;
 203 }
 204
 205 void btrfs_free_block_rsv(struct btrfs_fs_info *fs_info,
 206                           struct btrfs_block_rsv *rsv)
 207 {
 208         if (!rsv)
 209                 return;
 210         btrfs_block_rsv_release(fs_info, rsv, (u64)-1, NULL);
 211         kfree(rsv);
 212 }
 213
 214 int btrfs_block_rsv_add(struct btrfs_fs_info *fs_info,
 215                         struct btrfs_block_rsv *block_rsv, u64 num_bytes,
 216                         enum btrfs_reserve_flush_enum flush)
 217 {
 218         int ret;
 219
 220         if (num_bytes == 0)
 221                 return 0;
 222
 223         ret = btrfs_reserve_metadata_bytes(fs_info, block_rsv->space_info,
 224                                            num_bytes, flush);
 225         if (!ret)
 226                 btrfs_block_rsv_add_bytes(block_rsv, num_bytes, true);
 227
 228         return ret;
 229 }
 230
 231 int btrfs_block_rsv_check(struct btrfs_block_rsv *block_rsv, int min_percent)
 232 {
 233         u64 num_bytes = 0;
 234         int ret = -ENOSPC;
 235
 236         spin_lock(&block_rsv->lock);
 237         num_bytes = mult_perc(block_rsv->size, min_percent);
 238         if (block_rsv->reserved >= num_bytes)
 239                 ret = 0;
 240         spin_unlock(&block_rsv->lock);
 241
 242         return ret;
 243 }
 244
 245 int btrfs_block_rsv_refill(struct btrfs_fs_info *fs_info,
 246                            struct btrfs_block_rsv *block_rsv, u64 num_bytes,
 247                            enum btrfs_reserve_flush_enum flush)
 248 {
 249         int ret = -ENOSPC;
 250
 251         if (!block_rsv)
 252                 return 0;
 253
 254         spin_lock(&block_rsv->lock);
 255         if (block_rsv->reserved >= num_bytes)
 256                 ret = 0;
 257         else
 258                 num_bytes -= block_rsv->reserved;
 259         spin_unlock(&block_rsv->lock);
 260
 261         if (!ret)
 262                 return 0;
 263
 264         ret = btrfs_reserve_metadata_bytes(fs_info, block_rsv->space_info,
 265                                            num_bytes, flush);
 266         if (!ret) {
 267                 btrfs_block_rsv_add_bytes(block_rsv, num_bytes, false);
 268                 return 0;
 269         }
 270
 271         return ret;
 272 }
 273
 274 u64 btrfs_block_rsv_release(struct btrfs_fs_info *fs_info,
 275                             struct btrfs_block_rsv *block_rsv, u64 num_bytes,
 276                             u64 *qgroup_to_release)
 277 {
 278         struct btrfs_block_rsv *global_rsv = &fs_info->global_block_rsv;
 279         struct btrfs_block_rsv *delayed_rsv = &fs_info->delayed_refs_rsv;
 280         struct btrfs_block_rsv *target = NULL;
 281
 282         /*
 283          * If we are a delayed block reserve then push to the global rsv,
 284          * otherwise dump into the global delayed reserve if it is not full.
 285          */
 286         if (block_rsv->type == BTRFS_BLOCK_RSV_DELOPS)
 287                 target = global_rsv;
 288         else if (block_rsv != global_rsv && !btrfs_block_rsv_full(delayed_rsv))
 289                 target = delayed_rsv;
 290
 291         if (target && block_rsv->space_info != target->space_info)
 292                 target = NULL;
 293
 294         return block_rsv_release_bytes(fs_info, block_rsv, target, num_bytes,
 295                                        qgroup_to_release);
 296 }
 297
 298 int btrfs_block_rsv_use_bytes(struct btrfs_block_rsv *block_rsv, u64 num_bytes)
 299 {
 300         int ret = -ENOSPC;
 301
 302         spin_lock(&block_rsv->lock);
 303         if (block_rsv->reserved >= num_bytes) {
 304                 block_rsv->reserved -= num_bytes;
 305                 if (block_rsv->reserved < block_rsv->size)
 306                         block_rsv->full = false;
 307                 ret = 0;
 308         }
 309         spin_unlock(&block_rsv->lock);
 310         return ret;
 311 }
 312
 313 void btrfs_block_rsv_add_bytes(struct btrfs_block_rsv *block_rsv,
 314                                u64 num_bytes, bool update_size)
 315 {
 316         spin_lock(&block_rsv->lock);
 317         block_rsv->reserved += num_bytes;
 318         if (update_size)
 319                 block_rsv->size += num_bytes;
 320         else if (block_rsv->reserved >= block_rsv->size)
 321                 block_rsv->full = true;
 322         spin_unlock(&block_rsv->lock);
 323 }
 324
 325 void btrfs_update_global_block_rsv(struct btrfs_fs_info *fs_info)
 326 {
 327         struct btrfs_block_rsv *block_rsv = &fs_info->global_block_rsv;
 328         struct btrfs_space_info *sinfo = block_rsv->space_info;
 329         struct btrfs_root *root, *tmp;
 330         u64 num_bytes = btrfs_root_used(&fs_info->tree_root->root_item);
 331         unsigned int min_items = 1;
 332
 333         /*
 334          * The global block rsv is based on the size of the extent tree, the
 335          * checksum tree and the root tree.  If the fs is empty we want to set
 336          * it to a minimal amount for safety.
 337          *
 338          * We also are going to need to modify the minimum of the tree root and
 339          * any global roots we could touch.
 340          */
 341         read_lock(&fs_info->global_root_lock);
 342         rbtree_postorder_for_each_entry_safe(root, tmp, &fs_info->global_root_tree,
 343                                              rb_node) {
 344                 if (root->root_key.objectid == BTRFS_EXTENT_TREE_OBJECTID ||
 345                     root->root_key.objectid == BTRFS_CSUM_TREE_OBJECTID ||
 346                     root->root_key.objectid == BTRFS_FREE_SPACE_TREE_OBJECTID) {
 347                         num_bytes += btrfs_root_used(&root->root_item);
 348                         min_items++;
 349                 }
 350         }
 351         read_unlock(&fs_info->global_root_lock);
 352
 353         if (btrfs_fs_compat_ro(fs_info, BLOCK_GROUP_TREE)) {
 354                 num_bytes += btrfs_root_used(&fs_info->block_group_root->root_item);
 355                 min_items++;
 356         }
 357
 358         if (btrfs_fs_incompat(fs_info, RAID_STRIPE_TREE)) {
 359                 num_bytes += btrfs_root_used(&fs_info->stripe_root->root_item);
 360                 min_items++;
 361         }
 362
 363         /*
 364          * But we also want to reserve enough space so we can do the fallback
 365          * global reserve for an unlink, which is an additional
 366          * BTRFS_UNLINK_METADATA_UNITS items.
 367          *
 368          * But we also need space for the delayed ref updates from the unlink,
 369          * so add BTRFS_UNLINK_METADATA_UNITS units for delayed refs, one for
 370          * each unlink metadata item.
 371          */
 372         min_items += BTRFS_UNLINK_METADATA_UNITS;
 373
 374         num_bytes = max_t(u64, num_bytes,
 375                           btrfs_calc_insert_metadata_size(fs_info, min_items) +
 376                           btrfs_calc_delayed_ref_bytes(fs_info,
 377                                                BTRFS_UNLINK_METADATA_UNITS));
 378
 379         spin_lock(&sinfo->lock);
 380         spin_lock(&block_rsv->lock);
 381
 382         block_rsv->size = min_t(u64, num_bytes, SZ_512M);
 383
 384         if (block_rsv->reserved < block_rsv->size) {
 385                 num_bytes = block_rsv->size - block_rsv->reserved;
 386                 btrfs_space_info_update_bytes_may_use(fs_info, sinfo,
 387                                                       num_bytes);
 388                 block_rsv->reserved = block_rsv->size;
 389         } else if (block_rsv->reserved > block_rsv->size) {
 390                 num_bytes = block_rsv->reserved - block_rsv->size;
 391                 btrfs_space_info_update_bytes_may_use(fs_info, sinfo,
 392                                                       -num_bytes);
 393                 block_rsv->reserved = block_rsv->size;
 394                 btrfs_try_granting_tickets(fs_info, sinfo);
 395         }
 396
 397         block_rsv->full = (block_rsv->reserved == block_rsv->size);
 398
 399         if (block_rsv->size >= sinfo->total_bytes)
 400                 sinfo->force_alloc = CHUNK_ALLOC_FORCE;
 401         spin_unlock(&block_rsv->lock);
 402         spin_unlock(&sinfo->lock);
 403 }
 404
 405 void btrfs_init_root_block_rsv(struct btrfs_root *root)
 406 {
 407         struct btrfs_fs_info *fs_info = root->fs_info;
 408
 409         switch (root->root_key.objectid) {
 410         case BTRFS_CSUM_TREE_OBJECTID:
 411         case BTRFS_EXTENT_TREE_OBJECTID:
 412         case BTRFS_FREE_SPACE_TREE_OBJECTID:
 413         case BTRFS_BLOCK_GROUP_TREE_OBJECTID:
 414         case BTRFS_RAID_STRIPE_TREE_OBJECTID:
 415                 root->block_rsv = &fs_info->delayed_refs_rsv;
 416                 break;
 417         case BTRFS_ROOT_TREE_OBJECTID:
 418         case BTRFS_DEV_TREE_OBJECTID:
 419         case BTRFS_QUOTA_TREE_OBJECTID:
 420                 root->block_rsv = &fs_info->global_block_rsv;
 421                 break;
 422         case BTRFS_CHUNK_TREE_OBJECTID:
 423                 root->block_rsv = &fs_info->chunk_block_rsv;
 424                 break;
 425         default:
 426                 root->block_rsv = NULL;
 427                 break;
 428         }
 429 }
 430
 431 void btrfs_init_global_block_rsv(struct btrfs_fs_info *fs_info)
 432 {
 433         struct btrfs_space_info *space_info;
 434
 435         space_info = btrfs_find_space_info(fs_info, BTRFS_BLOCK_GROUP_SYSTEM);
 436         fs_info->chunk_block_rsv.space_info = space_info;
 437
 438         space_info = btrfs_find_space_info(fs_info, BTRFS_BLOCK_GROUP_METADATA);
 439         fs_info->global_block_rsv.space_info = space_info;
 440         fs_info->trans_block_rsv.space_info = space_info;
 441         fs_info->empty_block_rsv.space_info = space_info;
 442         fs_info->delayed_block_rsv.space_info = space_info;
 443         fs_info->delayed_refs_rsv.space_info = space_info;
 444
 445         btrfs_update_global_block_rsv(fs_info);
 446 }
 447
 448 void btrfs_release_global_block_rsv(struct btrfs_fs_info *fs_info)
 449 {
 450         btrfs_block_rsv_release(fs_info, &fs_info->global_block_rsv, (u64)-1,
 451                                 NULL);
 452         WARN_ON(fs_info->trans_block_rsv.size > 0);
 453         WARN_ON(fs_info->trans_block_rsv.reserved > 0);
 454         WARN_ON(fs_info->chunk_block_rsv.size > 0);
 455         WARN_ON(fs_info->chunk_block_rsv.reserved > 0);
 456         WARN_ON(fs_info->delayed_block_rsv.size > 0);
 457         WARN_ON(fs_info->delayed_block_rsv.reserved > 0);
 458         WARN_ON(fs_info->delayed_refs_rsv.reserved > 0);
 459         WARN_ON(fs_info->delayed_refs_rsv.size > 0);
 460 }
 461
 462 static struct btrfs_block_rsv *get_block_rsv(
 463                                         const struct btrfs_trans_handle *trans,
 464                                         const struct btrfs_root *root)
 465 {
 466         struct btrfs_fs_info *fs_info = root->fs_info;
 467         struct btrfs_block_rsv *block_rsv = NULL;
 468
 469         if (test_bit(BTRFS_ROOT_SHAREABLE, &root->state) ||
 470             (root == fs_info->uuid_root) ||
 471             (trans->adding_csums &&
 472              root->root_key.objectid == BTRFS_CSUM_TREE_OBJECTID))
 473                 block_rsv = trans->block_rsv;
 474
 475         if (!block_rsv)
 476                 block_rsv = root->block_rsv;
 477
 478         if (!block_rsv)
 479                 block_rsv = &fs_info->empty_block_rsv;
 480
 481         return block_rsv;
 482 }
 483
 484 struct btrfs_block_rsv *btrfs_use_block_rsv(struct btrfs_trans_handle *trans,
 485                                             struct btrfs_root *root,
 486                                             u32 blocksize)
 487 {
 488         struct btrfs_fs_info *fs_info = root->fs_info;
 489         struct btrfs_block_rsv *block_rsv;
 490         struct btrfs_block_rsv *global_rsv = &fs_info->global_block_rsv;
 491         int ret;
 492         bool global_updated = false;
 493
 494         block_rsv = get_block_rsv(trans, root);
 495
 496         if (unlikely(btrfs_block_rsv_size(block_rsv) == 0))
 497                 goto try_reserve;
 498 again:
 499         ret = btrfs_block_rsv_use_bytes(block_rsv, blocksize);
 500         if (!ret)
 501                 return block_rsv;
 502
 503         if (block_rsv->failfast)
 504                 return ERR_PTR(ret);
 505
 506         if (block_rsv->type == BTRFS_BLOCK_RSV_GLOBAL && !global_updated) {
 507                 global_updated = true;
 508                 btrfs_update_global_block_rsv(fs_info);
 509                 goto again;
 510         }
 511
 512         /*
 513          * The global reserve still exists to save us from ourselves, so don't
 514          * warn_on if we are short on our delayed refs reserve.
 515          */
 516         if (block_rsv->type != BTRFS_BLOCK_RSV_DELREFS &&
 517             btrfs_test_opt(fs_info, ENOSPC_DEBUG)) {
 518                 static DEFINE_RATELIMIT_STATE(_rs,
 519                                 DEFAULT_RATELIMIT_INTERVAL * 10,
 520                                 /*DEFAULT_RATELIMIT_BURST*/ 1);
 521                 if (__ratelimit(&_rs))
 522                         WARN(1, KERN_DEBUG
 523                                 "BTRFS: block rsv %d returned %d\n",
 524                                 block_rsv->type, ret);
 525         }
 526 try_reserve:
 527         ret = btrfs_reserve_metadata_bytes(fs_info, block_rsv->space_info,
 528                                            blocksize, BTRFS_RESERVE_NO_FLUSH);
 529         if (!ret)
 530                 return block_rsv;
 531         /*
 532          * If we couldn't reserve metadata bytes try and use some from
 533          * the global reserve if its space type is the same as the global
 534          * reservation.
 535          */
 536         if (block_rsv->type != BTRFS_BLOCK_RSV_GLOBAL &&
 537             block_rsv->space_info == global_rsv->space_info) {
 538                 ret = btrfs_block_rsv_use_bytes(global_rsv, blocksize);
 539                 if (!ret)
 540                         return global_rsv;
 541         }
 542
 543         /*
 544          * All hope is lost, but of course our reservations are overly
 545          * pessimistic, so instead of possibly having an ENOSPC abort here, try
 546          * one last time to force a reservation if there's enough actual space
 547          * on disk to make the reservation.
 548          */
 549         ret = btrfs_reserve_metadata_bytes(fs_info, block_rsv->space_info, blocksize,
 550                                            BTRFS_RESERVE_FLUSH_EMERGENCY);
 551         if (!ret)
 552                 return block_rsv;
 553
 554         return ERR_PTR(ret);
 555 }
 556
 557 int btrfs_check_trunc_cache_free_space(struct btrfs_fs_info *fs_info,
 558                                        struct btrfs_block_rsv *rsv)
 559 {
 560         u64 needed_bytes;
 561         int ret;
 562
 563         /* 1 for slack space, 1 for updating the inode */
 564         needed_bytes = btrfs_calc_insert_metadata_size(fs_info, 1) +
 565                 btrfs_calc_metadata_size(fs_info, 1);
 566
 567         spin_lock(&rsv->lock);
 568         if (rsv->reserved < needed_bytes)
 569                 ret = -ENOSPC;
 570         else
 571                 ret = 0;
 572         spin_unlock(&rsv->lock);
 573         return ret;
 574 }