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Linux/fs/ext4/readpage.c

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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_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 
 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 }
294 

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