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                         ret = btrfs_inc_extent_ref(trans, root,
 115                                     btrfs_file_extent_disk_blocknr(fi),
 116                                     btrfs_file_extent_disk_num_blocks(fi));
 117                         BUG_ON(ret);
 118                 } else {
 119                         blocknr = btrfs_node_blockptr(buf_node, i);
 120                         ret = btrfs_inc_extent_ref(trans, root, blocknr, 1);
 121                         BUG_ON(ret);
 122                 }
 123         }
 124         return 0;
 125 }
 126
 127 int btrfs_finish_extent_commit(struct btrfs_trans_handle *trans, struct
 128                                btrfs_root *root)
 129 {
 130         unsigned long gang[8];
 131         u64 first = 0;
 132         int ret;
 133         int i;
 134         struct radix_tree_root *pinned_radix = &root->fs_info->pinned_radix;
 135
 136         while(1) {
 137                 ret = find_first_radix_bit(pinned_radix, gang,
 138                                            ARRAY_SIZE(gang));
 139                 if (!ret)
 140                         break;
 141                 if (!first)
 142                         first = gang[0];
 143                 for (i = 0; i < ret; i++) {
 144                         clear_radix_bit(pinned_radix, gang[i]);
 145                 }
 146         }
 147         if (root->fs_info->last_insert.objectid > first)
 148                 root->fs_info->last_insert.objectid = first;
 149         root->fs_info->last_insert.offset = 0;
 150         return 0;
 151 }
 152
 153 static int finish_current_insert(struct btrfs_trans_handle *trans, struct
 154                                  btrfs_root *extent_root)
 155 {
 156         struct btrfs_key ins;
 157         struct btrfs_extent_item extent_item;
 158         int i;
 159         int ret;
 160         u64 super_blocks_used;
 161         struct btrfs_fs_info *info = extent_root->fs_info;
 162
 163         btrfs_set_extent_refs(&extent_item, 1);
 164         ins.offset = 1;
 165         ins.flags = 0;
 166         btrfs_set_key_type(&ins, BTRFS_EXTENT_ITEM_KEY);
 167
 168         for (i = 0; i < extent_root->fs_info->current_insert.flags; i++) {
 169                 ins.objectid = extent_root->fs_info->current_insert.objectid +
 170                                 i;
 171                 super_blocks_used = btrfs_super_blocks_used(info->disk_super);
 172                 btrfs_set_super_blocks_used(info->disk_super,
 173                                             super_blocks_used + 1);
 174                 ret = btrfs_insert_item(trans, extent_root, &ins, &extent_item,
 175                                         sizeof(extent_item));
 176                 BUG_ON(ret);
 177         }
 178         extent_root->fs_info->current_insert.offset = 0;
 179         return 0;
 180 }
 181
 182 static int pin_down_block(struct btrfs_root *root, u64 blocknr, int pending)
 183 {
 184         int err;
 185         struct btrfs_header *header;
 186         struct buffer_head *bh;
 187
 188         if (!pending) {
 189                 bh = btrfs_find_tree_block(root, blocknr);
 190                 if (bh) {
 191                         if (buffer_uptodate(bh)) {
 192                                 u64 transid =
 193                                     root->fs_info->running_transaction->transid;
 194                                 header = btrfs_buffer_header(bh);
 195                                 if (btrfs_header_generation(header) ==
 196                                     transid) {
 197                                         btrfs_block_release(root, bh);
 198                                         return 0;
 199                                 }
 200                         }
 201                         btrfs_block_release(root, bh);
 202                 }
 203                 err = set_radix_bit(&root->fs_info->pinned_radix, blocknr);
 204         } else {
 205                 err = set_radix_bit(&root->fs_info->pending_del_radix, blocknr);
 206         }
 207         BUG_ON(err);
 208         return 0;
 209 }
 210
 211 /*
 212  * remove an extent from the root, returns 0 on success
 213  */
 214 static int __free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 215                          *root, u64 blocknr, u64 num_blocks, int pin)
 216 {
 217         struct btrfs_path *path;
 218         struct btrfs_key key;
 219         struct btrfs_fs_info *info = root->fs_info;
 220         struct btrfs_root *extent_root = info->extent_root;
 221         int ret;
 222         struct btrfs_extent_item *ei;
 223         struct btrfs_key ins;
 224         u32 refs;
 225
 226         key.objectid = blocknr;
 227         key.flags = 0;
 228         btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
 229         key.offset = num_blocks;
 230
 231         find_free_extent(trans, root, 0, 0, (u64)-1, &ins);
 232         path = btrfs_alloc_path();
 233         BUG_ON(!path);
 234         btrfs_init_path(path);
 235
 236         ret = btrfs_search_slot(trans, extent_root, &key, path, -1, 1);
 237         if (ret) {
 238                 printk("failed to find %Lu\n", key.objectid);
 239                 btrfs_print_tree(extent_root, extent_root->node);
 240                 printk("failed to find %Lu\n", key.objectid);
 241                 BUG();
 242         }
 243         ei = btrfs_item_ptr(btrfs_buffer_leaf(path->nodes[0]), path->slots[0],
 244                             struct btrfs_extent_item);
 245         BUG_ON(ei->refs == 0);
 246         refs = btrfs_extent_refs(ei) - 1;
 247         btrfs_set_extent_refs(ei, refs);
 248         btrfs_mark_buffer_dirty(path->nodes[0]);
 249         if (refs == 0) {
 250                 u64 super_blocks_used;
 251
 252                 if (pin) {
 253                         ret = pin_down_block(root, blocknr, 0);
 254                         BUG_ON(ret);
 255                 }
 256
 257                 super_blocks_used = btrfs_super_blocks_used(info->disk_super);
 258                 btrfs_set_super_blocks_used(info->disk_super,
 259                                             super_blocks_used - num_blocks);
 260                 ret = btrfs_del_item(trans, extent_root, path);
 261                 if (ret)
 262                         BUG();
 263         }
 264         btrfs_release_path(extent_root, path);
 265         btrfs_free_path(path);
 266         finish_current_insert(trans, extent_root);
 267         return ret;
 268 }
 269
 270 /*
 271  * find all the blocks marked as pending in the radix tree and remove
 272  * them from the extent map
 273  */
 274 static int del_pending_extents(struct btrfs_trans_handle *trans, struct
 275                                btrfs_root *extent_root)
 276 {
 277         int ret;
 278         int wret;
 279         int err = 0;
 280         unsigned long gang[4];
 281         int i;
 282         struct radix_tree_root *pending_radix;
 283         struct radix_tree_root *pinned_radix;
 284
 285         pending_radix = &extent_root->fs_info->pending_del_radix;
 286         pinned_radix = &extent_root->fs_info->pinned_radix;
 287
 288         while(1) {
 289                 ret = find_first_radix_bit(pending_radix, gang,
 290                                            ARRAY_SIZE(gang));
 291                 if (!ret)
 292                         break;
 293                 for (i = 0; i < ret; i++) {
 294                         wret = set_radix_bit(pinned_radix, gang[i]);
 295                         BUG_ON(wret);
 296                         wret = clear_radix_bit(pending_radix, gang[i]);
 297                         BUG_ON(wret);
 298                         wret = __free_extent(trans, extent_root,
 299                                              gang[i], 1, 0);
 300                         if (wret)
 301                                 err = wret;
 302                 }
 303         }
 304         return err;
 305 }
 306
 307 /*
 308  * remove an extent from the root, returns 0 on success
 309  */
 310 int btrfs_free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 311                       *root, u64 blocknr, u64 num_blocks, int pin)
 312 {
 313         struct btrfs_root *extent_root = root->fs_info->extent_root;
 314         int pending_ret;
 315         int ret;
 316
 317         if (root == extent_root) {
 318                 pin_down_block(root, blocknr, 1);
 319                 return 0;
 320         }
 321         ret = __free_extent(trans, root, blocknr, num_blocks, pin);
 322         pending_ret = del_pending_extents(trans, root->fs_info->extent_root);
 323         return ret ? ret : pending_ret;
 324 }
 325
 326 /*
 327  * walks the btree of allocated extents and find a hole of a given size.
 328  * The key ins is changed to record the hole:
 329  * ins->objectid == block start
 330  * ins->flags = BTRFS_EXTENT_ITEM_KEY
 331  * ins->offset == number of blocks
 332  * Any available blocks before search_start are skipped.
 333  */
 334 static int find_free_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 335                             *orig_root, u64 num_blocks, u64 search_start, u64
 336                             search_end, struct btrfs_key *ins)
 337 {
 338         struct btrfs_path *path;
 339         struct btrfs_key key;
 340         int ret;
 341         u64 hole_size = 0;
 342         int slot = 0;
 343         u64 last_block = 0;
 344         u64 test_block;
 345         int start_found;
 346         struct btrfs_leaf *l;
 347         struct btrfs_root * root = orig_root->fs_info->extent_root;
 348         int total_needed = num_blocks;
 349         int level;
 350
 351         path = btrfs_alloc_path();
 352         ins->flags = 0;
 353         btrfs_set_key_type(ins, BTRFS_EXTENT_ITEM_KEY);
 354
 355         level = btrfs_header_level(btrfs_buffer_header(root->node));
 356         total_needed += (level + 1) * 3;
 357         if (root->fs_info->last_insert.objectid == 0 && search_end == (u64)-1) {
 358                 struct btrfs_disk_key *last_key;
 359                 btrfs_init_path(path);
 360                 ins->objectid = (u64)-1;
 361                 ins->offset = (u64)-1;
 362                 ret = btrfs_search_slot(trans, root, ins, path, 0, 0);
 363                 if (ret < 0)
 364                         goto error;
 365                 BUG_ON(ret == 0);
 366                 if (path->slots[0] > 0)
 367                         path->slots[0]--;
 368                 l = btrfs_buffer_leaf(path->nodes[0]);
 369                 last_key = &l->items[path->slots[0]].key;
 370                 search_start = btrfs_disk_key_objectid(last_key);
 371         }
 372         if (root->fs_info->last_insert.objectid > search_start)
 373                 search_start = root->fs_info->last_insert.objectid;
 374
 375 check_failed:
 376         btrfs_init_path(path);
 377         ins->objectid = search_start;
 378         ins->offset = 0;
 379         start_found = 0;
 380         ret = btrfs_search_slot(trans, root, ins, path, 0, 0);
 381         if (ret < 0)
 382                 goto error;
 383
 384         if (path->slots[0] > 0)
 385                 path->slots[0]--;
 386
 387         while (1) {
 388                 l = btrfs_buffer_leaf(path->nodes[0]);
 389                 slot = path->slots[0];
 390                 if (slot >= btrfs_header_nritems(&l->header)) {
 391                         ret = btrfs_next_leaf(root, path);
 392                         if (ret == 0)
 393                                 continue;
 394                         if (ret < 0)
 395                                 goto error;
 396                         if (!start_found) {
 397                                 ins->objectid = search_start;
 398                                 ins->offset = (u64)-1;
 399                                 start_found = 1;
 400                                 goto check_pending;
 401                         }
 402                         ins->objectid = last_block > search_start ?
 403                                         last_block : search_start;
 404                         ins->offset = (u64)-1;
 405                         goto check_pending;
 406                 }
 407                 btrfs_disk_key_to_cpu(&key, &l->items[slot].key);
 408                 if (key.objectid >= search_start) {
 409                         if (start_found) {
 410                                 if (last_block < search_start)
 411                                         last_block = search_start;
 412                                 hole_size = key.objectid - last_block;
 413                                 if (hole_size > total_needed) {
 414                                         ins->objectid = last_block;
 415                                         ins->offset = hole_size;
 416                                         goto check_pending;
 417                                 }
 418                         }
 419                 }
 420                 start_found = 1;
 421                 last_block = key.objectid + key.offset;
 422                 path->slots[0]++;
 423         }
 424         // FIXME -ENOSPC
 425 check_pending:
 426         /* we have to make sure we didn't find an extent that has already
 427          * been allocated by the map tree or the original allocation
 428          */
 429         btrfs_release_path(root, path);
 430         BUG_ON(ins->objectid < search_start);
 431         for (test_block = ins->objectid;
 432              test_block < ins->objectid + total_needed; test_block++) {
 433                 if (test_radix_bit(&root->fs_info->pinned_radix,
 434                                       test_block)) {
 435                         search_start = test_block + 1;
 436                         goto check_failed;
 437                 }
 438         }
 439         BUG_ON(root->fs_info->current_insert.offset);
 440         root->fs_info->current_insert.offset = total_needed - num_blocks;
 441         root->fs_info->current_insert.objectid = ins->objectid + num_blocks;
 442         root->fs_info->current_insert.flags = 0;
 443         root->fs_info->last_insert.objectid = ins->objectid;
 444         ins->offset = num_blocks;
 445         btrfs_free_path(path);
 446         return 0;
 447 error:
 448         btrfs_release_path(root, path);
 449         btrfs_free_path(path);
 450         return ret;
 451 }
 452
 453 /*
 454  * finds a free extent and does all the dirty work required for allocation
 455  * returns the key for the extent through ins, and a tree buffer for
 456  * the first block of the extent through buf.
 457  *
 458  * returns 0 if everything worked, non-zero otherwise.
 459  */
 460 int btrfs_alloc_extent(struct btrfs_trans_handle *trans, struct btrfs_root
 461                         *root, u64 num_blocks, u64 search_start, u64
 462                         search_end, struct btrfs_key *ins)
 463 {
 464         int ret;
 465         int pending_ret;
 466         u64 super_blocks_used;
 467         struct btrfs_fs_info *info = root->fs_info;
 468         struct btrfs_root *extent_root = info->extent_root;
 469         struct btrfs_extent_item extent_item;
 470
 471         btrfs_set_extent_refs(&extent_item, 1);
 472
 473         if (root == extent_root) {
 474                 BUG_ON(extent_root->fs_info->current_insert.offset == 0);
 475                 BUG_ON(num_blocks != 1);
 476                 BUG_ON(extent_root->fs_info->current_insert.flags ==
 477                        extent_root->fs_info->current_insert.offset);
 478                 ins->offset = 1;
 479                 ins->objectid = extent_root->fs_info->current_insert.objectid +
 480                                 extent_root->fs_info->current_insert.flags++;
 481                 return 0;
 482         }
 483         ret = find_free_extent(trans, root, num_blocks, search_start,
 484                                search_end, ins);
 485         if (ret)
 486                 return ret;
 487
 488         super_blocks_used = btrfs_super_blocks_used(info->disk_super);
 489         btrfs_set_super_blocks_used(info->disk_super, super_blocks_used +
 490                                     num_blocks);
 491         ret = btrfs_insert_item(trans, extent_root, ins, &extent_item,
 492                                 sizeof(extent_item));
 493
 494         finish_current_insert(trans, extent_root);
 495         pending_ret = del_pending_extents(trans, extent_root);
 496         if (ret)
 497                 return ret;
 498         if (pending_ret)
 499                 return pending_ret;
 500         return 0;
 501 }
 502
 503 /*
 504  * helper function to allocate a block for a given tree
 505  * returns the tree buffer or NULL.
 506  */
 507 struct buffer_head *btrfs_alloc_free_block(struct btrfs_trans_handle *trans,
 508                                             struct btrfs_root *root)
 509 {
 510         struct btrfs_key ins;
 511         int ret;
 512         struct buffer_head *buf;
 513
 514         ret = btrfs_alloc_extent(trans, root, 1, 0, (unsigned long)-1, &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_extent_ref(trans, root, bh_blocknr(path->nodes[*level]),
 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_extent_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                                 bh_blocknr(path->nodes[*level]), 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                                                 bh_blocknr(path->nodes[*level]),
 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 }