fs/ext4/readpage.c

   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 }