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 /*
  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, r.work);
  58         struct bio      *bio    = ctx->r.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(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)
 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 (bio->bi_error) {
 110                         ext4_release_crypto_ctx(ctx);
 111                 } else {
 112                         INIT_WORK(&ctx->r.work, completion_pages);
 113                         ctx->r.bio = bio;
 114                         queue_work(ext4_read_workqueue, &ctx->r.work);
 115                         return;
 116                 }
 117         }
 118         bio_for_each_segment_all(bv, bio, i) {
 119                 struct page *page = bv->bv_page;
 120
 121                 if (!bio->bi_error) {
 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_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, page->index,
 169                                   mapping_gfp_constraint(mapping, 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_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_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_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, GFP_NOFS);
 283                                 if (IS_ERR(ctx))
 284                                         goto set_error_page;
 285                         }
 286                         bio = bio_alloc(GFP_KERNEL,
 287                                 min_t(int, nr_pages, BIO_MAX_PAGES));
 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                         put_page(page);
 323         }
 324         BUG_ON(pages && !list_empty(pages));
 325         if (bio)
 326                 submit_bio(READ, bio);
 327         return 0;
 328 }