fs/btrfs/backref.c

   1 /*
   2  * Copyright (C) 2011 STRATO.  All rights reserved.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public
   6  * License v2 as published by the Free Software Foundation.
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  11  * General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public
  14  * License along with this program; if not, write to the
  15  * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  16  * Boston, MA 021110-1307, USA.
  17  */
  18
  19 #include <linux/vmalloc.h>
  20 #include "ctree.h"
  21 #include "disk-io.h"
  22 #include "backref.h"
  23 #include "ulist.h"
  24 #include "transaction.h"
  25 #include "delayed-ref.h"
  26 #include "locking.h"
  27
  28 /* Just an arbitrary number so we can be sure this happened */
  29 #define BACKREF_FOUND_SHARED 6
  30
  31 struct extent_inode_elem {
  32         u64 inum;
  33         u64 offset;
  34         struct extent_inode_elem *next;
  35 };
  36
  37 static int check_extent_in_eb(struct btrfs_key *key, struct extent_buffer *eb,
  38                                 struct btrfs_file_extent_item *fi,
  39                                 u64 extent_item_pos,
  40                                 struct extent_inode_elem **eie)
  41 {
  42         u64 offset = 0;
  43         struct extent_inode_elem *e;
  44
  45         if (!btrfs_file_extent_compression(eb, fi) &&
  46             !btrfs_file_extent_encryption(eb, fi) &&
  47             !btrfs_file_extent_other_encoding(eb, fi)) {
  48                 u64 data_offset;
  49                 u64 data_len;
  50
  51                 data_offset = btrfs_file_extent_offset(eb, fi);
  52                 data_len = btrfs_file_extent_num_bytes(eb, fi);
  53
  54                 if (extent_item_pos < data_offset ||
  55                     extent_item_pos >= data_offset + data_len)
  56                         return 1;
  57                 offset = extent_item_pos - data_offset;
  58         }
  59
  60         e = kmalloc(sizeof(*e), GFP_NOFS);
  61         if (!e)
  62                 return -ENOMEM;
  63
  64         e->next = *eie;
  65         e->inum = key->objectid;
  66         e->offset = key->offset + offset;
  67         *eie = e;
  68
  69         return 0;
  70 }
  71
  72 static void free_inode_elem_list(struct extent_inode_elem *eie)
  73 {
  74         struct extent_inode_elem *eie_next;
  75
  76         for (; eie; eie = eie_next) {
  77                 eie_next = eie->next;
  78                 kfree(eie);
  79         }
  80 }
  81
  82 static int find_extent_in_eb(struct extent_buffer *eb, u64 wanted_disk_byte,
  83                                 u64 extent_item_pos,
  84                                 struct extent_inode_elem **eie)
  85 {
  86         u64 disk_byte;
  87         struct btrfs_key key;
  88         struct btrfs_file_extent_item *fi;
  89         int slot;
  90         int nritems;
  91         int extent_type;
  92         int ret;
  93
  94         /*
  95          * from the shared data ref, we only have the leaf but we need
  96          * the key. thus, we must look into all items and see that we
  97          * find one (some) with a reference to our extent item.
  98          */
  99         nritems = btrfs_header_nritems(eb);
 100         for (slot = 0; slot < nritems; ++slot) {
 101                 btrfs_item_key_to_cpu(eb, &key, slot);
 102                 if (key.type != BTRFS_EXTENT_DATA_KEY)
 103                         continue;
 104                 fi = btrfs_item_ptr(eb, slot, struct btrfs_file_extent_item);
 105                 extent_type = btrfs_file_extent_type(eb, fi);
 106                 if (extent_type == BTRFS_FILE_EXTENT_INLINE)
 107                         continue;
 108                 /* don't skip BTRFS_FILE_EXTENT_PREALLOC, we can handle that */
 109                 disk_byte = btrfs_file_extent_disk_bytenr(eb, fi);
 110                 if (disk_byte != wanted_disk_byte)
 111                         continue;
 112
 113                 ret = check_extent_in_eb(&key, eb, fi, extent_item_pos, eie);
 114                 if (ret < 0)
 115                         return ret;
 116         }
 117
 118         return 0;
 119 }
 120
 121 /*
 122  * this structure records all encountered refs on the way up to the root
 123  */
 124 struct __prelim_ref {
 125         struct list_head list;
 126         u64 root_id;
 127         struct btrfs_key key_for_search;
 128         int level;
 129         int count;
 130         struct extent_inode_elem *inode_list;
 131         u64 parent;
 132         u64 wanted_disk_byte;
 133 };
 134
 135 static struct kmem_cache *btrfs_prelim_ref_cache;
 136
 137 int __init btrfs_prelim_ref_init(void)
 138 {
 139         btrfs_prelim_ref_cache = kmem_cache_create("btrfs_prelim_ref",
 140                                         sizeof(struct __prelim_ref),
 141                                         0,
 142                                         SLAB_MEM_SPREAD,
 143                                         NULL);
 144         if (!btrfs_prelim_ref_cache)
 145                 return -ENOMEM;
 146         return 0;
 147 }
 148
 149 void btrfs_prelim_ref_exit(void)
 150 {
 151         kmem_cache_destroy(btrfs_prelim_ref_cache);
 152 }
 153
 154 /*
 155  * the rules for all callers of this function are:
 156  * - obtaining the parent is the goal
 157  * - if you add a key, you must know that it is a correct key
 158  * - if you cannot add the parent or a correct key, then we will look into the
 159  *   block later to set a correct key
 160  *
 161  * delayed refs
 162  * ============
 163  *        backref type | shared | indirect | shared | indirect
 164  * information         |   tree |     tree |   data |     data
 165  * --------------------+--------+----------+--------+----------
 166  *      parent logical |    y   |     -    |    -   |     -
 167  *      key to resolve |    -   |     y    |    y   |     y
 168  *  tree block logical |    -   |     -    |    -   |     -
 169  *  root for resolving |    y   |     y    |    y   |     y
 170  *
 171  * - column 1:       we've the parent -> done
 172  * - column 2, 3, 4: we use the key to find the parent
 173  *
 174  * on disk refs (inline or keyed)
 175  * ==============================
 176  *        backref type | shared | indirect | shared | indirect
 177  * information         |   tree |     tree |   data |     data
 178  * --------------------+--------+----------+--------+----------
 179  *      parent logical |    y   |     -    |    y   |     -
 180  *      key to resolve |    -   |     -    |    -   |     y
 181  *  tree block logical |    y   |     y    |    y   |     y
 182  *  root for resolving |    -   |     y    |    y   |     y
 183  *
 184  * - column 1, 3: we've the parent -> done
 185  * - column 2:    we take the first key from the block to find the parent
 186  *                (see __add_missing_keys)
 187  * - column 4:    we use the key to find the parent
 188  *
 189  * additional information that's available but not required to find the parent
 190  * block might help in merging entries to gain some speed.
 191  */
 192
 193 static int __add_prelim_ref(struct list_head *head, u64 root_id,
 194                             struct btrfs_key *key, int level,
 195                             u64 parent, u64 wanted_disk_byte, int count,
 196                             gfp_t gfp_mask)
 197 {
 198         struct __prelim_ref *ref;
 199
 200         if (root_id == BTRFS_DATA_RELOC_TREE_OBJECTID)
 201                 return 0;
 202
 203         ref = kmem_cache_alloc(btrfs_prelim_ref_cache, gfp_mask);
 204         if (!ref)
 205                 return -ENOMEM;
 206
 207         ref->root_id = root_id;
 208         if (key) {
 209                 ref->key_for_search = *key;
 210                 /*
 211                  * We can often find data backrefs with an offset that is too
 212                  * large (>= LLONG_MAX, maximum allowed file offset) due to
 213                  * underflows when subtracting a file's offset with the data
 214                  * offset of its corresponding extent data item. This can
 215                  * happen for example in the clone ioctl.
 216                  * So if we detect such case we set the search key's offset to
 217                  * zero to make sure we will find the matching file extent item
 218                  * at add_all_parents(), otherwise we will miss it because the
 219                  * offset taken form the backref is much larger then the offset
 220                  * of the file extent item. This can make us scan a very large
 221                  * number of file extent items, but at least it will not make
 222                  * us miss any.
 223                  * This is an ugly workaround for a behaviour that should have
 224                  * never existed, but it does and a fix for the clone ioctl
 225                  * would touch a lot of places, cause backwards incompatibility
 226                  * and would not fix the problem for extents cloned with older
 227                  * kernels.
 228                  */
 229                 if (ref->key_for_search.type == BTRFS_EXTENT_DATA_KEY &&
 230                     ref->key_for_search.offset >= LLONG_MAX)
 231                         ref->key_for_search.offset = 0;
 232         } else {
 233                 memset(&ref->key_for_search, 0, sizeof(ref->key_for_search));
 234         }
 235
 236         ref->inode_list = NULL;
 237         ref->level = level;
 238         ref->count = count;
 239         ref->parent = parent;
 240         ref->wanted_disk_byte = wanted_disk_byte;
 241         list_add_tail(&ref->list, head);
 242
 243         return 0;
 244 }
 245
 246 static int add_all_parents(struct btrfs_root *root, struct btrfs_path *path,
 247                            struct ulist *parents, struct __prelim_ref *ref,
 248                            int level, u64 time_seq, const u64 *extent_item_pos,
 249                            u64 total_refs)
 250 {
 251         int ret = 0;
 252         int slot;
 253         struct extent_buffer *eb;
 254         struct btrfs_key key;
 255         struct btrfs_key *key_for_search = &ref->key_for_search;
 256         struct btrfs_file_extent_item *fi;
 257         struct extent_inode_elem *eie = NULL, *old = NULL;
 258         u64 disk_byte;
 259         u64 wanted_disk_byte = ref->wanted_disk_byte;
 260         u64 count = 0;
 261
 262         if (level != 0) {
 263                 eb = path->nodes[level];
 264                 ret = ulist_add(parents, eb->start, 0, GFP_NOFS);
 265                 if (ret < 0)
 266                         return ret;
 267                 return 0;
 268         }
 269
 270         /*
 271          * We normally enter this function with the path already pointing to
 272          * the first item to check. But sometimes, we may enter it with
 273          * slot==nritems. In that case, go to the next leaf before we continue.
 274          */
 275         if (path->slots[0] >= btrfs_header_nritems(path->nodes[0])) {
 276                 if (time_seq == (u64)-1)
 277                         ret = btrfs_next_leaf(root, path);
 278                 else
 279                         ret = btrfs_next_old_leaf(root, path, time_seq);
 280         }
 281
 282         while (!ret && count < total_refs) {
 283                 eb = path->nodes[0];
 284                 slot = path->slots[0];
 285
 286                 btrfs_item_key_to_cpu(eb, &key, slot);
 287
 288                 if (key.objectid != key_for_search->objectid ||
 289                     key.type != BTRFS_EXTENT_DATA_KEY)
 290                         break;
 291
 292                 fi = btrfs_item_ptr(eb, slot, struct btrfs_file_extent_item);
 293                 disk_byte = btrfs_file_extent_disk_bytenr(eb, fi);
 294
 295                 if (disk_byte == wanted_disk_byte) {
 296                         eie = NULL;
 297                         old = NULL;
 298                         count++;
 299                         if (extent_item_pos) {
 300                                 ret = check_extent_in_eb(&key, eb, fi,
 301                                                 *extent_item_pos,
 302                                                 &eie);
 303                                 if (ret < 0)
 304                                         break;
 305                         }
 306                         if (ret > 0)
 307                                 goto next;
 308                         ret = ulist_add_merge_ptr(parents, eb->start,
 309                                                   eie, (void **)&old, GFP_NOFS);
 310                         if (ret < 0)
 311                                 break;
 312                         if (!ret && extent_item_pos) {
 313                                 while (old->next)
 314                                         old = old->next;
 315                                 old->next = eie;
 316                         }
 317                         eie = NULL;
 318                 }
 319 next:
 320                 if (time_seq == (u64)-1)
 321                         ret = btrfs_next_item(root, path);
 322                 else
 323                         ret = btrfs_next_old_item(root, path, time_seq);
 324         }
 325
 326         if (ret > 0)
 327                 ret = 0;
 328         else if (ret < 0)
 329                 free_inode_elem_list(eie);
 330         return ret;
 331 }
 332
 333 /*
 334  * resolve an indirect backref in the form (root_id, key, level)
 335  * to a logical address
 336  */
 337 static int __resolve_indirect_ref(struct btrfs_fs_info *fs_info,
 338                                   struct btrfs_path *path, u64 time_seq,
 339                                   struct __prelim_ref *ref,
 340                                   struct ulist *parents,
 341                                   const u64 *extent_item_pos, u64 total_refs)
 342 {
 343         struct btrfs_root *root;
 344         struct btrfs_key root_key;
 345         struct extent_buffer *eb;
 346         int ret = 0;
 347         int root_level;
 348         int level = ref->level;
 349         int index;
 350
 351         root_key.objectid = ref->root_id;
 352         root_key.type = BTRFS_ROOT_ITEM_KEY;
 353         root_key.offset = (u64)-1;
 354
 355         index = srcu_read_lock(&fs_info->subvol_srcu);
 356
 357         root = btrfs_get_fs_root(fs_info, &root_key, false);
 358         if (IS_ERR(root)) {
 359                 srcu_read_unlock(&fs_info->subvol_srcu, index);
 360                 ret = PTR_ERR(root);
 361                 goto out;
 362         }
 363
 364         if (btrfs_is_testing(fs_info)) {
 365                 srcu_read_unlock(&fs_info->subvol_srcu, index);
 366                 ret = -ENOENT;
 367                 goto out;
 368         }
 369
 370         if (path->search_commit_root)
 371                 root_level = btrfs_header_level(root->commit_root);
 372         else if (time_seq == (u64)-1)
 373                 root_level = btrfs_header_level(root->node);
 374         else
 375                 root_level = btrfs_old_root_level(root, time_seq);
 376
 377         if (root_level + 1 == level) {
 378                 srcu_read_unlock(&fs_info->subvol_srcu, index);
 379                 goto out;
 380         }
 381
 382         path->lowest_level = level;
 383         if (time_seq == (u64)-1)
 384                 ret = btrfs_search_slot(NULL, root, &ref->key_for_search, path,
 385                                         0, 0);
 386         else
 387                 ret = btrfs_search_old_slot(root, &ref->key_for_search, path,
 388                                             time_seq);
 389
 390         /* root node has been locked, we can release @subvol_srcu safely here */
 391         srcu_read_unlock(&fs_info->subvol_srcu, index);
 392
 393         pr_debug("search slot in root %llu (level %d, ref count %d) returned "
 394                  "%d for key (%llu %u %llu)\n",
 395                  ref->root_id, level, ref->count, ret,
 396                  ref->key_for_search.objectid, ref->key_for_search.type,
 397                  ref->key_for_search.offset);
 398         if (ret < 0)
 399                 goto out;
 400
 401         eb = path->nodes[level];
 402         while (!eb) {
 403                 if (WARN_ON(!level)) {
 404                         ret = 1;
 405                         goto out;
 406                 }
 407                 level--;
 408                 eb = path->nodes[level];
 409         }
 410
 411         ret = add_all_parents(root, path, parents, ref, level, time_seq,
 412                               extent_item_pos, total_refs);
 413 out:
 414         path->lowest_level = 0;
 415         btrfs_release_path(path);
 416         return ret;
 417 }
 418
 419 /*
 420  * resolve all indirect backrefs from the list
 421  */
 422 static int __resolve_indirect_refs(struct btrfs_fs_info *fs_info,
 423                                    struct btrfs_path *path, u64 time_seq,
 424                                    struct list_head *head,
 425                                    const u64 *extent_item_pos, u64 total_refs,
 426                                    u64 root_objectid)
 427 {
 428         int err;
 429         int ret = 0;
 430         struct __prelim_ref *ref;
 431         struct __prelim_ref *ref_safe;
 432         struct __prelim_ref *new_ref;
 433         struct ulist *parents;
 434         struct ulist_node *node;
 435         struct ulist_iterator uiter;
 436
 437         parents = ulist_alloc(GFP_NOFS);
 438         if (!parents)
 439                 return -ENOMEM;
 440
 441         /*
 442          * _safe allows us to insert directly after the current item without
 443          * iterating over the newly inserted items.
 444          * we're also allowed to re-assign ref during iteration.
 445          */
 446         list_for_each_entry_safe(ref, ref_safe, head, list) {
 447                 if (ref->parent)        /* already direct */
 448                         continue;
 449                 if (ref->count == 0)
 450                         continue;
 451                 if (root_objectid && ref->root_id != root_objectid) {
 452                         ret = BACKREF_FOUND_SHARED;
 453                         goto out;
 454                 }
 455                 err = __resolve_indirect_ref(fs_info, path, time_seq, ref,
 456                                              parents, extent_item_pos,
 457                                              total_refs);
 458                 /*
 459                  * we can only tolerate ENOENT,otherwise,we should catch error
 460                  * and return directly.
 461                  */
 462                 if (err == -ENOENT) {
 463                         continue;
 464                 } else if (err) {
 465                         ret = err;
 466                         goto out;
 467                 }
 468
 469                 /* we put the first parent into the ref at hand */
 470                 ULIST_ITER_INIT(&uiter);
 471                 node = ulist_next(parents, &uiter);
 472                 ref->parent = node ? node->val : 0;
 473                 ref->inode_list = node ?
 474                         (struct extent_inode_elem *)(uintptr_t)node->aux : NULL;
 475
 476                 /* additional parents require new refs being added here */
 477                 while ((node = ulist_next(parents, &uiter))) {
 478                         new_ref = kmem_cache_alloc(btrfs_prelim_ref_cache,
 479                                                    GFP_NOFS);
 480                         if (!new_ref) {
 481                                 ret = -ENOMEM;
 482                                 goto out;
 483                         }
 484                         memcpy(new_ref, ref, sizeof(*ref));
 485                         new_ref->parent = node->val;
 486                         new_ref->inode_list = (struct extent_inode_elem *)
 487                                                         (uintptr_t)node->aux;
 488                         list_add(&new_ref->list, &ref->list);
 489                 }
 490                 ulist_reinit(parents);
 491         }
 492 out:
 493         ulist_free(parents);
 494         return ret;
 495 }
 496
 497 static inline int ref_for_same_block(struct __prelim_ref *ref1,
 498                                      struct __prelim_ref *ref2)
 499 {
 500         if (ref1->level != ref2->level)
 501                 return 0;
 502         if (ref1->root_id != ref2->root_id)
 503                 return 0;
 504         if (ref1->key_for_search.type != ref2->key_for_search.type)
 505                 return 0;
 506         if (ref1->key_for_search.objectid != ref2->key_for_search.objectid)
 507                 return 0;
 508         if (ref1->key_for_search.offset != ref2->key_for_search.offset)
 509                 return 0;
 510         if (ref1->parent != ref2->parent)
 511                 return 0;
 512
 513         return 1;
 514 }
 515
 516 /*
 517  * read tree blocks and add keys where required.
 518  */
 519 static int __add_missing_keys(struct btrfs_fs_info *fs_info,
 520                               struct list_head *head)
 521 {
 522         struct __prelim_ref *ref;
 523         struct extent_buffer *eb;
 524
 525         list_for_each_entry(ref, head, list) {
 526                 if (ref->parent)
 527                         continue;
 528                 if (ref->key_for_search.type)
 529                         continue;
 530                 BUG_ON(!ref->wanted_disk_byte);
 531                 eb = read_tree_block(fs_info->tree_root, ref->wanted_disk_byte,
 532                                      0);
 533                 if (IS_ERR(eb)) {
 534                         return PTR_ERR(eb);
 535                 } else if (!extent_buffer_uptodate(eb)) {
 536                         free_extent_buffer(eb);
 537                         return -EIO;
 538                 }
 539                 btrfs_tree_read_lock(eb);
 540                 if (btrfs_header_level(eb) == 0)
 541                         btrfs_item_key_to_cpu(eb, &ref->key_for_search, 0);
 542                 else
 543                         btrfs_node_key_to_cpu(eb, &ref->key_for_search, 0);
 544                 btrfs_tree_read_unlock(eb);
 545                 free_extent_buffer(eb);
 546         }
 547         return 0;
 548 }
 549
 550 /*
 551  * merge backrefs and adjust counts accordingly
 552  *
 553  * mode = 1: merge identical keys, if key is set
 554  *    FIXME: if we add more keys in __add_prelim_ref, we can merge more here.
 555  *           additionally, we could even add a key range for the blocks we
 556  *           looked into to merge even more (-> replace unresolved refs by those
 557  *           having a parent).
 558  * mode = 2: merge identical parents
 559  */
 560 static void __merge_refs(struct list_head *head, int mode)
 561 {
 562         struct __prelim_ref *pos1;
 563
 564         list_for_each_entry(pos1, head, list) {
 565                 struct __prelim_ref *pos2 = pos1, *tmp;
 566
 567                 list_for_each_entry_safe_continue(pos2, tmp, head, list) {
 568                         struct __prelim_ref *ref1 = pos1, *ref2 = pos2;
 569                         struct extent_inode_elem *eie;
 570
 571                         if (!ref_for_same_block(ref1, ref2))
 572                                 continue;
 573                         if (mode == 1) {
 574                                 if (!ref1->parent && ref2->parent)
 575                                         swap(ref1, ref2);
 576                         } else {
 577                                 if (ref1->parent != ref2->parent)
 578                                         continue;
 579                         }
 580
 581                         eie = ref1->inode_list;
 582                         while (eie && eie->next)
 583                                 eie = eie->next;
 584                         if (eie)
 585                                 eie->next = ref2->inode_list;
 586                         else
 587                                 ref1->inode_list = ref2->inode_list;
 588                         ref1->count += ref2->count;
 589
 590                         list_del(&ref2->list);
 591                         kmem_cache_free(btrfs_prelim_ref_cache, ref2);
 592                         cond_resched();
 593                 }
 594
 595         }
 596 }
 597
 598 /*
 599  * add all currently queued delayed refs from this head whose seq nr is
 600  * smaller or equal that seq to the list
 601  */
 602 static int __add_delayed_refs(struct btrfs_delayed_ref_head *head, u64 seq,
 603                               struct list_head *prefs, u64 *total_refs,
 604                               u64 inum)
 605 {
 606         struct btrfs_delayed_ref_node *node;
 607         struct btrfs_delayed_extent_op *extent_op = head->extent_op;
 608         struct btrfs_key key;
 609         struct btrfs_key op_key = {0};
 610         int sgn;
 611         int ret = 0;
 612
 613         if (extent_op && extent_op->update_key)
 614                 btrfs_disk_key_to_cpu(&op_key, &extent_op->key);
 615
 616         spin_lock(&head->lock);
 617         list_for_each_entry(node, &head->ref_list, list) {
 618                 if (node->seq > seq)
 619                         continue;
 620
 621                 switch (node->action) {
 622                 case BTRFS_ADD_DELAYED_EXTENT:
 623                 case BTRFS_UPDATE_DELAYED_HEAD:
 624                         WARN_ON(1);
 625                         continue;
 626                 case BTRFS_ADD_DELAYED_REF:
 627                         sgn = 1;
 628                         break;
 629                 case BTRFS_DROP_DELAYED_REF:
 630                         sgn = -1;
 631                         break;
 632                 default:
 633                         BUG_ON(1);
 634                 }
 635                 *total_refs += (node->ref_mod * sgn);
 636                 switch (node->type) {
 637                 case BTRFS_TREE_BLOCK_REF_KEY: {
 638                         struct btrfs_delayed_tree_ref *ref;
 639
 640                         ref = btrfs_delayed_node_to_tree_ref(node);
 641                         ret = __add_prelim_ref(prefs, ref->root, &op_key,
 642                                                ref->level + 1, 0, node->bytenr,
 643                                                node->ref_mod * sgn, GFP_ATOMIC);
 644                         break;
 645                 }
 646                 case BTRFS_SHARED_BLOCK_REF_KEY: {
 647                         struct btrfs_delayed_tree_ref *ref;
 648
 649                         ref = btrfs_delayed_node_to_tree_ref(node);
 650                         ret = __add_prelim_ref(prefs, 0, NULL,
 651                                                ref->level + 1, ref->parent,
 652                                                node->bytenr,
 653                                                node->ref_mod * sgn, GFP_ATOMIC);
 654                         break;
 655                 }
 656                 case BTRFS_EXTENT_DATA_REF_KEY: {
 657                         struct btrfs_delayed_data_ref *ref;
 658                         ref = btrfs_delayed_node_to_data_ref(node);
 659
 660                         key.objectid = ref->objectid;
 661                         key.type = BTRFS_EXTENT_DATA_KEY;
 662                         key.offset = ref->offset;
 663
 664                         /*
 665                          * Found a inum that doesn't match our known inum, we
 666                          * know it's shared.
 667                          */
 668                         if (inum && ref->objectid != inum) {
 669                                 ret = BACKREF_FOUND_SHARED;
 670                                 break;
 671                         }
 672
 673                         ret = __add_prelim_ref(prefs, ref->root, &key, 0, 0,
 674                                                node->bytenr,
 675                                                node->ref_mod * sgn, GFP_ATOMIC);
 676                         break;
 677                 }
 678                 case BTRFS_SHARED_DATA_REF_KEY: {
 679                         struct btrfs_delayed_data_ref *ref;
 680
 681                         ref = btrfs_delayed_node_to_data_ref(node);
 682                         ret = __add_prelim_ref(prefs, 0, NULL, 0,
 683                                                ref->parent, node->bytenr,
 684                                                node->ref_mod * sgn, GFP_ATOMIC);
 685                         break;
 686                 }
 687                 default:
 688                         WARN_ON(1);
 689                 }
 690                 if (ret)
 691                         break;
 692         }
 693         spin_unlock(&head->lock);
 694         return ret;
 695 }
 696
 697 /*
 698  * add all inline backrefs for bytenr to the list
 699  */
 700 static int __add_inline_refs(struct btrfs_fs_info *fs_info,
 701                              struct btrfs_path *path, u64 bytenr,
 702                              int *info_level, struct list_head *prefs,
 703                              u64 *total_refs, u64 inum)
 704 {
 705         int ret = 0;
 706         int slot;
 707         struct extent_buffer *leaf;
 708         struct btrfs_key key;
 709         struct btrfs_key found_key;
 710         unsigned long ptr;
 711         unsigned long end;
 712         struct btrfs_extent_item *ei;
 713         u64 flags;
 714         u64 item_size;
 715
 716         /*
 717          * enumerate all inline refs
 718          */
 719         leaf = path->nodes[0];
 720         slot = path->slots[0];
 721
 722         item_size = btrfs_item_size_nr(leaf, slot);
 723         BUG_ON(item_size < sizeof(*ei));
 724
 725         ei = btrfs_item_ptr(leaf, slot, struct btrfs_extent_item);
 726         flags = btrfs_extent_flags(leaf, ei);
 727         *total_refs += btrfs_extent_refs(leaf, ei);
 728         btrfs_item_key_to_cpu(leaf, &found_key, slot);
 729
 730         ptr = (unsigned long)(ei + 1);
 731         end = (unsigned long)ei + item_size;
 732
 733         if (found_key.type == BTRFS_EXTENT_ITEM_KEY &&
 734             flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
 735                 struct btrfs_tree_block_info *info;
 736
 737                 info = (struct btrfs_tree_block_info *)ptr;
 738                 *info_level = btrfs_tree_block_level(leaf, info);
 739                 ptr += sizeof(struct btrfs_tree_block_info);
 740                 BUG_ON(ptr > end);
 741         } else if (found_key.type == BTRFS_METADATA_ITEM_KEY) {
 742                 *info_level = found_key.offset;
 743         } else {
 744                 BUG_ON(!(flags & BTRFS_EXTENT_FLAG_DATA));
 745         }
 746
 747         while (ptr < end) {
 748                 struct btrfs_extent_inline_ref *iref;
 749                 u64 offset;
 750                 int type;
 751
 752                 iref = (struct btrfs_extent_inline_ref *)ptr;
 753                 type = btrfs_extent_inline_ref_type(leaf, iref);
 754                 offset = btrfs_extent_inline_ref_offset(leaf, iref);
 755
 756                 switch (type) {
 757                 case BTRFS_SHARED_BLOCK_REF_KEY:
 758                         ret = __add_prelim_ref(prefs, 0, NULL,
 759                                                 *info_level + 1, offset,
 760                                                 bytenr, 1, GFP_NOFS);
 761                         break;
 762                 case BTRFS_SHARED_DATA_REF_KEY: {
 763                         struct btrfs_shared_data_ref *sdref;
 764                         int count;
 765
 766                         sdref = (struct btrfs_shared_data_ref *)(iref + 1);
 767                         count = btrfs_shared_data_ref_count(leaf, sdref);
 768                         ret = __add_prelim_ref(prefs, 0, NULL, 0, offset,
 769                                                bytenr, count, GFP_NOFS);
 770                         break;
 771                 }
 772                 case BTRFS_TREE_BLOCK_REF_KEY:
 773                         ret = __add_prelim_ref(prefs, offset, NULL,
 774                                                *info_level + 1, 0,
 775                                                bytenr, 1, GFP_NOFS);
 776                         break;
 777                 case BTRFS_EXTENT_DATA_REF_KEY: {
 778                         struct btrfs_extent_data_ref *dref;
 779                         int count;
 780                         u64 root;
 781
 782                         dref = (struct btrfs_extent_data_ref *)(&iref->offset);
 783                         count = btrfs_extent_data_ref_count(leaf, dref);
 784                         key.objectid = btrfs_extent_data_ref_objectid(leaf,
 785                                                                       dref);
 786                         key.type = BTRFS_EXTENT_DATA_KEY;
 787                         key.offset = btrfs_extent_data_ref_offset(leaf, dref);
 788
 789                         if (inum && key.objectid != inum) {
 790                                 ret = BACKREF_FOUND_SHARED;
 791                                 break;
 792                         }
 793
 794                         root = btrfs_extent_data_ref_root(leaf, dref);
 795                         ret = __add_prelim_ref(prefs, root, &key, 0, 0,
 796                                                bytenr, count, GFP_NOFS);
 797                         break;
 798                 }
 799                 default:
 800                         WARN_ON(1);
 801                 }
 802                 if (ret)
 803                         return ret;
 804                 ptr += btrfs_extent_inline_ref_size(type);
 805         }
 806
 807         return 0;
 808 }
 809
 810 /*
 811  * add all non-inline backrefs for bytenr to the list
 812  */
 813 static int __add_keyed_refs(struct btrfs_fs_info *fs_info,
 814                             struct btrfs_path *path, u64 bytenr,
 815                             int info_level, struct list_head *prefs, u64 inum)
 816 {
 817         struct btrfs_root *extent_root = fs_info->extent_root;
 818         int ret;
 819         int slot;
 820         struct extent_buffer *leaf;
 821         struct btrfs_key key;
 822
 823         while (1) {
 824                 ret = btrfs_next_item(extent_root, path);
 825                 if (ret < 0)
 826                         break;
 827                 if (ret) {
 828                         ret = 0;
 829                         break;
 830                 }
 831
 832                 slot = path->slots[0];
 833                 leaf = path->nodes[0];
 834                 btrfs_item_key_to_cpu(leaf, &key, slot);
 835
 836                 if (key.objectid != bytenr)
 837                         break;
 838                 if (key.type < BTRFS_TREE_BLOCK_REF_KEY)
 839                         continue;
 840                 if (key.type > BTRFS_SHARED_DATA_REF_KEY)
 841                         break;
 842
 843                 switch (key.type) {
 844                 case BTRFS_SHARED_BLOCK_REF_KEY:
 845                         ret = __add_prelim_ref(prefs, 0, NULL,
 846                                                 info_level + 1, key.offset,
 847                                                 bytenr, 1, GFP_NOFS);
 848                         break;
 849                 case BTRFS_SHARED_DATA_REF_KEY: {
 850                         struct btrfs_shared_data_ref *sdref;
 851                         int count;
 852
 853                         sdref = btrfs_item_ptr(leaf, slot,
 854                                               struct btrfs_shared_data_ref);
 855                         count = btrfs_shared_data_ref_count(leaf, sdref);
 856                         ret = __add_prelim_ref(prefs, 0, NULL, 0, key.offset,
 857                                                 bytenr, count, GFP_NOFS);
 858                         break;
 859                 }
 860                 case BTRFS_TREE_BLOCK_REF_KEY:
 861                         ret = __add_prelim_ref(prefs, key.offset, NULL,
 862                                                info_level + 1, 0,
 863                                                bytenr, 1, GFP_NOFS);
 864                         break;
 865                 case BTRFS_EXTENT_DATA_REF_KEY: {
 866                         struct btrfs_extent_data_ref *dref;
 867                         int count;
 868                         u64 root;
 869
 870                         dref = btrfs_item_ptr(leaf, slot,
 871                                               struct btrfs_extent_data_ref);
 872                         count = btrfs_extent_data_ref_count(leaf, dref);
 873                         key.objectid = btrfs_extent_data_ref_objectid(leaf,
 874                                                                       dref);
 875                         key.type = BTRFS_EXTENT_DATA_KEY;
 876                         key.offset = btrfs_extent_data_ref_offset(leaf, dref);
 877
 878                         if (inum && key.objectid != inum) {
 879                                 ret = BACKREF_FOUND_SHARED;
 880                                 break;
 881                         }
 882
 883                         root = btrfs_extent_data_ref_root(leaf, dref);
 884                         ret = __add_prelim_ref(prefs, root, &key, 0, 0,
 885                                                bytenr, count, GFP_NOFS);
 886                         break;
 887                 }
 888                 default:
 889                         WARN_ON(1);
 890                 }
 891                 if (ret)
 892                         return ret;
 893
 894         }
 895
 896         return ret;
 897 }
 898
 899 /*
 900  * this adds all existing backrefs (inline backrefs, backrefs and delayed
 901  * refs) for the given bytenr to the refs list, merges duplicates and resolves
 902  * indirect refs to their parent bytenr.
 903  * When roots are found, they're added to the roots list
 904  *
 905  * NOTE: This can return values > 0
 906  *
 907  * If time_seq is set to (u64)-1, it will not search delayed_refs, and behave
 908  * much like trans == NULL case, the difference only lies in it will not
 909  * commit root.
 910  * The special case is for qgroup to search roots in commit_transaction().
 911  *
 912  * FIXME some caching might speed things up
 913  */
 914 static int find_parent_nodes(struct btrfs_trans_handle *trans,
 915                              struct btrfs_fs_info *fs_info, u64 bytenr,
 916                              u64 time_seq, struct ulist *refs,
 917                              struct ulist *roots, const u64 *extent_item_pos,
 918                              u64 root_objectid, u64 inum)
 919 {
 920         struct btrfs_key key;
 921         struct btrfs_path *path;
 922         struct btrfs_delayed_ref_root *delayed_refs = NULL;
 923         struct btrfs_delayed_ref_head *head;
 924         int info_level = 0;
 925         int ret;
 926         struct list_head prefs_delayed;
 927         struct list_head prefs;
 928         struct __prelim_ref *ref;
 929         struct extent_inode_elem *eie = NULL;
 930         u64 total_refs = 0;
 931
 932         INIT_LIST_HEAD(&prefs);
 933         INIT_LIST_HEAD(&prefs_delayed);
 934
 935         key.objectid = bytenr;
 936         key.offset = (u64)-1;
 937         if (btrfs_fs_incompat(fs_info, SKINNY_METADATA))
 938                 key.type = BTRFS_METADATA_ITEM_KEY;
 939         else
 940                 key.type = BTRFS_EXTENT_ITEM_KEY;
 941
 942         path = btrfs_alloc_path();
 943         if (!path)
 944                 return -ENOMEM;
 945         if (!trans) {
 946                 path->search_commit_root = 1;
 947                 path->skip_locking = 1;
 948         }
 949
 950         if (time_seq == (u64)-1)
 951                 path->skip_locking = 1;
 952
 953         /*
 954          * grab both a lock on the path and a lock on the delayed ref head.
 955          * We need both to get a consistent picture of how the refs look
 956          * at a specified point in time
 957          */
 958 again:
 959         head = NULL;
 960
 961         ret = btrfs_search_slot(trans, fs_info->extent_root, &key, path, 0, 0);
 962         if (ret < 0)
 963                 goto out;
 964         BUG_ON(ret == 0);
 965
 966 #ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
 967         if (trans && likely(trans->type != __TRANS_DUMMY) &&
 968             time_seq != (u64)-1) {
 969 #else
 970         if (trans && time_seq != (u64)-1) {
 971 #endif
 972                 /*
 973                  * look if there are updates for this ref queued and lock the
 974                  * head
 975                  */
 976                 delayed_refs = &trans->transaction->delayed_refs;
 977                 spin_lock(&delayed_refs->lock);
 978                 head = btrfs_find_delayed_ref_head(trans, bytenr);
 979                 if (head) {
 980                         if (!mutex_trylock(&head->mutex)) {
 981                                 atomic_inc(&head->node.refs);
 982                                 spin_unlock(&delayed_refs->lock);
 983
 984                                 btrfs_release_path(path);
 985
 986                                 /*
 987                                  * Mutex was contended, block until it's
 988                                  * released and try again
 989                                  */
 990                                 mutex_lock(&head->mutex);
 991                                 mutex_unlock(&head->mutex);
 992                                 btrfs_put_delayed_ref(&head->node);
 993                                 goto again;
 994                         }
 995                         spin_unlock(&delayed_refs->lock);
 996                         ret = __add_delayed_refs(head, time_seq,
 997                                                  &prefs_delayed, &total_refs,
 998                                                  inum);
 999                         mutex_unlock(&head->mutex);
1000                         if (ret)
1001                                 goto out;
1002                 } else {
1003                         spin_unlock(&delayed_refs->lock);
1004                 }
1005         }
1006
1007         if (path->slots[0]) {
1008                 struct extent_buffer *leaf;
1009                 int slot;
1010
1011                 path->slots[0]--;
1012                 leaf = path->nodes[0];
1013                 slot = path->slots[0];
1014                 btrfs_item_key_to_cpu(leaf, &key, slot);
1015                 if (key.objectid == bytenr &&
1016                     (key.type == BTRFS_EXTENT_ITEM_KEY ||
1017                      key.type == BTRFS_METADATA_ITEM_KEY)) {
1018                         ret = __add_inline_refs(fs_info, path, bytenr,
1019                                                 &info_level, &prefs,
1020                                                 &total_refs, inum);
1021                         if (ret)
1022                                 goto out;
1023                         ret = __add_keyed_refs(fs_info, path, bytenr,
1024                                                info_level, &prefs, inum);
1025                         if (ret)
1026                                 goto out;
1027                 }
1028         }
1029         btrfs_release_path(path);
1030
1031         list_splice_init(&prefs_delayed, &prefs);
1032
1033         ret = __add_missing_keys(fs_info, &prefs);
1034         if (ret)
1035                 goto out;
1036
1037         __merge_refs(&prefs, 1);
1038
1039         ret = __resolve_indirect_refs(fs_info, path, time_seq, &prefs,
1040                                       extent_item_pos, total_refs,
1041                                       root_objectid);
1042         if (ret)
1043                 goto out;
1044
1045         __merge_refs(&prefs, 2);
1046
1047         while (!list_empty(&prefs)) {
1048                 ref = list_first_entry(&prefs, struct __prelim_ref, list);
1049                 WARN_ON(ref->count < 0);
1050                 if (roots && ref->count && ref->root_id && ref->parent == 0) {
1051                         if (root_objectid && ref->root_id != root_objectid) {
1052                                 ret = BACKREF_FOUND_SHARED;
1053                                 goto out;
1054                         }
1055
1056                         /* no parent == root of tree */
1057                         ret = ulist_add(roots, ref->root_id, 0, GFP_NOFS);
1058                         if (ret < 0)
1059                                 goto out;
1060                 }
1061                 if (ref->count && ref->parent) {
1062                         if (extent_item_pos && !ref->inode_list &&
1063                             ref->level == 0) {
1064                                 struct extent_buffer *eb;
1065
1066                                 eb = read_tree_block(fs_info->extent_root,
1067                                                            ref->parent, 0);
1068                                 if (IS_ERR(eb)) {
1069                                         ret = PTR_ERR(eb);
1070                                         goto out;
1071                                 } else if (!extent_buffer_uptodate(eb)) {
1072                                         free_extent_buffer(eb);
1073                                         ret = -EIO;
1074                                         goto out;
1075                                 }
1076                                 btrfs_tree_read_lock(eb);
1077                                 btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
1078                                 ret = find_extent_in_eb(eb, bytenr,
1079                                                         *extent_item_pos, &eie);
1080                                 btrfs_tree_read_unlock_blocking(eb);
1081                                 free_extent_buffer(eb);
1082                                 if (ret < 0)
1083                                         goto out;
1084                                 ref->inode_list = eie;
1085                         }
1086                         ret = ulist_add_merge_ptr(refs, ref->parent,
1087                                                   ref->inode_list,
1088                                                   (void **)&eie, GFP_NOFS);
1089                         if (ret < 0)
1090                                 goto out;
1091                         if (!ret && extent_item_pos) {
1092                                 /*
1093                                  * we've recorded that parent, so we must extend
1094                                  * its inode list here
1095                                  */
1096                                 BUG_ON(!eie);
1097                                 while (eie->next)
1098                                         eie = eie->next;
1099                                 eie->next = ref->inode_list;
1100                         }
1101                         eie = NULL;
1102                 }
1103                 list_del(&ref->list);
1104                 kmem_cache_free(btrfs_prelim_ref_cache, ref);
1105         }
1106
1107 out:
1108         btrfs_free_path(path);
1109         while (!list_empty(&prefs)) {
1110                 ref = list_first_entry(&prefs, struct __prelim_ref, list);
1111                 list_del(&ref->list);
1112                 kmem_cache_free(btrfs_prelim_ref_cache, ref);
1113         }
1114         while (!list_empty(&prefs_delayed)) {
1115                 ref = list_first_entry(&prefs_delayed, struct __prelim_ref,
1116                                        list);
1117                 list_del(&ref->list);
1118                 kmem_cache_free(btrfs_prelim_ref_cache, ref);
1119         }
1120         if (ret < 0)
1121                 free_inode_elem_list(eie);
1122         return ret;
1123 }
1124
1125 static void free_leaf_list(struct ulist *blocks)
1126 {
1127         struct ulist_node *node = NULL;
1128         struct extent_inode_elem *eie;
1129         struct ulist_iterator uiter;
1130
1131         ULIST_ITER_INIT(&uiter);
1132         while ((node = ulist_next(blocks, &uiter))) {
1133                 if (!node->aux)
1134                         continue;
1135                 eie = (struct extent_inode_elem *)(uintptr_t)node->aux;
1136                 free_inode_elem_list(eie);
1137                 node->aux = 0;
1138         }
1139
1140         ulist_free(blocks);
1141 }
1142
1143 /*
1144  * Finds all leafs with a reference to the specified combination of bytenr and
1145  * offset. key_list_head will point to a list of corresponding keys (caller must
1146  * free each list element). The leafs will be stored in the leafs ulist, which
1147  * must be freed with ulist_free.
1148  *
1149  * returns 0 on success, <0 on error
1150  */
1151 static int btrfs_find_all_leafs(struct btrfs_trans_handle *trans,
1152                                 struct btrfs_fs_info *fs_info, u64 bytenr,
1153                                 u64 time_seq, struct ulist **leafs,
1154                                 const u64 *extent_item_pos)
1155 {
1156         int ret;
1157
1158         *leafs = ulist_alloc(GFP_NOFS);
1159         if (!*leafs)
1160                 return -ENOMEM;
1161
1162         ret = find_parent_nodes(trans, fs_info, bytenr,
1163                                 time_seq, *leafs, NULL, extent_item_pos, 0, 0);
1164         if (ret < 0 && ret != -ENOENT) {
1165                 free_leaf_list(*leafs);
1166                 return ret;
1167         }
1168
1169         return 0;
1170 }
1171
1172 /*
1173  * walk all backrefs for a given extent to find all roots that reference this
1174  * extent. Walking a backref means finding all extents that reference this
1175  * extent and in turn walk the backrefs of those, too. Naturally this is a
1176  * recursive process, but here it is implemented in an iterative fashion: We
1177  * find all referencing extents for the extent in question and put them on a
1178  * list. In turn, we find all referencing extents for those, further appending
1179  * to the list. The way we iterate the list allows adding more elements after
1180  * the current while iterating. The process stops when we reach the end of the
1181  * list. Found roots are added to the roots list.
1182  *
1183  * returns 0 on success, < 0 on error.
1184  */
1185 static int __btrfs_find_all_roots(struct btrfs_trans_handle *trans,
1186                                   struct btrfs_fs_info *fs_info, u64 bytenr,
1187                                   u64 time_seq, struct ulist **roots)
1188 {
1189         struct ulist *tmp;
1190         struct ulist_node *node = NULL;
1191         struct ulist_iterator uiter;
1192         int ret;
1193
1194         tmp = ulist_alloc(GFP_NOFS);
1195         if (!tmp)
1196                 return -ENOMEM;
1197         *roots = ulist_alloc(GFP_NOFS);
1198         if (!*roots) {
1199                 ulist_free(tmp);
1200                 return -ENOMEM;
1201         }
1202
1203         ULIST_ITER_INIT(&uiter);
1204         while (1) {
1205                 ret = find_parent_nodes(trans, fs_info, bytenr,
1206                                         time_seq, tmp, *roots, NULL, 0, 0);
1207                 if (ret < 0 && ret != -ENOENT) {
1208                         ulist_free(tmp);
1209                         ulist_free(*roots);
1210                         return ret;
1211                 }
1212                 node = ulist_next(tmp, &uiter);
1213                 if (!node)
1214                         break;
1215                 bytenr = node->val;
1216                 cond_resched();
1217         }
1218
1219         ulist_free(tmp);
1220         return 0;
1221 }
1222
1223 int btrfs_find_all_roots(struct btrfs_trans_handle *trans,
1224                          struct btrfs_fs_info *fs_info, u64 bytenr,
1225                          u64 time_seq, struct ulist **roots)
1226 {
1227         int ret;
1228
1229         if (!trans)
1230                 down_read(&fs_info->commit_root_sem);
1231         ret = __btrfs_find_all_roots(trans, fs_info, bytenr, time_seq, roots);
1232         if (!trans)
1233                 up_read(&fs_info->commit_root_sem);
1234         return ret;
1235 }
1236
1237 /**
1238  * btrfs_check_shared - tell us whether an extent is shared
1239  *
1240  * @trans: optional trans handle
1241  *
1242  * btrfs_check_shared uses the backref walking code but will short
1243  * circuit as soon as it finds a root or inode that doesn't match the
1244  * one passed in. This provides a significant performance benefit for
1245  * callers (such as fiemap) which want to know whether the extent is
1246  * shared but do not need a ref count.
1247  *
1248  * Return: 0 if extent is not shared, 1 if it is shared, < 0 on error.
1249  */
1250 int btrfs_check_shared(struct btrfs_trans_handle *trans,
1251                        struct btrfs_fs_info *fs_info, u64 root_objectid,
1252                        u64 inum, u64 bytenr)
1253 {
1254         struct ulist *tmp = NULL;
1255         struct ulist *roots = NULL;
1256         struct ulist_iterator uiter;
1257         struct ulist_node *node;
1258         struct seq_list elem = SEQ_LIST_INIT(elem);
1259         int ret = 0;
1260
1261         tmp = ulist_alloc(GFP_NOFS);
1262         roots = ulist_alloc(GFP_NOFS);
1263         if (!tmp || !roots) {
1264                 ulist_free(tmp);
1265                 ulist_free(roots);
1266                 return -ENOMEM;
1267         }
1268
1269         if (trans)
1270                 btrfs_get_tree_mod_seq(fs_info, &elem);
1271         else
1272                 down_read(&fs_info->commit_root_sem);
1273         ULIST_ITER_INIT(&uiter);
1274         while (1) {
1275                 ret = find_parent_nodes(trans, fs_info, bytenr, elem.seq, tmp,
1276                                         roots, NULL, root_objectid, inum);
1277                 if (ret == BACKREF_FOUND_SHARED) {
1278                         /* this is the only condition under which we return 1 */
1279                         ret = 1;
1280                         break;
1281                 }
1282                 if (ret < 0 && ret != -ENOENT)
1283                         break;
1284                 ret = 0;
1285                 node = ulist_next(tmp, &uiter);
1286                 if (!node)
1287                         break;
1288                 bytenr = node->val;
1289                 cond_resched();
1290         }
1291         if (trans)
1292                 btrfs_put_tree_mod_seq(fs_info, &elem);
1293         else
1294                 up_read(&fs_info->commit_root_sem);
1295         ulist_free(tmp);
1296         ulist_free(roots);
1297         return ret;
1298 }
1299
1300 int btrfs_find_one_extref(struct btrfs_root *root, u64 inode_objectid,
1301                           u64 start_off, struct btrfs_path *path,
1302                           struct btrfs_inode_extref **ret_extref,
1303                           u64 *found_off)
1304 {
1305         int ret, slot;
1306         struct btrfs_key key;
1307         struct btrfs_key found_key;
1308         struct btrfs_inode_extref *extref;
1309         struct extent_buffer *leaf;
1310         unsigned long ptr;
1311
1312         key.objectid = inode_objectid;
1313         key.type = BTRFS_INODE_EXTREF_KEY;
1314         key.offset = start_off;
1315
1316         ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
1317         if (ret < 0)
1318                 return ret;
1319
1320         while (1) {
1321                 leaf = path->nodes[0];
1322                 slot = path->slots[0];
1323                 if (slot >= btrfs_header_nritems(leaf)) {
1324                         /*
1325                          * If the item at offset is not found,
1326                          * btrfs_search_slot will point us to the slot
1327                          * where it should be inserted. In our case
1328                          * that will be the slot directly before the
1329                          * next INODE_REF_KEY_V2 item. In the case
1330                          * that we're pointing to the last slot in a
1331                          * leaf, we must move one leaf over.
1332                          */
1333                         ret = btrfs_next_leaf(root, path);
1334                         if (ret) {
1335                                 if (ret >= 1)
1336                                         ret = -ENOENT;
1337                                 break;
1338                         }
1339                         continue;
1340                 }
1341
1342                 btrfs_item_key_to_cpu(leaf, &found_key, slot);
1343
1344                 /*
1345                  * Check that we're still looking at an extended ref key for
1346                  * this particular objectid. If we have different
1347                  * objectid or type then there are no more to be found
1348                  * in the tree and we can exit.
1349                  */
1350                 ret = -ENOENT;
1351                 if (found_key.objectid != inode_objectid)
1352                         break;
1353                 if (found_key.type != BTRFS_INODE_EXTREF_KEY)
1354                         break;
1355
1356                 ret = 0;
1357                 ptr = btrfs_item_ptr_offset(leaf, path->slots[0]);
1358                 extref = (struct btrfs_inode_extref *)ptr;
1359                 *ret_extref = extref;
1360                 if (found_off)
1361                         *found_off = found_key.offset;
1362                 break;
1363         }
1364
1365         return ret;
1366 }
1367
1368 /*
1369  * this iterates to turn a name (from iref/extref) into a full filesystem path.
1370  * Elements of the path are separated by '/' and the path is guaranteed to be
1371  * 0-terminated. the path is only given within the current file system.
1372  * Therefore, it never starts with a '/'. the caller is responsible to provide
1373  * "size" bytes in "dest". the dest buffer will be filled backwards. finally,
1374  * the start point of the resulting string is returned. this pointer is within
1375  * dest, normally.
1376  * in case the path buffer would overflow, the pointer is decremented further
1377  * as if output was written to the buffer, though no more output is actually
1378  * generated. that way, the caller can determine how much space would be
1379  * required for the path to fit into the buffer. in that case, the returned
1380  * value will be smaller than dest. callers must check this!
1381  */
1382 char *btrfs_ref_to_path(struct btrfs_root *fs_root, struct btrfs_path *path,
1383                         u32 name_len, unsigned long name_off,
1384                         struct extent_buffer *eb_in, u64 parent,
1385                         char *dest, u32 size)
1386 {
1387         int slot;
1388         u64 next_inum;
1389         int ret;
1390         s64 bytes_left = ((s64)size) - 1;
1391         struct extent_buffer *eb = eb_in;
1392         struct btrfs_key found_key;
1393         int leave_spinning = path->leave_spinning;
1394         struct btrfs_inode_ref *iref;
1395
1396         if (bytes_left >= 0)
1397                 dest[bytes_left] = '\0';
1398
1399         path->leave_spinning = 1;
1400         while (1) {
1401                 bytes_left -= name_len;
1402                 if (bytes_left >= 0)
1403                         read_extent_buffer(eb, dest + bytes_left,
1404                                            name_off, name_len);
1405                 if (eb != eb_in) {
1406                         if (!path->skip_locking)
1407                                 btrfs_tree_read_unlock_blocking(eb);
1408                         free_extent_buffer(eb);
1409                 }
1410                 ret = btrfs_find_item(fs_root, path, parent, 0,
1411                                 BTRFS_INODE_REF_KEY, &found_key);
1412                 if (ret > 0)
1413                         ret = -ENOENT;
1414                 if (ret)
1415                         break;
1416
1417                 next_inum = found_key.offset;
1418
1419                 /* regular exit ahead */
1420                 if (parent == next_inum)
1421                         break;
1422
1423                 slot = path->slots[0];
1424                 eb = path->nodes[0];
1425                 /* make sure we can use eb after releasing the path */
1426                 if (eb != eb_in) {
1427                         if (!path->skip_locking)
1428                                 btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
1429                         path->nodes[0] = NULL;
1430                         path->locks[0] = 0;
1431                 }
1432                 btrfs_release_path(path);
1433                 iref = btrfs_item_ptr(eb, slot, struct btrfs_inode_ref);
1434
1435                 name_len = btrfs_inode_ref_name_len(eb, iref);
1436                 name_off = (unsigned long)(iref + 1);
1437
1438                 parent = next_inum;
1439                 --bytes_left;
1440                 if (bytes_left >= 0)
1441                         dest[bytes_left] = '/';
1442         }
1443
1444         btrfs_release_path(path);
1445         path->leave_spinning = leave_spinning;
1446
1447         if (ret)
1448                 return ERR_PTR(ret);
1449
1450         return dest + bytes_left;
1451 }
1452
1453 /*
1454  * this makes the path point to (logical EXTENT_ITEM *)
1455  * returns BTRFS_EXTENT_FLAG_DATA for data, BTRFS_EXTENT_FLAG_TREE_BLOCK for
1456  * tree blocks and <0 on error.
1457  */
1458 int extent_from_logical(struct btrfs_fs_info *fs_info, u64 logical,
1459                         struct btrfs_path *path, struct btrfs_key *found_key,
1460                         u64 *flags_ret)
1461 {
1462         int ret;
1463         u64 flags;
1464         u64 size = 0;
1465         u32 item_size;
1466         struct extent_buffer *eb;
1467         struct btrfs_extent_item *ei;
1468         struct btrfs_key key;
1469
1470         if (btrfs_fs_incompat(fs_info, SKINNY_METADATA))
1471                 key.type = BTRFS_METADATA_ITEM_KEY;
1472         else
1473                 key.type = BTRFS_EXTENT_ITEM_KEY;
1474         key.objectid = logical;
1475         key.offset = (u64)-1;
1476
1477         ret = btrfs_search_slot(NULL, fs_info->extent_root, &key, path, 0, 0);
1478         if (ret < 0)
1479                 return ret;
1480
1481         ret = btrfs_previous_extent_item(fs_info->extent_root, path, 0);
1482         if (ret) {
1483                 if (ret > 0)
1484                         ret = -ENOENT;
1485                 return ret;
1486         }
1487         btrfs_item_key_to_cpu(path->nodes[0], found_key, path->slots[0]);
1488         if (found_key->type == BTRFS_METADATA_ITEM_KEY)
1489                 size = fs_info->extent_root->nodesize;
1490         else if (found_key->type == BTRFS_EXTENT_ITEM_KEY)
1491                 size = found_key->offset;
1492
1493         if (found_key->objectid > logical ||
1494             found_key->objectid + size <= logical) {
1495                 pr_debug("logical %llu is not within any extent\n", logical);
1496                 return -ENOENT;
1497         }
1498
1499         eb = path->nodes[0];
1500         item_size = btrfs_item_size_nr(eb, path->slots[0]);
1501         BUG_ON(item_size < sizeof(*ei));
1502
1503         ei = btrfs_item_ptr(eb, path->slots[0], struct btrfs_extent_item);
1504         flags = btrfs_extent_flags(eb, ei);
1505
1506         pr_debug("logical %llu is at position %llu within the extent (%llu "
1507                  "EXTENT_ITEM %llu) flags %#llx size %u\n",
1508                  logical, logical - found_key->objectid, found_key->objectid,
1509                  found_key->offset, flags, item_size);
1510
1511         WARN_ON(!flags_ret);
1512         if (flags_ret) {
1513                 if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK)
1514                         *flags_ret = BTRFS_EXTENT_FLAG_TREE_BLOCK;
1515                 else if (flags & BTRFS_EXTENT_FLAG_DATA)
1516                         *flags_ret = BTRFS_EXTENT_FLAG_DATA;
1517                 else
1518                         BUG_ON(1);
1519                 return 0;
1520         }
1521
1522         return -EIO;
1523 }
1524
1525 /*
1526  * helper function to iterate extent inline refs. ptr must point to a 0 value
1527  * for the first call and may be modified. it is used to track state.
1528  * if more refs exist, 0 is returned and the next call to
1529  * __get_extent_inline_ref must pass the modified ptr parameter to get the
1530  * next ref. after the last ref was processed, 1 is returned.
1531  * returns <0 on error
1532  */
1533 static int __get_extent_inline_ref(unsigned long *ptr, struct extent_buffer *eb,
1534                                    struct btrfs_key *key,
1535                                    struct btrfs_extent_item *ei, u32 item_size,
1536                                    struct btrfs_extent_inline_ref **out_eiref,
1537                                    int *out_type)
1538 {
1539         unsigned long end;
1540         u64 flags;
1541         struct btrfs_tree_block_info *info;
1542
1543         if (!*ptr) {
1544                 /* first call */
1545                 flags = btrfs_extent_flags(eb, ei);
1546                 if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
1547                         if (key->type == BTRFS_METADATA_ITEM_KEY) {
1548                                 /* a skinny metadata extent */
1549                                 *out_eiref =
1550                                      (struct btrfs_extent_inline_ref *)(ei + 1);
1551                         } else {
1552                                 WARN_ON(key->type != BTRFS_EXTENT_ITEM_KEY);
1553                                 info = (struct btrfs_tree_block_info *)(ei + 1);
1554                                 *out_eiref =
1555                                    (struct btrfs_extent_inline_ref *)(info + 1);
1556                         }
1557                 } else {
1558                         *out_eiref = (struct btrfs_extent_inline_ref *)(ei + 1);
1559                 }
1560                 *ptr = (unsigned long)*out_eiref;
1561                 if ((unsigned long)(*ptr) >= (unsigned long)ei + item_size)
1562                         return -ENOENT;
1563         }
1564
1565         end = (unsigned long)ei + item_size;
1566         *out_eiref = (struct btrfs_extent_inline_ref *)(*ptr);
1567         *out_type = btrfs_extent_inline_ref_type(eb, *out_eiref);
1568
1569         *ptr += btrfs_extent_inline_ref_size(*out_type);
1570         WARN_ON(*ptr > end);
1571         if (*ptr == end)
1572                 return 1; /* last */
1573
1574         return 0;
1575 }
1576
1577 /*
1578  * reads the tree block backref for an extent. tree level and root are returned
1579  * through out_level and out_root. ptr must point to a 0 value for the first
1580  * call and may be modified (see __get_extent_inline_ref comment).
1581  * returns 0 if data was provided, 1 if there was no more data to provide or
1582  * <0 on error.
1583  */
1584 int tree_backref_for_extent(unsigned long *ptr, struct extent_buffer *eb,
1585                             struct btrfs_key *key, struct btrfs_extent_item *ei,
1586                             u32 item_size, u64 *out_root, u8 *out_level)
1587 {
1588         int ret;
1589         int type;
1590         struct btrfs_extent_inline_ref *eiref;
1591
1592         if (*ptr == (unsigned long)-1)
1593                 return 1;
1594
1595         while (1) {
1596                 ret = __get_extent_inline_ref(ptr, eb, key, ei, item_size,
1597                                               &eiref, &type);
1598                 if (ret < 0)
1599                         return ret;
1600
1601                 if (type == BTRFS_TREE_BLOCK_REF_KEY ||
1602                     type == BTRFS_SHARED_BLOCK_REF_KEY)
1603                         break;
1604
1605                 if (ret == 1)
1606                         return 1;
1607         }
1608
1609         /* we can treat both ref types equally here */
1610         *out_root = btrfs_extent_inline_ref_offset(eb, eiref);
1611
1612         if (key->type == BTRFS_EXTENT_ITEM_KEY) {
1613                 struct btrfs_tree_block_info *info;
1614
1615                 info = (struct btrfs_tree_block_info *)(ei + 1);
1616                 *out_level = btrfs_tree_block_level(eb, info);
1617         } else {
1618                 ASSERT(key->type == BTRFS_METADATA_ITEM_KEY);
1619                 *out_level = (u8)key->offset;
1620         }
1621
1622         if (ret == 1)
1623                 *ptr = (unsigned long)-1;
1624
1625         return 0;
1626 }
1627
1628 static int iterate_leaf_refs(struct extent_inode_elem *inode_list,
1629                                 u64 root, u64 extent_item_objectid,
1630                                 iterate_extent_inodes_t *iterate, void *ctx)
1631 {
1632         struct extent_inode_elem *eie;
1633         int ret = 0;
1634
1635         for (eie = inode_list; eie; eie = eie->next) {
1636                 pr_debug("ref for %llu resolved, key (%llu EXTEND_DATA %llu), "
1637                          "root %llu\n", extent_item_objectid,
1638                          eie->inum, eie->offset, root);
1639                 ret = iterate(eie->inum, eie->offset, root, ctx);
1640                 if (ret) {
1641                         pr_debug("stopping iteration for %llu due to ret=%d\n",
1642                                  extent_item_objectid, ret);
1643                         break;
1644                 }
1645         }
1646
1647         return ret;
1648 }
1649
1650 /*
1651  * calls iterate() for every inode that references the extent identified by
1652  * the given parameters.
1653  * when the iterator function returns a non-zero value, iteration stops.
1654  */
1655 int iterate_extent_inodes(struct btrfs_fs_info *fs_info,
1656                                 u64 extent_item_objectid, u64 extent_item_pos,
1657                                 int search_commit_root,
1658                                 iterate_extent_inodes_t *iterate, void *ctx)
1659 {
1660         int ret;
1661         struct btrfs_trans_handle *trans = NULL;
1662         struct ulist *refs = NULL;
1663         struct ulist *roots = NULL;
1664         struct ulist_node *ref_node = NULL;
1665         struct ulist_node *root_node = NULL;
1666         struct seq_list tree_mod_seq_elem = SEQ_LIST_INIT(tree_mod_seq_elem);
1667         struct ulist_iterator ref_uiter;
1668         struct ulist_iterator root_uiter;
1669
1670         pr_debug("resolving all inodes for extent %llu\n",
1671                         extent_item_objectid);
1672
1673         if (!search_commit_root) {
1674                 trans = btrfs_join_transaction(fs_info->extent_root);
1675                 if (IS_ERR(trans))
1676                         return PTR_ERR(trans);
1677                 btrfs_get_tree_mod_seq(fs_info, &tree_mod_seq_elem);
1678         } else {
1679                 down_read(&fs_info->commit_root_sem);
1680         }
1681
1682         ret = btrfs_find_all_leafs(trans, fs_info, extent_item_objectid,
1683                                    tree_mod_seq_elem.seq, &refs,
1684                                    &extent_item_pos);
1685         if (ret)
1686                 goto out;
1687
1688         ULIST_ITER_INIT(&ref_uiter);
1689         while (!ret && (ref_node = ulist_next(refs, &ref_uiter))) {
1690                 ret = __btrfs_find_all_roots(trans, fs_info, ref_node->val,
1691                                              tree_mod_seq_elem.seq, &roots);
1692                 if (ret)
1693                         break;
1694                 ULIST_ITER_INIT(&root_uiter);
1695                 while (!ret && (root_node = ulist_next(roots, &root_uiter))) {
1696                         pr_debug("root %llu references leaf %llu, data list "
1697                                  "%#llx\n", root_node->val, ref_node->val,
1698                                  ref_node->aux);
1699                         ret = iterate_leaf_refs((struct extent_inode_elem *)
1700                                                 (uintptr_t)ref_node->aux,
1701                                                 root_node->val,
1702                                                 extent_item_objectid,
1703                                                 iterate, ctx);
1704                 }
1705                 ulist_free(roots);
1706         }
1707
1708         free_leaf_list(refs);
1709 out:
1710         if (!search_commit_root) {
1711                 btrfs_put_tree_mod_seq(fs_info, &tree_mod_seq_elem);
1712                 btrfs_end_transaction(trans, fs_info->extent_root);
1713         } else {
1714                 up_read(&fs_info->commit_root_sem);
1715         }
1716
1717         return ret;
1718 }
1719
1720 int iterate_inodes_from_logical(u64 logical, struct btrfs_fs_info *fs_info,
1721                                 struct btrfs_path *path,
1722                                 iterate_extent_inodes_t *iterate, void *ctx)
1723 {
1724         int ret;
1725         u64 extent_item_pos;
1726         u64 flags = 0;
1727         struct btrfs_key found_key;
1728         int search_commit_root = path->search_commit_root;
1729
1730         ret = extent_from_logical(fs_info, logical, path, &found_key, &flags);
1731         btrfs_release_path(path);
1732         if (ret < 0)
1733                 return ret;
1734         if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK)
1735                 return -EINVAL;
1736
1737         extent_item_pos = logical - found_key.objectid;
1738         ret = iterate_extent_inodes(fs_info, found_key.objectid,
1739                                         extent_item_pos, search_commit_root,
1740                                         iterate, ctx);
1741
1742         return ret;
1743 }
1744
1745 typedef int (iterate_irefs_t)(u64 parent, u32 name_len, unsigned long name_off,
1746                               struct extent_buffer *eb, void *ctx);
1747
1748 static int iterate_inode_refs(u64 inum, struct btrfs_root *fs_root,
1749                               struct btrfs_path *path,
1750                               iterate_irefs_t *iterate, void *ctx)
1751 {
1752         int ret = 0;
1753         int slot;
1754         u32 cur;
1755         u32 len;
1756         u32 name_len;
1757         u64 parent = 0;
1758         int found = 0;
1759         struct extent_buffer *eb;
1760         struct btrfs_item *item;
1761         struct btrfs_inode_ref *iref;
1762         struct btrfs_key found_key;
1763
1764         while (!ret) {
1765                 ret = btrfs_find_item(fs_root, path, inum,
1766                                 parent ? parent + 1 : 0, BTRFS_INODE_REF_KEY,
1767                                 &found_key);
1768
1769                 if (ret < 0)
1770                         break;
1771                 if (ret) {
1772                         ret = found ? 0 : -ENOENT;
1773                         break;
1774                 }
1775                 ++found;
1776
1777                 parent = found_key.offset;
1778                 slot = path->slots[0];
1779                 eb = btrfs_clone_extent_buffer(path->nodes[0]);
1780                 if (!eb) {
1781                         ret = -ENOMEM;
1782                         break;
1783                 }
1784                 extent_buffer_get(eb);
1785                 btrfs_tree_read_lock(eb);
1786                 btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
1787                 btrfs_release_path(path);
1788
1789                 item = btrfs_item_nr(slot);
1790                 iref = btrfs_item_ptr(eb, slot, struct btrfs_inode_ref);
1791
1792                 for (cur = 0; cur < btrfs_item_size(eb, item); cur += len) {
1793                         name_len = btrfs_inode_ref_name_len(eb, iref);
1794                         /* path must be released before calling iterate()! */
1795                         pr_debug("following ref at offset %u for inode %llu in "
1796                                  "tree %llu\n", cur, found_key.objectid,
1797                                  fs_root->objectid);
1798                         ret = iterate(parent, name_len,
1799                                       (unsigned long)(iref + 1), eb, ctx);
1800                         if (ret)
1801                                 break;
1802                         len = sizeof(*iref) + name_len;
1803                         iref = (struct btrfs_inode_ref *)((char *)iref + len);
1804                 }
1805                 btrfs_tree_read_unlock_blocking(eb);
1806                 free_extent_buffer(eb);
1807         }
1808
1809         btrfs_release_path(path);
1810
1811         return ret;
1812 }
1813
1814 static int iterate_inode_extrefs(u64 inum, struct btrfs_root *fs_root,
1815                                  struct btrfs_path *path,
1816                                  iterate_irefs_t *iterate, void *ctx)
1817 {
1818         int ret;
1819         int slot;
1820         u64 offset = 0;
1821         u64 parent;
1822         int found = 0;
1823         struct extent_buffer *eb;
1824         struct btrfs_inode_extref *extref;
1825         u32 item_size;
1826         u32 cur_offset;
1827         unsigned long ptr;
1828
1829         while (1) {
1830                 ret = btrfs_find_one_extref(fs_root, inum, offset, path, &extref,
1831                                             &offset);
1832                 if (ret < 0)
1833                         break;
1834                 if (ret) {
1835                         ret = found ? 0 : -ENOENT;
1836                         break;
1837                 }
1838                 ++found;
1839
1840                 slot = path->slots[0];
1841                 eb = btrfs_clone_extent_buffer(path->nodes[0]);
1842                 if (!eb) {
1843                         ret = -ENOMEM;
1844                         break;
1845                 }
1846                 extent_buffer_get(eb);
1847
1848                 btrfs_tree_read_lock(eb);
1849                 btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
1850                 btrfs_release_path(path);
1851
1852                 item_size = btrfs_item_size_nr(eb, slot);
1853                 ptr = btrfs_item_ptr_offset(eb, slot);
1854                 cur_offset = 0;
1855
1856                 while (cur_offset < item_size) {
1857                         u32 name_len;
1858
1859                         extref = (struct btrfs_inode_extref *)(ptr + cur_offset);
1860                         parent = btrfs_inode_extref_parent(eb, extref);
1861                         name_len = btrfs_inode_extref_name_len(eb, extref);
1862                         ret = iterate(parent, name_len,
1863                                       (unsigned long)&extref->name, eb, ctx);
1864                         if (ret)
1865                                 break;
1866
1867                         cur_offset += btrfs_inode_extref_name_len(eb, extref);
1868                         cur_offset += sizeof(*extref);
1869                 }
1870                 btrfs_tree_read_unlock_blocking(eb);
1871                 free_extent_buffer(eb);
1872
1873                 offset++;
1874         }
1875
1876         btrfs_release_path(path);
1877
1878         return ret;
1879 }
1880
1881 static int iterate_irefs(u64 inum, struct btrfs_root *fs_root,
1882                          struct btrfs_path *path, iterate_irefs_t *iterate,
1883                          void *ctx)
1884 {
1885         int ret;
1886         int found_refs = 0;
1887
1888         ret = iterate_inode_refs(inum, fs_root, path, iterate, ctx);
1889         if (!ret)
1890                 ++found_refs;
1891         else if (ret != -ENOENT)
1892                 return ret;
1893
1894         ret = iterate_inode_extrefs(inum, fs_root, path, iterate, ctx);
1895         if (ret == -ENOENT && found_refs)
1896                 return 0;
1897
1898         return ret;
1899 }
1900
1901 /*
1902  * returns 0 if the path could be dumped (probably truncated)
1903  * returns <0 in case of an error
1904  */
1905 static int inode_to_path(u64 inum, u32 name_len, unsigned long name_off,
1906                          struct extent_buffer *eb, void *ctx)
1907 {
1908         struct inode_fs_paths *ipath = ctx;
1909         char *fspath;
1910         char *fspath_min;
1911         int i = ipath->fspath->elem_cnt;
1912         const int s_ptr = sizeof(char *);
1913         u32 bytes_left;
1914
1915         bytes_left = ipath->fspath->bytes_left > s_ptr ?
1916                                         ipath->fspath->bytes_left - s_ptr : 0;
1917
1918         fspath_min = (char *)ipath->fspath->val + (i + 1) * s_ptr;
1919         fspath = btrfs_ref_to_path(ipath->fs_root, ipath->btrfs_path, name_len,
1920                                    name_off, eb, inum, fspath_min, bytes_left);
1921         if (IS_ERR(fspath))
1922                 return PTR_ERR(fspath);
1923
1924         if (fspath > fspath_min) {
1925                 ipath->fspath->val[i] = (u64)(unsigned long)fspath;
1926                 ++ipath->fspath->elem_cnt;
1927                 ipath->fspath->bytes_left = fspath - fspath_min;
1928         } else {
1929                 ++ipath->fspath->elem_missed;
1930                 ipath->fspath->bytes_missing += fspath_min - fspath;
1931                 ipath->fspath->bytes_left = 0;
1932         }
1933
1934         return 0;
1935 }
1936
1937 /*
1938  * this dumps all file system paths to the inode into the ipath struct, provided
1939  * is has been created large enough. each path is zero-terminated and accessed
1940  * from ipath->fspath->val[i].
1941  * when it returns, there are ipath->fspath->elem_cnt number of paths available
1942  * in ipath->fspath->val[]. when the allocated space wasn't sufficient, the
1943  * number of missed paths is recorded in ipath->fspath->elem_missed, otherwise,
1944  * it's zero. ipath->fspath->bytes_missing holds the number of bytes that would
1945  * have been needed to return all paths.
1946  */
1947 int paths_from_inode(u64 inum, struct inode_fs_paths *ipath)
1948 {
1949         return iterate_irefs(inum, ipath->fs_root, ipath->btrfs_path,
1950                              inode_to_path, ipath);
1951 }
1952
1953 struct btrfs_data_container *init_data_container(u32 total_bytes)
1954 {
1955         struct btrfs_data_container *data;
1956         size_t alloc_bytes;
1957
1958         alloc_bytes = max_t(size_t, total_bytes, sizeof(*data));
1959         data = vmalloc(alloc_bytes);
1960         if (!data)
1961                 return ERR_PTR(-ENOMEM);
1962
1963         if (total_bytes >= sizeof(*data)) {
1964                 data->bytes_left = total_bytes - sizeof(*data);
1965                 data->bytes_missing = 0;
1966         } else {
1967                 data->bytes_missing = sizeof(*data) - total_bytes;
1968                 data->bytes_left = 0;
1969         }
1970
1971         data->elem_cnt = 0;
1972         data->elem_missed = 0;
1973
1974         return data;
1975 }
1976
1977 /*
1978  * allocates space to return multiple file system paths for an inode.
1979  * total_bytes to allocate are passed, note that space usable for actual path
1980  * information will be total_bytes - sizeof(struct inode_fs_paths).
1981  * the returned pointer must be freed with free_ipath() in the end.
1982  */
1983 struct inode_fs_paths *init_ipath(s32 total_bytes, struct btrfs_root *fs_root,
1984                                         struct btrfs_path *path)
1985 {
1986         struct inode_fs_paths *ifp;
1987         struct btrfs_data_container *fspath;
1988
1989         fspath = init_data_container(total_bytes);
1990         if (IS_ERR(fspath))
1991                 return (void *)fspath;
1992
1993         ifp = kmalloc(sizeof(*ifp), GFP_NOFS);
1994         if (!ifp) {
1995                 vfree(fspath);
1996                 return ERR_PTR(-ENOMEM);
1997         }
1998
1999         ifp->btrfs_path = path;
2000         ifp->fspath = fspath;
2001         ifp->fs_root = fs_root;
2002
2003         return ifp;
2004 }
2005
2006 void free_ipath(struct inode_fs_paths *ipath)
2007 {
2008         if (!ipath)
2009                 return;
2010         vfree(ipath->fspath);
2011         kfree(ipath);
2012 }