xfs: support returning partial reflink results

Back when the XFS reflink code only supported clone_file_range, we were
only able to return zero or negative error codes to userspace.  However,
now that copy_file_range (which returns bytes copied) can use XFS'
clone_file_range, we have the opportunity to return partial results.
For example, if userspace sends a 1GB clone request and we run out of
space halfway through, we at least can tell userspace that we completed
512M of that request like a regular write.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_file.c

@@ -928,14 +928,11 @@ xfs_file_remap_range(
 	loff_t		len,
 	unsigned int	remap_flags)
 {
-	int		ret;
-
 	if (remap_flags & ~(REMAP_FILE_DEDUP | REMAP_FILE_ADVISORY))
 		return -EINVAL;
 
-	ret = xfs_reflink_remap_range(file_in, pos_in, file_out, pos_out,
+	return xfs_reflink_remap_range(file_in, pos_in, file_out, pos_out,
 			len, remap_flags);
-	return ret < 0 ? ret : len;
 }
 
 STATIC int

fs/xfs/xfs_reflink.c

@@ -1122,13 +1122,15 @@ xfs_reflink_remap_blocks(
 	loff_t			pos_in,
 	struct xfs_inode	*dest,
 	loff_t			pos_out,
-	loff_t			remap_len)
+	loff_t			remap_len,
+	loff_t			*remapped)
 {
 	struct xfs_bmbt_irec	imap;
 	xfs_fileoff_t		srcoff;
 	xfs_fileoff_t		destoff;
 	xfs_filblks_t		len;
 	xfs_filblks_t		range_len;
+	xfs_filblks_t		remapped_len = 0;
 	xfs_off_t		new_isize = pos_out + remap_len;
 	int			nimaps;
 	int			error = 0;
@@ -1175,10 +1177,13 @@ xfs_reflink_remap_blocks(
 		srcoff += range_len;
 		destoff += range_len;
 		len -= range_len;
+		remapped_len += range_len;
 	}
 
 	if (error)
 		trace_xfs_reflink_remap_blocks_error(dest, error, _RET_IP_);
+	*remapped = min_t(loff_t, remap_len,
+			  XFS_FSB_TO_B(src->i_mount, remapped_len));
 	return error;
 }
 
@@ -1387,7 +1392,7 @@ xfs_reflink_remap_prep(
 /*
  * Link a range of blocks from one file to another.
  */
-int
+loff_t
 xfs_reflink_remap_range(
 	struct file		*file_in,
 	loff_t			pos_in,
@@ -1401,8 +1406,9 @@ xfs_reflink_remap_range(
 	struct inode		*inode_out = file_inode(file_out);
 	struct xfs_inode	*dest = XFS_I(inode_out);
 	struct xfs_mount	*mp = src->i_mount;
+	loff_t			remapped = 0;
 	xfs_extlen_t		cowextsize;
-	ssize_t			ret;
+	int			ret;
 
 	if (!xfs_sb_version_hasreflink(&mp->m_sb))
 		return -EOPNOTSUPP;
@@ -1418,7 +1424,8 @@ xfs_reflink_remap_range(
 
 	trace_xfs_reflink_remap_range(src, pos_in, len, dest, pos_out);
 
-	ret = xfs_reflink_remap_blocks(src, pos_in, dest, pos_out, len);
+	ret = xfs_reflink_remap_blocks(src, pos_in, dest, pos_out, len,
+			&remapped);
 	if (ret)
 		goto out_unlock;
 
@@ -1441,7 +1448,7 @@ xfs_reflink_remap_range(
 	xfs_reflink_remap_unlock(file_in, file_out);
 	if (ret)
 		trace_xfs_reflink_remap_range_error(dest, ret, _RET_IP_);
-	return ret;
+	return remapped > 0 ? remapped : ret;
 }
 
 /*

fs/xfs/xfs_reflink.h

@@ -27,7 +27,7 @@ extern int xfs_reflink_cancel_cow_range(struct xfs_inode *ip, xfs_off_t offset,
 extern int xfs_reflink_end_cow(struct xfs_inode *ip, xfs_off_t offset,
 		xfs_off_t count);
 extern int xfs_reflink_recover_cow(struct xfs_mount *mp);
-extern int xfs_reflink_remap_range(struct file *file_in, loff_t pos_in,
+extern loff_t xfs_reflink_remap_range(struct file *file_in, loff_t pos_in,
 		struct file *file_out, loff_t pos_out, loff_t len,
 		unsigned int remap_flags);
 extern int xfs_reflink_inode_has_shared_extents(struct xfs_trans *tp,