SAFE public projects git trees. - safe/jmp/linux-2.6/blob - fs/btrfs/extent-tree.c

   1 #include <linux/module.h>
   2 #include "ctree.h"
   3 #include "disk-io.h"
   4 #include "print-tree.h"
   5 #include "transaction.h"
   6
   7 static int find_free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
   8                             *orig_root, u64 num_blocks, u64 search_start, u64
   9                             search_end, struct btrfs_key *ins);
  10 static int finish_current_insert(struct btrfs_trans_handle *trans, struct
  11                                  btrfs_root *extent_root);
  12 static int del_pending_extents(struct btrfs_trans_handle *trans, struct
  13                                btrfs_root *extent_root);
  14
  15 static int inc_block_ref(struct btrfs_trans_handle *trans, struct btrfs_root
  16                          *root, u64 blocknr, u64 num_blocks)
  17 {
  18         struct btrfs_path path;
  19         int ret;
  20         struct btrfs_key key;
  21         struct btrfs_leaf *l;
  22         struct btrfs_extent_item *item;
  23         struct btrfs_key ins;
  24         u32 refs;
  25
  26         find_free_extent(trans, root->fs_info->extent_root, 0, 0, (u64)-1,
  27                          &ins);
  28         btrfs_init_path(&path);
  29         key.objectid = blocknr;
  30         key.flags = 0;
  31         btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
  32         key.offset = num_blocks;
  33         ret = btrfs_search_slot(trans, root->fs_info->extent_root, &key, &path,
  34                                 0, 1);
  35         if (ret != 0)
  36                 BUG();
  37         BUG_ON(ret != 0);
  38         l = btrfs_buffer_leaf(path.nodes[0]);
  39         item = btrfs_item_ptr(l, path.slots[0], struct btrfs_extent_item);
  40         refs = btrfs_extent_refs(item);
  41         btrfs_set_extent_refs(item, refs + 1);
  42         mark_buffer_dirty(path.nodes[0]);
  43
  44         btrfs_release_path(root->fs_info->extent_root, &path);
  45         finish_current_insert(trans, root->fs_info->extent_root);
  46         del_pending_extents(trans, root->fs_info->extent_root);
  47         return 0;
  48 }
  49
  50 static int lookup_block_ref(struct btrfs_trans_handle *trans, struct btrfs_root
  51                             *root, u64 blocknr, u64 num_blocks, u32 *refs)
  52 {
  53         struct btrfs_path path;
  54         int ret;
  55         struct btrfs_key key;
  56         struct btrfs_leaf *l;
  57         struct btrfs_extent_item *item;
  58         btrfs_init_path(&path);
  59         key.objectid = blocknr;
  60         key.offset = num_blocks;
  61         key.flags = 0;
  62         btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
  63         ret = btrfs_search_slot(trans, root->fs_info->extent_root, &key, &path,
  64                                 0, 0);
  65         if (ret != 0)
  66                 BUG();
  67         l = btrfs_buffer_leaf(path.nodes[0]);
  68         item = btrfs_item_ptr(l, path.slots[0], struct btrfs_extent_item);
  69         *refs = btrfs_extent_refs(item);
  70         btrfs_release_path(root->fs_info->extent_root, &path);
  71         return 0;
  72 }
  73
  74 int btrfs_inc_ref(struct btrfs_trans_handle *trans, struct btrfs_root *root,
  75                   struct buffer_head *buf)
  76 {
  77         u64 blocknr;
  78         struct btrfs_node *buf_node;
  79         struct btrfs_leaf *buf_leaf;
  80         struct btrfs_disk_key *key;
  81         struct btrfs_file_extent_item *fi;
  82         int i;
  83         int leaf;
  84         int ret;
  85
  86         if (!root->ref_cows)
  87                 return 0;
  88         buf_node = btrfs_buffer_node(buf);
  89         leaf = btrfs_is_leaf(buf_node);
  90         buf_leaf = btrfs_buffer_leaf(buf);
  91         for (i = 0; i < btrfs_header_nritems(&buf_node->header); i++) {
  92                 if (leaf) {
  93                         key = &buf_leaf->items[i].key;
  94                         if (btrfs_disk_key_type(key) != BTRFS_EXTENT_DATA_KEY)
  95                                 continue;
  96                         fi = btrfs_item_ptr(buf_leaf, i,
  97                                             struct btrfs_file_extent_item);
  98                         ret = inc_block_ref(trans, root,
  99                                     btrfs_file_extent_disk_blocknr(fi),
 100                                     btrfs_file_extent_disk_num_blocks(fi));
 101                         BUG_ON(ret);
 102                 } else {
 103                         blocknr = btrfs_node_blockptr(buf_node, i);
 104                         ret = inc_block_ref(trans, root, blocknr, 1);
 105                         BUG_ON(ret);
 106                 }
 107         }
 108         return 0;
 109 }
 110
 111 int btrfs_finish_extent_commit(struct btrfs_trans_handle *trans, struct
 112                                btrfs_root *root)
 113 {
 114         unsigned long gang[8];
 115         u64 first = 0;
 116         int ret;
 117         int i;
 118         struct radix_tree_root *pinned_radix = &root->fs_info->pinned_radix;
 119
 120         while(1) {
 121                 ret = find_first_radix_bit(pinned_radix, gang,
 122                                            ARRAY_SIZE(gang));
 123                 if (!ret)
 124                         break;
 125                 if (!first)
 126                         first = gang[0];
 127                 for (i = 0; i < ret; i++) {
 128                         clear_radix_bit(pinned_radix, gang[i]);
 129                 }
 130         }
 131         if (root->fs_info->last_insert.objectid > first)
 132                 root->fs_info->last_insert.objectid = first;
 133         root->fs_info->last_insert.offset = 0;
 134         return 0;
 135 }
 136
 137 static int finish_current_insert(struct btrfs_trans_handle *trans, struct
 138                                  btrfs_root *extent_root)
 139 {
 140         struct btrfs_key ins;
 141         struct btrfs_extent_item extent_item;
 142         int i;
 143         int ret;
 144         u64 super_blocks_used;
 145         struct btrfs_fs_info *info = extent_root->fs_info;
 146
 147         btrfs_set_extent_refs(&extent_item, 1);
 148         btrfs_set_extent_owner(&extent_item,
 149                 btrfs_header_parentid(btrfs_buffer_header(extent_root->node)));
 150         ins.offset = 1;
 151         ins.flags = 0;
 152         btrfs_set_key_type(&ins, BTRFS_EXTENT_ITEM_KEY);
 153
 154         for (i = 0; i < extent_root->fs_info->current_insert.flags; i++) {
 155                 ins.objectid = extent_root->fs_info->current_insert.objectid +
 156                                 i;
 157                 super_blocks_used = btrfs_super_blocks_used(info->disk_super);
 158                 btrfs_set_super_blocks_used(info->disk_super,
 159                                             super_blocks_used + 1);
 160                 ret = btrfs_insert_item(trans, extent_root, &ins, &extent_item,
 161                                         sizeof(extent_item));
 162                 BUG_ON(ret);
 163         }
 164         extent_root->fs_info->current_insert.offset = 0;
 165         return 0;
 166 }
 167
 168 static int pin_down_block(struct btrfs_root *root, u64 blocknr, int pending)
 169 {
 170         int err;
 171         struct btrfs_header *header;
 172         struct buffer_head *bh;
 173
 174         if (!pending) {
 175                 bh = btrfs_find_tree_block(root, blocknr);
 176                 if (bh && buffer_uptodate(bh)) {
 177                         header = btrfs_buffer_header(bh);
 178                         if (btrfs_header_generation(header) ==
 179                             root->fs_info->running_transaction->transid) {
 180                                 brelse(bh);
 181                                 return 0;
 182                         }
 183                         brelse(bh);
 184                 }
 185                 err = set_radix_bit(&root->fs_info->pinned_radix, blocknr);
 186         } else {
 187                 err = set_radix_bit(&root->fs_info->pending_del_radix, blocknr);
 188         }
 189         BUG_ON(err);
 190         return 0;
 191 }
 192
 193 /*
 194  * remove an extent from the root, returns 0 on success
 195  */
 196 static int __free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 197                          *root, u64 blocknr, u64 num_blocks, int pin)
 198 {
 199         struct btrfs_path path;
 200         struct btrfs_key key;
 201         struct btrfs_fs_info *info = root->fs_info;
 202         struct btrfs_root *extent_root = info->extent_root;
 203         int ret;
 204         struct btrfs_extent_item *ei;
 205         struct btrfs_key ins;
 206         u32 refs;
 207
 208         key.objectid = blocknr;
 209         key.flags = 0;
 210         btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
 211         key.offset = num_blocks;
 212
 213         find_free_extent(trans, root, 0, 0, (u64)-1, &ins);
 214         btrfs_init_path(&path);
 215         ret = btrfs_search_slot(trans, extent_root, &key, &path, -1, 1);
 216         if (ret) {
 217                 printk("failed to find %Lu\n", key.objectid);
 218                 btrfs_print_tree(extent_root, extent_root->node);
 219                 printk("failed to find %Lu\n", key.objectid);
 220                 BUG();
 221         }
 222         ei = btrfs_item_ptr(btrfs_buffer_leaf(path.nodes[0]), path.slots[0],
 223                             struct btrfs_extent_item);
 224         BUG_ON(ei->refs == 0);
 225         refs = btrfs_extent_refs(ei) - 1;
 226         btrfs_set_extent_refs(ei, refs);
 227         mark_buffer_dirty(path.nodes[0]);
 228         if (refs == 0) {
 229                 u64 super_blocks_used;
 230
 231                 if (pin) {
 232                         ret = pin_down_block(root, blocknr, 0);
 233                         BUG_ON(ret);
 234                 }
 235
 236                 super_blocks_used = btrfs_super_blocks_used(info->disk_super);
 237                 btrfs_set_super_blocks_used(info->disk_super,
 238                                             super_blocks_used - num_blocks);
 239                 ret = btrfs_del_item(trans, extent_root, &path);
 240                 if (extent_root->fs_info->last_insert.objectid > blocknr)
 241                         extent_root->fs_info->last_insert.objectid = blocknr;
 242                 if (ret)
 243                         BUG();
 244         }
 245         btrfs_release_path(extent_root, &path);
 246         finish_current_insert(trans, extent_root);
 247         return ret;
 248 }
 249
 250 /*
 251  * find all the blocks marked as pending in the radix tree and remove
 252  * them from the extent map
 253  */
 254 static int del_pending_extents(struct btrfs_trans_handle *trans, struct
 255                                btrfs_root *extent_root)
 256 {
 257         int ret;
 258         int wret;
 259         int err = 0;
 260         unsigned long gang[4];
 261         int i;
 262         struct radix_tree_root *pending_radix;
 263         struct radix_tree_root *pinned_radix;
 264
 265         pending_radix = &extent_root->fs_info->pending_del_radix;
 266         pinned_radix = &extent_root->fs_info->pinned_radix;
 267
 268         while(1) {
 269                 ret = find_first_radix_bit(pending_radix, gang,
 270                                            ARRAY_SIZE(gang));
 271                 if (!ret)
 272                         break;
 273                 for (i = 0; i < ret; i++) {
 274                         wret = set_radix_bit(pinned_radix, gang[i]);
 275                         BUG_ON(wret);
 276                         wret = clear_radix_bit(pending_radix, gang[i]);
 277                         BUG_ON(wret);
 278                         wret = __free_extent(trans, extent_root,
 279                                              gang[i], 1, 0);
 280                         if (wret)
 281                                 err = wret;
 282                 }
 283         }
 284         return err;
 285 }
 286
 287 /*
 288  * remove an extent from the root, returns 0 on success
 289  */
 290 int btrfs_free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 291                       *root, u64 blocknr, u64 num_blocks, int pin)
 292 {
 293         struct btrfs_root *extent_root = root->fs_info->extent_root;
 294         int pending_ret;
 295         int ret;
 296
 297         if (root == extent_root) {
 298                 pin_down_block(root, blocknr, 1);
 299                 return 0;
 300         }
 301         ret = __free_extent(trans, root, blocknr, num_blocks, pin);
 302         pending_ret = del_pending_extents(trans, root->fs_info->extent_root);
 303         return ret ? ret : pending_ret;
 304 }
 305
 306 /*
 307  * walks the btree of allocated extents and find a hole of a given size.
 308  * The key ins is changed to record the hole:
 309  * ins->objectid == block start
 310  * ins->flags = BTRFS_EXTENT_ITEM_KEY
 311  * ins->offset == number of blocks
 312  * Any available blocks before search_start are skipped.
 313  */
 314 static int find_free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 315                             *orig_root, u64 num_blocks, u64 search_start, u64
 316                             search_end, struct btrfs_key *ins)
 317 {
 318         struct btrfs_path path;
 319         struct btrfs_key key;
 320         int ret;
 321         u64 hole_size = 0;
 322         int slot = 0;
 323         u64 last_block = 0;
 324         u64 test_block;
 325         int start_found;
 326         struct btrfs_leaf *l;
 327         struct btrfs_root * root = orig_root->fs_info->extent_root;
 328         int total_needed = num_blocks;
 329         int level;
 330
 331         level = btrfs_header_level(btrfs_buffer_header(root->node));
 332         total_needed += (level + 1) * 3;
 333         if (root->fs_info->last_insert.objectid > search_start)
 334                 search_start = root->fs_info->last_insert.objectid;
 335
 336         ins->flags = 0;
 337         btrfs_set_key_type(ins, BTRFS_EXTENT_ITEM_KEY);
 338
 339 check_failed:
 340         btrfs_init_path(&path);
 341         ins->objectid = search_start;
 342         ins->offset = 0;
 343         start_found = 0;
 344         ret = btrfs_search_slot(trans, root, ins, &path, 0, 0);
 345         if (ret < 0)
 346                 goto error;
 347
 348         if (path.slots[0] > 0)
 349                 path.slots[0]--;
 350
 351         while (1) {
 352                 l = btrfs_buffer_leaf(path.nodes[0]);
 353                 slot = path.slots[0];
 354                 if (slot >= btrfs_header_nritems(&l->header)) {
 355                         ret = btrfs_next_leaf(root, &path);
 356                         if (ret == 0)
 357                                 continue;
 358                         if (ret < 0)
 359                                 goto error;
 360                         if (!start_found) {
 361                                 ins->objectid = search_start;
 362                                 ins->offset = (u64)-1;
 363                                 start_found = 1;
 364                                 goto check_pending;
 365                         }
 366                         ins->objectid = last_block > search_start ?
 367                                         last_block : search_start;
 368                         ins->offset = (u64)-1;
 369                         goto check_pending;
 370                 }
 371                 btrfs_disk_key_to_cpu(&key, &l->items[slot].key);
 372                 if (key.objectid >= search_start) {
 373                         if (start_found) {
 374                                 if (last_block < search_start)
 375                                         last_block = search_start;
 376                                 hole_size = key.objectid - last_block;
 377                                 if (hole_size > total_needed) {
 378                                         ins->objectid = last_block;
 379                                         ins->offset = hole_size;
 380                                         goto check_pending;
 381                                 }
 382                         }
 383                 }
 384                 start_found = 1;
 385                 last_block = key.objectid + key.offset;
 386                 path.slots[0]++;
 387         }
 388         // FIXME -ENOSPC
 389 check_pending:
 390         /* we have to make sure we didn't find an extent that has already
 391          * been allocated by the map tree or the original allocation
 392          */
 393         btrfs_release_path(root, &path);
 394         BUG_ON(ins->objectid < search_start);
 395         for (test_block = ins->objectid;
 396              test_block < ins->objectid + total_needed; test_block++) {
 397                 if (test_radix_bit(&root->fs_info->pinned_radix,
 398                                       test_block)) {
 399                         search_start = test_block + 1;
 400                         goto check_failed;
 401                 }
 402         }
 403         BUG_ON(root->fs_info->current_insert.offset);
 404         root->fs_info->current_insert.offset = total_needed - num_blocks;
 405         root->fs_info->current_insert.objectid = ins->objectid + num_blocks;
 406         root->fs_info->current_insert.flags = 0;
 407         root->fs_info->last_insert.objectid = ins->objectid;
 408         ins->offset = num_blocks;
 409         return 0;
 410 error:
 411         btrfs_release_path(root, &path);
 412         return ret;
 413 }
 414
 415 /*
 416  * finds a free extent and does all the dirty work required for allocation
 417  * returns the key for the extent through ins, and a tree buffer for
 418  * the first block of the extent through buf.
 419  *
 420  * returns 0 if everything worked, non-zero otherwise.
 421  */
 422 int btrfs_alloc_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 423                         *root, u64 num_blocks, u64 search_start, u64
 424                         search_end, u64 owner, struct btrfs_key *ins)
 425 {
 426         int ret;
 427         int pending_ret;
 428         u64 super_blocks_used;
 429         struct btrfs_fs_info *info = root->fs_info;
 430         struct btrfs_root *extent_root = info->extent_root;
 431         struct btrfs_extent_item extent_item;
 432
 433         btrfs_set_extent_refs(&extent_item, 1);
 434         btrfs_set_extent_owner(&extent_item, owner);
 435
 436         if (root == extent_root) {
 437                 BUG_ON(extent_root->fs_info->current_insert.offset == 0);
 438                 BUG_ON(num_blocks != 1);
 439                 BUG_ON(extent_root->fs_info->current_insert.flags ==
 440                        extent_root->fs_info->current_insert.offset);
 441                 ins->offset = 1;
 442                 ins->objectid = extent_root->fs_info->current_insert.objectid +
 443                                 extent_root->fs_info->current_insert.flags++;
 444                 return 0;
 445         }
 446         ret = find_free_extent(trans, root, num_blocks, search_start,
 447                                search_end, ins);
 448         if (ret)
 449                 return ret;
 450
 451         super_blocks_used = btrfs_super_blocks_used(info->disk_super);
 452         btrfs_set_super_blocks_used(info->disk_super, super_blocks_used +
 453                                     num_blocks);
 454         ret = btrfs_insert_item(trans, extent_root, ins, &extent_item,
 455                                 sizeof(extent_item));
 456
 457         finish_current_insert(trans, extent_root);
 458         pending_ret = del_pending_extents(trans, extent_root);
 459         if (ret)
 460                 return ret;
 461         if (pending_ret)
 462                 return pending_ret;
 463         return 0;
 464 }
 465
 466 /*
 467  * helper function to allocate a block for a given tree
 468  * returns the tree buffer or NULL.
 469  */
 470 struct buffer_head *btrfs_alloc_free_block(struct btrfs_trans_handle *trans,
 471                                             struct btrfs_root *root)
 472 {
 473         struct btrfs_key ins;
 474         int ret;
 475         struct buffer_head *buf;
 476
 477         ret = btrfs_alloc_extent(trans, root, 1, 0, (unsigned long)-1,
 478                 btrfs_header_parentid(btrfs_buffer_header(root->node)), &ins);
 479         if (ret) {
 480                 BUG();
 481                 return NULL;
 482         }
 483         buf = btrfs_find_create_tree_block(root, ins.objectid);
 484         set_buffer_uptodate(buf);
 485         return buf;
 486 }
 487
 488 static int drop_leaf_ref(struct btrfs_trans_handle *trans,
 489                          struct btrfs_root *root, struct buffer_head *cur)
 490 {
 491         struct btrfs_disk_key *key;
 492         struct btrfs_leaf *leaf;
 493         struct btrfs_file_extent_item *fi;
 494         int i;
 495         int nritems;
 496         int ret;
 497
 498         BUG_ON(!btrfs_is_leaf(btrfs_buffer_node(cur)));
 499         leaf = btrfs_buffer_leaf(cur);
 500         nritems = btrfs_header_nritems(&leaf->header);
 501         for (i = 0; i < nritems; i++) {
 502                 key = &leaf->items[i].key;
 503                 if (btrfs_disk_key_type(key) != BTRFS_EXTENT_DATA_KEY)
 504                         continue;
 505                 fi = btrfs_item_ptr(leaf, i, struct btrfs_file_extent_item);
 506                 /*
 507                  * FIXME make sure to insert a trans record that
 508                  * repeats the snapshot del on crash
 509                  */
 510                 ret = btrfs_free_extent(trans, root,
 511                                         btrfs_file_extent_disk_blocknr(fi),
 512                                         btrfs_file_extent_disk_num_blocks(fi),
 513                                         0);
 514                 BUG_ON(ret);
 515         }
 516         return 0;
 517 }
 518
 519 /*
 520  * helper function for drop_snapshot, this walks down the tree dropping ref
 521  * counts as it goes.
 522  */
 523 static int walk_down_tree(struct btrfs_trans_handle *trans, struct btrfs_root
 524                           *root, struct btrfs_path *path, int *level)
 525 {
 526         struct buffer_head *next;
 527         struct buffer_head *cur;
 528         u64 blocknr;
 529         int ret;
 530         u32 refs;
 531
 532         ret = lookup_block_ref(trans, root, path->nodes[*level]->b_blocknr,
 533                                1, &refs);
 534         BUG_ON(ret);
 535         if (refs > 1)
 536                 goto out;
 537         /*
 538          * walk down to the last node level and free all the leaves
 539          */
 540         while(*level >= 0) {
 541                 cur = path->nodes[*level];
 542                 if (path->slots[*level] >=
 543                     btrfs_header_nritems(btrfs_buffer_header(cur)))
 544                         break;
 545                 if (*level == 0) {
 546                         ret = drop_leaf_ref(trans, root, cur);
 547                         BUG_ON(ret);
 548                         break;
 549                 }
 550                 blocknr = btrfs_node_blockptr(btrfs_buffer_node(cur),
 551                                               path->slots[*level]);
 552                 ret = lookup_block_ref(trans, root, blocknr, 1, &refs);
 553                 BUG_ON(ret);
 554                 if (refs != 1) {
 555                         path->slots[*level]++;
 556                         ret = btrfs_free_extent(trans, root, blocknr, 1, 1);
 557                         BUG_ON(ret);
 558                         continue;
 559                 }
 560                 next = read_tree_block(root, blocknr);
 561                 if (path->nodes[*level-1])
 562                         btrfs_block_release(root, path->nodes[*level-1]);
 563                 path->nodes[*level-1] = next;
 564                 *level = btrfs_header_level(btrfs_buffer_header(next));
 565                 path->slots[*level] = 0;
 566         }
 567 out:
 568         ret = btrfs_free_extent(trans, root,
 569                                 path->nodes[*level]->b_blocknr, 1, 1);
 570         btrfs_block_release(root, path->nodes[*level]);
 571         path->nodes[*level] = NULL;
 572         *level += 1;
 573         BUG_ON(ret);
 574         return 0;
 575 }
 576
 577 /*
 578  * helper for dropping snapshots.  This walks back up the tree in the path
 579  * to find the first node higher up where we haven't yet gone through
 580  * all the slots
 581  */
 582 static int walk_up_tree(struct btrfs_trans_handle *trans, struct btrfs_root
 583                         *root, struct btrfs_path *path, int *level)
 584 {
 585         int i;
 586         int slot;
 587         int ret;
 588         for(i = *level; i < BTRFS_MAX_LEVEL - 1 && path->nodes[i]; i++) {
 589                 slot = path->slots[i];
 590                 if (slot < btrfs_header_nritems(
 591                     btrfs_buffer_header(path->nodes[i])) - 1) {
 592                         path->slots[i]++;
 593                         *level = i;
 594                         return 0;
 595                 } else {
 596                         ret = btrfs_free_extent(trans, root,
 597                                                 path->nodes[*level]->b_blocknr,
 598                                                 1, 1);
 599                         BUG_ON(ret);
 600                         btrfs_block_release(root, path->nodes[*level]);
 601                         path->nodes[*level] = NULL;
 602                         *level = i + 1;
 603                 }
 604         }
 605         return 1;
 606 }
 607
 608 /*
 609  * drop the reference count on the tree rooted at 'snap'.  This traverses
 610  * the tree freeing any blocks that have a ref count of zero after being
 611  * decremented.
 612  */
 613 int btrfs_drop_snapshot(struct btrfs_trans_handle *trans, struct btrfs_root
 614                         *root, struct buffer_head *snap)
 615 {
 616         int ret = 0;
 617         int wret;
 618         int level;
 619         struct btrfs_path path;
 620         int i;
 621         int orig_level;
 622
 623         btrfs_init_path(&path);
 624
 625         level = btrfs_header_level(btrfs_buffer_header(snap));
 626         orig_level = level;
 627         path.nodes[level] = snap;
 628         path.slots[level] = 0;
 629         while(1) {
 630                 wret = walk_down_tree(trans, root, &path, &level);
 631                 if (wret > 0)
 632                         break;
 633                 if (wret < 0)
 634                         ret = wret;
 635
 636                 wret = walk_up_tree(trans, root, &path, &level);
 637                 if (wret > 0)
 638                         break;
 639                 if (wret < 0)
 640                         ret = wret;
 641         }
 642         for (i = 0; i <= orig_level; i++) {
 643                 if (path.nodes[i]) {
 644                         btrfs_block_release(root, path.nodes[i]);
 645                 }
 646         }
 647         return ret;
 648 }