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         path = btrfs_alloc_path();
  29         BUG_ON(!path);
  30         btrfs_init_path(path);
  31         key.objectid = blocknr;
  32         key.flags = 0;
  33         btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
  34         key.offset = num_blocks;
  35         ret = btrfs_search_slot(trans, root->fs_info->extent_root, &key, path,
  36                                 0, 1);
  37         if (ret != 0)
  38                 BUG();
  39         BUG_ON(ret != 0);
  40         l = btrfs_buffer_leaf(path->nodes[0]);
  41         item = btrfs_item_ptr(l, path->slots[0], struct btrfs_extent_item);
  42         refs = btrfs_extent_refs(item);
  43         btrfs_set_extent_refs(item, refs + 1);
  44         btrfs_mark_buffer_dirty(path->nodes[0]);
  45
  46         btrfs_release_path(root->fs_info->extent_root, path);
  47         btrfs_free_path(path);
  48         finish_current_insert(trans, root->fs_info->extent_root);
  49         del_pending_extents(trans, root->fs_info->extent_root);
  50         return 0;
  51 }
  52
  53 static int lookup_block_ref(struct btrfs_trans_handle *trans, struct btrfs_root
  54                             *root, u64 blocknr, u64 num_blocks, u32 *refs)
  55 {
  56         struct btrfs_path *path;
  57         int ret;
  58         struct btrfs_key key;
  59         struct btrfs_leaf *l;
  60         struct btrfs_extent_item *item;
  61
  62         path = btrfs_alloc_path();
  63         btrfs_init_path(path);
  64         key.objectid = blocknr;
  65         key.offset = num_blocks;
  66         key.flags = 0;
  67         btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
  68         ret = btrfs_search_slot(trans, root->fs_info->extent_root, &key, path,
  69                                 0, 0);
  70         if (ret != 0)
  71                 BUG();
  72         l = btrfs_buffer_leaf(path->nodes[0]);
  73         item = btrfs_item_ptr(l, path->slots[0], struct btrfs_extent_item);
  74         *refs = btrfs_extent_refs(item);
  75         btrfs_release_path(root->fs_info->extent_root, path);
  76         btrfs_free_path(path);
  77         return 0;
  78 }
  79
  80 int btrfs_inc_ref(struct btrfs_trans_handle *trans, struct btrfs_root *root,
  81                   struct buffer_head *buf)
  82 {
  83         u64 blocknr;
  84         struct btrfs_node *buf_node;
  85         struct btrfs_leaf *buf_leaf;
  86         struct btrfs_disk_key *key;
  87         struct btrfs_file_extent_item *fi;
  88         int i;
  89         int leaf;
  90         int ret;
  91
  92         if (!root->ref_cows)
  93                 return 0;
  94         buf_node = btrfs_buffer_node(buf);
  95         leaf = btrfs_is_leaf(buf_node);
  96         buf_leaf = btrfs_buffer_leaf(buf);
  97         for (i = 0; i < btrfs_header_nritems(&buf_node->header); i++) {
  98                 if (leaf) {
  99                         key = &buf_leaf->items[i].key;
 100                         if (btrfs_disk_key_type(key) != BTRFS_EXTENT_DATA_KEY)
 101                                 continue;
 102                         fi = btrfs_item_ptr(buf_leaf, i,
 103                                             struct btrfs_file_extent_item);
 104                         ret = inc_block_ref(trans, root,
 105                                     btrfs_file_extent_disk_blocknr(fi),
 106                                     btrfs_file_extent_disk_num_blocks(fi));
 107                         BUG_ON(ret);
 108                 } else {
 109                         blocknr = btrfs_node_blockptr(buf_node, i);
 110                         ret = inc_block_ref(trans, root, blocknr, 1);
 111                         BUG_ON(ret);
 112                 }
 113         }
 114         return 0;
 115 }
 116
 117 int btrfs_finish_extent_commit(struct btrfs_trans_handle *trans, struct
 118                                btrfs_root *root)
 119 {
 120         unsigned long gang[8];
 121         u64 first = 0;
 122         int ret;
 123         int i;
 124         struct radix_tree_root *pinned_radix = &root->fs_info->pinned_radix;
 125
 126         while(1) {
 127                 ret = find_first_radix_bit(pinned_radix, gang,
 128                                            ARRAY_SIZE(gang));
 129                 if (!ret)
 130                         break;
 131                 if (!first)
 132                         first = gang[0];
 133                 for (i = 0; i < ret; i++) {
 134                         clear_radix_bit(pinned_radix, gang[i]);
 135                 }
 136         }
 137         if (root->fs_info->last_insert.objectid > first)
 138                 root->fs_info->last_insert.objectid = first;
 139         root->fs_info->last_insert.offset = 0;
 140         return 0;
 141 }
 142
 143 static int finish_current_insert(struct btrfs_trans_handle *trans, struct
 144                                  btrfs_root *extent_root)
 145 {
 146         struct btrfs_key ins;
 147         struct btrfs_extent_item extent_item;
 148         int i;
 149         int ret;
 150         u64 super_blocks_used;
 151         struct btrfs_fs_info *info = extent_root->fs_info;
 152
 153         btrfs_set_extent_refs(&extent_item, 1);
 154         btrfs_set_extent_owner(&extent_item,
 155                 btrfs_header_parentid(btrfs_buffer_header(extent_root->node)));
 156         ins.offset = 1;
 157         ins.flags = 0;
 158         btrfs_set_key_type(&ins, BTRFS_EXTENT_ITEM_KEY);
 159
 160         for (i = 0; i < extent_root->fs_info->current_insert.flags; i++) {
 161                 ins.objectid = extent_root->fs_info->current_insert.objectid +
 162                                 i;
 163                 super_blocks_used = btrfs_super_blocks_used(info->disk_super);
 164                 btrfs_set_super_blocks_used(info->disk_super,
 165                                             super_blocks_used + 1);
 166                 ret = btrfs_insert_item(trans, extent_root, &ins, &extent_item,
 167                                         sizeof(extent_item));
 168                 BUG_ON(ret);
 169         }
 170         extent_root->fs_info->current_insert.offset = 0;
 171         return 0;
 172 }
 173
 174 static int pin_down_block(struct btrfs_root *root, u64 blocknr, int pending)
 175 {
 176         int err;
 177         struct btrfs_header *header;
 178         struct buffer_head *bh;
 179
 180         if (!pending) {
 181                 bh = btrfs_find_tree_block(root, blocknr);
 182                 if (bh) {
 183                         if (buffer_uptodate(bh)) {
 184                                 u64 transid =
 185                                     root->fs_info->running_transaction->transid;
 186                                 header = btrfs_buffer_header(bh);
 187                                 if (btrfs_header_generation(header) ==
 188                                     transid) {
 189                                         btrfs_block_release(root, bh);
 190                                         return 0;
 191                                 }
 192                         }
 193                         btrfs_block_release(root, bh);
 194                 }
 195                 err = set_radix_bit(&root->fs_info->pinned_radix, blocknr);
 196         } else {
 197                 err = set_radix_bit(&root->fs_info->pending_del_radix, blocknr);
 198         }
 199         BUG_ON(err);
 200         return 0;
 201 }
 202
 203 /*
 204  * remove an extent from the root, returns 0 on success
 205  */
 206 static int __free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 207                          *root, u64 blocknr, u64 num_blocks, int pin)
 208 {
 209         struct btrfs_path *path;
 210         struct btrfs_key key;
 211         struct btrfs_fs_info *info = root->fs_info;
 212         struct btrfs_root *extent_root = info->extent_root;
 213         int ret;
 214         struct btrfs_extent_item *ei;
 215         struct btrfs_key ins;
 216         u32 refs;
 217
 218         key.objectid = blocknr;
 219         key.flags = 0;
 220         btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
 221         key.offset = num_blocks;
 222
 223         find_free_extent(trans, root, 0, 0, (u64)-1, &ins);
 224         path = btrfs_alloc_path();
 225         BUG_ON(!path);
 226         btrfs_init_path(path);
 227         ret = btrfs_search_slot(trans, extent_root, &key, path, -1, 1);
 228         if (ret) {
 229                 printk("failed to find %Lu\n", key.objectid);
 230                 btrfs_print_tree(extent_root, extent_root->node);
 231                 printk("failed to find %Lu\n", key.objectid);
 232                 BUG();
 233         }
 234         ei = btrfs_item_ptr(btrfs_buffer_leaf(path->nodes[0]), path->slots[0],
 235                             struct btrfs_extent_item);
 236         BUG_ON(ei->refs == 0);
 237         refs = btrfs_extent_refs(ei) - 1;
 238         btrfs_set_extent_refs(ei, refs);
 239         btrfs_mark_buffer_dirty(path->nodes[0]);
 240         if (refs == 0) {
 241                 u64 super_blocks_used;
 242
 243                 if (pin) {
 244                         ret = pin_down_block(root, blocknr, 0);
 245                         BUG_ON(ret);
 246                 }
 247
 248                 super_blocks_used = btrfs_super_blocks_used(info->disk_super);
 249                 btrfs_set_super_blocks_used(info->disk_super,
 250                                             super_blocks_used - num_blocks);
 251                 ret = btrfs_del_item(trans, extent_root, path);
 252                 if (ret)
 253                         BUG();
 254         }
 255         btrfs_release_path(extent_root, path);
 256         btrfs_free_path(path);
 257         finish_current_insert(trans, extent_root);
 258         return ret;
 259 }
 260
 261 /*
 262  * find all the blocks marked as pending in the radix tree and remove
 263  * them from the extent map
 264  */
 265 static int del_pending_extents(struct btrfs_trans_handle *trans, struct
 266                                btrfs_root *extent_root)
 267 {
 268         int ret;
 269         int wret;
 270         int err = 0;
 271         unsigned long gang[4];
 272         int i;
 273         struct radix_tree_root *pending_radix;
 274         struct radix_tree_root *pinned_radix;
 275
 276         pending_radix = &extent_root->fs_info->pending_del_radix;
 277         pinned_radix = &extent_root->fs_info->pinned_radix;
 278
 279         while(1) {
 280                 ret = find_first_radix_bit(pending_radix, gang,
 281                                            ARRAY_SIZE(gang));
 282                 if (!ret)
 283                         break;
 284                 for (i = 0; i < ret; i++) {
 285                         wret = set_radix_bit(pinned_radix, gang[i]);
 286                         BUG_ON(wret);
 287                         wret = clear_radix_bit(pending_radix, gang[i]);
 288                         BUG_ON(wret);
 289                         wret = __free_extent(trans, extent_root,
 290                                              gang[i], 1, 0);
 291                         if (wret)
 292                                 err = wret;
 293                 }
 294         }
 295         return err;
 296 }
 297
 298 /*
 299  * remove an extent from the root, returns 0 on success
 300  */
 301 int btrfs_free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 302                       *root, u64 blocknr, u64 num_blocks, int pin)
 303 {
 304         struct btrfs_root *extent_root = root->fs_info->extent_root;
 305         int pending_ret;
 306         int ret;
 307
 308         if (root == extent_root) {
 309                 pin_down_block(root, blocknr, 1);
 310                 return 0;
 311         }
 312         ret = __free_extent(trans, root, blocknr, num_blocks, pin);
 313         pending_ret = del_pending_extents(trans, root->fs_info->extent_root);
 314         return ret ? ret : pending_ret;
 315 }
 316
 317 /*
 318  * walks the btree of allocated extents and find a hole of a given size.
 319  * The key ins is changed to record the hole:
 320  * ins->objectid == block start
 321  * ins->flags = BTRFS_EXTENT_ITEM_KEY
 322  * ins->offset == number of blocks
 323  * Any available blocks before search_start are skipped.
 324  */
 325 static int find_free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 326                             *orig_root, u64 num_blocks, u64 search_start, u64
 327                             search_end, struct btrfs_key *ins)
 328 {
 329         struct btrfs_path *path;
 330         struct btrfs_key key;
 331         int ret;
 332         u64 hole_size = 0;
 333         int slot = 0;
 334         u64 last_block = 0;
 335         u64 test_block;
 336         int start_found;
 337         struct btrfs_leaf *l;
 338         struct btrfs_root * root = orig_root->fs_info->extent_root;
 339         int total_needed = num_blocks;
 340         int level;
 341
 342         level = btrfs_header_level(btrfs_buffer_header(root->node));
 343         total_needed += (level + 1) * 3;
 344         if (root->fs_info->last_insert.objectid > search_start)
 345                 search_start = root->fs_info->last_insert.objectid;
 346
 347         ins->flags = 0;
 348         btrfs_set_key_type(ins, BTRFS_EXTENT_ITEM_KEY);
 349         path = btrfs_alloc_path();
 350
 351 check_failed:
 352         btrfs_init_path(path);
 353         ins->objectid = search_start;
 354         ins->offset = 0;
 355         start_found = 0;
 356         ret = btrfs_search_slot(trans, root, ins, path, 0, 0);
 357         if (ret < 0)
 358                 goto error;
 359
 360         if (path->slots[0] > 0)
 361                 path->slots[0]--;
 362
 363         while (1) {
 364                 l = btrfs_buffer_leaf(path->nodes[0]);
 365                 slot = path->slots[0];
 366                 if (slot >= btrfs_header_nritems(&l->header)) {
 367                         ret = btrfs_next_leaf(root, path);
 368                         if (ret == 0)
 369                                 continue;
 370                         if (ret < 0)
 371                                 goto error;
 372                         if (!start_found) {
 373                                 ins->objectid = search_start;
 374                                 ins->offset = (u64)-1;
 375                                 start_found = 1;
 376                                 goto check_pending;
 377                         }
 378                         ins->objectid = last_block > search_start ?
 379                                         last_block : search_start;
 380                         ins->offset = (u64)-1;
 381                         goto check_pending;
 382                 }
 383                 btrfs_disk_key_to_cpu(&key, &l->items[slot].key);
 384                 if (key.objectid >= search_start) {
 385                         if (start_found) {
 386                                 if (last_block < search_start)
 387                                         last_block = search_start;
 388                                 hole_size = key.objectid - last_block;
 389                                 if (hole_size > total_needed) {
 390                                         ins->objectid = last_block;
 391                                         ins->offset = hole_size;
 392                                         goto check_pending;
 393                                 }
 394                         }
 395                 }
 396                 start_found = 1;
 397                 last_block = key.objectid + key.offset;
 398                 path->slots[0]++;
 399         }
 400         // FIXME -ENOSPC
 401 check_pending:
 402         /* we have to make sure we didn't find an extent that has already
 403          * been allocated by the map tree or the original allocation
 404          */
 405         btrfs_release_path(root, path);
 406         BUG_ON(ins->objectid < search_start);
 407         for (test_block = ins->objectid;
 408              test_block < ins->objectid + total_needed; test_block++) {
 409                 if (test_radix_bit(&root->fs_info->pinned_radix,
 410                                       test_block)) {
 411                         search_start = test_block + 1;
 412                         goto check_failed;
 413                 }
 414         }
 415         BUG_ON(root->fs_info->current_insert.offset);
 416         root->fs_info->current_insert.offset = total_needed - num_blocks;
 417         root->fs_info->current_insert.objectid = ins->objectid + num_blocks;
 418         root->fs_info->current_insert.flags = 0;
 419         root->fs_info->last_insert.objectid = ins->objectid;
 420         ins->offset = num_blocks;
 421         btrfs_free_path(path);
 422         return 0;
 423 error:
 424         btrfs_release_path(root, path);
 425         btrfs_free_path(path);
 426         return ret;
 427 }
 428
 429 /*
 430  * finds a free extent and does all the dirty work required for allocation
 431  * returns the key for the extent through ins, and a tree buffer for
 432  * the first block of the extent through buf.
 433  *
 434  * returns 0 if everything worked, non-zero otherwise.
 435  */
 436 int btrfs_alloc_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 437                         *root, u64 num_blocks, u64 search_start, u64
 438                         search_end, u64 owner, struct btrfs_key *ins)
 439 {
 440         int ret;
 441         int pending_ret;
 442         u64 super_blocks_used;
 443         struct btrfs_fs_info *info = root->fs_info;
 444         struct btrfs_root *extent_root = info->extent_root;
 445         struct btrfs_extent_item extent_item;
 446
 447         btrfs_set_extent_refs(&extent_item, 1);
 448         btrfs_set_extent_owner(&extent_item, owner);
 449
 450         if (root == extent_root) {
 451                 BUG_ON(extent_root->fs_info->current_insert.offset == 0);
 452                 BUG_ON(num_blocks != 1);
 453                 BUG_ON(extent_root->fs_info->current_insert.flags ==
 454                        extent_root->fs_info->current_insert.offset);
 455                 ins->offset = 1;
 456                 ins->objectid = extent_root->fs_info->current_insert.objectid +
 457                                 extent_root->fs_info->current_insert.flags++;
 458                 return 0;
 459         }
 460         ret = find_free_extent(trans, root, num_blocks, search_start,
 461                                search_end, ins);
 462         if (ret)
 463                 return ret;
 464
 465         super_blocks_used = btrfs_super_blocks_used(info->disk_super);
 466         btrfs_set_super_blocks_used(info->disk_super, super_blocks_used +
 467                                     num_blocks);
 468         ret = btrfs_insert_item(trans, extent_root, ins, &extent_item,
 469                                 sizeof(extent_item));
 470
 471         finish_current_insert(trans, extent_root);
 472         pending_ret = del_pending_extents(trans, extent_root);
 473         if (ret)
 474                 return ret;
 475         if (pending_ret)
 476                 return pending_ret;
 477         return 0;
 478 }
 479
 480 /*
 481  * helper function to allocate a block for a given tree
 482  * returns the tree buffer or NULL.
 483  */
 484 struct buffer_head *btrfs_alloc_free_block(struct btrfs_trans_handle *trans,
 485                                             struct btrfs_root *root)
 486 {
 487         struct btrfs_key ins;
 488         int ret;
 489         struct buffer_head *buf;
 490
 491         ret = btrfs_alloc_extent(trans, root, 1, 0, (unsigned long)-1,
 492                 btrfs_header_parentid(btrfs_buffer_header(root->node)), &ins);
 493         if (ret) {
 494                 BUG();
 495                 return NULL;
 496         }
 497         buf = btrfs_find_create_tree_block(root, ins.objectid);
 498         set_buffer_uptodate(buf);
 499         return buf;
 500 }
 501
 502 static int drop_leaf_ref(struct btrfs_trans_handle *trans,
 503                          struct btrfs_root *root, struct buffer_head *cur)
 504 {
 505         struct btrfs_disk_key *key;
 506         struct btrfs_leaf *leaf;
 507         struct btrfs_file_extent_item *fi;
 508         int i;
 509         int nritems;
 510         int ret;
 511
 512         BUG_ON(!btrfs_is_leaf(btrfs_buffer_node(cur)));
 513         leaf = btrfs_buffer_leaf(cur);
 514         nritems = btrfs_header_nritems(&leaf->header);
 515         for (i = 0; i < nritems; i++) {
 516                 key = &leaf->items[i].key;
 517                 if (btrfs_disk_key_type(key) != BTRFS_EXTENT_DATA_KEY)
 518                         continue;
 519                 fi = btrfs_item_ptr(leaf, i, struct btrfs_file_extent_item);
 520                 /*
 521                  * FIXME make sure to insert a trans record that
 522                  * repeats the snapshot del on crash
 523                  */
 524                 ret = btrfs_free_extent(trans, root,
 525                                         btrfs_file_extent_disk_blocknr(fi),
 526                                         btrfs_file_extent_disk_num_blocks(fi),
 527                                         0);
 528                 BUG_ON(ret);
 529         }
 530         return 0;
 531 }
 532
 533 /*
 534  * helper function for drop_snapshot, this walks down the tree dropping ref
 535  * counts as it goes.
 536  */
 537 static int walk_down_tree(struct btrfs_trans_handle *trans, struct btrfs_root
 538                           *root, struct btrfs_path *path, int *level)
 539 {
 540         struct buffer_head *next;
 541         struct buffer_head *cur;
 542         u64 blocknr;
 543         int ret;
 544         u32 refs;
 545
 546         WARN_ON(*level < 0);
 547         WARN_ON(*level >= BTRFS_MAX_LEVEL);
 548         ret = lookup_block_ref(trans, root, path->nodes[*level]->b_blocknr,
 549                                1, &refs);
 550         BUG_ON(ret);
 551         if (refs > 1)
 552                 goto out;
 553         /*
 554          * walk down to the last node level and free all the leaves
 555          */
 556         while(*level >= 0) {
 557                 WARN_ON(*level < 0);
 558                 WARN_ON(*level >= BTRFS_MAX_LEVEL);
 559                 cur = path->nodes[*level];
 560                 if (btrfs_header_level(btrfs_buffer_header(cur)) != *level)
 561                         WARN_ON(1);
 562                 if (path->slots[*level] >=
 563                     btrfs_header_nritems(btrfs_buffer_header(cur)))
 564                         break;
 565                 if (*level == 0) {
 566                         ret = drop_leaf_ref(trans, root, cur);
 567                         BUG_ON(ret);
 568                         break;
 569                 }
 570                 blocknr = btrfs_node_blockptr(btrfs_buffer_node(cur),
 571                                               path->slots[*level]);
 572                 ret = lookup_block_ref(trans, root, blocknr, 1, &refs);
 573                 BUG_ON(ret);
 574                 if (refs != 1) {
 575                         path->slots[*level]++;
 576                         ret = btrfs_free_extent(trans, root, blocknr, 1, 1);
 577                         BUG_ON(ret);
 578                         continue;
 579                 }
 580                 next = read_tree_block(root, blocknr);
 581                 WARN_ON(*level <= 0);
 582                 if (path->nodes[*level-1])
 583                         btrfs_block_release(root, path->nodes[*level-1]);
 584                 path->nodes[*level-1] = next;
 585                 *level = btrfs_header_level(btrfs_buffer_header(next));
 586                 path->slots[*level] = 0;
 587         }
 588 out:
 589         WARN_ON(*level < 0);
 590         WARN_ON(*level >= BTRFS_MAX_LEVEL);
 591         ret = btrfs_free_extent(trans, root,
 592                                 path->nodes[*level]->b_blocknr, 1, 1);
 593         btrfs_block_release(root, path->nodes[*level]);
 594         path->nodes[*level] = NULL;
 595         *level += 1;
 596         BUG_ON(ret);
 597         return 0;
 598 }
 599
 600 /*
 601  * helper for dropping snapshots.  This walks back up the tree in the path
 602  * to find the first node higher up where we haven't yet gone through
 603  * all the slots
 604  */
 605 static int walk_up_tree(struct btrfs_trans_handle *trans, struct btrfs_root
 606                         *root, struct btrfs_path *path, int *level)
 607 {
 608         int i;
 609         int slot;
 610         int ret;
 611         for(i = *level; i < BTRFS_MAX_LEVEL - 1 && path->nodes[i]; i++) {
 612                 slot = path->slots[i];
 613                 if (slot < btrfs_header_nritems(
 614                     btrfs_buffer_header(path->nodes[i])) - 1) {
 615                         path->slots[i]++;
 616                         *level = i;
 617                         return 0;
 618                 } else {
 619                         ret = btrfs_free_extent(trans, root,
 620                                                 path->nodes[*level]->b_blocknr,
 621                                                 1, 1);
 622                         BUG_ON(ret);
 623                         btrfs_block_release(root, path->nodes[*level]);
 624                         path->nodes[*level] = NULL;
 625                         *level = i + 1;
 626                 }
 627         }
 628         return 1;
 629 }
 630
 631 /*
 632  * drop the reference count on the tree rooted at 'snap'.  This traverses
 633  * the tree freeing any blocks that have a ref count of zero after being
 634  * decremented.
 635  */
 636 int btrfs_drop_snapshot(struct btrfs_trans_handle *trans, struct btrfs_root
 637                         *root, struct buffer_head *snap)
 638 {
 639         int ret = 0;
 640         int wret;
 641         int level;
 642         struct btrfs_path *path;
 643         int i;
 644         int orig_level;
 645
 646         path = btrfs_alloc_path();
 647         BUG_ON(!path);
 648         btrfs_init_path(path);
 649
 650         level = btrfs_header_level(btrfs_buffer_header(snap));
 651         orig_level = level;
 652         path->nodes[level] = snap;
 653         path->slots[level] = 0;
 654         while(1) {
 655                 wret = walk_down_tree(trans, root, path, &level);
 656                 if (wret > 0)
 657                         break;
 658                 if (wret < 0)
 659                         ret = wret;
 660
 661                 wret = walk_up_tree(trans, root, path, &level);
 662                 if (wret > 0)
 663                         break;
 664                 if (wret < 0)
 665                         ret = wret;
 666         }
 667         for (i = 0; i <= orig_level; i++) {
 668                 if (path->nodes[i]) {
 669                         btrfs_block_release(root, path->nodes[i]);
 670                 }
 671         }
 672         btrfs_free_path(path);
 673         return ret;
 674 }