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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
49static 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 */
70static 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_error) {
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_error) {
87 SetPageUptodate(page);
88 } else {
89 ClearPageUptodate(page);
90 SetPageError(page);
91 }
92 unlock_page(page);
93 }
94
95 bio_put(bio);
96}
97
98int 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}