/*
   * Copyright (c) 2008,2009 NEC Software Tohoku, Ltd.
   * Written by Takashi Sato <t-sato@yk.jp.nec.com>
   *            Akira Fujita <a-fujita@rs.jp.nec.com>
   *
   * This program is free software; you can redistribute it and/or modify it
   * under the terms of version 2.1 of the GNU Lesser General Public License
   * as published by the Free Software Foundation.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   */
  
  #include <linux/fs.h>
  #include <linux/quotaops.h>

  #include <linux/slab.h>

  #include "ext4_jbd2.h"

  #include "ext4.h"

  #include "ext4_extents.h"

  /**
   * get_ext_path - Find an extent path for designated logical block number.
   *
   * @inode:	an inode which is searched
   * @lblock:	logical block number to find an extent path
   * @path:	pointer to an extent path pointer (for output)
   *

   * ext4_find_extent wrapper. Return 0 on success, or a negative error value

   * on failure.
   */
  static inline int
  get_ext_path(struct inode *inode, ext4_lblk_t lblock,

  		struct ext4_ext_path **ppath)

  {

  	struct ext4_ext_path *path;

  	path = ext4_find_extent(inode, lblock, ppath, EXT4_EX_NOCACHE);

  	if (IS_ERR(path))

  		return PTR_ERR(path);
  	if (path[ext_depth(inode)].p_ext == NULL) {
  		ext4_ext_drop_refs(path);
  		kfree(path);
  		*ppath = NULL;
  		return -ENODATA;
  	}
  	*ppath = path;
  	return 0;

  }

  
  /**

   * ext4_double_down_write_data_sem - Acquire two inodes' write lock
   *                                   of i_data_sem

   *

   * Acquire write lock of i_data_sem of the two inodes

   */

  void
  ext4_double_down_write_data_sem(struct inode *first, struct inode *second)

  {

  	if (first < second) {
  		down_write(&EXT4_I(first)->i_data_sem);
  		down_write_nested(&EXT4_I(second)->i_data_sem, SINGLE_DEPTH_NESTING);
  	} else {
  		down_write(&EXT4_I(second)->i_data_sem);
  		down_write_nested(&EXT4_I(first)->i_data_sem, SINGLE_DEPTH_NESTING);

  	}

  }
  
  /**

   * ext4_double_up_write_data_sem - Release two inodes' write lock of i_data_sem

   *
   * @orig_inode:		original inode structure to be released its lock first
   * @donor_inode:	donor inode structure to be released its lock second

   * Release write lock of i_data_sem of two inodes (orig and donor).

   */

  void
  ext4_double_up_write_data_sem(struct inode *orig_inode,
  			      struct inode *donor_inode)

  {

  	up_write(&EXT4_I(orig_inode)->i_data_sem);
  	up_write(&EXT4_I(donor_inode)->i_data_sem);
  }
  
  /**

   * mext_check_coverage - Check that all extents in range has the same type
   *
   * @inode:		inode in question
   * @from:		block offset of inode
   * @count:		block count to be checked

   * @unwritten:		extents expected to be unwritten

   * @err:		pointer to save error value
   *
   * Return 1 if all extents in range has expected type, and zero otherwise.
   */
  static int
  mext_check_coverage(struct inode *inode, ext4_lblk_t from, ext4_lblk_t count,

  		    int unwritten, int *err)

  {
  	struct ext4_ext_path *path = NULL;
  	struct ext4_extent *ext;

  	int ret = 0;

  	ext4_lblk_t last = from + count;
  	while (from < last) {
  		*err = get_ext_path(inode, from, &path);
  		if (*err)

  			goto out;

  		ext = path[ext_depth(inode)].p_ext;

  		if (unwritten != ext4_ext_is_unwritten(ext))

  			goto out;

  		from += ext4_ext_get_actual_len(ext);
  		ext4_ext_drop_refs(path);
  	}

  	ret = 1;
  out:

  	ext4_ext_drop_refs(path);
  	kfree(path);

  	return ret;

  }
  
  /**

   * mext_page_double_lock - Grab and lock pages on both @inode1 and @inode2
   *
   * @inode1:	the inode structure
   * @inode2:	the inode structure

   * @index1:	page index
   * @index2:	page index

   * @page:	result page vector
   *
   * Grab two locked pages for inode's by inode order
   */
  static int
  mext_page_double_lock(struct inode *inode1, struct inode *inode2,

  		      pgoff_t index1, pgoff_t index2, struct page *page[2])

  {
  	struct address_space *mapping[2];
  	unsigned fl = AOP_FLAG_NOFS;
  
  	BUG_ON(!inode1 || !inode2);
  	if (inode1 < inode2) {
  		mapping[0] = inode1->i_mapping;
  		mapping[1] = inode2->i_mapping;
  	} else {

  		pgoff_t tmp = index1;
  		index1 = index2;
  		index2 = tmp;

  		mapping[0] = inode2->i_mapping;
  		mapping[1] = inode1->i_mapping;
  	}

  	page[0] = grab_cache_page_write_begin(mapping[0], index1, fl);

  	if (!page[0])
  		return -ENOMEM;

  	page[1] = grab_cache_page_write_begin(mapping[1], index2, fl);

  	if (!page[1]) {
  		unlock_page(page[0]);
  		page_cache_release(page[0]);
  		return -ENOMEM;
  	}

  	/*
  	 * grab_cache_page_write_begin() may not wait on page's writeback if
  	 * BDI not demand that. But it is reasonable to be very conservative
  	 * here and explicitly wait on page's writeback
  	 */
  	wait_on_page_writeback(page[0]);
  	wait_on_page_writeback(page[1]);

  	if (inode1 > inode2) {
  		struct page *tmp;
  		tmp = page[0];
  		page[0] = page[1];
  		page[1] = tmp;
  	}
  	return 0;
  }
  
  /* Force page buffers uptodate w/o dropping page's lock */
  static int
  mext_page_mkuptodate(struct page *page, unsigned from, unsigned to)
  {
  	struct inode *inode = page->mapping->host;
  	sector_t block;
  	struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
  	unsigned int blocksize, block_start, block_end;
  	int i, err,  nr = 0, partial = 0;
  	BUG_ON(!PageLocked(page));
  	BUG_ON(PageWriteback(page));
  
  	if (PageUptodate(page))
  		return 0;
  
  	blocksize = 1 << inode->i_blkbits;
  	if (!page_has_buffers(page))
  		create_empty_buffers(page, blocksize, 0);
  
  	head = page_buffers(page);
  	block = (sector_t)page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
  	for (bh = head, block_start = 0; bh != head || !block_start;
  	     block++, block_start = block_end, bh = bh->b_this_page) {
  		block_end = block_start + blocksize;
  		if (block_end <= from || block_start >= to) {
  			if (!buffer_uptodate(bh))
  				partial = 1;
  			continue;
  		}
  		if (buffer_uptodate(bh))
  			continue;
  		if (!buffer_mapped(bh)) {

  			err = ext4_get_block(inode, block, bh, 0);
  			if (err) {
  				SetPageError(page);
  				return err;
  			}
  			if (!buffer_mapped(bh)) {
  				zero_user(page, block_start, blocksize);

  				set_buffer_uptodate(bh);

  				continue;
  			}
  		}
  		BUG_ON(nr >= MAX_BUF_PER_PAGE);
  		arr[nr++] = bh;
  	}
  	/* No io required */
  	if (!nr)
  		goto out;
  
  	for (i = 0; i < nr; i++) {
  		bh = arr[i];
  		if (!bh_uptodate_or_lock(bh)) {
  			err = bh_submit_read(bh);
  			if (err)
  				return err;
  		}
  	}
  out:
  	if (!partial)
  		SetPageUptodate(page);
  	return 0;
  }
  
  /**

   * move_extent_per_page - Move extent data per page
   *
   * @o_filp:			file structure of original file
   * @donor_inode:		donor inode
   * @orig_page_offset:		page index on original file

   * @donor_page_offset:		page index on donor file

   * @data_offset_in_page:	block index where data swapping starts
   * @block_len_in_page:		the number of blocks to be swapped

   * @unwritten:			orig extent is unwritten or not

   * @err:			pointer to save return value

   *
   * Save the data in original inode blocks and replace original inode extents

   * with donor inode extents by calling ext4_swap_extents().

   * Finally, write out the saved data in new original inode blocks. Return
   * replaced block count.

   */
  static int

  move_extent_per_page(struct file *o_filp, struct inode *donor_inode,

  		     pgoff_t orig_page_offset, pgoff_t donor_page_offset,
  		     int data_offset_in_page,
  		     int block_len_in_page, int unwritten, int *err)

  {

  	struct inode *orig_inode = file_inode(o_filp);

  	struct page *pagep[2] = {NULL, NULL};

  	handle_t *handle;

  	ext4_lblk_t orig_blk_offset, donor_blk_offset;

  	unsigned long blocksize = orig_inode->i_sb->s_blocksize;

  	unsigned int tmp_data_size, data_size, replaced_size;

  	int err2, jblocks, retries = 0;

  	int replaced_count = 0;

  	int from = data_offset_in_page << orig_inode->i_blkbits;

  	int blocks_per_page = PAGE_CACHE_SIZE >> orig_inode->i_blkbits;

  	struct super_block *sb = orig_inode->i_sb;

  
  	/*
  	 * It needs twice the amount of ordinary journal buffers because
  	 * inode and donor_inode may change each different metadata blocks.
  	 */

  again:
  	*err = 0;

  	jblocks = ext4_writepage_trans_blocks(orig_inode) * 2;

  	handle = ext4_journal_start(orig_inode, EXT4_HT_MOVE_EXTENTS, jblocks);

  	if (IS_ERR(handle)) {

  		*err = PTR_ERR(handle);
  		return 0;

  	}

  	orig_blk_offset = orig_page_offset * blocks_per_page +
  		data_offset_in_page;

  	donor_blk_offset = donor_page_offset * blocks_per_page +
  		data_offset_in_page;

  	/* Calculate data_size */

  	if ((orig_blk_offset + block_len_in_page - 1) ==
  	    ((orig_inode->i_size - 1) >> orig_inode->i_blkbits)) {
  		/* Replace the last block */

  		tmp_data_size = orig_inode->i_size & (blocksize - 1);

  		/*

  		 * If data_size equal zero, it shows data_size is multiples of

  		 * blocksize. So we set appropriate value.
  		 */

  		if (tmp_data_size == 0)
  			tmp_data_size = blocksize;

  		data_size = tmp_data_size +

  			((block_len_in_page - 1) << orig_inode->i_blkbits);

  	} else
  		data_size = block_len_in_page << orig_inode->i_blkbits;
  
  	replaced_size = data_size;

  	*err = mext_page_double_lock(orig_inode, donor_inode, orig_page_offset,

  				     donor_page_offset, pagep);

  	if (unlikely(*err < 0))

  		goto stop_journal;

  	/*

  	 * If orig extent was unwritten it can become initialized

  	 * at any time after i_data_sem was dropped, in order to
  	 * serialize with delalloc we have recheck extent while we
  	 * hold page's lock, if it is still the case data copy is not
  	 * necessary, just swap data blocks between orig and donor.
  	 */

  	if (unwritten) {

  		ext4_double_down_write_data_sem(orig_inode, donor_inode);

  		/* If any of extents in range became initialized we have to
  		 * fallback to data copying */

  		unwritten = mext_check_coverage(orig_inode, orig_blk_offset,
  						block_len_in_page, 1, err);

  		if (*err)
  			goto drop_data_sem;

  		unwritten &= mext_check_coverage(donor_inode, donor_blk_offset,

  						 block_len_in_page, 1, err);

  		if (*err)
  			goto drop_data_sem;

  		if (!unwritten) {

  			ext4_double_up_write_data_sem(orig_inode, donor_inode);

  			goto data_copy;
  		}
  		if ((page_has_private(pagep[0]) &&
  		     !try_to_release_page(pagep[0], 0)) ||
  		    (page_has_private(pagep[1]) &&
  		     !try_to_release_page(pagep[1], 0))) {
  			*err = -EBUSY;
  			goto drop_data_sem;
  		}

  		replaced_count = ext4_swap_extents(handle, orig_inode,
  						   donor_inode, orig_blk_offset,
  						   donor_blk_offset,
  						   block_len_in_page, 1, err);

  	drop_data_sem:

  		ext4_double_up_write_data_sem(orig_inode, donor_inode);

  		goto unlock_pages;
  	}
  data_copy:

  	*err = mext_page_mkuptodate(pagep[0], from, from + replaced_size);
  	if (*err)
  		goto unlock_pages;
  
  	/* At this point all buffers in range are uptodate, old mapping layout
  	 * is no longer required, try to drop it now. */
  	if ((page_has_private(pagep[0]) && !try_to_release_page(pagep[0], 0)) ||
  	    (page_has_private(pagep[1]) && !try_to_release_page(pagep[1], 0))) {
  		*err = -EBUSY;
  		goto unlock_pages;

  	}

  	ext4_double_down_write_data_sem(orig_inode, donor_inode);

  	replaced_count = ext4_swap_extents(handle, orig_inode, donor_inode,
  					       orig_blk_offset, donor_blk_offset,
  					   block_len_in_page, 1, err);

  	ext4_double_up_write_data_sem(orig_inode, donor_inode);

  	if (*err) {

  		if (replaced_count) {
  			block_len_in_page = replaced_count;
  			replaced_size =
  				block_len_in_page << orig_inode->i_blkbits;

  		} else

  			goto unlock_pages;

  	}

  	/* Perform all necessary steps similar write_begin()/write_end()
  	 * but keeping in mind that i_size will not change */

  	*err = __block_write_begin(pagep[0], from, replaced_size,

  				   ext4_get_block);
  	if (!*err)
  		*err = block_commit_write(pagep[0], from, from + replaced_size);

  	if (unlikely(*err < 0))
  		goto repair_branches;
  
  	/* Even in case of data=writeback it is reasonable to pin
  	 * inode to transaction, to prevent unexpected data loss */
  	*err = ext4_jbd2_file_inode(handle, orig_inode);
  
  unlock_pages:
  	unlock_page(pagep[0]);
  	page_cache_release(pagep[0]);
  	unlock_page(pagep[1]);
  	page_cache_release(pagep[1]);
  stop_journal:

  	ext4_journal_stop(handle);

  	if (*err == -ENOSPC &&
  	    ext4_should_retry_alloc(sb, &retries))
  		goto again;

  	/* Buffer was busy because probably is pinned to journal transaction,
  	 * force transaction commit may help to free it. */

  	if (*err == -EBUSY && retries++ < 4 && EXT4_SB(sb)->s_journal &&
  	    jbd2_journal_force_commit_nested(EXT4_SB(sb)->s_journal))

  		goto again;

  	return replaced_count;

  
  repair_branches:
  	/*
  	 * This should never ever happen!
  	 * Extents are swapped already, but we are not able to copy data.
  	 * Try to swap extents to it's original places
  	 */

  	ext4_double_down_write_data_sem(orig_inode, donor_inode);

  	replaced_count = ext4_swap_extents(handle, donor_inode, orig_inode,
  					       orig_blk_offset, donor_blk_offset,
  					   block_len_in_page, 0, &err2);

  	ext4_double_up_write_data_sem(orig_inode, donor_inode);

  	if (replaced_count != block_len_in_page) {
  		EXT4_ERROR_INODE_BLOCK(orig_inode, (sector_t)(orig_blk_offset),
  				       "Unable to copy data block,"
  				       " data will be lost.");
  		*err = -EIO;
  	}
  	replaced_count = 0;
  	goto unlock_pages;

  }
  
  /**

   * mext_check_arguments - Check whether move extent can be done

   *
   * @orig_inode:		original inode
   * @donor_inode:	donor inode
   * @orig_start:		logical start offset in block for orig
   * @donor_start:	logical start offset in block for donor
   * @len:		the number of blocks to be moved

   *
   * Check the arguments of ext4_move_extents() whether the files can be
   * exchanged with each other.
   * Return 0 on success, or a negative error value on failure.
   */
  static int
  mext_check_arguments(struct inode *orig_inode,

  		     struct inode *donor_inode, __u64 orig_start,
  		     __u64 donor_start, __u64 *len)

  {

  	__u64 orig_eof, donor_eof;

  	unsigned int blkbits = orig_inode->i_blkbits;
  	unsigned int blocksize = 1 << blkbits;

  	orig_eof = (i_size_read(orig_inode) + blocksize - 1) >> blkbits;
  	donor_eof = (i_size_read(donor_inode) + blocksize - 1) >> blkbits;

  	if (donor_inode->i_mode & (S_ISUID|S_ISGID)) {
  		ext4_debug("ext4 move extent: suid or sgid is set"
  			   " to donor file [ino:orig %lu, donor %lu]
  ",
  			   orig_inode->i_ino, donor_inode->i_ino);
  		return -EINVAL;
  	}

  	if (IS_IMMUTABLE(donor_inode) || IS_APPEND(donor_inode))
  		return -EPERM;

  	/* Ext4 move extent does not support swapfile */
  	if (IS_SWAPFILE(orig_inode) || IS_SWAPFILE(donor_inode)) {
  		ext4_debug("ext4 move extent: The argument files should "
  			"not be swapfile [ino:orig %lu, donor %lu]
  ",
  			orig_inode->i_ino, donor_inode->i_ino);

  		return -EBUSY;

  	}

  	/* Ext4 move extent supports only extent based file */

  	if (!(ext4_test_inode_flag(orig_inode, EXT4_INODE_EXTENTS))) {

  		ext4_debug("ext4 move extent: orig file is not extents "
  			"based file [ino:orig %lu]
  ", orig_inode->i_ino);
  		return -EOPNOTSUPP;

  	} else if (!(ext4_test_inode_flag(donor_inode, EXT4_INODE_EXTENTS))) {

  		ext4_debug("ext4 move extent: donor file is not extents "
  			"based file [ino:donor %lu]
  ", donor_inode->i_ino);
  		return -EOPNOTSUPP;
  	}
  
  	if ((!orig_inode->i_size) || (!donor_inode->i_size)) {
  		ext4_debug("ext4 move extent: File size is 0 byte
  ");
  		return -EINVAL;
  	}
  
  	/* Start offset should be same */

  	if ((orig_start & ~(PAGE_MASK >> orig_inode->i_blkbits)) !=
  	    (donor_start & ~(PAGE_MASK >> orig_inode->i_blkbits))) {

  		ext4_debug("ext4 move extent: orig and donor's start "

  			"offset are not alligned [ino:orig %lu, donor %lu]
  ",

  			orig_inode->i_ino, donor_inode->i_ino);
  		return -EINVAL;
  	}

  	if ((orig_start >= EXT_MAX_BLOCKS) ||

  	    (donor_start >= EXT_MAX_BLOCKS) ||

  	    (*len > EXT_MAX_BLOCKS) ||

  	    (donor_start + *len >= EXT_MAX_BLOCKS) ||

  	    (orig_start + *len >= EXT_MAX_BLOCKS))  {

  		ext4_debug("ext4 move extent: Can't handle over [%u] blocks "

  			"[ino:orig %lu, donor %lu]
  ", EXT_MAX_BLOCKS,

  			orig_inode->i_ino, donor_inode->i_ino);
  		return -EINVAL;
  	}

  	if (orig_eof < orig_start + *len - 1)
  		*len = orig_eof - orig_start;
  	if (donor_eof < donor_start + *len - 1)
  		*len = donor_eof - donor_start;

  	if (!*len) {

  		ext4_debug("ext4 move extent: len should not be 0 "

  			"[ino:orig %lu, donor %lu]
  ", orig_inode->i_ino,
  			donor_inode->i_ino);
  		return -EINVAL;
  	}
  
  	return 0;
  }
  
  /**

   * ext4_move_extents - Exchange the specified range of a file
   *
   * @o_filp:		file structure of the original file
   * @d_filp:		file structure of the donor file

   * @orig_blk:		start offset in block for orig
   * @donor_blk:		start offset in block for donor

   * @len:		the number of blocks to be moved
   * @moved_len:		moved block length
   *
   * This function returns 0 and moved block length is set in moved_len
   * if succeed, otherwise returns error value.
   *

   */
  int

  ext4_move_extents(struct file *o_filp, struct file *d_filp, __u64 orig_blk,
  		  __u64 donor_blk, __u64 len, __u64 *moved_len)

  {

  	struct inode *orig_inode = file_inode(o_filp);
  	struct inode *donor_inode = file_inode(d_filp);

  	struct ext4_ext_path *path = NULL;

  	int blocks_per_page = PAGE_CACHE_SIZE >> orig_inode->i_blkbits;

  	ext4_lblk_t o_end, o_start = orig_blk;
  	ext4_lblk_t d_start = donor_blk;
  	int ret;

  	if (orig_inode->i_sb != donor_inode->i_sb) {
  		ext4_debug("ext4 move extent: The argument files "
  			"should be in same FS [ino:orig %lu, donor %lu]
  ",
  			orig_inode->i_ino, donor_inode->i_ino);
  		return -EINVAL;
  	}
  
  	/* orig and donor should be different inodes */
  	if (orig_inode == donor_inode) {

  		ext4_debug("ext4 move extent: The argument files should not "

  			"be same inode [ino:orig %lu, donor %lu]
  ",

  			orig_inode->i_ino, donor_inode->i_ino);
  		return -EINVAL;
  	}

  	/* Regular file check */
  	if (!S_ISREG(orig_inode->i_mode) || !S_ISREG(donor_inode->i_mode)) {
  		ext4_debug("ext4 move extent: The argument files should be "
  			"regular file [ino:orig %lu, donor %lu]
  ",
  			orig_inode->i_ino, donor_inode->i_ino);
  		return -EINVAL;
  	}

  	/* TODO: This is non obvious task to swap blocks for inodes with full
  	   jornaling enabled */
  	if (ext4_should_journal_data(orig_inode) ||
  	    ext4_should_journal_data(donor_inode)) {
  		return -EINVAL;
  	}

  	/* Protect orig and donor inodes against a truncate */

  	lock_two_nondirectories(orig_inode, donor_inode);

  	/* Wait for all existing dio workers */
  	ext4_inode_block_unlocked_dio(orig_inode);
  	ext4_inode_block_unlocked_dio(donor_inode);
  	inode_dio_wait(orig_inode);
  	inode_dio_wait(donor_inode);

  	/* Protect extent tree against block allocations via delalloc */

  	ext4_double_down_write_data_sem(orig_inode, donor_inode);

  	/* Check the filesystem environment whether move_extent can be done */

  	ret = mext_check_arguments(orig_inode, donor_inode, orig_blk,
  				    donor_blk, &len);

  	if (ret)

  		goto out;

  	o_end = o_start + len;

  	while (o_start < o_end) {
  		struct ext4_extent *ex;
  		ext4_lblk_t cur_blk, next_blk;
  		pgoff_t orig_page_index, donor_page_index;
  		int offset_in_page;
  		int unwritten, cur_len;

  		ret = get_ext_path(orig_inode, o_start, &path);
  		if (ret)

  			goto out;

  		ex = path[path->p_depth].p_ext;
  		next_blk = ext4_ext_next_allocated_block(path);
  		cur_blk = le32_to_cpu(ex->ee_block);
  		cur_len = ext4_ext_get_actual_len(ex);
  		/* Check hole before the start pos */
  		if (cur_blk + cur_len - 1 < o_start) {
  			if (next_blk == EXT_MAX_BLOCKS) {
  				o_start = o_end;
  				ret = -ENODATA;
  				goto out;
  			}
  			d_start += next_blk - o_start;
  			o_start = next_blk;

  			continue;

  		/* Check hole after the start pos */
  		} else if (cur_blk > o_start) {
  			/* Skip hole */
  			d_start += cur_blk - o_start;
  			o_start = cur_blk;
  			/* Extent inside requested range ?*/
  			if (cur_blk >= o_end)
  				goto out;
  		} else { /* in_range(o_start, o_blk, o_len) */
  			cur_len += cur_blk - o_start;

  		}

  		unwritten = ext4_ext_is_unwritten(ex);
  		if (o_end - o_start < cur_len)
  			cur_len = o_end - o_start;
  
  		orig_page_index = o_start >> (PAGE_CACHE_SHIFT -
  					       orig_inode->i_blkbits);
  		donor_page_index = d_start >> (PAGE_CACHE_SHIFT -
  					       donor_inode->i_blkbits);
  		offset_in_page = o_start % blocks_per_page;
  		if (cur_len > blocks_per_page- offset_in_page)
  			cur_len = blocks_per_page - offset_in_page;

  		/*
  		 * Up semaphore to avoid following problems:
  		 * a. transaction deadlock among ext4_journal_start,
  		 *    ->write_begin via pagefault, and jbd2_journal_commit
  		 * b. racing with ->readpage, ->write_begin, and ext4_get_block
  		 *    in move_extent_per_page
  		 */

  		ext4_double_up_write_data_sem(orig_inode, donor_inode);

  		/* Swap original branches with new branches */
  		move_extent_per_page(o_filp, donor_inode,
  				     orig_page_index, donor_page_index,
  				     offset_in_page, cur_len,
  				     unwritten, &ret);

  		ext4_double_down_write_data_sem(orig_inode, donor_inode);

  		if (ret < 0)

  			break;

  		o_start += cur_len;
  		d_start += cur_len;

  	}

  	*moved_len = o_start - orig_blk;
  	if (*moved_len > len)
  		*moved_len = len;

  out:

  	if (*moved_len) {
  		ext4_discard_preallocations(orig_inode);
  		ext4_discard_preallocations(donor_inode);
  	}

  	ext4_ext_drop_refs(path);
  	kfree(path);

  	ext4_double_up_write_data_sem(orig_inode, donor_inode);

  	ext4_inode_resume_unlocked_dio(orig_inode);
  	ext4_inode_resume_unlocked_dio(donor_inode);

  	unlock_two_nondirectories(orig_inode, donor_inode);

  	return ret;

  }