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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                 (DIV_ROUND_UP(disk_size, root->sectorsize)) * csum_size;
 95 }
 96 
 97 static struct bio *compressed_bio_alloc(struct block_device *bdev,
 98                                         u64 first_byte, gfp_t gfp_flags)
 99 {
100         return btrfs_bio_alloc(bdev, first_byte >> 9, BIO_MAX_PAGES, gfp_flags);
101 }
102 
103 static int check_compressed_csum(struct inode *inode,
104                                  struct compressed_bio *cb,
105                                  u64 disk_start)
106 {
107         int ret;
108         struct page *page;
109         unsigned long i;
110         char *kaddr;
111         u32 csum;
112         u32 *cb_sum = &cb->sums;
113 
114         if (BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)
115                 return 0;
116 
117         for (i = 0; i < cb->nr_pages; i++) {
118                 page = cb->compressed_pages[i];
119                 csum = ~(u32)0;
120 
121                 kaddr = kmap_atomic(page);
122                 csum = btrfs_csum_data(kaddr, csum, PAGE_SIZE);
123                 btrfs_csum_final(csum, (char *)&csum);
124                 kunmap_atomic(kaddr);
125 
126                 if (csum != *cb_sum) {
127                         btrfs_info(BTRFS_I(inode)->root->fs_info,
128                            "csum failed ino %llu extent %llu csum %u wanted %u mirror %d",
129                            btrfs_ino(inode), disk_start, csum, *cb_sum,
130                            cb->mirror_num);
131                         ret = -EIO;
132                         goto fail;
133                 }
134                 cb_sum++;
135 
136         }
137         ret = 0;
138 fail:
139         return ret;
140 }
141 
142 /* when we finish reading compressed pages from the disk, we
143  * decompress them and then run the bio end_io routines on the
144  * decompressed pages (in the inode address space).
145  *
146  * This allows the checksumming and other IO error handling routines
147  * to work normally
148  *
149  * The compressed pages are freed here, and it must be run
150  * in process context
151  */
152 static void end_compressed_bio_read(struct bio *bio)
153 {
154         struct compressed_bio *cb = bio->bi_private;
155         struct inode *inode;
156         struct page *page;
157         unsigned long index;
158         int ret;
159 
160         if (bio->bi_error)
161                 cb->errors = 1;
162 
163         /* if there are more bios still pending for this compressed
164          * extent, just exit
165          */
166         if (!atomic_dec_and_test(&cb->pending_bios))
167                 goto out;
168 
169         inode = cb->inode;
170         ret = check_compressed_csum(inode, cb,
171                                     (u64)bio->bi_iter.bi_sector << 9);
172         if (ret)
173                 goto csum_failed;
174 
175         /* ok, we're the last bio for this extent, lets start
176          * the decompression.
177          */
178         ret = btrfs_decompress_biovec(cb->compress_type,
179                                       cb->compressed_pages,
180                                       cb->start,
181                                       cb->orig_bio->bi_io_vec,
182                                       cb->orig_bio->bi_vcnt,
183                                       cb->compressed_len);
184 csum_failed:
185         if (ret)
186                 cb->errors = 1;
187 
188         /* release the compressed pages */
189         index = 0;
190         for (index = 0; index < cb->nr_pages; index++) {
191                 page = cb->compressed_pages[index];
192                 page->mapping = NULL;
193                 put_page(page);
194         }
195 
196         /* do io completion on the original bio */
197         if (cb->errors) {
198                 bio_io_error(cb->orig_bio);
199         } else {
200                 int i;
201                 struct bio_vec *bvec;
202 
203                 /*
204                  * we have verified the checksum already, set page
205                  * checked so the end_io handlers know about it
206                  */
207                 bio_for_each_segment_all(bvec, cb->orig_bio, i)
208                         SetPageChecked(bvec->bv_page);
209 
210                 bio_endio(cb->orig_bio);
211         }
212 
213         /* finally free the cb struct */
214         kfree(cb->compressed_pages);
215         kfree(cb);
216 out:
217         bio_put(bio);
218 }
219 
220 /*
221  * Clear the writeback bits on all of the file
222  * pages for a compressed write
223  */
224 static noinline void end_compressed_writeback(struct inode *inode,
225                                               const struct compressed_bio *cb)
226 {
227         unsigned long index = cb->start >> PAGE_SHIFT;
228         unsigned long end_index = (cb->start + cb->len - 1) >> PAGE_SHIFT;
229         struct page *pages[16];
230         unsigned long nr_pages = end_index - index + 1;
231         int i;
232         int ret;
233 
234         if (cb->errors)
235                 mapping_set_error(inode->i_mapping, -EIO);
236 
237         while (nr_pages > 0) {
238                 ret = find_get_pages_contig(inode->i_mapping, index,
239                                      min_t(unsigned long,
240                                      nr_pages, ARRAY_SIZE(pages)), pages);
241                 if (ret == 0) {
242                         nr_pages -= 1;
243                         index += 1;
244                         continue;
245                 }
246                 for (i = 0; i < ret; i++) {
247                         if (cb->errors)
248                                 SetPageError(pages[i]);
249                         end_page_writeback(pages[i]);
250                         put_page(pages[i]);
251                 }
252                 nr_pages -= ret;
253                 index += ret;
254         }
255         /* the inode may be gone now */
256 }
257 
258 /*
259  * do the cleanup once all the compressed pages hit the disk.
260  * This will clear writeback on the file pages and free the compressed
261  * pages.
262  *
263  * This also calls the writeback end hooks for the file pages so that
264  * metadata and checksums can be updated in the file.
265  */
266 static void end_compressed_bio_write(struct bio *bio)
267 {
268         struct extent_io_tree *tree;
269         struct compressed_bio *cb = bio->bi_private;
270         struct inode *inode;
271         struct page *page;
272         unsigned long index;
273 
274         if (bio->bi_error)
275                 cb->errors = 1;
276 
277         /* if there are more bios still pending for this compressed
278          * extent, just exit
279          */
280         if (!atomic_dec_and_test(&cb->pending_bios))
281                 goto out;
282 
283         /* ok, we're the last bio for this extent, step one is to
284          * call back into the FS and do all the end_io operations
285          */
286         inode = cb->inode;
287         tree = &BTRFS_I(inode)->io_tree;
288         cb->compressed_pages[0]->mapping = cb->inode->i_mapping;
289         tree->ops->writepage_end_io_hook(cb->compressed_pages[0],
290                                          cb->start,
291                                          cb->start + cb->len - 1,
292                                          NULL,
293                                          bio->bi_error ? 0 : 1);
294         cb->compressed_pages[0]->mapping = NULL;
295 
296         end_compressed_writeback(inode, cb);
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                 put_page(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_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_set_op_attrs(bio, REQ_OP_WRITE, 0);
367         bio->bi_private = cb;
368         bio->bi_end_io = end_compressed_bio_write;
369         atomic_inc(&cb->pending_bios);
370 
371         /* create and submit bios for the compressed pages */
372         bytes_left = compressed_len;
373         for (pg_index = 0; pg_index < cb->nr_pages; pg_index++) {
374                 page = compressed_pages[pg_index];
375                 page->mapping = inode->i_mapping;
376                 if (bio->bi_iter.bi_size)
377                         ret = io_tree->ops->merge_bio_hook(page, 0,
378                                                            PAGE_SIZE,
379                                                            bio, 0);
380                 else
381                         ret = 0;
382 
383                 page->mapping = NULL;
384                 if (ret || bio_add_page(bio, page, PAGE_SIZE, 0) <
385                     PAGE_SIZE) {
386                         bio_get(bio);
387 
388                         /*
389                          * inc the count before we submit the bio so
390                          * we know the end IO handler won't happen before
391                          * we inc the count.  Otherwise, the cb might get
392                          * freed before we're done setting it up
393                          */
394                         atomic_inc(&cb->pending_bios);
395                         ret = btrfs_bio_wq_end_io(root->fs_info, bio,
396                                         BTRFS_WQ_ENDIO_DATA);
397                         BUG_ON(ret); /* -ENOMEM */
398 
399                         if (!skip_sum) {
400                                 ret = btrfs_csum_one_bio(root, inode, bio,
401                                                          start, 1);
402                                 BUG_ON(ret); /* -ENOMEM */
403                         }
404 
405                         ret = btrfs_map_bio(root, bio, 0, 1);
406                         if (ret) {
407                                 bio->bi_error = ret;
408                                 bio_endio(bio);
409                         }
410 
411                         bio_put(bio);
412 
413                         bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS);
414                         BUG_ON(!bio);
415                         bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
416                         bio->bi_private = cb;
417                         bio->bi_end_io = end_compressed_bio_write;
418                         bio_add_page(bio, page, PAGE_SIZE, 0);
419                 }
420                 if (bytes_left < PAGE_SIZE) {
421                         btrfs_info(BTRFS_I(inode)->root->fs_info,
422                                         "bytes left %lu compress len %lu nr %lu",
423                                bytes_left, cb->compressed_len, cb->nr_pages);
424                 }
425                 bytes_left -= PAGE_SIZE;
426                 first_byte += PAGE_SIZE;
427                 cond_resched();
428         }
429         bio_get(bio);
430 
431         ret = btrfs_bio_wq_end_io(root->fs_info, bio, BTRFS_WQ_ENDIO_DATA);
432         BUG_ON(ret); /* -ENOMEM */
433 
434         if (!skip_sum) {
435                 ret = btrfs_csum_one_bio(root, inode, bio, start, 1);
436                 BUG_ON(ret); /* -ENOMEM */
437         }
438 
439         ret = btrfs_map_bio(root, bio, 0, 1);
440         if (ret) {
441                 bio->bi_error = ret;
442                 bio_endio(bio);
443         }
444 
445         bio_put(bio);
446         return 0;
447 }
448 
449 static noinline int add_ra_bio_pages(struct inode *inode,
450                                      u64 compressed_end,
451                                      struct compressed_bio *cb)
452 {
453         unsigned long end_index;
454         unsigned long pg_index;
455         u64 last_offset;
456         u64 isize = i_size_read(inode);
457         int ret;
458         struct page *page;
459         unsigned long nr_pages = 0;
460         struct extent_map *em;
461         struct address_space *mapping = inode->i_mapping;
462         struct extent_map_tree *em_tree;
463         struct extent_io_tree *tree;
464         u64 end;
465         int misses = 0;
466 
467         page = cb->orig_bio->bi_io_vec[cb->orig_bio->bi_vcnt - 1].bv_page;
468         last_offset = (page_offset(page) + PAGE_SIZE);
469         em_tree = &BTRFS_I(inode)->extent_tree;
470         tree = &BTRFS_I(inode)->io_tree;
471 
472         if (isize == 0)
473                 return 0;
474 
475         end_index = (i_size_read(inode) - 1) >> PAGE_SHIFT;
476 
477         while (last_offset < compressed_end) {
478                 pg_index = last_offset >> PAGE_SHIFT;
479 
480                 if (pg_index > end_index)
481                         break;
482 
483                 rcu_read_lock();
484                 page = radix_tree_lookup(&mapping->page_tree, pg_index);
485                 rcu_read_unlock();
486                 if (page && !radix_tree_exceptional_entry(page)) {
487                         misses++;
488                         if (misses > 4)
489                                 break;
490                         goto next;
491                 }
492 
493                 page = __page_cache_alloc(mapping_gfp_constraint(mapping,
494                                                                  ~__GFP_FS));
495                 if (!page)
496                         break;
497 
498                 if (add_to_page_cache_lru(page, mapping, pg_index, GFP_NOFS)) {
499                         put_page(page);
500                         goto next;
501                 }
502 
503                 end = last_offset + PAGE_SIZE - 1;
504                 /*
505                  * at this point, we have a locked page in the page cache
506                  * for these bytes in the file.  But, we have to make
507                  * sure they map to this compressed extent on disk.
508                  */
509                 set_page_extent_mapped(page);
510                 lock_extent(tree, last_offset, end);
511                 read_lock(&em_tree->lock);
512                 em = lookup_extent_mapping(em_tree, last_offset,
513                                            PAGE_SIZE);
514                 read_unlock(&em_tree->lock);
515 
516                 if (!em || last_offset < em->start ||
517                     (last_offset + PAGE_SIZE > extent_map_end(em)) ||
518                     (em->block_start >> 9) != cb->orig_bio->bi_iter.bi_sector) {
519                         free_extent_map(em);
520                         unlock_extent(tree, last_offset, end);
521                         unlock_page(page);
522                         put_page(page);
523                         break;
524                 }
525                 free_extent_map(em);
526 
527                 if (page->index == end_index) {
528                         char *userpage;
529                         size_t zero_offset = isize & (PAGE_SIZE - 1);
530 
531                         if (zero_offset) {
532                                 int zeros;
533                                 zeros = PAGE_SIZE - zero_offset;
534                                 userpage = kmap_atomic(page);
535                                 memset(userpage + zero_offset, 0, zeros);
536                                 flush_dcache_page(page);
537                                 kunmap_atomic(userpage);
538                         }
539                 }
540 
541                 ret = bio_add_page(cb->orig_bio, page,
542                                    PAGE_SIZE, 0);
543 
544                 if (ret == PAGE_SIZE) {
545                         nr_pages++;
546                         put_page(page);
547                 } else {
548                         unlock_extent(tree, last_offset, end);
549                         unlock_page(page);
550                         put_page(page);
551                         break;
552                 }
553 next:
554                 last_offset += PAGE_SIZE;
555         }
556         return 0;
557 }
558 
559 /*
560  * for a compressed read, the bio we get passed has all the inode pages
561  * in it.  We don't actually do IO on those pages but allocate new ones
562  * to hold the compressed pages on disk.
563  *
564  * bio->bi_iter.bi_sector points to the compressed extent on disk
565  * bio->bi_io_vec points to all of the inode pages
566  * bio->bi_vcnt is a count of pages
567  *
568  * After the compressed pages are read, we copy the bytes into the
569  * bio we were passed and then call the bio end_io calls
570  */
571 int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
572                                  int mirror_num, unsigned long bio_flags)
573 {
574         struct extent_io_tree *tree;
575         struct extent_map_tree *em_tree;
576         struct compressed_bio *cb;
577         struct btrfs_root *root = BTRFS_I(inode)->root;
578         unsigned long uncompressed_len = bio->bi_vcnt * PAGE_SIZE;
579         unsigned long compressed_len;
580         unsigned long nr_pages;
581         unsigned long pg_index;
582         struct page *page;
583         struct block_device *bdev;
584         struct bio *comp_bio;
585         u64 cur_disk_byte = (u64)bio->bi_iter.bi_sector << 9;
586         u64 em_len;
587         u64 em_start;
588         struct extent_map *em;
589         int ret = -ENOMEM;
590         int faili = 0;
591         u32 *sums;
592 
593         tree = &BTRFS_I(inode)->io_tree;
594         em_tree = &BTRFS_I(inode)->extent_tree;
595 
596         /* we need the actual starting offset of this extent in the file */
597         read_lock(&em_tree->lock);
598         em = lookup_extent_mapping(em_tree,
599                                    page_offset(bio->bi_io_vec->bv_page),
600                                    PAGE_SIZE);
601         read_unlock(&em_tree->lock);
602         if (!em)
603                 return -EIO;
604 
605         compressed_len = em->block_len;
606         cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS);
607         if (!cb)
608                 goto out;
609 
610         atomic_set(&cb->pending_bios, 0);
611         cb->errors = 0;
612         cb->inode = inode;
613         cb->mirror_num = mirror_num;
614         sums = &cb->sums;
615 
616         cb->start = em->orig_start;
617         em_len = em->len;
618         em_start = em->start;
619 
620         free_extent_map(em);
621         em = NULL;
622 
623         cb->len = uncompressed_len;
624         cb->compressed_len = compressed_len;
625         cb->compress_type = extent_compress_type(bio_flags);
626         cb->orig_bio = bio;
627 
628         nr_pages = DIV_ROUND_UP(compressed_len, PAGE_SIZE);
629         cb->compressed_pages = kcalloc(nr_pages, sizeof(struct page *),
630                                        GFP_NOFS);
631         if (!cb->compressed_pages)
632                 goto fail1;
633 
634         bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;
635 
636         for (pg_index = 0; pg_index < nr_pages; pg_index++) {
637                 cb->compressed_pages[pg_index] = alloc_page(GFP_NOFS |
638                                                               __GFP_HIGHMEM);
639                 if (!cb->compressed_pages[pg_index]) {
640                         faili = pg_index - 1;
641                         ret = -ENOMEM;
642                         goto fail2;
643                 }
644         }
645         faili = nr_pages - 1;
646         cb->nr_pages = nr_pages;
647 
648         add_ra_bio_pages(inode, em_start + em_len, cb);
649 
650         /* include any pages we added in add_ra-bio_pages */
651         uncompressed_len = bio->bi_vcnt * PAGE_SIZE;
652         cb->len = uncompressed_len;
653 
654         comp_bio = compressed_bio_alloc(bdev, cur_disk_byte, GFP_NOFS);
655         if (!comp_bio)
656                 goto fail2;
657         bio_set_op_attrs (comp_bio, REQ_OP_READ, 0);
658         comp_bio->bi_private = cb;
659         comp_bio->bi_end_io = end_compressed_bio_read;
660         atomic_inc(&cb->pending_bios);
661 
662         for (pg_index = 0; pg_index < nr_pages; pg_index++) {
663                 page = cb->compressed_pages[pg_index];
664                 page->mapping = inode->i_mapping;
665                 page->index = em_start >> PAGE_SHIFT;
666 
667                 if (comp_bio->bi_iter.bi_size)
668                         ret = tree->ops->merge_bio_hook(page, 0,
669                                                         PAGE_SIZE,
670                                                         comp_bio, 0);
671                 else
672                         ret = 0;
673 
674                 page->mapping = NULL;
675                 if (ret || bio_add_page(comp_bio, page, PAGE_SIZE, 0) <
676                     PAGE_SIZE) {
677                         bio_get(comp_bio);
678 
679                         ret = btrfs_bio_wq_end_io(root->fs_info, comp_bio,
680                                         BTRFS_WQ_ENDIO_DATA);
681                         BUG_ON(ret); /* -ENOMEM */
682 
683                         /*
684                          * inc the count before we submit the bio so
685                          * we know the end IO handler won't happen before
686                          * we inc the count.  Otherwise, the cb might get
687                          * freed before we're done setting it up
688                          */
689                         atomic_inc(&cb->pending_bios);
690 
691                         if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
692                                 ret = btrfs_lookup_bio_sums(root, inode,
693                                                         comp_bio, sums);
694                                 BUG_ON(ret); /* -ENOMEM */
695                         }
696                         sums += DIV_ROUND_UP(comp_bio->bi_iter.bi_size,
697                                              root->sectorsize);
698 
699                         ret = btrfs_map_bio(root, comp_bio, mirror_num, 0);
700                         if (ret) {
701                                 comp_bio->bi_error = ret;
702                                 bio_endio(comp_bio);
703                         }
704 
705                         bio_put(comp_bio);
706 
707                         comp_bio = compressed_bio_alloc(bdev, cur_disk_byte,
708                                                         GFP_NOFS);
709                         BUG_ON(!comp_bio);
710                         bio_set_op_attrs(comp_bio, REQ_OP_READ, 0);
711                         comp_bio->bi_private = cb;
712                         comp_bio->bi_end_io = end_compressed_bio_read;
713 
714                         bio_add_page(comp_bio, page, PAGE_SIZE, 0);
715                 }
716                 cur_disk_byte += PAGE_SIZE;
717         }
718         bio_get(comp_bio);
719 
720         ret = btrfs_bio_wq_end_io(root->fs_info, comp_bio,
721                         BTRFS_WQ_ENDIO_DATA);
722         BUG_ON(ret); /* -ENOMEM */
723 
724         if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
725                 ret = btrfs_lookup_bio_sums(root, inode, comp_bio, sums);
726                 BUG_ON(ret); /* -ENOMEM */
727         }
728 
729         ret = btrfs_map_bio(root, comp_bio, mirror_num, 0);
730         if (ret) {
731                 comp_bio->bi_error = ret;
732                 bio_endio(comp_bio);
733         }
734 
735         bio_put(comp_bio);
736         return 0;
737 
738 fail2:
739         while (faili >= 0) {
740                 __free_page(cb->compressed_pages[faili]);
741                 faili--;
742         }
743 
744         kfree(cb->compressed_pages);
745 fail1:
746         kfree(cb);
747 out:
748         free_extent_map(em);
749         return ret;
750 }
751 
752 static struct {
753         struct list_head idle_ws;
754         spinlock_t ws_lock;
755         /* Number of free workspaces */
756         int free_ws;
757         /* Total number of allocated workspaces */
758         atomic_t total_ws;
759         /* Waiters for a free workspace */
760         wait_queue_head_t ws_wait;
761 } btrfs_comp_ws[BTRFS_COMPRESS_TYPES];
762 
763 static const struct btrfs_compress_op * const btrfs_compress_op[] = {
764         &btrfs_zlib_compress,
765         &btrfs_lzo_compress,
766 };
767 
768 void __init btrfs_init_compress(void)
769 {
770         int i;
771 
772         for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) {
773                 struct list_head *workspace;
774 
775                 INIT_LIST_HEAD(&btrfs_comp_ws[i].idle_ws);
776                 spin_lock_init(&btrfs_comp_ws[i].ws_lock);
777                 atomic_set(&btrfs_comp_ws[i].total_ws, 0);
778                 init_waitqueue_head(&btrfs_comp_ws[i].ws_wait);
779 
780                 /*
781                  * Preallocate one workspace for each compression type so
782                  * we can guarantee forward progress in the worst case
783                  */
784                 workspace = btrfs_compress_op[i]->alloc_workspace();
785                 if (IS_ERR(workspace)) {
786                         printk(KERN_WARNING
787         "BTRFS: cannot preallocate compression workspace, will try later");
788                 } else {
789                         atomic_set(&btrfs_comp_ws[i].total_ws, 1);
790                         btrfs_comp_ws[i].free_ws = 1;
791                         list_add(workspace, &btrfs_comp_ws[i].idle_ws);
792                 }
793         }
794 }
795 
796 /*
797  * This finds an available workspace or allocates a new one.
798  * If it's not possible to allocate a new one, waits until there's one.
799  * Preallocation makes a forward progress guarantees and we do not return
800  * errors.
801  */
802 static struct list_head *find_workspace(int type)
803 {
804         struct list_head *workspace;
805         int cpus = num_online_cpus();
806         int idx = type - 1;
807 
808         struct list_head *idle_ws       = &btrfs_comp_ws[idx].idle_ws;
809         spinlock_t *ws_lock             = &btrfs_comp_ws[idx].ws_lock;
810         atomic_t *total_ws              = &btrfs_comp_ws[idx].total_ws;
811         wait_queue_head_t *ws_wait      = &btrfs_comp_ws[idx].ws_wait;
812         int *free_ws                    = &btrfs_comp_ws[idx].free_ws;
813 again:
814         spin_lock(ws_lock);
815         if (!list_empty(idle_ws)) {
816                 workspace = idle_ws->next;
817                 list_del(workspace);
818                 (*free_ws)--;
819                 spin_unlock(ws_lock);
820                 return workspace;
821 
822         }
823         if (atomic_read(total_ws) > cpus) {
824                 DEFINE_WAIT(wait);
825 
826                 spin_unlock(ws_lock);
827                 prepare_to_wait(ws_wait, &wait, TASK_UNINTERRUPTIBLE);
828                 if (atomic_read(total_ws) > cpus && !*free_ws)
829                         schedule();
830                 finish_wait(ws_wait, &wait);
831                 goto again;
832         }
833         atomic_inc(total_ws);
834         spin_unlock(ws_lock);
835 
836         workspace = btrfs_compress_op[idx]->alloc_workspace();
837         if (IS_ERR(workspace)) {
838                 atomic_dec(total_ws);
839                 wake_up(ws_wait);
840 
841                 /*
842                  * Do not return the error but go back to waiting. There's a
843                  * workspace preallocated for each type and the compression
844                  * time is bounded so we get to a workspace eventually. This
845                  * makes our caller's life easier.
846                  *
847                  * To prevent silent and low-probability deadlocks (when the
848                  * initial preallocation fails), check if there are any
849                  * workspaces at all.
850                  */
851                 if (atomic_read(total_ws) == 0) {
852                         static DEFINE_RATELIMIT_STATE(_rs,
853                                         /* once per minute */ 60 * HZ,
854                                         /* no burst */ 1);
855 
856                         if (__ratelimit(&_rs)) {
857                                 printk(KERN_WARNING
858                             "no compression workspaces, low memory, retrying");
859                         }
860                 }
861                 goto again;
862         }
863         return workspace;
864 }
865 
866 /*
867  * put a workspace struct back on the list or free it if we have enough
868  * idle ones sitting around
869  */
870 static void free_workspace(int type, struct list_head *workspace)
871 {
872         int idx = type - 1;
873         struct list_head *idle_ws       = &btrfs_comp_ws[idx].idle_ws;
874         spinlock_t *ws_lock             = &btrfs_comp_ws[idx].ws_lock;
875         atomic_t *total_ws              = &btrfs_comp_ws[idx].total_ws;
876         wait_queue_head_t *ws_wait      = &btrfs_comp_ws[idx].ws_wait;
877         int *free_ws                    = &btrfs_comp_ws[idx].free_ws;
878 
879         spin_lock(ws_lock);
880         if (*free_ws < num_online_cpus()) {
881                 list_add(workspace, idle_ws);
882                 (*free_ws)++;
883                 spin_unlock(ws_lock);
884                 goto wake;
885         }
886         spin_unlock(ws_lock);
887 
888         btrfs_compress_op[idx]->free_workspace(workspace);
889         atomic_dec(total_ws);
890 wake:
891         /*
892          * Make sure counter is updated before we wake up waiters.
893          */
894         smp_mb();
895         if (waitqueue_active(ws_wait))
896                 wake_up(ws_wait);
897 }
898 
899 /*
900  * cleanup function for module exit
901  */
902 static void free_workspaces(void)
903 {
904         struct list_head *workspace;
905         int i;
906 
907         for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) {
908                 while (!list_empty(&btrfs_comp_ws[i].idle_ws)) {
909                         workspace = btrfs_comp_ws[i].idle_ws.next;
910                         list_del(workspace);
911                         btrfs_compress_op[i]->free_workspace(workspace);
912                         atomic_dec(&btrfs_comp_ws[i].total_ws);
913                 }
914         }
915 }
916 
917 /*
918  * given an address space and start/len, compress the bytes.
919  *
920  * pages are allocated to hold the compressed result and stored
921  * in 'pages'
922  *
923  * out_pages is used to return the number of pages allocated.  There
924  * may be pages allocated even if we return an error
925  *
926  * total_in is used to return the number of bytes actually read.  It
927  * may be smaller then len if we had to exit early because we
928  * ran out of room in the pages array or because we cross the
929  * max_out threshold.
930  *
931  * total_out is used to return the total number of compressed bytes
932  *
933  * max_out tells us the max number of bytes that we're allowed to
934  * stuff into pages
935  */
936 int btrfs_compress_pages(int type, struct address_space *mapping,
937                          u64 start, unsigned long len,
938                          struct page **pages,
939                          unsigned long nr_dest_pages,
940                          unsigned long *out_pages,
941                          unsigned long *total_in,
942                          unsigned long *total_out,
943                          unsigned long max_out)
944 {
945         struct list_head *workspace;
946         int ret;
947 
948         workspace = find_workspace(type);
949 
950         ret = btrfs_compress_op[type-1]->compress_pages(workspace, mapping,
951                                                       start, len, pages,
952                                                       nr_dest_pages, out_pages,
953                                                       total_in, total_out,
954                                                       max_out);
955         free_workspace(type, workspace);
956         return ret;
957 }
958 
959 /*
960  * pages_in is an array of pages with compressed data.
961  *
962  * disk_start is the starting logical offset of this array in the file
963  *
964  * bvec is a bio_vec of pages from the file that we want to decompress into
965  *
966  * vcnt is the count of pages in the biovec
967  *
968  * srclen is the number of bytes in pages_in
969  *
970  * The basic idea is that we have a bio that was created by readpages.
971  * The pages in the bio are for the uncompressed data, and they may not
972  * be contiguous.  They all correspond to the range of bytes covered by
973  * the compressed extent.
974  */
975 static int btrfs_decompress_biovec(int type, struct page **pages_in,
976                                    u64 disk_start, struct bio_vec *bvec,
977                                    int vcnt, size_t srclen)
978 {
979         struct list_head *workspace;
980         int ret;
981 
982         workspace = find_workspace(type);
983 
984         ret = btrfs_compress_op[type-1]->decompress_biovec(workspace, pages_in,
985                                                          disk_start,
986                                                          bvec, vcnt, srclen);
987         free_workspace(type, workspace);
988         return ret;
989 }
990 
991 /*
992  * a less complex decompression routine.  Our compressed data fits in a
993  * single page, and we want to read a single page out of it.
994  * start_byte tells us the offset into the compressed data we're interested in
995  */
996 int btrfs_decompress(int type, unsigned char *data_in, struct page *dest_page,
997                      unsigned long start_byte, size_t srclen, size_t destlen)
998 {
999         struct list_head *workspace;
1000         int ret;
1001 
1002         workspace = find_workspace(type);
1003 
1004         ret = btrfs_compress_op[type-1]->decompress(workspace, data_in,
1005                                                   dest_page, start_byte,
1006                                                   srclen, destlen);
1007 
1008         free_workspace(type, workspace);
1009         return ret;
1010 }
1011 
1012 void btrfs_exit_compress(void)
1013 {
1014         free_workspaces();
1015 }
1016 
1017 /*
1018  * Copy uncompressed data from working buffer to pages.
1019  *
1020  * buf_start is the byte offset we're of the start of our workspace buffer.
1021  *
1022  * total_out is the last byte of the buffer
1023  */
1024 int btrfs_decompress_buf2page(char *buf, unsigned long buf_start,
1025                               unsigned long total_out, u64 disk_start,
1026                               struct bio_vec *bvec, int vcnt,
1027                               unsigned long *pg_index,
1028                               unsigned long *pg_offset)
1029 {
1030         unsigned long buf_offset;
1031         unsigned long current_buf_start;
1032         unsigned long start_byte;
1033         unsigned long working_bytes = total_out - buf_start;
1034         unsigned long bytes;
1035         char *kaddr;
1036         struct page *page_out = bvec[*pg_index].bv_page;
1037 
1038         /*
1039          * start byte is the first byte of the page we're currently
1040          * copying into relative to the start of the compressed data.
1041          */
1042         start_byte = page_offset(page_out) - disk_start;
1043 
1044         /* we haven't yet hit data corresponding to this page */
1045         if (total_out <= start_byte)
1046                 return 1;
1047 
1048         /*
1049          * the start of the data we care about is offset into
1050          * the middle of our working buffer
1051          */
1052         if (total_out > start_byte && buf_start < start_byte) {
1053                 buf_offset = start_byte - buf_start;
1054                 working_bytes -= buf_offset;
1055         } else {
1056                 buf_offset = 0;
1057         }
1058         current_buf_start = buf_start;
1059 
1060         /* copy bytes from the working buffer into the pages */
1061         while (working_bytes > 0) {
1062                 bytes = min(PAGE_SIZE - *pg_offset,
1063                             PAGE_SIZE - buf_offset);
1064                 bytes = min(bytes, working_bytes);
1065                 kaddr = kmap_atomic(page_out);
1066                 memcpy(kaddr + *pg_offset, buf + buf_offset, bytes);
1067                 kunmap_atomic(kaddr);
1068                 flush_dcache_page(page_out);
1069 
1070                 *pg_offset += bytes;
1071                 buf_offset += bytes;
1072                 working_bytes -= bytes;
1073                 current_buf_start += bytes;
1074 
1075                 /* check if we need to pick another page */
1076                 if (*pg_offset == PAGE_SIZE) {
1077                         (*pg_index)++;
1078                         if (*pg_index >= vcnt)
1079                                 return 0;
1080 
1081                         page_out = bvec[*pg_index].bv_page;
1082                         *pg_offset = 0;
1083                         start_byte = page_offset(page_out) - disk_start;
1084 
1085                         /*
1086                          * make sure our new page is covered by this
1087                          * working buffer
1088                          */
1089                         if (total_out <= start_byte)
1090                                 return 1;
1091 
1092                         /*
1093                          * the next page in the biovec might not be adjacent
1094                          * to the last page, but it might still be found
1095                          * inside this working buffer. bump our offset pointer
1096                          */
1097                         if (total_out > start_byte &&
1098                             current_buf_start < start_byte) {
1099                                 buf_offset = start_byte - buf_start;
1100                                 working_bytes = total_out - start_byte;
1101                                 current_buf_start = buf_start + buf_offset;
1102                         }
1103                 }
1104         }
1105 
1106         return 1;
1107 }
1108 
1109 /*
1110  * When uncompressing data, we need to make sure and zero any parts of
1111  * the biovec that were not filled in by the decompression code.  pg_index
1112  * and pg_offset indicate the last page and the last offset of that page
1113  * that have been filled in.  This will zero everything remaining in the
1114  * biovec.
1115  */
1116 void btrfs_clear_biovec_end(struct bio_vec *bvec, int vcnt,
1117                                    unsigned long pg_index,
1118                                    unsigned long pg_offset)
1119 {
1120         while (pg_index < vcnt) {
1121                 struct page *page = bvec[pg_index].bv_page;
1122                 unsigned long off = bvec[pg_index].bv_offset;
1123                 unsigned long len = bvec[pg_index].bv_len;
1124 
1125                 if (pg_offset < off)
1126                         pg_offset = off;
1127                 if (pg_offset < off + len) {
1128                         unsigned long bytes = off + len - pg_offset;
1129                         char *kaddr;
1130 
1131                         kaddr = kmap_atomic(page);
1132                         memset(kaddr + pg_offset, 0, bytes);
1133                         kunmap_atomic(kaddr);
1134                 }
1135                 pg_index++;
1136                 pg_offset = 0;
1137         }
1138 }
1139 

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