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TOMOYO Linux Cross Reference
Linux/fs/btrfs/compression.c

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  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 "ctree.h"
 36 #include "disk-io.h"
 37 #include "transaction.h"
 38 #include "btrfs_inode.h"
 39 #include "volumes.h"
 40 #include "ordered-data.h"
 41 #include "compression.h"
 42 #include "extent_io.h"
 43 #include "extent_map.h"
 44 
 45 struct compressed_bio {
 46         /* number of bios pending for this compressed extent */
 47         atomic_t pending_bios;
 48 
 49         /* the pages with the compressed data on them */
 50         struct page **compressed_pages;
 51 
 52         /* inode that owns this data */
 53         struct inode *inode;
 54 
 55         /* starting offset in the inode for our pages */
 56         u64 start;
 57 
 58         /* number of bytes in the inode we're working on */
 59         unsigned long len;
 60 
 61         /* number of bytes on disk */
 62         unsigned long compressed_len;
 63 
 64         /* the compression algorithm for this bio */
 65         int compress_type;
 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 int btrfs_decompress_biovec(int type, struct page **pages_in,
 85                                    u64 disk_start, struct bio_vec *bvec,
 86                                    int vcnt, size_t srclen);
 87 
 88 static inline int compressed_bio_size(struct btrfs_root *root,
 89                                       unsigned long disk_size)
 90 {
 91         u16 csum_size = btrfs_super_csum_size(root->fs_info->super_copy);
 92 
 93         return sizeof(struct compressed_bio) +
 94                 ((disk_size + root->sectorsize - 1) / root->sectorsize) *
 95                 csum_size;
 96 }
 97 
 98 static struct bio *compressed_bio_alloc(struct block_device *bdev,
 99                                         u64 first_byte, gfp_t gfp_flags)
100 {
101         int nr_vecs;
102 
103         nr_vecs = bio_get_nr_vecs(bdev);
104         return btrfs_bio_alloc(bdev, first_byte >> 9, nr_vecs, gfp_flags);
105 }
106 
107 static int check_compressed_csum(struct inode *inode,
108                                  struct compressed_bio *cb,
109                                  u64 disk_start)
110 {
111         int ret;
112         struct page *page;
113         unsigned long i;
114         char *kaddr;
115         u32 csum;
116         u32 *cb_sum = &cb->sums;
117 
118         if (BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)
119                 return 0;
120 
121         for (i = 0; i < cb->nr_pages; i++) {
122                 page = cb->compressed_pages[i];
123                 csum = ~(u32)0;
124 
125                 kaddr = kmap_atomic(page);
126                 csum = btrfs_csum_data(kaddr, csum, PAGE_CACHE_SIZE);
127                 btrfs_csum_final(csum, (char *)&csum);
128                 kunmap_atomic(kaddr);
129 
130                 if (csum != *cb_sum) {
131                         printk(KERN_INFO "btrfs csum failed ino %llu "
132                                "extent %llu csum %u "
133                                "wanted %u mirror %d\n",
134                                btrfs_ino(inode), disk_start, csum, *cb_sum,
135                                cb->mirror_num);
136                         ret = -EIO;
137                         goto fail;
138                 }
139                 cb_sum++;
140 
141         }
142         ret = 0;
143 fail:
144         return ret;
145 }
146 
147 /* when we finish reading compressed pages from the disk, we
148  * decompress them and then run the bio end_io routines on the
149  * decompressed pages (in the inode address space).
150  *
151  * This allows the checksumming and other IO error handling routines
152  * to work normally
153  *
154  * The compressed pages are freed here, and it must be run
155  * in process context
156  */
157 static void end_compressed_bio_read(struct bio *bio, int err)
158 {
159         struct compressed_bio *cb = bio->bi_private;
160         struct inode *inode;
161         struct page *page;
162         unsigned long index;
163         int ret;
164 
165         if (err)
166                 cb->errors = 1;
167 
168         /* if there are more bios still pending for this compressed
169          * extent, just exit
170          */
171         if (!atomic_dec_and_test(&cb->pending_bios))
172                 goto out;
173 
174         inode = cb->inode;
175         ret = check_compressed_csum(inode, cb, (u64)bio->bi_sector << 9);
176         if (ret)
177                 goto csum_failed;
178 
179         /* ok, we're the last bio for this extent, lets start
180          * the decompression.
181          */
182         ret = btrfs_decompress_biovec(cb->compress_type,
183                                       cb->compressed_pages,
184                                       cb->start,
185                                       cb->orig_bio->bi_io_vec,
186                                       cb->orig_bio->bi_vcnt,
187                                       cb->compressed_len);
188 csum_failed:
189         if (ret)
190                 cb->errors = 1;
191 
192         /* release the compressed pages */
193         index = 0;
194         for (index = 0; index < cb->nr_pages; index++) {
195                 page = cb->compressed_pages[index];
196                 page->mapping = NULL;
197                 page_cache_release(page);
198         }
199 
200         /* do io completion on the original bio */
201         if (cb->errors) {
202                 bio_io_error(cb->orig_bio);
203         } else {
204                 int bio_index = 0;
205                 struct bio_vec *bvec = cb->orig_bio->bi_io_vec;
206 
207                 /*
208                  * we have verified the checksum already, set page
209                  * checked so the end_io handlers know about it
210                  */
211                 while (bio_index < cb->orig_bio->bi_vcnt) {
212                         SetPageChecked(bvec->bv_page);
213                         bvec++;
214                         bio_index++;
215                 }
216                 bio_endio(cb->orig_bio, 0);
217         }
218 
219         /* finally free the cb struct */
220         kfree(cb->compressed_pages);
221         kfree(cb);
222 out:
223         bio_put(bio);
224 }
225 
226 /*
227  * Clear the writeback bits on all of the file
228  * pages for a compressed write
229  */
230 static noinline void end_compressed_writeback(struct inode *inode, u64 start,
231                                               unsigned long ram_size)
232 {
233         unsigned long index = start >> PAGE_CACHE_SHIFT;
234         unsigned long end_index = (start + ram_size - 1) >> PAGE_CACHE_SHIFT;
235         struct page *pages[16];
236         unsigned long nr_pages = end_index - index + 1;
237         int i;
238         int ret;
239 
240         while (nr_pages > 0) {
241                 ret = find_get_pages_contig(inode->i_mapping, index,
242                                      min_t(unsigned long,
243                                      nr_pages, ARRAY_SIZE(pages)), pages);
244                 if (ret == 0) {
245                         nr_pages -= 1;
246                         index += 1;
247                         continue;
248                 }
249                 for (i = 0; i < ret; i++) {
250                         end_page_writeback(pages[i]);
251                         page_cache_release(pages[i]);
252                 }
253                 nr_pages -= ret;
254                 index += ret;
255         }
256         /* the inode may be gone now */
257 }
258 
259 /*
260  * do the cleanup once all the compressed pages hit the disk.
261  * This will clear writeback on the file pages and free the compressed
262  * pages.
263  *
264  * This also calls the writeback end hooks for the file pages so that
265  * metadata and checksums can be updated in the file.
266  */
267 static void end_compressed_bio_write(struct bio *bio, int err)
268 {
269         struct extent_io_tree *tree;
270         struct compressed_bio *cb = bio->bi_private;
271         struct inode *inode;
272         struct page *page;
273         unsigned long index;
274 
275         if (err)
276                 cb->errors = 1;
277 
278         /* if there are more bios still pending for this compressed
279          * extent, just exit
280          */
281         if (!atomic_dec_and_test(&cb->pending_bios))
282                 goto out;
283 
284         /* ok, we're the last bio for this extent, step one is to
285          * call back into the FS and do all the end_io operations
286          */
287         inode = cb->inode;
288         tree = &BTRFS_I(inode)->io_tree;
289         cb->compressed_pages[0]->mapping = cb->inode->i_mapping;
290         tree->ops->writepage_end_io_hook(cb->compressed_pages[0],
291                                          cb->start,
292                                          cb->start + cb->len - 1,
293                                          NULL, 1);
294         cb->compressed_pages[0]->mapping = NULL;
295 
296         end_compressed_writeback(inode, cb->start, cb->len);
297         /* note, our inode could be gone now */
298 
299         /*
300          * release the compressed pages, these came from alloc_page and
301          * are not attached to the inode at all
302          */
303         index = 0;
304         for (index = 0; index < cb->nr_pages; index++) {
305                 page = cb->compressed_pages[index];
306                 page->mapping = NULL;
307                 page_cache_release(page);
308         }
309 
310         /* finally free the cb struct */
311         kfree(cb->compressed_pages);
312         kfree(cb);
313 out:
314         bio_put(bio);
315 }
316 
317 /*
318  * worker function to build and submit bios for previously compressed pages.
319  * The corresponding pages in the inode should be marked for writeback
320  * and the compressed pages should have a reference on them for dropping
321  * when the IO is complete.
322  *
323  * This also checksums the file bytes and gets things ready for
324  * the end io hooks.
325  */
326 int btrfs_submit_compressed_write(struct inode *inode, u64 start,
327                                  unsigned long len, u64 disk_start,
328                                  unsigned long compressed_len,
329                                  struct page **compressed_pages,
330                                  unsigned long nr_pages)
331 {
332         struct bio *bio = NULL;
333         struct btrfs_root *root = BTRFS_I(inode)->root;
334         struct compressed_bio *cb;
335         unsigned long bytes_left;
336         struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
337         int pg_index = 0;
338         struct page *page;
339         u64 first_byte = disk_start;
340         struct block_device *bdev;
341         int ret;
342         int skip_sum = BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM;
343 
344         WARN_ON(start & ((u64)PAGE_CACHE_SIZE - 1));
345         cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS);
346         if (!cb)
347                 return -ENOMEM;
348         atomic_set(&cb->pending_bios, 0);
349         cb->errors = 0;
350         cb->inode = inode;
351         cb->start = start;
352         cb->len = len;
353         cb->mirror_num = 0;
354         cb->compressed_pages = compressed_pages;
355         cb->compressed_len = compressed_len;
356         cb->orig_bio = NULL;
357         cb->nr_pages = nr_pages;
358 
359         bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;
360 
361         bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS);
362         if (!bio) {
363                 kfree(cb);
364                 return -ENOMEM;
365         }
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 (pg_index = 0; pg_index < cb->nr_pages; pg_index++) {
373                 page = compressed_pages[pg_index];
374                 page->mapping = inode->i_mapping;
375                 if (bio->bi_size)
376                         ret = io_tree->ops->merge_bio_hook(WRITE, 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); /* -ENOMEM */
396 
397                         if (!skip_sum) {
398                                 ret = btrfs_csum_one_bio(root, inode, bio,
399                                                          start, 1);
400                                 BUG_ON(ret); /* -ENOMEM */
401                         }
402 
403                         ret = btrfs_map_bio(root, WRITE, bio, 0, 1);
404                         BUG_ON(ret); /* -ENOMEM */
405 
406                         bio_put(bio);
407 
408                         bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS);
409                         BUG_ON(!bio);
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); /* -ENOMEM */
426 
427         if (!skip_sum) {
428                 ret = btrfs_csum_one_bio(root, inode, bio, start, 1);
429                 BUG_ON(ret); /* -ENOMEM */
430         }
431 
432         ret = btrfs_map_bio(root, WRITE, bio, 0, 1);
433         BUG_ON(ret); /* -ENOMEM */
434 
435         bio_put(bio);
436         return 0;
437 }
438 
439 static noinline int add_ra_bio_pages(struct inode *inode,
440                                      u64 compressed_end,
441                                      struct compressed_bio *cb)
442 {
443         unsigned long end_index;
444         unsigned long pg_index;
445         u64 last_offset;
446         u64 isize = i_size_read(inode);
447         int ret;
448         struct page *page;
449         unsigned long nr_pages = 0;
450         struct extent_map *em;
451         struct address_space *mapping = inode->i_mapping;
452         struct extent_map_tree *em_tree;
453         struct extent_io_tree *tree;
454         u64 end;
455         int misses = 0;
456 
457         page = cb->orig_bio->bi_io_vec[cb->orig_bio->bi_vcnt - 1].bv_page;
458         last_offset = (page_offset(page) + PAGE_CACHE_SIZE);
459         em_tree = &BTRFS_I(inode)->extent_tree;
460         tree = &BTRFS_I(inode)->io_tree;
461 
462         if (isize == 0)
463                 return 0;
464 
465         end_index = (i_size_read(inode) - 1) >> PAGE_CACHE_SHIFT;
466 
467         while (last_offset < compressed_end) {
468                 pg_index = last_offset >> PAGE_CACHE_SHIFT;
469 
470                 if (pg_index > end_index)
471                         break;
472 
473                 rcu_read_lock();
474                 page = radix_tree_lookup(&mapping->page_tree, pg_index);
475                 rcu_read_unlock();
476                 if (page) {
477                         misses++;
478                         if (misses > 4)
479                                 break;
480                         goto next;
481                 }
482 
483                 page = __page_cache_alloc(mapping_gfp_mask(mapping) &
484                                                                 ~__GFP_FS);
485                 if (!page)
486                         break;
487 
488                 if (add_to_page_cache_lru(page, mapping, pg_index,
489                                                                 GFP_NOFS)) {
490                         page_cache_release(page);
491                         goto next;
492                 }
493 
494                 end = last_offset + PAGE_CACHE_SIZE - 1;
495                 /*
496                  * at this point, we have a locked page in the page cache
497                  * for these bytes in the file.  But, we have to make
498                  * sure they map to this compressed extent on disk.
499                  */
500                 set_page_extent_mapped(page);
501                 lock_extent(tree, last_offset, end);
502                 read_lock(&em_tree->lock);
503                 em = lookup_extent_mapping(em_tree, last_offset,
504                                            PAGE_CACHE_SIZE);
505                 read_unlock(&em_tree->lock);
506 
507                 if (!em || last_offset < em->start ||
508                     (last_offset + PAGE_CACHE_SIZE > extent_map_end(em)) ||
509                     (em->block_start >> 9) != cb->orig_bio->bi_sector) {
510                         free_extent_map(em);
511                         unlock_extent(tree, last_offset, end);
512                         unlock_page(page);
513                         page_cache_release(page);
514                         break;
515                 }
516                 free_extent_map(em);
517 
518                 if (page->index == end_index) {
519                         char *userpage;
520                         size_t zero_offset = isize & (PAGE_CACHE_SIZE - 1);
521 
522                         if (zero_offset) {
523                                 int zeros;
524                                 zeros = PAGE_CACHE_SIZE - zero_offset;
525                                 userpage = kmap_atomic(page);
526                                 memset(userpage + zero_offset, 0, zeros);
527                                 flush_dcache_page(page);
528                                 kunmap_atomic(userpage);
529                         }
530                 }
531 
532                 ret = bio_add_page(cb->orig_bio, page,
533                                    PAGE_CACHE_SIZE, 0);
534 
535                 if (ret == PAGE_CACHE_SIZE) {
536                         nr_pages++;
537                         page_cache_release(page);
538                 } else {
539                         unlock_extent(tree, last_offset, end);
540                         unlock_page(page);
541                         page_cache_release(page);
542                         break;
543                 }
544 next:
545                 last_offset += PAGE_CACHE_SIZE;
546         }
547         return 0;
548 }
549 
550 /*
551  * for a compressed read, the bio we get passed has all the inode pages
552  * in it.  We don't actually do IO on those pages but allocate new ones
553  * to hold the compressed pages on disk.
554  *
555  * bio->bi_sector points to the compressed extent on disk
556  * bio->bi_io_vec points to all of the inode pages
557  * bio->bi_vcnt is a count of pages
558  *
559  * After the compressed pages are read, we copy the bytes into the
560  * bio we were passed and then call the bio end_io calls
561  */
562 int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
563                                  int mirror_num, unsigned long bio_flags)
564 {
565         struct extent_io_tree *tree;
566         struct extent_map_tree *em_tree;
567         struct compressed_bio *cb;
568         struct btrfs_root *root = BTRFS_I(inode)->root;
569         unsigned long uncompressed_len = bio->bi_vcnt * PAGE_CACHE_SIZE;
570         unsigned long compressed_len;
571         unsigned long nr_pages;
572         unsigned long pg_index;
573         struct page *page;
574         struct block_device *bdev;
575         struct bio *comp_bio;
576         u64 cur_disk_byte = (u64)bio->bi_sector << 9;
577         u64 em_len;
578         u64 em_start;
579         struct extent_map *em;
580         int ret = -ENOMEM;
581         int faili = 0;
582         u32 *sums;
583 
584         tree = &BTRFS_I(inode)->io_tree;
585         em_tree = &BTRFS_I(inode)->extent_tree;
586 
587         /* we need the actual starting offset of this extent in the file */
588         read_lock(&em_tree->lock);
589         em = lookup_extent_mapping(em_tree,
590                                    page_offset(bio->bi_io_vec->bv_page),
591                                    PAGE_CACHE_SIZE);
592         read_unlock(&em_tree->lock);
593         if (!em)
594                 return -EIO;
595 
596         compressed_len = em->block_len;
597         cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS);
598         if (!cb)
599                 goto out;
600 
601         atomic_set(&cb->pending_bios, 0);
602         cb->errors = 0;
603         cb->inode = inode;
604         cb->mirror_num = mirror_num;
605         sums = &cb->sums;
606 
607         cb->start = em->orig_start;
608         em_len = em->len;
609         em_start = em->start;
610 
611         free_extent_map(em);
612         em = NULL;
613 
614         cb->len = uncompressed_len;
615         cb->compressed_len = compressed_len;
616         cb->compress_type = extent_compress_type(bio_flags);
617         cb->orig_bio = bio;
618 
619         nr_pages = (compressed_len + PAGE_CACHE_SIZE - 1) /
620                                  PAGE_CACHE_SIZE;
621         cb->compressed_pages = kzalloc(sizeof(struct page *) * nr_pages,
622                                        GFP_NOFS);
623         if (!cb->compressed_pages)
624                 goto fail1;
625 
626         bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;
627 
628         for (pg_index = 0; pg_index < nr_pages; pg_index++) {
629                 cb->compressed_pages[pg_index] = alloc_page(GFP_NOFS |
630                                                               __GFP_HIGHMEM);
631                 if (!cb->compressed_pages[pg_index]) {
632                         faili = pg_index - 1;
633                         ret = -ENOMEM;
634                         goto fail2;
635                 }
636         }
637         faili = nr_pages - 1;
638         cb->nr_pages = nr_pages;
639 
640         /* In the parent-locked case, we only locked the range we are
641          * interested in.  In all other cases, we can opportunistically
642          * cache decompressed data that goes beyond the requested range. */
643         if (!(bio_flags & EXTENT_BIO_PARENT_LOCKED))
644                 add_ra_bio_pages(inode, em_start + em_len, cb);
645 
646         /* include any pages we added in add_ra-bio_pages */
647         uncompressed_len = bio->bi_vcnt * PAGE_CACHE_SIZE;
648         cb->len = uncompressed_len;
649 
650         comp_bio = compressed_bio_alloc(bdev, cur_disk_byte, GFP_NOFS);
651         if (!comp_bio)
652                 goto fail2;
653         comp_bio->bi_private = cb;
654         comp_bio->bi_end_io = end_compressed_bio_read;
655         atomic_inc(&cb->pending_bios);
656 
657         for (pg_index = 0; pg_index < nr_pages; pg_index++) {
658                 page = cb->compressed_pages[pg_index];
659                 page->mapping = inode->i_mapping;
660                 page->index = em_start >> PAGE_CACHE_SHIFT;
661 
662                 if (comp_bio->bi_size)
663                         ret = tree->ops->merge_bio_hook(READ, page, 0,
664                                                         PAGE_CACHE_SIZE,
665                                                         comp_bio, 0);
666                 else
667                         ret = 0;
668 
669                 page->mapping = NULL;
670                 if (ret || bio_add_page(comp_bio, page, PAGE_CACHE_SIZE, 0) <
671                     PAGE_CACHE_SIZE) {
672                         bio_get(comp_bio);
673 
674                         ret = btrfs_bio_wq_end_io(root->fs_info, comp_bio, 0);
675                         BUG_ON(ret); /* -ENOMEM */
676 
677                         /*
678                          * inc the count before we submit the bio so
679                          * we know the end IO handler won't happen before
680                          * we inc the count.  Otherwise, the cb might get
681                          * freed before we're done setting it up
682                          */
683                         atomic_inc(&cb->pending_bios);
684 
685                         if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
686                                 ret = btrfs_lookup_bio_sums(root, inode,
687                                                         comp_bio, sums);
688                                 BUG_ON(ret); /* -ENOMEM */
689                         }
690                         sums += (comp_bio->bi_size + root->sectorsize - 1) /
691                                 root->sectorsize;
692 
693                         ret = btrfs_map_bio(root, READ, comp_bio,
694                                             mirror_num, 0);
695                         if (ret)
696                                 bio_endio(comp_bio, ret);
697 
698                         bio_put(comp_bio);
699 
700                         comp_bio = compressed_bio_alloc(bdev, cur_disk_byte,
701                                                         GFP_NOFS);
702                         BUG_ON(!comp_bio);
703                         comp_bio->bi_private = cb;
704                         comp_bio->bi_end_io = end_compressed_bio_read;
705 
706                         bio_add_page(comp_bio, page, PAGE_CACHE_SIZE, 0);
707                 }
708                 cur_disk_byte += PAGE_CACHE_SIZE;
709         }
710         bio_get(comp_bio);
711 
712         ret = btrfs_bio_wq_end_io(root->fs_info, comp_bio, 0);
713         BUG_ON(ret); /* -ENOMEM */
714 
715         if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
716                 ret = btrfs_lookup_bio_sums(root, inode, comp_bio, sums);
717                 BUG_ON(ret); /* -ENOMEM */
718         }
719 
720         ret = btrfs_map_bio(root, READ, comp_bio, mirror_num, 0);
721         if (ret)
722                 bio_endio(comp_bio, ret);
723 
724         bio_put(comp_bio);
725         return 0;
726 
727 fail2:
728         while (faili >= 0) {
729                 __free_page(cb->compressed_pages[faili]);
730                 faili--;
731         }
732 
733         kfree(cb->compressed_pages);
734 fail1:
735         kfree(cb);
736 out:
737         free_extent_map(em);
738         return ret;
739 }
740 
741 static struct list_head comp_idle_workspace[BTRFS_COMPRESS_TYPES];
742 static spinlock_t comp_workspace_lock[BTRFS_COMPRESS_TYPES];
743 static int comp_num_workspace[BTRFS_COMPRESS_TYPES];
744 static atomic_t comp_alloc_workspace[BTRFS_COMPRESS_TYPES];
745 static wait_queue_head_t comp_workspace_wait[BTRFS_COMPRESS_TYPES];
746 
747 static struct btrfs_compress_op *btrfs_compress_op[] = {
748         &btrfs_zlib_compress,
749         &btrfs_lzo_compress,
750 };
751 
752 void __init btrfs_init_compress(void)
753 {
754         int i;
755 
756         for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) {
757                 INIT_LIST_HEAD(&comp_idle_workspace[i]);
758                 spin_lock_init(&comp_workspace_lock[i]);
759                 atomic_set(&comp_alloc_workspace[i], 0);
760                 init_waitqueue_head(&comp_workspace_wait[i]);
761         }
762 }
763 
764 /*
765  * this finds an available workspace or allocates a new one
766  * ERR_PTR is returned if things go bad.
767  */
768 static struct list_head *find_workspace(int type)
769 {
770         struct list_head *workspace;
771         int cpus = num_online_cpus();
772         int idx = type - 1;
773 
774         struct list_head *idle_workspace        = &comp_idle_workspace[idx];
775         spinlock_t *workspace_lock              = &comp_workspace_lock[idx];
776         atomic_t *alloc_workspace               = &comp_alloc_workspace[idx];
777         wait_queue_head_t *workspace_wait       = &comp_workspace_wait[idx];
778         int *num_workspace                      = &comp_num_workspace[idx];
779 again:
780         spin_lock(workspace_lock);
781         if (!list_empty(idle_workspace)) {
782                 workspace = idle_workspace->next;
783                 list_del(workspace);
784                 (*num_workspace)--;
785                 spin_unlock(workspace_lock);
786                 return workspace;
787 
788         }
789         if (atomic_read(alloc_workspace) > cpus) {
790                 DEFINE_WAIT(wait);
791 
792                 spin_unlock(workspace_lock);
793                 prepare_to_wait(workspace_wait, &wait, TASK_UNINTERRUPTIBLE);
794                 if (atomic_read(alloc_workspace) > cpus && !*num_workspace)
795                         schedule();
796                 finish_wait(workspace_wait, &wait);
797                 goto again;
798         }
799         atomic_inc(alloc_workspace);
800         spin_unlock(workspace_lock);
801 
802         workspace = btrfs_compress_op[idx]->alloc_workspace();
803         if (IS_ERR(workspace)) {
804                 atomic_dec(alloc_workspace);
805                 wake_up(workspace_wait);
806         }
807         return workspace;
808 }
809 
810 /*
811  * put a workspace struct back on the list or free it if we have enough
812  * idle ones sitting around
813  */
814 static void free_workspace(int type, struct list_head *workspace)
815 {
816         int idx = type - 1;
817         struct list_head *idle_workspace        = &comp_idle_workspace[idx];
818         spinlock_t *workspace_lock              = &comp_workspace_lock[idx];
819         atomic_t *alloc_workspace               = &comp_alloc_workspace[idx];
820         wait_queue_head_t *workspace_wait       = &comp_workspace_wait[idx];
821         int *num_workspace                      = &comp_num_workspace[idx];
822 
823         spin_lock(workspace_lock);
824         if (*num_workspace < num_online_cpus()) {
825                 list_add_tail(workspace, idle_workspace);
826                 (*num_workspace)++;
827                 spin_unlock(workspace_lock);
828                 goto wake;
829         }
830         spin_unlock(workspace_lock);
831 
832         btrfs_compress_op[idx]->free_workspace(workspace);
833         atomic_dec(alloc_workspace);
834 wake:
835         smp_mb();
836         if (waitqueue_active(workspace_wait))
837                 wake_up(workspace_wait);
838 }
839 
840 /*
841  * cleanup function for module exit
842  */
843 static void free_workspaces(void)
844 {
845         struct list_head *workspace;
846         int i;
847 
848         for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) {
849                 while (!list_empty(&comp_idle_workspace[i])) {
850                         workspace = comp_idle_workspace[i].next;
851                         list_del(workspace);
852                         btrfs_compress_op[i]->free_workspace(workspace);
853                         atomic_dec(&comp_alloc_workspace[i]);
854                 }
855         }
856 }
857 
858 /*
859  * given an address space and start/len, compress the bytes.
860  *
861  * pages are allocated to hold the compressed result and stored
862  * in 'pages'
863  *
864  * out_pages is used to return the number of pages allocated.  There
865  * may be pages allocated even if we return an error
866  *
867  * total_in is used to return the number of bytes actually read.  It
868  * may be smaller then len if we had to exit early because we
869  * ran out of room in the pages array or because we cross the
870  * max_out threshold.
871  *
872  * total_out is used to return the total number of compressed bytes
873  *
874  * max_out tells us the max number of bytes that we're allowed to
875  * stuff into pages
876  */
877 int btrfs_compress_pages(int type, struct address_space *mapping,
878                          u64 start, unsigned long len,
879                          struct page **pages,
880                          unsigned long nr_dest_pages,
881                          unsigned long *out_pages,
882                          unsigned long *total_in,
883                          unsigned long *total_out,
884                          unsigned long max_out)
885 {
886         struct list_head *workspace;
887         int ret;
888 
889         workspace = find_workspace(type);
890         if (IS_ERR(workspace))
891                 return -1;
892 
893         ret = btrfs_compress_op[type-1]->compress_pages(workspace, mapping,
894                                                       start, len, pages,
895                                                       nr_dest_pages, out_pages,
896                                                       total_in, total_out,
897                                                       max_out);
898         free_workspace(type, workspace);
899         return ret;
900 }
901 
902 /*
903  * pages_in is an array of pages with compressed data.
904  *
905  * disk_start is the starting logical offset of this array in the file
906  *
907  * bvec is a bio_vec of pages from the file that we want to decompress into
908  *
909  * vcnt is the count of pages in the biovec
910  *
911  * srclen is the number of bytes in pages_in
912  *
913  * The basic idea is that we have a bio that was created by readpages.
914  * The pages in the bio are for the uncompressed data, and they may not
915  * be contiguous.  They all correspond to the range of bytes covered by
916  * the compressed extent.
917  */
918 static int btrfs_decompress_biovec(int type, struct page **pages_in,
919                                    u64 disk_start, struct bio_vec *bvec,
920                                    int vcnt, size_t srclen)
921 {
922         struct list_head *workspace;
923         int ret;
924 
925         workspace = find_workspace(type);
926         if (IS_ERR(workspace))
927                 return -ENOMEM;
928 
929         ret = btrfs_compress_op[type-1]->decompress_biovec(workspace, pages_in,
930                                                          disk_start,
931                                                          bvec, vcnt, srclen);
932         free_workspace(type, workspace);
933         return ret;
934 }
935 
936 /*
937  * a less complex decompression routine.  Our compressed data fits in a
938  * single page, and we want to read a single page out of it.
939  * start_byte tells us the offset into the compressed data we're interested in
940  */
941 int btrfs_decompress(int type, unsigned char *data_in, struct page *dest_page,
942                      unsigned long start_byte, size_t srclen, size_t destlen)
943 {
944         struct list_head *workspace;
945         int ret;
946 
947         workspace = find_workspace(type);
948         if (IS_ERR(workspace))
949                 return -ENOMEM;
950 
951         ret = btrfs_compress_op[type-1]->decompress(workspace, data_in,
952                                                   dest_page, start_byte,
953                                                   srclen, destlen);
954 
955         free_workspace(type, workspace);
956         return ret;
957 }
958 
959 void btrfs_exit_compress(void)
960 {
961         free_workspaces();
962 }
963 
964 /*
965  * Copy uncompressed data from working buffer to pages.
966  *
967  * buf_start is the byte offset we're of the start of our workspace buffer.
968  *
969  * total_out is the last byte of the buffer
970  */
971 int btrfs_decompress_buf2page(char *buf, unsigned long buf_start,
972                               unsigned long total_out, u64 disk_start,
973                               struct bio_vec *bvec, int vcnt,
974                               unsigned long *pg_index,
975                               unsigned long *pg_offset)
976 {
977         unsigned long buf_offset;
978         unsigned long current_buf_start;
979         unsigned long start_byte;
980         unsigned long working_bytes = total_out - buf_start;
981         unsigned long bytes;
982         char *kaddr;
983         struct page *page_out = bvec[*pg_index].bv_page;
984 
985         /*
986          * start byte is the first byte of the page we're currently
987          * copying into relative to the start of the compressed data.
988          */
989         start_byte = page_offset(page_out) - disk_start;
990 
991         /* we haven't yet hit data corresponding to this page */
992         if (total_out <= start_byte)
993                 return 1;
994 
995         /*
996          * the start of the data we care about is offset into
997          * the middle of our working buffer
998          */
999         if (total_out > start_byte && buf_start < start_byte) {
1000                 buf_offset = start_byte - buf_start;
1001                 working_bytes -= buf_offset;
1002         } else {
1003                 buf_offset = 0;
1004         }
1005         current_buf_start = buf_start;
1006 
1007         /* copy bytes from the working buffer into the pages */
1008         while (working_bytes > 0) {
1009                 bytes = min(PAGE_CACHE_SIZE - *pg_offset,
1010                             PAGE_CACHE_SIZE - buf_offset);
1011                 bytes = min(bytes, working_bytes);
1012                 kaddr = kmap_atomic(page_out);
1013                 memcpy(kaddr + *pg_offset, buf + buf_offset, bytes);
1014                 if (*pg_index == (vcnt - 1) && *pg_offset == 0)
1015                         memset(kaddr + bytes, 0, PAGE_CACHE_SIZE - bytes);
1016                 kunmap_atomic(kaddr);
1017                 flush_dcache_page(page_out);
1018 
1019                 *pg_offset += bytes;
1020                 buf_offset += bytes;
1021                 working_bytes -= bytes;
1022                 current_buf_start += bytes;
1023 
1024                 /* check if we need to pick another page */
1025                 if (*pg_offset == PAGE_CACHE_SIZE) {
1026                         (*pg_index)++;
1027                         if (*pg_index >= vcnt)
1028                                 return 0;
1029 
1030                         page_out = bvec[*pg_index].bv_page;
1031                         *pg_offset = 0;
1032                         start_byte = page_offset(page_out) - disk_start;
1033 
1034                         /*
1035                          * make sure our new page is covered by this
1036                          * working buffer
1037                          */
1038                         if (total_out <= start_byte)
1039                                 return 1;
1040 
1041                         /*
1042                          * the next page in the biovec might not be adjacent
1043                          * to the last page, but it might still be found
1044                          * inside this working buffer. bump our offset pointer
1045                          */
1046                         if (total_out > start_byte &&
1047                             current_buf_start < start_byte) {
1048                                 buf_offset = start_byte - buf_start;
1049                                 working_bytes = total_out - start_byte;
1050                                 current_buf_start = buf_start + buf_offset;
1051                         }
1052                 }
1053         }
1054 
1055         return 1;
1056 }
1057 

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