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@lougher.demon.co.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 isssues 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/zlib.h>
55 #include <linux/pagemap.h>
56
57 #include "squashfs_fs.h"
58 #include "squashfs_fs_sb.h"
59 #include "squashfs_fs_i.h"
60 #include "squashfs.h"
61
62 /*
63 * Look-up block in cache, and increment usage count. If not in cache, read
64 * and decompress it from disk.
65 */
squashfs_cache_get(struct super_block * sb,struct squashfs_cache * cache,u64 block,int length)66 struct squashfs_cache_entry *squashfs_cache_get(struct super_block *sb,
67 struct squashfs_cache *cache, u64 block, int length)
68 {
69 int i, n;
70 struct squashfs_cache_entry *entry;
71
72 spin_lock(&cache->lock);
73
74 while (1) {
75 for (i = 0; i < cache->entries; i++)
76 if (cache->entry[i].block == block)
77 break;
78
79 if (i == cache->entries) {
80 /*
81 * Block not in cache, if all cache entries are used
82 * go to sleep waiting for one to become available.
83 */
84 if (cache->unused == 0) {
85 cache->num_waiters++;
86 spin_unlock(&cache->lock);
87 wait_event(cache->wait_queue, cache->unused);
88 spin_lock(&cache->lock);
89 cache->num_waiters--;
90 continue;
91 }
92
93 /*
94 * At least one unused cache entry. A simple
95 * round-robin strategy is used to choose the entry to
96 * be evicted from the cache.
97 */
98 i = cache->next_blk;
99 for (n = 0; n < cache->entries; n++) {
100 if (cache->entry[i].refcount == 0)
101 break;
102 i = (i + 1) % cache->entries;
103 }
104
105 cache->next_blk = (i + 1) % cache->entries;
106 entry = &cache->entry[i];
107
108 /*
109 * Initialise choosen cache entry, and fill it in from
110 * disk.
111 */
112 cache->unused--;
113 entry->block = block;
114 entry->refcount = 1;
115 entry->pending = 1;
116 entry->num_waiters = 0;
117 entry->error = 0;
118 spin_unlock(&cache->lock);
119
120 entry->length = squashfs_read_data(sb, entry->data,
121 block, length, &entry->next_index,
122 cache->block_size);
123
124 spin_lock(&cache->lock);
125
126 if (entry->length < 0)
127 entry->error = entry->length;
128
129 entry->pending = 0;
130
131 /*
132 * While filling this entry one or more other processes
133 * have looked it up in the cache, and have slept
134 * waiting for it to become available.
135 */
136 if (entry->num_waiters) {
137 spin_unlock(&cache->lock);
138 wake_up_all(&entry->wait_queue);
139 } else
140 spin_unlock(&cache->lock);
141
142 goto out;
143 }
144
145 /*
146 * Block already in cache. Increment refcount so it doesn't
147 * get reused until we're finished with it, if it was
148 * previously unused there's one less cache entry available
149 * for reuse.
150 */
151 entry = &cache->entry[i];
152 if (entry->refcount == 0)
153 cache->unused--;
154 entry->refcount++;
155
156 /*
157 * If the entry is currently being filled in by another process
158 * go to sleep waiting for it to become available.
159 */
160 if (entry->pending) {
161 entry->num_waiters++;
162 spin_unlock(&cache->lock);
163 wait_event(entry->wait_queue, !entry->pending);
164 } else
165 spin_unlock(&cache->lock);
166
167 goto out;
168 }
169
170 out:
171 TRACE("Got %s %d, start block %lld, refcount %d, error %d\n",
172 cache->name, i, entry->block, entry->refcount, entry->error);
173
174 if (entry->error)
175 ERROR("Unable to read %s cache entry [%llx]\n", cache->name,
176 block);
177 return entry;
178 }
179
180
181 /*
182 * Release cache entry, once usage count is zero it can be reused.
183 */
squashfs_cache_put(struct squashfs_cache_entry * entry)184 void squashfs_cache_put(struct squashfs_cache_entry *entry)
185 {
186 struct squashfs_cache *cache = entry->cache;
187
188 spin_lock(&cache->lock);
189 entry->refcount--;
190 if (entry->refcount == 0) {
191 cache->unused++;
192 /*
193 * If there's any processes waiting for a block to become
194 * available, wake one up.
195 */
196 if (cache->num_waiters) {
197 spin_unlock(&cache->lock);
198 wake_up(&cache->wait_queue);
199 return;
200 }
201 }
202 spin_unlock(&cache->lock);
203 }
204
205 /*
206 * Delete cache reclaiming all kmalloced buffers.
207 */
squashfs_cache_delete(struct squashfs_cache * cache)208 void squashfs_cache_delete(struct squashfs_cache *cache)
209 {
210 int i, j;
211
212 if (cache == NULL)
213 return;
214
215 for (i = 0; i < cache->entries; i++) {
216 if (cache->entry[i].data) {
217 for (j = 0; j < cache->pages; j++)
218 kfree(cache->entry[i].data[j]);
219 kfree(cache->entry[i].data);
220 }
221 }
222
223 kfree(cache->entry);
224 kfree(cache);
225 }
226
227
228 /*
229 * Initialise cache allocating the specified number of entries, each of
230 * size block_size. To avoid vmalloc fragmentation issues each entry
231 * is allocated as a sequence of kmalloced PAGE_CACHE_SIZE buffers.
232 */
squashfs_cache_init(char * name,int entries,int block_size)233 struct squashfs_cache *squashfs_cache_init(char *name, int entries,
234 int block_size)
235 {
236 int i, j;
237 struct squashfs_cache *cache = kzalloc(sizeof(*cache), GFP_KERNEL);
238
239 if (cache == NULL) {
240 ERROR("Failed to allocate %s cache\n", name);
241 return NULL;
242 }
243
244 cache->entry = kcalloc(entries, sizeof(*(cache->entry)), GFP_KERNEL);
245 if (cache->entry == NULL) {
246 ERROR("Failed to allocate %s cache\n", name);
247 goto cleanup;
248 }
249
250 cache->next_blk = 0;
251 cache->unused = entries;
252 cache->entries = entries;
253 cache->block_size = block_size;
254 cache->pages = block_size >> PAGE_CACHE_SHIFT;
255 cache->name = name;
256 cache->num_waiters = 0;
257 spin_lock_init(&cache->lock);
258 init_waitqueue_head(&cache->wait_queue);
259
260 for (i = 0; i < entries; i++) {
261 struct squashfs_cache_entry *entry = &cache->entry[i];
262
263 init_waitqueue_head(&cache->entry[i].wait_queue);
264 entry->cache = cache;
265 entry->block = SQUASHFS_INVALID_BLK;
266 entry->data = kcalloc(cache->pages, sizeof(void *), GFP_KERNEL);
267 if (entry->data == NULL) {
268 ERROR("Failed to allocate %s cache entry\n", name);
269 goto cleanup;
270 }
271
272 for (j = 0; j < cache->pages; j++) {
273 entry->data[j] = kmalloc(PAGE_CACHE_SIZE, GFP_KERNEL);
274 if (entry->data[j] == NULL) {
275 ERROR("Failed to allocate %s buffer\n", name);
276 goto cleanup;
277 }
278 }
279 }
280
281 return cache;
282
283 cleanup:
284 squashfs_cache_delete(cache);
285 return NULL;
286 }
287
288
289 /*
290 * Copy upto length bytes from cache entry to buffer starting at offset bytes
291 * into the cache entry. If there's not length bytes then copy the number of
292 * bytes available. In all cases return the number of bytes copied.
293 */
squashfs_copy_data(void * buffer,struct squashfs_cache_entry * entry,int offset,int length)294 int squashfs_copy_data(void *buffer, struct squashfs_cache_entry *entry,
295 int offset, int length)
296 {
297 int remaining = length;
298
299 if (length == 0)
300 return 0;
301 else if (buffer == NULL)
302 return min(length, entry->length - offset);
303
304 while (offset < entry->length) {
305 void *buff = entry->data[offset / PAGE_CACHE_SIZE]
306 + (offset % PAGE_CACHE_SIZE);
307 int bytes = min_t(int, entry->length - offset,
308 PAGE_CACHE_SIZE - (offset % PAGE_CACHE_SIZE));
309
310 if (bytes >= remaining) {
311 memcpy(buffer, buff, remaining);
312 remaining = 0;
313 break;
314 }
315
316 memcpy(buffer, buff, bytes);
317 buffer += bytes;
318 remaining -= bytes;
319 offset += bytes;
320 }
321
322 return length - remaining;
323 }
324
325
326 /*
327 * Read length bytes from metadata position <block, offset> (block is the
328 * start of the compressed block on disk, and offset is the offset into
329 * the block once decompressed). Data is packed into consecutive blocks,
330 * and length bytes may require reading more than one block.
331 */
squashfs_read_metadata(struct super_block * sb,void * buffer,u64 * block,int * offset,int length)332 int squashfs_read_metadata(struct super_block *sb, void *buffer,
333 u64 *block, int *offset, int length)
334 {
335 struct squashfs_sb_info *msblk = sb->s_fs_info;
336 int bytes, copied = length;
337 struct squashfs_cache_entry *entry;
338
339 TRACE("Entered squashfs_read_metadata [%llx:%x]\n", *block, *offset);
340
341 while (length) {
342 entry = squashfs_cache_get(sb, msblk->block_cache, *block, 0);
343 if (entry->error)
344 return entry->error;
345 else if (*offset >= entry->length)
346 return -EIO;
347
348 bytes = squashfs_copy_data(buffer, entry, *offset, length);
349 if (buffer)
350 buffer += bytes;
351 length -= bytes;
352 *offset += bytes;
353
354 if (*offset == entry->length) {
355 *block = entry->next_index;
356 *offset = 0;
357 }
358
359 squashfs_cache_put(entry);
360 }
361
362 return copied;
363 }
364
365
366 /*
367 * Look-up in the fragmment cache the fragment located at <start_block> in the
368 * filesystem. If necessary read and decompress it from disk.
369 */
squashfs_get_fragment(struct super_block * sb,u64 start_block,int length)370 struct squashfs_cache_entry *squashfs_get_fragment(struct super_block *sb,
371 u64 start_block, int length)
372 {
373 struct squashfs_sb_info *msblk = sb->s_fs_info;
374
375 return squashfs_cache_get(sb, msblk->fragment_cache, start_block,
376 length);
377 }
378
379
380 /*
381 * Read and decompress the datablock located at <start_block> in the
382 * filesystem. The cache is used here to avoid duplicating locking and
383 * read/decompress code.
384 */
squashfs_get_datablock(struct super_block * sb,u64 start_block,int length)385 struct squashfs_cache_entry *squashfs_get_datablock(struct super_block *sb,
386 u64 start_block, int length)
387 {
388 struct squashfs_sb_info *msblk = sb->s_fs_info;
389
390 return squashfs_cache_get(sb, msblk->read_page, start_block, length);
391 }
392
393
394 /*
395 * Read a filesystem table (uncompressed sequence of bytes) from disk
396 */
squashfs_read_table(struct super_block * sb,void * buffer,u64 block,int length)397 int squashfs_read_table(struct super_block *sb, void *buffer, u64 block,
398 int length)
399 {
400 int pages = (length + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
401 int i, res;
402 void **data = kcalloc(pages, sizeof(void *), GFP_KERNEL);
403 if (data == NULL)
404 return -ENOMEM;
405
406 for (i = 0; i < pages; i++, buffer += PAGE_CACHE_SIZE)
407 data[i] = buffer;
408 res = squashfs_read_data(sb, data, block, length |
409 SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, length);
410 kfree(data);
411 return res;
412 }
413