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Phillip Lougher1701aec2009-01-05 08:46:24 +00001/*
2 * Squashfs - a compressed read only filesystem for Linux
3 *
4 * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
Phillip Lougherd7f2ff62011-05-26 10:39:56 +01005 * Phillip Lougher <phillip@squashfs.org.uk>
Phillip Lougher1701aec2009-01-05 08:46:24 +00006 *
7 * This program is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU General Public License
9 * as published by the Free Software Foundation; either version 2,
10 * or (at your option) any later version.
11 *
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 * GNU General Public License for more details.
16 *
17 * You should have received a copy of the GNU General Public License
18 * along with this program; if not, write to the Free Software
19 * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
20 *
21 * file.c
22 */
23
24/*
25 * This file contains code for handling regular files. A regular file
26 * consists of a sequence of contiguous compressed blocks, and/or a
27 * compressed fragment block (tail-end packed block). The compressed size
28 * of each datablock is stored in a block list contained within the
29 * file inode (itself stored in one or more compressed metadata blocks).
30 *
31 * To speed up access to datablocks when reading 'large' files (256 Mbytes or
32 * larger), the code implements an index cache that caches the mapping from
33 * block index to datablock location on disk.
34 *
35 * The index cache allows Squashfs to handle large files (up to 1.75 TiB) while
36 * retaining a simple and space-efficient block list on disk. The cache
37 * is split into slots, caching up to eight 224 GiB files (128 KiB blocks).
38 * Larger files use multiple slots, with 1.75 TiB files using all 8 slots.
39 * The index cache is designed to be memory efficient, and by default uses
40 * 16 KiB.
41 */
42
43#include <linux/fs.h>
44#include <linux/vfs.h>
45#include <linux/kernel.h>
46#include <linux/slab.h>
47#include <linux/string.h>
48#include <linux/pagemap.h>
49#include <linux/mutex.h>
Phillip Lougher1701aec2009-01-05 08:46:24 +000050
51#include "squashfs_fs.h"
52#include "squashfs_fs_sb.h"
53#include "squashfs_fs_i.h"
54#include "squashfs.h"
55
56/*
57 * Locate cache slot in range [offset, index] for specified inode. If
58 * there's more than one return the slot closest to index.
59 */
60static struct meta_index *locate_meta_index(struct inode *inode, int offset,
61 int index)
62{
63 struct meta_index *meta = NULL;
64 struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
65 int i;
66
67 mutex_lock(&msblk->meta_index_mutex);
68
69 TRACE("locate_meta_index: index %d, offset %d\n", index, offset);
70
71 if (msblk->meta_index == NULL)
72 goto not_allocated;
73
74 for (i = 0; i < SQUASHFS_META_SLOTS; i++) {
75 if (msblk->meta_index[i].inode_number == inode->i_ino &&
76 msblk->meta_index[i].offset >= offset &&
77 msblk->meta_index[i].offset <= index &&
78 msblk->meta_index[i].locked == 0) {
79 TRACE("locate_meta_index: entry %d, offset %d\n", i,
80 msblk->meta_index[i].offset);
81 meta = &msblk->meta_index[i];
82 offset = meta->offset;
83 }
84 }
85
86 if (meta)
87 meta->locked = 1;
88
89not_allocated:
90 mutex_unlock(&msblk->meta_index_mutex);
91
92 return meta;
93}
94
95
96/*
97 * Find and initialise an empty cache slot for index offset.
98 */
99static struct meta_index *empty_meta_index(struct inode *inode, int offset,
100 int skip)
101{
102 struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
103 struct meta_index *meta = NULL;
104 int i;
105
106 mutex_lock(&msblk->meta_index_mutex);
107
108 TRACE("empty_meta_index: offset %d, skip %d\n", offset, skip);
109
110 if (msblk->meta_index == NULL) {
111 /*
112 * First time cache index has been used, allocate and
113 * initialise. The cache index could be allocated at
114 * mount time but doing it here means it is allocated only
115 * if a 'large' file is read.
116 */
117 msblk->meta_index = kcalloc(SQUASHFS_META_SLOTS,
118 sizeof(*(msblk->meta_index)), GFP_KERNEL);
119 if (msblk->meta_index == NULL) {
120 ERROR("Failed to allocate meta_index\n");
121 goto failed;
122 }
123 for (i = 0; i < SQUASHFS_META_SLOTS; i++) {
124 msblk->meta_index[i].inode_number = 0;
125 msblk->meta_index[i].locked = 0;
126 }
127 msblk->next_meta_index = 0;
128 }
129
130 for (i = SQUASHFS_META_SLOTS; i &&
131 msblk->meta_index[msblk->next_meta_index].locked; i--)
132 msblk->next_meta_index = (msblk->next_meta_index + 1) %
133 SQUASHFS_META_SLOTS;
134
135 if (i == 0) {
136 TRACE("empty_meta_index: failed!\n");
137 goto failed;
138 }
139
140 TRACE("empty_meta_index: returned meta entry %d, %p\n",
141 msblk->next_meta_index,
142 &msblk->meta_index[msblk->next_meta_index]);
143
144 meta = &msblk->meta_index[msblk->next_meta_index];
145 msblk->next_meta_index = (msblk->next_meta_index + 1) %
146 SQUASHFS_META_SLOTS;
147
148 meta->inode_number = inode->i_ino;
149 meta->offset = offset;
150 meta->skip = skip;
151 meta->entries = 0;
152 meta->locked = 1;
153
154failed:
155 mutex_unlock(&msblk->meta_index_mutex);
156 return meta;
157}
158
159
160static void release_meta_index(struct inode *inode, struct meta_index *meta)
161{
162 struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
163 mutex_lock(&msblk->meta_index_mutex);
164 meta->locked = 0;
165 mutex_unlock(&msblk->meta_index_mutex);
166}
167
168
169/*
170 * Read the next n blocks from the block list, starting from
171 * metadata block <start_block, offset>.
172 */
173static long long read_indexes(struct super_block *sb, int n,
174 u64 *start_block, int *offset)
175{
176 int err, i;
177 long long block = 0;
178 __le32 *blist = kmalloc(PAGE_CACHE_SIZE, GFP_KERNEL);
179
180 if (blist == NULL) {
181 ERROR("read_indexes: Failed to allocate block_list\n");
182 return -ENOMEM;
183 }
184
185 while (n) {
186 int blocks = min_t(int, n, PAGE_CACHE_SIZE >> 2);
187
188 err = squashfs_read_metadata(sb, blist, start_block,
189 offset, blocks << 2);
190 if (err < 0) {
191 ERROR("read_indexes: reading block [%llx:%x]\n",
192 *start_block, *offset);
193 goto failure;
194 }
195
196 for (i = 0; i < blocks; i++) {
197 int size = le32_to_cpu(blist[i]);
198 block += SQUASHFS_COMPRESSED_SIZE_BLOCK(size);
199 }
200 n -= blocks;
201 }
202
203 kfree(blist);
204 return block;
205
206failure:
207 kfree(blist);
208 return err;
209}
210
211
212/*
213 * Each cache index slot has SQUASHFS_META_ENTRIES, each of which
214 * can cache one index -> datablock/blocklist-block mapping. We wish
215 * to distribute these over the length of the file, entry[0] maps index x,
216 * entry[1] maps index x + skip, entry[2] maps index x + 2 * skip, and so on.
217 * The larger the file, the greater the skip factor. The skip factor is
218 * limited to the size of the metadata cache (SQUASHFS_CACHED_BLKS) to ensure
219 * the number of metadata blocks that need to be read fits into the cache.
220 * If the skip factor is limited in this way then the file will use multiple
221 * slots.
222 */
223static inline int calculate_skip(int blocks)
224{
225 int skip = blocks / ((SQUASHFS_META_ENTRIES + 1)
226 * SQUASHFS_META_INDEXES);
227 return min(SQUASHFS_CACHED_BLKS - 1, skip + 1);
228}
229
230
231/*
232 * Search and grow the index cache for the specified inode, returning the
233 * on-disk locations of the datablock and block list metadata block
234 * <index_block, index_offset> for index (scaled to nearest cache index).
235 */
236static int fill_meta_index(struct inode *inode, int index,
237 u64 *index_block, int *index_offset, u64 *data_block)
238{
239 struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
240 int skip = calculate_skip(i_size_read(inode) >> msblk->block_log);
241 int offset = 0;
242 struct meta_index *meta;
243 struct meta_entry *meta_entry;
244 u64 cur_index_block = squashfs_i(inode)->block_list_start;
245 int cur_offset = squashfs_i(inode)->offset;
246 u64 cur_data_block = squashfs_i(inode)->start;
247 int err, i;
248
249 /*
250 * Scale index to cache index (cache slot entry)
251 */
252 index /= SQUASHFS_META_INDEXES * skip;
253
254 while (offset < index) {
255 meta = locate_meta_index(inode, offset + 1, index);
256
257 if (meta == NULL) {
258 meta = empty_meta_index(inode, offset + 1, skip);
259 if (meta == NULL)
260 goto all_done;
261 } else {
262 offset = index < meta->offset + meta->entries ? index :
263 meta->offset + meta->entries - 1;
264 meta_entry = &meta->meta_entry[offset - meta->offset];
265 cur_index_block = meta_entry->index_block +
266 msblk->inode_table;
267 cur_offset = meta_entry->offset;
268 cur_data_block = meta_entry->data_block;
269 TRACE("get_meta_index: offset %d, meta->offset %d, "
270 "meta->entries %d\n", offset, meta->offset,
271 meta->entries);
272 TRACE("get_meta_index: index_block 0x%llx, offset 0x%x"
273 " data_block 0x%llx\n", cur_index_block,
274 cur_offset, cur_data_block);
275 }
276
277 /*
278 * If necessary grow cache slot by reading block list. Cache
279 * slot is extended up to index or to the end of the slot, in
280 * which case further slots will be used.
281 */
282 for (i = meta->offset + meta->entries; i <= index &&
283 i < meta->offset + SQUASHFS_META_ENTRIES; i++) {
284 int blocks = skip * SQUASHFS_META_INDEXES;
285 long long res = read_indexes(inode->i_sb, blocks,
286 &cur_index_block, &cur_offset);
287
288 if (res < 0) {
289 if (meta->entries == 0)
290 /*
291 * Don't leave an empty slot on read
292 * error allocated to this inode...
293 */
294 meta->inode_number = 0;
295 err = res;
296 goto failed;
297 }
298
299 cur_data_block += res;
300 meta_entry = &meta->meta_entry[i - meta->offset];
301 meta_entry->index_block = cur_index_block -
302 msblk->inode_table;
303 meta_entry->offset = cur_offset;
304 meta_entry->data_block = cur_data_block;
305 meta->entries++;
306 offset++;
307 }
308
309 TRACE("get_meta_index: meta->offset %d, meta->entries %d\n",
310 meta->offset, meta->entries);
311
312 release_meta_index(inode, meta);
313 }
314
315all_done:
316 *index_block = cur_index_block;
317 *index_offset = cur_offset;
318 *data_block = cur_data_block;
319
320 /*
321 * Scale cache index (cache slot entry) to index
322 */
323 return offset * SQUASHFS_META_INDEXES * skip;
324
325failed:
326 release_meta_index(inode, meta);
327 return err;
328}
329
330
331/*
332 * Get the on-disk location and compressed size of the datablock
333 * specified by index. Fill_meta_index() does most of the work.
334 */
335static int read_blocklist(struct inode *inode, int index, u64 *block)
336{
337 u64 start;
338 long long blks;
339 int offset;
340 __le32 size;
341 int res = fill_meta_index(inode, index, &start, &offset, block);
342
343 TRACE("read_blocklist: res %d, index %d, start 0x%llx, offset"
344 " 0x%x, block 0x%llx\n", res, index, start, offset,
345 *block);
346
347 if (res < 0)
348 return res;
349
350 /*
351 * res contains the index of the mapping returned by fill_meta_index(),
352 * this will likely be less than the desired index (because the
353 * meta_index cache works at a higher granularity). Read any
354 * extra block indexes needed.
355 */
356 if (res < index) {
357 blks = read_indexes(inode->i_sb, index - res, &start, &offset);
358 if (blks < 0)
359 return (int) blks;
360 *block += blks;
361 }
362
363 /*
364 * Read length of block specified by index.
365 */
366 res = squashfs_read_metadata(inode->i_sb, &size, &start, &offset,
367 sizeof(size));
368 if (res < 0)
369 return res;
370 return le32_to_cpu(size);
371}
372
373
374static int squashfs_readpage(struct file *file, struct page *page)
375{
376 struct inode *inode = page->mapping->host;
377 struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
378 int bytes, i, offset = 0, sparse = 0;
379 struct squashfs_cache_entry *buffer = NULL;
380 void *pageaddr;
381
382 int mask = (1 << (msblk->block_log - PAGE_CACHE_SHIFT)) - 1;
383 int index = page->index >> (msblk->block_log - PAGE_CACHE_SHIFT);
384 int start_index = page->index & ~mask;
385 int end_index = start_index | mask;
386 int file_end = i_size_read(inode) >> msblk->block_log;
387
388 TRACE("Entered squashfs_readpage, page index %lx, start block %llx\n",
389 page->index, squashfs_i(inode)->start);
390
391 if (page->index >= ((i_size_read(inode) + PAGE_CACHE_SIZE - 1) >>
392 PAGE_CACHE_SHIFT))
393 goto out;
394
395 if (index < file_end || squashfs_i(inode)->fragment_block ==
396 SQUASHFS_INVALID_BLK) {
397 /*
398 * Reading a datablock from disk. Need to read block list
399 * to get location and block size.
400 */
401 u64 block = 0;
402 int bsize = read_blocklist(inode, index, &block);
403 if (bsize < 0)
404 goto error_out;
405
406 if (bsize == 0) { /* hole */
407 bytes = index == file_end ?
408 (i_size_read(inode) & (msblk->block_size - 1)) :
409 msblk->block_size;
410 sparse = 1;
411 } else {
412 /*
413 * Read and decompress datablock.
414 */
415 buffer = squashfs_get_datablock(inode->i_sb,
416 block, bsize);
417 if (buffer->error) {
418 ERROR("Unable to read page, block %llx, size %x"
419 "\n", block, bsize);
420 squashfs_cache_put(buffer);
421 goto error_out;
422 }
423 bytes = buffer->length;
424 }
425 } else {
426 /*
427 * Datablock is stored inside a fragment (tail-end packed
428 * block).
429 */
430 buffer = squashfs_get_fragment(inode->i_sb,
431 squashfs_i(inode)->fragment_block,
432 squashfs_i(inode)->fragment_size);
433
434 if (buffer->error) {
435 ERROR("Unable to read page, block %llx, size %x\n",
436 squashfs_i(inode)->fragment_block,
437 squashfs_i(inode)->fragment_size);
438 squashfs_cache_put(buffer);
439 goto error_out;
440 }
441 bytes = i_size_read(inode) & (msblk->block_size - 1);
442 offset = squashfs_i(inode)->fragment_offset;
443 }
444
445 /*
446 * Loop copying datablock into pages. As the datablock likely covers
447 * many PAGE_CACHE_SIZE pages (default block size is 128 KiB) explicitly
448 * grab the pages from the page cache, except for the page that we've
449 * been called to fill.
450 */
451 for (i = start_index; i <= end_index && bytes > 0; i++,
452 bytes -= PAGE_CACHE_SIZE, offset += PAGE_CACHE_SIZE) {
453 struct page *push_page;
454 int avail = sparse ? 0 : min_t(int, bytes, PAGE_CACHE_SIZE);
455
456 TRACE("bytes %d, i %d, available_bytes %d\n", bytes, i, avail);
457
458 push_page = (i == page->index) ? page :
459 grab_cache_page_nowait(page->mapping, i);
460
461 if (!push_page)
462 continue;
463
464 if (PageUptodate(push_page))
465 goto skip_page;
466
Cong Wang53b55e52011-11-25 23:14:36 +0800467 pageaddr = kmap_atomic(push_page);
Phillip Lougher1701aec2009-01-05 08:46:24 +0000468 squashfs_copy_data(pageaddr, buffer, offset, avail);
469 memset(pageaddr + avail, 0, PAGE_CACHE_SIZE - avail);
Cong Wang53b55e52011-11-25 23:14:36 +0800470 kunmap_atomic(pageaddr);
Phillip Lougher1701aec2009-01-05 08:46:24 +0000471 flush_dcache_page(push_page);
472 SetPageUptodate(push_page);
473skip_page:
474 unlock_page(push_page);
475 if (i != page->index)
476 page_cache_release(push_page);
477 }
478
479 if (!sparse)
480 squashfs_cache_put(buffer);
481
482 return 0;
483
484error_out:
485 SetPageError(page);
486out:
Cong Wang53b55e52011-11-25 23:14:36 +0800487 pageaddr = kmap_atomic(page);
Phillip Lougher1701aec2009-01-05 08:46:24 +0000488 memset(pageaddr, 0, PAGE_CACHE_SIZE);
Cong Wang53b55e52011-11-25 23:14:36 +0800489 kunmap_atomic(pageaddr);
Phillip Lougher1701aec2009-01-05 08:46:24 +0000490 flush_dcache_page(page);
491 if (!PageError(page))
492 SetPageUptodate(page);
493 unlock_page(page);
494
495 return 0;
496}
497
498
499const struct address_space_operations squashfs_aops = {
500 .readpage = squashfs_readpage
501};