text: /*
   * 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_extents.h"
  #include "ext4.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_ext_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 **path)
  {
  	int ret = 0;
  
  	*path = ext4_ext_find_extent(inode, lblock, *path);
  	if (IS_ERR(*path)) {
  		ret = PTR_ERR(*path);
  		*path = NULL;
  	} else if ((*path)[ext_depth(inode)].p_ext == NULL)
  		ret = -ENODATA;
  
  	return ret;
  }
  
  /**
   * copy_extent_status - Copy the extent's initialization status
   *
   * @src:	an extent for getting initialize status
   * @dest:	an extent to be set the status
   */
  static void
  copy_extent_status(struct ext4_extent *src, struct ext4_extent *dest)
  {
  	if (ext4_ext_is_uninitialized(src))
  		ext4_ext_mark_uninitialized(dest);
  	else
  		dest->ee_len = cpu_to_le16(ext4_ext_get_actual_len(dest));
  }
  
  /**
   * mext_next_extent - Search for the next extent and set it to "extent"
   *
   * @inode:	inode which is searched
   * @path:	this will obtain data for the next extent
   * @extent:	pointer to the next extent we have just gotten
   *
   * Search the next extent in the array of ext4_ext_path structure (@path)
   * and set it to ext4_extent structure (@extent). In addition, the member of
   * @path (->p_ext) also points the next extent. Return 0 on success, 1 if
   * ext4_ext_path structure refers to the last extent, or a negative error
   * value on failure.
   */
  static int
  mext_next_extent(struct inode *inode, struct ext4_ext_path *path,
  		      struct ext4_extent **extent)
  {
  	struct ext4_extent_header *eh;
  	int ppos, leaf_ppos = path->p_depth;
  
  	ppos = leaf_ppos;
  	if (EXT_LAST_EXTENT(path[ppos].p_hdr) > path[ppos].p_ext) {
  		/* leaf block */
  		*extent = ++path[ppos].p_ext;
  		path[ppos].p_block = ext_pblock(path[ppos].p_ext);
  		return 0;
  	}
  
  	while (--ppos >= 0) {
  		if (EXT_LAST_INDEX(path[ppos].p_hdr) >
  		    path[ppos].p_idx) {
  			int cur_ppos = ppos;
  
  			/* index block */
  			path[ppos].p_idx++;
  			path[ppos].p_block = idx_pblock(path[ppos].p_idx);
  			if (path[ppos+1].p_bh)
  				brelse(path[ppos+1].p_bh);
  			path[ppos+1].p_bh =
  				sb_bread(inode->i_sb, path[ppos].p_block);
  			if (!path[ppos+1].p_bh)
  				return -EIO;
  			path[ppos+1].p_hdr =
  				ext_block_hdr(path[ppos+1].p_bh);
  
  			/* Halfway index block */
  			while (++cur_ppos < leaf_ppos) {
  				path[cur_ppos].p_idx =
  					EXT_FIRST_INDEX(path[cur_ppos].p_hdr);
  				path[cur_ppos].p_block =
  					idx_pblock(path[cur_ppos].p_idx);
  				if (path[cur_ppos+1].p_bh)
  					brelse(path[cur_ppos+1].p_bh);
  				path[cur_ppos+1].p_bh = sb_bread(inode->i_sb,
  					path[cur_ppos].p_block);
  				if (!path[cur_ppos+1].p_bh)
  					return -EIO;
  				path[cur_ppos+1].p_hdr =
  					ext_block_hdr(path[cur_ppos+1].p_bh);
  			}
  
  			path[leaf_ppos].p_ext = *extent = NULL;
  
  			eh = path[leaf_ppos].p_hdr;
  			if (le16_to_cpu(eh->eh_entries) == 0)
  				/* empty leaf is found */
  				return -ENODATA;
  
  			/* leaf block */
  			path[leaf_ppos].p_ext = *extent =
  				EXT_FIRST_EXTENT(path[leaf_ppos].p_hdr);
  			path[leaf_ppos].p_block =
  					ext_pblock(path[leaf_ppos].p_ext);
  			return 0;
  		}
  	}
  	/* We found the last extent */
  	return 1;
  }
  
  /**
   * mext_check_null_inode - NULL check for two inodes
   *
   * If inode1 or inode2 is NULL, return -EIO. Otherwise, return 0.
   */
  static int
  mext_check_null_inode(struct inode *inode1, struct inode *inode2,
  		const char *function)
  {
  	int ret = 0;
  
  	if (inode1 == NULL) {
  		__ext4_error(inode2->i_sb, function,
  			"Both inodes should not be NULL: "
  			"inode1 NULL inode2 %lu", inode2->i_ino);
  		ret = -EIO;
  	} else if (inode2 == NULL) {
  		__ext4_error(inode1->i_sb, function,
  			"Both inodes should not be NULL: "
  			"inode1 %lu inode2 NULL", inode1->i_ino);
  		ret = -EIO;
  	}
  	return ret;
  }
  
  /**
   * double_down_write_data_sem - Acquire two inodes' write lock of i_data_sem
   *
   * @orig_inode:		original inode structure
   * @donor_inode:	donor inode structure
   * Acquire write lock of i_data_sem of the two inodes (orig and donor) by
   * i_ino order.
   */
  static void
  double_down_write_data_sem(struct inode *orig_inode, struct inode *donor_inode)
  {
  	struct inode *first = orig_inode, *second = donor_inode;
  
  	/*
  	 * Use the inode number to provide the stable locking order instead
  	 * of its address, because the C language doesn't guarantee you can
  	 * compare pointers that don't come from the same array.
  	 */
  	if (donor_inode->i_ino < orig_inode->i_ino) {
  		first = donor_inode;
  		second = orig_inode;
  	}
  
  	down_write(&EXT4_I(first)->i_data_sem);
  	down_write_nested(&EXT4_I(second)->i_data_sem, SINGLE_DEPTH_NESTING);
  }
  
  /**
   * 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).
   */
  static void
  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_insert_across_blocks - Insert extents across leaf block
   *
   * @handle:		journal handle
   * @orig_inode:		original inode
   * @o_start:		first original extent to be changed
   * @o_end:		last original extent to be changed
   * @start_ext:		first new extent to be inserted
   * @new_ext:		middle of new extent to be inserted
   * @end_ext:		last new extent to be inserted
   *
   * Allocate a new leaf block and insert extents into it. Return 0 on success,
   * or a negative error value on failure.
   */
  static int
  mext_insert_across_blocks(handle_t *handle, struct inode *orig_inode,
  		struct ext4_extent *o_start, struct ext4_extent *o_end,
  		struct ext4_extent *start_ext, struct ext4_extent *new_ext,
  		struct ext4_extent *end_ext)
  {
  	struct ext4_ext_path *orig_path = NULL;
  	ext4_lblk_t eblock = 0;
  	int new_flag = 0;
  	int end_flag = 0;
  	int err = 0;
  
  	if (start_ext->ee_len && new_ext->ee_len && end_ext->ee_len) {
  		if (o_start == o_end) {
  
  			/*       start_ext   new_ext    end_ext
  			 * donor |---------|-----------|--------|
  			 * orig  |------------------------------|
  			 */
  			end_flag = 1;
  		} else {
  
  			/*       start_ext   new_ext   end_ext
  			 * donor |---------|----------|---------|
  			 * orig  |---------------|--------------|
  			 */
  			o_end->ee_block = end_ext->ee_block;
  			o_end->ee_len = end_ext->ee_len;
  			ext4_ext_store_pblock(o_end, ext_pblock(end_ext));
  		}
  
  		o_start->ee_len = start_ext->ee_len;
  		eblock = le32_to_cpu(start_ext->ee_block);
  		new_flag = 1;
  
  	} else if (start_ext->ee_len && new_ext->ee_len &&
  		   !end_ext->ee_len && o_start == o_end) {
  
  		/*	 start_ext	new_ext
  		 * donor |--------------|---------------|
  		 * orig  |------------------------------|
  		 */
  		o_start->ee_len = start_ext->ee_len;
  		eblock = le32_to_cpu(start_ext->ee_block);
  		new_flag = 1;
  
  	} else if (!start_ext->ee_len && new_ext->ee_len &&
  		   end_ext->ee_len && o_start == o_end) {
  
  		/*	  new_ext	end_ext
  		 * donor |--------------|---------------|
  		 * orig  |------------------------------|
  		 */
  		o_end->ee_block = end_ext->ee_block;
  		o_end->ee_len = end_ext->ee_len;
  		ext4_ext_store_pblock(o_end, ext_pblock(end_ext));
  
  		/*
  		 * Set 0 to the extent block if new_ext was
  		 * the first block.
  		 */
  		if (new_ext->ee_block)
  			eblock = le32_to_cpu(new_ext->ee_block);
  
  		new_flag = 1;
  	} else {
  		ext4_debug("ext4 move extent: Unexpected insert case\n");
  		return -EIO;
  	}
  
  	if (new_flag) {
  		err = get_ext_path(orig_inode, eblock, &orig_path);
  		if (err)
  			goto out;
  
  		if (ext4_ext_insert_extent(handle, orig_inode,
  					orig_path, new_ext, 0))
  			goto out;
  	}
  
  	if (end_flag) {
  		err = get_ext_path(orig_inode,
  				le32_to_cpu(end_ext->ee_block) - 1, &orig_path);
  		if (err)
  			goto out;
  
  		if (ext4_ext_insert_extent(handle, orig_inode,
  					   orig_path, end_ext, 0))
  			goto out;
  	}
  out:
  	if (orig_path) {
  		ext4_ext_drop_refs(orig_path);
  		kfree(orig_path);
  	}
  
  	return err;
  
  }
  
  /**
   * mext_insert_inside_block - Insert new extent to the extent block
   *
   * @o_start:		first original extent to be moved
   * @o_end:		last original extent to be moved
   * @start_ext:		first new extent to be inserted
   * @new_ext:		middle of new extent to be inserted
   * @end_ext:		last new extent to be inserted
   * @eh:			extent header of target leaf block
   * @range_to_move:	used to decide how to insert extent
   *
   * Insert extents into the leaf block. The extent (@o_start) is overwritten
   * by inserted extents.
   */
  static void
  mext_insert_inside_block(struct ext4_extent *o_start,
  			      struct ext4_extent *o_end,
  			      struct ext4_extent *start_ext,
  			      struct ext4_extent *new_ext,
  			      struct ext4_extent *end_ext,
  			      struct ext4_extent_header *eh,
  			      int range_to_move)
  {
  	int i = 0;
  	unsigned long len;
  
  	/* Move the existing extents */
  	if (range_to_move && o_end < EXT_LAST_EXTENT(eh)) {
  		len = (unsigned long)(EXT_LAST_EXTENT(eh) + 1) -
  			(unsigned long)(o_end + 1);
  		memmove(o_end + 1 + range_to_move, o_end + 1, len);
  	}
  
  	/* Insert start entry */
  	if (start_ext->ee_len)
  		o_start[i++].ee_len = start_ext->ee_len;
  
  	/* Insert new entry */
  	if (new_ext->ee_len) {
  		o_start[i] = *new_ext;
  		ext4_ext_store_pblock(&o_start[i++], ext_pblock(new_ext));
  	}
  
  	/* Insert end entry */
  	if (end_ext->ee_len)
  		o_start[i] = *end_ext;
  
  	/* Increment the total entries counter on the extent block */
  	le16_add_cpu(&eh->eh_entries, range_to_move);
  }
  
  /**
   * mext_insert_extents - Insert new extent
   *
   * @handle:	journal handle
   * @orig_inode:	original inode
   * @orig_path:	path indicates first extent to be changed
   * @o_start:	first original extent to be changed
   * @o_end:	last original extent to be changed
   * @start_ext:	first new extent to be inserted
   * @new_ext:	middle of new extent to be inserted
   * @end_ext:	last new extent to be inserted
   *
   * Call the function to insert extents. If we cannot add more extents into
   * the leaf block, we call mext_insert_across_blocks() to create a
   * new leaf block. Otherwise call mext_insert_inside_block(). Return 0
   * on success, or a negative error value on failure.
   */
  static int
  mext_insert_extents(handle_t *handle, struct inode *orig_inode,
  			 struct ext4_ext_path *orig_path,
  			 struct ext4_extent *o_start,
  			 struct ext4_extent *o_end,
  			 struct ext4_extent *start_ext,
  			 struct ext4_extent *new_ext,
  			 struct ext4_extent *end_ext)
  {
  	struct  ext4_extent_header *eh;
  	unsigned long need_slots, slots_range;
  	int	range_to_move, depth, ret;
  
  	/*
  	 * The extents need to be inserted
  	 * start_extent + new_extent + end_extent.
  	 */
  	need_slots = (start_ext->ee_len ? 1 : 0) + (end_ext->ee_len ? 1 : 0) +
  		(new_ext->ee_len ? 1 : 0);
  
  	/* The number of slots between start and end */
  	slots_range = ((unsigned long)(o_end + 1) - (unsigned long)o_start + 1)
  		/ sizeof(struct ext4_extent);
  
  	/* Range to move the end of extent */
  	range_to_move = need_slots - slots_range;
  	depth = orig_path->p_depth;
  	orig_path += depth;
  	eh = orig_path->p_hdr;
  
  	if (depth) {
  		/* Register to journal */
  		ret = ext4_journal_get_write_access(handle, orig_path->p_bh);
  		if (ret)
  			return ret;
  	}
  
  	/* Expansion */
  	if (range_to_move > 0 &&
  		(range_to_move > le16_to_cpu(eh->eh_max)
  			- le16_to_cpu(eh->eh_entries))) {
  
  		ret = mext_insert_across_blocks(handle, orig_inode, o_start,
  					o_end, start_ext, new_ext, end_ext);
  		if (ret < 0)
  			return ret;
  	} else
  		mext_insert_inside_block(o_start, o_end, start_ext, new_ext,
  						end_ext, eh, range_to_move);
  
  	if (depth) {
  		ret = ext4_handle_dirty_metadata(handle, orig_inode,
  						 orig_path->p_bh);
  		if (ret)
  			return ret;
  	} else {
  		ret = ext4_mark_inode_dirty(handle, orig_inode);
  		if (ret < 0)
  			return ret;
  	}
  
  	return 0;
  }
  
  /**
   * mext_leaf_block - Move one leaf extent block into the inode.
   *
   * @handle:		journal handle
   * @orig_inode:		original inode
   * @orig_path:		path indicates first extent to be changed
   * @dext:		donor extent
   * @from:		start offset on the target file
   *
   * In order to insert extents into the leaf block, we must divide the extent
   * in the leaf block into three extents. The one is located to be inserted
   * extents, and the others are located around it.
   *
   * Therefore, this function creates structures to save extents of the leaf
   * block, and inserts extents by calling mext_insert_extents() with
   * created extents. Return 0 on success, or a negative error value on failure.
   */
  static int
  mext_leaf_block(handle_t *handle, struct inode *orig_inode,
  		     struct ext4_ext_path *orig_path, struct ext4_extent *dext,
  		     ext4_lblk_t *from)
  {
  	struct ext4_extent *oext, *o_start, *o_end, *prev_ext;
  	struct ext4_extent new_ext, start_ext, end_ext;
  	ext4_lblk_t new_ext_end;
  	int oext_alen, new_ext_alen, end_ext_alen;
  	int depth = ext_depth(orig_inode);
  	int ret;
  
  	o_start = o_end = oext = orig_path[depth].p_ext;
  	oext_alen = ext4_ext_get_actual_len(oext);
  	start_ext.ee_len = end_ext.ee_len = 0;
  
  	new_ext.ee_block = cpu_to_le32(*from);
  	ext4_ext_store_pblock(&new_ext, ext_pblock(dext));
  	new_ext.ee_len = dext->ee_len;
  	new_ext_alen = ext4_ext_get_actual_len(&new_ext);
  	new_ext_end = le32_to_cpu(new_ext.ee_block) + new_ext_alen - 1;
  
  	/*
  	 * Case: original extent is first
  	 * oext      |--------|
  	 * new_ext      |--|
  	 * start_ext |--|
  	 */
  	if (le32_to_cpu(oext->ee_block) < le32_to_cpu(new_ext.ee_block) &&
  		le32_to_cpu(new_ext.ee_block) <
  		le32_to_cpu(oext->ee_block) + oext_alen) {
  		start_ext.ee_len = cpu_to_le16(le32_to_cpu(new_ext.ee_block) -
  					       le32_to_cpu(oext->ee_block));
  		start_ext.ee_block = oext->ee_block;
  		copy_extent_status(oext, &start_ext);
  	} else if (oext > EXT_FIRST_EXTENT(orig_path[depth].p_hdr)) {
  		prev_ext = oext - 1;
  		/*
  		 * We can merge new_ext into previous extent,
  		 * if these are contiguous and same extent type.
  		 */
  		if (ext4_can_extents_be_merged(orig_inode, prev_ext,
  					       &new_ext)) {
  			o_start = prev_ext;
  			start_ext.ee_len = cpu_to_le16(
  				ext4_ext_get_actual_len(prev_ext) +
  				new_ext_alen);
  			start_ext.ee_block = oext->ee_block;
  			copy_extent_status(prev_ext, &start_ext);
  			new_ext.ee_len = 0;
  		}
  	}
  
  	/*
  	 * Case: new_ext_end must be less than oext
  	 * oext      |-----------|
  	 * new_ext       |-------|
  	 */
  	if (le32_to_cpu(oext->ee_block) + oext_alen - 1 < new_ext_end) {
  		ext4_error(orig_inode->i_sb,
  			"new_ext_end(%u) should be less than or equal to "
  			"oext->ee_block(%u) + oext_alen(%d) - 1",
  			new_ext_end, le32_to_cpu(oext->ee_block),
  			oext_alen);
  		ret = -EIO;
  		goto out;
  	}
  
  	/*
  	 * Case: new_ext is smaller than original extent
  	 * oext    |---------------|
  	 * new_ext |-----------|
  	 * end_ext             |---|
  	 */
  	if (le32_to_cpu(oext->ee_block) <= new_ext_end &&
  		new_ext_end < le32_to_cpu(oext->ee_block) + oext_alen - 1) {
  		end_ext.ee_len =
  			cpu_to_le16(le32_to_cpu(oext->ee_block) +
  			oext_alen - 1 - new_ext_end);
  		copy_extent_status(oext, &end_ext);
  		end_ext_alen = ext4_ext_get_actual_len(&end_ext);
  		ext4_ext_store_pblock(&end_ext,
  			(ext_pblock(o_end) + oext_alen - end_ext_alen));
  		end_ext.ee_block =
  			cpu_to_le32(le32_to_cpu(o_end->ee_block) +
  			oext_alen - end_ext_alen);
  	}
  
  	ret = mext_insert_extents(handle, orig_inode, orig_path, o_start,
  				o_end, &start_ext, &new_ext, &end_ext);
  out:
  	return ret;
  }
  
  /**
   * mext_calc_swap_extents - Calculate extents for extent swapping.
   *
   * @tmp_dext:		the extent that will belong to the original inode
   * @tmp_oext:		the extent that will belong to the donor inode
   * @orig_off:		block offset of original inode
   * @donor_off:		block offset of donor inode
   * @max_count:		the maximum length of extents
   *
   * Return 0 on success, or a negative error value on failure.
   */
  static int
  mext_calc_swap_extents(struct ext4_extent *tmp_dext,
  			      struct ext4_extent *tmp_oext,
  			      ext4_lblk_t orig_off, ext4_lblk_t donor_off,
  			      ext4_lblk_t max_count)
  {
  	ext4_lblk_t diff, orig_diff;
  	struct ext4_extent dext_old, oext_old;
  
  	BUG_ON(orig_off != donor_off);
  
  	/* original and donor extents have to cover the same block offset */
  	if (orig_off < le32_to_cpu(tmp_oext->ee_block) ||
  	    le32_to_cpu(tmp_oext->ee_block) +
  			ext4_ext_get_actual_len(tmp_oext) - 1 < orig_off)
  		return -ENODATA;
  
  	if (orig_off < le32_to_cpu(tmp_dext->ee_block) ||
  	    le32_to_cpu(tmp_dext->ee_block) +
  			ext4_ext_get_actual_len(tmp_dext) - 1 < orig_off)
  		return -ENODATA;
  
  	dext_old = *tmp_dext;
  	oext_old = *tmp_oext;
  
  	/* When tmp_dext is too large, pick up the target range. */
  	diff = donor_off - le32_to_cpu(tmp_dext->ee_block);
  
  	ext4_ext_store_pblock(tmp_dext, ext_pblock(tmp_dext) + diff);
  	tmp_dext->ee_block =
  			cpu_to_le32(le32_to_cpu(tmp_dext->ee_block) + diff);
  	tmp_dext->ee_len = cpu_to_le16(le16_to_cpu(tmp_dext->ee_len) - diff);
  
  	if (max_count < ext4_ext_get_actual_len(tmp_dext))
  		tmp_dext->ee_len = cpu_to_le16(max_count);
  
  	orig_diff = orig_off - le32_to_cpu(tmp_oext->ee_block);
  	ext4_ext_store_pblock(tmp_oext, ext_pblock(tmp_oext) + orig_diff);
  
  	/* Adjust extent length if donor extent is larger than orig */
  	if (ext4_ext_get_actual_len(tmp_dext) >
  	    ext4_ext_get_actual_len(tmp_oext) - orig_diff)
  		tmp_dext->ee_len = cpu_to_le16(le16_to_cpu(tmp_oext->ee_len) -
  						orig_diff);
  
  	tmp_oext->ee_len = cpu_to_le16(ext4_ext_get_actual_len(tmp_dext));
  
  	copy_extent_status(&oext_old, tmp_dext);
  	copy_extent_status(&dext_old, tmp_oext);
  
  	return 0;
  }
  
  /**
   * mext_replace_branches - Replace original extents with new extents
   *
   * @handle:		journal handle
   * @orig_inode:		original inode
   * @donor_inode:	donor inode
   * @from:		block offset of orig_inode
   * @count:		block count to be replaced
   * @err:		pointer to save return value
   *
   * Replace original inode extents and donor inode extents page by page.
   * We implement this replacement in the following three steps:
   * 1. Save the block information of original and donor inodes into
   *    dummy extents.
   * 2. Change the block information of original inode to point at the
   *    donor inode blocks.
   * 3. Change the block information of donor inode to point at the saved
   *    original inode blocks in the dummy extents.
   *
   * Return replaced block count.
   */
  static int
  mext_replace_branches(handle_t *handle, struct inode *orig_inode,
  			   struct inode *donor_inode, ext4_lblk_t from,
  			   ext4_lblk_t count, int *err)
  {
  	struct ext4_ext_path *orig_path = NULL;
  	struct ext4_ext_path *donor_path = NULL;
  	struct ext4_extent *oext, *dext;
  	struct ext4_extent tmp_dext, tmp_oext;
  	ext4_lblk_t orig_off = from, donor_off = from;
  	int depth;
  	int replaced_count = 0;
  	int dext_alen;
  
  	/* Protect extent trees against block allocations via delalloc */
  	double_down_write_data_sem(orig_inode, donor_inode);
  
  	/* Get the original extent for the block "orig_off" */
  	*err = get_ext_path(orig_inode, orig_off, &orig_path);
  	if (*err)
  		goto out;
  
  	/* Get the donor extent for the head */
  	*err = get_ext_path(donor_inode, donor_off, &donor_path);
  	if (*err)
  		goto out;
  	depth = ext_depth(orig_inode);
  	oext = orig_path[depth].p_ext;
  	tmp_oext = *oext;
  
  	depth = ext_depth(donor_inode);
  	dext = donor_path[depth].p_ext;
  	tmp_dext = *dext;
  
  	*err = mext_calc_swap_extents(&tmp_dext, &tmp_oext, orig_off,
  				      donor_off, count);
  	if (*err)
  		goto out;
  
  	/* Loop for the donor extents */
  	while (1) {
  		/* The extent for donor must be found. */
  		if (!dext) {
  			ext4_error(donor_inode->i_sb,
  				   "The extent for donor must be found");
  			*err = -EIO;
  			goto out;
  		} else if (donor_off != le32_to_cpu(tmp_dext.ee_block)) {
  			ext4_error(donor_inode->i_sb,
  				"Donor offset(%u) and the first block of donor "
  				"extent(%u) should be equal",
  				donor_off,
  				le32_to_cpu(tmp_dext.ee_block));
  			*err = -EIO;
  			goto out;
  		}
  
  		/* Set donor extent to orig extent */
  		*err = mext_leaf_block(handle, orig_inode,
  					   orig_path, &tmp_dext, &orig_off);
  		if (*err)
  			goto out;
  
  		/* Set orig extent to donor extent */
  		*err = mext_leaf_block(handle, donor_inode,
  					   donor_path, &tmp_oext, &donor_off);
  		if (*err)
  			goto out;
  
  		dext_alen = ext4_ext_get_actual_len(&tmp_dext);
  		replaced_count += dext_alen;
  		donor_off += dext_alen;
  		orig_off += dext_alen;
  
  		/* Already moved the expected blocks */
  		if (replaced_count >= count)
  			break;
  
  		if (orig_path)
  			ext4_ext_drop_refs(orig_path);
  		*err = get_ext_path(orig_inode, orig_off, &orig_path);
  		if (*err)
  			goto out;
  		depth = ext_depth(orig_inode);
  		oext = orig_path[depth].p_ext;
  		tmp_oext = *oext;
  
  		if (donor_path)
  			ext4_ext_drop_refs(donor_path);
  		*err = get_ext_path(donor_inode, donor_off, &donor_path);
  		if (*err)
  			goto out;
  		depth = ext_depth(donor_inode);
  		dext = donor_path[depth].p_ext;
  		tmp_dext = *dext;
  
  		*err = mext_calc_swap_extents(&tmp_dext, &tmp_oext, orig_off,
  					   donor_off, count - replaced_count);
  		if (*err)
  			goto out;
  	}
  
  out:
  	if (orig_path) {
  		ext4_ext_drop_refs(orig_path);
  		kfree(orig_path);
  	}
  	if (donor_path) {
  		ext4_ext_drop_refs(donor_path);
  		kfree(donor_path);
  	}
  
  	ext4_ext_invalidate_cache(orig_inode);
  	ext4_ext_invalidate_cache(donor_inode);
  
  	double_up_write_data_sem(orig_inode, donor_inode);
  
  	return replaced_count;
  }
  
  /**
   * 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
   * @data_offset_in_page:	block index where data swapping starts
   * @block_len_in_page:		the number of blocks to be swapped
   * @uninit:			orig extent is uninitialized 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 mext_replace_branches().
   * 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, int data_offset_in_page,
  		  int block_len_in_page, int uninit, int *err)
  {
  	struct inode *orig_inode = o_filp->f_dentry->d_inode;
  	struct address_space *mapping = orig_inode->i_mapping;
  	struct buffer_head *bh;
  	struct page *page = NULL;
  	const struct address_space_operations *a_ops = mapping->a_ops;
  	handle_t *handle;
  	ext4_lblk_t orig_blk_offset;
  	long long offs = orig_page_offset << PAGE_CACHE_SHIFT;
  	unsigned long blocksize = orig_inode->i_sb->s_blocksize;
  	unsigned int w_flags = 0;
  	unsigned int tmp_data_size, data_size, replaced_size;
  	void *fsdata;
  	int i, jblocks;
  	int err2 = 0;
  	int replaced_count = 0;
  	int blocks_per_page = PAGE_CACHE_SIZE >> orig_inode->i_blkbits;
  
  	/*
  	 * It needs twice the amount of ordinary journal buffers because
  	 * inode and donor_inode may change each different metadata blocks.
  	 */
  	jblocks = ext4_writepage_trans_blocks(orig_inode) * 2;
  	handle = ext4_journal_start(orig_inode, jblocks);
  	if (IS_ERR(handle)) {
  		*err = PTR_ERR(handle);
  		return 0;
  	}
  
  	if (segment_eq(get_fs(), KERNEL_DS))
  		w_flags |= AOP_FLAG_UNINTERRUPTIBLE;
  
  	orig_blk_offset = orig_page_offset * blocks_per_page +
  		data_offset_in_page;
  
  	/*
  	 * If orig extent is uninitialized one,
  	 * it's not necessary force the page into memory
  	 * and then force it to be written out again.
  	 * Just swap data blocks between orig and donor.
  	 */
  	if (uninit) {
  		replaced_count = mext_replace_branches(handle, orig_inode,
  						donor_inode, orig_blk_offset,
  						block_len_in_page, err);
  		goto out2;
  	}
  
  	offs = (long long)orig_blk_offset << orig_inode->i_blkbits;
  
  	/* 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 = a_ops->write_begin(o_filp, mapping, offs, data_size, w_flags,
  				 &page, &fsdata);
  	if (unlikely(*err < 0))
  		goto out;
  
  	if (!PageUptodate(page)) {
  		mapping->a_ops->readpage(o_filp, page);
  		lock_page(page);
  	}
  
  	/*
  	 * try_to_release_page() doesn't call releasepage in writeback mode.
  	 * We should care about the order of writing to the same file
  	 * by multiple move extent processes.
  	 * It needs to call wait_on_page_writeback() to wait for the
  	 * writeback of the page.
  	 */
  	if (PageWriteback(page))
  		wait_on_page_writeback(page);
  
  	/* Release old bh and drop refs */
  	try_to_release_page(page, 0);
  
  	replaced_count = mext_replace_branches(handle, orig_inode, donor_inode,
  					orig_blk_offset, block_len_in_page,
  					&err2);
  	if (err2) {
  		if (replaced_count) {
  			block_len_in_page = replaced_count;
  			replaced_size =
  				block_len_in_page << orig_inode->i_blkbits;
  		} else
  			goto out;
  	}
  
  	if (!page_has_buffers(page))
  		create_empty_buffers(page, 1 << orig_inode->i_blkbits, 0);
  
  	bh = page_buffers(page);
  	for (i = 0; i < data_offset_in_page; i++)
  		bh = bh->b_this_page;
  
  	for (i = 0; i < block_len_in_page; i++) {
  		*err = ext4_get_block(orig_inode,
  				(sector_t)(orig_blk_offset + i), bh, 0);
  		if (*err < 0)
  			goto out;
  
  		if (bh->b_this_page != NULL)
  			bh = bh->b_this_page;
  	}
  
  	*err = a_ops->write_end(o_filp, mapping, offs, data_size, replaced_size,
  			       page, fsdata);
  	page = NULL;
  
  out:
  	if (unlikely(page)) {
  		if (PageLocked(page))
  			unlock_page(page);
  		page_cache_release(page);
  		ext4_journal_stop(handle);
  	}
  out2:
  	ext4_journal_stop(handle);
  
  	if (err2)
  		*err = err2;
  
  	return replaced_count;
  }
  
  /**
   * 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)
  {
  	ext4_lblk_t orig_blocks, donor_blocks;
  	unsigned int blkbits = orig_inode->i_blkbits;
  	unsigned int 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]\n",
  			   orig_inode->i_ino, donor_inode->i_ino);
  		return -EINVAL;
  	}
  
  	/* 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]\n",
  			orig_inode->i_ino, donor_inode->i_ino);
  		return -EINVAL;
  	}
  
  	/* Files should be in the same ext4 FS */
  	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]\n",
  			orig_inode->i_ino, donor_inode->i_ino);
  		return -EINVAL;
  	}
  
  	/* Ext4 move extent supports only extent based file */
  	if (!(EXT4_I(orig_inode)->i_flags & EXT4_EXTENTS_FL)) {
  		ext4_debug("ext4 move extent: orig file is not extents "
  			"based file [ino:orig %lu]\n", orig_inode->i_ino);
  		return -EOPNOTSUPP;
  	} else if (!(EXT4_I(donor_inode)->i_flags & EXT4_EXTENTS_FL)) {
  		ext4_debug("ext4 move extent: donor file is not extents "
  			"based file [ino:donor %lu]\n", 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\n");
  		return -EINVAL;
  	}
  
  	/* Start offset should be same */
  	if (orig_start != donor_start) {
  		ext4_debug("ext4 move extent: orig and donor's start "
  			"offset are not same [ino:orig %lu, donor %lu]\n",
  			orig_inode->i_ino, donor_inode->i_ino);
  		return -EINVAL;
  	}
  
  	if ((orig_start > EXT_MAX_BLOCK) ||
  	    (donor_start > EXT_MAX_BLOCK) ||
  	    (*len > EXT_MAX_BLOCK) ||
  	    (orig_start + *len > EXT_MAX_BLOCK))  {
  		ext4_debug("ext4 move extent: Can't handle over [%u] blocks "
  			"[ino:orig %lu, donor %lu]\n", EXT_MAX_BLOCK,
  			orig_inode->i_ino, donor_inode->i_ino);
  		return -EINVAL;
  	}
  
  	if (orig_inode->i_size > donor_inode->i_size) {
  		donor_blocks = (donor_inode->i_size + blocksize - 1) >> blkbits;
  		/* TODO: eliminate this artificial restriction */
  		if (orig_start >= donor_blocks) {
  			ext4_debug("ext4 move extent: orig start offset "
  			"[%llu] should be less than donor file blocks "
  			"[%u] [ino:orig %lu, donor %lu]\n",
  			orig_start, donor_blocks,
  			orig_inode->i_ino, donor_inode->i_ino);
  			return -EINVAL;
  		}
  
  		/* TODO: eliminate this artificial restriction */
  		if (orig_start + *len > donor_blocks) {
  			ext4_debug("ext4 move extent: End offset [%llu] should "
  				"be less than donor file blocks [%u]."
  				"So adjust length from %llu to %llu "
  				"[ino:orig %lu, donor %lu]\n",
  				orig_start + *len, donor_blocks,
  				*len, donor_blocks - orig_start,
  				orig_inode->i_ino, donor_inode->i_ino);
  			*len = donor_blocks - orig_start;
  		}
  	} else {
  		orig_blocks = (orig_inode->i_size + blocksize - 1) >> blkbits;
  		if (orig_start >= orig_blocks) {
  			ext4_debug("ext4 move extent: start offset [%llu] "
  				"should be less than original file blocks "
  				"[%u] [ino:orig %lu, donor %lu]\n",
  				 orig_start, orig_blocks,
  				orig_inode->i_ino, donor_inode->i_ino);
  			return -EINVAL;
  		}
  
  		if (orig_start + *len > orig_blocks) {
  			ext4_debug("ext4 move extent: Adjust length "
  				"from %llu to %llu. Because it should be "
  				"less than original file blocks "
  				"[ino:orig %lu, donor %lu]\n",
  				*len, orig_blocks - orig_start,
  				orig_inode->i_ino, donor_inode->i_ino);
  			*len = orig_blocks - orig_start;
  		}
  	}
  
  	if (!*len) {
  		ext4_debug("ext4 move extent: len should not be 0 "
  			"[ino:orig %lu, donor %lu]\n", orig_inode->i_ino,
  			donor_inode->i_ino);
  		return -EINVAL;
  	}
  
  	return 0;
  }
  
  /**
   * mext_inode_double_lock - Lock i_mutex on both @inode1 and @inode2
   *
   * @inode1:	the inode structure
   * @inode2:	the inode structure
   *
   * Lock two inodes' i_mutex by i_ino order.
   * If inode1 or inode2 is NULL, return -EIO. Otherwise, return 0.
   */
  static int
  mext_inode_double_lock(struct inode *inode1, struct inode *inode2)
  {
  	int ret = 0;
  
  	BUG_ON(inode1 == NULL && inode2 == NULL);
  
  	ret = mext_check_null_inode(inode1, inode2, __func__);
  	if (ret < 0)
  		goto out;
  
  	if (inode1 == inode2) {
  		mutex_lock(&inode1->i_mutex);
  		goto out;
  	}
  
  	if (inode1->i_ino < inode2->i_ino) {
  		mutex_lock_nested(&inode1->i_mutex, I_MUTEX_PARENT);
  		mutex_lock_nested(&inode2->i_mutex, I_MUTEX_CHILD);
  	} else {
  		mutex_lock_nested(&inode2->i_mutex, I_MUTEX_PARENT);
  		mutex_lock_nested(&inode1->i_mutex, I_MUTEX_CHILD);
  	}
  
  out:
  	return ret;
  }
  
  /**
   * mext_inode_double_unlock - Release i_mutex on both @inode1 and @inode2
   *
   * @inode1:     the inode that is released first
   * @inode2:     the inode that is released second
   *
   * If inode1 or inode2 is NULL, return -EIO. Otherwise, return 0.
   */
  
  static int
  mext_inode_double_unlock(struct inode *inode1, struct inode *inode2)
  {
  	int ret = 0;
  
  	BUG_ON(inode1 == NULL && inode2 == NULL);
  
  	ret = mext_check_null_inode(inode1, inode2, __func__);
  	if (ret < 0)
  		goto out;
  
  	if (inode1)
  		mutex_unlock(&inode1->i_mutex);
  
  	if (inode2 && inode2 != inode1)
  		mutex_unlock(&inode2->i_mutex);
  
  out:
  	return ret;
  }
  
  /**
   * 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_start:		start offset in block for orig
   * @donor_start:	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.
   *
   * Note: ext4_move_extents() proceeds the following order.
   * 1:ext4_move_extents() calculates the last block number of moving extent
   *   function by the start block number (orig_start) and the number of blocks
   *   to be moved (len) specified as arguments.
   *   If the {orig, donor}_start points a hole, the extent's start offset
   *   pointed by ext_cur (current extent), holecheck_path, orig_path are set
   *   after hole behind.
   * 2:Continue step 3 to step 5, until the holecheck_path points to last_extent
   *   or the ext_cur exceeds the block_end which is last logical block number.
   * 3:To get the length of continues area, call mext_next_extent()
   *   specified with the ext_cur (initial value is holecheck_path) re-cursive,
   *   until find un-continuous extent, the start logical block number exceeds
   *   the block_end or the extent points to the last extent.
   * 4:Exchange the original inode data with donor inode data
   *   from orig_page_offset to seq_end_page.
   *   The start indexes of data are specified as arguments.
   *   That of the original inode is orig_page_offset,
   *   and the donor inode is also orig_page_offset
   *   (To easily handle blocksize != pagesize case, the offset for the
   *   donor inode is block unit).
   * 5:Update holecheck_path and orig_path to points a next proceeding extent,
   *   then returns to step 2.
   * 6:Release holecheck_path, orig_path and set the len to moved_len
   *   which shows the number of moved blocks.
   *   The moved_len is useful for the command to calculate the file offset
   *   for starting next move extent ioctl.
   * 7:Return 0 on success, or a negative error value on failure.
   */
  int
  ext4_move_extents(struct file *o_filp, struct file *d_filp,
  		 __u64 orig_start, __u64 donor_start, __u64 len,
  		 __u64 *moved_len)
  {
  	struct inode *orig_inode = o_filp->f_dentry->d_inode;
  	struct inode *donor_inode = d_filp->f_dentry->d_inode;
  	struct ext4_ext_path *orig_path = NULL, *holecheck_path = NULL;
  	struct ext4_extent *ext_prev, *ext_cur, *ext_dummy;
  	ext4_lblk_t block_start = orig_start;
  	ext4_lblk_t block_end, seq_start, add_blocks, file_end, seq_blocks = 0;
  	ext4_lblk_t rest_blocks;
  	pgoff_t orig_page_offset = 0, seq_end_page;
  	int ret1, ret2, depth, last_extent = 0;
  	int blocks_per_page = PAGE_CACHE_SIZE >> orig_inode->i_blkbits;
  	int data_offset_in_page;
  	int block_len_in_page;
  	int uninit;
  
  	/* orig and donor should be different file */
  	if (orig_inode->i_ino == donor_inode->i_ino) {
  		ext4_debug("ext4 move extent: The argument files should not "
  			"be same file [ino:orig %lu, donor %lu]\n",
  			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]\n",
  			orig_inode->i_ino, donor_inode->i_ino);
  		return -EINVAL;
  	}
  
  	/* Protect orig and donor inodes against a truncate */
  	ret1 = mext_inode_double_lock(orig_inode, donor_inode);
  	if (ret1 < 0)
  		return ret1;
  
  	/* Protect extent tree against block allocations via delalloc */
  	double_down_write_data_sem(orig_inode, donor_inode);
  	/* Check the filesystem environment whether move_extent can be done */
  	ret1 = mext_check_arguments(orig_inode, donor_inode, orig_start,
  				    donor_start, &len);
  	if (ret1)
  		goto out;
  
  	file_end = (i_size_read(orig_inode) - 1) >> orig_inode->i_blkbits;
  	block_end = block_start + len - 1;
  	if (file_end < block_end)
  		len -= block_end - file_end;
  
  	ret1 = get_ext_path(orig_inode, block_start, &orig_path);
  	if (ret1)
  		goto out;
  
  	/* Get path structure to check the hole */
  	ret1 = get_ext_path(orig_inode, block_start, &holecheck_path);
  	if (ret1)
  		goto out;
  
  	depth = ext_depth(orig_inode);
  	ext_cur = holecheck_path[depth].p_ext;
  
  	/*
  	 * Get proper starting location of block replacement if block_start was
  	 * within the hole.
  	 */
  	if (le32_to_cpu(ext_cur->ee_block) +
  		ext4_ext_get_actual_len(ext_cur) - 1 < block_start) {
  		/*
  		 * The hole exists between extents or the tail of
  		 * original file.
  		 */
  		last_extent = mext_next_extent(orig_inode,
  					holecheck_path, &ext_cur);
  		if (last_extent < 0) {
  			ret1 = last_extent;
  			goto out;
  		}
  		last_extent = mext_next_extent(orig_inode, orig_path,
  							&ext_dummy);
  		if (last_extent < 0) {
  			ret1 = last_extent;
  			goto out;
  		}
  		seq_start = le32_to_cpu(ext_cur->ee_block);
  	} else if (le32_to_cpu(ext_cur->ee_block) > block_start)
  		/* The hole exists at the beginning of original file. */
  		seq_start = le32_to_cpu(ext_cur->ee_block);
  	else
  		seq_start = block_start;
  
  	/* No blocks within the specified range. */
  	if (le32_to_cpu(ext_cur->ee_block) > block_end) {
  		ext4_debug("ext4 move extent: The specified range of file "
  							"may be the hole\n");
  		ret1 = -EINVAL;
  		goto out;
  	}
  
  	/* Adjust start blocks */
  	add_blocks = min(le32_to_cpu(ext_cur->ee_block) +
  			 ext4_ext_get_actual_len(ext_cur), block_end + 1) -
  		     max(le32_to_cpu(ext_cur->ee_block), block_start);
  
  	while (!last_extent && le32_to_cpu(ext_cur->ee_block) <= block_end) {
  		seq_blocks += add_blocks;
  
  		/* Adjust tail blocks */
  		if (seq_start + seq_blocks - 1 > block_end)
  			seq_blocks = block_end - seq_start + 1;
  
  		ext_prev = ext_cur;
  		last_extent = mext_next_extent(orig_inode, holecheck_path,
  						&ext_cur);
  		if (last_extent < 0) {
  			ret1 = last_extent;
  			break;
  		}
  		add_blocks = ext4_ext_get_actual_len(ext_cur);
  
  		/*
  		 * Extend the length of contiguous block (seq_blocks)
  		 * if extents are contiguous.
  		 */
  		if (ext4_can_extents_be_merged(orig_inode,
  					       ext_prev, ext_cur) &&
  		    block_end >= le32_to_cpu(ext_cur->ee_block) &&
  		    !last_extent)
  			continue;
  
  		/* Is original extent is uninitialized */
  		uninit = ext4_ext_is_uninitialized(ext_prev);
  
  		data_offset_in_page = seq_start % blocks_per_page;
  
  		/*
  		 * Calculate data blocks count that should be swapped
  		 * at the first page.
  		 */
  		if (data_offset_in_page + seq_blocks > blocks_per_page) {
  			/* Swapped blocks are across pages */
  			block_len_in_page =
  					blocks_per_page - data_offset_in_page;
  		} else {
  			/* Swapped blocks are in a page */
  			block_len_in_page = seq_blocks;
  		}
  
  		orig_page_offset = seq_start >>
  				(PAGE_CACHE_SHIFT - orig_inode->i_blkbits);
  		seq_end_page = (seq_start + seq_blocks - 1) >>
  				(PAGE_CACHE_SHIFT - orig_inode->i_blkbits);
  		seq_start = le32_to_cpu(ext_cur->ee_block);
  		rest_blocks = seq_blocks;
  
  		/*
  		 * 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
  		 */
  		double_up_write_data_sem(orig_inode, donor_inode);
  
  		while (orig_page_offset <= seq_end_page) {
  
  			/* Swap original branches with new branches */
  			block_len_in_page = move_extent_per_page(
  						o_filp, donor_inode,
  						orig_page_offset,
  						data_offset_in_page,
  						block_len_in_page, uninit,
  						&ret1);
  
  			/* Count how many blocks we have exchanged */
  			*moved_len += block_len_in_page;
  			if (ret1 < 0)
  				break;
  			if (*moved_len > len) {
  				ext4_error(orig_inode->i_sb,
  					"We replaced blocks too much! "
  					"sum of replaced: %llu requested: %llu",
  					*moved_len, len);
  				ret1 = -EIO;
  				break;
  			}
  
  			orig_page_offset++;
  			data_offset_in_page = 0;
  			rest_blocks -= block_len_in_page;
  			if (rest_blocks > blocks_per_page)
  				block_len_in_page = blocks_per_page;
  			else
  				block_len_in_page = rest_blocks;
  		}
  
  		double_down_write_data_sem(orig_inode, donor_inode);
  		if (ret1 < 0)
  			break;
  
  		/* Decrease buffer counter */
  		if (holecheck_path)
  			ext4_ext_drop_refs(holecheck_path);
  		ret1 = get_ext_path(orig_inode, seq_start, &holecheck_path);
  		if (ret1)
  			break;
  		depth = holecheck_path->p_depth;
  
  		/* Decrease buffer counter */
  		if (orig_path)
  			ext4_ext_drop_refs(orig_path);
  		ret1 = get_ext_path(orig_inode, seq_start, &orig_path);
  		if (ret1)
  			break;
  
  		ext_cur = holecheck_path[depth].p_ext;
  		add_blocks = ext4_ext_get_actual_len(ext_cur);
  		seq_blocks = 0;
  
  	}
  out:
  	if (*moved_len) {
  		ext4_discard_preallocations(orig_inode);
  		ext4_discard_preallocations(donor_inode);
  	}
  
  	if (orig_path) {
  		ext4_ext_drop_refs(orig_path);
  		kfree(orig_path);
  	}
  	if (holecheck_path) {
  		ext4_ext_drop_refs(holecheck_path);
  		kfree(holecheck_path);
  	}
  	double_up_write_data_sem(orig_inode, donor_inode);
  	ret2 = mext_inode_double_unlock(orig_inode, donor_inode);
  
  	if (ret1)
  		return ret1;
  	else if (ret2)
  		return ret2;
  
  	return 0;
  }
  