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 * file.c
9 */
10
11 /*
12 * This file contains code for handling regular files. A regular file
13 * consists of a sequence of contiguous compressed blocks, and/or a
14 * compressed fragment block (tail-end packed block). The compressed size
15 * of each datablock is stored in a block list contained within the
16 * file inode (itself stored in one or more compressed metadata blocks).
17 *
18 * To speed up access to datablocks when reading 'large' files (256 Mbytes or
19 * larger), the code implements an index cache that caches the mapping from
20 * block index to datablock location on disk.
21 *
22 * The index cache allows Squashfs to handle large files (up to 1.75 TiB) while
23 * retaining a simple and space-efficient block list on disk. The cache
24 * is split into slots, caching up to eight 224 GiB files (128 KiB blocks).
25 * Larger files use multiple slots, with 1.75 TiB files using all 8 slots.
26 * The index cache is designed to be memory efficient, and by default uses
27 * 16 KiB.
28 */
29
30 #include <linux/fs.h>
31 #include <linux/vfs.h>
32 #include <linux/kernel.h>
33 #include <linux/slab.h>
34 #include <linux/string.h>
35 #include <linux/pagemap.h>
36 #include <linux/mutex.h>
37
38 #include "squashfs_fs.h"
39 #include "squashfs_fs_sb.h"
40 #include "squashfs_fs_i.h"
41 #include "squashfs.h"
42
43 /*
44 * Locate cache slot in range [offset, index] for specified inode. If
45 * there's more than one return the slot closest to index.
46 */
locate_meta_index(struct inode * inode,int offset,int index)47 static struct meta_index *locate_meta_index(struct inode *inode, int offset,
48 int index)
49 {
50 struct meta_index *meta = NULL;
51 struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
52 int i;
53
54 mutex_lock(&msblk->meta_index_mutex);
55
56 TRACE("locate_meta_index: index %d, offset %d\n", index, offset);
57
58 if (msblk->meta_index == NULL)
59 goto not_allocated;
60
61 for (i = 0; i < SQUASHFS_META_SLOTS; i++) {
62 if (msblk->meta_index[i].inode_number == inode->i_ino &&
63 msblk->meta_index[i].offset >= offset &&
64 msblk->meta_index[i].offset <= index &&
65 msblk->meta_index[i].locked == 0) {
66 TRACE("locate_meta_index: entry %d, offset %d\n", i,
67 msblk->meta_index[i].offset);
68 meta = &msblk->meta_index[i];
69 offset = meta->offset;
70 }
71 }
72
73 if (meta)
74 meta->locked = 1;
75
76 not_allocated:
77 mutex_unlock(&msblk->meta_index_mutex);
78
79 return meta;
80 }
81
82
83 /*
84 * Find and initialise an empty cache slot for index offset.
85 */
empty_meta_index(struct inode * inode,int offset,int skip)86 static struct meta_index *empty_meta_index(struct inode *inode, int offset,
87 int skip)
88 {
89 struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
90 struct meta_index *meta = NULL;
91 int i;
92
93 mutex_lock(&msblk->meta_index_mutex);
94
95 TRACE("empty_meta_index: offset %d, skip %d\n", offset, skip);
96
97 if (msblk->meta_index == NULL) {
98 /*
99 * First time cache index has been used, allocate and
100 * initialise. The cache index could be allocated at
101 * mount time but doing it here means it is allocated only
102 * if a 'large' file is read.
103 */
104 msblk->meta_index = kcalloc(SQUASHFS_META_SLOTS,
105 sizeof(*(msblk->meta_index)), GFP_KERNEL);
106 if (msblk->meta_index == NULL) {
107 ERROR("Failed to allocate meta_index\n");
108 goto failed;
109 }
110 for (i = 0; i < SQUASHFS_META_SLOTS; i++) {
111 msblk->meta_index[i].inode_number = 0;
112 msblk->meta_index[i].locked = 0;
113 }
114 msblk->next_meta_index = 0;
115 }
116
117 for (i = SQUASHFS_META_SLOTS; i &&
118 msblk->meta_index[msblk->next_meta_index].locked; i--)
119 msblk->next_meta_index = (msblk->next_meta_index + 1) %
120 SQUASHFS_META_SLOTS;
121
122 if (i == 0) {
123 TRACE("empty_meta_index: failed!\n");
124 goto failed;
125 }
126
127 TRACE("empty_meta_index: returned meta entry %d, %p\n",
128 msblk->next_meta_index,
129 &msblk->meta_index[msblk->next_meta_index]);
130
131 meta = &msblk->meta_index[msblk->next_meta_index];
132 msblk->next_meta_index = (msblk->next_meta_index + 1) %
133 SQUASHFS_META_SLOTS;
134
135 meta->inode_number = inode->i_ino;
136 meta->offset = offset;
137 meta->skip = skip;
138 meta->entries = 0;
139 meta->locked = 1;
140
141 failed:
142 mutex_unlock(&msblk->meta_index_mutex);
143 return meta;
144 }
145
146
release_meta_index(struct inode * inode,struct meta_index * meta)147 static void release_meta_index(struct inode *inode, struct meta_index *meta)
148 {
149 struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
150 mutex_lock(&msblk->meta_index_mutex);
151 meta->locked = 0;
152 mutex_unlock(&msblk->meta_index_mutex);
153 }
154
155
156 /*
157 * Read the next n blocks from the block list, starting from
158 * metadata block <start_block, offset>.
159 */
read_indexes(struct super_block * sb,int n,u64 * start_block,int * offset)160 static long long read_indexes(struct super_block *sb, int n,
161 u64 *start_block, int *offset)
162 {
163 int err, i;
164 long long block = 0;
165 __le32 *blist = kmalloc(PAGE_SIZE, GFP_KERNEL);
166
167 if (blist == NULL) {
168 ERROR("read_indexes: Failed to allocate block_list\n");
169 return -ENOMEM;
170 }
171
172 while (n) {
173 int blocks = min_t(int, n, PAGE_SIZE >> 2);
174
175 err = squashfs_read_metadata(sb, blist, start_block,
176 offset, blocks << 2);
177 if (err < 0) {
178 ERROR("read_indexes: reading block [%llx:%x]\n",
179 *start_block, *offset);
180 goto failure;
181 }
182
183 for (i = 0; i < blocks; i++) {
184 int size = squashfs_block_size(blist[i]);
185 if (size < 0) {
186 err = size;
187 goto failure;
188 }
189 block += SQUASHFS_COMPRESSED_SIZE_BLOCK(size);
190 }
191 n -= blocks;
192 }
193
194 kfree(blist);
195 return block;
196
197 failure:
198 kfree(blist);
199 return err;
200 }
201
202
203 /*
204 * Each cache index slot has SQUASHFS_META_ENTRIES, each of which
205 * can cache one index -> datablock/blocklist-block mapping. We wish
206 * to distribute these over the length of the file, entry[0] maps index x,
207 * entry[1] maps index x + skip, entry[2] maps index x + 2 * skip, and so on.
208 * The larger the file, the greater the skip factor. The skip factor is
209 * limited to the size of the metadata cache (SQUASHFS_CACHED_BLKS) to ensure
210 * the number of metadata blocks that need to be read fits into the cache.
211 * If the skip factor is limited in this way then the file will use multiple
212 * slots.
213 */
calculate_skip(u64 blocks)214 static inline int calculate_skip(u64 blocks)
215 {
216 u64 skip = blocks / ((SQUASHFS_META_ENTRIES + 1)
217 * SQUASHFS_META_INDEXES);
218 return min((u64) SQUASHFS_CACHED_BLKS - 1, skip + 1);
219 }
220
221
222 /*
223 * Search and grow the index cache for the specified inode, returning the
224 * on-disk locations of the datablock and block list metadata block
225 * <index_block, index_offset> for index (scaled to nearest cache index).
226 */
fill_meta_index(struct inode * inode,int index,u64 * index_block,int * index_offset,u64 * data_block)227 static int fill_meta_index(struct inode *inode, int index,
228 u64 *index_block, int *index_offset, u64 *data_block)
229 {
230 struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
231 int skip = calculate_skip(i_size_read(inode) >> msblk->block_log);
232 int offset = 0;
233 struct meta_index *meta;
234 struct meta_entry *meta_entry;
235 u64 cur_index_block = squashfs_i(inode)->block_list_start;
236 int cur_offset = squashfs_i(inode)->offset;
237 u64 cur_data_block = squashfs_i(inode)->start;
238 int err, i;
239
240 /*
241 * Scale index to cache index (cache slot entry)
242 */
243 index /= SQUASHFS_META_INDEXES * skip;
244
245 while (offset < index) {
246 meta = locate_meta_index(inode, offset + 1, index);
247
248 if (meta == NULL) {
249 meta = empty_meta_index(inode, offset + 1, skip);
250 if (meta == NULL)
251 goto all_done;
252 } else {
253 offset = index < meta->offset + meta->entries ? index :
254 meta->offset + meta->entries - 1;
255 meta_entry = &meta->meta_entry[offset - meta->offset];
256 cur_index_block = meta_entry->index_block +
257 msblk->inode_table;
258 cur_offset = meta_entry->offset;
259 cur_data_block = meta_entry->data_block;
260 TRACE("get_meta_index: offset %d, meta->offset %d, "
261 "meta->entries %d\n", offset, meta->offset,
262 meta->entries);
263 TRACE("get_meta_index: index_block 0x%llx, offset 0x%x"
264 " data_block 0x%llx\n", cur_index_block,
265 cur_offset, cur_data_block);
266 }
267
268 /*
269 * If necessary grow cache slot by reading block list. Cache
270 * slot is extended up to index or to the end of the slot, in
271 * which case further slots will be used.
272 */
273 for (i = meta->offset + meta->entries; i <= index &&
274 i < meta->offset + SQUASHFS_META_ENTRIES; i++) {
275 int blocks = skip * SQUASHFS_META_INDEXES;
276 long long res = read_indexes(inode->i_sb, blocks,
277 &cur_index_block, &cur_offset);
278
279 if (res < 0) {
280 if (meta->entries == 0)
281 /*
282 * Don't leave an empty slot on read
283 * error allocated to this inode...
284 */
285 meta->inode_number = 0;
286 err = res;
287 goto failed;
288 }
289
290 cur_data_block += res;
291 meta_entry = &meta->meta_entry[i - meta->offset];
292 meta_entry->index_block = cur_index_block -
293 msblk->inode_table;
294 meta_entry->offset = cur_offset;
295 meta_entry->data_block = cur_data_block;
296 meta->entries++;
297 offset++;
298 }
299
300 TRACE("get_meta_index: meta->offset %d, meta->entries %d\n",
301 meta->offset, meta->entries);
302
303 release_meta_index(inode, meta);
304 }
305
306 all_done:
307 *index_block = cur_index_block;
308 *index_offset = cur_offset;
309 *data_block = cur_data_block;
310
311 /*
312 * Scale cache index (cache slot entry) to index
313 */
314 return offset * SQUASHFS_META_INDEXES * skip;
315
316 failed:
317 release_meta_index(inode, meta);
318 return err;
319 }
320
321
322 /*
323 * Get the on-disk location and compressed size of the datablock
324 * specified by index. Fill_meta_index() does most of the work.
325 */
read_blocklist(struct inode * inode,int index,u64 * block)326 static int read_blocklist(struct inode *inode, int index, u64 *block)
327 {
328 u64 start;
329 long long blks;
330 int offset;
331 __le32 size;
332 int res = fill_meta_index(inode, index, &start, &offset, block);
333
334 TRACE("read_blocklist: res %d, index %d, start 0x%llx, offset"
335 " 0x%x, block 0x%llx\n", res, index, start, offset,
336 *block);
337
338 if (res < 0)
339 return res;
340
341 /*
342 * res contains the index of the mapping returned by fill_meta_index(),
343 * this will likely be less than the desired index (because the
344 * meta_index cache works at a higher granularity). Read any
345 * extra block indexes needed.
346 */
347 if (res < index) {
348 blks = read_indexes(inode->i_sb, index - res, &start, &offset);
349 if (blks < 0)
350 return (int) blks;
351 *block += blks;
352 }
353
354 /*
355 * Read length of block specified by index.
356 */
357 res = squashfs_read_metadata(inode->i_sb, &size, &start, &offset,
358 sizeof(size));
359 if (res < 0)
360 return res;
361 return squashfs_block_size(size);
362 }
363
squashfs_fill_page(struct page * page,struct squashfs_cache_entry * buffer,int offset,int avail)364 void squashfs_fill_page(struct page *page, struct squashfs_cache_entry *buffer, int offset, int avail)
365 {
366 int copied;
367 void *pageaddr;
368
369 pageaddr = kmap_atomic(page);
370 copied = squashfs_copy_data(pageaddr, buffer, offset, avail);
371 memset(pageaddr + copied, 0, PAGE_SIZE - copied);
372 kunmap_atomic(pageaddr);
373
374 flush_dcache_page(page);
375 if (copied == avail)
376 SetPageUptodate(page);
377 else
378 SetPageError(page);
379 }
380
381 /* Copy data into page cache */
squashfs_copy_cache(struct page * page,struct squashfs_cache_entry * buffer,int bytes,int offset)382 void squashfs_copy_cache(struct page *page, struct squashfs_cache_entry *buffer,
383 int bytes, int offset)
384 {
385 struct inode *inode = page->mapping->host;
386 struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
387 int i, mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
388 int start_index = page->index & ~mask, end_index = start_index | mask;
389
390 /*
391 * Loop copying datablock into pages. As the datablock likely covers
392 * many PAGE_SIZE pages (default block size is 128 KiB) explicitly
393 * grab the pages from the page cache, except for the page that we've
394 * been called to fill.
395 */
396 for (i = start_index; i <= end_index && bytes > 0; i++,
397 bytes -= PAGE_SIZE, offset += PAGE_SIZE) {
398 struct page *push_page;
399 int avail = buffer ? min_t(int, bytes, PAGE_SIZE) : 0;
400
401 TRACE("bytes %d, i %d, available_bytes %d\n", bytes, i, avail);
402
403 push_page = (i == page->index) ? page :
404 grab_cache_page_nowait(page->mapping, i);
405
406 if (!push_page)
407 continue;
408
409 if (PageUptodate(push_page))
410 goto skip_page;
411
412 squashfs_fill_page(push_page, buffer, offset, avail);
413 skip_page:
414 unlock_page(push_page);
415 if (i != page->index)
416 put_page(push_page);
417 }
418 }
419
420 /* Read datablock stored packed inside a fragment (tail-end packed block) */
squashfs_readpage_fragment(struct page * page,int expected)421 static int squashfs_readpage_fragment(struct page *page, int expected)
422 {
423 struct inode *inode = page->mapping->host;
424 struct squashfs_cache_entry *buffer = squashfs_get_fragment(inode->i_sb,
425 squashfs_i(inode)->fragment_block,
426 squashfs_i(inode)->fragment_size);
427 int res = buffer->error;
428
429 if (res)
430 ERROR("Unable to read page, block %llx, size %x\n",
431 squashfs_i(inode)->fragment_block,
432 squashfs_i(inode)->fragment_size);
433 else
434 squashfs_copy_cache(page, buffer, expected,
435 squashfs_i(inode)->fragment_offset);
436
437 squashfs_cache_put(buffer);
438 return res;
439 }
440
squashfs_readpage_sparse(struct page * page,int expected)441 static int squashfs_readpage_sparse(struct page *page, int expected)
442 {
443 squashfs_copy_cache(page, NULL, expected, 0);
444 return 0;
445 }
446
squashfs_readpage(struct file * file,struct page * page)447 static int squashfs_readpage(struct file *file, struct page *page)
448 {
449 struct inode *inode = page->mapping->host;
450 struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
451 int index = page->index >> (msblk->block_log - PAGE_SHIFT);
452 int file_end = i_size_read(inode) >> msblk->block_log;
453 int expected = index == file_end ?
454 (i_size_read(inode) & (msblk->block_size - 1)) :
455 msblk->block_size;
456 int res;
457 void *pageaddr;
458
459 TRACE("Entered squashfs_readpage, page index %lx, start block %llx\n",
460 page->index, squashfs_i(inode)->start);
461
462 if (page->index >= ((i_size_read(inode) + PAGE_SIZE - 1) >>
463 PAGE_SHIFT))
464 goto out;
465
466 if (index < file_end || squashfs_i(inode)->fragment_block ==
467 SQUASHFS_INVALID_BLK) {
468 u64 block = 0;
469 int bsize = read_blocklist(inode, index, &block);
470 if (bsize < 0)
471 goto error_out;
472
473 if (bsize == 0)
474 res = squashfs_readpage_sparse(page, expected);
475 else
476 res = squashfs_readpage_block(page, block, bsize, expected);
477 } else
478 res = squashfs_readpage_fragment(page, expected);
479
480 if (!res)
481 return 0;
482
483 error_out:
484 SetPageError(page);
485 out:
486 pageaddr = kmap_atomic(page);
487 memset(pageaddr, 0, PAGE_SIZE);
488 kunmap_atomic(pageaddr);
489 flush_dcache_page(page);
490 if (!PageError(page))
491 SetPageUptodate(page);
492 unlock_page(page);
493
494 return 0;
495 }
496
497
498 const struct address_space_operations squashfs_aops = {
499 .readpage = squashfs_readpage
500 };
501