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