xref: /openbmc/linux/fs/squashfs/cache.c (revision 81d67439)
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  */
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 = 0; i < cache->entries; i++)
74 			if (cache->entry[i].block == block)
75 				break;
76 
77 		if (i == cache->entries) {
78 			/*
79 			 * Block not in cache, if all cache entries are used
80 			 * go to sleep waiting for one to become available.
81 			 */
82 			if (cache->unused == 0) {
83 				cache->num_waiters++;
84 				spin_unlock(&cache->lock);
85 				wait_event(cache->wait_queue, cache->unused);
86 				spin_lock(&cache->lock);
87 				cache->num_waiters--;
88 				continue;
89 			}
90 
91 			/*
92 			 * At least one unused cache entry.  A simple
93 			 * round-robin strategy is used to choose the entry to
94 			 * be evicted from the cache.
95 			 */
96 			i = cache->next_blk;
97 			for (n = 0; n < cache->entries; n++) {
98 				if (cache->entry[i].refcount == 0)
99 					break;
100 				i = (i + 1) % cache->entries;
101 			}
102 
103 			cache->next_blk = (i + 1) % cache->entries;
104 			entry = &cache->entry[i];
105 
106 			/*
107 			 * Initialise chosen cache entry, and fill it in from
108 			 * disk.
109 			 */
110 			cache->unused--;
111 			entry->block = block;
112 			entry->refcount = 1;
113 			entry->pending = 1;
114 			entry->num_waiters = 0;
115 			entry->error = 0;
116 			spin_unlock(&cache->lock);
117 
118 			entry->length = squashfs_read_data(sb, entry->data,
119 				block, length, &entry->next_index,
120 				cache->block_size, cache->pages);
121 
122 			spin_lock(&cache->lock);
123 
124 			if (entry->length < 0)
125 				entry->error = entry->length;
126 
127 			entry->pending = 0;
128 
129 			/*
130 			 * While filling this entry one or more other processes
131 			 * have looked it up in the cache, and have slept
132 			 * waiting for it to become available.
133 			 */
134 			if (entry->num_waiters) {
135 				spin_unlock(&cache->lock);
136 				wake_up_all(&entry->wait_queue);
137 			} else
138 				spin_unlock(&cache->lock);
139 
140 			goto out;
141 		}
142 
143 		/*
144 		 * Block already in cache.  Increment refcount so it doesn't
145 		 * get reused until we're finished with it, if it was
146 		 * previously unused there's one less cache entry available
147 		 * for reuse.
148 		 */
149 		entry = &cache->entry[i];
150 		if (entry->refcount == 0)
151 			cache->unused--;
152 		entry->refcount++;
153 
154 		/*
155 		 * If the entry is currently being filled in by another process
156 		 * go to sleep waiting for it to become available.
157 		 */
158 		if (entry->pending) {
159 			entry->num_waiters++;
160 			spin_unlock(&cache->lock);
161 			wait_event(entry->wait_queue, !entry->pending);
162 		} else
163 			spin_unlock(&cache->lock);
164 
165 		goto out;
166 	}
167 
168 out:
169 	TRACE("Got %s %d, start block %lld, refcount %d, error %d\n",
170 		cache->name, i, entry->block, entry->refcount, entry->error);
171 
172 	if (entry->error)
173 		ERROR("Unable to read %s cache entry [%llx]\n", cache->name,
174 							block);
175 	return entry;
176 }
177 
178 
179 /*
180  * Release cache entry, once usage count is zero it can be reused.
181  */
182 void squashfs_cache_put(struct squashfs_cache_entry *entry)
183 {
184 	struct squashfs_cache *cache = entry->cache;
185 
186 	spin_lock(&cache->lock);
187 	entry->refcount--;
188 	if (entry->refcount == 0) {
189 		cache->unused++;
190 		/*
191 		 * If there's any processes waiting for a block to become
192 		 * available, wake one up.
193 		 */
194 		if (cache->num_waiters) {
195 			spin_unlock(&cache->lock);
196 			wake_up(&cache->wait_queue);
197 			return;
198 		}
199 	}
200 	spin_unlock(&cache->lock);
201 }
202 
203 /*
204  * Delete cache reclaiming all kmalloced buffers.
205  */
206 void squashfs_cache_delete(struct squashfs_cache *cache)
207 {
208 	int i, j;
209 
210 	if (cache == NULL)
211 		return;
212 
213 	for (i = 0; i < cache->entries; i++) {
214 		if (cache->entry[i].data) {
215 			for (j = 0; j < cache->pages; j++)
216 				kfree(cache->entry[i].data[j]);
217 			kfree(cache->entry[i].data);
218 		}
219 	}
220 
221 	kfree(cache->entry);
222 	kfree(cache);
223 }
224 
225 
226 /*
227  * Initialise cache allocating the specified number of entries, each of
228  * size block_size.  To avoid vmalloc fragmentation issues each entry
229  * is allocated as a sequence of kmalloced PAGE_CACHE_SIZE buffers.
230  */
231 struct squashfs_cache *squashfs_cache_init(char *name, int entries,
232 	int block_size)
233 {
234 	int i, j;
235 	struct squashfs_cache *cache = kzalloc(sizeof(*cache), GFP_KERNEL);
236 
237 	if (cache == NULL) {
238 		ERROR("Failed to allocate %s cache\n", name);
239 		return NULL;
240 	}
241 
242 	cache->entry = kcalloc(entries, sizeof(*(cache->entry)), GFP_KERNEL);
243 	if (cache->entry == NULL) {
244 		ERROR("Failed to allocate %s cache\n", name);
245 		goto cleanup;
246 	}
247 
248 	cache->next_blk = 0;
249 	cache->unused = entries;
250 	cache->entries = entries;
251 	cache->block_size = block_size;
252 	cache->pages = block_size >> PAGE_CACHE_SHIFT;
253 	cache->pages = cache->pages ? cache->pages : 1;
254 	cache->name = name;
255 	cache->num_waiters = 0;
256 	spin_lock_init(&cache->lock);
257 	init_waitqueue_head(&cache->wait_queue);
258 
259 	for (i = 0; i < entries; i++) {
260 		struct squashfs_cache_entry *entry = &cache->entry[i];
261 
262 		init_waitqueue_head(&cache->entry[i].wait_queue);
263 		entry->cache = cache;
264 		entry->block = SQUASHFS_INVALID_BLK;
265 		entry->data = kcalloc(cache->pages, sizeof(void *), GFP_KERNEL);
266 		if (entry->data == NULL) {
267 			ERROR("Failed to allocate %s cache entry\n", name);
268 			goto cleanup;
269 		}
270 
271 		for (j = 0; j < cache->pages; j++) {
272 			entry->data[j] = kmalloc(PAGE_CACHE_SIZE, GFP_KERNEL);
273 			if (entry->data[j] == NULL) {
274 				ERROR("Failed to allocate %s buffer\n", name);
275 				goto cleanup;
276 			}
277 		}
278 	}
279 
280 	return cache;
281 
282 cleanup:
283 	squashfs_cache_delete(cache);
284 	return NULL;
285 }
286 
287 
288 /*
289  * Copy up to length bytes from cache entry to buffer starting at offset bytes
290  * into the cache entry.  If there's not length bytes then copy the number of
291  * bytes available.  In all cases return the number of bytes copied.
292  */
293 int squashfs_copy_data(void *buffer, struct squashfs_cache_entry *entry,
294 		int offset, int length)
295 {
296 	int remaining = length;
297 
298 	if (length == 0)
299 		return 0;
300 	else if (buffer == NULL)
301 		return min(length, entry->length - offset);
302 
303 	while (offset < entry->length) {
304 		void *buff = entry->data[offset / PAGE_CACHE_SIZE]
305 				+ (offset % PAGE_CACHE_SIZE);
306 		int bytes = min_t(int, entry->length - offset,
307 				PAGE_CACHE_SIZE - (offset % PAGE_CACHE_SIZE));
308 
309 		if (bytes >= remaining) {
310 			memcpy(buffer, buff, remaining);
311 			remaining = 0;
312 			break;
313 		}
314 
315 		memcpy(buffer, buff, bytes);
316 		buffer += bytes;
317 		remaining -= bytes;
318 		offset += bytes;
319 	}
320 
321 	return length - remaining;
322 }
323 
324 
325 /*
326  * Read length bytes from metadata position <block, offset> (block is the
327  * start of the compressed block on disk, and offset is the offset into
328  * the block once decompressed).  Data is packed into consecutive blocks,
329  * and length bytes may require reading more than one block.
330  */
331 int squashfs_read_metadata(struct super_block *sb, void *buffer,
332 		u64 *block, int *offset, int length)
333 {
334 	struct squashfs_sb_info *msblk = sb->s_fs_info;
335 	int bytes, copied = length;
336 	struct squashfs_cache_entry *entry;
337 
338 	TRACE("Entered squashfs_read_metadata [%llx:%x]\n", *block, *offset);
339 
340 	while (length) {
341 		entry = squashfs_cache_get(sb, msblk->block_cache, *block, 0);
342 		if (entry->error)
343 			return entry->error;
344 		else if (*offset >= entry->length)
345 			return -EIO;
346 
347 		bytes = squashfs_copy_data(buffer, entry, *offset, length);
348 		if (buffer)
349 			buffer += bytes;
350 		length -= bytes;
351 		*offset += bytes;
352 
353 		if (*offset == entry->length) {
354 			*block = entry->next_index;
355 			*offset = 0;
356 		}
357 
358 		squashfs_cache_put(entry);
359 	}
360 
361 	return copied;
362 }
363 
364 
365 /*
366  * Look-up in the fragmment cache the fragment located at <start_block> in the
367  * filesystem.  If necessary read and decompress it from disk.
368  */
369 struct squashfs_cache_entry *squashfs_get_fragment(struct super_block *sb,
370 				u64 start_block, int length)
371 {
372 	struct squashfs_sb_info *msblk = sb->s_fs_info;
373 
374 	return squashfs_cache_get(sb, msblk->fragment_cache, start_block,
375 		length);
376 }
377 
378 
379 /*
380  * Read and decompress the datablock located at <start_block> in the
381  * filesystem.  The cache is used here to avoid duplicating locking and
382  * read/decompress code.
383  */
384 struct squashfs_cache_entry *squashfs_get_datablock(struct super_block *sb,
385 				u64 start_block, int length)
386 {
387 	struct squashfs_sb_info *msblk = sb->s_fs_info;
388 
389 	return squashfs_cache_get(sb, msblk->read_page, start_block, length);
390 }
391 
392 
393 /*
394  * Read a filesystem table (uncompressed sequence of bytes) from disk
395  */
396 void *squashfs_read_table(struct super_block *sb, u64 block, int length)
397 {
398 	int pages = (length + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
399 	int i, res;
400 	void *table, *buffer, **data;
401 
402 	table = buffer = kmalloc(length, GFP_KERNEL);
403 	if (table == NULL)
404 		return ERR_PTR(-ENOMEM);
405 
406 	data = kcalloc(pages, sizeof(void *), GFP_KERNEL);
407 	if (data == NULL) {
408 		res = -ENOMEM;
409 		goto failed;
410 	}
411 
412 	for (i = 0; i < pages; i++, buffer += PAGE_CACHE_SIZE)
413 		data[i] = buffer;
414 
415 	res = squashfs_read_data(sb, data, block, length |
416 		SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, length, pages);
417 
418 	kfree(data);
419 
420 	if (res < 0)
421 		goto failed;
422 
423 	return table;
424 
425 failed:
426 	kfree(table);
427 	return ERR_PTR(res);
428 }
429