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1 | /* | |
2 | * linux/fs/ext4/readpage.c | |
3 | * | |
4 | * Copyright (C) 2002, Linus Torvalds. | |
5 | * Copyright (C) 2015, Google, Inc. | |
6 | * | |
7 | * This was originally taken from fs/mpage.c | |
8 | * | |
9 | * The intent is the ext4_mpage_readpages() function here is intended | |
10 | * to replace mpage_readpages() in the general case, not just for | |
11 | * encrypted files. It has some limitations (see below), where it | |
12 | * will fall back to read_block_full_page(), but these limitations | |
13 | * should only be hit when page_size != block_size. | |
14 | * | |
15 | * This will allow us to attach a callback function to support ext4 | |
16 | * encryption. | |
17 | * | |
18 | * If anything unusual happens, such as: | |
19 | * | |
20 | * - encountering a page which has buffers | |
21 | * - encountering a page which has a non-hole after a hole | |
22 | * - encountering a page with non-contiguous blocks | |
23 | * | |
24 | * then this code just gives up and calls the buffer_head-based read function. | |
25 | * It does handle a page which has holes at the end - that is a common case: | |
26 | * the end-of-file on blocksize < PAGE_SIZE setups. | |
27 | * | |
28 | */ | |
29 | ||
30 | #include <linux/kernel.h> | |
31 | #include <linux/export.h> | |
32 | #include <linux/mm.h> | |
33 | #include <linux/kdev_t.h> | |
34 | #include <linux/gfp.h> | |
35 | #include <linux/bio.h> | |
36 | #include <linux/fs.h> | |
37 | #include <linux/buffer_head.h> | |
38 | #include <linux/blkdev.h> | |
39 | #include <linux/highmem.h> | |
40 | #include <linux/prefetch.h> | |
41 | #include <linux/mpage.h> | |
42 | #include <linux/writeback.h> | |
43 | #include <linux/backing-dev.h> | |
44 | #include <linux/pagevec.h> | |
45 | #include <linux/cleancache.h> | |
46 | ||
47 | #include "ext4.h" | |
48 | ||
49 | static inline bool ext4_bio_encrypted(struct bio *bio) | |
50 | { | |
51 | #ifdef CONFIG_EXT4_FS_ENCRYPTION | |
52 | return unlikely(bio->bi_private != NULL); | |
53 | #else | |
54 | return false; | |
55 | #endif | |
56 | } | |
57 | ||
58 | /* | |
59 | * I/O completion handler for multipage BIOs. | |
60 | * | |
61 | * The mpage code never puts partial pages into a BIO (except for end-of-file). | |
62 | * If a page does not map to a contiguous run of blocks then it simply falls | |
63 | * back to block_read_full_page(). | |
64 | * | |
65 | * Why is this? If a page's completion depends on a number of different BIOs | |
66 | * which can complete in any order (or at the same time) then determining the | |
67 | * status of that page is hard. See end_buffer_async_read() for the details. | |
68 | * There is no point in duplicating all that complexity. | |
69 | */ | |
70 | static void mpage_end_io(struct bio *bio) | |
71 | { | |
72 | struct bio_vec *bv; | |
73 | int i; | |
74 | ||
75 | if (ext4_bio_encrypted(bio)) { | |
76 | if (bio->bi_status) { | |
77 | fscrypt_release_ctx(bio->bi_private); | |
78 | } else { | |
79 | fscrypt_decrypt_bio_pages(bio->bi_private, bio); | |
80 | return; | |
81 | } | |
82 | } | |
83 | bio_for_each_segment_all(bv, bio, i) { | |
84 | struct page *page = bv->bv_page; | |
85 | ||
86 | if (!bio->bi_status) { | |
87 | SetPageUptodate(page); | |
88 | } else { | |
89 | ClearPageUptodate(page); | |
90 | SetPageError(page); | |
91 | } | |
92 | unlock_page(page); | |
93 | } | |
94 | ||
95 | bio_put(bio); | |
96 | } | |
97 | ||
98 | int ext4_mpage_readpages(struct address_space *mapping, | |
99 | struct list_head *pages, struct page *page, | |
100 | unsigned nr_pages) | |
101 | { | |
102 | struct bio *bio = NULL; | |
103 | sector_t last_block_in_bio = 0; | |
104 | ||
105 | struct inode *inode = mapping->host; | |
106 | const unsigned blkbits = inode->i_blkbits; | |
107 | const unsigned blocks_per_page = PAGE_SIZE >> blkbits; | |
108 | const unsigned blocksize = 1 << blkbits; | |
109 | sector_t block_in_file; | |
110 | sector_t last_block; | |
111 | sector_t last_block_in_file; | |
112 | sector_t blocks[MAX_BUF_PER_PAGE]; | |
113 | unsigned page_block; | |
114 | struct block_device *bdev = inode->i_sb->s_bdev; | |
115 | int length; | |
116 | unsigned relative_block = 0; | |
117 | struct ext4_map_blocks map; | |
118 | ||
119 | map.m_pblk = 0; | |
120 | map.m_lblk = 0; | |
121 | map.m_len = 0; | |
122 | map.m_flags = 0; | |
123 | ||
124 | for (; nr_pages; nr_pages--) { | |
125 | int fully_mapped = 1; | |
126 | unsigned first_hole = blocks_per_page; | |
127 | ||
128 | prefetchw(&page->flags); | |
129 | if (pages) { | |
130 | page = list_entry(pages->prev, struct page, lru); | |
131 | list_del(&page->lru); | |
132 | if (add_to_page_cache_lru(page, mapping, page->index, | |
133 | readahead_gfp_mask(mapping))) | |
134 | goto next_page; | |
135 | } | |
136 | ||
137 | if (page_has_buffers(page)) | |
138 | goto confused; | |
139 | ||
140 | block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits); | |
141 | last_block = block_in_file + nr_pages * blocks_per_page; | |
142 | last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits; | |
143 | if (last_block > last_block_in_file) | |
144 | last_block = last_block_in_file; | |
145 | page_block = 0; | |
146 | ||
147 | /* | |
148 | * Map blocks using the previous result first. | |
149 | */ | |
150 | if ((map.m_flags & EXT4_MAP_MAPPED) && | |
151 | block_in_file > map.m_lblk && | |
152 | block_in_file < (map.m_lblk + map.m_len)) { | |
153 | unsigned map_offset = block_in_file - map.m_lblk; | |
154 | unsigned last = map.m_len - map_offset; | |
155 | ||
156 | for (relative_block = 0; ; relative_block++) { | |
157 | if (relative_block == last) { | |
158 | /* needed? */ | |
159 | map.m_flags &= ~EXT4_MAP_MAPPED; | |
160 | break; | |
161 | } | |
162 | if (page_block == blocks_per_page) | |
163 | break; | |
164 | blocks[page_block] = map.m_pblk + map_offset + | |
165 | relative_block; | |
166 | page_block++; | |
167 | block_in_file++; | |
168 | } | |
169 | } | |
170 | ||
171 | /* | |
172 | * Then do more ext4_map_blocks() calls until we are | |
173 | * done with this page. | |
174 | */ | |
175 | while (page_block < blocks_per_page) { | |
176 | if (block_in_file < last_block) { | |
177 | map.m_lblk = block_in_file; | |
178 | map.m_len = last_block - block_in_file; | |
179 | ||
180 | if (ext4_map_blocks(NULL, inode, &map, 0) < 0) { | |
181 | set_error_page: | |
182 | SetPageError(page); | |
183 | zero_user_segment(page, 0, | |
184 | PAGE_SIZE); | |
185 | unlock_page(page); | |
186 | goto next_page; | |
187 | } | |
188 | } | |
189 | if ((map.m_flags & EXT4_MAP_MAPPED) == 0) { | |
190 | fully_mapped = 0; | |
191 | if (first_hole == blocks_per_page) | |
192 | first_hole = page_block; | |
193 | page_block++; | |
194 | block_in_file++; | |
195 | continue; | |
196 | } | |
197 | if (first_hole != blocks_per_page) | |
198 | goto confused; /* hole -> non-hole */ | |
199 | ||
200 | /* Contiguous blocks? */ | |
201 | if (page_block && blocks[page_block-1] != map.m_pblk-1) | |
202 | goto confused; | |
203 | for (relative_block = 0; ; relative_block++) { | |
204 | if (relative_block == map.m_len) { | |
205 | /* needed? */ | |
206 | map.m_flags &= ~EXT4_MAP_MAPPED; | |
207 | break; | |
208 | } else if (page_block == blocks_per_page) | |
209 | break; | |
210 | blocks[page_block] = map.m_pblk+relative_block; | |
211 | page_block++; | |
212 | block_in_file++; | |
213 | } | |
214 | } | |
215 | if (first_hole != blocks_per_page) { | |
216 | zero_user_segment(page, first_hole << blkbits, | |
217 | PAGE_SIZE); | |
218 | if (first_hole == 0) { | |
219 | SetPageUptodate(page); | |
220 | unlock_page(page); | |
221 | goto next_page; | |
222 | } | |
223 | } else if (fully_mapped) { | |
224 | SetPageMappedToDisk(page); | |
225 | } | |
226 | if (fully_mapped && blocks_per_page == 1 && | |
227 | !PageUptodate(page) && cleancache_get_page(page) == 0) { | |
228 | SetPageUptodate(page); | |
229 | goto confused; | |
230 | } | |
231 | ||
232 | /* | |
233 | * This page will go to BIO. Do we need to send this | |
234 | * BIO off first? | |
235 | */ | |
236 | if (bio && (last_block_in_bio != blocks[0] - 1)) { | |
237 | submit_and_realloc: | |
238 | submit_bio(bio); | |
239 | bio = NULL; | |
240 | } | |
241 | if (bio == NULL) { | |
242 | struct fscrypt_ctx *ctx = NULL; | |
243 | ||
244 | if (ext4_encrypted_inode(inode) && | |
245 | S_ISREG(inode->i_mode)) { | |
246 | ctx = fscrypt_get_ctx(inode, GFP_NOFS); | |
247 | if (IS_ERR(ctx)) | |
248 | goto set_error_page; | |
249 | } | |
250 | bio = bio_alloc(GFP_KERNEL, | |
251 | min_t(int, nr_pages, BIO_MAX_PAGES)); | |
252 | if (!bio) { | |
253 | if (ctx) | |
254 | fscrypt_release_ctx(ctx); | |
255 | goto set_error_page; | |
256 | } | |
257 | bio->bi_bdev = bdev; | |
258 | bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9); | |
259 | bio->bi_end_io = mpage_end_io; | |
260 | bio->bi_private = ctx; | |
261 | bio_set_op_attrs(bio, REQ_OP_READ, 0); | |
262 | } | |
263 | ||
264 | length = first_hole << blkbits; | |
265 | if (bio_add_page(bio, page, length, 0) < length) | |
266 | goto submit_and_realloc; | |
267 | ||
268 | if (((map.m_flags & EXT4_MAP_BOUNDARY) && | |
269 | (relative_block == map.m_len)) || | |
270 | (first_hole != blocks_per_page)) { | |
271 | submit_bio(bio); | |
272 | bio = NULL; | |
273 | } else | |
274 | last_block_in_bio = blocks[blocks_per_page - 1]; | |
275 | goto next_page; | |
276 | confused: | |
277 | if (bio) { | |
278 | submit_bio(bio); | |
279 | bio = NULL; | |
280 | } | |
281 | if (!PageUptodate(page)) | |
282 | block_read_full_page(page, ext4_get_block); | |
283 | else | |
284 | unlock_page(page); | |
285 | next_page: | |
286 | if (pages) | |
287 | put_page(page); | |
288 | } | |
289 | BUG_ON(pages && !list_empty(pages)); | |
290 | if (bio) | |
291 | submit_bio(bio); | |
292 | return 0; | |
293 | } |