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