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#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 */
65struct 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
172out:
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 */
186void 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 */
210void 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_CACHE_SIZE buffers.
235 */
236struct 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_CACHE_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_CACHE_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
295cleanup:
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 */
306int 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_CACHE_SIZE]
318				+ (offset % PAGE_CACHE_SIZE);
319		int bytes = min_t(int, entry->length - offset,
320				PAGE_CACHE_SIZE - (offset % PAGE_CACHE_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 */
344int 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	while (length) {
354		entry = squashfs_cache_get(sb, msblk->block_cache, *block, 0);
355		if (entry->error) {
356			res = entry->error;
357			goto error;
358		} else if (*offset >= entry->length) {
359			res = -EIO;
360			goto error;
361		}
362
363		bytes = squashfs_copy_data(buffer, entry, *offset, length);
364		if (buffer)
365			buffer += bytes;
366		length -= bytes;
367		*offset += bytes;
368
369		if (*offset == entry->length) {
370			*block = entry->next_index;
371			*offset = 0;
372		}
373
374		squashfs_cache_put(entry);
375	}
376
377	return res;
378
379error:
380	squashfs_cache_put(entry);
381	return res;
382}
383
384
385/*
386 * Look-up in the fragmment cache the fragment located at <start_block> in the
387 * filesystem.  If necessary read and decompress it from disk.
388 */
389struct squashfs_cache_entry *squashfs_get_fragment(struct super_block *sb,
390				u64 start_block, int length)
391{
392	struct squashfs_sb_info *msblk = sb->s_fs_info;
393
394	return squashfs_cache_get(sb, msblk->fragment_cache, start_block,
395		length);
396}
397
398
399/*
400 * Read and decompress the datablock located at <start_block> in the
401 * filesystem.  The cache is used here to avoid duplicating locking and
402 * read/decompress code.
403 */
404struct squashfs_cache_entry *squashfs_get_datablock(struct super_block *sb,
405				u64 start_block, int length)
406{
407	struct squashfs_sb_info *msblk = sb->s_fs_info;
408
409	return squashfs_cache_get(sb, msblk->read_page, start_block, length);
410}
411
412
413/*
414 * Read a filesystem table (uncompressed sequence of bytes) from disk
415 */
416void *squashfs_read_table(struct super_block *sb, u64 block, int length)
417{
418	int pages = (length + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
419	int i, res;
420	void *table, *buffer, **data;
421	struct squashfs_page_actor *actor;
422
423	table = buffer = kmalloc(length, GFP_KERNEL);
424	if (table == NULL)
425		return ERR_PTR(-ENOMEM);
426
427	data = kcalloc(pages, sizeof(void *), GFP_KERNEL);
428	if (data == NULL) {
429		res = -ENOMEM;
430		goto failed;
431	}
432
433	actor = squashfs_page_actor_init(data, pages, length);
434	if (actor == NULL) {
435		res = -ENOMEM;
436		goto failed2;
437	}
438
439	for (i = 0; i < pages; i++, buffer += PAGE_CACHE_SIZE)
440		data[i] = buffer;
441
442	res = squashfs_read_data(sb, block, length |
443		SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, actor);
444
445	kfree(data);
446	kfree(actor);
447
448	if (res < 0)
449		goto failed;
450
451	return table;
452
453failed2:
454	kfree(data);
455failed:
456	kfree(table);
457	return ERR_PTR(res);
458}
459