1 /*
2 * Squashfs - a compressed read only filesystem for Linux
3 *
4 * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
5 * Phillip Lougher <phillip@squashfs.org.uk>
6 *
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 * cache.c
22 */
23
24 /*
25 * Blocks in Squashfs are compressed. To avoid repeatedly decompressing
26 * recently accessed data Squashfs uses two small metadata and fragment caches.
27 *
28 * This file implements a generic cache implementation used for both caches,
29 * plus functions layered ontop of the generic cache implementation to
30 * access the metadata and fragment caches.
31 *
32 * To avoid out of memory and fragmentation issues with vmalloc the cache
33 * uses sequences of kmalloced PAGE_CACHE_SIZE buffers.
34 *
35 * It should be noted that the cache is not used for file datablocks, these
36 * are decompressed and cached in the page-cache in the normal way. The
37 * cache is only used to temporarily cache fragment and metadata blocks
38 * which have been read as as a result of a metadata (i.e. inode or
39 * directory) or fragment access. Because metadata and fragments are packed
40 * together into blocks (to gain greater compression) the read of a particular
41 * piece of metadata or fragment will retrieve other metadata/fragments which
42 * have been packed with it, these because of locality-of-reference may be read
43 * in the near future. Temporarily caching them ensures they are available for
44 * near future access without requiring an additional read and decompress.
45 */
46
47 #include <linux/fs.h>
48 #include <linux/vfs.h>
49 #include <linux/slab.h>
50 #include <linux/vmalloc.h>
51 #include <linux/sched.h>
52 #include <linux/spinlock.h>
53 #include <linux/wait.h>
54 #include <linux/pagemap.h>
55
56 #include "squashfs_fs.h"
57 #include "squashfs_fs_sb.h"
58 #include "squashfs.h"
59
60 /*
61 * Look-up block in cache, and increment usage count. If not in cache, read
62 * and decompress it from disk.
63 */
squashfs_cache_get(struct super_block * sb,struct squashfs_cache * cache,u64 block,int length)64 struct squashfs_cache_entry *squashfs_cache_get(struct super_block *sb,
65 struct squashfs_cache *cache, u64 block, int length)
66 {
67 int i, n;
68 struct squashfs_cache_entry *entry;
69
70 spin_lock(&cache->lock);
71
72 while (1) {
73 for (i = cache->curr_blk, n = 0; n < cache->entries; n++) {
74 if (cache->entry[i].block == block) {
75 cache->curr_blk = i;
76 break;
77 }
78 i = (i + 1) % cache->entries;
79 }
80
81 if (n == cache->entries) {
82 /*
83 * Block not in cache, if all cache entries are used
84 * go to sleep waiting for one to become available.
85 */
86 if (cache->unused == 0) {
87 cache->num_waiters++;
88 spin_unlock(&cache->lock);
89 wait_event(cache->wait_queue, cache->unused);
90 spin_lock(&cache->lock);
91 cache->num_waiters--;
92 continue;
93 }
94
95 /*
96 * At least one unused cache entry. A simple
97 * round-robin strategy is used to choose the entry to
98 * be evicted from the cache.
99 */
100 i = cache->next_blk;
101 for (n = 0; n < cache->entries; n++) {
102 if (cache->entry[i].refcount == 0)
103 break;
104 i = (i + 1) % cache->entries;
105 }
106
107 cache->next_blk = (i + 1) % cache->entries;
108 entry = &cache->entry[i];
109
110 /*
111 * Initialise chosen cache entry, and fill it in from
112 * disk.
113 */
114 cache->unused--;
115 entry->block = block;
116 entry->refcount = 1;
117 entry->pending = 1;
118 entry->num_waiters = 0;
119 entry->error = 0;
120 spin_unlock(&cache->lock);
121
122 entry->length = squashfs_read_data(sb, entry->data,
123 block, length, &entry->next_index,
124 cache->block_size, cache->pages);
125
126 spin_lock(&cache->lock);
127
128 if (entry->length < 0)
129 entry->error = entry->length;
130
131 entry->pending = 0;
132
133 /*
134 * While filling this entry one or more other processes
135 * have looked it up in the cache, and have slept
136 * waiting for it to become available.
137 */
138 if (entry->num_waiters) {
139 spin_unlock(&cache->lock);
140 wake_up_all(&entry->wait_queue);
141 } else
142 spin_unlock(&cache->lock);
143
144 goto out;
145 }
146
147 /*
148 * Block already in cache. Increment refcount so it doesn't
149 * get reused until we're finished with it, if it was
150 * previously unused there's one less cache entry available
151 * for reuse.
152 */
153 entry = &cache->entry[i];
154 if (entry->refcount == 0)
155 cache->unused--;
156 entry->refcount++;
157
158 /*
159 * If the entry is currently being filled in by another process
160 * go to sleep waiting for it to become available.
161 */
162 if (entry->pending) {
163 entry->num_waiters++;
164 spin_unlock(&cache->lock);
165 wait_event(entry->wait_queue, !entry->pending);
166 } else
167 spin_unlock(&cache->lock);
168
169 goto out;
170 }
171
172 out:
173 TRACE("Got %s %d, start block %lld, refcount %d, error %d\n",
174 cache->name, i, entry->block, entry->refcount, entry->error);
175
176 if (entry->error)
177 ERROR("Unable to read %s cache entry [%llx]\n", cache->name,
178 block);
179 return entry;
180 }
181
182
183 /*
184 * Release cache entry, once usage count is zero it can be reused.
185 */
squashfs_cache_put(struct squashfs_cache_entry * entry)186 void squashfs_cache_put(struct squashfs_cache_entry *entry)
187 {
188 struct squashfs_cache *cache = entry->cache;
189
190 spin_lock(&cache->lock);
191 entry->refcount--;
192 if (entry->refcount == 0) {
193 cache->unused++;
194 /*
195 * If there's any processes waiting for a block to become
196 * available, wake one up.
197 */
198 if (cache->num_waiters) {
199 spin_unlock(&cache->lock);
200 wake_up(&cache->wait_queue);
201 return;
202 }
203 }
204 spin_unlock(&cache->lock);
205 }
206
207 /*
208 * Delete cache reclaiming all kmalloced buffers.
209 */
squashfs_cache_delete(struct squashfs_cache * cache)210 void squashfs_cache_delete(struct squashfs_cache *cache)
211 {
212 int i, j;
213
214 if (cache == NULL)
215 return;
216
217 for (i = 0; i < cache->entries; i++) {
218 if (cache->entry[i].data) {
219 for (j = 0; j < cache->pages; j++)
220 kfree(cache->entry[i].data[j]);
221 kfree(cache->entry[i].data);
222 }
223 }
224
225 kfree(cache->entry);
226 kfree(cache);
227 }
228
229
230 /*
231 * Initialise cache allocating the specified number of entries, each of
232 * size block_size. To avoid vmalloc fragmentation issues each entry
233 * is allocated as a sequence of kmalloced PAGE_CACHE_SIZE buffers.
234 */
squashfs_cache_init(char * name,int entries,int block_size)235 struct squashfs_cache *squashfs_cache_init(char *name, int entries,
236 int block_size)
237 {
238 int i, j;
239 struct squashfs_cache *cache = kzalloc(sizeof(*cache), GFP_KERNEL);
240
241 if (cache == NULL) {
242 ERROR("Failed to allocate %s cache\n", name);
243 return NULL;
244 }
245
246 cache->entry = kcalloc(entries, sizeof(*(cache->entry)), GFP_KERNEL);
247 if (cache->entry == NULL) {
248 ERROR("Failed to allocate %s cache\n", name);
249 goto cleanup;
250 }
251
252 cache->curr_blk = 0;
253 cache->next_blk = 0;
254 cache->unused = entries;
255 cache->entries = entries;
256 cache->block_size = block_size;
257 cache->pages = block_size >> PAGE_CACHE_SHIFT;
258 cache->pages = cache->pages ? cache->pages : 1;
259 cache->name = name;
260 cache->num_waiters = 0;
261 spin_lock_init(&cache->lock);
262 init_waitqueue_head(&cache->wait_queue);
263
264 for (i = 0; i < entries; i++) {
265 struct squashfs_cache_entry *entry = &cache->entry[i];
266
267 init_waitqueue_head(&cache->entry[i].wait_queue);
268 entry->cache = cache;
269 entry->block = SQUASHFS_INVALID_BLK;
270 entry->data = kcalloc(cache->pages, sizeof(void *), GFP_KERNEL);
271 if (entry->data == NULL) {
272 ERROR("Failed to allocate %s cache entry\n", name);
273 goto cleanup;
274 }
275
276 for (j = 0; j < cache->pages; j++) {
277 entry->data[j] = kmalloc(PAGE_CACHE_SIZE, GFP_KERNEL);
278 if (entry->data[j] == NULL) {
279 ERROR("Failed to allocate %s buffer\n", name);
280 goto cleanup;
281 }
282 }
283 }
284
285 return cache;
286
287 cleanup:
288 squashfs_cache_delete(cache);
289 return NULL;
290 }
291
292
293 /*
294 * Copy up to length bytes from cache entry to buffer starting at offset bytes
295 * into the cache entry. If there's not length bytes then copy the number of
296 * bytes available. In all cases return the number of bytes copied.
297 */
squashfs_copy_data(void * buffer,struct squashfs_cache_entry * entry,int offset,int length)298 int squashfs_copy_data(void *buffer, struct squashfs_cache_entry *entry,
299 int offset, int length)
300 {
301 int remaining = length;
302
303 if (length == 0)
304 return 0;
305 else if (buffer == NULL)
306 return min(length, entry->length - offset);
307
308 while (offset < entry->length) {
309 void *buff = entry->data[offset / PAGE_CACHE_SIZE]
310 + (offset % PAGE_CACHE_SIZE);
311 int bytes = min_t(int, entry->length - offset,
312 PAGE_CACHE_SIZE - (offset % PAGE_CACHE_SIZE));
313
314 if (bytes >= remaining) {
315 memcpy(buffer, buff, remaining);
316 remaining = 0;
317 break;
318 }
319
320 memcpy(buffer, buff, bytes);
321 buffer += bytes;
322 remaining -= bytes;
323 offset += bytes;
324 }
325
326 return length - remaining;
327 }
328
329
330 /*
331 * Read length bytes from metadata position <block, offset> (block is the
332 * start of the compressed block on disk, and offset is the offset into
333 * the block once decompressed). Data is packed into consecutive blocks,
334 * and length bytes may require reading more than one block.
335 */
squashfs_read_metadata(struct super_block * sb,void * buffer,u64 * block,int * offset,int length)336 int squashfs_read_metadata(struct super_block *sb, void *buffer,
337 u64 *block, int *offset, int length)
338 {
339 struct squashfs_sb_info *msblk = sb->s_fs_info;
340 int bytes, res = length;
341 struct squashfs_cache_entry *entry;
342
343 TRACE("Entered squashfs_read_metadata [%llx:%x]\n", *block, *offset);
344
345 while (length) {
346 entry = squashfs_cache_get(sb, msblk->block_cache, *block, 0);
347 if (entry->error) {
348 res = entry->error;
349 goto error;
350 } else if (*offset >= entry->length) {
351 res = -EIO;
352 goto error;
353 }
354
355 bytes = squashfs_copy_data(buffer, entry, *offset, length);
356 if (buffer)
357 buffer += bytes;
358 length -= bytes;
359 *offset += bytes;
360
361 if (*offset == entry->length) {
362 *block = entry->next_index;
363 *offset = 0;
364 }
365
366 squashfs_cache_put(entry);
367 }
368
369 return res;
370
371 error:
372 squashfs_cache_put(entry);
373 return res;
374 }
375
376
377 /*
378 * Look-up in the fragmment cache the fragment located at <start_block> in the
379 * filesystem. If necessary read and decompress it from disk.
380 */
squashfs_get_fragment(struct super_block * sb,u64 start_block,int length)381 struct squashfs_cache_entry *squashfs_get_fragment(struct super_block *sb,
382 u64 start_block, int length)
383 {
384 struct squashfs_sb_info *msblk = sb->s_fs_info;
385
386 return squashfs_cache_get(sb, msblk->fragment_cache, start_block,
387 length);
388 }
389
390
391 /*
392 * Read and decompress the datablock located at <start_block> in the
393 * filesystem. The cache is used here to avoid duplicating locking and
394 * read/decompress code.
395 */
squashfs_get_datablock(struct super_block * sb,u64 start_block,int length)396 struct squashfs_cache_entry *squashfs_get_datablock(struct super_block *sb,
397 u64 start_block, int length)
398 {
399 struct squashfs_sb_info *msblk = sb->s_fs_info;
400
401 return squashfs_cache_get(sb, msblk->read_page, start_block, length);
402 }
403
404
405 /*
406 * Read a filesystem table (uncompressed sequence of bytes) from disk
407 */
squashfs_read_table(struct super_block * sb,u64 block,int length)408 void *squashfs_read_table(struct super_block *sb, u64 block, int length)
409 {
410 int pages = (length + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
411 int i, res;
412 void *table, *buffer, **data;
413
414 table = buffer = kmalloc(length, GFP_KERNEL);
415 if (table == NULL)
416 return ERR_PTR(-ENOMEM);
417
418 data = kcalloc(pages, sizeof(void *), GFP_KERNEL);
419 if (data == NULL) {
420 res = -ENOMEM;
421 goto failed;
422 }
423
424 for (i = 0; i < pages; i++, buffer += PAGE_CACHE_SIZE)
425 data[i] = buffer;
426
427 res = squashfs_read_data(sb, data, block, length |
428 SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, length, pages);
429
430 kfree(data);
431
432 if (res < 0)
433 goto failed;
434
435 return table;
436
437 failed:
438 kfree(table);
439 return ERR_PTR(res);
440 }
441