fs/btrfs/extent-tree.c

   1 #include <linux/module.h>
   2 #include "ctree.h"
   3 #include "disk-io.h"
   4 #include "print-tree.h"
   5 #include "transaction.h"
   6
   7 static int find_free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
   8                             *orig_root, u64 num_blocks, u64 search_start, u64
   9                             search_end, struct btrfs_key *ins);
  10 static int finish_current_insert(struct btrfs_trans_handle *trans, struct
  11                                  btrfs_root *extent_root);
  12 static int del_pending_extents(struct btrfs_trans_handle *trans, struct
  13                                btrfs_root *extent_root);
  14
  15 static int inc_block_ref(struct btrfs_trans_handle *trans, struct btrfs_root
  16                          *root, u64 blocknr, u64 num_blocks)
  17 {
  18         struct btrfs_path *path;
  19         int ret;
  20         struct btrfs_key key;
  21         struct btrfs_leaf *l;
  22         struct btrfs_extent_item *item;
  23         struct btrfs_key ins;
  24         u32 refs;
  25
  26         find_free_extent(trans, root->fs_info->extent_root, 0, 0, (u64)-1,
  27                          &ins);
  28         path = btrfs_alloc_path();
  29         BUG_ON(!path);
  30         btrfs_init_path(path);
  31         key.objectid = blocknr;
  32         key.flags = 0;
  33         btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
  34         key.offset = num_blocks;
  35         ret = btrfs_search_slot(trans, root->fs_info->extent_root, &key, path,
  36                                 0, 1);
  37         if (ret != 0)
  38                 BUG();
  39         BUG_ON(ret != 0);
  40         l = btrfs_buffer_leaf(path->nodes[0]);
  41         item = btrfs_item_ptr(l, path->slots[0], struct btrfs_extent_item);
  42         refs = btrfs_extent_refs(item);
  43         btrfs_set_extent_refs(item, refs + 1);
  44         btrfs_mark_buffer_dirty(path->nodes[0]);
  45
  46         btrfs_release_path(root->fs_info->extent_root, path);
  47         btrfs_free_path(path);
  48         finish_current_insert(trans, root->fs_info->extent_root);
  49         del_pending_extents(trans, root->fs_info->extent_root);
  50         return 0;
  51 }
  52
  53 static int lookup_block_ref(struct btrfs_trans_handle *trans, struct btrfs_root
  54                             *root, u64 blocknr, u64 num_blocks, u32 *refs)
  55 {
  56         struct btrfs_path *path;
  57         int ret;
  58         struct btrfs_key key;
  59         struct btrfs_leaf *l;
  60         struct btrfs_extent_item *item;
  61
  62         path = btrfs_alloc_path();
  63         btrfs_init_path(path);
  64         key.objectid = blocknr;
  65         key.offset = num_blocks;
  66         key.flags = 0;
  67         btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
  68         ret = btrfs_search_slot(trans, root->fs_info->extent_root, &key, path,
  69                                 0, 0);
  70         if (ret != 0)
  71                 BUG();
  72         l = btrfs_buffer_leaf(path->nodes[0]);
  73         item = btrfs_item_ptr(l, path->slots[0], struct btrfs_extent_item);
  74         *refs = btrfs_extent_refs(item);
  75         btrfs_release_path(root->fs_info->extent_root, path);
  76         btrfs_free_path(path);
  77         return 0;
  78 }
  79
  80 int btrfs_inc_ref(struct btrfs_trans_handle *trans, struct btrfs_root *root,
  81                   struct buffer_head *buf)
  82 {
  83         u64 blocknr;
  84         struct btrfs_node *buf_node;
  85         struct btrfs_leaf *buf_leaf;
  86         struct btrfs_disk_key *key;
  87         struct btrfs_file_extent_item *fi;
  88         int i;
  89         int leaf;
  90         int ret;
  91
  92         if (!root->ref_cows)
  93                 return 0;
  94         buf_node = btrfs_buffer_node(buf);
  95         leaf = btrfs_is_leaf(buf_node);
  96         buf_leaf = btrfs_buffer_leaf(buf);
  97         for (i = 0; i < btrfs_header_nritems(&buf_node->header); i++) {
  98                 if (leaf) {
  99                         key = &buf_leaf->items[i].key;
 100                         if (btrfs_disk_key_type(key) != BTRFS_EXTENT_DATA_KEY)
 101                                 continue;
 102                         fi = btrfs_item_ptr(buf_leaf, i,
 103                                             struct btrfs_file_extent_item);
 104                         ret = inc_block_ref(trans, root,
 105                                     btrfs_file_extent_disk_blocknr(fi),
 106                                     btrfs_file_extent_disk_num_blocks(fi));
 107                         BUG_ON(ret);
 108                 } else {
 109                         blocknr = btrfs_node_blockptr(buf_node, i);
 110                         ret = inc_block_ref(trans, root, blocknr, 1);
 111                         BUG_ON(ret);
 112                 }
 113         }
 114         return 0;
 115 }
 116
 117 int btrfs_finish_extent_commit(struct btrfs_trans_handle *trans, struct
 118                                btrfs_root *root)
 119 {
 120         unsigned long gang[8];
 121         u64 first = 0;
 122         int ret;
 123         int i;
 124         struct radix_tree_root *pinned_radix = &root->fs_info->pinned_radix;
 125
 126         while(1) {
 127                 ret = find_first_radix_bit(pinned_radix, gang,
 128                                            ARRAY_SIZE(gang));
 129                 if (!ret)
 130                         break;
 131                 if (!first)
 132                         first = gang[0];
 133                 for (i = 0; i < ret; i++) {
 134                         clear_radix_bit(pinned_radix, gang[i]);
 135                 }
 136         }
 137         if (root->fs_info->last_insert.objectid > first)
 138                 root->fs_info->last_insert.objectid = first;
 139         root->fs_info->last_insert.offset = 0;
 140         return 0;
 141 }
 142
 143 static int finish_current_insert(struct btrfs_trans_handle *trans, struct
 144                                  btrfs_root *extent_root)
 145 {
 146         struct btrfs_key ins;
 147         struct btrfs_extent_item extent_item;
 148         int i;
 149         int ret;
 150         u64 super_blocks_used;
 151         struct btrfs_fs_info *info = extent_root->fs_info;
 152
 153         btrfs_set_extent_refs(&extent_item, 1);
 154         btrfs_set_extent_owner(&extent_item,
 155                 btrfs_header_parentid(btrfs_buffer_header(extent_root->node)));
 156         ins.offset = 1;
 157         ins.flags = 0;
 158         btrfs_set_key_type(&ins, BTRFS_EXTENT_ITEM_KEY);
 159
 160         for (i = 0; i < extent_root->fs_info->current_insert.flags; i++) {
 161                 ins.objectid = extent_root->fs_info->current_insert.objectid +
 162                                 i;
 163                 super_blocks_used = btrfs_super_blocks_used(info->disk_super);
 164                 btrfs_set_super_blocks_used(info->disk_super,
 165                                             super_blocks_used + 1);
 166                 ret = btrfs_insert_item(trans, extent_root, &ins, &extent_item,
 167                                         sizeof(extent_item));
 168                 BUG_ON(ret);
 169         }
 170         extent_root->fs_info->current_insert.offset = 0;
 171         return 0;
 172 }
 173
 174 static int pin_down_block(struct btrfs_root *root, u64 blocknr, int pending)
 175 {
 176         int err;
 177         struct btrfs_header *header;
 178         struct buffer_head *bh;
 179
 180         if (!pending) {
 181                 bh = btrfs_find_tree_block(root, blocknr);
 182                 if (bh) {
 183                         if (buffer_uptodate(bh)) {
 184                                 u64 transid =
 185                                     root->fs_info->running_transaction->transid;
 186                                 header = btrfs_buffer_header(bh);
 187                                 if (btrfs_header_generation(header) ==
 188                                     transid) {
 189                                         btrfs_block_release(root, bh);
 190                                         return 0;
 191                                 }
 192                         }
 193                         btrfs_block_release(root, bh);
 194                 }
 195                 err = set_radix_bit(&root->fs_info->pinned_radix, blocknr);
 196         } else {
 197                 err = set_radix_bit(&root->fs_info->pending_del_radix, blocknr);
 198         }
 199         BUG_ON(err);
 200         return 0;
 201 }
 202
 203 /*
 204  * remove an extent from the root, returns 0 on success
 205  */
 206 static int __free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 207                          *root, u64 blocknr, u64 num_blocks, int pin)
 208 {
 209         struct btrfs_path *path;
 210         struct btrfs_key key;
 211         struct btrfs_fs_info *info = root->fs_info;
 212         struct btrfs_root *extent_root = info->extent_root;
 213         int ret;
 214         struct btrfs_extent_item *ei;
 215         struct btrfs_key ins;
 216         u32 refs;
 217
 218         key.objectid = blocknr;
 219         key.flags = 0;
 220         btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
 221         key.offset = num_blocks;
 222
 223         find_free_extent(trans, root, 0, 0, (u64)-1, &ins);
 224         path = btrfs_alloc_path();
 225         BUG_ON(!path);
 226         btrfs_init_path(path);
 227         ret = btrfs_search_slot(trans, extent_root, &key, path, -1, 1);
 228         if (ret) {
 229                 printk("failed to find %Lu\n", key.objectid);
 230                 btrfs_print_tree(extent_root, extent_root->node);
 231                 printk("failed to find %Lu\n", key.objectid);
 232                 BUG();
 233         }
 234         ei = btrfs_item_ptr(btrfs_buffer_leaf(path->nodes[0]), path->slots[0],
 235                             struct btrfs_extent_item);
 236         BUG_ON(ei->refs == 0);
 237         refs = btrfs_extent_refs(ei) - 1;
 238         btrfs_set_extent_refs(ei, refs);
 239         btrfs_mark_buffer_dirty(path->nodes[0]);
 240         if (refs == 0) {
 241                 u64 super_blocks_used;
 242
 243                 if (pin) {
 244                         ret = pin_down_block(root, blocknr, 0);
 245                         BUG_ON(ret);
 246                 }
 247
 248                 super_blocks_used = btrfs_super_blocks_used(info->disk_super);
 249                 btrfs_set_super_blocks_used(info->disk_super,
 250                                             super_blocks_used - num_blocks);
 251                 ret = btrfs_del_item(trans, extent_root, path);
 252                 if (ret)
 253                         BUG();
 254         }
 255         btrfs_release_path(extent_root, path);
 256         btrfs_free_path(path);
 257         finish_current_insert(trans, extent_root);
 258         return ret;
 259 }
 260
 261 /*
 262  * find all the blocks marked as pending in the radix tree and remove
 263  * them from the extent map
 264  */
 265 static int del_pending_extents(struct btrfs_trans_handle *trans, struct
 266                                btrfs_root *extent_root)
 267 {
 268         int ret;
 269         int wret;
 270         int err = 0;
 271         unsigned long gang[4];
 272         int i;
 273         struct radix_tree_root *pending_radix;
 274         struct radix_tree_root *pinned_radix;
 275
 276         pending_radix = &extent_root->fs_info->pending_del_radix;
 277         pinned_radix = &extent_root->fs_info->pinned_radix;
 278
 279         while(1) {
 280                 ret = find_first_radix_bit(pending_radix, gang,
 281                                            ARRAY_SIZE(gang));
 282                 if (!ret)
 283                         break;
 284                 for (i = 0; i < ret; i++) {
 285                         wret = set_radix_bit(pinned_radix, gang[i]);
 286                         BUG_ON(wret);
 287                         wret = clear_radix_bit(pending_radix, gang[i]);
 288                         BUG_ON(wret);
 289                         wret = __free_extent(trans, extent_root,
 290                                              gang[i], 1, 0);
 291                         if (wret)
 292                                 err = wret;
 293                 }
 294         }
 295         return err;
 296 }
 297
 298 /*
 299  * remove an extent from the root, returns 0 on success
 300  */
 301 int btrfs_free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 302                       *root, u64 blocknr, u64 num_blocks, int pin)
 303 {
 304         struct btrfs_root *extent_root = root->fs_info->extent_root;
 305         int pending_ret;
 306         int ret;
 307
 308         if (root == extent_root) {
 309                 pin_down_block(root, blocknr, 1);
 310                 return 0;
 311         }
 312         ret = __free_extent(trans, root, blocknr, num_blocks, pin);
 313         pending_ret = del_pending_extents(trans, root->fs_info->extent_root);
 314         return ret ? ret : pending_ret;
 315 }
 316
 317 /*
 318  * walks the btree of allocated extents and find a hole of a given size.
 319  * The key ins is changed to record the hole:
 320  * ins->objectid == block start
 321  * ins->flags = BTRFS_EXTENT_ITEM_KEY
 322  * ins->offset == number of blocks
 323  * Any available blocks before search_start are skipped.
 324  */
 325 static int find_free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 326                             *orig_root, u64 num_blocks, u64 search_start, u64
 327                             search_end, struct btrfs_key *ins)
 328 {
 329         struct btrfs_path *path;
 330         struct btrfs_key key;
 331         int ret;
 332         u64 hole_size = 0;
 333         int slot = 0;
 334         u64 last_block = 0;
 335         u64 test_block;
 336         int start_found;
 337         struct btrfs_leaf *l;
 338         struct btrfs_root * root = orig_root->fs_info->extent_root;
 339         int total_needed = num_blocks;
 340         int level;
 341
 342         path = btrfs_alloc_path();
 343         ins->flags = 0;
 344         btrfs_set_key_type(ins, BTRFS_EXTENT_ITEM_KEY);
 345
 346         level = btrfs_header_level(btrfs_buffer_header(root->node));
 347         total_needed += (level + 1) * 3;
 348         if (root->fs_info->last_insert.objectid == 0 && search_end == (u64)-1) {
 349                 struct btrfs_disk_key *last_key;
 350                 btrfs_init_path(path);
 351                 ins->objectid = (u64)-1;
 352                 ins->offset = (u64)-1;
 353                 ret = btrfs_search_slot(trans, root, ins, path, 0, 0);
 354                 if (ret < 0)
 355                         goto error;
 356                 BUG_ON(ret == 0);
 357                 if (path->slots[0] > 0)
 358                         path->slots[0]--;
 359                 l = btrfs_buffer_leaf(path->nodes[0]);
 360                 last_key = &l->items[path->slots[0]].key;
 361                 search_start = btrfs_disk_key_objectid(last_key);
 362         }
 363         if (root->fs_info->last_insert.objectid > search_start)
 364                 search_start = root->fs_info->last_insert.objectid;
 365
 366         path = btrfs_alloc_path();
 367
 368 check_failed:
 369         btrfs_init_path(path);
 370         ins->objectid = search_start;
 371         ins->offset = 0;
 372         start_found = 0;
 373         ret = btrfs_search_slot(trans, root, ins, path, 0, 0);
 374         if (ret < 0)
 375                 goto error;
 376
 377         if (path->slots[0] > 0)
 378                 path->slots[0]--;
 379
 380         while (1) {
 381                 l = btrfs_buffer_leaf(path->nodes[0]);
 382                 slot = path->slots[0];
 383                 if (slot >= btrfs_header_nritems(&l->header)) {
 384                         ret = btrfs_next_leaf(root, path);
 385                         if (ret == 0)
 386                                 continue;
 387                         if (ret < 0)
 388                                 goto error;
 389                         if (!start_found) {
 390                                 ins->objectid = search_start;
 391                                 ins->offset = (u64)-1;
 392                                 start_found = 1;
 393                                 goto check_pending;
 394                         }
 395                         ins->objectid = last_block > search_start ?
 396                                         last_block : search_start;
 397                         ins->offset = (u64)-1;
 398                         goto check_pending;
 399                 }
 400                 btrfs_disk_key_to_cpu(&key, &l->items[slot].key);
 401                 if (key.objectid >= search_start) {
 402                         if (start_found) {
 403                                 if (last_block < search_start)
 404                                         last_block = search_start;
 405                                 hole_size = key.objectid - last_block;
 406                                 if (hole_size > total_needed) {
 407                                         ins->objectid = last_block;
 408                                         ins->offset = hole_size;
 409                                         goto check_pending;
 410                                 }
 411                         }
 412                 }
 413                 start_found = 1;
 414                 last_block = key.objectid + key.offset;
 415                 path->slots[0]++;
 416         }
 417         // FIXME -ENOSPC
 418 check_pending:
 419         /* we have to make sure we didn't find an extent that has already
 420          * been allocated by the map tree or the original allocation
 421          */
 422         btrfs_release_path(root, path);
 423         BUG_ON(ins->objectid < search_start);
 424         for (test_block = ins->objectid;
 425              test_block < ins->objectid + total_needed; test_block++) {
 426                 if (test_radix_bit(&root->fs_info->pinned_radix,
 427                                       test_block)) {
 428                         search_start = test_block + 1;
 429                         goto check_failed;
 430                 }
 431         }
 432         BUG_ON(root->fs_info->current_insert.offset);
 433         root->fs_info->current_insert.offset = total_needed - num_blocks;
 434         root->fs_info->current_insert.objectid = ins->objectid + num_blocks;
 435         root->fs_info->current_insert.flags = 0;
 436         root->fs_info->last_insert.objectid = ins->objectid;
 437         ins->offset = num_blocks;
 438         btrfs_free_path(path);
 439         return 0;
 440 error:
 441         btrfs_release_path(root, path);
 442         btrfs_free_path(path);
 443         return ret;
 444 }
 445
 446 /*
 447  * finds a free extent and does all the dirty work required for allocation
 448  * returns the key for the extent through ins, and a tree buffer for
 449  * the first block of the extent through buf.
 450  *
 451  * returns 0 if everything worked, non-zero otherwise.
 452  */
 453 int btrfs_alloc_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 454                         *root, u64 num_blocks, u64 search_start, u64
 455                         search_end, u64 owner, struct btrfs_key *ins)
 456 {
 457         int ret;
 458         int pending_ret;
 459         u64 super_blocks_used;
 460         struct btrfs_fs_info *info = root->fs_info;
 461         struct btrfs_root *extent_root = info->extent_root;
 462         struct btrfs_extent_item extent_item;
 463
 464         btrfs_set_extent_refs(&extent_item, 1);
 465         btrfs_set_extent_owner(&extent_item, owner);
 466
 467         if (root == extent_root) {
 468                 BUG_ON(extent_root->fs_info->current_insert.offset == 0);
 469                 BUG_ON(num_blocks != 1);
 470                 BUG_ON(extent_root->fs_info->current_insert.flags ==
 471                        extent_root->fs_info->current_insert.offset);
 472                 ins->offset = 1;
 473                 ins->objectid = extent_root->fs_info->current_insert.objectid +
 474                                 extent_root->fs_info->current_insert.flags++;
 475                 return 0;
 476         }
 477         ret = find_free_extent(trans, root, num_blocks, search_start,
 478                                search_end, ins);
 479         if (ret)
 480                 return ret;
 481
 482         super_blocks_used = btrfs_super_blocks_used(info->disk_super);
 483         btrfs_set_super_blocks_used(info->disk_super, super_blocks_used +
 484                                     num_blocks);
 485         ret = btrfs_insert_item(trans, extent_root, ins, &extent_item,
 486                                 sizeof(extent_item));
 487
 488         finish_current_insert(trans, extent_root);
 489         pending_ret = del_pending_extents(trans, extent_root);
 490         if (ret)
 491                 return ret;
 492         if (pending_ret)
 493                 return pending_ret;
 494         return 0;
 495 }
 496
 497 /*
 498  * helper function to allocate a block for a given tree
 499  * returns the tree buffer or NULL.
 500  */
 501 struct buffer_head *btrfs_alloc_free_block(struct btrfs_trans_handle *trans,
 502                                             struct btrfs_root *root)
 503 {
 504         struct btrfs_key ins;
 505         int ret;
 506         struct buffer_head *buf;
 507
 508         ret = btrfs_alloc_extent(trans, root, 1, 0, (unsigned long)-1,
 509                 btrfs_header_parentid(btrfs_buffer_header(root->node)), &ins);
 510         if (ret) {
 511                 BUG();
 512                 return NULL;
 513         }
 514         buf = btrfs_find_create_tree_block(root, ins.objectid);
 515         set_buffer_uptodate(buf);
 516         return buf;
 517 }
 518
 519 static int drop_leaf_ref(struct btrfs_trans_handle *trans,
 520                          struct btrfs_root *root, struct buffer_head *cur)
 521 {
 522         struct btrfs_disk_key *key;
 523         struct btrfs_leaf *leaf;
 524         struct btrfs_file_extent_item *fi;
 525         int i;
 526         int nritems;
 527         int ret;
 528
 529         BUG_ON(!btrfs_is_leaf(btrfs_buffer_node(cur)));
 530         leaf = btrfs_buffer_leaf(cur);
 531         nritems = btrfs_header_nritems(&leaf->header);
 532         for (i = 0; i < nritems; i++) {
 533                 key = &leaf->items[i].key;
 534                 if (btrfs_disk_key_type(key) != BTRFS_EXTENT_DATA_KEY)
 535                         continue;
 536                 fi = btrfs_item_ptr(leaf, i, struct btrfs_file_extent_item);
 537                 /*
 538                  * FIXME make sure to insert a trans record that
 539                  * repeats the snapshot del on crash
 540                  */
 541                 ret = btrfs_free_extent(trans, root,
 542                                         btrfs_file_extent_disk_blocknr(fi),
 543                                         btrfs_file_extent_disk_num_blocks(fi),
 544                                         0);
 545                 BUG_ON(ret);
 546         }
 547         return 0;
 548 }
 549
 550 /*
 551  * helper function for drop_snapshot, this walks down the tree dropping ref
 552  * counts as it goes.
 553  */
 554 static int walk_down_tree(struct btrfs_trans_handle *trans, struct btrfs_root
 555                           *root, struct btrfs_path *path, int *level)
 556 {
 557         struct buffer_head *next;
 558         struct buffer_head *cur;
 559         u64 blocknr;
 560         int ret;
 561         u32 refs;
 562
 563         WARN_ON(*level < 0);
 564         WARN_ON(*level >= BTRFS_MAX_LEVEL);
 565         ret = lookup_block_ref(trans, root, path->nodes[*level]->b_blocknr,
 566                                1, &refs);
 567         BUG_ON(ret);
 568         if (refs > 1)
 569                 goto out;
 570         /*
 571          * walk down to the last node level and free all the leaves
 572          */
 573         while(*level >= 0) {
 574                 WARN_ON(*level < 0);
 575                 WARN_ON(*level >= BTRFS_MAX_LEVEL);
 576                 cur = path->nodes[*level];
 577                 if (btrfs_header_level(btrfs_buffer_header(cur)) != *level)
 578                         WARN_ON(1);
 579                 if (path->slots[*level] >=
 580                     btrfs_header_nritems(btrfs_buffer_header(cur)))
 581                         break;
 582                 if (*level == 0) {
 583                         ret = drop_leaf_ref(trans, root, cur);
 584                         BUG_ON(ret);
 585                         break;
 586                 }
 587                 blocknr = btrfs_node_blockptr(btrfs_buffer_node(cur),
 588                                               path->slots[*level]);
 589                 ret = lookup_block_ref(trans, root, blocknr, 1, &refs);
 590                 BUG_ON(ret);
 591                 if (refs != 1) {
 592                         path->slots[*level]++;
 593                         ret = btrfs_free_extent(trans, root, blocknr, 1, 1);
 594                         BUG_ON(ret);
 595                         continue;
 596                 }
 597                 next = read_tree_block(root, blocknr);
 598                 WARN_ON(*level <= 0);
 599                 if (path->nodes[*level-1])
 600                         btrfs_block_release(root, path->nodes[*level-1]);
 601                 path->nodes[*level-1] = next;
 602                 *level = btrfs_header_level(btrfs_buffer_header(next));
 603                 path->slots[*level] = 0;
 604         }
 605 out:
 606         WARN_ON(*level < 0);
 607         WARN_ON(*level >= BTRFS_MAX_LEVEL);
 608         ret = btrfs_free_extent(trans, root,
 609                                 path->nodes[*level]->b_blocknr, 1, 1);
 610         btrfs_block_release(root, path->nodes[*level]);
 611         path->nodes[*level] = NULL;
 612         *level += 1;
 613         BUG_ON(ret);
 614         return 0;
 615 }
 616
 617 /*
 618  * helper for dropping snapshots.  This walks back up the tree in the path
 619  * to find the first node higher up where we haven't yet gone through
 620  * all the slots
 621  */
 622 static int walk_up_tree(struct btrfs_trans_handle *trans, struct btrfs_root
 623                         *root, struct btrfs_path *path, int *level)
 624 {
 625         int i;
 626         int slot;
 627         int ret;
 628         for(i = *level; i < BTRFS_MAX_LEVEL - 1 && path->nodes[i]; i++) {
 629                 slot = path->slots[i];
 630                 if (slot < btrfs_header_nritems(
 631                     btrfs_buffer_header(path->nodes[i])) - 1) {
 632                         path->slots[i]++;
 633                         *level = i;
 634                         return 0;
 635                 } else {
 636                         ret = btrfs_free_extent(trans, root,
 637                                                 path->nodes[*level]->b_blocknr,
 638                                                 1, 1);
 639                         BUG_ON(ret);
 640                         btrfs_block_release(root, path->nodes[*level]);
 641                         path->nodes[*level] = NULL;
 642                         *level = i + 1;
 643                 }
 644         }
 645         return 1;
 646 }
 647
 648 /*
 649  * drop the reference count on the tree rooted at 'snap'.  This traverses
 650  * the tree freeing any blocks that have a ref count of zero after being
 651  * decremented.
 652  */
 653 int btrfs_drop_snapshot(struct btrfs_trans_handle *trans, struct btrfs_root
 654                         *root, struct buffer_head *snap)
 655 {
 656         int ret = 0;
 657         int wret;
 658         int level;
 659         struct btrfs_path *path;
 660         int i;
 661         int orig_level;
 662
 663         path = btrfs_alloc_path();
 664         BUG_ON(!path);
 665         btrfs_init_path(path);
 666
 667         level = btrfs_header_level(btrfs_buffer_header(snap));
 668         orig_level = level;
 669         path->nodes[level] = snap;
 670         path->slots[level] = 0;
 671         while(1) {
 672                 wret = walk_down_tree(trans, root, path, &level);
 673                 if (wret > 0)
 674                         break;
 675                 if (wret < 0)
 676                         ret = wret;
 677
 678                 wret = walk_up_tree(trans, root, path, &level);
 679                 if (wret > 0)
 680                         break;
 681                 if (wret < 0)
 682                         ret = wret;
 683         }
 684         for (i = 0; i <= orig_level; i++) {
 685                 if (path->nodes[i]) {
 686                         btrfs_block_release(root, path->nodes[i]);
 687                 }
 688         }
 689         btrfs_free_path(path);
 690         return ret;
 691 }