vfs: vfs_dedupe_file_range() doesn't return EOPNOTSUPP

It returns EINVAL when the operation is not supported by the
filesystem. Fix it to return EOPNOTSUPP to be consistent with
the man page and clone_file_range().

Clean up the inconsistent error return handling while I'm there.
(I know, lipstick on a pig, but every little bit helps...)
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/read_write.c

@@ -2094,17 +2094,18 @@ int vfs_dedupe_file_range(struct file *file, struct file_dedupe_range *same)
 	off = same->src_offset;
 	len = same->src_length;
 
-	ret = -EISDIR;
 	if (S_ISDIR(src->i_mode))
-		goto out;
+		return -EISDIR;
 
-	ret = -EINVAL;
 	if (!S_ISREG(src->i_mode))
-		goto out;
+		return -EINVAL;
+
+	if (!file->f_op->remap_file_range)
+		return -EOPNOTSUPP;
 
 	ret = remap_verify_area(file, off, len, false);
 	if (ret < 0)
-		goto out;
+		return ret;
 	ret = 0;
 
 	if (off + len > i_size_read(src))
@@ -2147,10 +2148,8 @@ int vfs_dedupe_file_range(struct file *file, struct file_dedupe_range *same)
 		fdput(dst_fd);
 next_loop:
 		if (fatal_signal_pending(current))
-			goto out;
+			break;
 	}
-
-out:
 	return ret;
 }
 EXPORT_SYMBOL(vfs_dedupe_file_range);