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Commit f64e02fe authored by Theodore Ts'o's avatar Theodore Ts'o
Browse files

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: default avatarTheodore Ts'o <tytso@mit.edu>
parent e12fb972

fs/ext4/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -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

fs/ext4/ext4.h

+4 −0
Original line number Diff line number Diff line
@@ -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;

fs/ext4/inode.c

+2 −2
Original line number Diff line number Diff line
@@ -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,

fs/ext4/readpage.c

0 → 100644
+264 −0
Original line number Diff line number Diff line 
/*

 * 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;

}