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