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