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Linux/fs/ext4/readpage.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*
  3  * linux/fs/ext4/readpage.c
  4  *
  5  * Copyright (C) 2002, Linus Torvalds.
  6  * Copyright (C) 2015, Google, Inc.
  7  *
  8  * This was originally taken from fs/mpage.c
  9  *
 10  * The intent is the ext4_mpage_readpages() function here is intended
 11  * to replace mpage_readpages() in the general case, not just for
 12  * encrypted files.  It has some limitations (see below), where it
 13  * will fall back to read_block_full_page(), but these limitations
 14  * should only be hit when page_size != block_size.
 15  *
 16  * This will allow us to attach a callback function to support ext4
 17  * encryption.
 18  *
 19  * If anything unusual happens, such as:
 20  *
 21  * - encountering a page which has buffers
 22  * - encountering a page which has a non-hole after a hole
 23  * - encountering a page with non-contiguous blocks
 24  *
 25  * then this code just gives up and calls the buffer_head-based read function.
 26  * It does handle a page which has holes at the end - that is a common case:
 27  * the end-of-file on blocksize < PAGE_SIZE setups.
 28  *
 29  */
 30 
 31 #include <linux/kernel.h>
 32 #include <linux/export.h>
 33 #include <linux/mm.h>
 34 #include <linux/kdev_t.h>
 35 #include <linux/gfp.h>
 36 #include <linux/bio.h>
 37 #include <linux/fs.h>
 38 #include <linux/buffer_head.h>
 39 #include <linux/blkdev.h>
 40 #include <linux/highmem.h>
 41 #include <linux/prefetch.h>
 42 #include <linux/mpage.h>
 43 #include <linux/writeback.h>
 44 #include <linux/backing-dev.h>
 45 #include <linux/pagevec.h>
 46 #include <linux/cleancache.h>
 47 
 48 #include "ext4.h"
 49 
 50 static inline bool ext4_bio_encrypted(struct bio *bio)
 51 {
 52 #ifdef CONFIG_EXT4_FS_ENCRYPTION
 53         return unlikely(bio->bi_private != NULL);
 54 #else
 55         return false;
 56 #endif
 57 }
 58 
 59 /*
 60  * I/O completion handler for multipage BIOs.
 61  *
 62  * The mpage code never puts partial pages into a BIO (except for end-of-file).
 63  * If a page does not map to a contiguous run of blocks then it simply falls
 64  * back to block_read_full_page().
 65  *
 66  * Why is this?  If a page's completion depends on a number of different BIOs
 67  * which can complete in any order (or at the same time) then determining the
 68  * status of that page is hard.  See end_buffer_async_read() for the details.
 69  * There is no point in duplicating all that complexity.
 70  */
 71 static void mpage_end_io(struct bio *bio)
 72 {
 73         struct bio_vec *bv;
 74         int i;
 75 
 76         if (ext4_bio_encrypted(bio)) {
 77                 if (bio->bi_status) {
 78                         fscrypt_release_ctx(bio->bi_private);
 79                 } else {
 80                         fscrypt_decrypt_bio_pages(bio->bi_private, bio);
 81                         return;
 82                 }
 83         }
 84         bio_for_each_segment_all(bv, bio, i) {
 85                 struct page *page = bv->bv_page;
 86 
 87                 if (!bio->bi_status) {
 88                         SetPageUptodate(page);
 89                 } else {
 90                         ClearPageUptodate(page);
 91                         SetPageError(page);
 92                 }
 93                 unlock_page(page);
 94         }
 95 
 96         bio_put(bio);
 97 }
 98 
 99 int ext4_mpage_readpages(struct address_space *mapping,
100                          struct list_head *pages, struct page *page,
101                          unsigned nr_pages)
102 {
103         struct bio *bio = NULL;
104         sector_t last_block_in_bio = 0;
105 
106         struct inode *inode = mapping->host;
107         const unsigned blkbits = inode->i_blkbits;
108         const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
109         const unsigned blocksize = 1 << blkbits;
110         sector_t block_in_file;
111         sector_t last_block;
112         sector_t last_block_in_file;
113         sector_t blocks[MAX_BUF_PER_PAGE];
114         unsigned page_block;
115         struct block_device *bdev = inode->i_sb->s_bdev;
116         int length;
117         unsigned relative_block = 0;
118         struct ext4_map_blocks map;
119 
120         map.m_pblk = 0;
121         map.m_lblk = 0;
122         map.m_len = 0;
123         map.m_flags = 0;
124 
125         for (; nr_pages; nr_pages--) {
126                 int fully_mapped = 1;
127                 unsigned first_hole = blocks_per_page;
128 
129                 prefetchw(&page->flags);
130                 if (pages) {
131                         page = list_entry(pages->prev, struct page, lru);
132                         list_del(&page->lru);
133                         if (add_to_page_cache_lru(page, mapping, page->index,
134                                   readahead_gfp_mask(mapping)))
135                                 goto next_page;
136                 }
137 
138                 if (page_has_buffers(page))
139                         goto confused;
140 
141                 block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
142                 last_block = block_in_file + nr_pages * blocks_per_page;
143                 last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
144                 if (last_block > last_block_in_file)
145                         last_block = last_block_in_file;
146                 page_block = 0;
147 
148                 /*
149                  * Map blocks using the previous result first.
150                  */
151                 if ((map.m_flags & EXT4_MAP_MAPPED) &&
152                     block_in_file > map.m_lblk &&
153                     block_in_file < (map.m_lblk + map.m_len)) {
154                         unsigned map_offset = block_in_file - map.m_lblk;
155                         unsigned last = map.m_len - map_offset;
156 
157                         for (relative_block = 0; ; relative_block++) {
158                                 if (relative_block == last) {
159                                         /* needed? */
160                                         map.m_flags &= ~EXT4_MAP_MAPPED;
161                                         break;
162                                 }
163                                 if (page_block == blocks_per_page)
164                                         break;
165                                 blocks[page_block] = map.m_pblk + map_offset +
166                                         relative_block;
167                                 page_block++;
168                                 block_in_file++;
169                         }
170                 }
171 
172                 /*
173                  * Then do more ext4_map_blocks() calls until we are
174                  * done with this page.
175                  */
176                 while (page_block < blocks_per_page) {
177                         if (block_in_file < last_block) {
178                                 map.m_lblk = block_in_file;
179                                 map.m_len = last_block - block_in_file;
180 
181                                 if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
182                                 set_error_page:
183                                         SetPageError(page);
184                                         zero_user_segment(page, 0,
185                                                           PAGE_SIZE);
186                                         unlock_page(page);
187                                         goto next_page;
188                                 }
189                         }
190                         if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
191                                 fully_mapped = 0;
192                                 if (first_hole == blocks_per_page)
193                                         first_hole = page_block;
194                                 page_block++;
195                                 block_in_file++;
196                                 continue;
197                         }
198                         if (first_hole != blocks_per_page)
199                                 goto confused;          /* hole -> non-hole */
200 
201                         /* Contiguous blocks? */
202                         if (page_block && blocks[page_block-1] != map.m_pblk-1)
203                                 goto confused;
204                         for (relative_block = 0; ; relative_block++) {
205                                 if (relative_block == map.m_len) {
206                                         /* needed? */
207                                         map.m_flags &= ~EXT4_MAP_MAPPED;
208                                         break;
209                                 } else if (page_block == blocks_per_page)
210                                         break;
211                                 blocks[page_block] = map.m_pblk+relative_block;
212                                 page_block++;
213                                 block_in_file++;
214                         }
215                 }
216                 if (first_hole != blocks_per_page) {
217                         zero_user_segment(page, first_hole << blkbits,
218                                           PAGE_SIZE);
219                         if (first_hole == 0) {
220                                 SetPageUptodate(page);
221                                 unlock_page(page);
222                                 goto next_page;
223                         }
224                 } else if (fully_mapped) {
225                         SetPageMappedToDisk(page);
226                 }
227                 if (fully_mapped && blocks_per_page == 1 &&
228                     !PageUptodate(page) && cleancache_get_page(page) == 0) {
229                         SetPageUptodate(page);
230                         goto confused;
231                 }
232 
233                 /*
234                  * This page will go to BIO.  Do we need to send this
235                  * BIO off first?
236                  */
237                 if (bio && (last_block_in_bio != blocks[0] - 1)) {
238                 submit_and_realloc:
239                         submit_bio(bio);
240                         bio = NULL;
241                 }
242                 if (bio == NULL) {
243                         struct fscrypt_ctx *ctx = NULL;
244 
245                         if (ext4_encrypted_inode(inode) &&
246                             S_ISREG(inode->i_mode)) {
247                                 ctx = fscrypt_get_ctx(inode, GFP_NOFS);
248                                 if (IS_ERR(ctx))
249                                         goto set_error_page;
250                         }
251                         bio = bio_alloc(GFP_KERNEL,
252                                 min_t(int, nr_pages, BIO_MAX_PAGES));
253                         if (!bio) {
254                                 if (ctx)
255                                         fscrypt_release_ctx(ctx);
256                                 goto set_error_page;
257                         }
258                         bio_set_dev(bio, bdev);
259                         bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
260                         bio->bi_end_io = mpage_end_io;
261                         bio->bi_private = ctx;
262                         bio_set_op_attrs(bio, REQ_OP_READ, 0);
263                 }
264 
265                 length = first_hole << blkbits;
266                 if (bio_add_page(bio, page, length, 0) < length)
267                         goto submit_and_realloc;
268 
269                 if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
270                      (relative_block == map.m_len)) ||
271                     (first_hole != blocks_per_page)) {
272                         submit_bio(bio);
273                         bio = NULL;
274                 } else
275                         last_block_in_bio = blocks[blocks_per_page - 1];
276                 goto next_page;
277         confused:
278                 if (bio) {
279                         submit_bio(bio);
280                         bio = NULL;
281                 }
282                 if (!PageUptodate(page))
283                         block_read_full_page(page, ext4_get_block);
284                 else
285                         unlock_page(page);
286         next_page:
287                 if (pages)
288                         put_page(page);
289         }
290         BUG_ON(pages && !list_empty(pages));
291         if (bio)
292                 submit_bio(bio);
293         return 0;
294 }
295 

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