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Message-Id: <1428012659-12709-2-git-send-email-tytso@mit.edu>
Date: Thu, 2 Apr 2015 18:10:38 -0400
From: Theodore Ts'o <tytso@....edu>
To: Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc: jaegeuk@...nel.org, mhalcrow@...gle.com,
Theodore Ts'o <tytso@....edu>
Subject: [PATCH 01/22] ext4: add ext4_mpage_readpages()
This takes code from fs/mpage.c and optimizes it for ext4. Its
primary reason is to allow us to more easily add encryption to ext4's
read path in an efficient manner.
Change-Id: I0a115e90ab13861ab3e96641a0eb82b951198ecc
Signed-off-by: Theodore Ts'o <tytso@....edu>
---
fs/ext4/Makefile | 2 +-
fs/ext4/ext4.h | 4 +
fs/ext4/inode.c | 4 +-
fs/ext4/readpage.c | 261 +++++++++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 268 insertions(+), 3 deletions(-)
create mode 100644 fs/ext4/readpage.c
diff --git a/fs/ext4/Makefile b/fs/ext4/Makefile
index 0310fec..cd6f50f 100644
--- a/fs/ext4/Makefile
+++ b/fs/ext4/Makefile
@@ -8,7 +8,7 @@ ext4-y := balloc.o bitmap.o dir.o file.o fsync.o ialloc.o inode.o page-io.o \
ioctl.o namei.o super.o symlink.o hash.o resize.o extents.o \
ext4_jbd2.o migrate.o mballoc.o block_validity.o move_extent.o \
mmp.o indirect.o extents_status.o xattr.o xattr_user.o \
- xattr_trusted.o inline.o
+ xattr_trusted.o inline.o readpage.o
ext4-$(CONFIG_EXT4_FS_POSIX_ACL) += acl.o
ext4-$(CONFIG_EXT4_FS_SECURITY) += xattr_security.o
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index a75fba6..06e8add 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2683,6 +2683,10 @@ static inline void ext4_set_de_type(struct super_block *sb,
de->file_type = ext4_type_by_mode[(mode & S_IFMT)>>S_SHIFT];
}
+/* readpages.c */
+extern int ext4_mpage_readpages(struct address_space *mapping,
+ struct list_head *pages, struct page *page,
+ unsigned nr_pages);
/* symlink.c */
extern const struct inode_operations ext4_symlink_inode_operations;
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 5653fa4..a68cacc 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2798,7 +2798,7 @@ static int ext4_readpage(struct file *file, struct page *page)
ret = ext4_readpage_inline(inode, page);
if (ret == -EAGAIN)
- return mpage_readpage(page, ext4_get_block);
+ return ext4_mpage_readpages(page->mapping, NULL, page, 1);
return ret;
}
@@ -2813,7 +2813,7 @@ ext4_readpages(struct file *file, struct address_space *mapping,
if (ext4_has_inline_data(inode))
return 0;
- return mpage_readpages(mapping, pages, nr_pages, ext4_get_block);
+ return ext4_mpage_readpages(mapping, pages, NULL, nr_pages);
}
static void ext4_invalidatepage(struct page *page, unsigned int offset,
diff --git a/fs/ext4/readpage.c b/fs/ext4/readpage.c
new file mode 100644
index 0000000..9ca4dfc
--- /dev/null
+++ b/fs/ext4/readpage.c
@@ -0,0 +1,261 @@
+/*
+ * linux/fs/ext4/readpage.c
+ *
+ * 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 never 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_CACHE_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"
+
+/*
+ * 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, int err)
+{
+ struct bio_vec *bv;
+ int i;
+
+ bio_for_each_segment_all(bv, bio, i) {
+ struct page *page = bv->bv_page;
+
+ if (!err) {
+ 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)
+{
+ struct bio *bio = NULL;
+ unsigned page_idx;
+ sector_t last_block_in_bio = 0;
+
+ struct inode *inode = mapping->host;
+ const unsigned blkbits = inode->i_blkbits;
+ const unsigned blocks_per_page = PAGE_CACHE_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 (page_idx = 0; nr_pages; page_idx++, 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, GFP_KERNEL))
+ goto next_page;
+ }
+
+ if (page_has_buffers(page))
+ goto confused;
+
+ block_in_file = (sector_t)page->index << (PAGE_CACHE_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_CACHE_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_CACHE_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(READ, bio);
+ bio = NULL;
+ }
+ if (bio == NULL) {
+ bio = bio_alloc(GFP_KERNEL,
+ min_t(int, nr_pages, bio_get_nr_vecs(bdev)));
+ if (!bio)
+ goto set_error_page;
+ bio->bi_bdev = bdev;
+ bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
+ bio->bi_end_io = mpage_end_io;
+ }
+
+ 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(READ, bio);
+ bio = NULL;
+ } else
+ last_block_in_bio = blocks[blocks_per_page - 1];
+ goto next_page;
+ confused:
+ if (bio) {
+ submit_bio(READ, bio);
+ bio = NULL;
+ }
+ if (!PageUptodate(page))
+ block_read_full_page(page, ext4_get_block);
+ else
+ unlock_page(page);
+ next_page:
+ if (pages)
+ page_cache_release(page);
+ }
+ BUG_ON(pages && !list_empty(pages));
+ if (bio)
+ submit_bio(READ, bio);
+ return 0;
+}
--
2.3.0
--
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