linux/fs/squashfs/cache.c
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   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 */
  64struct 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 = cache->curr_blk, n = 0; n < cache->entries; n++) {
  74                        if (cache->entry[i].block == block) {
  75                                cache->curr_blk = i;
  76                                break;
  77                        }
  78                        i = (i + 1) % cache->entries;
  79                }
  80
  81                if (n == cache->entries) {
  82                        /*
  83                         * Block not in cache, if all cache entries are used
  84                         * go to sleep waiting for one to become available.
  85                         */
  86                        if (cache->unused == 0) {
  87                                cache->num_waiters++;
  88                                spin_unlock(&cache->lock);
  89                                wait_event(cache->wait_queue, cache->unused);
  90                                spin_lock(&cache->lock);
  91                                cache->num_waiters--;
  92                                continue;
  93                        }
  94
  95                        /*
  96                         * At least one unused cache entry.  A simple
  97                         * round-robin strategy is used to choose the entry to
  98                         * be evicted from the cache.
  99                         */
 100                        i = cache->next_blk;
 101                        for (n = 0; n < cache->entries; n++) {
 102                                if (cache->entry[i].refcount == 0)
 103                                        break;
 104                                i = (i + 1) % cache->entries;
 105                        }
 106
 107                        cache->next_blk = (i + 1) % cache->entries;
 108                        entry = &cache->entry[i];
 109
 110                        /*
 111                         * Initialise chosen cache entry, and fill it in from
 112                         * disk.
 113                         */
 114                        cache->unused--;
 115                        entry->block = block;
 116                        entry->refcount = 1;
 117                        entry->pending = 1;
 118                        entry->num_waiters = 0;
 119                        entry->error = 0;
 120                        spin_unlock(&cache->lock);
 121
 122                        entry->length = squashfs_read_data(sb, entry->data,
 123                                block, length, &entry->next_index,
 124                                cache->block_size, cache->pages);
 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        }
 224
 225        kfree(cache->entry);
 226        kfree(cache);
 227}
 228
 229
 230/*
 231 * Initialise cache allocating the specified number of entries, each of
 232 * size block_size.  To avoid vmalloc fragmentation issues each entry
 233 * is allocated as a sequence of kmalloced PAGE_CACHE_SIZE buffers.
 234 */
 235struct squashfs_cache *squashfs_cache_init(char *name, int entries,
 236        int block_size)
 237{
 238        int i, j;
 239        struct squashfs_cache *cache = kzalloc(sizeof(*cache), GFP_KERNEL);
 240
 241        if (cache == NULL) {
 242                ERROR("Failed to allocate %s cache\n", name);
 243                return NULL;
 244        }
 245
 246        cache->entry = kcalloc(entries, sizeof(*(cache->entry)), GFP_KERNEL);
 247        if (cache->entry == NULL) {
 248                ERROR("Failed to allocate %s cache\n", name);
 249                goto cleanup;
 250        }
 251
 252        cache->curr_blk = 0;
 253        cache->next_blk = 0;
 254        cache->unused = entries;
 255        cache->entries = entries;
 256        cache->block_size = block_size;
 257        cache->pages = block_size >> PAGE_CACHE_SHIFT;
 258        cache->pages = cache->pages ? cache->pages : 1;
 259        cache->name = name;
 260        cache->num_waiters = 0;
 261        spin_lock_init(&cache->lock);
 262        init_waitqueue_head(&cache->wait_queue);
 263
 264        for (i = 0; i < entries; i++) {
 265                struct squashfs_cache_entry *entry = &cache->entry[i];
 266
 267                init_waitqueue_head(&cache->entry[i].wait_queue);
 268                entry->cache = cache;
 269                entry->block = SQUASHFS_INVALID_BLK;
 270                entry->data = kcalloc(cache->pages, sizeof(void *), GFP_KERNEL);
 271                if (entry->data == NULL) {
 272                        ERROR("Failed to allocate %s cache entry\n", name);
 273                        goto cleanup;
 274                }
 275
 276                for (j = 0; j < cache->pages; j++) {
 277                        entry->data[j] = kmalloc(PAGE_CACHE_SIZE, GFP_KERNEL);
 278                        if (entry->data[j] == NULL) {
 279                                ERROR("Failed to allocate %s buffer\n", name);
 280                                goto cleanup;
 281                        }
 282                }
 283        }
 284
 285        return cache;
 286
 287cleanup:
 288        squashfs_cache_delete(cache);
 289        return NULL;
 290}
 291
 292
 293/*
 294 * Copy up to length bytes from cache entry to buffer starting at offset bytes
 295 * into the cache entry.  If there's not length bytes then copy the number of
 296 * bytes available.  In all cases return the number of bytes copied.
 297 */
 298int squashfs_copy_data(void *buffer, struct squashfs_cache_entry *entry,
 299                int offset, int length)
 300{
 301        int remaining = length;
 302
 303        if (length == 0)
 304                return 0;
 305        else if (buffer == NULL)
 306                return min(length, entry->length - offset);
 307
 308        while (offset < entry->length) {
 309                void *buff = entry->data[offset / PAGE_CACHE_SIZE]
 310                                + (offset % PAGE_CACHE_SIZE);
 311                int bytes = min_t(int, entry->length - offset,
 312                                PAGE_CACHE_SIZE - (offset % PAGE_CACHE_SIZE));
 313
 314                if (bytes >= remaining) {
 315                        memcpy(buffer, buff, remaining);
 316                        remaining = 0;
 317                        break;
 318                }
 319
 320                memcpy(buffer, buff, bytes);
 321                buffer += bytes;
 322                remaining -= bytes;
 323                offset += bytes;
 324        }
 325
 326        return length - remaining;
 327}
 328
 329
 330/*
 331 * Read length bytes from metadata position <block, offset> (block is the
 332 * start of the compressed block on disk, and offset is the offset into
 333 * the block once decompressed).  Data is packed into consecutive blocks,
 334 * and length bytes may require reading more than one block.
 335 */
 336int squashfs_read_metadata(struct super_block *sb, void *buffer,
 337                u64 *block, int *offset, int length)
 338{
 339        struct squashfs_sb_info *msblk = sb->s_fs_info;
 340        int bytes, res = length;
 341        struct squashfs_cache_entry *entry;
 342
 343        TRACE("Entered squashfs_read_metadata [%llx:%x]\n", *block, *offset);
 344
 345        while (length) {
 346                entry = squashfs_cache_get(sb, msblk->block_cache, *block, 0);
 347                if (entry->error) {
 348                        res = entry->error;
 349                        goto error;
 350                } else if (*offset >= entry->length) {
 351                        res = -EIO;
 352                        goto error;
 353                }
 354
 355                bytes = squashfs_copy_data(buffer, entry, *offset, length);
 356                if (buffer)
 357                        buffer += bytes;
 358                length -= bytes;
 359                *offset += bytes;
 360
 361                if (*offset == entry->length) {
 362                        *block = entry->next_index;
 363                        *offset = 0;
 364                }
 365
 366                squashfs_cache_put(entry);
 367        }
 368
 369        return res;
 370
 371error:
 372        squashfs_cache_put(entry);
 373        return res;
 374}
 375
 376
 377/*
 378 * Look-up in the fragmment cache the fragment located at <start_block> in the
 379 * filesystem.  If necessary read and decompress it from disk.
 380 */
 381struct squashfs_cache_entry *squashfs_get_fragment(struct super_block *sb,
 382                                u64 start_block, int length)
 383{
 384        struct squashfs_sb_info *msblk = sb->s_fs_info;
 385
 386        return squashfs_cache_get(sb, msblk->fragment_cache, start_block,
 387                length);
 388}
 389
 390
 391/*
 392 * Read and decompress the datablock located at <start_block> in the
 393 * filesystem.  The cache is used here to avoid duplicating locking and
 394 * read/decompress code.
 395 */
 396struct squashfs_cache_entry *squashfs_get_datablock(struct super_block *sb,
 397                                u64 start_block, int length)
 398{
 399        struct squashfs_sb_info *msblk = sb->s_fs_info;
 400
 401        return squashfs_cache_get(sb, msblk->read_page, start_block, length);
 402}
 403
 404
 405/*
 406 * Read a filesystem table (uncompressed sequence of bytes) from disk
 407 */
 408void *squashfs_read_table(struct super_block *sb, u64 block, int length)
 409{
 410        int pages = (length + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
 411        int i, res;
 412        void *table, *buffer, **data;
 413
 414        table = buffer = kmalloc(length, GFP_KERNEL);
 415        if (table == NULL)
 416                return ERR_PTR(-ENOMEM);
 417
 418        data = kcalloc(pages, sizeof(void *), GFP_KERNEL);
 419        if (data == NULL) {
 420                res = -ENOMEM;
 421                goto failed;
 422        }
 423
 424        for (i = 0; i < pages; i++, buffer += PAGE_CACHE_SIZE)
 425                data[i] = buffer;
 426
 427        res = squashfs_read_data(sb, data, block, length |
 428                SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, length, pages);
 429
 430        kfree(data);
 431
 432        if (res < 0)
 433                goto failed;
 434
 435        return table;
 436
 437failed:
 438        kfree(table);
 439        return ERR_PTR(res);
 440}
 441
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