ext4 crypto: 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.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Theodore Ts'o 2015-04-08 00:00:32 -04:00
parent e12fb97222
commit f64e02fe9b
4 changed files with 271 additions and 3 deletions

View File

@ -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

View File

@ -2699,6 +2699,10 @@ 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;

View File

@ -2820,7 +2820,7 @@ 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;
}
@ -2835,7 +2835,7 @@ 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,

264
fs/ext4/readpage.c Normal file
View File

@ -0,0 +1,264 @@
/*
* 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_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;
}