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/smp_lock.h>
  30 #include <linux/backing-dev.h>
  31 #include <linux/mpage.h>
  32 #include <linux/swap.h>
  33 #include <linux/writeback.h>
  34 #include <linux/bit_spinlock.h>
  35 #include <linux/version.h>
  36 #include <linux/pagevec.h>
  37 #include "compat.h"
  38 #include "ctree.h"
  39 #include "disk-io.h"
  40 #include "transaction.h"
  41 #include "btrfs_inode.h"
  42 #include "volumes.h"
  43 #include "ordered-data.h"
  44 #include "compression.h"
  45 #include "extent_io.h"
  46 #include "extent_map.h"
  47
  48 struct compressed_bio {
  49         /* number of bios pending for this compressed extent */
  50         atomic_t pending_bios;
  51
  52         /* the pages with the compressed data on them */
  53         struct page **compressed_pages;
  54
  55         /* inode that owns this data */
  56         struct inode *inode;
  57
  58         /* starting offset in the inode for our pages */
  59         u64 start;
  60
  61         /* number of bytes in the inode we're working on */
  62         unsigned long len;
  63
  64         /* number of bytes on disk */
  65         unsigned long compressed_len;
  66
  67         /* number of compressed pages in the array */
  68         unsigned long nr_pages;
  69
  70         /* IO errors */
  71         int errors;
  72         int mirror_num;
  73
  74         /* for reads, this is the bio we are copying the data into */
  75         struct bio *orig_bio;
  76
  77         /*
  78          * the start of a variable length array of checksums only
  79          * used by reads
  80          */
  81         u32 sums;
  82 };
  83
  84 static inline int compressed_bio_size(struct btrfs_root *root,
  85                                       unsigned long disk_size)
  86 {
  87         u16 csum_size = btrfs_super_csum_size(&root->fs_info->super_copy);
  88         return sizeof(struct compressed_bio) +
  89                 ((disk_size + root->sectorsize - 1) / root->sectorsize) *
  90                 csum_size;
  91 }
  92
  93 static struct bio *compressed_bio_alloc(struct block_device *bdev,
  94                                         u64 first_byte, gfp_t gfp_flags)
  95 {
  96         struct bio *bio;
  97         int nr_vecs;
  98
  99         nr_vecs = bio_get_nr_vecs(bdev);
 100         bio = bio_alloc(gfp_flags, nr_vecs);
 101
 102         if (bio == NULL && (current->flags & PF_MEMALLOC)) {
 103                 while (!bio && (nr_vecs /= 2))
 104                         bio = bio_alloc(gfp_flags, nr_vecs);
 105         }
 106
 107         if (bio) {
 108                 bio->bi_size = 0;
 109                 bio->bi_bdev = bdev;
 110                 bio->bi_sector = first_byte >> 9;
 111         }
 112         return bio;
 113 }
 114
 115 static int check_compressed_csum(struct inode *inode,
 116                                  struct compressed_bio *cb,
 117                                  u64 disk_start)
 118 {
 119         int ret;
 120         struct btrfs_root *root = BTRFS_I(inode)->root;
 121         struct page *page;
 122         unsigned long i;
 123         char *kaddr;
 124         u32 csum;
 125         u32 *cb_sum = &cb->sums;
 126
 127         if (btrfs_test_flag(inode, NODATASUM))
 128                 return 0;
 129
 130         for (i = 0; i < cb->nr_pages; i++) {
 131                 page = cb->compressed_pages[i];
 132                 csum = ~(u32)0;
 133
 134                 kaddr = kmap_atomic(page, KM_USER0);
 135                 csum = btrfs_csum_data(root, kaddr, csum, PAGE_CACHE_SIZE);
 136                 btrfs_csum_final(csum, (char *)&csum);
 137                 kunmap_atomic(kaddr, KM_USER0);
 138
 139                 if (csum != *cb_sum) {
 140                         printk(KERN_INFO "btrfs csum failed ino %lu "
 141                                "extent %llu csum %u "
 142                                "wanted %u mirror %d\n", inode->i_ino,
 143                                (unsigned long long)disk_start,
 144                                csum, *cb_sum, cb->mirror_num);
 145                         ret = -EIO;
 146                         goto fail;
 147                 }
 148                 cb_sum++;
 149
 150         }
 151         ret = 0;
 152 fail:
 153         return ret;
 154 }
 155
 156 /* when we finish reading compressed pages from the disk, we
 157  * decompress them and then run the bio end_io routines on the
 158  * decompressed pages (in the inode address space).
 159  *
 160  * This allows the checksumming and other IO error handling routines
 161  * to work normally
 162  *
 163  * The compressed pages are freed here, and it must be run
 164  * in process context
 165  */
 166 static void end_compressed_bio_read(struct bio *bio, int err)
 167 {
 168         struct extent_io_tree *tree;
 169         struct compressed_bio *cb = bio->bi_private;
 170         struct inode *inode;
 171         struct page *page;
 172         unsigned long index;
 173         int ret;
 174
 175         if (err)
 176                 cb->errors = 1;
 177
 178         /* if there are more bios still pending for this compressed
 179          * extent, just exit
 180          */
 181         if (!atomic_dec_and_test(&cb->pending_bios))
 182                 goto out;
 183
 184         inode = cb->inode;
 185         ret = check_compressed_csum(inode, cb, (u64)bio->bi_sector << 9);
 186         if (ret)
 187                 goto csum_failed;
 188
 189         /* ok, we're the last bio for this extent, lets start
 190          * the decompression.
 191          */
 192         tree = &BTRFS_I(inode)->io_tree;
 193         ret = btrfs_zlib_decompress_biovec(cb->compressed_pages,
 194                                         cb->start,
 195                                         cb->orig_bio->bi_io_vec,
 196                                         cb->orig_bio->bi_vcnt,
 197                                         cb->compressed_len);
 198 csum_failed:
 199         if (ret)
 200                 cb->errors = 1;
 201
 202         /* release the compressed pages */
 203         index = 0;
 204         for (index = 0; index < cb->nr_pages; index++) {
 205                 page = cb->compressed_pages[index];
 206                 page->mapping = NULL;
 207                 page_cache_release(page);
 208         }
 209
 210         /* do io completion on the original bio */
 211         if (cb->errors) {
 212                 bio_io_error(cb->orig_bio);
 213         } else {
 214                 int bio_index = 0;
 215                 struct bio_vec *bvec = cb->orig_bio->bi_io_vec;
 216
 217                 /*
 218                  * we have verified the checksum already, set page
 219                  * checked so the end_io handlers know about it
 220                  */
 221                 while (bio_index < cb->orig_bio->bi_vcnt) {
 222                         SetPageChecked(bvec->bv_page);
 223                         bvec++;
 224                         bio_index++;
 225                 }
 226                 bio_endio(cb->orig_bio, 0);
 227         }
 228
 229         /* finally free the cb struct */
 230         kfree(cb->compressed_pages);
 231         kfree(cb);
 232 out:
 233         bio_put(bio);
 234 }
 235
 236 /*
 237  * Clear the writeback bits on all of the file
 238  * pages for a compressed write
 239  */
 240 static noinline int end_compressed_writeback(struct inode *inode, u64 start,
 241                                              unsigned long ram_size)
 242 {
 243         unsigned long index = start >> PAGE_CACHE_SHIFT;
 244         unsigned long end_index = (start + ram_size - 1) >> PAGE_CACHE_SHIFT;
 245         struct page *pages[16];
 246         unsigned long nr_pages = end_index - index + 1;
 247         int i;
 248         int ret;
 249
 250         while (nr_pages > 0) {
 251                 ret = find_get_pages_contig(inode->i_mapping, index,
 252                                      min_t(unsigned long,
 253                                      nr_pages, ARRAY_SIZE(pages)), pages);
 254                 if (ret == 0) {
 255                         nr_pages -= 1;
 256                         index += 1;
 257                         continue;
 258                 }
 259                 for (i = 0; i < ret; i++) {
 260                         end_page_writeback(pages[i]);
 261                         page_cache_release(pages[i]);
 262                 }
 263                 nr_pages -= ret;
 264                 index += ret;
 265         }
 266         /* the inode may be gone now */
 267         return 0;
 268 }
 269
 270 /*
 271  * do the cleanup once all the compressed pages hit the disk.
 272  * This will clear writeback on the file pages and free the compressed
 273  * pages.
 274  *
 275  * This also calls the writeback end hooks for the file pages so that
 276  * metadata and checksums can be updated in the file.
 277  */
 278 static void end_compressed_bio_write(struct bio *bio, int err)
 279 {
 280         struct extent_io_tree *tree;
 281         struct compressed_bio *cb = bio->bi_private;
 282         struct inode *inode;
 283         struct page *page;
 284         unsigned long index;
 285
 286         if (err)
 287                 cb->errors = 1;
 288
 289         /* if there are more bios still pending for this compressed
 290          * extent, just exit
 291          */
 292         if (!atomic_dec_and_test(&cb->pending_bios))
 293                 goto out;
 294
 295         /* ok, we're the last bio for this extent, step one is to
 296          * call back into the FS and do all the end_io operations
 297          */
 298         inode = cb->inode;
 299         tree = &BTRFS_I(inode)->io_tree;
 300         cb->compressed_pages[0]->mapping = cb->inode->i_mapping;
 301         tree->ops->writepage_end_io_hook(cb->compressed_pages[0],
 302                                          cb->start,
 303                                          cb->start + cb->len - 1,
 304                                          NULL, 1);
 305         cb->compressed_pages[0]->mapping = NULL;
 306
 307         end_compressed_writeback(inode, cb->start, cb->len);
 308         /* note, our inode could be gone now */
 309
 310         /*
 311          * release the compressed pages, these came from alloc_page and
 312          * are not attached to the inode at all
 313          */
 314         index = 0;
 315         for (index = 0; index < cb->nr_pages; index++) {
 316                 page = cb->compressed_pages[index];
 317                 page->mapping = NULL;
 318                 page_cache_release(page);
 319         }
 320
 321         /* finally free the cb struct */
 322         kfree(cb->compressed_pages);
 323         kfree(cb);
 324 out:
 325         bio_put(bio);
 326 }
 327
 328 /*
 329  * worker function to build and submit bios for previously compressed pages.
 330  * The corresponding pages in the inode should be marked for writeback
 331  * and the compressed pages should have a reference on them for dropping
 332  * when the IO is complete.
 333  *
 334  * This also checksums the file bytes and gets things ready for
 335  * the end io hooks.
 336  */
 337 int btrfs_submit_compressed_write(struct inode *inode, u64 start,
 338                                  unsigned long len, u64 disk_start,
 339                                  unsigned long compressed_len,
 340                                  struct page **compressed_pages,
 341                                  unsigned long nr_pages)
 342 {
 343         struct bio *bio = NULL;
 344         struct btrfs_root *root = BTRFS_I(inode)->root;
 345         struct compressed_bio *cb;
 346         unsigned long bytes_left;
 347         struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
 348         int page_index = 0;
 349         struct page *page;
 350         u64 first_byte = disk_start;
 351         struct block_device *bdev;
 352         int ret;
 353
 354         WARN_ON(start & ((u64)PAGE_CACHE_SIZE - 1));
 355         cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS);
 356         atomic_set(&cb->pending_bios, 0);
 357         cb->errors = 0;
 358         cb->inode = inode;
 359         cb->start = start;
 360         cb->len = len;
 361         cb->mirror_num = 0;
 362         cb->compressed_pages = compressed_pages;
 363         cb->compressed_len = compressed_len;
 364         cb->orig_bio = NULL;
 365         cb->nr_pages = nr_pages;
 366
 367         bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;
 368
 369         bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS);
 370         bio->bi_private = cb;
 371         bio->bi_end_io = end_compressed_bio_write;
 372         atomic_inc(&cb->pending_bios);
 373
 374         /* create and submit bios for the compressed pages */
 375         bytes_left = compressed_len;
 376         for (page_index = 0; page_index < cb->nr_pages; page_index++) {
 377                 page = compressed_pages[page_index];
 378                 page->mapping = inode->i_mapping;
 379                 if (bio->bi_size)
 380                         ret = io_tree->ops->merge_bio_hook(page, 0,
 381                                                            PAGE_CACHE_SIZE,
 382                                                            bio, 0);
 383                 else
 384                         ret = 0;
 385
 386                 page->mapping = NULL;
 387                 if (ret || bio_add_page(bio, page, PAGE_CACHE_SIZE, 0) <
 388                     PAGE_CACHE_SIZE) {
 389                         bio_get(bio);
 390
 391                         /*
 392                          * inc the count before we submit the bio so
 393                          * we know the end IO handler won't happen before
 394                          * we inc the count.  Otherwise, the cb might get
 395                          * freed before we're done setting it up
 396                          */
 397                         atomic_inc(&cb->pending_bios);
 398                         ret = btrfs_bio_wq_end_io(root->fs_info, bio, 0);
 399                         BUG_ON(ret);
 400
 401                         ret = btrfs_csum_one_bio(root, inode, bio, start, 1);
 402                         BUG_ON(ret);
 403
 404                         ret = btrfs_map_bio(root, WRITE, bio, 0, 1);
 405                         BUG_ON(ret);
 406
 407                         bio_put(bio);
 408
 409                         bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS);
 410                         bio->bi_private = cb;
 411                         bio->bi_end_io = end_compressed_bio_write;
 412                         bio_add_page(bio, page, PAGE_CACHE_SIZE, 0);
 413                 }
 414                 if (bytes_left < PAGE_CACHE_SIZE) {
 415                         printk("bytes left %lu compress len %lu nr %lu\n",
 416                                bytes_left, cb->compressed_len, cb->nr_pages);
 417                 }
 418                 bytes_left -= PAGE_CACHE_SIZE;
 419                 first_byte += PAGE_CACHE_SIZE;
 420                 cond_resched();
 421         }
 422         bio_get(bio);
 423
 424         ret = btrfs_bio_wq_end_io(root->fs_info, bio, 0);
 425         BUG_ON(ret);
 426
 427         ret = btrfs_csum_one_bio(root, inode, bio, start, 1);
 428         BUG_ON(ret);
 429
 430         ret = btrfs_map_bio(root, WRITE, bio, 0, 1);
 431         BUG_ON(ret);
 432
 433         bio_put(bio);
 434         return 0;
 435 }
 436
 437 static noinline int add_ra_bio_pages(struct inode *inode,
 438                                      u64 compressed_end,
 439                                      struct compressed_bio *cb)
 440 {
 441         unsigned long end_index;
 442         unsigned long page_index;
 443         u64 last_offset;
 444         u64 isize = i_size_read(inode);
 445         int ret;
 446         struct page *page;
 447         unsigned long nr_pages = 0;
 448         struct extent_map *em;
 449         struct address_space *mapping = inode->i_mapping;
 450         struct pagevec pvec;
 451         struct extent_map_tree *em_tree;
 452         struct extent_io_tree *tree;
 453         u64 end;
 454         int misses = 0;
 455
 456         page = cb->orig_bio->bi_io_vec[cb->orig_bio->bi_vcnt - 1].bv_page;
 457         last_offset = (page_offset(page) + PAGE_CACHE_SIZE);
 458         em_tree = &BTRFS_I(inode)->extent_tree;
 459         tree = &BTRFS_I(inode)->io_tree;
 460
 461         if (isize == 0)
 462                 return 0;
 463
 464         end_index = (i_size_read(inode) - 1) >> PAGE_CACHE_SHIFT;
 465
 466         pagevec_init(&pvec, 0);
 467         while (last_offset < compressed_end) {
 468                 page_index = last_offset >> PAGE_CACHE_SHIFT;
 469
 470                 if (page_index > end_index)
 471                         break;
 472
 473                 rcu_read_lock();
 474                 page = radix_tree_lookup(&mapping->page_tree, page_index);
 475                 rcu_read_unlock();
 476                 if (page) {
 477                         misses++;
 478                         if (misses > 4)
 479                                 break;
 480                         goto next;
 481                 }
 482
 483                 page = alloc_page(mapping_gfp_mask(mapping) | GFP_NOFS);
 484                 if (!page)
 485                         break;
 486
 487                 page->index = page_index;
 488                 /*
 489                  * what we want to do here is call add_to_page_cache_lru,
 490                  * but that isn't exported, so we reproduce it here
 491                  */
 492                 if (add_to_page_cache(page, mapping,
 493                                       page->index, GFP_NOFS)) {
 494                         page_cache_release(page);
 495                         goto next;
 496                 }
 497
 498                 /* open coding of lru_cache_add, also not exported */
 499                 page_cache_get(page);
 500                 if (!pagevec_add(&pvec, page))
 501                         __pagevec_lru_add_file(&pvec);
 502
 503                 end = last_offset + PAGE_CACHE_SIZE - 1;
 504                 /*
 505                  * at this point, we have a locked page in the page cache
 506                  * for these bytes in the file.  But, we have to make
 507                  * sure they map to this compressed extent on disk.
 508                  */
 509                 set_page_extent_mapped(page);
 510                 lock_extent(tree, last_offset, end, GFP_NOFS);
 511                 spin_lock(&em_tree->lock);
 512                 em = lookup_extent_mapping(em_tree, last_offset,
 513                                            PAGE_CACHE_SIZE);
 514                 spin_unlock(&em_tree->lock);
 515
 516                 if (!em || last_offset < em->start ||
 517                     (last_offset + PAGE_CACHE_SIZE > extent_map_end(em)) ||
 518                     (em->block_start >> 9) != cb->orig_bio->bi_sector) {
 519                         free_extent_map(em);
 520                         unlock_extent(tree, last_offset, end, GFP_NOFS);
 521                         unlock_page(page);
 522                         page_cache_release(page);
 523                         break;
 524                 }
 525                 free_extent_map(em);
 526
 527                 if (page->index == end_index) {
 528                         char *userpage;
 529                         size_t zero_offset = isize & (PAGE_CACHE_SIZE - 1);
 530
 531                         if (zero_offset) {
 532                                 int zeros;
 533                                 zeros = PAGE_CACHE_SIZE - zero_offset;
 534                                 userpage = kmap_atomic(page, KM_USER0);
 535                                 memset(userpage + zero_offset, 0, zeros);
 536                                 flush_dcache_page(page);
 537                                 kunmap_atomic(userpage, KM_USER0);
 538                         }
 539                 }
 540
 541                 ret = bio_add_page(cb->orig_bio, page,
 542                                    PAGE_CACHE_SIZE, 0);
 543
 544                 if (ret == PAGE_CACHE_SIZE) {
 545                         nr_pages++;
 546                         page_cache_release(page);
 547                 } else {
 548                         unlock_extent(tree, last_offset, end, GFP_NOFS);
 549                         unlock_page(page);
 550                         page_cache_release(page);
 551                         break;
 552                 }
 553 next:
 554                 last_offset += PAGE_CACHE_SIZE;
 555         }
 556         if (pagevec_count(&pvec))
 557                 __pagevec_lru_add_file(&pvec);
 558         return 0;
 559 }
 560
 561 /*
 562  * for a compressed read, the bio we get passed has all the inode pages
 563  * in it.  We don't actually do IO on those pages but allocate new ones
 564  * to hold the compressed pages on disk.
 565  *
 566  * bio->bi_sector points to the compressed extent on disk
 567  * bio->bi_io_vec points to all of the inode pages
 568  * bio->bi_vcnt is a count of pages
 569  *
 570  * After the compressed pages are read, we copy the bytes into the
 571  * bio we were passed and then call the bio end_io calls
 572  */
 573 int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 574                                  int mirror_num, unsigned long bio_flags)
 575 {
 576         struct extent_io_tree *tree;
 577         struct extent_map_tree *em_tree;
 578         struct compressed_bio *cb;
 579         struct btrfs_root *root = BTRFS_I(inode)->root;
 580         unsigned long uncompressed_len = bio->bi_vcnt * PAGE_CACHE_SIZE;
 581         unsigned long compressed_len;
 582         unsigned long nr_pages;
 583         unsigned long page_index;
 584         struct page *page;
 585         struct block_device *bdev;
 586         struct bio *comp_bio;
 587         u64 cur_disk_byte = (u64)bio->bi_sector << 9;
 588         u64 em_len;
 589         u64 em_start;
 590         struct extent_map *em;
 591         int ret;
 592         u32 *sums;
 593
 594         tree = &BTRFS_I(inode)->io_tree;
 595         em_tree = &BTRFS_I(inode)->extent_tree;
 596
 597         /* we need the actual starting offset of this extent in the file */
 598         spin_lock(&em_tree->lock);
 599         em = lookup_extent_mapping(em_tree,
 600                                    page_offset(bio->bi_io_vec->bv_page),
 601                                    PAGE_CACHE_SIZE);
 602         spin_unlock(&em_tree->lock);
 603
 604         compressed_len = em->block_len;
 605         cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS);
 606         atomic_set(&cb->pending_bios, 0);
 607         cb->errors = 0;
 608         cb->inode = inode;
 609         cb->mirror_num = mirror_num;
 610         sums = &cb->sums;
 611
 612         cb->start = em->orig_start;
 613         em_len = em->len;
 614         em_start = em->start;
 615
 616         free_extent_map(em);
 617         em = NULL;
 618
 619         cb->len = uncompressed_len;
 620         cb->compressed_len = compressed_len;
 621         cb->orig_bio = bio;
 622
 623         nr_pages = (compressed_len + PAGE_CACHE_SIZE - 1) /
 624                                  PAGE_CACHE_SIZE;
 625         cb->compressed_pages = kmalloc(sizeof(struct page *) * nr_pages,
 626                                        GFP_NOFS);
 627         bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;
 628
 629         for (page_index = 0; page_index < nr_pages; page_index++) {
 630                 cb->compressed_pages[page_index] = alloc_page(GFP_NOFS |
 631                                                               __GFP_HIGHMEM);
 632         }
 633         cb->nr_pages = nr_pages;
 634
 635         add_ra_bio_pages(inode, em_start + em_len, cb);
 636
 637         /* include any pages we added in add_ra-bio_pages */
 638         uncompressed_len = bio->bi_vcnt * PAGE_CACHE_SIZE;
 639         cb->len = uncompressed_len;
 640
 641         comp_bio = compressed_bio_alloc(bdev, cur_disk_byte, GFP_NOFS);
 642         comp_bio->bi_private = cb;
 643         comp_bio->bi_end_io = end_compressed_bio_read;
 644         atomic_inc(&cb->pending_bios);
 645
 646         for (page_index = 0; page_index < nr_pages; page_index++) {
 647                 page = cb->compressed_pages[page_index];
 648                 page->mapping = inode->i_mapping;
 649                 page->index = em_start >> PAGE_CACHE_SHIFT;
 650
 651                 if (comp_bio->bi_size)
 652                         ret = tree->ops->merge_bio_hook(page, 0,
 653                                                         PAGE_CACHE_SIZE,
 654                                                         comp_bio, 0);
 655                 else
 656                         ret = 0;
 657
 658                 page->mapping = NULL;
 659                 if (ret || bio_add_page(comp_bio, page, PAGE_CACHE_SIZE, 0) <
 660                     PAGE_CACHE_SIZE) {
 661                         bio_get(comp_bio);
 662
 663                         ret = btrfs_bio_wq_end_io(root->fs_info, comp_bio, 0);
 664                         BUG_ON(ret);
 665
 666                         /*
 667                          * inc the count before we submit the bio so
 668                          * we know the end IO handler won't happen before
 669                          * we inc the count.  Otherwise, the cb might get
 670                          * freed before we're done setting it up
 671                          */
 672                         atomic_inc(&cb->pending_bios);
 673
 674                         if (!btrfs_test_flag(inode, NODATASUM)) {
 675                                 btrfs_lookup_bio_sums(root, inode, comp_bio,
 676                                                       sums);
 677                         }
 678                         sums += (comp_bio->bi_size + root->sectorsize - 1) /
 679                                 root->sectorsize;
 680
 681                         ret = btrfs_map_bio(root, READ, comp_bio,
 682                                             mirror_num, 0);
 683                         BUG_ON(ret);
 684
 685                         bio_put(comp_bio);
 686
 687                         comp_bio = compressed_bio_alloc(bdev, cur_disk_byte,
 688                                                         GFP_NOFS);
 689                         comp_bio->bi_private = cb;
 690                         comp_bio->bi_end_io = end_compressed_bio_read;
 691
 692                         bio_add_page(comp_bio, page, PAGE_CACHE_SIZE, 0);
 693                 }
 694                 cur_disk_byte += PAGE_CACHE_SIZE;
 695         }
 696         bio_get(comp_bio);
 697
 698         ret = btrfs_bio_wq_end_io(root->fs_info, comp_bio, 0);
 699         BUG_ON(ret);
 700
 701         if (!btrfs_test_flag(inode, NODATASUM))
 702                 btrfs_lookup_bio_sums(root, inode, comp_bio, sums);
 703
 704         ret = btrfs_map_bio(root, READ, comp_bio, mirror_num, 0);
 705         BUG_ON(ret);
 706
 707         bio_put(comp_bio);
 708         return 0;
 709 }