source: src/linux/universal/linux-4.9/fs/squashfs/cache.c @ 31630

Last change on this file since 31630 was 31630, checked in by brainslayer, 2 weeks ago

new fs is compatible with standard squashfs, just smaller

File size: 11.6 KB
Line 
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 */
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_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_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
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_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 */
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_SIZE - 1) >> PAGE_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_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}
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