ext4: exchange the blocks between two inodes

index f5d75c2..8ae5a48 100644
@@ -134,6 +134,188 @@ int ext4_defrag_ioctl(struct inode *inode, struct file *filp, unsigned int cmd,
 }
 
 /**
+ * ext4_defrag_merge_across_blocks - Merge extents across leaf block
+ *
+ * @handle:		journal handle
+ * @org_inode:		original inode
+ * @o_start:		first original extent to be defraged
+ * @o_end:		last original extent to be defraged
+ * @start_ext:		first new extent to be merged
+ * @new_ext:		middle of new extent to be merged
+ * @end_ext:		last new extent to be merged
+ *
+ * This function returns 0 if succeed, otherwise returns error value.
+ */
+static int
+ext4_defrag_merge_across_blocks(handle_t *handle, struct inode *org_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 *org_path = NULL;
+	ext4_lblk_t eblock = 0;
+	int new_flag = 0;
+	int end_flag = 0;
+	int err;
+
+	if (le16_to_cpu(start_ext->ee_len) &&
+		le16_to_cpu(new_ext->ee_len) &&
+		le16_to_cpu(end_ext->ee_len)) {
+
+		if (o_start == o_end) {
+
+			/*       start_ext   new_ext    end_ext
+			 * dest |---------|-----------|--------|
+			 * org  |------------------------------|
+			 */
+
+			end_flag = 1;
+		} else {
+
+			/*       start_ext   new_ext   end_ext
+			 * dest |---------|----------|---------|
+			 * org  |---------------|--------------|
+			 */
+
+			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;
+		new_flag = 1;
+
+	} else if (le16_to_cpu(start_ext->ee_len) &&
+			le16_to_cpu(new_ext->ee_len) &&
+			!le16_to_cpu(end_ext->ee_len) &&
+			o_start == o_end) {
+
+		/*	 start_ext	new_ext
+		 * dest |--------------|---------------|
+		 * org  |------------------------------|
+		 */
+
+		o_start->ee_len = start_ext->ee_len;
+		new_flag = 1;
+
+	} else if (!le16_to_cpu(start_ext->ee_len) &&
+			le16_to_cpu(new_ext->ee_len) &&
+			le16_to_cpu(end_ext->ee_len) &&
+			o_start == o_end) {
+
+		/*	  new_ext	end_ext
+		 * dest |--------------|---------------|
+		 * org  |------------------------------|
+		 */
+
+		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 = 0;
+		else
+			eblock = le32_to_cpu(new_ext->ee_block);
+
+		new_flag = 1;
+	} else {
+		printk(KERN_ERR "ext4 defrag: Unexpected merge case\n");
+		return -EIO;
+	}
+
+	if (new_flag) {
+		org_path = ext4_ext_find_extent(org_inode, eblock, NULL);
+		if (IS_ERR(org_path)) {
+			err = PTR_ERR(org_path);
+			org_path = NULL;
+			goto out;
+		}
+		err = ext4_ext_insert_extent(handle, org_inode,
+					org_path, new_ext);
+		if (err)
+			goto out;
+	}
+
+	if (end_flag) {
+		org_path = ext4_ext_find_extent(org_inode,
+				le32_to_cpu(end_ext->ee_block) - 1, org_path);
+		if (IS_ERR(org_path)) {
+			err = PTR_ERR(org_path);
+			org_path = NULL;
+			goto out;
+		}
+		err = ext4_ext_insert_extent(handle, org_inode,
+					org_path, end_ext);
+		if (err)
+			goto out;
+	}
+out:
+	if (org_path) {
+		ext4_ext_drop_refs(org_path);
+		kfree(org_path);
+	}
+
+	return err;
+
+}
+
+/**
+ * ext4_defrag_merge_inside_block - Merge new extent to the extent block
+ *
+ * @o_start:		first original extent to be merged
+ * @o_end:		last original extent to be merged
+ * @start_ext:		first new extent to be merged
+ * @new_ext:		middle of new extent to be merged
+ * @end_ext:		last new extent to be merged
+ * @eh:			extent header of target leaf block
+ * @replaced:		the number of blocks which will be replaced with new_ext
+ * @range_to_move:	used to decide how to merge
+ *
+ * This function always returns 0.
+ */
+static int
+ext4_defrag_merge_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, ext4_fsblk_t replaced,
+		int range_to_move)
+{
+	int i = 0;
+	unsigned 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 (le16_to_cpu(start_ext->ee_len))
+		o_start[i++].ee_len = start_ext->ee_len;
+
+	/* Insert new entry */
+	if (le16_to_cpu(new_ext->ee_len)) {
+		o_start[i].ee_block = new_ext->ee_block;
+		o_start[i].ee_len = cpu_to_le16(replaced);
+		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);
+
+	return 0;
+}
+
+/**
  * ext4_defrag_merge_extents - Merge new extent
  *
  * @handle:	journal handle

@@ -155,7 +337,65 @@ ext4_defrag_merge_extents(handle_t *handle, struct inode *org_inode,
 		struct ext4_extent *start_ext, struct ext4_extent *new_ext,
 		struct ext4_extent *end_ext, ext4_fsblk_t replaced)
 {
+	struct  ext4_extent_header *eh;
+	unsigned need_slots, slots_range;
+	int	range_to_move, depth, ret;
+
+	/*
+	 * The extents need to be inserted
+	 * start_extent + new_extent + end_extent.
+	 */
+	need_slots = (le16_to_cpu(start_ext->ee_len) ? 1 : 0) +
+			(le16_to_cpu(end_ext->ee_len) ? 1 : 0) +
+			(le16_to_cpu(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 = org_path->p_depth;
+	org_path += depth;
+	eh = org_path->p_hdr;
+
+	if (depth) {
+		/* Register to journal */
+		ret = ext4_journal_get_write_access(handle, org_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 = ext4_defrag_merge_across_blocks(handle, org_inode,
+					o_start, o_end, start_ext, new_ext,
+					end_ext);
+		if (ret < 0)
+			return ret;
+	} else {
+		ret = ext4_defrag_merge_inside_block(o_start, o_end,
+					start_ext, new_ext, end_ext, eh,
+					replaced, range_to_move);
+		if (ret < 0)
+			return ret;
+	}
+
+	if (depth) {
+		ret = ext4_journal_dirty_metadata(handle, org_path->p_bh);
+		if (ret)
+			return ret;
+	} else {
+		ret = ext4_mark_inode_dirty(handle, org_inode);
+		if (ret < 0)
+			return ret;
+	}
+
 	return 0;
+
 }
 
 /**