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_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 #include "page_actor.h"
60 
61 /*
62  * Look-up block in cache, and increment usage count.  If not in cache, read
63  * and decompress it from disk.
64  */
squashfs_cache_get(struct super_block * sb,struct squashfs_cache * cache,u64 block,int length)65 struct squashfs_cache_entry *squashfs_cache_get(struct super_block *sb,
66 	struct squashfs_cache *cache, u64 block, int length)
67 {
68 	int i, n;
69 	struct squashfs_cache_entry *entry;
70 
71 	spin_lock(&cache->lock);
72 
73 	while (1) {
74 		for (i = cache->curr_blk, n = 0; n < cache->entries; n++) {
75 			if (cache->entry[i].block == block) {
76 				cache->curr_blk = i;
77 				break;
78 			}
79 			i = (i + 1) % cache->entries;
80 		}
81 
82 		if (n == cache->entries) {
83 			/*
84 			 * Block not in cache, if all cache entries are used
85 			 * go to sleep waiting for one to become available.
86 			 */
87 			if (cache->unused == 0) {
88 				cache->num_waiters++;
89 				spin_unlock(&cache->lock);
90 				wait_event(cache->wait_queue, cache->unused);
91 				spin_lock(&cache->lock);
92 				cache->num_waiters--;
93 				continue;
94 			}
95 
96 			/*
97 			 * At least one unused cache entry.  A simple
98 			 * round-robin strategy is used to choose the entry to
99 			 * be evicted from the cache.
100 			 */
101 			i = cache->next_blk;
102 			for (n = 0; n < cache->entries; n++) {
103 				if (cache->entry[i].refcount == 0)
104 					break;
105 				i = (i + 1) % cache->entries;
106 			}
107 
108 			cache->next_blk = (i + 1) % cache->entries;
109 			entry = &cache->entry[i];
110 
111 			/*
112 			 * Initialise chosen cache entry, and fill it in from
113 			 * disk.
114 			 */
115 			cache->unused--;
116 			entry->block = block;
117 			entry->refcount = 1;
118 			entry->pending = 1;
119 			entry->num_waiters = 0;
120 			entry->error = 0;
121 			spin_unlock(&cache->lock);
122 
123 			entry->length = squashfs_read_data(sb, block, length,
124 				&entry->next_index, entry->actor);
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 		kfree(cache->entry[i].actor);
224 	}
225 
226 	kfree(cache->entry);
227 	kfree(cache);
228 }
229 
230 
231 /*
232  * Initialise cache allocating the specified number of entries, each of
233  * size block_size.  To avoid vmalloc fragmentation issues each entry
234  * is allocated as a sequence of kmalloced PAGE_SIZE buffers.
235  */
squashfs_cache_init(char * name,int entries,int block_size)236 struct squashfs_cache *squashfs_cache_init(char *name, int entries,
237 	int block_size)
238 {
239 	int i, j;
240 	struct squashfs_cache *cache = kzalloc(sizeof(*cache), GFP_KERNEL);
241 
242 	if (cache == NULL) {
243 		ERROR("Failed to allocate %s cache\n", name);
244 		return NULL;
245 	}
246 
247 	cache->entry = kcalloc(entries, sizeof(*(cache->entry)), GFP_KERNEL);
248 	if (cache->entry == NULL) {
249 		ERROR("Failed to allocate %s cache\n", name);
250 		goto cleanup;
251 	}
252 
253 	cache->curr_blk = 0;
254 	cache->next_blk = 0;
255 	cache->unused = entries;
256 	cache->entries = entries;
257 	cache->block_size = block_size;
258 	cache->pages = block_size >> PAGE_SHIFT;
259 	cache->pages = cache->pages ? cache->pages : 1;
260 	cache->name = name;
261 	cache->num_waiters = 0;
262 	spin_lock_init(&cache->lock);
263 	init_waitqueue_head(&cache->wait_queue);
264 
265 	for (i = 0; i < entries; i++) {
266 		struct squashfs_cache_entry *entry = &cache->entry[i];
267 
268 		init_waitqueue_head(&cache->entry[i].wait_queue);
269 		entry->cache = cache;
270 		entry->block = SQUASHFS_INVALID_BLK;
271 		entry->data = kcalloc(cache->pages, sizeof(void *), GFP_KERNEL);
272 		if (entry->data == NULL) {
273 			ERROR("Failed to allocate %s cache entry\n", name);
274 			goto cleanup;
275 		}
276 
277 		for (j = 0; j < cache->pages; j++) {
278 			entry->data[j] = kmalloc(PAGE_SIZE, GFP_KERNEL);
279 			if (entry->data[j] == NULL) {
280 				ERROR("Failed to allocate %s buffer\n", name);
281 				goto cleanup;
282 			}
283 		}
284 
285 		entry->actor = squashfs_page_actor_init(entry->data,
286 						cache->pages, 0);
287 		if (entry->actor == NULL) {
288 			ERROR("Failed to allocate %s cache entry\n", name);
289 			goto cleanup;
290 		}
291 	}
292 
293 	return cache;
294 
295 cleanup:
296 	squashfs_cache_delete(cache);
297 	return NULL;
298 }
299 
300 
301 /*
302  * Copy up to length bytes from cache entry to buffer starting at offset bytes
303  * into the cache entry.  If there's not length bytes then copy the number of
304  * bytes available.  In all cases return the number of bytes copied.
305  */
squashfs_copy_data(void * buffer,struct squashfs_cache_entry * entry,int offset,int length)306 int squashfs_copy_data(void *buffer, struct squashfs_cache_entry *entry,
307 		int offset, int length)
308 {
309 	int remaining = length;
310 
311 	if (length == 0)
312 		return 0;
313 	else if (buffer == NULL)
314 		return min(length, entry->length - offset);
315 
316 	while (offset < entry->length) {
317 		void *buff = entry->data[offset / PAGE_SIZE]
318 				+ (offset % PAGE_SIZE);
319 		int bytes = min_t(int, entry->length - offset,
320 				PAGE_SIZE - (offset % PAGE_SIZE));
321 
322 		if (bytes >= remaining) {
323 			memcpy(buffer, buff, remaining);
324 			remaining = 0;
325 			break;
326 		}
327 
328 		memcpy(buffer, buff, bytes);
329 		buffer += bytes;
330 		remaining -= bytes;
331 		offset += bytes;
332 	}
333 
334 	return length - remaining;
335 }
336 
337 
338 /*
339  * Read length bytes from metadata position <block, offset> (block is the
340  * start of the compressed block on disk, and offset is the offset into
341  * the block once decompressed).  Data is packed into consecutive blocks,
342  * and length bytes may require reading more than one block.
343  */
squashfs_read_metadata(struct super_block * sb,void * buffer,u64 * block,int * offset,int length)344 int squashfs_read_metadata(struct super_block *sb, void *buffer,
345 		u64 *block, int *offset, int length)
346 {
347 	struct squashfs_sb_info *msblk = sb->s_fs_info;
348 	int bytes, res = length;
349 	struct squashfs_cache_entry *entry;
350 
351 	TRACE("Entered squashfs_read_metadata [%llx:%x]\n", *block, *offset);
352 
353 	if (unlikely(length < 0))
354 		return -EIO;
355 
356 	while (length) {
357 		entry = squashfs_cache_get(sb, msblk->block_cache, *block, 0);
358 		if (entry->error) {
359 			res = entry->error;
360 			goto error;
361 		} else if (*offset >= entry->length) {
362 			res = -EIO;
363 			goto error;
364 		}
365 
366 		bytes = squashfs_copy_data(buffer, entry, *offset, length);
367 		if (buffer)
368 			buffer += bytes;
369 		length -= bytes;
370 		*offset += bytes;
371 
372 		if (*offset == entry->length) {
373 			*block = entry->next_index;
374 			*offset = 0;
375 		}
376 
377 		squashfs_cache_put(entry);
378 	}
379 
380 	return res;
381 
382 error:
383 	squashfs_cache_put(entry);
384 	return res;
385 }
386 
387 
388 /*
389  * Look-up in the fragmment cache the fragment located at <start_block> in the
390  * filesystem.  If necessary read and decompress it from disk.
391  */
squashfs_get_fragment(struct super_block * sb,u64 start_block,int length)392 struct squashfs_cache_entry *squashfs_get_fragment(struct super_block *sb,
393 				u64 start_block, int length)
394 {
395 	struct squashfs_sb_info *msblk = sb->s_fs_info;
396 
397 	return squashfs_cache_get(sb, msblk->fragment_cache, start_block,
398 		length);
399 }
400 
401 
402 /*
403  * Read and decompress the datablock located at <start_block> in the
404  * filesystem.  The cache is used here to avoid duplicating locking and
405  * read/decompress code.
406  */
squashfs_get_datablock(struct super_block * sb,u64 start_block,int length)407 struct squashfs_cache_entry *squashfs_get_datablock(struct super_block *sb,
408 				u64 start_block, int length)
409 {
410 	struct squashfs_sb_info *msblk = sb->s_fs_info;
411 
412 	return squashfs_cache_get(sb, msblk->read_page, start_block, length);
413 }
414 
415 
416 /*
417  * Read a filesystem table (uncompressed sequence of bytes) from disk
418  */
squashfs_read_table(struct super_block * sb,u64 block,int length)419 void *squashfs_read_table(struct super_block *sb, u64 block, int length)
420 {
421 	int pages = (length + PAGE_SIZE - 1) >> PAGE_SHIFT;
422 	int i, res;
423 	void *table, *buffer, **data;
424 	struct squashfs_page_actor *actor;
425 
426 	table = buffer = kmalloc(length, GFP_KERNEL);
427 	if (table == NULL)
428 		return ERR_PTR(-ENOMEM);
429 
430 	data = kcalloc(pages, sizeof(void *), GFP_KERNEL);
431 	if (data == NULL) {
432 		res = -ENOMEM;
433 		goto failed;
434 	}
435 
436 	actor = squashfs_page_actor_init(data, pages, length);
437 	if (actor == NULL) {
438 		res = -ENOMEM;
439 		goto failed2;
440 	}
441 
442 	for (i = 0; i < pages; i++, buffer += PAGE_SIZE)
443 		data[i] = buffer;
444 
445 	res = squashfs_read_data(sb, block, length |
446 		SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, actor);
447 
448 	kfree(data);
449 	kfree(actor);
450 
451 	if (res < 0)
452 		goto failed;
453 
454 	return table;
455 
456 failed2:
457 	kfree(data);
458 failed:
459 	kfree(table);
460 	return ERR_PTR(res);
461 }
462