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