ext4: initialize moved_len before calling ext4_move_extents()

The move_extent.moved_len is used to pass back the number of exchanged
blocks count to user space.  Currently the caller must clear this
field; but we spend more code space checking for this requirement than
simply zeroing the field ourselves, so let's just make life easier for
everyone all around.

Signed-off-by: Kazuya Mio <k-mio@sx.jp.nec.com>
Signed-off-by: Akira Fujita <a-fujita@rs.jp.nec.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/ioctl.c

@@ -239,6 +239,7 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 			}
 		}
 
+		me.moved_len = 0;
 		err = ext4_move_extents(filp, donor_filp, me.orig_start,
 					me.donor_start, me.len, &me.moved_len);
 		fput(donor_filp);

fs/ext4/move_extent.c

@@ -947,16 +947,15 @@ move_extent_per_page(struct file *o_filp, struct 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
- * @moved_len:		moved block length
  *
  * 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 moved_len)
+		     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;
@@ -1010,13 +1009,6 @@ mext_check_arguments(struct inode *orig_inode,
 		return -EINVAL;
 	}
 
-	if (moved_len) {
-		ext4_debug("ext4 move extent: moved_len should be 0 "
-			"[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) ||
@@ -1226,7 +1218,7 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp,
 	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, *moved_len);
+				    donor_start, &len);
 	if (ret1)
 		goto out;