fs/ext4/page-io.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * linux/fs/ext4/page-io.c
  *
  * This contains the new page_io functions for ext4
  *
  * Written by Theodore Ts'o, 2010.
  */

 #include <linux/fs.h>
 #include <linux/time.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 <linux/mm.h>
 #include <linux/backing-dev.h>

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

 static struct kmem_cache *io_end_cachep;

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

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

 /*
  * 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)
 {
 	printk_ratelimited(KERN_ERR "Buffer I/O error on device %pg, logical block %llu\n",
 		       bh->b_bdev,
 			(unsigned long long)bh->b_blocknr);
 }

 static void ext4_finish_bio(struct bio *bio)
 {
 	int i;
 	struct bio_vec *bvec;

 	bio_for_each_segment_all(bvec, bio, i) {
 		struct page *page = bvec->bv_page;
 #ifdef CONFIG_EXT4_FS_ENCRYPTION
 		struct page *data_page = NULL;
 #endif
 		struct buffer_head *bh, *head;
 		unsigned bio_start = bvec->bv_offset;
 		unsigned bio_end = bio_start + bvec->bv_len;
 		unsigned under_io = 0;
 		unsigned long flags;

 		if (!page)
 			continue;

 #ifdef CONFIG_EXT4_FS_ENCRYPTION
 		if (!page->mapping) {
 			/* The bounce data pages are unmapped. */
 			data_page = page;
 			fscrypt_pullback_bio_page(&page, false);
 		}
 #endif

 		if (bio->bi_status) {
 			SetPageError(page);
 			mapping_set_error(page->mapping, -EIO);
 		}
 		bh = head = page_buffers(page);
 		/*
 		 * We check all buffers in the page under BH_Uptodate_Lock
 		 * to avoid races with other end io clearing async_write flags
 		 */
 		local_irq_save(flags);
 		bit_spin_lock(BH_Uptodate_Lock, &head->b_state);
 		do {
 			if (bh_offset(bh) < bio_start ||
 			    bh_offset(bh) + bh->b_size > bio_end) {
 				if (buffer_async_write(bh))
 					under_io++;
 				continue;
 			}
 			clear_buffer_async_write(bh);
 			if (bio->bi_status)
 				buffer_io_error(bh);
 		} while ((bh = bh->b_this_page) != head);
 		bit_spin_unlock(BH_Uptodate_Lock, &head->b_state);
 		local_irq_restore(flags);
 		if (!under_io) {
 #ifdef CONFIG_EXT4_FS_ENCRYPTION
 			if (data_page)
 				fscrypt_restore_control_page(data_page);
 #endif
 			end_page_writeback(page);
 		}
 	}
 }

 static void ext4_release_io_end(ext4_io_end_t *io_end)
 {
 	struct bio *bio, *next_bio;

 	BUG_ON(!list_empty(&io_end->list));
 	BUG_ON(io_end->flag & EXT4_IO_END_UNWRITTEN);
 	WARN_ON(io_end->handle);

 	for (bio = io_end->bio; bio; bio = next_bio) {
 		next_bio = bio->bi_private;
 		ext4_finish_bio(bio);
 		bio_put(bio);
 	}
 	kmem_cache_free(io_end_cachep, io_end);
 }

 /*
  * Check a range of space and convert unwritten extents to written. Note that
  * we are protected from truncate touching same part of extent tree by the
  * fact that truncate code waits for all DIO to finish (thus exclusion from
  * direct IO is achieved) and also waits for PageWriteback bits. Thus we
  * cannot get to ext4_ext_truncate() before all IOs overlapping that range are
  * completed (happens from ext4_free_ioend()).
  */
 static int ext4_end_io(ext4_io_end_t *io)
 {
 	struct inode *inode = io->inode;
 	loff_t offset = io->offset;
 	ssize_t size = io->size;
 	handle_t *handle = io->handle;
 	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);

 	io->handle = NULL;	/* Following call will use up the handle */
 	ret = ext4_convert_unwritten_extents(handle, inode, offset, size);
 	if (ret < 0 && !ext4_forced_shutdown(EXT4_SB(inode->i_sb))) {
 		ext4_msg(inode->i_sb, KERN_EMERG,
 			 "failed to convert unwritten extents to written "
 			 "extents -- potential data loss!  "
 			 "(inode %lu, offset %llu, size %zd, error %d)",
 			 inode->i_ino, offset, size, ret);
 	}
 	ext4_clear_io_unwritten_flag(io);
 	ext4_release_io_end(io);
 	return ret;
 }

 static void dump_completed_IO(struct inode *inode, struct list_head *head)
 {
 #ifdef	EXT4FS_DEBUG
 	struct list_head *cur, *before, *after;
 	ext4_io_end_t *io, *io0, *io1;

 	if (list_empty(head))
 		return;

 	ext4_debug("Dump inode %lu completed io list\n", inode->i_ino);
 	list_for_each_entry(io, head, list) {
 		cur = &io->list;
 		before = cur->prev;
 		io0 = container_of(before, ext4_io_end_t, list);
 		after = cur->next;
 		io1 = container_of(after, ext4_io_end_t, list);

 		ext4_debug("io 0x%p from inode %lu,prev 0x%p,next 0x%p\n",
 			    io, inode->i_ino, io0, io1);
 	}
 #endif
 }

 /* Add the io_end to per-inode completed end_io list. */
 static void ext4_add_complete_io(ext4_io_end_t *io_end)
 {
 	struct ext4_inode_info *ei = EXT4_I(io_end->inode);
 	struct ext4_sb_info *sbi = EXT4_SB(io_end->inode->i_sb);
 	struct workqueue_struct *wq;
 	unsigned long flags;

 	/* Only reserved conversions from writeback should enter here */
 	WARN_ON(!(io_end->flag & EXT4_IO_END_UNWRITTEN));
 	WARN_ON(!io_end->handle && sbi->s_journal);
 	spin_lock_irqsave(&ei->i_completed_io_lock, flags);
 	wq = sbi->rsv_conversion_wq;
 	if (list_empty(&ei->i_rsv_conversion_list))
 		queue_work(wq, &ei->i_rsv_conversion_work);
 	list_add_tail(&io_end->list, &ei->i_rsv_conversion_list);
 	spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
 }

 static int ext4_do_flush_completed_IO(struct inode *inode,
 				      struct list_head *head)
 {
 	ext4_io_end_t *io;
 	struct list_head unwritten;
 	unsigned long flags;
 	struct ext4_inode_info *ei = EXT4_I(inode);
 	int err, ret = 0;

 	spin_lock_irqsave(&ei->i_completed_io_lock, flags);
 	dump_completed_IO(inode, head);
 	list_replace_init(head, &unwritten);
 	spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);

 	while (!list_empty(&unwritten)) {
 		io = list_entry(unwritten.next, ext4_io_end_t, list);
 		BUG_ON(!(io->flag & EXT4_IO_END_UNWRITTEN));
 		list_del_init(&io->list);

 		err = ext4_end_io(io);
 		if (unlikely(!ret && err))
 			ret = err;
 	}
 	return ret;
 }

 /*
  * work on completed IO, to convert unwritten extents to extents
  */
 void ext4_end_io_rsv_work(struct work_struct *work)
 {
 	struct ext4_inode_info *ei = container_of(work, struct ext4_inode_info,
 						  i_rsv_conversion_work);
 	ext4_do_flush_completed_IO(&ei->vfs_inode, &ei->i_rsv_conversion_list);
 }

 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) {
 		io->inode = inode;
 		INIT_LIST_HEAD(&io->list);
 		atomic_set(&io->count, 1);
 	}
 	return io;
 }

 void ext4_put_io_end_defer(ext4_io_end_t *io_end)
 {
 	if (atomic_dec_and_test(&io_end->count)) {
 		if (!(io_end->flag & EXT4_IO_END_UNWRITTEN) || !io_end->size) {
 			ext4_release_io_end(io_end);
 			return;
 		}
 		ext4_add_complete_io(io_end);
 	}
 }

 int ext4_put_io_end(ext4_io_end_t *io_end)
 {
 	int err = 0;

 	if (atomic_dec_and_test(&io_end->count)) {
 		if (io_end->flag & EXT4_IO_END_UNWRITTEN) {
 			err = ext4_convert_unwritten_extents(io_end->handle,
 						io_end->inode, io_end->offset,
 						io_end->size);
 			io_end->handle = NULL;
 			ext4_clear_io_unwritten_flag(io_end);
 		}
 		ext4_release_io_end(io_end);
 	}
 	return err;
 }

 ext4_io_end_t *ext4_get_io_end(ext4_io_end_t *io_end)
 {
 	atomic_inc(&io_end->count);
 	return io_end;
 }

 /* BIO completion function for page writeback */
 static void ext4_end_bio(struct bio *bio)
 {
 	ext4_io_end_t *io_end = bio->bi_private;
 	sector_t bi_sector = bio->bi_iter.bi_sector;
 	char b[BDEVNAME_SIZE];

 	if (WARN_ONCE(!io_end, "io_end is NULL: %s: sector %Lu len %u err %d\n",
 		      bio_devname(bio, b),
 		      (long long) bio->bi_iter.bi_sector,
 		      (unsigned) bio_sectors(bio),
 		      bio->bi_status)) {
 		ext4_finish_bio(bio);
 		bio_put(bio);
 		return;
 	}
 	bio->bi_end_io = NULL;

 	if (bio->bi_status) {
 		struct inode *inode = io_end->inode;

 		ext4_warning(inode->i_sb, "I/O error %d writing to inode %lu "
 			     "(offset %llu size %ld starting block %llu)",
 			     bio->bi_status, inode->i_ino,
 			     (unsigned long long) io_end->offset,
 			     (long) io_end->size,
 			     (unsigned long long)
 			     bi_sector >> (inode->i_blkbits - 9));
 		mapping_set_error(inode->i_mapping,
 				blk_status_to_errno(bio->bi_status));
 	}

 	if (io_end->flag & EXT4_IO_END_UNWRITTEN) {
 		/*
 		 * Link bio into list hanging from io_end. We have to do it
 		 * atomically as bio completions can be racing against each
 		 * other.
 		 */
 		bio->bi_private = xchg(&io_end->bio, bio);
 		ext4_put_io_end_defer(io_end);
 	} else {
 		/*
 		 * Drop io_end reference early. Inode can get freed once
 		 * we finish the bio.
 		 */
 		ext4_put_io_end_defer(io_end);
 		ext4_finish_bio(bio);
 		bio_put(bio);
 	}
 }

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

 	if (bio) {
 		int io_op_flags = io->io_wbc->sync_mode == WB_SYNC_ALL ?
 				  REQ_SYNC : 0;
 		io->io_bio->bi_write_hint = io->io_end->inode->i_write_hint;
 		bio_set_op_attrs(io->io_bio, REQ_OP_WRITE, io_op_flags);
 		submit_bio(io->io_bio);
 	}
 	io->io_bio = NULL;
 }

 void ext4_io_submit_init(struct ext4_io_submit *io,
 			 struct writeback_control *wbc)
 {
 	io->io_wbc = wbc;
 	io->io_bio = NULL;
 	io->io_end = NULL;
 }

 static int io_submit_init_bio(struct ext4_io_submit *io,
 			      struct buffer_head *bh)
 {
 	struct bio *bio;

 	bio = bio_alloc(GFP_NOIO, BIO_MAX_PAGES);
 	if (!bio)
 		return -ENOMEM;
 	bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
 	bio_set_dev(bio, bh->b_bdev);
 	bio->bi_end_io = ext4_end_bio;
 	bio->bi_private = ext4_get_io_end(io->io_end);
 	io->io_bio = bio;
 	io->io_next_block = bh->b_blocknr;
 	wbc_init_bio(io->io_wbc, bio);
 	return 0;
 }

 static int io_submit_add_bh(struct ext4_io_submit *io,
 			    struct inode *inode,
 			    struct page *page,
 			    struct buffer_head *bh)
 {
 	int ret;

 	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_bio(io, bh);
 		if (ret)
 			return ret;
 		io->io_bio->bi_write_hint = inode->i_write_hint;
 	}
 	ret = bio_add_page(io->io_bio, page, bh->b_size, bh_offset(bh));
 	if (ret != bh->b_size)
 		goto submit_and_retry;
 	wbc_account_io(io->io_wbc, page, bh->b_size);
 	io->io_next_block++;
 	return 0;
 }

 int ext4_bio_write_page(struct ext4_io_submit *io,
 			struct page *page,
 			int len,
 			struct writeback_control *wbc,
 			bool keep_towrite)
 {
 	struct page *data_page = NULL;
 	struct inode *inode = page->mapping->host;
 	unsigned block_start;
 	struct buffer_head *bh, *head;
 	int ret = 0;
 	int nr_submitted = 0;
 	int nr_to_submit = 0;

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

 	if (keep_towrite)
 		set_page_writeback_keepwrite(page);
 	else
 		set_page_writeback(page);
 	ClearPageError(page);

 	/*
 	 * Comments copied from block_write_full_page:
 	 *
 	 * 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."
 	 */
 	if (len < PAGE_SIZE)
 		zero_user_segment(page, len, PAGE_SIZE);
 	/*
 	 * In the first loop we prepare and mark buffers to submit. We have to
 	 * mark all buffers in the page before submitting so that
 	 * end_page_writeback() cannot be called from ext4_bio_end_io() when IO
 	 * on the first buffer finishes and we are still working on submitting
 	 * the second buffer.
 	 */
 	bh = head = page_buffers(page);
 	do {
 		block_start = bh_offset(bh);
 		if (block_start >= len) {
 			clear_buffer_dirty(bh);
 			set_buffer_uptodate(bh);
 			continue;
 		}
 		if (!buffer_dirty(bh) || buffer_delay(bh) ||
 		    !buffer_mapped(bh) || buffer_unwritten(bh)) {
 			/* A hole? We can safely clear the dirty bit */
 			if (!buffer_mapped(bh))
 				clear_buffer_dirty(bh);
 			if (io->io_bio)
 				ext4_io_submit(io);
 			continue;
 		}
 		if (buffer_new(bh)) {
 			clear_buffer_new(bh);
 			clean_bdev_bh_alias(bh);
 		}
 		set_buffer_async_write(bh);
 		nr_to_submit++;
 	} while ((bh = bh->b_this_page) != head);

 	bh = head = page_buffers(page);

 	if (ext4_encrypted_inode(inode) && S_ISREG(inode->i_mode) &&
 	    nr_to_submit) {
 		gfp_t gfp_flags = GFP_NOFS;

 	retry_encrypt:
 		data_page = fscrypt_encrypt_page(inode, page, PAGE_SIZE, 0,
 						page->index, gfp_flags);
 		if (IS_ERR(data_page)) {
 			ret = PTR_ERR(data_page);
 			if (ret == -ENOMEM && wbc->sync_mode == WB_SYNC_ALL) {
 				if (io->io_bio) {
 					ext4_io_submit(io);
 					congestion_wait(BLK_RW_ASYNC, HZ/50);
 				}
 				gfp_flags |= __GFP_NOFAIL;
 				goto retry_encrypt;
 			}
 			data_page = NULL;
 			goto out;
 		}
 	}

 	/* Now submit buffers to write */
 	do {
 		if (!buffer_async_write(bh))
 			continue;
 		ret = io_submit_add_bh(io, inode,
 				       data_page ? data_page : page, 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.
 			 */
 			break;
 		}
 		nr_submitted++;
 		clear_buffer_dirty(bh);
 	} while ((bh = bh->b_this_page) != head);

 	/* Error stopped previous loop? Clean up buffers... */
 	if (ret) {
 	out:
 		if (data_page)
 			fscrypt_restore_control_page(data_page);
 		printk_ratelimited(KERN_ERR "%s: ret = %d\n", __func__, ret);
 		redirty_page_for_writepage(wbc, page);
 		do {
 			clear_buffer_async_write(bh);
 			bh = bh->b_this_page;
 		} while (bh != head);
 	}
 	unlock_page(page);
 	/* Nothing submitted - we have to end page writeback */
 	if (!nr_submitted)
 		end_page_writeback(page);
 	return ret;
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	* linux/fs/ext4/page-io.c
	*
	* This contains the new page_io functions for ext4
	*
	* Written by Theodore Ts'o, 2010.
	*/

	#include <linux/fs.h>
	#include <linux/time.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 <linux/mm.h>
	#include <linux/backing-dev.h>

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

	static struct kmem_cache *io_end_cachep;

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

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

	/*
	* 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)
	{
	printk_ratelimited(KERN_ERR "Buffer I/O error on device %pg, logical block %llu\n",
	bh->b_bdev,
	(unsigned long long)bh->b_blocknr);
	}

	static void ext4_finish_bio(struct bio *bio)
	{
	int i;
	struct bio_vec *bvec;

	bio_for_each_segment_all(bvec, bio, i) {
	struct page *page = bvec->bv_page;
	#ifdef CONFIG_EXT4_FS_ENCRYPTION
	struct page *data_page = NULL;
	#endif
	struct buffer_head bh, head;
	unsigned bio_start = bvec->bv_offset;
	unsigned bio_end = bio_start + bvec->bv_len;
	unsigned under_io = 0;
	unsigned long flags;

	if (!page)
	continue;

	#ifdef CONFIG_EXT4_FS_ENCRYPTION
	if (!page->mapping) {
	/* The bounce data pages are unmapped. */
	data_page = page;
	fscrypt_pullback_bio_page(&page, false);
	}
	#endif

	if (bio->bi_status) {
	SetPageError(page);
	mapping_set_error(page->mapping, -EIO);
	}
	bh = head = page_buffers(page);
	/*
	* We check all buffers in the page under BH_Uptodate_Lock
	* to avoid races with other end io clearing async_write flags
	*/
	local_irq_save(flags);
	bit_spin_lock(BH_Uptodate_Lock, &head->b_state);
	do {
	if (bh_offset(bh) < bio_start \|\|
	bh_offset(bh) + bh->b_size > bio_end) {
	if (buffer_async_write(bh))
	under_io++;
	continue;
	}
	clear_buffer_async_write(bh);
	if (bio->bi_status)
	buffer_io_error(bh);
	} while ((bh = bh->b_this_page) != head);
	bit_spin_unlock(BH_Uptodate_Lock, &head->b_state);
	local_irq_restore(flags);
	if (!under_io) {
	#ifdef CONFIG_EXT4_FS_ENCRYPTION
	if (data_page)
	fscrypt_restore_control_page(data_page);
	#endif
	end_page_writeback(page);
	}
	}
	}

	static void ext4_release_io_end(ext4_io_end_t *io_end)
	{
	struct bio bio, next_bio;

	BUG_ON(!list_empty(&io_end->list));
	BUG_ON(io_end->flag & EXT4_IO_END_UNWRITTEN);
	WARN_ON(io_end->handle);

	for (bio = io_end->bio; bio; bio = next_bio) {
	next_bio = bio->bi_private;
	ext4_finish_bio(bio);
	bio_put(bio);
	}
	kmem_cache_free(io_end_cachep, io_end);
	}

	/*
	* Check a range of space and convert unwritten extents to written. Note that
	* we are protected from truncate touching same part of extent tree by the
	* fact that truncate code waits for all DIO to finish (thus exclusion from
	* direct IO is achieved) and also waits for PageWriteback bits. Thus we
	* cannot get to ext4_ext_truncate() before all IOs overlapping that range are
	* completed (happens from ext4_free_ioend()).
	*/
	static int ext4_end_io(ext4_io_end_t *io)
	{
	struct inode *inode = io->inode;
	loff_t offset = io->offset;
	ssize_t size = io->size;
	handle_t *handle = io->handle;
	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);

	io->handle = NULL; /* Following call will use up the handle */
	ret = ext4_convert_unwritten_extents(handle, inode, offset, size);
	if (ret < 0 && !ext4_forced_shutdown(EXT4_SB(inode->i_sb))) {
	ext4_msg(inode->i_sb, KERN_EMERG,
	"failed to convert unwritten extents to written "
	"extents -- potential data loss! "
	"(inode %lu, offset %llu, size %zd, error %d)",
	inode->i_ino, offset, size, ret);
	}
	ext4_clear_io_unwritten_flag(io);
	ext4_release_io_end(io);
	return ret;
	}

	static void dump_completed_IO(struct inode inode, struct list_head head)
	{
	#ifdef EXT4FS_DEBUG
	struct list_head cur, before, *after;
	ext4_io_end_t io, io0, *io1;

	if (list_empty(head))
	return;

	ext4_debug("Dump inode %lu completed io list\n", inode->i_ino);
	list_for_each_entry(io, head, list) {
	cur = &io->list;
	before = cur->prev;
	io0 = container_of(before, ext4_io_end_t, list);
	after = cur->next;
	io1 = container_of(after, ext4_io_end_t, list);

	ext4_debug("io 0x%p from inode %lu,prev 0x%p,next 0x%p\n",
	io, inode->i_ino, io0, io1);
	}
	#endif
	}

	/* Add the io_end to per-inode completed end_io list. */
	static void ext4_add_complete_io(ext4_io_end_t *io_end)
	{
	struct ext4_inode_info *ei = EXT4_I(io_end->inode);
	struct ext4_sb_info *sbi = EXT4_SB(io_end->inode->i_sb);
	struct workqueue_struct *wq;
	unsigned long flags;

	/* Only reserved conversions from writeback should enter here */
	WARN_ON(!(io_end->flag & EXT4_IO_END_UNWRITTEN));
	WARN_ON(!io_end->handle && sbi->s_journal);
	spin_lock_irqsave(&ei->i_completed_io_lock, flags);
	wq = sbi->rsv_conversion_wq;
	if (list_empty(&ei->i_rsv_conversion_list))
	queue_work(wq, &ei->i_rsv_conversion_work);
	list_add_tail(&io_end->list, &ei->i_rsv_conversion_list);
	spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
	}

	static int ext4_do_flush_completed_IO(struct inode *inode,
	struct list_head *head)
	{
	ext4_io_end_t *io;
	struct list_head unwritten;
	unsigned long flags;
	struct ext4_inode_info *ei = EXT4_I(inode);
	int err, ret = 0;

	spin_lock_irqsave(&ei->i_completed_io_lock, flags);
	dump_completed_IO(inode, head);
	list_replace_init(head, &unwritten);
	spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);

	while (!list_empty(&unwritten)) {
	io = list_entry(unwritten.next, ext4_io_end_t, list);
	BUG_ON(!(io->flag & EXT4_IO_END_UNWRITTEN));
	list_del_init(&io->list);

	err = ext4_end_io(io);
	if (unlikely(!ret && err))
	ret = err;
	}
	return ret;
	}

	/*
	* work on completed IO, to convert unwritten extents to extents
	*/
	void ext4_end_io_rsv_work(struct work_struct *work)
	{
	struct ext4_inode_info *ei = container_of(work, struct ext4_inode_info,
	i_rsv_conversion_work);
	ext4_do_flush_completed_IO(&ei->vfs_inode, &ei->i_rsv_conversion_list);
	}

	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) {
	io->inode = inode;
	INIT_LIST_HEAD(&io->list);
	atomic_set(&io->count, 1);
	}
	return io;
	}

	void ext4_put_io_end_defer(ext4_io_end_t *io_end)
	{
	if (atomic_dec_and_test(&io_end->count)) {
	if (!(io_end->flag & EXT4_IO_END_UNWRITTEN) \|\| !io_end->size) {
	ext4_release_io_end(io_end);
	return;
	}
	ext4_add_complete_io(io_end);
	}
	}

	int ext4_put_io_end(ext4_io_end_t *io_end)
	{
	int err = 0;

	if (atomic_dec_and_test(&io_end->count)) {
	if (io_end->flag & EXT4_IO_END_UNWRITTEN) {
	err = ext4_convert_unwritten_extents(io_end->handle,
	io_end->inode, io_end->offset,
	io_end->size);
	io_end->handle = NULL;
	ext4_clear_io_unwritten_flag(io_end);
	}
	ext4_release_io_end(io_end);
	}
	return err;
	}

	ext4_io_end_t ext4_get_io_end(ext4_io_end_t io_end)
	{
	atomic_inc(&io_end->count);
	return io_end;
	}

	/* BIO completion function for page writeback */
	static void ext4_end_bio(struct bio *bio)
	{
	ext4_io_end_t *io_end = bio->bi_private;
	sector_t bi_sector = bio->bi_iter.bi_sector;
	char b[BDEVNAME_SIZE];

	if (WARN_ONCE(!io_end, "io_end is NULL: %s: sector %Lu len %u err %d\n",
	bio_devname(bio, b),
	(long long) bio->bi_iter.bi_sector,
	(unsigned) bio_sectors(bio),
	bio->bi_status)) {
	ext4_finish_bio(bio);
	bio_put(bio);
	return;
	}
	bio->bi_end_io = NULL;

	if (bio->bi_status) {
	struct inode *inode = io_end->inode;

	ext4_warning(inode->i_sb, "I/O error %d writing to inode %lu "
	"(offset %llu size %ld starting block %llu)",
	bio->bi_status, inode->i_ino,
	(unsigned long long) io_end->offset,
	(long) io_end->size,
	(unsigned long long)
	bi_sector >> (inode->i_blkbits - 9));
	mapping_set_error(inode->i_mapping,
	blk_status_to_errno(bio->bi_status));
	}

	if (io_end->flag & EXT4_IO_END_UNWRITTEN) {
	/*
	* Link bio into list hanging from io_end. We have to do it
	* atomically as bio completions can be racing against each
	* other.
	*/
	bio->bi_private = xchg(&io_end->bio, bio);
	ext4_put_io_end_defer(io_end);
	} else {
	/*
	* Drop io_end reference early. Inode can get freed once
	* we finish the bio.
	*/
	ext4_put_io_end_defer(io_end);
	ext4_finish_bio(bio);
	bio_put(bio);
	}
	}

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

	if (bio) {
	int io_op_flags = io->io_wbc->sync_mode == WB_SYNC_ALL ?
	REQ_SYNC : 0;
	io->io_bio->bi_write_hint = io->io_end->inode->i_write_hint;
	bio_set_op_attrs(io->io_bio, REQ_OP_WRITE, io_op_flags);
	submit_bio(io->io_bio);
	}
	io->io_bio = NULL;
	}

	void ext4_io_submit_init(struct ext4_io_submit *io,
	struct writeback_control *wbc)
	{
	io->io_wbc = wbc;
	io->io_bio = NULL;
	io->io_end = NULL;
	}

	static int io_submit_init_bio(struct ext4_io_submit *io,
	struct buffer_head *bh)
	{
	struct bio *bio;

	bio = bio_alloc(GFP_NOIO, BIO_MAX_PAGES);
	if (!bio)
	return -ENOMEM;
	bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
	bio_set_dev(bio, bh->b_bdev);
	bio->bi_end_io = ext4_end_bio;
	bio->bi_private = ext4_get_io_end(io->io_end);
	io->io_bio = bio;
	io->io_next_block = bh->b_blocknr;
	wbc_init_bio(io->io_wbc, bio);
	return 0;
	}

	static int io_submit_add_bh(struct ext4_io_submit *io,
	struct inode *inode,
	struct page *page,
	struct buffer_head *bh)
	{
	int ret;

	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_bio(io, bh);
	if (ret)
	return ret;
	io->io_bio->bi_write_hint = inode->i_write_hint;
	}
	ret = bio_add_page(io->io_bio, page, bh->b_size, bh_offset(bh));
	if (ret != bh->b_size)
	goto submit_and_retry;
	wbc_account_io(io->io_wbc, page, bh->b_size);
	io->io_next_block++;
	return 0;
	}

	int ext4_bio_write_page(struct ext4_io_submit *io,
	struct page *page,
	int len,
	struct writeback_control *wbc,
	bool keep_towrite)
	{
	struct page *data_page = NULL;
	struct inode *inode = page->mapping->host;
	unsigned block_start;
	struct buffer_head bh, head;
	int ret = 0;
	int nr_submitted = 0;
	int nr_to_submit = 0;

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

	if (keep_towrite)
	set_page_writeback_keepwrite(page);
	else
	set_page_writeback(page);
	ClearPageError(page);

	/*
	* Comments copied from block_write_full_page:
	*
	* 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."
	*/
	if (len < PAGE_SIZE)
	zero_user_segment(page, len, PAGE_SIZE);
	/*
	* In the first loop we prepare and mark buffers to submit. We have to
	* mark all buffers in the page before submitting so that
	* end_page_writeback() cannot be called from ext4_bio_end_io() when IO
	* on the first buffer finishes and we are still working on submitting
	* the second buffer.
	*/
	bh = head = page_buffers(page);
	do {
	block_start = bh_offset(bh);
	if (block_start >= len) {
	clear_buffer_dirty(bh);
	set_buffer_uptodate(bh);
	continue;
	}
	if (!buffer_dirty(bh) \|\| buffer_delay(bh) \|\|
	!buffer_mapped(bh) \|\| buffer_unwritten(bh)) {
	/* A hole? We can safely clear the dirty bit */
	if (!buffer_mapped(bh))
	clear_buffer_dirty(bh);
	if (io->io_bio)
	ext4_io_submit(io);
	continue;
	}
	if (buffer_new(bh)) {
	clear_buffer_new(bh);
	clean_bdev_bh_alias(bh);
	}
	set_buffer_async_write(bh);
	nr_to_submit++;
	} while ((bh = bh->b_this_page) != head);

	bh = head = page_buffers(page);

	if (ext4_encrypted_inode(inode) && S_ISREG(inode->i_mode) &&
	nr_to_submit) {
	gfp_t gfp_flags = GFP_NOFS;

	retry_encrypt:
	data_page = fscrypt_encrypt_page(inode, page, PAGE_SIZE, 0,
	page->index, gfp_flags);
	if (IS_ERR(data_page)) {
	ret = PTR_ERR(data_page);
	if (ret == -ENOMEM && wbc->sync_mode == WB_SYNC_ALL) {
	if (io->io_bio) {
	ext4_io_submit(io);
	congestion_wait(BLK_RW_ASYNC, HZ/50);
	}
	gfp_flags \|= __GFP_NOFAIL;
	goto retry_encrypt;
	}
	data_page = NULL;
	goto out;
	}
	}

	/* Now submit buffers to write */
	do {
	if (!buffer_async_write(bh))
	continue;
	ret = io_submit_add_bh(io, inode,
	data_page ? data_page : page, 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.
	*/
	break;
	}
	nr_submitted++;
	clear_buffer_dirty(bh);
	} while ((bh = bh->b_this_page) != head);

	/* Error stopped previous loop? Clean up buffers... */
	if (ret) {
	out:
	if (data_page)
	fscrypt_restore_control_page(data_page);
	printk_ratelimited(KERN_ERR "%s: ret = %d\n", __func__, ret);
	redirty_page_for_writepage(wbc, page);
	do {
	clear_buffer_async_write(bh);
	bh = bh->b_this_page;
	} while (bh != head);
	}
	unlock_page(page);
	/* Nothing submitted - we have to end page writeback */
	if (!nr_submitted)
	end_page_writeback(page);
	return ret;
	}