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