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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/*
50 * Call ext4_decrypt on every single page, reusing the encryption
51 * context.
52 */
53static void completion_pages(struct work_struct *work)
54{
55#ifdef CONFIG_EXT4_FS_ENCRYPTION
56 struct ext4_crypto_ctx *ctx =
57 container_of(work, struct ext4_crypto_ctx, r.work);
58 struct bio *bio = ctx->r.bio;
59 struct bio_vec *bv;
60 int i;
61
62 bio_for_each_segment_all(bv, bio, i) {
63 struct page *page = bv->bv_page;
64
65 int ret = ext4_decrypt(page);
66 if (ret) {
67 WARN_ON_ONCE(1);
68 SetPageError(page);
69 } else
70 SetPageUptodate(page);
71 unlock_page(page);
72 }
73 ext4_release_crypto_ctx(ctx);
74 bio_put(bio);
75#else
76 BUG();
77#endif
78}
79
80static inline bool ext4_bio_encrypted(struct bio *bio)
81{
82#ifdef CONFIG_EXT4_FS_ENCRYPTION
83 return unlikely(bio->bi_private != NULL);
84#else
85 return false;
86#endif
87}
88
89/*
90 * I/O completion handler for multipage BIOs.
91 *
92 * The mpage code never puts partial pages into a BIO (except for end-of-file).
93 * If a page does not map to a contiguous run of blocks then it simply falls
94 * back to block_read_full_page().
95 *
96 * Why is this? If a page's completion depends on a number of different BIOs
97 * which can complete in any order (or at the same time) then determining the
98 * status of that page is hard. See end_buffer_async_read() for the details.
99 * There is no point in duplicating all that complexity.
100 */
101static void mpage_end_io(struct bio *bio)
102{
103 struct bio_vec *bv;
104 int i;
105
106 if (ext4_bio_encrypted(bio)) {
107 struct ext4_crypto_ctx *ctx = bio->bi_private;
108
109 if (bio->bi_error) {
110 ext4_release_crypto_ctx(ctx);
111 } else {
112 INIT_WORK(&ctx->r.work, completion_pages);
113 ctx->r.bio = bio;
114 queue_work(ext4_read_workqueue, &ctx->r.work);
115 return;
116 }
117 }
118 bio_for_each_segment_all(bv, bio, i) {
119 struct page *page = bv->bv_page;
120
121 if (!bio->bi_error) {
122 SetPageUptodate(page);
123 } else {
124 ClearPageUptodate(page);
125 SetPageError(page);
126 }
127 unlock_page(page);
128 }
129
130 bio_put(bio);
131}
132
133int ext4_mpage_readpages(struct address_space *mapping,
134 struct list_head *pages, struct page *page,
135 unsigned nr_pages)
136{
137 struct bio *bio = NULL;
138 unsigned page_idx;
139 sector_t last_block_in_bio = 0;
140
141 struct inode *inode = mapping->host;
142 const unsigned blkbits = inode->i_blkbits;
143 const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
144 const unsigned blocksize = 1 << blkbits;
145 sector_t block_in_file;
146 sector_t last_block;
147 sector_t last_block_in_file;
148 sector_t blocks[MAX_BUF_PER_PAGE];
149 unsigned page_block;
150 struct block_device *bdev = inode->i_sb->s_bdev;
151 int length;
152 unsigned relative_block = 0;
153 struct ext4_map_blocks map;
154
155 map.m_pblk = 0;
156 map.m_lblk = 0;
157 map.m_len = 0;
158 map.m_flags = 0;
159
160 for (page_idx = 0; nr_pages; page_idx++, nr_pages--) {
161 int fully_mapped = 1;
162 unsigned first_hole = blocks_per_page;
163
164 prefetchw(&page->flags);
165 if (pages) {
166 page = list_entry(pages->prev, struct page, lru);
167 list_del(&page->lru);
168 if (add_to_page_cache_lru(page, mapping, page->index,
169 mapping_gfp_constraint(mapping, GFP_KERNEL)))
170 goto next_page;
171 }
172
173 if (page_has_buffers(page))
174 goto confused;
175
176 block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
177 last_block = block_in_file + nr_pages * blocks_per_page;
178 last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
179 if (last_block > last_block_in_file)
180 last_block = last_block_in_file;
181 page_block = 0;
182
183 /*
184 * Map blocks using the previous result first.
185 */
186 if ((map.m_flags & EXT4_MAP_MAPPED) &&
187 block_in_file > map.m_lblk &&
188 block_in_file < (map.m_lblk + map.m_len)) {
189 unsigned map_offset = block_in_file - map.m_lblk;
190 unsigned last = map.m_len - map_offset;
191
192 for (relative_block = 0; ; relative_block++) {
193 if (relative_block == last) {
194 /* needed? */
195 map.m_flags &= ~EXT4_MAP_MAPPED;
196 break;
197 }
198 if (page_block == blocks_per_page)
199 break;
200 blocks[page_block] = map.m_pblk + map_offset +
201 relative_block;
202 page_block++;
203 block_in_file++;
204 }
205 }
206
207 /*
208 * Then do more ext4_map_blocks() calls until we are
209 * done with this page.
210 */
211 while (page_block < blocks_per_page) {
212 if (block_in_file < last_block) {
213 map.m_lblk = block_in_file;
214 map.m_len = last_block - block_in_file;
215
216 if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
217 set_error_page:
218 SetPageError(page);
219 zero_user_segment(page, 0,
220 PAGE_SIZE);
221 unlock_page(page);
222 goto next_page;
223 }
224 }
225 if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
226 fully_mapped = 0;
227 if (first_hole == blocks_per_page)
228 first_hole = page_block;
229 page_block++;
230 block_in_file++;
231 continue;
232 }
233 if (first_hole != blocks_per_page)
234 goto confused; /* hole -> non-hole */
235
236 /* Contiguous blocks? */
237 if (page_block && blocks[page_block-1] != map.m_pblk-1)
238 goto confused;
239 for (relative_block = 0; ; relative_block++) {
240 if (relative_block == map.m_len) {
241 /* needed? */
242 map.m_flags &= ~EXT4_MAP_MAPPED;
243 break;
244 } else if (page_block == blocks_per_page)
245 break;
246 blocks[page_block] = map.m_pblk+relative_block;
247 page_block++;
248 block_in_file++;
249 }
250 }
251 if (first_hole != blocks_per_page) {
252 zero_user_segment(page, first_hole << blkbits,
253 PAGE_SIZE);
254 if (first_hole == 0) {
255 SetPageUptodate(page);
256 unlock_page(page);
257 goto next_page;
258 }
259 } else if (fully_mapped) {
260 SetPageMappedToDisk(page);
261 }
262 if (fully_mapped && blocks_per_page == 1 &&
263 !PageUptodate(page) && cleancache_get_page(page) == 0) {
264 SetPageUptodate(page);
265 goto confused;
266 }
267
268 /*
269 * This page will go to BIO. Do we need to send this
270 * BIO off first?
271 */
272 if (bio && (last_block_in_bio != blocks[0] - 1)) {
273 submit_and_realloc:
274 submit_bio(READ, bio);
275 bio = NULL;
276 }
277 if (bio == NULL) {
278 struct ext4_crypto_ctx *ctx = NULL;
279
280 if (ext4_encrypted_inode(inode) &&
281 S_ISREG(inode->i_mode)) {
282 ctx = ext4_get_crypto_ctx(inode, GFP_NOFS);
283 if (IS_ERR(ctx))
284 goto set_error_page;
285 }
286 bio = bio_alloc(GFP_KERNEL,
287 min_t(int, nr_pages, BIO_MAX_PAGES));
288 if (!bio) {
289 if (ctx)
290 ext4_release_crypto_ctx(ctx);
291 goto set_error_page;
292 }
293 bio->bi_bdev = bdev;
294 bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
295 bio->bi_end_io = mpage_end_io;
296 bio->bi_private = ctx;
297 }
298
299 length = first_hole << blkbits;
300 if (bio_add_page(bio, page, length, 0) < length)
301 goto submit_and_realloc;
302
303 if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
304 (relative_block == map.m_len)) ||
305 (first_hole != blocks_per_page)) {
306 submit_bio(READ, bio);
307 bio = NULL;
308 } else
309 last_block_in_bio = blocks[blocks_per_page - 1];
310 goto next_page;
311 confused:
312 if (bio) {
313 submit_bio(READ, bio);
314 bio = NULL;
315 }
316 if (!PageUptodate(page))
317 block_read_full_page(page, ext4_get_block);
318 else
319 unlock_page(page);
320 next_page:
321 if (pages)
322 put_page(page);
323 }
324 BUG_ON(pages && !list_empty(pages));
325 if (bio)
326 submit_bio(READ, bio);
327 return 0;
328}