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         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 compressed_bio *cb = bio->bi_private;
 167         struct inode *inode;
 168         struct page *page;
 169         unsigned long index;
 170         int ret;
 171
 172         if (err)
 173                 cb->errors = 1;
 174
 175         /* if there are more bios still pending for this compressed
 176          * extent, just exit
 177          */
 178         if (!atomic_dec_and_test(&cb->pending_bios))
 179                 goto out;
 180
 181         inode = cb->inode;
 182         ret = check_compressed_csum(inode, cb, (u64)bio->bi_sector << 9);
 183         if (ret)
 184                 goto csum_failed;
 185
 186         /* ok, we're the last bio for this extent, lets start
 187          * the decompression.
 188          */
 189         ret = btrfs_zlib_decompress_biovec(cb->compressed_pages,
 190                                         cb->start,
 191                                         cb->orig_bio->bi_io_vec,
 192                                         cb->orig_bio->bi_vcnt,
 193                                         cb->compressed_len);
 194 csum_failed:
 195         if (ret)
 196                 cb->errors = 1;
 197
 198         /* release the compressed pages */
 199         index = 0;
 200         for (index = 0; index < cb->nr_pages; index++) {
 201                 page = cb->compressed_pages[index];
 202                 page->mapping = NULL;
 203                 page_cache_release(page);
 204         }
 205
 206         /* do io completion on the original bio */
 207         if (cb->errors) {
 208                 bio_io_error(cb->orig_bio);
 209         } else {
 210                 int bio_index = 0;
 211                 struct bio_vec *bvec = cb->orig_bio->bi_io_vec;
 212
 213                 /*
 214                  * we have verified the checksum already, set page
 215                  * checked so the end_io handlers know about it
 216                  */
 217                 while (bio_index < cb->orig_bio->bi_vcnt) {
 218                         SetPageChecked(bvec->bv_page);
 219                         bvec++;
 220                         bio_index++;
 221                 }
 222                 bio_endio(cb->orig_bio, 0);
 223         }
 224
 225         /* finally free the cb struct */
 226         kfree(cb->compressed_pages);
 227         kfree(cb);
 228 out:
 229         bio_put(bio);
 230 }
 231
 232 /*
 233  * Clear the writeback bits on all of the file
 234  * pages for a compressed write
 235  */
 236 static noinline int end_compressed_writeback(struct inode *inode, u64 start,
 237                                              unsigned long ram_size)
 238 {
 239         unsigned long index = start >> PAGE_CACHE_SHIFT;
 240         unsigned long end_index = (start + ram_size - 1) >> PAGE_CACHE_SHIFT;
 241         struct page *pages[16];
 242         unsigned long nr_pages = end_index - index + 1;
 243         int i;
 244         int ret;
 245
 246         while (nr_pages > 0) {
 247                 ret = find_get_pages_contig(inode->i_mapping, index,
 248                                      min_t(unsigned long,
 249                                      nr_pages, ARRAY_SIZE(pages)), pages);
 250                 if (ret == 0) {
 251                         nr_pages -= 1;
 252                         index += 1;
 253                         continue;
 254                 }
 255                 for (i = 0; i < ret; i++) {
 256                         end_page_writeback(pages[i]);
 257                         page_cache_release(pages[i]);
 258                 }
 259                 nr_pages -= ret;
 260                 index += ret;
 261         }
 262         /* the inode may be gone now */
 263         return 0;
 264 }
 265
 266 /*
 267  * do the cleanup once all the compressed pages hit the disk.
 268  * This will clear writeback on the file pages and free the compressed
 269  * pages.
 270  *
 271  * This also calls the writeback end hooks for the file pages so that
 272  * metadata and checksums can be updated in the file.
 273  */
 274 static void end_compressed_bio_write(struct bio *bio, int err)
 275 {
 276         struct extent_io_tree *tree;
 277         struct compressed_bio *cb = bio->bi_private;
 278         struct inode *inode;
 279         struct page *page;
 280         unsigned long index;
 281
 282         if (err)
 283                 cb->errors = 1;
 284
 285         /* if there are more bios still pending for this compressed
 286          * extent, just exit
 287          */
 288         if (!atomic_dec_and_test(&cb->pending_bios))
 289                 goto out;
 290
 291         /* ok, we're the last bio for this extent, step one is to
 292          * call back into the FS and do all the end_io operations
 293          */
 294         inode = cb->inode;
 295         tree = &BTRFS_I(inode)->io_tree;
 296         cb->compressed_pages[0]->mapping = cb->inode->i_mapping;
 297         tree->ops->writepage_end_io_hook(cb->compressed_pages[0],
 298                                          cb->start,
 299                                          cb->start + cb->len - 1,
 300                                          NULL, 1);
 301         cb->compressed_pages[0]->mapping = NULL;
 302
 303         end_compressed_writeback(inode, cb->start, cb->len);
 304         /* note, our inode could be gone now */
 305
 306         /*
 307          * release the compressed pages, these came from alloc_page and
 308          * are not attached to the inode at all
 309          */
 310         index = 0;
 311         for (index = 0; index < cb->nr_pages; index++) {
 312                 page = cb->compressed_pages[index];
 313                 page->mapping = NULL;
 314                 page_cache_release(page);
 315         }
 316
 317         /* finally free the cb struct */
 318         kfree(cb->compressed_pages);
 319         kfree(cb);
 320 out:
 321         bio_put(bio);
 322 }
 323
 324 /*
 325  * worker function to build and submit bios for previously compressed pages.
 326  * The corresponding pages in the inode should be marked for writeback
 327  * and the compressed pages should have a reference on them for dropping
 328  * when the IO is complete.
 329  *
 330  * This also checksums the file bytes and gets things ready for
 331  * the end io hooks.
 332  */
 333 int btrfs_submit_compressed_write(struct inode *inode, u64 start,
 334                                  unsigned long len, u64 disk_start,
 335                                  unsigned long compressed_len,
 336                                  struct page **compressed_pages,
 337                                  unsigned long nr_pages)
 338 {
 339         struct bio *bio = NULL;
 340         struct btrfs_root *root = BTRFS_I(inode)->root;
 341         struct compressed_bio *cb;
 342         unsigned long bytes_left;
 343         struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
 344         int page_index = 0;
 345         struct page *page;
 346         u64 first_byte = disk_start;
 347         struct block_device *bdev;
 348         int ret;
 349
 350         WARN_ON(start & ((u64)PAGE_CACHE_SIZE - 1));
 351         cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS);
 352         atomic_set(&cb->pending_bios, 0);
 353         cb->errors = 0;
 354         cb->inode = inode;
 355         cb->start = start;
 356         cb->len = len;
 357         cb->mirror_num = 0;
 358         cb->compressed_pages = compressed_pages;
 359         cb->compressed_len = compressed_len;
 360         cb->orig_bio = NULL;
 361         cb->nr_pages = nr_pages;
 362
 363         bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;
 364
 365         bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS);
 366         bio->bi_private = cb;
 367         bio->bi_end_io = end_compressed_bio_write;
 368         atomic_inc(&cb->pending_bios);
 369
 370         /* create and submit bios for the compressed pages */
 371         bytes_left = compressed_len;
 372         for (page_index = 0; page_index < cb->nr_pages; page_index++) {
 373                 page = compressed_pages[page_index];
 374                 page->mapping = inode->i_mapping;
 375                 if (bio->bi_size)
 376                         ret = io_tree->ops->merge_bio_hook(page, 0,
 377                                                            PAGE_CACHE_SIZE,
 378                                                            bio, 0);
 379                 else
 380                         ret = 0;
 381
 382                 page->mapping = NULL;
 383                 if (ret || bio_add_page(bio, page, PAGE_CACHE_SIZE, 0) <
 384                     PAGE_CACHE_SIZE) {
 385                         bio_get(bio);
 386
 387                         /*
 388                          * inc the count before we submit the bio so
 389                          * we know the end IO handler won't happen before
 390                          * we inc the count.  Otherwise, the cb might get
 391                          * freed before we're done setting it up
 392                          */
 393                         atomic_inc(&cb->pending_bios);
 394                         ret = btrfs_bio_wq_end_io(root->fs_info, bio, 0);
 395                         BUG_ON(ret);
 396
 397                         ret = btrfs_csum_one_bio(root, inode, bio, start, 1);
 398                         BUG_ON(ret);
 399
 400                         ret = btrfs_map_bio(root, WRITE, bio, 0, 1);
 401                         BUG_ON(ret);
 402
 403                         bio_put(bio);
 404
 405                         bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS);
 406                         bio->bi_private = cb;
 407                         bio->bi_end_io = end_compressed_bio_write;
 408                         bio_add_page(bio, page, PAGE_CACHE_SIZE, 0);
 409                 }
 410                 if (bytes_left < PAGE_CACHE_SIZE) {
 411                         printk("bytes left %lu compress len %lu nr %lu\n",
 412                                bytes_left, cb->compressed_len, cb->nr_pages);
 413                 }
 414                 bytes_left -= PAGE_CACHE_SIZE;
 415                 first_byte += PAGE_CACHE_SIZE;
 416                 cond_resched();
 417         }
 418         bio_get(bio);
 419
 420         ret = btrfs_bio_wq_end_io(root->fs_info, bio, 0);
 421         BUG_ON(ret);
 422
 423         ret = btrfs_csum_one_bio(root, inode, bio, start, 1);
 424         BUG_ON(ret);
 425
 426         ret = btrfs_map_bio(root, WRITE, bio, 0, 1);
 427         BUG_ON(ret);
 428
 429         bio_put(bio);
 430         return 0;
 431 }
 432
 433 static noinline int add_ra_bio_pages(struct inode *inode,
 434                                      u64 compressed_end,
 435                                      struct compressed_bio *cb)
 436 {
 437         unsigned long end_index;
 438         unsigned long page_index;
 439         u64 last_offset;
 440         u64 isize = i_size_read(inode);
 441         int ret;
 442         struct page *page;
 443         unsigned long nr_pages = 0;
 444         struct extent_map *em;
 445         struct address_space *mapping = inode->i_mapping;
 446         struct extent_map_tree *em_tree;
 447         struct extent_io_tree *tree;
 448         u64 end;
 449         int misses = 0;
 450
 451         page = cb->orig_bio->bi_io_vec[cb->orig_bio->bi_vcnt - 1].bv_page;
 452         last_offset = (page_offset(page) + PAGE_CACHE_SIZE);
 453         em_tree = &BTRFS_I(inode)->extent_tree;
 454         tree = &BTRFS_I(inode)->io_tree;
 455
 456         if (isize == 0)
 457                 return 0;
 458
 459         end_index = (i_size_read(inode) - 1) >> PAGE_CACHE_SHIFT;
 460
 461         while (last_offset < compressed_end) {
 462                 page_index = last_offset >> PAGE_CACHE_SHIFT;
 463
 464                 if (page_index > end_index)
 465                         break;
 466
 467                 rcu_read_lock();
 468                 page = radix_tree_lookup(&mapping->page_tree, page_index);
 469                 rcu_read_unlock();
 470                 if (page) {
 471                         misses++;
 472                         if (misses > 4)
 473                                 break;
 474                         goto next;
 475                 }
 476
 477                 page = __page_cache_alloc(mapping_gfp_mask(mapping) &
 478                                                                 ~__GFP_FS);
 479                 if (!page)
 480                         break;
 481
 482                 if (add_to_page_cache_lru(page, mapping, page_index,
 483                                                                 GFP_NOFS)) {
 484                         page_cache_release(page);
 485                         goto next;
 486                 }
 487
 488                 end = last_offset + PAGE_CACHE_SIZE - 1;
 489                 /*
 490                  * at this point, we have a locked page in the page cache
 491                  * for these bytes in the file.  But, we have to make
 492                  * sure they map to this compressed extent on disk.
 493                  */
 494                 set_page_extent_mapped(page);
 495                 lock_extent(tree, last_offset, end, GFP_NOFS);
 496                 read_lock(&em_tree->lock);
 497                 em = lookup_extent_mapping(em_tree, last_offset,
 498                                            PAGE_CACHE_SIZE);
 499                 read_unlock(&em_tree->lock);
 500
 501                 if (!em || last_offset < em->start ||
 502                     (last_offset + PAGE_CACHE_SIZE > extent_map_end(em)) ||
 503                     (em->block_start >> 9) != cb->orig_bio->bi_sector) {
 504                         free_extent_map(em);
 505                         unlock_extent(tree, last_offset, end, GFP_NOFS);
 506                         unlock_page(page);
 507                         page_cache_release(page);
 508                         break;
 509                 }
 510                 free_extent_map(em);
 511
 512                 if (page->index == end_index) {
 513                         char *userpage;
 514                         size_t zero_offset = isize & (PAGE_CACHE_SIZE - 1);
 515
 516                         if (zero_offset) {
 517                                 int zeros;
 518                                 zeros = PAGE_CACHE_SIZE - zero_offset;
 519                                 userpage = kmap_atomic(page, KM_USER0);
 520                                 memset(userpage + zero_offset, 0, zeros);
 521                                 flush_dcache_page(page);
 522                                 kunmap_atomic(userpage, KM_USER0);
 523                         }
 524                 }
 525
 526                 ret = bio_add_page(cb->orig_bio, page,
 527                                    PAGE_CACHE_SIZE, 0);
 528
 529                 if (ret == PAGE_CACHE_SIZE) {
 530                         nr_pages++;
 531                         page_cache_release(page);
 532                 } else {
 533                         unlock_extent(tree, last_offset, end, GFP_NOFS);
 534                         unlock_page(page);
 535                         page_cache_release(page);
 536                         break;
 537                 }
 538 next:
 539                 last_offset += PAGE_CACHE_SIZE;
 540         }
 541         return 0;
 542 }
 543
 544 /*
 545  * for a compressed read, the bio we get passed has all the inode pages
 546  * in it.  We don't actually do IO on those pages but allocate new ones
 547  * to hold the compressed pages on disk.
 548  *
 549  * bio->bi_sector points to the compressed extent on disk
 550  * bio->bi_io_vec points to all of the inode pages
 551  * bio->bi_vcnt is a count of pages
 552  *
 553  * After the compressed pages are read, we copy the bytes into the
 554  * bio we were passed and then call the bio end_io calls
 555  */
 556 int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 557                                  int mirror_num, unsigned long bio_flags)
 558 {
 559         struct extent_io_tree *tree;
 560         struct extent_map_tree *em_tree;
 561         struct compressed_bio *cb;
 562         struct btrfs_root *root = BTRFS_I(inode)->root;
 563         unsigned long uncompressed_len = bio->bi_vcnt * PAGE_CACHE_SIZE;
 564         unsigned long compressed_len;
 565         unsigned long nr_pages;
 566         unsigned long page_index;
 567         struct page *page;
 568         struct block_device *bdev;
 569         struct bio *comp_bio;
 570         u64 cur_disk_byte = (u64)bio->bi_sector << 9;
 571         u64 em_len;
 572         u64 em_start;
 573         struct extent_map *em;
 574         int ret;
 575         u32 *sums;
 576
 577         tree = &BTRFS_I(inode)->io_tree;
 578         em_tree = &BTRFS_I(inode)->extent_tree;
 579
 580         /* we need the actual starting offset of this extent in the file */
 581         read_lock(&em_tree->lock);
 582         em = lookup_extent_mapping(em_tree,
 583                                    page_offset(bio->bi_io_vec->bv_page),
 584                                    PAGE_CACHE_SIZE);
 585         read_unlock(&em_tree->lock);
 586
 587         compressed_len = em->block_len;
 588         cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS);
 589         atomic_set(&cb->pending_bios, 0);
 590         cb->errors = 0;
 591         cb->inode = inode;
 592         cb->mirror_num = mirror_num;
 593         sums = &cb->sums;
 594
 595         cb->start = em->orig_start;
 596         em_len = em->len;
 597         em_start = em->start;
 598
 599         free_extent_map(em);
 600         em = NULL;
 601
 602         cb->len = uncompressed_len;
 603         cb->compressed_len = compressed_len;
 604         cb->orig_bio = bio;
 605
 606         nr_pages = (compressed_len + PAGE_CACHE_SIZE - 1) /
 607                                  PAGE_CACHE_SIZE;
 608         cb->compressed_pages = kmalloc(sizeof(struct page *) * nr_pages,
 609                                        GFP_NOFS);
 610         bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;
 611
 612         for (page_index = 0; page_index < nr_pages; page_index++) {
 613                 cb->compressed_pages[page_index] = alloc_page(GFP_NOFS |
 614                                                               __GFP_HIGHMEM);
 615         }
 616         cb->nr_pages = nr_pages;
 617
 618         add_ra_bio_pages(inode, em_start + em_len, cb);
 619
 620         /* include any pages we added in add_ra-bio_pages */
 621         uncompressed_len = bio->bi_vcnt * PAGE_CACHE_SIZE;
 622         cb->len = uncompressed_len;
 623
 624         comp_bio = compressed_bio_alloc(bdev, cur_disk_byte, GFP_NOFS);
 625         comp_bio->bi_private = cb;
 626         comp_bio->bi_end_io = end_compressed_bio_read;
 627         atomic_inc(&cb->pending_bios);
 628
 629         for (page_index = 0; page_index < nr_pages; page_index++) {
 630                 page = cb->compressed_pages[page_index];
 631                 page->mapping = inode->i_mapping;
 632                 page->index = em_start >> PAGE_CACHE_SHIFT;
 633
 634                 if (comp_bio->bi_size)
 635                         ret = tree->ops->merge_bio_hook(page, 0,
 636                                                         PAGE_CACHE_SIZE,
 637                                                         comp_bio, 0);
 638                 else
 639                         ret = 0;
 640
 641                 page->mapping = NULL;
 642                 if (ret || bio_add_page(comp_bio, page, PAGE_CACHE_SIZE, 0) <
 643                     PAGE_CACHE_SIZE) {
 644                         bio_get(comp_bio);
 645
 646                         ret = btrfs_bio_wq_end_io(root->fs_info, comp_bio, 0);
 647                         BUG_ON(ret);
 648
 649                         /*
 650                          * inc the count before we submit the bio so
 651                          * we know the end IO handler won't happen before
 652                          * we inc the count.  Otherwise, the cb might get
 653                          * freed before we're done setting it up
 654                          */
 655                         atomic_inc(&cb->pending_bios);
 656
 657                         if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
 658                                 btrfs_lookup_bio_sums(root, inode, comp_bio,
 659                                                       sums);
 660                         }
 661                         sums += (comp_bio->bi_size + root->sectorsize - 1) /
 662                                 root->sectorsize;
 663
 664                         ret = btrfs_map_bio(root, READ, comp_bio,
 665                                             mirror_num, 0);
 666                         BUG_ON(ret);
 667
 668                         bio_put(comp_bio);
 669
 670                         comp_bio = compressed_bio_alloc(bdev, cur_disk_byte,
 671                                                         GFP_NOFS);
 672                         comp_bio->bi_private = cb;
 673                         comp_bio->bi_end_io = end_compressed_bio_read;
 674
 675                         bio_add_page(comp_bio, page, PAGE_CACHE_SIZE, 0);
 676                 }
 677                 cur_disk_byte += PAGE_CACHE_SIZE;
 678         }
 679         bio_get(comp_bio);
 680
 681         ret = btrfs_bio_wq_end_io(root->fs_info, comp_bio, 0);
 682         BUG_ON(ret);
 683
 684         if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM))
 685                 btrfs_lookup_bio_sums(root, inode, comp_bio, sums);
 686
 687         ret = btrfs_map_bio(root, READ, comp_bio, mirror_num, 0);
 688         BUG_ON(ret);
 689
 690         bio_put(comp_bio);
 691         return 0;
 692 }