fs/ext4/page-io.c - kernel/msm-4.19 - Gitiles

 /*
  * linux/fs/ext4/page-io.c
  *
  * This contains the new page_io functions for ext4
  *
  * Written by Theodore Ts'o, 2010.
  */

 #include <linux/module.h>
 #include <linux/fs.h>
 #include <linux/time.h>
 #include <linux/jbd2.h>
 #include <linux/highuid.h>
 #include <linux/pagemap.h>
 #include <linux/quotaops.h>
 #include <linux/string.h>
 #include <linux/buffer_head.h>
 #include <linux/writeback.h>
 #include <linux/pagevec.h>
 #include <linux/mpage.h>
 #include <linux/namei.h>
 #include <linux/uio.h>
 #include <linux/bio.h>
 #include <linux/workqueue.h>
 #include <linux/kernel.h>
 #include <linux/slab.h>

 #include "ext4_jbd2.h"
 #include "xattr.h"
 #include "acl.h"
 #include "ext4_extents.h"

 static struct kmem_cache *io_page_cachep, *io_end_cachep;

 int __init ext4_init_pageio(void)
 {
 	io_page_cachep = KMEM_CACHE(ext4_io_page, SLAB_RECLAIM_ACCOUNT);
 	if (io_page_cachep == NULL)
 		return -ENOMEM;
 	io_end_cachep = KMEM_CACHE(ext4_io_end, SLAB_RECLAIM_ACCOUNT);
 	if (io_end_cachep == NULL) {
 		kmem_cache_destroy(io_page_cachep);
 		return -ENOMEM;
 	}
 	return 0;
 }

 void ext4_exit_pageio(void)
 {
 	kmem_cache_destroy(io_end_cachep);
 	kmem_cache_destroy(io_page_cachep);
 }

 void ext4_ioend_wait(struct inode *inode)
 {
 	wait_queue_head_t *wq = ext4_ioend_wq(inode);

 	wait_event(*wq, (atomic_read(&EXT4_I(inode)->i_ioend_count) == 0));
 }

 static void put_io_page(struct ext4_io_page *io_page)
 {
 	if (atomic_dec_and_test(&io_page->p_count)) {
 		end_page_writeback(io_page->p_page);
 		put_page(io_page->p_page);
 		kmem_cache_free(io_page_cachep, io_page);
 	}
 }

 void ext4_free_io_end(ext4_io_end_t *io)
 {
 	int i;
 	wait_queue_head_t *wq;

 	BUG_ON(!io);
 	if (io->page)
 		put_page(io->page);
 	for (i = 0; i < io->num_io_pages; i++)
 		put_io_page(io->pages[i]);
 	io->num_io_pages = 0;
 	wq = ext4_ioend_wq(io->inode);
 	if (atomic_dec_and_test(&EXT4_I(io->inode)->i_ioend_count) &&
 	    waitqueue_active(wq))
 		wake_up_all(wq);
 	kmem_cache_free(io_end_cachep, io);
 }

 /*
  * check a range of space and convert unwritten extents to written.
  */
 int ext4_end_io_nolock(ext4_io_end_t *io)
 {
 	struct inode *inode = io->inode;
 	loff_t offset = io->offset;
 	ssize_t size = io->size;
 	wait_queue_head_t *wq;
 	int ret = 0;

 	ext4_debug("ext4_end_io_nolock: io 0x%p from inode %lu,list->next 0x%p,"
 		   "list->prev 0x%p\n",
 		   io, inode->i_ino, io->list.next, io->list.prev);

 	if (list_empty(&io->list))
 		return ret;

 	if (!(io->flag & EXT4_IO_END_UNWRITTEN))
 		return ret;

 	ret = ext4_convert_unwritten_extents(inode, offset, size);
 	if (ret < 0) {
 		printk(KERN_EMERG "%s: failed to convert unwritten "
 			"extents to written extents, error is %d "
 			"io is still on inode %lu aio dio list\n",
 		       __func__, ret, inode->i_ino);
 		return ret;
 	}

 	if (io->iocb)
 		aio_complete(io->iocb, io->result, 0);
 	/* clear the DIO AIO unwritten flag */
 	if (io->flag & EXT4_IO_END_UNWRITTEN) {
 		io->flag &= ~EXT4_IO_END_UNWRITTEN;
 		/* Wake up anyone waiting on unwritten extent conversion */
 		wq = ext4_ioend_wq(io->inode);
 		if (atomic_dec_and_test(&EXT4_I(inode)->i_aiodio_unwritten) &&
 		    waitqueue_active(wq)) {
 			wake_up_all(wq);
 		}
 	}

 	return ret;
 }

 /*
  * work on completed aio dio IO, to convert unwritten extents to extents
  */
 static void ext4_end_io_work(struct work_struct *work)
 {
 	ext4_io_end_t		*io = container_of(work, ext4_io_end_t, work);
 	struct inode		*inode = io->inode;
 	struct ext4_inode_info	*ei = EXT4_I(inode);
 	unsigned long		flags;
 	int			ret;

 	mutex_lock(&inode->i_mutex);
 	ret = ext4_end_io_nolock(io);
 	if (ret < 0) {
 		mutex_unlock(&inode->i_mutex);
 		return;
 	}

 	spin_lock_irqsave(&ei->i_completed_io_lock, flags);
 	if (!list_empty(&io->list))
 		list_del_init(&io->list);
 	spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
 	mutex_unlock(&inode->i_mutex);
 	ext4_free_io_end(io);
 }

 ext4_io_end_t *ext4_init_io_end(struct inode *inode, gfp_t flags)
 {
 	ext4_io_end_t *io = kmem_cache_zalloc(io_end_cachep, flags);
 	if (io) {
 		atomic_inc(&EXT4_I(inode)->i_ioend_count);
 		io->inode = inode;
 		INIT_WORK(&io->work, ext4_end_io_work);
 		INIT_LIST_HEAD(&io->list);
 	}
 	return io;
 }

 /*
  * Print an buffer I/O error compatible with the fs/buffer.c.  This
  * provides compatibility with dmesg scrapers that look for a specific
  * buffer I/O error message.  We really need a unified error reporting
  * structure to userspace ala Digital Unix's uerf system, but it's
  * probably not going to happen in my lifetime, due to LKML politics...
  */
 static void buffer_io_error(struct buffer_head *bh)
 {
 	char b[BDEVNAME_SIZE];
 	printk(KERN_ERR "Buffer I/O error on device %s, logical block %llu\n",
 			bdevname(bh->b_bdev, b),
 			(unsigned long long)bh->b_blocknr);
 }

 static void ext4_end_bio(struct bio *bio, int error)
 {
 	ext4_io_end_t *io_end = bio->bi_private;
 	struct workqueue_struct *wq;
 	struct inode *inode;
 	unsigned long flags;
 	int i;
 	sector_t bi_sector = bio->bi_sector;

 	BUG_ON(!io_end);
 	bio->bi_private = NULL;
 	bio->bi_end_io = NULL;
 	if (test_bit(BIO_UPTODATE, &bio->bi_flags))
 		error = 0;
 	bio_put(bio);

 	for (i = 0; i < io_end->num_io_pages; i++) {
 		struct page *page = io_end->pages[i]->p_page;
 		struct buffer_head *bh, *head;
 		int partial_write = 0;

 		head = page_buffers(page);
 		if (error)
 			SetPageError(page);
 		BUG_ON(!head);
 		if (head->b_size != PAGE_CACHE_SIZE) {
 			loff_t offset;
 			loff_t io_end_offset = io_end->offset + io_end->size;

 			offset = (sector_t) page->index << PAGE_CACHE_SHIFT;
 			bh = head;
 			do {
 				if ((offset >= io_end->offset) &&
 				    (offset+bh->b_size <= io_end_offset)) {
 					if (error)
 						buffer_io_error(bh);

 				}
 				if (buffer_delay(bh))
 					partial_write = 1;
 				else if (!buffer_mapped(bh))
 					clear_buffer_dirty(bh);
 				else if (buffer_dirty(bh))
 					partial_write = 1;
 				offset += bh->b_size;
 				bh = bh->b_this_page;
 			} while (bh != head);
 		}

 		/*
 		 * If this is a partial write which happened to make
 		 * all buffers uptodate then we can optimize away a
 		 * bogus readpage() for the next read(). Here we
 		 * 'discover' whether the page went uptodate as a
 		 * result of this (potentially partial) write.
 		 */
 		if (!partial_write)
 			SetPageUptodate(page);

 		put_io_page(io_end->pages[i]);
 	}
 	io_end->num_io_pages = 0;
 	inode = io_end->inode;

 	if (error) {
 		io_end->flag |= EXT4_IO_END_ERROR;
 		ext4_warning(inode->i_sb, "I/O error writing to inode %lu "
 			     "(offset %llu size %ld starting block %llu)",
 			     inode->i_ino,
 			     (unsigned long long) io_end->offset,
 			     (long) io_end->size,
 			     (unsigned long long)
 			     bi_sector >> (inode->i_blkbits - 9));
 	}

 	/* Add the io_end to per-inode completed io list*/
 	spin_lock_irqsave(&EXT4_I(inode)->i_completed_io_lock, flags);
 	list_add_tail(&io_end->list, &EXT4_I(inode)->i_completed_io_list);
 	spin_unlock_irqrestore(&EXT4_I(inode)->i_completed_io_lock, flags);

 	wq = EXT4_SB(inode->i_sb)->dio_unwritten_wq;
 	/* queue the work to convert unwritten extents to written */
 	queue_work(wq, &io_end->work);
 }

 void ext4_io_submit(struct ext4_io_submit *io)
 {
 	struct bio *bio = io->io_bio;

 	if (bio) {
 		bio_get(io->io_bio);
 		submit_bio(io->io_op, io->io_bio);
 		BUG_ON(bio_flagged(io->io_bio, BIO_EOPNOTSUPP));
 		bio_put(io->io_bio);
 	}
 	io->io_bio = NULL;
 	io->io_op = 0;
 	io->io_end = NULL;
 }

 static int io_submit_init(struct ext4_io_submit *io,
 			  struct inode *inode,
 			  struct writeback_control *wbc,
 			  struct buffer_head *bh)
 {
 	ext4_io_end_t *io_end;
 	struct page *page = bh->b_page;
 	int nvecs = bio_get_nr_vecs(bh->b_bdev);
 	struct bio *bio;

 	io_end = ext4_init_io_end(inode, GFP_NOFS);
 	if (!io_end)
 		return -ENOMEM;
 	do {
 		bio = bio_alloc(GFP_NOIO, nvecs);
 		nvecs >>= 1;
 	} while (bio == NULL);

 	bio->bi_sector = bh->b_blocknr * (bh->b_size >> 9);
 	bio->bi_bdev = bh->b_bdev;
 	bio->bi_private = io->io_end = io_end;
 	bio->bi_end_io = ext4_end_bio;

 	io_end->offset = (page->index << PAGE_CACHE_SHIFT) + bh_offset(bh);

 	io->io_bio = bio;
 	io->io_op = (wbc->sync_mode == WB_SYNC_ALL ?
 			WRITE_SYNC_PLUG : WRITE);
 	io->io_next_block = bh->b_blocknr;
 	return 0;
 }

 static int io_submit_add_bh(struct ext4_io_submit *io,
 			    struct ext4_io_page *io_page,
 			    struct inode *inode,
 			    struct writeback_control *wbc,
 			    struct buffer_head *bh)
 {
 	ext4_io_end_t *io_end;
 	int ret;

 	if (buffer_new(bh)) {
 		clear_buffer_new(bh);
 		unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
 	}

 	if (!buffer_mapped(bh) || buffer_delay(bh)) {
 		if (!buffer_mapped(bh))
 			clear_buffer_dirty(bh);
 		if (io->io_bio)
 			ext4_io_submit(io);
 		return 0;
 	}

 	if (io->io_bio && bh->b_blocknr != io->io_next_block) {
 submit_and_retry:
 		ext4_io_submit(io);
 	}
 	if (io->io_bio == NULL) {
 		ret = io_submit_init(io, inode, wbc, bh);
 		if (ret)
 			return ret;
 	}
 	io_end = io->io_end;
 	if ((io_end->num_io_pages >= MAX_IO_PAGES) &&
 	    (io_end->pages[io_end->num_io_pages-1] != io_page))
 		goto submit_and_retry;
 	if (buffer_uninit(bh))
 		io->io_end->flag |= EXT4_IO_END_UNWRITTEN;
 	io->io_end->size += bh->b_size;
 	io->io_next_block++;
 	ret = bio_add_page(io->io_bio, bh->b_page, bh->b_size, bh_offset(bh));
 	if (ret != bh->b_size)
 		goto submit_and_retry;
 	if ((io_end->num_io_pages == 0) ||
 	    (io_end->pages[io_end->num_io_pages-1] != io_page)) {
 		io_end->pages[io_end->num_io_pages++] = io_page;
 		atomic_inc(&io_page->p_count);
 	}
 	return 0;
 }

 int ext4_bio_write_page(struct ext4_io_submit *io,
 			struct page *page,
 			int len,
 			struct writeback_control *wbc)
 {
 	struct inode *inode = page->mapping->host;
 	unsigned block_start, block_end, blocksize;
 	struct ext4_io_page *io_page;
 	struct buffer_head *bh, *head;
 	int ret = 0;

 	blocksize = 1 << inode->i_blkbits;

 	BUG_ON(!PageLocked(page));
 	BUG_ON(PageWriteback(page));

 	io_page = kmem_cache_alloc(io_page_cachep, GFP_NOFS);
 	if (!io_page) {
 		set_page_dirty(page);
 		unlock_page(page);
 		return -ENOMEM;
 	}
 	io_page->p_page = page;
 	atomic_set(&io_page->p_count, 1);
 	get_page(page);
 	set_page_writeback(page);
 	ClearPageError(page);

 	for (bh = head = page_buffers(page), block_start = 0;
 	     bh != head || !block_start;
 	     block_start = block_end, bh = bh->b_this_page) {

 		block_end = block_start + blocksize;
 		if (block_start >= len) {
 			clear_buffer_dirty(bh);
 			set_buffer_uptodate(bh);
 			continue;
 		}
 		clear_buffer_dirty(bh);
 		ret = io_submit_add_bh(io, io_page, inode, wbc, bh);
 		if (ret) {
 			/*
 			 * We only get here on ENOMEM.  Not much else
 			 * we can do but mark the page as dirty, and
 			 * better luck next time.
 			 */
 			set_page_dirty(page);
 			break;
 		}
 	}
 	unlock_page(page);
 	/*
 	 * If the page was truncated before we could do the writeback,
 	 * or we had a memory allocation error while trying to write
 	 * the first buffer head, we won't have submitted any pages for
 	 * I/O.  In that case we need to make sure we've cleared the
 	 * PageWriteback bit from the page to prevent the system from
 	 * wedging later on.
 	 */
 	put_io_page(io_page);
 	return ret;
 }
	/*
	* linux/fs/ext4/page-io.c
	*
	* This contains the new page_io functions for ext4
	*
	* Written by Theodore Ts'o, 2010.
	*/

	#include <linux/module.h>
	#include <linux/fs.h>
	#include <linux/time.h>
	#include <linux/jbd2.h>
	#include <linux/highuid.h>
	#include <linux/pagemap.h>
	#include <linux/quotaops.h>
	#include <linux/string.h>
	#include <linux/buffer_head.h>
	#include <linux/writeback.h>
	#include <linux/pagevec.h>
	#include <linux/mpage.h>
	#include <linux/namei.h>
	#include <linux/uio.h>
	#include <linux/bio.h>
	#include <linux/workqueue.h>
	#include <linux/kernel.h>
	#include <linux/slab.h>

	#include "ext4_jbd2.h"
	#include "xattr.h"
	#include "acl.h"
	#include "ext4_extents.h"

	static struct kmem_cache io_page_cachep, io_end_cachep;

	int __init ext4_init_pageio(void)
	{
	io_page_cachep = KMEM_CACHE(ext4_io_page, SLAB_RECLAIM_ACCOUNT);
	if (io_page_cachep == NULL)
	return -ENOMEM;
	io_end_cachep = KMEM_CACHE(ext4_io_end, SLAB_RECLAIM_ACCOUNT);
	if (io_end_cachep == NULL) {
	kmem_cache_destroy(io_page_cachep);
	return -ENOMEM;
	}
	return 0;
	}

	void ext4_exit_pageio(void)
	{
	kmem_cache_destroy(io_end_cachep);
	kmem_cache_destroy(io_page_cachep);
	}

	void ext4_ioend_wait(struct inode *inode)
	{
	wait_queue_head_t *wq = ext4_ioend_wq(inode);

	wait_event(*wq, (atomic_read(&EXT4_I(inode)->i_ioend_count) == 0));
	}

	static void put_io_page(struct ext4_io_page *io_page)
	{
	if (atomic_dec_and_test(&io_page->p_count)) {
	end_page_writeback(io_page->p_page);
	put_page(io_page->p_page);
	kmem_cache_free(io_page_cachep, io_page);
	}
	}

	void ext4_free_io_end(ext4_io_end_t *io)
	{
	int i;
	wait_queue_head_t *wq;

	BUG_ON(!io);
	if (io->page)
	put_page(io->page);
	for (i = 0; i < io->num_io_pages; i++)
	put_io_page(io->pages[i]);
	io->num_io_pages = 0;
	wq = ext4_ioend_wq(io->inode);
	if (atomic_dec_and_test(&EXT4_I(io->inode)->i_ioend_count) &&
	waitqueue_active(wq))
	wake_up_all(wq);
	kmem_cache_free(io_end_cachep, io);
	}

	/*
	* check a range of space and convert unwritten extents to written.
	*/
	int ext4_end_io_nolock(ext4_io_end_t *io)
	{
	struct inode *inode = io->inode;
	loff_t offset = io->offset;
	ssize_t size = io->size;
	wait_queue_head_t *wq;
	int ret = 0;

	ext4_debug("ext4_end_io_nolock: io 0x%p from inode %lu,list->next 0x%p,"
	"list->prev 0x%p\n",
	io, inode->i_ino, io->list.next, io->list.prev);

	if (list_empty(&io->list))
	return ret;

	if (!(io->flag & EXT4_IO_END_UNWRITTEN))
	return ret;

	ret = ext4_convert_unwritten_extents(inode, offset, size);
	if (ret < 0) {
	printk(KERN_EMERG "%s: failed to convert unwritten "
	"extents to written extents, error is %d "
	"io is still on inode %lu aio dio list\n",
	__func__, ret, inode->i_ino);
	return ret;
	}

	if (io->iocb)
	aio_complete(io->iocb, io->result, 0);
	/* clear the DIO AIO unwritten flag */
	if (io->flag & EXT4_IO_END_UNWRITTEN) {
	io->flag &= ~EXT4_IO_END_UNWRITTEN;
	/* Wake up anyone waiting on unwritten extent conversion */
	wq = ext4_ioend_wq(io->inode);
	if (atomic_dec_and_test(&EXT4_I(inode)->i_aiodio_unwritten) &&
	waitqueue_active(wq)) {
	wake_up_all(wq);
	}
	}

	return ret;
	}

	/*
	* work on completed aio dio IO, to convert unwritten extents to extents
	*/
	static void ext4_end_io_work(struct work_struct *work)
	{
	ext4_io_end_t *io = container_of(work, ext4_io_end_t, work);
	struct inode *inode = io->inode;
	struct ext4_inode_info *ei = EXT4_I(inode);
	unsigned long flags;
	int ret;

	mutex_lock(&inode->i_mutex);
	ret = ext4_end_io_nolock(io);
	if (ret < 0) {
	mutex_unlock(&inode->i_mutex);
	return;
	}

	spin_lock_irqsave(&ei->i_completed_io_lock, flags);
	if (!list_empty(&io->list))
	list_del_init(&io->list);
	spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
	mutex_unlock(&inode->i_mutex);
	ext4_free_io_end(io);
	}

	ext4_io_end_t ext4_init_io_end(struct inode inode, gfp_t flags)
	{
	ext4_io_end_t *io = kmem_cache_zalloc(io_end_cachep, flags);
	if (io) {
	atomic_inc(&EXT4_I(inode)->i_ioend_count);
	io->inode = inode;
	INIT_WORK(&io->work, ext4_end_io_work);
	INIT_LIST_HEAD(&io->list);
	}
	return io;
	}

	/*
	* Print an buffer I/O error compatible with the fs/buffer.c. This
	* provides compatibility with dmesg scrapers that look for a specific
	* buffer I/O error message. We really need a unified error reporting
	* structure to userspace ala Digital Unix's uerf system, but it's
	* probably not going to happen in my lifetime, due to LKML politics...
	*/
	static void buffer_io_error(struct buffer_head *bh)
	{
	char b[BDEVNAME_SIZE];
	printk(KERN_ERR "Buffer I/O error on device %s, logical block %llu\n",
	bdevname(bh->b_bdev, b),
	(unsigned long long)bh->b_blocknr);
	}

	static void ext4_end_bio(struct bio *bio, int error)
	{
	ext4_io_end_t *io_end = bio->bi_private;
	struct workqueue_struct *wq;
	struct inode *inode;
	unsigned long flags;
	int i;
	sector_t bi_sector = bio->bi_sector;

	BUG_ON(!io_end);
	bio->bi_private = NULL;
	bio->bi_end_io = NULL;
	if (test_bit(BIO_UPTODATE, &bio->bi_flags))
	error = 0;
	bio_put(bio);

	for (i = 0; i < io_end->num_io_pages; i++) {
	struct page *page = io_end->pages[i]->p_page;
	struct buffer_head bh, head;
	int partial_write = 0;

	head = page_buffers(page);
	if (error)
	SetPageError(page);
	BUG_ON(!head);
	if (head->b_size != PAGE_CACHE_SIZE) {
	loff_t offset;
	loff_t io_end_offset = io_end->offset + io_end->size;

	offset = (sector_t) page->index << PAGE_CACHE_SHIFT;
	bh = head;
	do {
	if ((offset >= io_end->offset) &&
	(offset+bh->b_size <= io_end_offset)) {
	if (error)
	buffer_io_error(bh);

	}
	if (buffer_delay(bh))
	partial_write = 1;
	else if (!buffer_mapped(bh))
	clear_buffer_dirty(bh);
	else if (buffer_dirty(bh))
	partial_write = 1;
	offset += bh->b_size;
	bh = bh->b_this_page;
	} while (bh != head);
	}

	/*
	* If this is a partial write which happened to make
	* all buffers uptodate then we can optimize away a
	* bogus readpage() for the next read(). Here we
	* 'discover' whether the page went uptodate as a
	* result of this (potentially partial) write.
	*/
	if (!partial_write)
	SetPageUptodate(page);

	put_io_page(io_end->pages[i]);
	}
	io_end->num_io_pages = 0;
	inode = io_end->inode;

	if (error) {
	io_end->flag \|= EXT4_IO_END_ERROR;
	ext4_warning(inode->i_sb, "I/O error writing to inode %lu "
	"(offset %llu size %ld starting block %llu)",
	inode->i_ino,
	(unsigned long long) io_end->offset,
	(long) io_end->size,
	(unsigned long long)
	bi_sector >> (inode->i_blkbits - 9));
	}

	/* Add the io_end to per-inode completed io list*/
	spin_lock_irqsave(&EXT4_I(inode)->i_completed_io_lock, flags);
	list_add_tail(&io_end->list, &EXT4_I(inode)->i_completed_io_list);
	spin_unlock_irqrestore(&EXT4_I(inode)->i_completed_io_lock, flags);

	wq = EXT4_SB(inode->i_sb)->dio_unwritten_wq;
	/* queue the work to convert unwritten extents to written */
	queue_work(wq, &io_end->work);
	}

	void ext4_io_submit(struct ext4_io_submit *io)
	{
	struct bio *bio = io->io_bio;

	if (bio) {
	bio_get(io->io_bio);
	submit_bio(io->io_op, io->io_bio);
	BUG_ON(bio_flagged(io->io_bio, BIO_EOPNOTSUPP));
	bio_put(io->io_bio);
	}
	io->io_bio = NULL;
	io->io_op = 0;
	io->io_end = NULL;
	}

	static int io_submit_init(struct ext4_io_submit *io,
	struct inode *inode,
	struct writeback_control *wbc,
	struct buffer_head *bh)
	{
	ext4_io_end_t *io_end;
	struct page *page = bh->b_page;
	int nvecs = bio_get_nr_vecs(bh->b_bdev);
	struct bio *bio;

	io_end = ext4_init_io_end(inode, GFP_NOFS);
	if (!io_end)
	return -ENOMEM;
	do {
	bio = bio_alloc(GFP_NOIO, nvecs);
	nvecs >>= 1;
	} while (bio == NULL);

	bio->bi_sector = bh->b_blocknr * (bh->b_size >> 9);
	bio->bi_bdev = bh->b_bdev;
	bio->bi_private = io->io_end = io_end;
	bio->bi_end_io = ext4_end_bio;

	io_end->offset = (page->index << PAGE_CACHE_SHIFT) + bh_offset(bh);

	io->io_bio = bio;
	io->io_op = (wbc->sync_mode == WB_SYNC_ALL ?
	WRITE_SYNC_PLUG : WRITE);
	io->io_next_block = bh->b_blocknr;
	return 0;
	}

	static int io_submit_add_bh(struct ext4_io_submit *io,
	struct ext4_io_page *io_page,
	struct inode *inode,
	struct writeback_control *wbc,
	struct buffer_head *bh)
	{
	ext4_io_end_t *io_end;
	int ret;

	if (buffer_new(bh)) {
	clear_buffer_new(bh);
	unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
	}

	if (!buffer_mapped(bh) \|\| buffer_delay(bh)) {
	if (!buffer_mapped(bh))
	clear_buffer_dirty(bh);
	if (io->io_bio)
	ext4_io_submit(io);
	return 0;
	}

	if (io->io_bio && bh->b_blocknr != io->io_next_block) {
	submit_and_retry:
	ext4_io_submit(io);
	}
	if (io->io_bio == NULL) {
	ret = io_submit_init(io, inode, wbc, bh);
	if (ret)
	return ret;
	}
	io_end = io->io_end;
	if ((io_end->num_io_pages >= MAX_IO_PAGES) &&
	(io_end->pages[io_end->num_io_pages-1] != io_page))
	goto submit_and_retry;
	if (buffer_uninit(bh))
	io->io_end->flag \|= EXT4_IO_END_UNWRITTEN;
	io->io_end->size += bh->b_size;
	io->io_next_block++;
	ret = bio_add_page(io->io_bio, bh->b_page, bh->b_size, bh_offset(bh));
	if (ret != bh->b_size)
	goto submit_and_retry;
	if ((io_end->num_io_pages == 0) \|\|
	(io_end->pages[io_end->num_io_pages-1] != io_page)) {
	io_end->pages[io_end->num_io_pages++] = io_page;
	atomic_inc(&io_page->p_count);
	}
	return 0;
	}

	int ext4_bio_write_page(struct ext4_io_submit *io,
	struct page *page,
	int len,
	struct writeback_control *wbc)
	{
	struct inode *inode = page->mapping->host;
	unsigned block_start, block_end, blocksize;
	struct ext4_io_page *io_page;
	struct buffer_head bh, head;
	int ret = 0;

	blocksize = 1 << inode->i_blkbits;

	BUG_ON(!PageLocked(page));
	BUG_ON(PageWriteback(page));

	io_page = kmem_cache_alloc(io_page_cachep, GFP_NOFS);
	if (!io_page) {
	set_page_dirty(page);
	unlock_page(page);
	return -ENOMEM;
	}
	io_page->p_page = page;
	atomic_set(&io_page->p_count, 1);
	get_page(page);
	set_page_writeback(page);
	ClearPageError(page);

	for (bh = head = page_buffers(page), block_start = 0;
	bh != head \|\| !block_start;
	block_start = block_end, bh = bh->b_this_page) {

	block_end = block_start + blocksize;
	if (block_start >= len) {
	clear_buffer_dirty(bh);
	set_buffer_uptodate(bh);
	continue;
	}
	clear_buffer_dirty(bh);
	ret = io_submit_add_bh(io, io_page, inode, wbc, bh);
	if (ret) {
	/*
	* We only get here on ENOMEM. Not much else
	* we can do but mark the page as dirty, and
	* better luck next time.
	*/
	set_page_dirty(page);
	break;
	}
	}
	unlock_page(page);
	/*
	* If the page was truncated before we could do the writeback,
	* or we had a memory allocation error while trying to write
	* the first buffer head, we won't have submitted any pages for
	* I/O. In that case we need to make sure we've cleared the
	* PageWriteback bit from the page to prevent the system from
	* wedging later on.
	*/
	put_io_page(io_page);
	return ret;
	}