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-rw-r--r--fs/ext4/readpage.c295
1 files changed, 295 insertions, 0 deletions
diff --git a/fs/ext4/readpage.c b/fs/ext4/readpage.c
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+// SPDX-License-Identifier: GPL-2.0
+/*
+ * linux/fs/ext4/readpage.c
+ *
+ * Copyright (C) 2002, Linus Torvalds.
+ * Copyright (C) 2015, Google, Inc.
+ *
+ * This was originally taken from fs/mpage.c
+ *
+ * The intent is the ext4_mpage_readpages() function here is intended
+ * to replace mpage_readpages() in the general case, not just for
+ * encrypted files. It has some limitations (see below), where it
+ * will fall back to read_block_full_page(), but these limitations
+ * should only be hit when page_size != block_size.
+ *
+ * This will allow us to attach a callback function to support ext4
+ * encryption.
+ *
+ * If anything unusual happens, such as:
+ *
+ * - encountering a page which has buffers
+ * - encountering a page which has a non-hole after a hole
+ * - encountering a page with non-contiguous blocks
+ *
+ * then this code just gives up and calls the buffer_head-based read function.
+ * It does handle a page which has holes at the end - that is a common case:
+ * the end-of-file on blocksize < PAGE_SIZE setups.
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/export.h>
+#include <linux/mm.h>
+#include <linux/kdev_t.h>
+#include <linux/gfp.h>
+#include <linux/bio.h>
+#include <linux/fs.h>
+#include <linux/buffer_head.h>
+#include <linux/blkdev.h>
+#include <linux/highmem.h>
+#include <linux/prefetch.h>
+#include <linux/mpage.h>
+#include <linux/writeback.h>
+#include <linux/backing-dev.h>
+#include <linux/pagevec.h>
+#include <linux/cleancache.h>
+
+#include "ext4.h"
+
+static inline bool ext4_bio_encrypted(struct bio *bio)
+{
+#ifdef CONFIG_EXT4_FS_ENCRYPTION
+ return unlikely(bio->bi_private != NULL);
+#else
+ return false;
+#endif
+}
+
+/*
+ * I/O completion handler for multipage BIOs.
+ *
+ * The mpage code never puts partial pages into a BIO (except for end-of-file).
+ * If a page does not map to a contiguous run of blocks then it simply falls
+ * back to block_read_full_page().
+ *
+ * Why is this? If a page's completion depends on a number of different BIOs
+ * which can complete in any order (or at the same time) then determining the
+ * status of that page is hard. See end_buffer_async_read() for the details.
+ * There is no point in duplicating all that complexity.
+ */
+static void mpage_end_io(struct bio *bio)
+{
+ struct bio_vec *bv;
+ int i;
+
+ if (ext4_bio_encrypted(bio)) {
+ if (bio->bi_status) {
+ fscrypt_release_ctx(bio->bi_private);
+ } else {
+ fscrypt_enqueue_decrypt_bio(bio->bi_private, bio);
+ return;
+ }
+ }
+ bio_for_each_segment_all(bv, bio, i) {
+ struct page *page = bv->bv_page;
+
+ if (!bio->bi_status) {
+ SetPageUptodate(page);
+ } else {
+ ClearPageUptodate(page);
+ SetPageError(page);
+ }
+ unlock_page(page);
+ }
+
+ bio_put(bio);
+}
+
+int ext4_mpage_readpages(struct address_space *mapping,
+ struct list_head *pages, struct page *page,
+ unsigned nr_pages, bool is_readahead)
+{
+ struct bio *bio = NULL;
+ sector_t last_block_in_bio = 0;
+
+ struct inode *inode = mapping->host;
+ const unsigned blkbits = inode->i_blkbits;
+ const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
+ const unsigned blocksize = 1 << blkbits;
+ sector_t block_in_file;
+ sector_t last_block;
+ sector_t last_block_in_file;
+ sector_t blocks[MAX_BUF_PER_PAGE];
+ unsigned page_block;
+ struct block_device *bdev = inode->i_sb->s_bdev;
+ int length;
+ unsigned relative_block = 0;
+ struct ext4_map_blocks map;
+
+ map.m_pblk = 0;
+ map.m_lblk = 0;
+ map.m_len = 0;
+ map.m_flags = 0;
+
+ for (; nr_pages; nr_pages--) {
+ int fully_mapped = 1;
+ unsigned first_hole = blocks_per_page;
+
+ prefetchw(&page->flags);
+ if (pages) {
+ page = list_entry(pages->prev, struct page, lru);
+ list_del(&page->lru);
+ if (add_to_page_cache_lru(page, mapping, page->index,
+ readahead_gfp_mask(mapping)))
+ goto next_page;
+ }
+
+ if (page_has_buffers(page))
+ goto confused;
+
+ block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
+ last_block = block_in_file + nr_pages * blocks_per_page;
+ last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
+ if (last_block > last_block_in_file)
+ last_block = last_block_in_file;
+ page_block = 0;
+
+ /*
+ * Map blocks using the previous result first.
+ */
+ if ((map.m_flags & EXT4_MAP_MAPPED) &&
+ block_in_file > map.m_lblk &&
+ block_in_file < (map.m_lblk + map.m_len)) {
+ unsigned map_offset = block_in_file - map.m_lblk;
+ unsigned last = map.m_len - map_offset;
+
+ for (relative_block = 0; ; relative_block++) {
+ if (relative_block == last) {
+ /* needed? */
+ map.m_flags &= ~EXT4_MAP_MAPPED;
+ break;
+ }
+ if (page_block == blocks_per_page)
+ break;
+ blocks[page_block] = map.m_pblk + map_offset +
+ relative_block;
+ page_block++;
+ block_in_file++;
+ }
+ }
+
+ /*
+ * Then do more ext4_map_blocks() calls until we are
+ * done with this page.
+ */
+ while (page_block < blocks_per_page) {
+ if (block_in_file < last_block) {
+ map.m_lblk = block_in_file;
+ map.m_len = last_block - block_in_file;
+
+ if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
+ set_error_page:
+ SetPageError(page);
+ zero_user_segment(page, 0,
+ PAGE_SIZE);
+ unlock_page(page);
+ goto next_page;
+ }
+ }
+ if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
+ fully_mapped = 0;
+ if (first_hole == blocks_per_page)
+ first_hole = page_block;
+ page_block++;
+ block_in_file++;
+ continue;
+ }
+ if (first_hole != blocks_per_page)
+ goto confused; /* hole -> non-hole */
+
+ /* Contiguous blocks? */
+ if (page_block && blocks[page_block-1] != map.m_pblk-1)
+ goto confused;
+ for (relative_block = 0; ; relative_block++) {
+ if (relative_block == map.m_len) {
+ /* needed? */
+ map.m_flags &= ~EXT4_MAP_MAPPED;
+ break;
+ } else if (page_block == blocks_per_page)
+ break;
+ blocks[page_block] = map.m_pblk+relative_block;
+ page_block++;
+ block_in_file++;
+ }
+ }
+ if (first_hole != blocks_per_page) {
+ zero_user_segment(page, first_hole << blkbits,
+ PAGE_SIZE);
+ if (first_hole == 0) {
+ SetPageUptodate(page);
+ unlock_page(page);
+ goto next_page;
+ }
+ } else if (fully_mapped) {
+ SetPageMappedToDisk(page);
+ }
+ if (fully_mapped && blocks_per_page == 1 &&
+ !PageUptodate(page) && cleancache_get_page(page) == 0) {
+ SetPageUptodate(page);
+ goto confused;
+ }
+
+ /*
+ * This page will go to BIO. Do we need to send this
+ * BIO off first?
+ */
+ if (bio && (last_block_in_bio != blocks[0] - 1)) {
+ submit_and_realloc:
+ submit_bio(bio);
+ bio = NULL;
+ }
+ if (bio == NULL) {
+ struct fscrypt_ctx *ctx = NULL;
+
+ if (ext4_encrypted_inode(inode) &&
+ S_ISREG(inode->i_mode)) {
+ ctx = fscrypt_get_ctx(inode, GFP_NOFS);
+ if (IS_ERR(ctx))
+ goto set_error_page;
+ }
+ bio = bio_alloc(GFP_KERNEL,
+ min_t(int, nr_pages, BIO_MAX_PAGES));
+ if (!bio) {
+ if (ctx)
+ fscrypt_release_ctx(ctx);
+ goto set_error_page;
+ }
+ bio_set_dev(bio, bdev);
+ bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
+ bio->bi_end_io = mpage_end_io;
+ bio->bi_private = ctx;
+ bio_set_op_attrs(bio, REQ_OP_READ,
+ is_readahead ? REQ_RAHEAD : 0);
+ }
+
+ length = first_hole << blkbits;
+ if (bio_add_page(bio, page, length, 0) < length)
+ goto submit_and_realloc;
+
+ if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
+ (relative_block == map.m_len)) ||
+ (first_hole != blocks_per_page)) {
+ submit_bio(bio);
+ bio = NULL;
+ } else
+ last_block_in_bio = blocks[blocks_per_page - 1];
+ goto next_page;
+ confused:
+ if (bio) {
+ submit_bio(bio);
+ bio = NULL;
+ }
+ if (!PageUptodate(page))
+ block_read_full_page(page, ext4_get_block);
+ else
+ unlock_page(page);
+ next_page:
+ if (pages)
+ put_page(page);
+ }
+ BUG_ON(pages && !list_empty(pages));
+ if (bio)
+ submit_bio(bio);
+ return 0;
+}
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