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_CACHE_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 */ 53 static 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, work); 58 struct bio *bio = ctx->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(ctx, 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 80 static 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 */ 101 static void mpage_end_io(struct bio *bio, int err) 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 (err) { 110 ext4_release_crypto_ctx(ctx); 111 } else { 112 INIT_WORK(&ctx->work, completion_pages); 113 ctx->bio = bio; 114 queue_work(ext4_read_workqueue, &ctx->work); 115 return; 116 } 117 } 118 bio_for_each_segment_all(bv, bio, i) { 119 struct page *page = bv->bv_page; 120 121 if (!err) { 122 SetPageUptodate(page); 123 } else { 124 ClearPageUptodate(page); 125 SetPageError(page); 126 } 127 unlock_page(page); 128 } 129 130 bio_put(bio); 131 } 132 133 int 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_CACHE_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, 169 page->index, 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_CACHE_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_CACHE_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_CACHE_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); 283 if (IS_ERR(ctx)) 284 goto set_error_page; 285 } 286 bio = bio_alloc(GFP_KERNEL, 287 min_t(int, nr_pages, bio_get_nr_vecs(bdev))); 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 page_cache_release(page); 323 } 324 BUG_ON(pages && !list_empty(pages)); 325 if (bio) 326 submit_bio(READ, bio); 327 return 0; 328 } 329