1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3  * Squashfs - a compressed read only filesystem for Linux
4  *
5  * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
6  * Phillip Lougher <phillip@squashfs.org.uk>
7  *
8  * cache.c
9  */
10 
11 /*
12  * Blocks in Squashfs are compressed.  To avoid repeatedly decompressing
13  * recently accessed data Squashfs uses two small metadata and fragment caches.
14  *
15  * This file implements a generic cache implementation used for both caches,
16  * plus functions layered ontop of the generic cache implementation to
17  * access the metadata and fragment caches.
18  *
19  * To avoid out of memory and fragmentation issues with vmalloc the cache
20  * uses sequences of kmalloced PAGE_SIZE buffers.
21  *
22  * It should be noted that the cache is not used for file datablocks, these
23  * are decompressed and cached in the page-cache in the normal way.  The
24  * cache is only used to temporarily cache fragment and metadata blocks
25  * which have been read as as a result of a metadata (i.e. inode or
26  * directory) or fragment access.  Because metadata and fragments are packed
27  * together into blocks (to gain greater compression) the read of a particular
28  * piece of metadata or fragment will retrieve other metadata/fragments which
29  * have been packed with it, these because of locality-of-reference may be read
30  * in the near future. Temporarily caching them ensures they are available for
31  * near future access without requiring an additional read and decompress.
32  */
33 
34 #include <linux/fs.h>
35 #include <linux/vfs.h>
36 #include <linux/slab.h>
37 #include <linux/vmalloc.h>
38 #include <linux/sched.h>
39 #include <linux/spinlock.h>
40 #include <linux/wait.h>
41 #include <linux/pagemap.h>
42 
43 #include "squashfs_fs.h"
44 #include "squashfs_fs_sb.h"
45 #include "squashfs.h"
46 #include "page_actor.h"
47 
48 /*
49  * Look-up block in cache, and increment usage count.  If not in cache, read
50  * and decompress it from disk.
51  */
squashfs_cache_get(struct super_block * sb,struct squashfs_cache * cache,u64 block,int length)52 struct squashfs_cache_entry *squashfs_cache_get(struct super_block *sb,
53 	struct squashfs_cache *cache, u64 block, int length)
54 {
55 	int i, n;
56 	struct squashfs_cache_entry *entry;
57 
58 	spin_lock(&cache->lock);
59 
60 	while (1) {
61 		for (i = cache->curr_blk, n = 0; n < cache->entries; n++) {
62 			if (cache->entry[i].block == block) {
63 				cache->curr_blk = i;
64 				break;
65 			}
66 			i = (i + 1) % cache->entries;
67 		}
68 
69 		if (n == cache->entries) {
70 			/*
71 			 * Block not in cache, if all cache entries are used
72 			 * go to sleep waiting for one to become available.
73 			 */
74 			if (cache->unused == 0) {
75 				cache->num_waiters++;
76 				spin_unlock(&cache->lock);
77 				wait_event(cache->wait_queue, cache->unused);
78 				spin_lock(&cache->lock);
79 				cache->num_waiters--;
80 				continue;
81 			}
82 
83 			/*
84 			 * At least one unused cache entry.  A simple
85 			 * round-robin strategy is used to choose the entry to
86 			 * be evicted from the cache.
87 			 */
88 			i = cache->next_blk;
89 			for (n = 0; n < cache->entries; n++) {
90 				if (cache->entry[i].refcount == 0)
91 					break;
92 				i = (i + 1) % cache->entries;
93 			}
94 
95 			cache->next_blk = (i + 1) % cache->entries;
96 			entry = &cache->entry[i];
97 
98 			/*
99 			 * Initialise chosen cache entry, and fill it in from
100 			 * disk.
101 			 */
102 			cache->unused--;
103 			entry->block = block;
104 			entry->refcount = 1;
105 			entry->pending = 1;
106 			entry->num_waiters = 0;
107 			entry->error = 0;
108 			spin_unlock(&cache->lock);
109 
110 			entry->length = squashfs_read_data(sb, block, length,
111 				&entry->next_index, entry->actor);
112 
113 			spin_lock(&cache->lock);
114 
115 			if (entry->length < 0)
116 				entry->error = entry->length;
117 
118 			entry->pending = 0;
119 
120 			/*
121 			 * While filling this entry one or more other processes
122 			 * have looked it up in the cache, and have slept
123 			 * waiting for it to become available.
124 			 */
125 			if (entry->num_waiters) {
126 				spin_unlock(&cache->lock);
127 				wake_up_all(&entry->wait_queue);
128 			} else
129 				spin_unlock(&cache->lock);
130 
131 			goto out;
132 		}
133 
134 		/*
135 		 * Block already in cache.  Increment refcount so it doesn't
136 		 * get reused until we're finished with it, if it was
137 		 * previously unused there's one less cache entry available
138 		 * for reuse.
139 		 */
140 		entry = &cache->entry[i];
141 		if (entry->refcount == 0)
142 			cache->unused--;
143 		entry->refcount++;
144 
145 		/*
146 		 * If the entry is currently being filled in by another process
147 		 * go to sleep waiting for it to become available.
148 		 */
149 		if (entry->pending) {
150 			entry->num_waiters++;
151 			spin_unlock(&cache->lock);
152 			wait_event(entry->wait_queue, !entry->pending);
153 		} else
154 			spin_unlock(&cache->lock);
155 
156 		goto out;
157 	}
158 
159 out:
160 	TRACE("Got %s %d, start block %lld, refcount %d, error %d\n",
161 		cache->name, i, entry->block, entry->refcount, entry->error);
162 
163 	if (entry->error)
164 		ERROR("Unable to read %s cache entry [%llx]\n", cache->name,
165 							block);
166 	return entry;
167 }
168 
169 
170 /*
171  * Release cache entry, once usage count is zero it can be reused.
172  */
squashfs_cache_put(struct squashfs_cache_entry * entry)173 void squashfs_cache_put(struct squashfs_cache_entry *entry)
174 {
175 	struct squashfs_cache *cache = entry->cache;
176 
177 	spin_lock(&cache->lock);
178 	entry->refcount--;
179 	if (entry->refcount == 0) {
180 		cache->unused++;
181 		/*
182 		 * If there's any processes waiting for a block to become
183 		 * available, wake one up.
184 		 */
185 		if (cache->num_waiters) {
186 			spin_unlock(&cache->lock);
187 			wake_up(&cache->wait_queue);
188 			return;
189 		}
190 	}
191 	spin_unlock(&cache->lock);
192 }
193 
194 /*
195  * Delete cache reclaiming all kmalloced buffers.
196  */
squashfs_cache_delete(struct squashfs_cache * cache)197 void squashfs_cache_delete(struct squashfs_cache *cache)
198 {
199 	int i, j;
200 
201 	if (cache == NULL)
202 		return;
203 
204 	for (i = 0; i < cache->entries; i++) {
205 		if (cache->entry[i].data) {
206 			for (j = 0; j < cache->pages; j++)
207 				kfree(cache->entry[i].data[j]);
208 			kfree(cache->entry[i].data);
209 		}
210 		kfree(cache->entry[i].actor);
211 	}
212 
213 	kfree(cache->entry);
214 	kfree(cache);
215 }
216 
217 
218 /*
219  * Initialise cache allocating the specified number of entries, each of
220  * size block_size.  To avoid vmalloc fragmentation issues each entry
221  * is allocated as a sequence of kmalloced PAGE_SIZE buffers.
222  */
squashfs_cache_init(char * name,int entries,int block_size)223 struct squashfs_cache *squashfs_cache_init(char *name, int entries,
224 	int block_size)
225 {
226 	int i, j;
227 	struct squashfs_cache *cache = kzalloc(sizeof(*cache), GFP_KERNEL);
228 
229 	if (cache == NULL) {
230 		ERROR("Failed to allocate %s cache\n", name);
231 		return NULL;
232 	}
233 
234 	cache->entry = kcalloc(entries, sizeof(*(cache->entry)), GFP_KERNEL);
235 	if (cache->entry == NULL) {
236 		ERROR("Failed to allocate %s cache\n", name);
237 		goto cleanup;
238 	}
239 
240 	cache->curr_blk = 0;
241 	cache->next_blk = 0;
242 	cache->unused = entries;
243 	cache->entries = entries;
244 	cache->block_size = block_size;
245 	cache->pages = block_size >> PAGE_SHIFT;
246 	cache->pages = cache->pages ? cache->pages : 1;
247 	cache->name = name;
248 	cache->num_waiters = 0;
249 	spin_lock_init(&cache->lock);
250 	init_waitqueue_head(&cache->wait_queue);
251 
252 	for (i = 0; i < entries; i++) {
253 		struct squashfs_cache_entry *entry = &cache->entry[i];
254 
255 		init_waitqueue_head(&cache->entry[i].wait_queue);
256 		entry->cache = cache;
257 		entry->block = SQUASHFS_INVALID_BLK;
258 		entry->data = kcalloc(cache->pages, sizeof(void *), GFP_KERNEL);
259 		if (entry->data == NULL) {
260 			ERROR("Failed to allocate %s cache entry\n", name);
261 			goto cleanup;
262 		}
263 
264 		for (j = 0; j < cache->pages; j++) {
265 			entry->data[j] = kmalloc(PAGE_SIZE, GFP_KERNEL);
266 			if (entry->data[j] == NULL) {
267 				ERROR("Failed to allocate %s buffer\n", name);
268 				goto cleanup;
269 			}
270 		}
271 
272 		entry->actor = squashfs_page_actor_init(entry->data,
273 						cache->pages, 0);
274 		if (entry->actor == NULL) {
275 			ERROR("Failed to allocate %s cache entry\n", name);
276 			goto cleanup;
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  */
squashfs_copy_data(void * buffer,struct squashfs_cache_entry * entry,int offset,int length)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_SIZE]
305 				+ (offset % PAGE_SIZE);
306 		int bytes = min_t(int, entry->length - offset,
307 				PAGE_SIZE - (offset % PAGE_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  */
squashfs_read_metadata(struct super_block * sb,void * buffer,u64 * block,int * offset,int length)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, res = length;
336 	struct squashfs_cache_entry *entry;
337 
338 	TRACE("Entered squashfs_read_metadata [%llx:%x]\n", *block, *offset);
339 
340 	if (unlikely(length < 0))
341 		return -EIO;
342 
343 	while (length) {
344 		entry = squashfs_cache_get(sb, msblk->block_cache, *block, 0);
345 		if (entry->error) {
346 			res = entry->error;
347 			goto error;
348 		} else if (*offset >= entry->length) {
349 			res = -EIO;
350 			goto error;
351 		}
352 
353 		bytes = squashfs_copy_data(buffer, entry, *offset, length);
354 		if (buffer)
355 			buffer += bytes;
356 		length -= bytes;
357 		*offset += bytes;
358 
359 		if (*offset == entry->length) {
360 			*block = entry->next_index;
361 			*offset = 0;
362 		}
363 
364 		squashfs_cache_put(entry);
365 	}
366 
367 	return res;
368 
369 error:
370 	squashfs_cache_put(entry);
371 	return res;
372 }
373 
374 
375 /*
376  * Look-up in the fragmment cache the fragment located at <start_block> in the
377  * filesystem.  If necessary read and decompress it from disk.
378  */
squashfs_get_fragment(struct super_block * sb,u64 start_block,int length)379 struct squashfs_cache_entry *squashfs_get_fragment(struct super_block *sb,
380 				u64 start_block, int length)
381 {
382 	struct squashfs_sb_info *msblk = sb->s_fs_info;
383 
384 	return squashfs_cache_get(sb, msblk->fragment_cache, start_block,
385 		length);
386 }
387 
388 
389 /*
390  * Read and decompress the datablock located at <start_block> in the
391  * filesystem.  The cache is used here to avoid duplicating locking and
392  * read/decompress code.
393  */
squashfs_get_datablock(struct super_block * sb,u64 start_block,int length)394 struct squashfs_cache_entry *squashfs_get_datablock(struct super_block *sb,
395 				u64 start_block, int length)
396 {
397 	struct squashfs_sb_info *msblk = sb->s_fs_info;
398 
399 	return squashfs_cache_get(sb, msblk->read_page, start_block, length);
400 }
401 
402 
403 /*
404  * Read a filesystem table (uncompressed sequence of bytes) from disk
405  */
squashfs_read_table(struct super_block * sb,u64 block,int length)406 void *squashfs_read_table(struct super_block *sb, u64 block, int length)
407 {
408 	int pages = (length + PAGE_SIZE - 1) >> PAGE_SHIFT;
409 	int i, res;
410 	void *table, *buffer, **data;
411 	struct squashfs_page_actor *actor;
412 
413 	table = buffer = kmalloc(length, GFP_KERNEL);
414 	if (table == NULL)
415 		return ERR_PTR(-ENOMEM);
416 
417 	data = kcalloc(pages, sizeof(void *), GFP_KERNEL);
418 	if (data == NULL) {
419 		res = -ENOMEM;
420 		goto failed;
421 	}
422 
423 	actor = squashfs_page_actor_init(data, pages, length);
424 	if (actor == NULL) {
425 		res = -ENOMEM;
426 		goto failed2;
427 	}
428 
429 	for (i = 0; i < pages; i++, buffer += PAGE_SIZE)
430 		data[i] = buffer;
431 
432 	res = squashfs_read_data(sb, block, length |
433 		SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, actor);
434 
435 	kfree(data);
436 	kfree(actor);
437 
438 	if (res < 0)
439 		goto failed;
440 
441 	return table;
442 
443 failed2:
444 	kfree(data);
445 failed:
446 	kfree(table);
447 	return ERR_PTR(res);
448 }
449