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 int btrfs_inc_extent_ref(struct btrfs_trans_handle *trans,
  16                                 struct btrfs_root *root,
  17                                 u64 blocknr, u64 num_blocks)
  18 {
  19         struct btrfs_path *path;
  20         int ret;
  21         struct btrfs_key key;
  22         struct btrfs_leaf *l;
  23         struct btrfs_extent_item *item;
  24         struct btrfs_key ins;
  25         u32 refs;
  26
  27         find_free_extent(trans, root->fs_info->extent_root, 0, 0, (u64)-1,
  28                          &ins);
  29         path = btrfs_alloc_path();
  30         BUG_ON(!path);
  31         btrfs_init_path(path);
  32         key.objectid = blocknr;
  33         key.flags = 0;
  34         btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
  35         key.offset = num_blocks;
  36         ret = btrfs_search_slot(trans, root->fs_info->extent_root, &key, path,
  37                                 0, 1);
  38         if (ret != 0) {
  39 printk("can't find block %Lu %Lu\n", blocknr, num_blocks);
  40                 BUG();
  41         }
  42         BUG_ON(ret != 0);
  43         l = btrfs_buffer_leaf(path->nodes[0]);
  44         item = btrfs_item_ptr(l, path->slots[0], struct btrfs_extent_item);
  45         refs = btrfs_extent_refs(item);
  46         btrfs_set_extent_refs(item, refs + 1);
  47         btrfs_mark_buffer_dirty(path->nodes[0]);
  48
  49         btrfs_release_path(root->fs_info->extent_root, path);
  50         btrfs_free_path(path);
  51         finish_current_insert(trans, root->fs_info->extent_root);
  52         del_pending_extents(trans, root->fs_info->extent_root);
  53         return 0;
  54 }
  55
  56 static int lookup_extent_ref(struct btrfs_trans_handle *trans,
  57                              struct btrfs_root *root, u64 blocknr,
  58                              u64 num_blocks, u32 *refs)
  59 {
  60         struct btrfs_path *path;
  61         int ret;
  62         struct btrfs_key key;
  63         struct btrfs_leaf *l;
  64         struct btrfs_extent_item *item;
  65
  66         path = btrfs_alloc_path();
  67         btrfs_init_path(path);
  68         key.objectid = blocknr;
  69         key.offset = num_blocks;
  70         key.flags = 0;
  71         btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
  72         ret = btrfs_search_slot(trans, root->fs_info->extent_root, &key, path,
  73                                 0, 0);
  74         if (ret != 0)
  75                 BUG();
  76         l = btrfs_buffer_leaf(path->nodes[0]);
  77         item = btrfs_item_ptr(l, path->slots[0], struct btrfs_extent_item);
  78         *refs = btrfs_extent_refs(item);
  79         btrfs_release_path(root->fs_info->extent_root, path);
  80         btrfs_free_path(path);
  81         return 0;
  82 }
  83
  84 int btrfs_inc_root_ref(struct btrfs_trans_handle *trans,
  85                        struct btrfs_root *root)
  86 {
  87         return btrfs_inc_extent_ref(trans, root, bh_blocknr(root->node), 1);
  88 }
  89
  90 int btrfs_inc_ref(struct btrfs_trans_handle *trans, struct btrfs_root *root,
  91                   struct buffer_head *buf)
  92 {
  93         u64 blocknr;
  94         struct btrfs_node *buf_node;
  95         struct btrfs_leaf *buf_leaf;
  96         struct btrfs_disk_key *key;
  97         struct btrfs_file_extent_item *fi;
  98         int i;
  99         int leaf;
 100         int ret;
 101
 102         if (!root->ref_cows)
 103                 return 0;
 104         buf_node = btrfs_buffer_node(buf);
 105         leaf = btrfs_is_leaf(buf_node);
 106         buf_leaf = btrfs_buffer_leaf(buf);
 107         for (i = 0; i < btrfs_header_nritems(&buf_node->header); i++) {
 108                 if (leaf) {
 109                         key = &buf_leaf->items[i].key;
 110                         if (btrfs_disk_key_type(key) != BTRFS_EXTENT_DATA_KEY)
 111                                 continue;
 112                         fi = btrfs_item_ptr(buf_leaf, i,
 113                                             struct btrfs_file_extent_item);
 114                         if (btrfs_file_extent_type(fi) ==
 115                             BTRFS_FILE_EXTENT_INLINE)
 116                                 continue;
 117                         ret = btrfs_inc_extent_ref(trans, root,
 118                                     btrfs_file_extent_disk_blocknr(fi),
 119                                     btrfs_file_extent_disk_num_blocks(fi));
 120                         BUG_ON(ret);
 121                 } else {
 122                         blocknr = btrfs_node_blockptr(buf_node, i);
 123                         ret = btrfs_inc_extent_ref(trans, root, blocknr, 1);
 124                         BUG_ON(ret);
 125                 }
 126         }
 127         return 0;
 128 }
 129
 130 int btrfs_finish_extent_commit(struct btrfs_trans_handle *trans, struct
 131                                btrfs_root *root)
 132 {
 133         unsigned long gang[8];
 134         u64 first = 0;
 135         int ret;
 136         int i;
 137         struct radix_tree_root *pinned_radix = &root->fs_info->pinned_radix;
 138
 139         while(1) {
 140                 ret = find_first_radix_bit(pinned_radix, gang,
 141                                            ARRAY_SIZE(gang));
 142                 if (!ret)
 143                         break;
 144                 if (!first)
 145                         first = gang[0];
 146                 for (i = 0; i < ret; i++) {
 147                         clear_radix_bit(pinned_radix, gang[i]);
 148                 }
 149         }
 150         if (root->fs_info->last_insert.objectid > first)
 151                 root->fs_info->last_insert.objectid = first;
 152         root->fs_info->last_insert.offset = 0;
 153         return 0;
 154 }
 155
 156 static int finish_current_insert(struct btrfs_trans_handle *trans, struct
 157                                  btrfs_root *extent_root)
 158 {
 159         struct btrfs_key ins;
 160         struct btrfs_extent_item extent_item;
 161         int i;
 162         int ret;
 163         u64 super_blocks_used;
 164         struct btrfs_fs_info *info = extent_root->fs_info;
 165
 166         btrfs_set_extent_refs(&extent_item, 1);
 167         ins.offset = 1;
 168         ins.flags = 0;
 169         btrfs_set_key_type(&ins, BTRFS_EXTENT_ITEM_KEY);
 170
 171         for (i = 0; i < extent_root->fs_info->current_insert.flags; i++) {
 172                 ins.objectid = extent_root->fs_info->current_insert.objectid +
 173                                 i;
 174                 super_blocks_used = btrfs_super_blocks_used(info->disk_super);
 175                 btrfs_set_super_blocks_used(info->disk_super,
 176                                             super_blocks_used + 1);
 177                 ret = btrfs_insert_item(trans, extent_root, &ins, &extent_item,
 178                                         sizeof(extent_item));
 179                 BUG_ON(ret);
 180         }
 181         extent_root->fs_info->current_insert.offset = 0;
 182         return 0;
 183 }
 184
 185 static int pin_down_block(struct btrfs_root *root, u64 blocknr, int pending)
 186 {
 187         int err;
 188         struct btrfs_header *header;
 189         struct buffer_head *bh;
 190
 191         if (!pending) {
 192                 bh = btrfs_find_tree_block(root, blocknr);
 193                 if (bh) {
 194                         if (buffer_uptodate(bh)) {
 195                                 u64 transid =
 196                                     root->fs_info->running_transaction->transid;
 197                                 header = btrfs_buffer_header(bh);
 198                                 if (btrfs_header_generation(header) ==
 199                                     transid) {
 200                                         btrfs_block_release(root, bh);
 201                                         return 0;
 202                                 }
 203                         }
 204                         btrfs_block_release(root, bh);
 205                 }
 206                 err = set_radix_bit(&root->fs_info->pinned_radix, blocknr);
 207         } else {
 208                 err = set_radix_bit(&root->fs_info->pending_del_radix, blocknr);
 209         }
 210         BUG_ON(err);
 211         return 0;
 212 }
 213
 214 /*
 215  * remove an extent from the root, returns 0 on success
 216  */
 217 static int __free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 218                          *root, u64 blocknr, u64 num_blocks, int pin)
 219 {
 220         struct btrfs_path *path;
 221         struct btrfs_key key;
 222         struct btrfs_fs_info *info = root->fs_info;
 223         struct btrfs_root *extent_root = info->extent_root;
 224         int ret;
 225         struct btrfs_extent_item *ei;
 226         struct btrfs_key ins;
 227         u32 refs;
 228
 229         key.objectid = blocknr;
 230         key.flags = 0;
 231         btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
 232         key.offset = num_blocks;
 233
 234         find_free_extent(trans, root, 0, 0, (u64)-1, &ins);
 235         path = btrfs_alloc_path();
 236         BUG_ON(!path);
 237         btrfs_init_path(path);
 238
 239         ret = btrfs_search_slot(trans, extent_root, &key, path, -1, 1);
 240         if (ret) {
 241                 printk("failed to find %Lu\n", key.objectid);
 242                 btrfs_print_tree(extent_root, extent_root->node);
 243                 printk("failed to find %Lu\n", key.objectid);
 244                 BUG();
 245         }
 246         ei = btrfs_item_ptr(btrfs_buffer_leaf(path->nodes[0]), path->slots[0],
 247                             struct btrfs_extent_item);
 248         BUG_ON(ei->refs == 0);
 249         refs = btrfs_extent_refs(ei) - 1;
 250         btrfs_set_extent_refs(ei, refs);
 251         btrfs_mark_buffer_dirty(path->nodes[0]);
 252         if (refs == 0) {
 253                 u64 super_blocks_used;
 254
 255                 if (pin) {
 256                         ret = pin_down_block(root, blocknr, 0);
 257                         BUG_ON(ret);
 258                 }
 259
 260                 super_blocks_used = btrfs_super_blocks_used(info->disk_super);
 261                 btrfs_set_super_blocks_used(info->disk_super,
 262                                             super_blocks_used - num_blocks);
 263                 ret = btrfs_del_item(trans, extent_root, path);
 264                 if (ret)
 265                         BUG();
 266         }
 267         btrfs_release_path(extent_root, path);
 268         btrfs_free_path(path);
 269         finish_current_insert(trans, extent_root);
 270         return ret;
 271 }
 272
 273 /*
 274  * find all the blocks marked as pending in the radix tree and remove
 275  * them from the extent map
 276  */
 277 static int del_pending_extents(struct btrfs_trans_handle *trans, struct
 278                                btrfs_root *extent_root)
 279 {
 280         int ret;
 281         int wret;
 282         int err = 0;
 283         unsigned long gang[4];
 284         int i;
 285         struct radix_tree_root *pending_radix;
 286         struct radix_tree_root *pinned_radix;
 287
 288         pending_radix = &extent_root->fs_info->pending_del_radix;
 289         pinned_radix = &extent_root->fs_info->pinned_radix;
 290
 291         while(1) {
 292                 ret = find_first_radix_bit(pending_radix, gang,
 293                                            ARRAY_SIZE(gang));
 294                 if (!ret)
 295                         break;
 296                 for (i = 0; i < ret; i++) {
 297                         wret = set_radix_bit(pinned_radix, gang[i]);
 298                         BUG_ON(wret);
 299                         wret = clear_radix_bit(pending_radix, gang[i]);
 300                         BUG_ON(wret);
 301                         wret = __free_extent(trans, extent_root,
 302                                              gang[i], 1, 0);
 303                         if (wret)
 304                                 err = wret;
 305                 }
 306         }
 307         return err;
 308 }
 309
 310 /*
 311  * remove an extent from the root, returns 0 on success
 312  */
 313 int btrfs_free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 314                       *root, u64 blocknr, u64 num_blocks, int pin)
 315 {
 316         struct btrfs_root *extent_root = root->fs_info->extent_root;
 317         int pending_ret;
 318         int ret;
 319
 320         if (root == extent_root) {
 321                 pin_down_block(root, blocknr, 1);
 322                 return 0;
 323         }
 324         ret = __free_extent(trans, root, blocknr, num_blocks, pin);
 325         pending_ret = del_pending_extents(trans, root->fs_info->extent_root);
 326         return ret ? ret : pending_ret;
 327 }
 328
 329 /*
 330  * walks the btree of allocated extents and find a hole of a given size.
 331  * The key ins is changed to record the hole:
 332  * ins->objectid == block start
 333  * ins->flags = BTRFS_EXTENT_ITEM_KEY
 334  * ins->offset == number of blocks
 335  * Any available blocks before search_start are skipped.
 336  */
 337 static int find_free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 338                             *orig_root, u64 num_blocks, u64 search_start, u64
 339                             search_end, struct btrfs_key *ins)
 340 {
 341         struct btrfs_path *path;
 342         struct btrfs_key key;
 343         int ret;
 344         u64 hole_size = 0;
 345         int slot = 0;
 346         u64 last_block = 0;
 347         u64 test_block;
 348         int start_found;
 349         struct btrfs_leaf *l;
 350         struct btrfs_root * root = orig_root->fs_info->extent_root;
 351         int total_needed = num_blocks;
 352         int level;
 353
 354         path = btrfs_alloc_path();
 355         ins->flags = 0;
 356         btrfs_set_key_type(ins, BTRFS_EXTENT_ITEM_KEY);
 357
 358         level = btrfs_header_level(btrfs_buffer_header(root->node));
 359         total_needed += (level + 1) * 3;
 360         if (root->fs_info->last_insert.objectid == 0 && search_end == (u64)-1) {
 361                 struct btrfs_disk_key *last_key;
 362                 btrfs_init_path(path);
 363                 ins->objectid = (u64)-1;
 364                 ins->offset = (u64)-1;
 365                 ret = btrfs_search_slot(trans, root, ins, path, 0, 0);
 366                 if (ret < 0)
 367                         goto error;
 368                 BUG_ON(ret == 0);
 369                 if (path->slots[0] > 0)
 370                         path->slots[0]--;
 371                 l = btrfs_buffer_leaf(path->nodes[0]);
 372                 last_key = &l->items[path->slots[0]].key;
 373                 search_start = btrfs_disk_key_objectid(last_key);
 374         }
 375         if (root->fs_info->last_insert.objectid > search_start)
 376                 search_start = root->fs_info->last_insert.objectid;
 377
 378 check_failed:
 379         btrfs_init_path(path);
 380         ins->objectid = search_start;
 381         ins->offset = 0;
 382         start_found = 0;
 383         ret = btrfs_search_slot(trans, root, ins, path, 0, 0);
 384         if (ret < 0)
 385                 goto error;
 386
 387         if (path->slots[0] > 0)
 388                 path->slots[0]--;
 389
 390         while (1) {
 391                 l = btrfs_buffer_leaf(path->nodes[0]);
 392                 slot = path->slots[0];
 393                 if (slot >= btrfs_header_nritems(&l->header)) {
 394                         ret = btrfs_next_leaf(root, path);
 395                         if (ret == 0)
 396                                 continue;
 397                         if (ret < 0)
 398                                 goto error;
 399                         if (!start_found) {
 400                                 ins->objectid = search_start;
 401                                 ins->offset = (u64)-1;
 402                                 start_found = 1;
 403                                 goto check_pending;
 404                         }
 405                         ins->objectid = last_block > search_start ?
 406                                         last_block : search_start;
 407                         ins->offset = (u64)-1;
 408                         goto check_pending;
 409                 }
 410                 btrfs_disk_key_to_cpu(&key, &l->items[slot].key);
 411                 if (key.objectid >= search_start) {
 412                         if (start_found) {
 413                                 if (last_block < search_start)
 414                                         last_block = search_start;
 415                                 hole_size = key.objectid - last_block;
 416                                 if (hole_size > total_needed) {
 417                                         ins->objectid = last_block;
 418                                         ins->offset = hole_size;
 419                                         goto check_pending;
 420                                 }
 421                         }
 422                 }
 423                 start_found = 1;
 424                 last_block = key.objectid + key.offset;
 425                 path->slots[0]++;
 426         }
 427         // FIXME -ENOSPC
 428 check_pending:
 429         /* we have to make sure we didn't find an extent that has already
 430          * been allocated by the map tree or the original allocation
 431          */
 432         btrfs_release_path(root, path);
 433         BUG_ON(ins->objectid < search_start);
 434         for (test_block = ins->objectid;
 435              test_block < ins->objectid + total_needed; test_block++) {
 436                 if (test_radix_bit(&root->fs_info->pinned_radix,
 437                                       test_block)) {
 438                         search_start = test_block + 1;
 439                         goto check_failed;
 440                 }
 441         }
 442         BUG_ON(root->fs_info->current_insert.offset);
 443         root->fs_info->current_insert.offset = total_needed - num_blocks;
 444         root->fs_info->current_insert.objectid = ins->objectid + num_blocks;
 445         root->fs_info->current_insert.flags = 0;
 446         root->fs_info->last_insert.objectid = ins->objectid;
 447         ins->offset = num_blocks;
 448         btrfs_free_path(path);
 449         return 0;
 450 error:
 451         btrfs_release_path(root, path);
 452         btrfs_free_path(path);
 453         return ret;
 454 }
 455
 456 /*
 457  * finds a free extent and does all the dirty work required for allocation
 458  * returns the key for the extent through ins, and a tree buffer for
 459  * the first block of the extent through buf.
 460  *
 461  * returns 0 if everything worked, non-zero otherwise.
 462  */
 463 int btrfs_alloc_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 464                         *root, u64 num_blocks, u64 search_start, u64
 465                         search_end, struct btrfs_key *ins)
 466 {
 467         int ret;
 468         int pending_ret;
 469         u64 super_blocks_used;
 470         struct btrfs_fs_info *info = root->fs_info;
 471         struct btrfs_root *extent_root = info->extent_root;
 472         struct btrfs_extent_item extent_item;
 473
 474         btrfs_set_extent_refs(&extent_item, 1);
 475
 476         if (root == extent_root) {
 477                 BUG_ON(extent_root->fs_info->current_insert.offset == 0);
 478                 BUG_ON(num_blocks != 1);
 479                 BUG_ON(extent_root->fs_info->current_insert.flags ==
 480                        extent_root->fs_info->current_insert.offset);
 481                 ins->offset = 1;
 482                 ins->objectid = extent_root->fs_info->current_insert.objectid +
 483                                 extent_root->fs_info->current_insert.flags++;
 484                 return 0;
 485         }
 486         ret = find_free_extent(trans, root, num_blocks, search_start,
 487                                search_end, ins);
 488         if (ret)
 489                 return ret;
 490
 491         super_blocks_used = btrfs_super_blocks_used(info->disk_super);
 492         btrfs_set_super_blocks_used(info->disk_super, super_blocks_used +
 493                                     num_blocks);
 494         ret = btrfs_insert_item(trans, extent_root, ins, &extent_item,
 495                                 sizeof(extent_item));
 496
 497         finish_current_insert(trans, extent_root);
 498         pending_ret = del_pending_extents(trans, extent_root);
 499         if (ret)
 500                 return ret;
 501         if (pending_ret)
 502                 return pending_ret;
 503         return 0;
 504 }
 505
 506 /*
 507  * helper function to allocate a block for a given tree
 508  * returns the tree buffer or NULL.
 509  */
 510 struct buffer_head *btrfs_alloc_free_block(struct btrfs_trans_handle *trans,
 511                                             struct btrfs_root *root)
 512 {
 513         struct btrfs_key ins;
 514         int ret;
 515         struct buffer_head *buf;
 516
 517         ret = btrfs_alloc_extent(trans, root, 1, 0, (unsigned long)-1, &ins);
 518         if (ret) {
 519                 BUG();
 520                 return NULL;
 521         }
 522         buf = btrfs_find_create_tree_block(root, ins.objectid);
 523         set_buffer_uptodate(buf);
 524         return buf;
 525 }
 526
 527 static int drop_leaf_ref(struct btrfs_trans_handle *trans,
 528                          struct btrfs_root *root, struct buffer_head *cur)
 529 {
 530         struct btrfs_disk_key *key;
 531         struct btrfs_leaf *leaf;
 532         struct btrfs_file_extent_item *fi;
 533         int i;
 534         int nritems;
 535         int ret;
 536
 537         BUG_ON(!btrfs_is_leaf(btrfs_buffer_node(cur)));
 538         leaf = btrfs_buffer_leaf(cur);
 539         nritems = btrfs_header_nritems(&leaf->header);
 540         for (i = 0; i < nritems; i++) {
 541                 key = &leaf->items[i].key;
 542                 if (btrfs_disk_key_type(key) != BTRFS_EXTENT_DATA_KEY)
 543                         continue;
 544                 fi = btrfs_item_ptr(leaf, i, struct btrfs_file_extent_item);
 545                 if (btrfs_file_extent_type(fi) == BTRFS_FILE_EXTENT_INLINE)
 546                         continue;
 547                 /*
 548                  * FIXME make sure to insert a trans record that
 549                  * repeats the snapshot del on crash
 550                  */
 551                 ret = btrfs_free_extent(trans, root,
 552                                         btrfs_file_extent_disk_blocknr(fi),
 553                                         btrfs_file_extent_disk_num_blocks(fi),
 554                                         0);
 555                 BUG_ON(ret);
 556         }
 557         return 0;
 558 }
 559
 560 /*
 561  * helper function for drop_snapshot, this walks down the tree dropping ref
 562  * counts as it goes.
 563  */
 564 static int walk_down_tree(struct btrfs_trans_handle *trans, struct btrfs_root
 565                           *root, struct btrfs_path *path, int *level)
 566 {
 567         struct buffer_head *next;
 568         struct buffer_head *cur;
 569         u64 blocknr;
 570         int ret;
 571         u32 refs;
 572
 573         WARN_ON(*level < 0);
 574         WARN_ON(*level >= BTRFS_MAX_LEVEL);
 575         ret = lookup_extent_ref(trans, root, bh_blocknr(path->nodes[*level]),
 576                                1, &refs);
 577         BUG_ON(ret);
 578         if (refs > 1)
 579                 goto out;
 580         /*
 581          * walk down to the last node level and free all the leaves
 582          */
 583         while(*level >= 0) {
 584                 WARN_ON(*level < 0);
 585                 WARN_ON(*level >= BTRFS_MAX_LEVEL);
 586                 cur = path->nodes[*level];
 587                 if (btrfs_header_level(btrfs_buffer_header(cur)) != *level)
 588                         WARN_ON(1);
 589                 if (path->slots[*level] >=
 590                     btrfs_header_nritems(btrfs_buffer_header(cur)))
 591                         break;
 592                 if (*level == 0) {
 593                         ret = drop_leaf_ref(trans, root, cur);
 594                         BUG_ON(ret);
 595                         break;
 596                 }
 597                 blocknr = btrfs_node_blockptr(btrfs_buffer_node(cur),
 598                                               path->slots[*level]);
 599                 ret = lookup_extent_ref(trans, root, blocknr, 1, &refs);
 600                 BUG_ON(ret);
 601                 if (refs != 1) {
 602                         path->slots[*level]++;
 603                         ret = btrfs_free_extent(trans, root, blocknr, 1, 1);
 604                         BUG_ON(ret);
 605                         continue;
 606                 }
 607                 next = read_tree_block(root, blocknr);
 608                 WARN_ON(*level <= 0);
 609                 if (path->nodes[*level-1])
 610                         btrfs_block_release(root, path->nodes[*level-1]);
 611                 path->nodes[*level-1] = next;
 612                 *level = btrfs_header_level(btrfs_buffer_header(next));
 613                 path->slots[*level] = 0;
 614         }
 615 out:
 616         WARN_ON(*level < 0);
 617         WARN_ON(*level >= BTRFS_MAX_LEVEL);
 618         ret = btrfs_free_extent(trans, root,
 619                                 bh_blocknr(path->nodes[*level]), 1, 1);
 620         btrfs_block_release(root, path->nodes[*level]);
 621         path->nodes[*level] = NULL;
 622         *level += 1;
 623         BUG_ON(ret);
 624         return 0;
 625 }
 626
 627 /*
 628  * helper for dropping snapshots.  This walks back up the tree in the path
 629  * to find the first node higher up where we haven't yet gone through
 630  * all the slots
 631  */
 632 static int walk_up_tree(struct btrfs_trans_handle *trans, struct btrfs_root
 633                         *root, struct btrfs_path *path, int *level)
 634 {
 635         int i;
 636         int slot;
 637         int ret;
 638         for(i = *level; i < BTRFS_MAX_LEVEL - 1 && path->nodes[i]; i++) {
 639                 slot = path->slots[i];
 640                 if (slot < btrfs_header_nritems(
 641                     btrfs_buffer_header(path->nodes[i])) - 1) {
 642                         path->slots[i]++;
 643                         *level = i;
 644                         return 0;
 645                 } else {
 646                         ret = btrfs_free_extent(trans, root,
 647                                                 bh_blocknr(path->nodes[*level]),
 648                                                 1, 1);
 649                         BUG_ON(ret);
 650                         btrfs_block_release(root, path->nodes[*level]);
 651                         path->nodes[*level] = NULL;
 652                         *level = i + 1;
 653                 }
 654         }
 655         return 1;
 656 }
 657
 658 /*
 659  * drop the reference count on the tree rooted at 'snap'.  This traverses
 660  * the tree freeing any blocks that have a ref count of zero after being
 661  * decremented.
 662  */
 663 int btrfs_drop_snapshot(struct btrfs_trans_handle *trans, struct btrfs_root
 664                         *root, struct buffer_head *snap)
 665 {
 666         int ret = 0;
 667         int wret;
 668         int level;
 669         struct btrfs_path *path;
 670         int i;
 671         int orig_level;
 672
 673         path = btrfs_alloc_path();
 674         BUG_ON(!path);
 675         btrfs_init_path(path);
 676
 677         level = btrfs_header_level(btrfs_buffer_header(snap));
 678         orig_level = level;
 679         path->nodes[level] = snap;
 680         path->slots[level] = 0;
 681         while(1) {
 682                 wret = walk_down_tree(trans, root, path, &level);
 683                 if (wret > 0)
 684                         break;
 685                 if (wret < 0)
 686                         ret = wret;
 687
 688                 wret = walk_up_tree(trans, root, path, &level);
 689                 if (wret > 0)
 690                         break;
 691                 if (wret < 0)
 692                         ret = wret;
 693         }
 694         for (i = 0; i <= orig_level; i++) {
 695                 if (path->nodes[i]) {
 696                         btrfs_block_release(root, path->nodes[i]);
 697                 }
 698         }
 699         btrfs_free_path(path);
 700         return ret;
 701 }