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_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  * I/O completion handler for multipage BIOs.
  51  *
  52  * The mpage code never puts partial pages into a BIO (except for end-of-file).
  53  * If a page does not map to a contiguous run of blocks then it simply falls
  54  * back to block_read_full_page().
  55  *
  56  * Why is this?  If a page's completion depends on a number of different BIOs
  57  * which can complete in any order (or at the same time) then determining the
  58  * status of that page is hard.  See end_buffer_async_read() for the details.
  59  * There is no point in duplicating all that complexity.
  60  */
  61 static void mpage_end_io(struct bio *bio, int err)
  62 {
  63         struct bio_vec *bv;
  64         int i;
  65
  66         bio_for_each_segment_all(bv, bio, i) {
  67                 struct page *page = bv->bv_page;
  68
  69                 if (!err) {
  70                         SetPageUptodate(page);
  71                 } else {
  72                         ClearPageUptodate(page);
  73                         SetPageError(page);
  74                 }
  75                 unlock_page(page);
  76         }
  77
  78         bio_put(bio);
  79 }
  80
  81 int ext4_mpage_readpages(struct address_space *mapping,
  82                          struct list_head *pages, struct page *page,
  83                          unsigned nr_pages)
  84 {
  85         struct bio *bio = NULL;
  86         unsigned page_idx;
  87         sector_t last_block_in_bio = 0;
  88
  89         struct inode *inode = mapping->host;
  90         const unsigned blkbits = inode->i_blkbits;
  91         const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
  92         const unsigned blocksize = 1 << blkbits;
  93         sector_t block_in_file;
  94         sector_t last_block;
  95         sector_t last_block_in_file;
  96         sector_t blocks[MAX_BUF_PER_PAGE];
  97         unsigned page_block;
  98         struct block_device *bdev = inode->i_sb->s_bdev;
  99         int length;
 100         unsigned relative_block = 0;
 101         struct ext4_map_blocks map;
 102
 103         map.m_pblk = 0;
 104         map.m_lblk = 0;
 105         map.m_len = 0;
 106         map.m_flags = 0;
 107
 108         for (page_idx = 0; nr_pages; page_idx++, nr_pages--) {
 109                 int fully_mapped = 1;
 110                 unsigned first_hole = blocks_per_page;
 111
 112                 prefetchw(&page->flags);
 113                 if (pages) {
 114                         page = list_entry(pages->prev, struct page, lru);
 115                         list_del(&page->lru);
 116                         if (add_to_page_cache_lru(page, mapping,
 117                                                   page->index, GFP_KERNEL))
 118                                 goto next_page;
 119                 }
 120
 121                 if (page_has_buffers(page))
 122                         goto confused;
 123
 124                 block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
 125                 last_block = block_in_file + nr_pages * blocks_per_page;
 126                 last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
 127                 if (last_block > last_block_in_file)
 128                         last_block = last_block_in_file;
 129                 page_block = 0;
 130
 131                 /*
 132                  * Map blocks using the previous result first.
 133                  */
 134                 if ((map.m_flags & EXT4_MAP_MAPPED) &&
 135                     block_in_file > map.m_lblk &&
 136                     block_in_file < (map.m_lblk + map.m_len)) {
 137                         unsigned map_offset = block_in_file - map.m_lblk;
 138                         unsigned last = map.m_len - map_offset;
 139
 140                         for (relative_block = 0; ; relative_block++) {
 141                                 if (relative_block == last) {
 142                                         /* needed? */
 143                                         map.m_flags &= ~EXT4_MAP_MAPPED;
 144                                         break;
 145                                 }
 146                                 if (page_block == blocks_per_page)
 147                                         break;
 148                                 blocks[page_block] = map.m_pblk + map_offset +
 149                                         relative_block;
 150                                 page_block++;
 151                                 block_in_file++;
 152                         }
 153                 }
 154
 155                 /*
 156                  * Then do more ext4_map_blocks() calls until we are
 157                  * done with this page.
 158                  */
 159                 while (page_block < blocks_per_page) {
 160                         if (block_in_file < last_block) {
 161                                 map.m_lblk = block_in_file;
 162                                 map.m_len = last_block - block_in_file;
 163
 164                                 if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
 165                                 set_error_page:
 166                                         SetPageError(page);
 167                                         zero_user_segment(page, 0,
 168                                                           PAGE_CACHE_SIZE);
 169                                         unlock_page(page);
 170                                         goto next_page;
 171                                 }
 172                         }
 173                         if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
 174                                 fully_mapped = 0;
 175                                 if (first_hole == blocks_per_page)
 176                                         first_hole = page_block;
 177                                 page_block++;
 178                                 block_in_file++;
 179                                 continue;
 180                         }
 181                         if (first_hole != blocks_per_page)
 182                                 goto confused;          /* hole -> non-hole */
 183
 184                         /* Contiguous blocks? */
 185                         if (page_block && blocks[page_block-1] != map.m_pblk-1)
 186                                 goto confused;
 187                         for (relative_block = 0; ; relative_block++) {
 188                                 if (relative_block == map.m_len) {
 189                                         /* needed? */
 190                                         map.m_flags &= ~EXT4_MAP_MAPPED;
 191                                         break;
 192                                 } else if (page_block == blocks_per_page)
 193                                         break;
 194                                 blocks[page_block] = map.m_pblk+relative_block;
 195                                 page_block++;
 196                                 block_in_file++;
 197                         }
 198                 }
 199                 if (first_hole != blocks_per_page) {
 200                         zero_user_segment(page, first_hole << blkbits,
 201                                           PAGE_CACHE_SIZE);
 202                         if (first_hole == 0) {
 203                                 SetPageUptodate(page);
 204                                 unlock_page(page);
 205                                 goto next_page;
 206                         }
 207                 } else if (fully_mapped) {
 208                         SetPageMappedToDisk(page);
 209                 }
 210                 if (fully_mapped && blocks_per_page == 1 &&
 211                     !PageUptodate(page) && cleancache_get_page(page) == 0) {
 212                         SetPageUptodate(page);
 213                         goto confused;
 214                 }
 215
 216                 /*
 217                  * This page will go to BIO.  Do we need to send this
 218                  * BIO off first?
 219                  */
 220                 if (bio && (last_block_in_bio != blocks[0] - 1)) {
 221                 submit_and_realloc:
 222                         submit_bio(READ, bio);
 223                         bio = NULL;
 224                 }
 225                 if (bio == NULL) {
 226                         bio = bio_alloc(GFP_KERNEL,
 227                                 min_t(int, nr_pages, bio_get_nr_vecs(bdev)));
 228                         if (!bio)
 229                                 goto set_error_page;
 230                         bio->bi_bdev = bdev;
 231                         bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
 232                         bio->bi_end_io = mpage_end_io;
 233                 }
 234
 235                 length = first_hole << blkbits;
 236                 if (bio_add_page(bio, page, length, 0) < length)
 237                         goto submit_and_realloc;
 238
 239                 if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
 240                      (relative_block == map.m_len)) ||
 241                     (first_hole != blocks_per_page)) {
 242                         submit_bio(READ, bio);
 243                         bio = NULL;
 244                 } else
 245                         last_block_in_bio = blocks[blocks_per_page - 1];
 246                 goto next_page;
 247         confused:
 248                 if (bio) {
 249                         submit_bio(READ, bio);
 250                         bio = NULL;
 251                 }
 252                 if (!PageUptodate(page))
 253                         block_read_full_page(page, ext4_get_block);
 254                 else
 255                         unlock_page(page);
 256         next_page:
 257                 if (pages)
 258                         page_cache_release(page);
 259         }
 260         BUG_ON(pages && !list_empty(pages));
 261         if (bio)
 262                 submit_bio(READ, bio);
 263         return 0;
 264 }