fs/ext4/readpage.c

   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 }