Theodore Ts'o | f64e02f | 2015-04-08 00:00:32 -0400 | [diff] [blame^] | 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 | } |