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         bh = sb_find_get_block(root->fs_info->sb, blocknr);
 175         if (bh) {
 176                 header = btrfs_buffer_header(bh);
 177                 if (btrfs_header_generation(header) ==
 178                     root->fs_info->running_transaction->transid) {
 179                         brelse(bh);
 180                         return 0;
 181                 }
 182                 brelse(bh);
 183         }
 184         if (pending)
 185                 err = set_radix_bit(&root->fs_info->pending_del_radix, blocknr);
 186         else
 187                 err = set_radix_bit(&root->fs_info->pinned_radix, blocknr);
 188         BUG_ON(err);
 189         return 0;
 190 }
 191
 192 /*
 193  * remove an extent from the root, returns 0 on success
 194  */
 195 static int __free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 196                          *root, u64 blocknr, u64 num_blocks, int pin)
 197 {
 198         struct btrfs_path path;
 199         struct btrfs_key key;
 200         struct btrfs_fs_info *info = root->fs_info;
 201         struct btrfs_root *extent_root = info->extent_root;
 202         int ret;
 203         struct btrfs_extent_item *ei;
 204         struct btrfs_key ins;
 205         u32 refs;
 206
 207         key.objectid = blocknr;
 208         key.flags = 0;
 209         btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
 210         key.offset = num_blocks;
 211
 212         find_free_extent(trans, root, 0, 0, (u64)-1, &ins);
 213         btrfs_init_path(&path);
 214         ret = btrfs_search_slot(trans, extent_root, &key, &path, -1, 1);
 215         if (ret) {
 216                 printk("failed to find %Lu\n", key.objectid);
 217                 btrfs_print_tree(extent_root, extent_root->node);
 218                 printk("failed to find %Lu\n", key.objectid);
 219                 BUG();
 220         }
 221         ei = btrfs_item_ptr(btrfs_buffer_leaf(path.nodes[0]), path.slots[0],
 222                             struct btrfs_extent_item);
 223         BUG_ON(ei->refs == 0);
 224         refs = btrfs_extent_refs(ei) - 1;
 225         btrfs_set_extent_refs(ei, refs);
 226         if (refs == 0) {
 227                 u64 super_blocks_used;
 228
 229                 if (pin) {
 230                         ret = pin_down_block(root, blocknr, 0);
 231                         BUG_ON(ret);
 232                 }
 233
 234                 super_blocks_used = btrfs_super_blocks_used(info->disk_super);
 235                 btrfs_set_super_blocks_used(info->disk_super,
 236                                             super_blocks_used - num_blocks);
 237                 ret = btrfs_del_item(trans, extent_root, &path);
 238                 if (extent_root->fs_info->last_insert.objectid > blocknr)
 239                         extent_root->fs_info->last_insert.objectid = blocknr;
 240                 if (ret)
 241                         BUG();
 242         }
 243         mark_buffer_dirty(path.nodes[0]);
 244         btrfs_release_path(extent_root, &path);
 245         finish_current_insert(trans, extent_root);
 246         return ret;
 247 }
 248
 249 /*
 250  * find all the blocks marked as pending in the radix tree and remove
 251  * them from the extent map
 252  */
 253 static int del_pending_extents(struct btrfs_trans_handle *trans, struct
 254                                btrfs_root *extent_root)
 255 {
 256         int ret;
 257         int wret;
 258         int err = 0;
 259         unsigned long gang[4];
 260         int i;
 261         struct radix_tree_root *pending_radix;
 262         struct radix_tree_root *pinned_radix;
 263
 264         pending_radix = &extent_root->fs_info->pending_del_radix;
 265         pinned_radix = &extent_root->fs_info->pinned_radix;
 266
 267         while(1) {
 268                 ret = find_first_radix_bit(pending_radix, gang,
 269                                            ARRAY_SIZE(gang));
 270                 if (!ret)
 271                         break;
 272                 for (i = 0; i < ret; i++) {
 273                         wret = set_radix_bit(pinned_radix, gang[i]);
 274                         BUG_ON(wret);
 275                         wret = clear_radix_bit(pending_radix, gang[i]);
 276                         BUG_ON(wret);
 277                         wret = __free_extent(trans, extent_root,
 278                                              gang[i], 1, 0);
 279                         if (wret)
 280                                 err = wret;
 281                 }
 282         }
 283         return err;
 284 }
 285
 286 /*
 287  * remove an extent from the root, returns 0 on success
 288  */
 289 int btrfs_free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 290                       *root, u64 blocknr, u64 num_blocks, int pin)
 291 {
 292         struct btrfs_root *extent_root = root->fs_info->extent_root;
 293         struct buffer_head *t;
 294         int pending_ret;
 295         int ret;
 296
 297         if (root == extent_root) {
 298                 t = find_tree_block(root, blocknr);
 299                 pin_down_block(root, blocknr, 1);
 300                 return 0;
 301         }
 302         ret = __free_extent(trans, root, blocknr, num_blocks, pin);
 303         pending_ret = del_pending_extents(trans, root->fs_info->extent_root);
 304         return ret ? ret : pending_ret;
 305 }
 306
 307 /*
 308  * walks the btree of allocated extents and find a hole of a given size.
 309  * The key ins is changed to record the hole:
 310  * ins->objectid == block start
 311  * ins->flags = BTRFS_EXTENT_ITEM_KEY
 312  * ins->offset == number of blocks
 313  * Any available blocks before search_start are skipped.
 314  */
 315 static int find_free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 316                             *orig_root, u64 num_blocks, u64 search_start, u64
 317                             search_end, struct btrfs_key *ins)
 318 {
 319         struct btrfs_path path;
 320         struct btrfs_key key;
 321         int ret;
 322         u64 hole_size = 0;
 323         int slot = 0;
 324         u64 last_block = 0;
 325         u64 test_block;
 326         int start_found;
 327         struct btrfs_leaf *l;
 328         struct btrfs_root * root = orig_root->fs_info->extent_root;
 329         int total_needed = num_blocks;
 330         int level;
 331
 332         level = btrfs_header_level(btrfs_buffer_header(root->node));
 333         total_needed += (level + 1) * 3;
 334         if (root->fs_info->last_insert.objectid > search_start)
 335                 search_start = root->fs_info->last_insert.objectid;
 336
 337         ins->flags = 0;
 338         btrfs_set_key_type(ins, BTRFS_EXTENT_ITEM_KEY);
 339
 340 check_failed:
 341         btrfs_init_path(&path);
 342         ins->objectid = search_start;
 343         ins->offset = 0;
 344         start_found = 0;
 345         ret = btrfs_search_slot(trans, root, ins, &path, 0, 0);
 346         if (ret < 0)
 347                 goto error;
 348
 349         if (path.slots[0] > 0)
 350                 path.slots[0]--;
 351
 352         while (1) {
 353                 l = btrfs_buffer_leaf(path.nodes[0]);
 354                 slot = path.slots[0];
 355                 if (slot >= btrfs_header_nritems(&l->header)) {
 356                         ret = btrfs_next_leaf(root, &path);
 357                         if (ret == 0)
 358                                 continue;
 359                         if (ret < 0)
 360                                 goto error;
 361                         if (!start_found) {
 362                                 ins->objectid = search_start;
 363                                 ins->offset = (u64)-1;
 364                                 start_found = 1;
 365                                 goto check_pending;
 366                         }
 367                         ins->objectid = last_block > search_start ?
 368                                         last_block : search_start;
 369                         ins->offset = (u64)-1;
 370                         goto check_pending;
 371                 }
 372                 btrfs_disk_key_to_cpu(&key, &l->items[slot].key);
 373                 if (key.objectid >= search_start) {
 374                         if (start_found) {
 375                                 if (last_block < search_start)
 376                                         last_block = search_start;
 377                                 hole_size = key.objectid - last_block;
 378                                 if (hole_size > total_needed) {
 379                                         ins->objectid = last_block;
 380                                         ins->offset = hole_size;
 381                                         goto check_pending;
 382                                 }
 383                         }
 384                 }
 385                 start_found = 1;
 386                 last_block = key.objectid + key.offset;
 387                 path.slots[0]++;
 388         }
 389         // FIXME -ENOSPC
 390 check_pending:
 391         /* we have to make sure we didn't find an extent that has already
 392          * been allocated by the map tree or the original allocation
 393          */
 394         btrfs_release_path(root, &path);
 395         BUG_ON(ins->objectid < search_start);
 396         for (test_block = ins->objectid;
 397              test_block < ins->objectid + total_needed; test_block++) {
 398                 if (test_radix_bit(&root->fs_info->pinned_radix,
 399                                       test_block)) {
 400                         search_start = test_block + 1;
 401                         goto check_failed;
 402                 }
 403         }
 404         BUG_ON(root->fs_info->current_insert.offset);
 405         root->fs_info->current_insert.offset = total_needed - num_blocks;
 406         root->fs_info->current_insert.objectid = ins->objectid + num_blocks;
 407         root->fs_info->current_insert.flags = 0;
 408         root->fs_info->last_insert.objectid = ins->objectid;
 409         ins->offset = num_blocks;
 410         return 0;
 411 error:
 412         btrfs_release_path(root, &path);
 413         return ret;
 414 }
 415
 416 /*
 417  * finds a free extent and does all the dirty work required for allocation
 418  * returns the key for the extent through ins, and a tree buffer for
 419  * the first block of the extent through buf.
 420  *
 421  * returns 0 if everything worked, non-zero otherwise.
 422  */
 423 int btrfs_alloc_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 424                         *root, u64 num_blocks, u64 search_start, u64
 425                         search_end, u64 owner, struct btrfs_key *ins)
 426 {
 427         int ret;
 428         int pending_ret;
 429         u64 super_blocks_used;
 430         struct btrfs_fs_info *info = root->fs_info;
 431         struct btrfs_root *extent_root = info->extent_root;
 432         struct btrfs_extent_item extent_item;
 433
 434         btrfs_set_extent_refs(&extent_item, 1);
 435         btrfs_set_extent_owner(&extent_item, owner);
 436
 437         if (root == extent_root) {
 438                 BUG_ON(extent_root->fs_info->current_insert.offset == 0);
 439                 BUG_ON(num_blocks != 1);
 440                 BUG_ON(extent_root->fs_info->current_insert.flags ==
 441                        extent_root->fs_info->current_insert.offset);
 442                 ins->offset = 1;
 443                 ins->objectid = extent_root->fs_info->current_insert.objectid +
 444                                 extent_root->fs_info->current_insert.flags++;
 445                 return 0;
 446         }
 447         ret = find_free_extent(trans, root, num_blocks, search_start,
 448                                search_end, ins);
 449         if (ret)
 450                 return ret;
 451
 452         super_blocks_used = btrfs_super_blocks_used(info->disk_super);
 453         btrfs_set_super_blocks_used(info->disk_super, super_blocks_used +
 454                                     num_blocks);
 455         ret = btrfs_insert_item(trans, extent_root, ins, &extent_item,
 456                                 sizeof(extent_item));
 457
 458         finish_current_insert(trans, extent_root);
 459         pending_ret = del_pending_extents(trans, extent_root);
 460         if (ret)
 461                 return ret;
 462         if (pending_ret)
 463                 return pending_ret;
 464         return 0;
 465 }
 466
 467 /*
 468  * helper function to allocate a block for a given tree
 469  * returns the tree buffer or NULL.
 470  */
 471 struct buffer_head *btrfs_alloc_free_block(struct btrfs_trans_handle *trans,
 472                                             struct btrfs_root *root)
 473 {
 474         struct btrfs_key ins;
 475         int ret;
 476         struct buffer_head *buf;
 477
 478         ret = btrfs_alloc_extent(trans, root, 1, 0, (unsigned long)-1,
 479                 btrfs_header_parentid(btrfs_buffer_header(root->node)), &ins);
 480         if (ret) {
 481                 BUG();
 482                 return NULL;
 483         }
 484         buf = find_tree_block(root, ins.objectid);
 485         set_buffer_uptodate(buf);
 486         return buf;
 487 }
 488
 489 static int drop_leaf_ref(struct btrfs_trans_handle *trans,
 490                          struct btrfs_root *root, struct buffer_head *cur)
 491 {
 492         struct btrfs_disk_key *key;
 493         struct btrfs_leaf *leaf;
 494         struct btrfs_file_extent_item *fi;
 495         int i;
 496         int nritems;
 497         int ret;
 498
 499         BUG_ON(!btrfs_is_leaf(btrfs_buffer_node(cur)));
 500         leaf = btrfs_buffer_leaf(cur);
 501         nritems = btrfs_header_nritems(&leaf->header);
 502         for (i = 0; i < nritems; i++) {
 503                 key = &leaf->items[i].key;
 504                 if (btrfs_disk_key_type(key) != BTRFS_EXTENT_DATA_KEY)
 505                         continue;
 506                 fi = btrfs_item_ptr(leaf, i, struct btrfs_file_extent_item);
 507                 /*
 508                  * FIXME make sure to insert a trans record that
 509                  * repeats the snapshot del on crash
 510                  */
 511                 ret = btrfs_free_extent(trans, root,
 512                                         btrfs_file_extent_disk_blocknr(fi),
 513                                         btrfs_file_extent_disk_num_blocks(fi),
 514                                         0);
 515                 BUG_ON(ret);
 516         }
 517         return 0;
 518 }
 519
 520 /*
 521  * helper function for drop_snapshot, this walks down the tree dropping ref
 522  * counts as it goes.
 523  */
 524 static int walk_down_tree(struct btrfs_trans_handle *trans, struct btrfs_root
 525                           *root, struct btrfs_path *path, int *level)
 526 {
 527         struct buffer_head *next;
 528         struct buffer_head *cur;
 529         u64 blocknr;
 530         int ret;
 531         u32 refs;
 532
 533         ret = lookup_block_ref(trans, root, path->nodes[*level]->b_blocknr,
 534                                1, &refs);
 535         BUG_ON(ret);
 536         if (refs > 1)
 537                 goto out;
 538         /*
 539          * walk down to the last node level and free all the leaves
 540          */
 541         while(*level >= 0) {
 542                 cur = path->nodes[*level];
 543                 if (path->slots[*level] >=
 544                     btrfs_header_nritems(btrfs_buffer_header(cur)))
 545                         break;
 546                 if (*level == 0) {
 547                         ret = drop_leaf_ref(trans, root, cur);
 548                         BUG_ON(ret);
 549                         break;
 550                 }
 551                 blocknr = btrfs_node_blockptr(btrfs_buffer_node(cur),
 552                                               path->slots[*level]);
 553                 ret = lookup_block_ref(trans, root, blocknr, 1, &refs);
 554                 BUG_ON(ret);
 555                 if (refs != 1) {
 556                         path->slots[*level]++;
 557                         ret = btrfs_free_extent(trans, root, blocknr, 1, 1);
 558                         BUG_ON(ret);
 559                         continue;
 560                 }
 561                 next = read_tree_block(root, blocknr);
 562                 if (path->nodes[*level-1])
 563                         btrfs_block_release(root, path->nodes[*level-1]);
 564                 path->nodes[*level-1] = next;
 565                 *level = btrfs_header_level(btrfs_buffer_header(next));
 566                 path->slots[*level] = 0;
 567         }
 568 out:
 569         ret = btrfs_free_extent(trans, root,
 570                                 path->nodes[*level]->b_blocknr, 1, 1);
 571         btrfs_block_release(root, path->nodes[*level]);
 572         path->nodes[*level] = NULL;
 573         *level += 1;
 574         BUG_ON(ret);
 575         return 0;
 576 }
 577
 578 /*
 579  * helper for dropping snapshots.  This walks back up the tree in the path
 580  * to find the first node higher up where we haven't yet gone through
 581  * all the slots
 582  */
 583 static int walk_up_tree(struct btrfs_trans_handle *trans, struct btrfs_root
 584                         *root, struct btrfs_path *path, int *level)
 585 {
 586         int i;
 587         int slot;
 588         int ret;
 589         for(i = *level; i < BTRFS_MAX_LEVEL - 1 && path->nodes[i]; i++) {
 590                 slot = path->slots[i];
 591                 if (slot < btrfs_header_nritems(
 592                     btrfs_buffer_header(path->nodes[i])) - 1) {
 593                         path->slots[i]++;
 594                         *level = i;
 595                         return 0;
 596                 } else {
 597                         ret = btrfs_free_extent(trans, root,
 598                                                 path->nodes[*level]->b_blocknr,
 599                                                 1, 1);
 600                         BUG_ON(ret);
 601                         btrfs_block_release(root, path->nodes[*level]);
 602                         path->nodes[*level] = NULL;
 603                         *level = i + 1;
 604                 }
 605         }
 606         return 1;
 607 }
 608
 609 /*
 610  * drop the reference count on the tree rooted at 'snap'.  This traverses
 611  * the tree freeing any blocks that have a ref count of zero after being
 612  * decremented.
 613  */
 614 int btrfs_drop_snapshot(struct btrfs_trans_handle *trans, struct btrfs_root
 615                         *root, struct buffer_head *snap)
 616 {
 617         int ret = 0;
 618         int wret;
 619         int level;
 620         struct btrfs_path path;
 621         int i;
 622         int orig_level;
 623
 624         btrfs_init_path(&path);
 625
 626         level = btrfs_header_level(btrfs_buffer_header(snap));
 627         orig_level = level;
 628         path.nodes[level] = snap;
 629         path.slots[level] = 0;
 630         while(1) {
 631                 wret = walk_down_tree(trans, root, &path, &level);
 632                 if (wret > 0)
 633                         break;
 634                 if (wret < 0)
 635                         ret = wret;
 636
 637                 wret = walk_up_tree(trans, root, &path, &level);
 638                 if (wret > 0)
 639                         break;
 640                 if (wret < 0)
 641                         ret = wret;
 642         }
 643         for (i = 0; i <= orig_level; i++) {
 644                 if (path.nodes[i]) {
 645                         btrfs_block_release(root, path.nodes[i]);
 646                 }
 647         }
 648         return ret;
 649 }