Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 759 insertions, 0 deletions

diff --git a/fs/mpage.c b/fs/mpage.c
new file mode 100644
index 000000000..c820dc9be
--- /dev/null
+++ b/fs/mpage.c
@@ -0,0 +1,759 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * fs/mpage.c
+ *
+ * Copyright (C) 2002, Linus Torvalds.
+ *
+ * Contains functions related to preparing and submitting BIOs which contain
+ * multiple pagecache pages.
+ *
+ * 15May2002	Andrew Morton
+ *		Initial version
+ * 27Jun2002	axboe@suse.de
+ *		use bio_add_page() to build bio's just the right size
+ */
+
+#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/mm_inline.h>
+#include <linux/writeback.h>
+#include <linux/backing-dev.h>
+#include <linux/pagevec.h>
+#include <linux/cleancache.h>
+#include "internal.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)
+{
+	struct bio_vec *bv;
+	int i;
+
+	bio_for_each_segment_all(bv, bio, i) {
+		struct page *page = bv->bv_page;
+		page_endio(page, bio_op(bio),
+			   blk_status_to_errno(bio->bi_status));
+	}
+
+	bio_put(bio);
+}
+
+static struct bio *mpage_bio_submit(int op, int op_flags, struct bio *bio)
+{
+	bio->bi_end_io = mpage_end_io;
+	bio_set_op_attrs(bio, op, op_flags);
+	guard_bio_eod(op, bio);
+	submit_bio(bio);
+	return NULL;
+}
+
+static struct bio *
+mpage_alloc(struct block_device *bdev,
+		sector_t first_sector, int nr_vecs,
+		gfp_t gfp_flags)
+{
+	struct bio *bio;
+
+	/* Restrict the given (page cache) mask for slab allocations */
+	gfp_flags &= GFP_KERNEL;
+	bio = bio_alloc(gfp_flags, nr_vecs);
+
+	if (bio == NULL && (current->flags & PF_MEMALLOC)) {
+		while (!bio && (nr_vecs /= 2))
+			bio = bio_alloc(gfp_flags, nr_vecs);
+	}
+
+	if (bio) {
+		bio_set_dev(bio, bdev);
+		bio->bi_iter.bi_sector = first_sector;
+	}
+	return bio;
+}
+
+/*
+ * support function for mpage_readpages.  The fs supplied get_block might
+ * return an up to date buffer.  This is used to map that buffer into
+ * the page, which allows readpage to avoid triggering a duplicate call
+ * to get_block.
+ *
+ * The idea is to avoid adding buffers to pages that don't already have
+ * them.  So when the buffer is up to date and the page size == block size,
+ * this marks the page up to date instead of adding new buffers.
+ */
+static void 
+map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block) 
+{
+	struct inode *inode = page->mapping->host;
+	struct buffer_head *page_bh, *head;
+	int block = 0;
+
+	if (!page_has_buffers(page)) {
+		/*
+		 * don't make any buffers if there is only one buffer on
+		 * the page and the page just needs to be set up to date
+		 */
+		if (inode->i_blkbits == PAGE_SHIFT &&
+		    buffer_uptodate(bh)) {
+			SetPageUptodate(page);    
+			return;
+		}
+		create_empty_buffers(page, i_blocksize(inode), 0);
+	}
+	head = page_buffers(page);
+	page_bh = head;
+	do {
+		if (block == page_block) {
+			page_bh->b_state = bh->b_state;
+			page_bh->b_bdev = bh->b_bdev;
+			page_bh->b_blocknr = bh->b_blocknr;
+			break;
+		}
+		page_bh = page_bh->b_this_page;
+		block++;
+	} while (page_bh != head);
+}
+
+struct mpage_readpage_args {
+	struct bio *bio;
+	struct page *page;
+	unsigned int nr_pages;
+	bool is_readahead;
+	sector_t last_block_in_bio;
+	struct buffer_head map_bh;
+	unsigned long first_logical_block;
+	get_block_t *get_block;
+};
+
+/*
+ * This is the worker routine which does all the work of mapping the disk
+ * blocks and constructs largest possible bios, submits them for IO if the
+ * blocks are not contiguous on the disk.
+ *
+ * We pass a buffer_head back and forth and use its buffer_mapped() flag to
+ * represent the validity of its disk mapping and to decide when to do the next
+ * get_block() call.
+ */
+static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
+{
+	struct page *page = args->page;
+	struct inode *inode = page->mapping->host;
+	const unsigned blkbits = inode->i_blkbits;
+	const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
+	const unsigned blocksize = 1 << blkbits;
+	struct buffer_head *map_bh = &args->map_bh;
+	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;
+	unsigned first_hole = blocks_per_page;
+	struct block_device *bdev = NULL;
+	int length;
+	int fully_mapped = 1;
+	int op_flags;
+	unsigned nblocks;
+	unsigned relative_block;
+	gfp_t gfp;
+
+	if (args->is_readahead) {
+		op_flags = REQ_RAHEAD;
+		gfp = readahead_gfp_mask(page->mapping);
+	} else {
+		op_flags = 0;
+		gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
+	}
+
+	if (page_has_buffers(page))
+		goto confused;
+
+	block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
+	last_block = block_in_file + args->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 result from the previous get_blocks call first.
+	 */
+	nblocks = map_bh->b_size >> blkbits;
+	if (buffer_mapped(map_bh) &&
+			block_in_file > args->first_logical_block &&
+			block_in_file < (args->first_logical_block + nblocks)) {
+		unsigned map_offset = block_in_file - args->first_logical_block;
+		unsigned last = nblocks - map_offset;
+
+		for (relative_block = 0; ; relative_block++) {
+			if (relative_block == last) {
+				clear_buffer_mapped(map_bh);
+				break;
+			}
+			if (page_block == blocks_per_page)
+				break;
+			blocks[page_block] = map_bh->b_blocknr + map_offset +
+						relative_block;
+			page_block++;
+			block_in_file++;
+		}
+		bdev = map_bh->b_bdev;
+	}
+
+	/*
+	 * Then do more get_blocks calls until we are done with this page.
+	 */
+	map_bh->b_page = page;
+	while (page_block < blocks_per_page) {
+		map_bh->b_state = 0;
+		map_bh->b_size = 0;
+
+		if (block_in_file < last_block) {
+			map_bh->b_size = (last_block-block_in_file) << blkbits;
+			if (args->get_block(inode, block_in_file, map_bh, 0))
+				goto confused;
+			args->first_logical_block = block_in_file;
+		}
+
+		if (!buffer_mapped(map_bh)) {
+			fully_mapped = 0;
+			if (first_hole == blocks_per_page)
+				first_hole = page_block;
+			page_block++;
+			block_in_file++;
+			continue;
+		}
+
+		/* some filesystems will copy data into the page during
+		 * the get_block call, in which case we don't want to
+		 * read it again.  map_buffer_to_page copies the data
+		 * we just collected from get_block into the page's buffers
+		 * so readpage doesn't have to repeat the get_block call
+		 */
+		if (buffer_uptodate(map_bh)) {
+			map_buffer_to_page(page, map_bh, page_block);
+			goto confused;
+		}
+	
+		if (first_hole != blocks_per_page)
+			goto confused;		/* hole -> non-hole */
+
+		/* Contiguous blocks? */
+		if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)
+			goto confused;
+		nblocks = map_bh->b_size >> blkbits;
+		for (relative_block = 0; ; relative_block++) {
+			if (relative_block == nblocks) {
+				clear_buffer_mapped(map_bh);
+				break;
+			} else if (page_block == blocks_per_page)
+				break;
+			blocks[page_block] = map_bh->b_blocknr+relative_block;
+			page_block++;
+			block_in_file++;
+		}
+		bdev = map_bh->b_bdev;
+	}
+
+	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 out;
+		}
+	} 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 (args->bio && (args->last_block_in_bio != blocks[0] - 1))
+		args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, args->bio);
+
+alloc_new:
+	if (args->bio == NULL) {
+		if (first_hole == blocks_per_page) {
+			if (!bdev_read_page(bdev, blocks[0] << (blkbits - 9),
+								page))
+				goto out;
+		}
+		args->bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
+					min_t(int, args->nr_pages,
+					      BIO_MAX_PAGES),
+					gfp);
+		if (args->bio == NULL)
+			goto confused;
+	}
+
+	length = first_hole << blkbits;
+	if (bio_add_page(args->bio, page, length, 0) < length) {
+		args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, args->bio);
+		goto alloc_new;
+	}
+
+	relative_block = block_in_file - args->first_logical_block;
+	nblocks = map_bh->b_size >> blkbits;
+	if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
+	    (first_hole != blocks_per_page))
+		args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, args->bio);
+	else
+		args->last_block_in_bio = blocks[blocks_per_page - 1];
+out:
+	return args->bio;
+
+confused:
+	if (args->bio)
+		args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, args->bio);
+	if (!PageUptodate(page))
+		block_read_full_page(page, args->get_block);
+	else
+		unlock_page(page);
+	goto out;
+}
+
+/**
+ * mpage_readpages - populate an address space with some pages & start reads against them
+ * @mapping: the address_space
+ * @pages: The address of a list_head which contains the target pages.  These
+ *   pages have their ->index populated and are otherwise uninitialised.
+ *   The page at @pages->prev has the lowest file offset, and reads should be
+ *   issued in @pages->prev to @pages->next order.
+ * @nr_pages: The number of pages at *@pages
+ * @get_block: The filesystem's block mapper function.
+ *
+ * This function walks the pages and the blocks within each page, building and
+ * emitting large BIOs.
+ *
+ * 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.
+ *
+ * BH_Boundary explanation:
+ *
+ * There is a problem.  The mpage read code assembles several pages, gets all
+ * their disk mappings, and then submits them all.  That's fine, but obtaining
+ * the disk mappings may require I/O.  Reads of indirect blocks, for example.
+ *
+ * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
+ * submitted in the following order:
+ *
+ * 	12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
+ *
+ * because the indirect block has to be read to get the mappings of blocks
+ * 13,14,15,16.  Obviously, this impacts performance.
+ *
+ * So what we do it to allow the filesystem's get_block() function to set
+ * BH_Boundary when it maps block 11.  BH_Boundary says: mapping of the block
+ * after this one will require I/O against a block which is probably close to
+ * this one.  So you should push what I/O you have currently accumulated.
+ *
+ * This all causes the disk requests to be issued in the correct order.
+ */
+int
+mpage_readpages(struct address_space *mapping, struct list_head *pages,
+				unsigned nr_pages, get_block_t get_block)
+{
+	struct mpage_readpage_args args = {
+		.get_block = get_block,
+		.is_readahead = true,
+	};
+	unsigned page_idx;
+
+	for (page_idx = 0; page_idx < nr_pages; page_idx++) {
+		struct page *page = lru_to_page(pages);
+
+		prefetchw(&page->flags);
+		list_del(&page->lru);
+		if (!add_to_page_cache_lru(page, mapping,
+					page->index,
+					readahead_gfp_mask(mapping))) {
+			args.page = page;
+			args.nr_pages = nr_pages - page_idx;
+			args.bio = do_mpage_readpage(&args);
+		}
+		put_page(page);
+	}
+	BUG_ON(!list_empty(pages));
+	if (args.bio)
+		mpage_bio_submit(REQ_OP_READ, REQ_RAHEAD, args.bio);
+	return 0;
+}
+EXPORT_SYMBOL(mpage_readpages);
+
+/*
+ * This isn't called much at all
+ */
+int mpage_readpage(struct page *page, get_block_t get_block)
+{
+	struct mpage_readpage_args args = {
+		.page = page,
+		.nr_pages = 1,
+		.get_block = get_block,
+	};
+
+	args.bio = do_mpage_readpage(&args);
+	if (args.bio)
+		mpage_bio_submit(REQ_OP_READ, 0, args.bio);
+	return 0;
+}
+EXPORT_SYMBOL(mpage_readpage);
+
+/*
+ * Writing is not so simple.
+ *
+ * If the page has buffers then they will be used for obtaining the disk
+ * mapping.  We only support pages which are fully mapped-and-dirty, with a
+ * special case for pages which are unmapped at the end: end-of-file.
+ *
+ * If the page has no buffers (preferred) then the page is mapped here.
+ *
+ * If all blocks are found to be contiguous then the page can go into the
+ * BIO.  Otherwise fall back to the mapping's writepage().
+ * 
+ * FIXME: This code wants an estimate of how many pages are still to be
+ * written, so it can intelligently allocate a suitably-sized BIO.  For now,
+ * just allocate full-size (16-page) BIOs.
+ */
+
+struct mpage_data {
+	struct bio *bio;
+	sector_t last_block_in_bio;
+	get_block_t *get_block;
+	unsigned use_writepage;
+};
+
+/*
+ * We have our BIO, so we can now mark the buffers clean.  Make
+ * sure to only clean buffers which we know we'll be writing.
+ */
+static void clean_buffers(struct page *page, unsigned first_unmapped)
+{
+	unsigned buffer_counter = 0;
+	struct buffer_head *bh, *head;
+	if (!page_has_buffers(page))
+		return;
+	head = page_buffers(page);
+	bh = head;
+
+	do {
+		if (buffer_counter++ == first_unmapped)
+			break;
+		clear_buffer_dirty(bh);
+		bh = bh->b_this_page;
+	} while (bh != head);
+
+	/*
+	 * we cannot drop the bh if the page is not uptodate or a concurrent
+	 * readpage would fail to serialize with the bh and it would read from
+	 * disk before we reach the platter.
+	 */
+	if (buffer_heads_over_limit && PageUptodate(page))
+		try_to_free_buffers(page);
+}
+
+/*
+ * For situations where we want to clean all buffers attached to a page.
+ * We don't need to calculate how many buffers are attached to the page,
+ * we just need to specify a number larger than the maximum number of buffers.
+ */
+void clean_page_buffers(struct page *page)
+{
+	clean_buffers(page, ~0U);
+}
+
+static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
+		      void *data)
+{
+	struct mpage_data *mpd = data;
+	struct bio *bio = mpd->bio;
+	struct address_space *mapping = page->mapping;
+	struct inode *inode = page->mapping->host;
+	const unsigned blkbits = inode->i_blkbits;
+	unsigned long end_index;
+	const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
+	sector_t last_block;
+	sector_t block_in_file;
+	sector_t blocks[MAX_BUF_PER_PAGE];
+	unsigned page_block;
+	unsigned first_unmapped = blocks_per_page;
+	struct block_device *bdev = NULL;
+	int boundary = 0;
+	sector_t boundary_block = 0;
+	struct block_device *boundary_bdev = NULL;
+	int length;
+	struct buffer_head map_bh;
+	loff_t i_size = i_size_read(inode);
+	int ret = 0;
+	int op_flags = wbc_to_write_flags(wbc);
+
+	if (page_has_buffers(page)) {
+		struct buffer_head *head = page_buffers(page);
+		struct buffer_head *bh = head;
+
+		/* If they're all mapped and dirty, do it */
+		page_block = 0;
+		do {
+			BUG_ON(buffer_locked(bh));
+			if (!buffer_mapped(bh)) {
+				/*
+				 * unmapped dirty buffers are created by
+				 * __set_page_dirty_buffers -> mmapped data
+				 */
+				if (buffer_dirty(bh))
+					goto confused;
+				if (first_unmapped == blocks_per_page)
+					first_unmapped = page_block;
+				continue;
+			}
+
+			if (first_unmapped != blocks_per_page)
+				goto confused;	/* hole -> non-hole */
+
+			if (!buffer_dirty(bh) || !buffer_uptodate(bh))
+				goto confused;
+			if (page_block) {
+				if (bh->b_blocknr != blocks[page_block-1] + 1)
+					goto confused;
+			}
+			blocks[page_block++] = bh->b_blocknr;
+			boundary = buffer_boundary(bh);
+			if (boundary) {
+				boundary_block = bh->b_blocknr;
+				boundary_bdev = bh->b_bdev;
+			}
+			bdev = bh->b_bdev;
+		} while ((bh = bh->b_this_page) != head);
+
+		if (first_unmapped)
+			goto page_is_mapped;
+
+		/*
+		 * Page has buffers, but they are all unmapped. The page was
+		 * created by pagein or read over a hole which was handled by
+		 * block_read_full_page().  If this address_space is also
+		 * using mpage_readpages then this can rarely happen.
+		 */
+		goto confused;
+	}
+
+	/*
+	 * The page has no buffers: map it to disk
+	 */
+	BUG_ON(!PageUptodate(page));
+	block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
+	last_block = (i_size - 1) >> blkbits;
+	map_bh.b_page = page;
+	for (page_block = 0; page_block < blocks_per_page; ) {
+
+		map_bh.b_state = 0;
+		map_bh.b_size = 1 << blkbits;
+		if (mpd->get_block(inode, block_in_file, &map_bh, 1))
+			goto confused;
+		if (buffer_new(&map_bh))
+			clean_bdev_bh_alias(&map_bh);
+		if (buffer_boundary(&map_bh)) {
+			boundary_block = map_bh.b_blocknr;
+			boundary_bdev = map_bh.b_bdev;
+		}
+		if (page_block) {
+			if (map_bh.b_blocknr != blocks[page_block-1] + 1)
+				goto confused;
+		}
+		blocks[page_block++] = map_bh.b_blocknr;
+		boundary = buffer_boundary(&map_bh);
+		bdev = map_bh.b_bdev;
+		if (block_in_file == last_block)
+			break;
+		block_in_file++;
+	}
+	BUG_ON(page_block == 0);
+
+	first_unmapped = page_block;
+
+page_is_mapped:
+	end_index = i_size >> PAGE_SHIFT;
+	if (page->index >= end_index) {
+		/*
+		 * The page straddles i_size.  It must be zeroed out on each
+		 * and every writepage invocation because it may be mmapped.
+		 * "A file is mapped in multiples of the page size.  For a file
+		 * that is not a multiple of the page size, the remaining memory
+		 * is zeroed when mapped, and writes to that region are not
+		 * written out to the file."
+		 */
+		unsigned offset = i_size & (PAGE_SIZE - 1);
+
+		if (page->index > end_index || !offset)
+			goto confused;
+		zero_user_segment(page, offset, PAGE_SIZE);
+	}
+
+	/*
+	 * This page will go to BIO.  Do we need to send this BIO off first?
+	 */
+	if (bio && mpd->last_block_in_bio != blocks[0] - 1)
+		bio = mpage_bio_submit(REQ_OP_WRITE, op_flags, bio);
+
+alloc_new:
+	if (bio == NULL) {
+		if (first_unmapped == blocks_per_page) {
+			if (!bdev_write_page(bdev, blocks[0] << (blkbits - 9),
+								page, wbc))
+				goto out;
+		}
+		bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
+				BIO_MAX_PAGES, GFP_NOFS|__GFP_HIGH);
+		if (bio == NULL)
+			goto confused;
+
+		wbc_init_bio(wbc, bio);
+		bio->bi_write_hint = inode->i_write_hint;
+	}
+
+	/*
+	 * Must try to add the page before marking the buffer clean or
+	 * the confused fail path above (OOM) will be very confused when
+	 * it finds all bh marked clean (i.e. it will not write anything)
+	 */
+	wbc_account_io(wbc, page, PAGE_SIZE);
+	length = first_unmapped << blkbits;
+	if (bio_add_page(bio, page, length, 0) < length) {
+		bio = mpage_bio_submit(REQ_OP_WRITE, op_flags, bio);
+		goto alloc_new;
+	}
+
+	clean_buffers(page, first_unmapped);
+
+	BUG_ON(PageWriteback(page));
+	set_page_writeback(page);
+	unlock_page(page);
+	if (boundary || (first_unmapped != blocks_per_page)) {
+		bio = mpage_bio_submit(REQ_OP_WRITE, op_flags, bio);
+		if (boundary_block) {
+			write_boundary_block(boundary_bdev,
+					boundary_block, 1 << blkbits);
+		}
+	} else {
+		mpd->last_block_in_bio = blocks[blocks_per_page - 1];
+	}
+	goto out;
+
+confused:
+	if (bio)
+		bio = mpage_bio_submit(REQ_OP_WRITE, op_flags, bio);
+
+	if (mpd->use_writepage) {
+		ret = mapping->a_ops->writepage(page, wbc);
+	} else {
+		ret = -EAGAIN;
+		goto out;
+	}
+	/*
+	 * The caller has a ref on the inode, so *mapping is stable
+	 */
+	mapping_set_error(mapping, ret);
+out:
+	mpd->bio = bio;
+	return ret;
+}
+
+/**
+ * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them
+ * @mapping: address space structure to write
+ * @wbc: subtract the number of written pages from *@wbc->nr_to_write
+ * @get_block: the filesystem's block mapper function.
+ *             If this is NULL then use a_ops->writepage.  Otherwise, go
+ *             direct-to-BIO.
+ *
+ * This is a library function, which implements the writepages()
+ * address_space_operation.
+ *
+ * If a page is already under I/O, generic_writepages() skips it, even
+ * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
+ * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
+ * and msync() need to guarantee that all the data which was dirty at the time
+ * the call was made get new I/O started against them.  If wbc->sync_mode is
+ * WB_SYNC_ALL then we were called for data integrity and we must wait for
+ * existing IO to complete.
+ */
+int
+mpage_writepages(struct address_space *mapping,
+		struct writeback_control *wbc, get_block_t get_block)
+{
+	struct blk_plug plug;
+	int ret;
+
+	blk_start_plug(&plug);
+
+	if (!get_block)
+		ret = generic_writepages(mapping, wbc);
+	else {
+		struct mpage_data mpd = {
+			.bio = NULL,
+			.last_block_in_bio = 0,
+			.get_block = get_block,
+			.use_writepage = 1,
+		};
+
+		ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
+		if (mpd.bio) {
+			int op_flags = (wbc->sync_mode == WB_SYNC_ALL ?
+				  REQ_SYNC : 0);
+			mpage_bio_submit(REQ_OP_WRITE, op_flags, mpd.bio);
+		}
+	}
+	blk_finish_plug(&plug);
+	return ret;
+}
+EXPORT_SYMBOL(mpage_writepages);
+
+int mpage_writepage(struct page *page, get_block_t get_block,
+	struct writeback_control *wbc)
+{
+	struct mpage_data mpd = {
+		.bio = NULL,
+		.last_block_in_bio = 0,
+		.get_block = get_block,
+		.use_writepage = 0,
+	};
+	int ret = __mpage_writepage(page, wbc, &mpd);
+	if (mpd.bio) {
+		int op_flags = (wbc->sync_mode == WB_SYNC_ALL ?
+			  REQ_SYNC : 0);
+		mpage_bio_submit(REQ_OP_WRITE, op_flags, mpd.bio);
+	}
+	return ret;
+}
+EXPORT_SYMBOL(mpage_writepage);