fs/btrfs/compression.c

   1 /*
   2  * Copyright (C) 2008 Oracle.  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/kernel.h>
  20 #include <linux/bio.h>
  21 #include <linux/buffer_head.h>
  22 #include <linux/file.h>
  23 #include <linux/fs.h>
  24 #include <linux/pagemap.h>
  25 #include <linux/highmem.h>
  26 #include <linux/time.h>
  27 #include <linux/init.h>
  28 #include <linux/string.h>
  29 #include <linux/backing-dev.h>
  30 #include <linux/mpage.h>
  31 #include <linux/swap.h>
  32 #include <linux/writeback.h>
  33 #include <linux/bit_spinlock.h>
  34 #include <linux/pagevec.h>
  35 #include "compat.h"
  36 #include "ctree.h"
  37 #include "disk-io.h"
  38 #include "transaction.h"
  39 #include "btrfs_inode.h"
  40 #include "volumes.h"
  41 #include "ordered-data.h"
  42 #include "compression.h"
  43 #include "extent_io.h"
  44 #include "extent_map.h"
  45
  46 struct compressed_bio {
  47         /* number of bios pending for this compressed extent */
  48         atomic_t pending_bios;
  49
  50         /* the pages with the compressed data on them */
  51         struct page **compressed_pages;
  52
  53         /* inode that owns this data */
  54         struct inode *inode;
  55
  56         /* starting offset in the inode for our pages */
  57         u64 start;
  58
  59         /* number of bytes in the inode we're working on */
  60         unsigned long len;
  61
  62         /* number of bytes on disk */
  63         unsigned long compressed_len;
  64
  65         /* number of compressed pages in the array */
  66         unsigned long nr_pages;
  67
  68         /* IO errors */
  69         int errors;
  70         int mirror_num;
  71
  72         /* for reads, this is the bio we are copying the data into */
  73         struct bio *orig_bio;
  74
  75         /*
  76          * the start of a variable length array of checksums only
  77          * used by reads
  78          */
  79         u32 sums;
  80 };
  81
  82 static inline int compressed_bio_size(struct btrfs_root *root,
  83                                       unsigned long disk_size)
  84 {
  85         u16 csum_size = btrfs_super_csum_size(&root->fs_info->super_copy);
  86         return sizeof(struct compressed_bio) +
  87                 ((disk_size + root->sectorsize - 1) / root->sectorsize) *
  88                 csum_size;
  89 }
  90
  91 static struct bio *compressed_bio_alloc(struct block_device *bdev,
  92                                         u64 first_byte, gfp_t gfp_flags)
  93 {
  94         struct bio *bio;
  95         int nr_vecs;
  96
  97         nr_vecs = bio_get_nr_vecs(bdev);
  98         bio = bio_alloc(gfp_flags, nr_vecs);
  99
 100         if (bio == NULL && (current->flags & PF_MEMALLOC)) {
 101                 while (!bio && (nr_vecs /= 2))
 102                         bio = bio_alloc(gfp_flags, nr_vecs);
 103         }
 104
 105         if (bio) {
 106                 bio->bi_size = 0;
 107                 bio->bi_bdev = bdev;
 108                 bio->bi_sector = first_byte >> 9;
 109         }
 110         return bio;
 111 }
 112
 113 static int check_compressed_csum(struct inode *inode,
 114                                  struct compressed_bio *cb,
 115                                  u64 disk_start)
 116 {
 117         int ret;
 118         struct btrfs_root *root = BTRFS_I(inode)->root;
 119         struct page *page;
 120         unsigned long i;
 121         char *kaddr;
 122         u32 csum;
 123         u32 *cb_sum = &cb->sums;
 124
 125         if (BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)
 126                 return 0;
 127
 128         for (i = 0; i < cb->nr_pages; i++) {
 129                 page = cb->compressed_pages[i];
 130                 csum = ~(u32)0;
 131
 132                 kaddr = kmap_atomic(page, KM_USER0);
 133                 csum = btrfs_csum_data(root, kaddr, csum, PAGE_CACHE_SIZE);
 134                 btrfs_csum_final(csum, (char *)&csum);
 135                 kunmap_atomic(kaddr, KM_USER0);
 136
 137                 if (csum != *cb_sum) {
 138                         printk(KERN_INFO "btrfs csum failed ino %lu "
 139                                "extent %llu csum %u "
 140                                "wanted %u mirror %d\n", inode->i_ino,
 141                                (unsigned long long)disk_start,
 142                                csum, *cb_sum, cb->mirror_num);
 143                         ret = -EIO;
 144                         goto fail;
 145                 }
 146                 cb_sum++;
 147
 148         }
 149         ret = 0;
 150 fail:
 151         return ret;
 152 }
 153
 154 /* when we finish reading compressed pages from the disk, we
 155  * decompress them and then run the bio end_io routines on the
 156  * decompressed pages (in the inode address space).
 157  *
 158  * This allows the checksumming and other IO error handling routines
 159  * to work normally
 160  *
 161  * The compressed pages are freed here, and it must be run
 162  * in process context
 163  */
 164 static void end_compressed_bio_read(struct bio *bio, int err)
 165 {
 166         struct extent_io_tree *tree;
 167         struct compressed_bio *cb = bio->bi_private;
 168         struct inode *inode;
 169         struct page *page;
 170         unsigned long index;
 171         int ret;
 172
 173         if (err)
 174                 cb->errors = 1;
 175
 176         /* if there are more bios still pending for this compressed
 177          * extent, just exit
 178          */
 179         if (!atomic_dec_and_test(&cb->pending_bios))
 180                 goto out;
 181
 182         inode = cb->inode;
 183         ret = check_compressed_csum(inode, cb, (u64)bio->bi_sector << 9);
 184         if (ret)
 185                 goto csum_failed;
 186
 187         /* ok, we're the last bio for this extent, lets start
 188          * the decompression.
 189          */
 190         tree = &BTRFS_I(inode)->io_tree;
 191         ret = btrfs_zlib_decompress_biovec(cb->compressed_pages,
 192                                         cb->start,
 193                                         cb->orig_bio->bi_io_vec,
 194                                         cb->orig_bio->bi_vcnt,
 195                                         cb->compressed_len);
 196 csum_failed:
 197         if (ret)
 198                 cb->errors = 1;
 199
 200         /* release the compressed pages */
 201         index = 0;
 202         for (index = 0; index < cb->nr_pages; index++) {
 203                 page = cb->compressed_pages[index];
 204                 page->mapping = NULL;
 205                 page_cache_release(page);
 206         }
 207
 208         /* do io completion on the original bio */
 209         if (cb->errors) {
 210                 bio_io_error(cb->orig_bio);
 211         } else {
 212                 int bio_index = 0;
 213                 struct bio_vec *bvec = cb->orig_bio->bi_io_vec;
 214
 215                 /*
 216                  * we have verified the checksum already, set page
 217                  * checked so the end_io handlers know about it
 218                  */
 219                 while (bio_index < cb->orig_bio->bi_vcnt) {
 220                         SetPageChecked(bvec->bv_page);
 221                         bvec++;
 222                         bio_index++;
 223                 }
 224                 bio_endio(cb->orig_bio, 0);
 225         }
 226
 227         /* finally free the cb struct */
 228         kfree(cb->compressed_pages);
 229         kfree(cb);
 230 out:
 231         bio_put(bio);
 232 }
 233
 234 /*
 235  * Clear the writeback bits on all of the file
 236  * pages for a compressed write
 237  */
 238 static noinline int end_compressed_writeback(struct inode *inode, u64 start,
 239                                              unsigned long ram_size)
 240 {
 241         unsigned long index = start >> PAGE_CACHE_SHIFT;
 242         unsigned long end_index = (start + ram_size - 1) >> PAGE_CACHE_SHIFT;
 243         struct page *pages[16];
 244         unsigned long nr_pages = end_index - index + 1;
 245         int i;
 246         int ret;
 247
 248         while (nr_pages > 0) {
 249                 ret = find_get_pages_contig(inode->i_mapping, index,
 250                                      min_t(unsigned long,
 251                                      nr_pages, ARRAY_SIZE(pages)), pages);
 252                 if (ret == 0) {
 253                         nr_pages -= 1;
 254                         index += 1;
 255                         continue;
 256                 }
 257                 for (i = 0; i < ret; i++) {
 258                         end_page_writeback(pages[i]);
 259                         page_cache_release(pages[i]);
 260                 }
 261                 nr_pages -= ret;
 262                 index += ret;
 263         }
 264         /* the inode may be gone now */
 265         return 0;
 266 }
 267
 268 /*
 269  * do the cleanup once all the compressed pages hit the disk.
 270  * This will clear writeback on the file pages and free the compressed
 271  * pages.
 272  *
 273  * This also calls the writeback end hooks for the file pages so that
 274  * metadata and checksums can be updated in the file.
 275  */
 276 static void end_compressed_bio_write(struct bio *bio, int err)
 277 {
 278         struct extent_io_tree *tree;
 279         struct compressed_bio *cb = bio->bi_private;
 280         struct inode *inode;
 281         struct page *page;
 282         unsigned long index;
 283
 284         if (err)
 285                 cb->errors = 1;
 286
 287         /* if there are more bios still pending for this compressed
 288          * extent, just exit
 289          */
 290         if (!atomic_dec_and_test(&cb->pending_bios))
 291                 goto out;
 292
 293         /* ok, we're the last bio for this extent, step one is to
 294          * call back into the FS and do all the end_io operations
 295          */
 296         inode = cb->inode;
 297         tree = &BTRFS_I(inode)->io_tree;
 298         cb->compressed_pages[0]->mapping = cb->inode->i_mapping;
 299         tree->ops->writepage_end_io_hook(cb->compressed_pages[0],
 300                                          cb->start,
 301                                          cb->start + cb->len - 1,
 302                                          NULL, 1);
 303         cb->compressed_pages[0]->mapping = NULL;
 304
 305         end_compressed_writeback(inode, cb->start, cb->len);
 306         /* note, our inode could be gone now */
 307
 308         /*
 309          * release the compressed pages, these came from alloc_page and
 310          * are not attached to the inode at all
 311          */
 312         index = 0;
 313         for (index = 0; index < cb->nr_pages; index++) {
 314                 page = cb->compressed_pages[index];
 315                 page->mapping = NULL;
 316                 page_cache_release(page);
 317         }
 318
 319         /* finally free the cb struct */
 320         kfree(cb->compressed_pages);
 321         kfree(cb);
 322 out:
 323         bio_put(bio);
 324 }
 325
 326 /*
 327  * worker function to build and submit bios for previously compressed pages.
 328  * The corresponding pages in the inode should be marked for writeback
 329  * and the compressed pages should have a reference on them for dropping
 330  * when the IO is complete.
 331  *
 332  * This also checksums the file bytes and gets things ready for
 333  * the end io hooks.
 334  */
 335 int btrfs_submit_compressed_write(struct inode *inode, u64 start,
 336                                  unsigned long len, u64 disk_start,
 337                                  unsigned long compressed_len,
 338                                  struct page **compressed_pages,
 339                                  unsigned long nr_pages)
 340 {
 341         struct bio *bio = NULL;
 342         struct btrfs_root *root = BTRFS_I(inode)->root;
 343         struct compressed_bio *cb;
 344         unsigned long bytes_left;
 345         struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
 346         int page_index = 0;
 347         struct page *page;
 348         u64 first_byte = disk_start;
 349         struct block_device *bdev;
 350         int ret;
 351
 352         WARN_ON(start & ((u64)PAGE_CACHE_SIZE - 1));
 353         cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS);
 354         atomic_set(&cb->pending_bios, 0);
 355         cb->errors = 0;
 356         cb->inode = inode;
 357         cb->start = start;
 358         cb->len = len;
 359         cb->mirror_num = 0;
 360         cb->compressed_pages = compressed_pages;
 361         cb->compressed_len = compressed_len;
 362         cb->orig_bio = NULL;
 363         cb->nr_pages = nr_pages;
 364
 365         bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;
 366
 367         bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS);
 368         bio->bi_private = cb;
 369         bio->bi_end_io = end_compressed_bio_write;
 370         atomic_inc(&cb->pending_bios);
 371
 372         /* create and submit bios for the compressed pages */
 373         bytes_left = compressed_len;
 374         for (page_index = 0; page_index < cb->nr_pages; page_index++) {
 375                 page = compressed_pages[page_index];
 376                 page->mapping = inode->i_mapping;
 377                 if (bio->bi_size)
 378                         ret = io_tree->ops->merge_bio_hook(page, 0,
 379                                                            PAGE_CACHE_SIZE,
 380                                                            bio, 0);
 381                 else
 382                         ret = 0;
 383
 384                 page->mapping = NULL;
 385                 if (ret || bio_add_page(bio, page, PAGE_CACHE_SIZE, 0) <
 386                     PAGE_CACHE_SIZE) {
 387                         bio_get(bio);
 388
 389                         /*
 390                          * inc the count before we submit the bio so
 391                          * we know the end IO handler won't happen before
 392                          * we inc the count.  Otherwise, the cb might get
 393                          * freed before we're done setting it up
 394                          */
 395                         atomic_inc(&cb->pending_bios);
 396                         ret = btrfs_bio_wq_end_io(root->fs_info, bio, 0);
 397                         BUG_ON(ret);
 398
 399                         ret = btrfs_csum_one_bio(root, inode, bio, start, 1);
 400                         BUG_ON(ret);
 401
 402                         ret = btrfs_map_bio(root, WRITE, bio, 0, 1);
 403                         BUG_ON(ret);
 404
 405                         bio_put(bio);
 406
 407                         bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS);
 408                         bio->bi_private = cb;
 409                         bio->bi_end_io = end_compressed_bio_write;
 410                         bio_add_page(bio, page, PAGE_CACHE_SIZE, 0);
 411                 }
 412                 if (bytes_left < PAGE_CACHE_SIZE) {
 413                         printk("bytes left %lu compress len %lu nr %lu\n",
 414                                bytes_left, cb->compressed_len, cb->nr_pages);
 415                 }
 416                 bytes_left -= PAGE_CACHE_SIZE;
 417                 first_byte += PAGE_CACHE_SIZE;
 418                 cond_resched();
 419         }
 420         bio_get(bio);
 421
 422         ret = btrfs_bio_wq_end_io(root->fs_info, bio, 0);
 423         BUG_ON(ret);
 424
 425         ret = btrfs_csum_one_bio(root, inode, bio, start, 1);
 426         BUG_ON(ret);
 427
 428         ret = btrfs_map_bio(root, WRITE, bio, 0, 1);
 429         BUG_ON(ret);
 430
 431         bio_put(bio);
 432         return 0;
 433 }
 434
 435 static noinline int add_ra_bio_pages(struct inode *inode,
 436                                      u64 compressed_end,
 437                                      struct compressed_bio *cb)
 438 {
 439         unsigned long end_index;
 440         unsigned long page_index;
 441         u64 last_offset;
 442         u64 isize = i_size_read(inode);
 443         int ret;
 444         struct page *page;
 445         unsigned long nr_pages = 0;
 446         struct extent_map *em;
 447         struct address_space *mapping = inode->i_mapping;
 448         struct pagevec pvec;
 449         struct extent_map_tree *em_tree;
 450         struct extent_io_tree *tree;
 451         u64 end;
 452         int misses = 0;
 453
 454         page = cb->orig_bio->bi_io_vec[cb->orig_bio->bi_vcnt - 1].bv_page;
 455         last_offset = (page_offset(page) + PAGE_CACHE_SIZE);
 456         em_tree = &BTRFS_I(inode)->extent_tree;
 457         tree = &BTRFS_I(inode)->io_tree;
 458
 459         if (isize == 0)
 460                 return 0;
 461
 462         end_index = (i_size_read(inode) - 1) >> PAGE_CACHE_SHIFT;
 463
 464         pagevec_init(&pvec, 0);
 465         while (last_offset < compressed_end) {
 466                 page_index = last_offset >> PAGE_CACHE_SHIFT;
 467
 468                 if (page_index > end_index)
 469                         break;
 470
 471                 rcu_read_lock();
 472                 page = radix_tree_lookup(&mapping->page_tree, page_index);
 473                 rcu_read_unlock();
 474                 if (page) {
 475                         misses++;
 476                         if (misses > 4)
 477                                 break;
 478                         goto next;
 479                 }
 480
 481                 page = alloc_page(mapping_gfp_mask(mapping) & ~__GFP_FS);
 482                 if (!page)
 483                         break;
 484
 485                 page->index = page_index;
 486                 /*
 487                  * what we want to do here is call add_to_page_cache_lru,
 488                  * but that isn't exported, so we reproduce it here
 489                  */
 490                 if (add_to_page_cache(page, mapping,
 491                                       page->index, GFP_NOFS)) {
 492                         page_cache_release(page);
 493                         goto next;
 494                 }
 495
 496                 /* open coding of lru_cache_add, also not exported */
 497                 page_cache_get(page);
 498                 if (!pagevec_add(&pvec, page))
 499                         __pagevec_lru_add_file(&pvec);
 500
 501                 end = last_offset + PAGE_CACHE_SIZE - 1;
 502                 /*
 503                  * at this point, we have a locked page in the page cache
 504                  * for these bytes in the file.  But, we have to make
 505                  * sure they map to this compressed extent on disk.
 506                  */
 507                 set_page_extent_mapped(page);
 508                 lock_extent(tree, last_offset, end, GFP_NOFS);
 509                 read_lock(&em_tree->lock);
 510                 em = lookup_extent_mapping(em_tree, last_offset,
 511                                            PAGE_CACHE_SIZE);
 512                 read_unlock(&em_tree->lock);
 513
 514                 if (!em || last_offset < em->start ||
 515                     (last_offset + PAGE_CACHE_SIZE > extent_map_end(em)) ||
 516                     (em->block_start >> 9) != cb->orig_bio->bi_sector) {
 517                         free_extent_map(em);
 518                         unlock_extent(tree, last_offset, end, GFP_NOFS);
 519                         unlock_page(page);
 520                         page_cache_release(page);
 521                         break;
 522                 }
 523                 free_extent_map(em);
 524
 525                 if (page->index == end_index) {
 526                         char *userpage;
 527                         size_t zero_offset = isize & (PAGE_CACHE_SIZE - 1);
 528
 529                         if (zero_offset) {
 530                                 int zeros;
 531                                 zeros = PAGE_CACHE_SIZE - zero_offset;
 532                                 userpage = kmap_atomic(page, KM_USER0);
 533                                 memset(userpage + zero_offset, 0, zeros);
 534                                 flush_dcache_page(page);
 535                                 kunmap_atomic(userpage, KM_USER0);
 536                         }
 537                 }
 538
 539                 ret = bio_add_page(cb->orig_bio, page,
 540                                    PAGE_CACHE_SIZE, 0);
 541
 542                 if (ret == PAGE_CACHE_SIZE) {
 543                         nr_pages++;
 544                         page_cache_release(page);
 545                 } else {
 546                         unlock_extent(tree, last_offset, end, GFP_NOFS);
 547                         unlock_page(page);
 548                         page_cache_release(page);
 549                         break;
 550                 }
 551 next:
 552                 last_offset += PAGE_CACHE_SIZE;
 553         }
 554         if (pagevec_count(&pvec))
 555                 __pagevec_lru_add_file(&pvec);
 556         return 0;
 557 }
 558
 559 /*
 560  * for a compressed read, the bio we get passed has all the inode pages
 561  * in it.  We don't actually do IO on those pages but allocate new ones
 562  * to hold the compressed pages on disk.
 563  *
 564  * bio->bi_sector points to the compressed extent on disk
 565  * bio->bi_io_vec points to all of the inode pages
 566  * bio->bi_vcnt is a count of pages
 567  *
 568  * After the compressed pages are read, we copy the bytes into the
 569  * bio we were passed and then call the bio end_io calls
 570  */
 571 int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 572                                  int mirror_num, unsigned long bio_flags)
 573 {
 574         struct extent_io_tree *tree;
 575         struct extent_map_tree *em_tree;
 576         struct compressed_bio *cb;
 577         struct btrfs_root *root = BTRFS_I(inode)->root;
 578         unsigned long uncompressed_len = bio->bi_vcnt * PAGE_CACHE_SIZE;
 579         unsigned long compressed_len;
 580         unsigned long nr_pages;
 581         unsigned long page_index;
 582         struct page *page;
 583         struct block_device *bdev;
 584         struct bio *comp_bio;
 585         u64 cur_disk_byte = (u64)bio->bi_sector << 9;
 586         u64 em_len;
 587         u64 em_start;
 588         struct extent_map *em;
 589         int ret;
 590         u32 *sums;
 591
 592         tree = &BTRFS_I(inode)->io_tree;
 593         em_tree = &BTRFS_I(inode)->extent_tree;
 594
 595         /* we need the actual starting offset of this extent in the file */
 596         read_lock(&em_tree->lock);
 597         em = lookup_extent_mapping(em_tree,
 598                                    page_offset(bio->bi_io_vec->bv_page),
 599                                    PAGE_CACHE_SIZE);
 600         read_unlock(&em_tree->lock);
 601
 602         compressed_len = em->block_len;
 603         cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS);
 604         atomic_set(&cb->pending_bios, 0);
 605         cb->errors = 0;
 606         cb->inode = inode;
 607         cb->mirror_num = mirror_num;
 608         sums = &cb->sums;
 609
 610         cb->start = em->orig_start;
 611         em_len = em->len;
 612         em_start = em->start;
 613
 614         free_extent_map(em);
 615         em = NULL;
 616
 617         cb->len = uncompressed_len;
 618         cb->compressed_len = compressed_len;
 619         cb->orig_bio = bio;
 620
 621         nr_pages = (compressed_len + PAGE_CACHE_SIZE - 1) /
 622                                  PAGE_CACHE_SIZE;
 623         cb->compressed_pages = kmalloc(sizeof(struct page *) * nr_pages,
 624                                        GFP_NOFS);
 625         bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;
 626
 627         for (page_index = 0; page_index < nr_pages; page_index++) {
 628                 cb->compressed_pages[page_index] = alloc_page(GFP_NOFS |
 629                                                               __GFP_HIGHMEM);
 630         }
 631         cb->nr_pages = nr_pages;
 632
 633         add_ra_bio_pages(inode, em_start + em_len, cb);
 634
 635         /* include any pages we added in add_ra-bio_pages */
 636         uncompressed_len = bio->bi_vcnt * PAGE_CACHE_SIZE;
 637         cb->len = uncompressed_len;
 638
 639         comp_bio = compressed_bio_alloc(bdev, cur_disk_byte, GFP_NOFS);
 640         comp_bio->bi_private = cb;
 641         comp_bio->bi_end_io = end_compressed_bio_read;
 642         atomic_inc(&cb->pending_bios);
 643
 644         for (page_index = 0; page_index < nr_pages; page_index++) {
 645                 page = cb->compressed_pages[page_index];
 646                 page->mapping = inode->i_mapping;
 647                 page->index = em_start >> PAGE_CACHE_SHIFT;
 648
 649                 if (comp_bio->bi_size)
 650                         ret = tree->ops->merge_bio_hook(page, 0,
 651                                                         PAGE_CACHE_SIZE,
 652                                                         comp_bio, 0);
 653                 else
 654                         ret = 0;
 655
 656                 page->mapping = NULL;
 657                 if (ret || bio_add_page(comp_bio, page, PAGE_CACHE_SIZE, 0) <
 658                     PAGE_CACHE_SIZE) {
 659                         bio_get(comp_bio);
 660
 661                         ret = btrfs_bio_wq_end_io(root->fs_info, comp_bio, 0);
 662                         BUG_ON(ret);
 663
 664                         /*
 665                          * inc the count before we submit the bio so
 666                          * we know the end IO handler won't happen before
 667                          * we inc the count.  Otherwise, the cb might get
 668                          * freed before we're done setting it up
 669                          */
 670                         atomic_inc(&cb->pending_bios);
 671
 672                         if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
 673                                 btrfs_lookup_bio_sums(root, inode, comp_bio,
 674                                                       sums);
 675                         }
 676                         sums += (comp_bio->bi_size + root->sectorsize - 1) /
 677                                 root->sectorsize;
 678
 679                         ret = btrfs_map_bio(root, READ, comp_bio,
 680                                             mirror_num, 0);
 681                         BUG_ON(ret);
 682
 683                         bio_put(comp_bio);
 684
 685                         comp_bio = compressed_bio_alloc(bdev, cur_disk_byte,
 686                                                         GFP_NOFS);
 687                         comp_bio->bi_private = cb;
 688                         comp_bio->bi_end_io = end_compressed_bio_read;
 689
 690                         bio_add_page(comp_bio, page, PAGE_CACHE_SIZE, 0);
 691                 }
 692                 cur_disk_byte += PAGE_CACHE_SIZE;
 693         }
 694         bio_get(comp_bio);
 695
 696         ret = btrfs_bio_wq_end_io(root->fs_info, comp_bio, 0);
 697         BUG_ON(ret);
 698
 699         if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM))
 700                 btrfs_lookup_bio_sums(root, inode, comp_bio, sums);
 701
 702         ret = btrfs_map_bio(root, READ, comp_bio, mirror_num, 0);
 703         BUG_ON(ret);
 704
 705         bio_put(comp_bio);
 706         return 0;
 707 }