btrfs: unify the ro checking for mount options

We're going to be adding more options that require RDONLY, so add a
helper to do the check and error out if we don't have RDONLY set.
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: NQu Wenruo <wqu@suse.com>
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/super.c

@@ -458,6 +458,17 @@ static const match_table_t rescue_tokens = {
 	{Opt_err, NULL},
 };
 
+static bool check_ro_option(struct btrfs_fs_info *fs_info, unsigned long opt,
+			    const char *opt_name)
+{
+	if (fs_info->mount_opt & opt) {
+		btrfs_err(fs_info, "%s must be used with ro mount option",
+			  opt_name);
+		return true;
+	}
+	return false;
+}
+
 static int parse_rescue_options(struct btrfs_fs_info *info, const char *options)
 {
 	char *opts;
@@ -968,14 +979,12 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char *options,
 		}
 	}
 check:
-	/*
-	 * Extra check for current option against current flag
-	 */
-	if (btrfs_test_opt(info, NOLOGREPLAY) && !(new_flags & SB_RDONLY)) {
-		btrfs_err(info,
-			  "nologreplay must be used with ro mount option");
+	/* We're read-only, don't have to check. */
+	if (new_flags & SB_RDONLY)
+		goto out;
+
+	if (check_ro_option(info, BTRFS_MOUNT_NOLOGREPLAY, "nologreplay"))
 		ret = -EINVAL;
-	}
 out:
 	if (btrfs_fs_compat_ro(info, FREE_SPACE_TREE) &&
 	    !btrfs_test_opt(info, FREE_SPACE_TREE) &&