aboutsummaryrefslogtreecommitdiffstats
path: root/fs/squashfs/cache.c
blob: f744be98cd5abc8dd6d93cf4a699981491f8e811 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
/*
 * Squashfs - a compressed read only filesystem for Linux
 *
 * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
 * Phillip Lougher <phillip@squashfs.org.uk>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2,
 * or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * cache.c
 */

/*
 * Blocks in Squashfs are compressed.  To avoid repeatedly decompressing
 * recently accessed data Squashfs uses two small metadata and fragment caches.
 *
 * This file implements a generic cache implementation used for both caches,
 * plus functions layered ontop of the generic cache implementation to
 * access the metadata and fragment caches.
 *
 * To avoid out of memory and fragmentation issues with vmalloc the cache
 * uses sequences of kmalloced PAGE_CACHE_SIZE buffers.
 *
 * It should be noted that the cache is not used for file datablocks, these
 * are decompressed and cached in the page-cache in the normal way.  The
 * cache is only used to temporarily cache fragment and metadata blocks
 * which have been read as as a result of a metadata (i.e. inode or
 * directory) or fragment access.  Because metadata and fragments are packed
 * together into blocks (to gain greater compression) the read of a particular
 * piece of metadata or fragment will retrieve other metadata/fragments which
 * have been packed with it, these because of locality-of-reference may be read
 * in the near future. Temporarily caching them ensures they are available for
 * near future access without requiring an additional read and decompress.
 */

#include <linux/fs.h>
#include <linux/vfs.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/sched.h>
#include <linux/spinlock.h>
#include <linux/wait.h>
#include <linux/pagemap.h>

#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
#include "squashfs.h"

/*
 * Look-up block in cache, and increment usage count.  If not in cache, read
 * and decompress it from disk.
 */
struct squashfs_cache_entry *squashfs_cache_get(struct super_block *sb,
	struct squashfs_cache *cache, u64 block, int length)
{
	int i, n;
	struct squashfs_cache_entry *entry;

	spin_lock(&cache->lock);

	while (1) {
		for (i = 0; i < cache->entries; i++)
			if (cache->entry[i].block == block)
				break;

		if (i == cache->entries) {
			/*
			 * Block not in cache, if all cache entries are used
			 * go to sleep waiting for one to become available.
			 */
			if (cache->unused == 0) {
				cache->num_waiters++;
				spin_unlock(&cache->lock);
				wait_event(cache->wait_queue, cache->unused);
				spin_lock(&cache->lock);
				cache->num_waiters--;
				continue;
			}

			/*
			 * At least one unused cache entry.  A simple
			 * round-robin strategy is used to choose the entry to
			 * be evicted from the cache.
			 */
			i = cache->next_blk;
			for (n = 0; n < cache->entries; n++) {
				if (cache->entry[i].refcount == 0)
					break;
				i = (i + 1) % cache->entries;
			}

			cache->next_blk = (i + 1) % cache->entries;
			entry = &cache->entry[i];

			/*
			 * Initialise chosen cache entry, and fill it in from
			 * disk.
			 */
			cache->unused--;
			entry->block = block;
			entry->refcount = 1;
			entry->pending = 1;
			entry->num_waiters = 0;
			entry->error = 0;
			spin_unlock(&cache->lock);

			entry->length = squashfs_read_data(sb, entry->data,
				block, length, &entry->next_index,
				cache->block_size, cache->pages);

			spin_lock(&cache->lock);

			if (entry->length < 0)
				entry->error = entry->length;

			entry->pending = 0;

			/*
			 * While filling this entry one or more other processes
			 * have looked it up in the cache, and have slept
			 * waiting for it to become available.
			 */
			if (entry->num_waiters) {
				spin_unlock(&cache->lock);
				wake_up_all(&entry->wait_queue);
			} else
				spin_unlock(&cache->lock);

			goto out;
		}

		/*
		 * Block already in cache.  Increment refcount so it doesn't
		 * get reused until we're finished with it, if it was
		 * previously unused there's one less cache entry available
		 * for reuse.
		 */
		entry = &cache->entry[i];
		if (entry->refcount == 0)
			cache->unused--;
		entry->refcount++;

		/*
		 * If the entry is currently being filled in by another process
		 * go to sleep waiting for it to become available.
		 */
		if (entry->pending) {
			entry->num_waiters++;
			spin_unlock(&cache->lock);
			wait_event(entry->wait_queue, !entry->pending);
		} else
			spin_unlock(&cache->lock);

		goto out;
	}

out:
	TRACE("Got %s %d, start block %lld, refcount %d, error %d\n",
		cache->name, i, entry->block, entry->refcount, entry->error);

	if (entry->error)
		ERROR("Unable to read %s cache entry [%llx]\n", cache->name,
							block);
	return entry;
}


/*
 * Release cache entry, once usage count is zero it can be reused.
 */
void squashfs_cache_put(struct squashfs_cache_entry *entry)
{
	struct squashfs_cache *cache = entry->cache;

	spin_lock(&cache->lock);
	entry->refcount--;
	if (entry->refcount == 0) {
		cache->unused++;
		/*
		 * If there's any processes waiting for a block to become
		 * available, wake one up.
		 */
		if (cache->num_waiters) {
			spin_unlock(&cache->lock);
			wake_up(&cache->wait_queue);
			return;
		}
	}
	spin_unlock(&cache->lock);
}

/*
 * Delete cache reclaiming all kmalloced buffers.
 */
void squashfs_cache_delete(struct squashfs_cache *cache)
{
	int i, j;

	if (cache == NULL)
		return;

	for (i = 0; i < cache->entries; i++) {
		if (cache->entry[i].data) {
			for (j = 0; j < cache->pages; j++)
				kfree(cache->entry[i].data[j]);
			kfree(cache->entry[i].data);
		}
	}

	kfree(cache->entry);
	kfree(cache);
}


/*
 * Initialise cache allocating the specified number of entries, each of
 * size block_size.  To avoid vmalloc fragmentation issues each entry
 * is allocated as a sequence of kmalloced PAGE_CACHE_SIZE buffers.
 */
struct squashfs_cache *squashfs_cache_init(char *name, int entries,
	int block_size)
{
	int i, j;
	struct squashfs_cache *cache = kzalloc(sizeof(*cache), GFP_KERNEL);

	if (cache == NULL) {
		ERROR("Failed to allocate %s cache\n", name);
		return NULL;
	}

	cache->entry = kcalloc(entries, sizeof(*(cache->entry)), GFP_KERNEL);
	if (cache->entry == NULL) {
		ERROR("Failed to allocate %s cache\n", name);
		goto cleanup;
	}

	cache->next_blk = 0;
	cache->unused = entries;
	cache->entries = entries;
	cache->block_size = block_size;
	cache->pages = block_size >> PAGE_CACHE_SHIFT;
	cache->pages = cache->pages ? cache->pages : 1;
	cache->name = name;
	cache->num_waiters = 0;
	spin_lock_init(&cache->lock);
	init_waitqueue_head(&cache->wait_queue);

	for (i = 0; i < entries; i++) {
		struct squashfs_cache_entry *entry = &cache->entry[i];

		init_waitqueue_head(&cache->entry[i].wait_queue);
		entry->cache = cache;
		entry->block = SQUASHFS_INVALID_BLK;
		entry->data = kcalloc(cache->pages, sizeof(void *), GFP_KERNEL);
		if (entry->data == NULL) {
			ERROR("Failed to allocate %s cache entry\n", name);
			goto cleanup;
		}

		for (j = 0; j < cache->pages; j++) {
			entry->data[j] = kmalloc(PAGE_CACHE_SIZE, GFP_KERNEL);
			if (entry->data[j] == NULL) {
				ERROR("Failed to allocate %s buffer\n", name);
				goto cleanup;
			}
		}
	}

	return cache;

cleanup:
	squashfs_cache_delete(cache);
	return NULL;
}


/*
 * Copy up to length bytes from cache entry to buffer starting at offset bytes
 * into the cache entry.  If there's not length bytes then copy the number of
 * bytes available.  In all cases return the number of bytes copied.
 */
int squashfs_copy_data(void *buffer, struct squashfs_cache_entry *entry,
		int offset, int length)
{
	int remaining = length;

	if (length == 0)
		return 0;
	else if (buffer == NULL)
		return min(length, entry->length - offset);

	while (offset < entry->length) {
		void *buff = entry->data[offset / PAGE_CACHE_SIZE]
				+ (offset % PAGE_CACHE_SIZE);
		int bytes = min_t(int, entry->length - offset,
				PAGE_CACHE_SIZE - (offset % PAGE_CACHE_SIZE));

		if (bytes >= remaining) {
			memcpy(buffer, buff, remaining);
			remaining = 0;
			break;
		}

		memcpy(buffer, buff, bytes);
		buffer += bytes;
		remaining -= bytes;
		offset += bytes;
	}

	return length - remaining;
}


/*
 * Read length bytes from metadata position <block, offset> (block is the
 * start of the compressed block on disk, and offset is the offset into
 * the block once decompressed).  Data is packed into consecutive blocks,
 * and length bytes may require reading more than one block.
 */
int squashfs_read_metadata(struct super_block *sb, void *buffer,
		u64 *block, int *offset, int length)
{
	struct squashfs_sb_info *msblk = sb->s_fs_info;
	int bytes, copied = length;
	struct squashfs_cache_entry *entry;

	TRACE("Entered squashfs_read_metadata [%llx:%x]\n", *block, *offset);

	while (length) {
		entry = squashfs_cache_get(sb, msblk->block_cache, *block, 0);
		if (entry->error)
			return entry->error;
		else if (*offset >= entry->length)
			return -EIO;

		bytes = squashfs_copy_data(buffer, entry, *offset, length);
		if (buffer)
			buffer += bytes;
		length -= bytes;
		*offset += bytes;

		if (*offset == entry->length) {
			*block = entry->next_index;
			*offset = 0;
		}

		squashfs_cache_put(entry);
	}

	return copied;
}


/*
 * Look-up in the fragmment cache the fragment located at <start_block> in the
 * filesystem.  If necessary read and decompress it from disk.
 */
struct squashfs_cache_entry *squashfs_get_fragment(struct super_block *sb,
				u64 start_block, int length)
{
	struct squashfs_sb_info *msblk = sb->s_fs_info;

	return squashfs_cache_get(sb, msblk->fragment_cache, start_block,
		length);
}


/*
 * Read and decompress the datablock located at <start_block> in the
 * filesystem.  The cache is used here to avoid duplicating locking and
 * read/decompress code.
 */
struct squashfs_cache_entry *squashfs_get_datablock(struct super_block *sb,
				u64 start_block, int length)
{
	struct squashfs_sb_info *msblk = sb->s_fs_info;

	return squashfs_cache_get(sb, msblk->read_page, start_block, length);
}


/*
 * Read a filesystem table (uncompressed sequence of bytes) from disk
 */
void *squashfs_read_table(struct super_block *sb, u64 block, int length)
{
	int pages = (length + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
	int i, res;
	void *table, *buffer, **data;

	table = buffer = kmalloc(length, GFP_KERNEL);
	if (table == NULL)
		return ERR_PTR(-ENOMEM);

	data = kcalloc(pages, sizeof(void *), GFP_KERNEL);
	if (data == NULL) {
		res = -ENOMEM;
		goto failed;
	}

	for (i = 0; i < pages; i++, buffer += PAGE_CACHE_SIZE)
		data[i] = buffer;

	res = squashfs_read_data(sb, data, block, length |
		SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, length, pages);

	kfree(data);

	if (res < 0)
		goto failed;

	return table;

failed:
	kfree(table);
	return ERR_PTR(res);
}