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         btrfs_set_extent_type(&extent_item, BTRFS_EXTENT_TREE);
 171         btrfs_set_extent_owner(&extent_item, extent_root->root_key.objectid);
 172
 173         for (i = 0; i < extent_root->fs_info->current_insert.flags; i++) {
 174                 ins.objectid = extent_root->fs_info->current_insert.objectid +
 175                                 i;
 176                 super_blocks_used = btrfs_super_blocks_used(info->disk_super);
 177                 btrfs_set_super_blocks_used(info->disk_super,
 178                                             super_blocks_used + 1);
 179                 ret = btrfs_insert_item(trans, extent_root, &ins, &extent_item,
 180                                         sizeof(extent_item));
 181                 BUG_ON(ret);
 182         }
 183         extent_root->fs_info->current_insert.offset = 0;
 184         return 0;
 185 }
 186
 187 static int pin_down_block(struct btrfs_root *root, u64 blocknr, int pending)
 188 {
 189         int err;
 190         struct btrfs_header *header;
 191         struct buffer_head *bh;
 192
 193         if (!pending) {
 194                 bh = btrfs_find_tree_block(root, blocknr);
 195                 if (bh) {
 196                         if (buffer_uptodate(bh)) {
 197                                 u64 transid =
 198                                     root->fs_info->running_transaction->transid;
 199                                 header = btrfs_buffer_header(bh);
 200                                 if (btrfs_header_generation(header) ==
 201                                     transid) {
 202                                         btrfs_block_release(root, bh);
 203                                         return 0;
 204                                 }
 205                         }
 206                         btrfs_block_release(root, bh);
 207                 }
 208                 err = set_radix_bit(&root->fs_info->pinned_radix, blocknr);
 209         } else {
 210                 err = set_radix_bit(&root->fs_info->pending_del_radix, blocknr);
 211         }
 212         BUG_ON(err);
 213         return 0;
 214 }
 215
 216 /*
 217  * remove an extent from the root, returns 0 on success
 218  */
 219 static int __free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 220                          *root, u64 blocknr, u64 num_blocks, int pin)
 221 {
 222         struct btrfs_path *path;
 223         struct btrfs_key key;
 224         struct btrfs_fs_info *info = root->fs_info;
 225         struct btrfs_root *extent_root = info->extent_root;
 226         int ret;
 227         struct btrfs_extent_item *ei;
 228         struct btrfs_key ins;
 229         u32 refs;
 230
 231         key.objectid = blocknr;
 232         key.flags = 0;
 233         btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
 234         key.offset = num_blocks;
 235
 236         find_free_extent(trans, root, 0, 0, (u64)-1, &ins);
 237         path = btrfs_alloc_path();
 238         BUG_ON(!path);
 239         btrfs_init_path(path);
 240
 241         ret = btrfs_search_slot(trans, extent_root, &key, path, -1, 1);
 242         if (ret) {
 243                 printk("failed to find %Lu\n", key.objectid);
 244                 btrfs_print_tree(extent_root, extent_root->node);
 245                 printk("failed to find %Lu\n", key.objectid);
 246                 BUG();
 247         }
 248         ei = btrfs_item_ptr(btrfs_buffer_leaf(path->nodes[0]), path->slots[0],
 249                             struct btrfs_extent_item);
 250         BUG_ON(ei->refs == 0);
 251         refs = btrfs_extent_refs(ei) - 1;
 252         btrfs_set_extent_refs(ei, refs);
 253         btrfs_mark_buffer_dirty(path->nodes[0]);
 254         if (refs == 0) {
 255                 u64 super_blocks_used;
 256
 257                 if (pin) {
 258                         ret = pin_down_block(root, blocknr, 0);
 259                         BUG_ON(ret);
 260                 }
 261
 262                 super_blocks_used = btrfs_super_blocks_used(info->disk_super);
 263                 btrfs_set_super_blocks_used(info->disk_super,
 264                                             super_blocks_used - num_blocks);
 265                 ret = btrfs_del_item(trans, extent_root, path);
 266                 if (ret)
 267                         BUG();
 268         }
 269         btrfs_release_path(extent_root, path);
 270         btrfs_free_path(path);
 271         finish_current_insert(trans, extent_root);
 272         return ret;
 273 }
 274
 275 /*
 276  * find all the blocks marked as pending in the radix tree and remove
 277  * them from the extent map
 278  */
 279 static int del_pending_extents(struct btrfs_trans_handle *trans, struct
 280                                btrfs_root *extent_root)
 281 {
 282         int ret;
 283         int wret;
 284         int err = 0;
 285         unsigned long gang[4];
 286         int i;
 287         struct radix_tree_root *pending_radix;
 288         struct radix_tree_root *pinned_radix;
 289
 290         pending_radix = &extent_root->fs_info->pending_del_radix;
 291         pinned_radix = &extent_root->fs_info->pinned_radix;
 292
 293         while(1) {
 294                 ret = find_first_radix_bit(pending_radix, gang,
 295                                            ARRAY_SIZE(gang));
 296                 if (!ret)
 297                         break;
 298                 for (i = 0; i < ret; i++) {
 299                         wret = set_radix_bit(pinned_radix, gang[i]);
 300                         BUG_ON(wret);
 301                         wret = clear_radix_bit(pending_radix, gang[i]);
 302                         BUG_ON(wret);
 303                         wret = __free_extent(trans, extent_root,
 304                                              gang[i], 1, 0);
 305                         if (wret)
 306                                 err = wret;
 307                 }
 308         }
 309         return err;
 310 }
 311
 312 /*
 313  * remove an extent from the root, returns 0 on success
 314  */
 315 int btrfs_free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 316                       *root, u64 blocknr, u64 num_blocks, int pin)
 317 {
 318         struct btrfs_root *extent_root = root->fs_info->extent_root;
 319         int pending_ret;
 320         int ret;
 321
 322         if (root == extent_root) {
 323                 pin_down_block(root, blocknr, 1);
 324                 return 0;
 325         }
 326         ret = __free_extent(trans, root, blocknr, num_blocks, pin);
 327         pending_ret = del_pending_extents(trans, root->fs_info->extent_root);
 328         return ret ? ret : pending_ret;
 329 }
 330
 331 /*
 332  * walks the btree of allocated extents and find a hole of a given size.
 333  * The key ins is changed to record the hole:
 334  * ins->objectid == block start
 335  * ins->flags = BTRFS_EXTENT_ITEM_KEY
 336  * ins->offset == number of blocks
 337  * Any available blocks before search_start are skipped.
 338  */
 339 static int find_free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 340                             *orig_root, u64 num_blocks, u64 search_start, u64
 341                             search_end, struct btrfs_key *ins)
 342 {
 343         struct btrfs_path *path;
 344         struct btrfs_key key;
 345         int ret;
 346         u64 hole_size = 0;
 347         int slot = 0;
 348         u64 last_block = 0;
 349         u64 test_block;
 350         int start_found;
 351         struct btrfs_leaf *l;
 352         struct btrfs_root * root = orig_root->fs_info->extent_root;
 353         int total_needed = num_blocks;
 354         int level;
 355
 356         path = btrfs_alloc_path();
 357         ins->flags = 0;
 358         btrfs_set_key_type(ins, BTRFS_EXTENT_ITEM_KEY);
 359
 360         level = btrfs_header_level(btrfs_buffer_header(root->node));
 361         total_needed += (level + 2) * 3;
 362         if (root->fs_info->last_insert.objectid == 0 && search_end == (u64)-1) {
 363                 struct btrfs_disk_key *last_key;
 364                 btrfs_init_path(path);
 365                 ins->objectid = (u64)-1;
 366                 ins->offset = (u64)-1;
 367                 ret = btrfs_search_slot(trans, root, ins, path, 0, 0);
 368                 if (ret < 0)
 369                         goto error;
 370                 BUG_ON(ret == 0);
 371                 if (path->slots[0] > 0)
 372                         path->slots[0]--;
 373                 l = btrfs_buffer_leaf(path->nodes[0]);
 374                 last_key = &l->items[path->slots[0]].key;
 375                 search_start = btrfs_disk_key_objectid(last_key);
 376         }
 377         if (root->fs_info->last_insert.objectid > search_start)
 378                 search_start = root->fs_info->last_insert.objectid;
 379
 380 check_failed:
 381         btrfs_init_path(path);
 382         ins->objectid = search_start;
 383         ins->offset = 0;
 384         start_found = 0;
 385         ret = btrfs_search_slot(trans, root, ins, path, 0, 0);
 386         if (ret < 0)
 387                 goto error;
 388
 389         if (path->slots[0] > 0)
 390                 path->slots[0]--;
 391
 392         while (1) {
 393                 l = btrfs_buffer_leaf(path->nodes[0]);
 394                 slot = path->slots[0];
 395                 if (slot >= btrfs_header_nritems(&l->header)) {
 396                         ret = btrfs_next_leaf(root, path);
 397                         if (ret == 0)
 398                                 continue;
 399                         if (ret < 0)
 400                                 goto error;
 401                         if (!start_found) {
 402                                 ins->objectid = search_start;
 403                                 ins->offset = (u64)-1;
 404                                 start_found = 1;
 405                                 goto check_pending;
 406                         }
 407                         ins->objectid = last_block > search_start ?
 408                                         last_block : search_start;
 409                         ins->offset = (u64)-1;
 410                         goto check_pending;
 411                 }
 412                 btrfs_disk_key_to_cpu(&key, &l->items[slot].key);
 413                 if (key.objectid >= search_start) {
 414                         if (start_found) {
 415                                 if (last_block < search_start)
 416                                         last_block = search_start;
 417                                 hole_size = key.objectid - last_block;
 418                                 if (hole_size > total_needed) {
 419                                         ins->objectid = last_block;
 420                                         ins->offset = hole_size;
 421                                         goto check_pending;
 422                                 }
 423                         }
 424                 }
 425                 start_found = 1;
 426                 last_block = key.objectid + key.offset;
 427                 path->slots[0]++;
 428         }
 429         // FIXME -ENOSPC
 430 check_pending:
 431         /* we have to make sure we didn't find an extent that has already
 432          * been allocated by the map tree or the original allocation
 433          */
 434         btrfs_release_path(root, path);
 435         BUG_ON(ins->objectid < search_start);
 436         for (test_block = ins->objectid;
 437              test_block < ins->objectid + total_needed; test_block++) {
 438                 if (test_radix_bit(&root->fs_info->pinned_radix,
 439                                       test_block)) {
 440                         search_start = test_block + 1;
 441                         goto check_failed;
 442                 }
 443         }
 444         BUG_ON(root->fs_info->current_insert.offset);
 445         root->fs_info->current_insert.offset = total_needed - num_blocks;
 446         root->fs_info->current_insert.objectid = ins->objectid + num_blocks;
 447         root->fs_info->current_insert.flags = 0;
 448         root->fs_info->last_insert.objectid = ins->objectid;
 449         ins->offset = num_blocks;
 450         btrfs_free_path(path);
 451         return 0;
 452 error:
 453         btrfs_release_path(root, path);
 454         btrfs_free_path(path);
 455         return ret;
 456 }
 457
 458 /*
 459  * finds a free extent and does all the dirty work required for allocation
 460  * returns the key for the extent through ins, and a tree buffer for
 461  * the first block of the extent through buf.
 462  *
 463  * returns 0 if everything worked, non-zero otherwise.
 464  */
 465 int btrfs_alloc_extent(struct btrfs_trans_handle *trans,
 466                        struct btrfs_root *root, u64 owner,
 467                        u8 type, u64 num_blocks, u64 search_start,
 468                        u64 search_end, struct btrfs_key *ins)
 469 {
 470         int ret;
 471         int pending_ret;
 472         u64 super_blocks_used;
 473         struct btrfs_fs_info *info = root->fs_info;
 474         struct btrfs_root *extent_root = info->extent_root;
 475         struct btrfs_extent_item extent_item;
 476
 477         btrfs_set_extent_refs(&extent_item, 1);
 478         btrfs_set_extent_owner(&extent_item, owner);
 479         btrfs_set_extent_type(&extent_item, type);
 480
 481         if (root == extent_root) {
 482                 BUG_ON(extent_root->fs_info->current_insert.offset == 0);
 483                 BUG_ON(num_blocks != 1);
 484                 BUG_ON(extent_root->fs_info->current_insert.flags ==
 485                        extent_root->fs_info->current_insert.offset);
 486                 ins->offset = 1;
 487                 ins->objectid = extent_root->fs_info->current_insert.objectid +
 488                                 extent_root->fs_info->current_insert.flags++;
 489                 return 0;
 490         }
 491         ret = find_free_extent(trans, root, num_blocks, search_start,
 492                                search_end, ins);
 493         if (ret)
 494                 return ret;
 495
 496         super_blocks_used = btrfs_super_blocks_used(info->disk_super);
 497         btrfs_set_super_blocks_used(info->disk_super, super_blocks_used +
 498                                     num_blocks);
 499         ret = btrfs_insert_item(trans, extent_root, ins, &extent_item,
 500                                 sizeof(extent_item));
 501
 502         finish_current_insert(trans, extent_root);
 503         pending_ret = del_pending_extents(trans, extent_root);
 504         if (ret)
 505                 return ret;
 506         if (pending_ret)
 507                 return pending_ret;
 508         return 0;
 509 }
 510
 511 /*
 512  * helper function to allocate a block for a given tree
 513  * returns the tree buffer or NULL.
 514  */
 515 struct buffer_head *btrfs_alloc_free_block(struct btrfs_trans_handle *trans,
 516                                            struct btrfs_root *root)
 517 {
 518         struct btrfs_key ins;
 519         int ret;
 520         struct buffer_head *buf;
 521
 522         ret = btrfs_alloc_extent(trans, root, root->root_key.objectid,
 523                                  BTRFS_EXTENT_TREE,
 524                                  1, 0, (unsigned long)-1, &ins);
 525         if (ret) {
 526                 BUG();
 527                 return NULL;
 528         }
 529         buf = btrfs_find_create_tree_block(root, ins.objectid);
 530         set_buffer_uptodate(buf);
 531         return buf;
 532 }
 533
 534 static int drop_leaf_ref(struct btrfs_trans_handle *trans,
 535                          struct btrfs_root *root, struct buffer_head *cur)
 536 {
 537         struct btrfs_disk_key *key;
 538         struct btrfs_leaf *leaf;
 539         struct btrfs_file_extent_item *fi;
 540         int i;
 541         int nritems;
 542         int ret;
 543
 544         BUG_ON(!btrfs_is_leaf(btrfs_buffer_node(cur)));
 545         leaf = btrfs_buffer_leaf(cur);
 546         nritems = btrfs_header_nritems(&leaf->header);
 547         for (i = 0; i < nritems; i++) {
 548                 key = &leaf->items[i].key;
 549                 if (btrfs_disk_key_type(key) != BTRFS_EXTENT_DATA_KEY)
 550                         continue;
 551                 fi = btrfs_item_ptr(leaf, i, struct btrfs_file_extent_item);
 552                 if (btrfs_file_extent_type(fi) == BTRFS_FILE_EXTENT_INLINE)
 553                         continue;
 554                 /*
 555                  * FIXME make sure to insert a trans record that
 556                  * repeats the snapshot del on crash
 557                  */
 558                 ret = btrfs_free_extent(trans, root,
 559                                         btrfs_file_extent_disk_blocknr(fi),
 560                                         btrfs_file_extent_disk_num_blocks(fi),
 561                                         0);
 562                 BUG_ON(ret);
 563         }
 564         return 0;
 565 }
 566
 567 /*
 568  * helper function for drop_snapshot, this walks down the tree dropping ref
 569  * counts as it goes.
 570  */
 571 static int walk_down_tree(struct btrfs_trans_handle *trans, struct btrfs_root
 572                           *root, struct btrfs_path *path, int *level)
 573 {
 574         struct buffer_head *next;
 575         struct buffer_head *cur;
 576         u64 blocknr;
 577         int ret;
 578         u32 refs;
 579
 580         WARN_ON(*level < 0);
 581         WARN_ON(*level >= BTRFS_MAX_LEVEL);
 582         ret = lookup_extent_ref(trans, root, bh_blocknr(path->nodes[*level]),
 583                                1, &refs);
 584         BUG_ON(ret);
 585         if (refs > 1)
 586                 goto out;
 587         /*
 588          * walk down to the last node level and free all the leaves
 589          */
 590         while(*level >= 0) {
 591                 WARN_ON(*level < 0);
 592                 WARN_ON(*level >= BTRFS_MAX_LEVEL);
 593                 cur = path->nodes[*level];
 594                 if (btrfs_header_level(btrfs_buffer_header(cur)) != *level)
 595                         WARN_ON(1);
 596                 if (path->slots[*level] >=
 597                     btrfs_header_nritems(btrfs_buffer_header(cur)))
 598                         break;
 599                 if (*level == 0) {
 600                         ret = drop_leaf_ref(trans, root, cur);
 601                         BUG_ON(ret);
 602                         break;
 603                 }
 604                 blocknr = btrfs_node_blockptr(btrfs_buffer_node(cur),
 605                                               path->slots[*level]);
 606                 ret = lookup_extent_ref(trans, root, blocknr, 1, &refs);
 607                 BUG_ON(ret);
 608                 if (refs != 1) {
 609                         path->slots[*level]++;
 610                         ret = btrfs_free_extent(trans, root, blocknr, 1, 1);
 611                         BUG_ON(ret);
 612                         continue;
 613                 }
 614                 next = read_tree_block(root, blocknr);
 615                 WARN_ON(*level <= 0);
 616                 if (path->nodes[*level-1])
 617                         btrfs_block_release(root, path->nodes[*level-1]);
 618                 path->nodes[*level-1] = next;
 619                 *level = btrfs_header_level(btrfs_buffer_header(next));
 620                 path->slots[*level] = 0;
 621         }
 622 out:
 623         WARN_ON(*level < 0);
 624         WARN_ON(*level >= BTRFS_MAX_LEVEL);
 625         ret = btrfs_free_extent(trans, root,
 626                                 bh_blocknr(path->nodes[*level]), 1, 1);
 627         btrfs_block_release(root, path->nodes[*level]);
 628         path->nodes[*level] = NULL;
 629         *level += 1;
 630         BUG_ON(ret);
 631         return 0;
 632 }
 633
 634 /*
 635  * helper for dropping snapshots.  This walks back up the tree in the path
 636  * to find the first node higher up where we haven't yet gone through
 637  * all the slots
 638  */
 639 static int walk_up_tree(struct btrfs_trans_handle *trans, struct btrfs_root
 640                         *root, struct btrfs_path *path, int *level)
 641 {
 642         int i;
 643         int slot;
 644         int ret;
 645         for(i = *level; i < BTRFS_MAX_LEVEL - 1 && path->nodes[i]; i++) {
 646                 slot = path->slots[i];
 647                 if (slot < btrfs_header_nritems(
 648                     btrfs_buffer_header(path->nodes[i])) - 1) {
 649                         path->slots[i]++;
 650                         *level = i;
 651                         return 0;
 652                 } else {
 653                         ret = btrfs_free_extent(trans, root,
 654                                                 bh_blocknr(path->nodes[*level]),
 655                                                 1, 1);
 656                         BUG_ON(ret);
 657                         btrfs_block_release(root, path->nodes[*level]);
 658                         path->nodes[*level] = NULL;
 659                         *level = i + 1;
 660                 }
 661         }
 662         return 1;
 663 }
 664
 665 /*
 666  * drop the reference count on the tree rooted at 'snap'.  This traverses
 667  * the tree freeing any blocks that have a ref count of zero after being
 668  * decremented.
 669  */
 670 int btrfs_drop_snapshot(struct btrfs_trans_handle *trans, struct btrfs_root
 671                         *root, struct buffer_head *snap)
 672 {
 673         int ret = 0;
 674         int wret;
 675         int level;
 676         struct btrfs_path *path;
 677         int i;
 678         int orig_level;
 679
 680         path = btrfs_alloc_path();
 681         BUG_ON(!path);
 682         btrfs_init_path(path);
 683
 684         level = btrfs_header_level(btrfs_buffer_header(snap));
 685         orig_level = level;
 686         path->nodes[level] = snap;
 687         path->slots[level] = 0;
 688         while(1) {
 689                 wret = walk_down_tree(trans, root, path, &level);
 690                 if (wret > 0)
 691                         break;
 692                 if (wret < 0)
 693                         ret = wret;
 694
 695                 wret = walk_up_tree(trans, root, path, &level);
 696                 if (wret > 0)
 697                         break;
 698                 if (wret < 0)
 699                         ret = wret;
 700         }
 701         for (i = 0; i <= orig_level; i++) {
 702                 if (path->nodes[i]) {
 703                         btrfs_block_release(root, path->nodes[i]);
 704                 }
 705         }
 706         btrfs_free_path(path);
 707         return ret;
 708 }