ext4: explicit mount options parsing cleanup

Currently MOPT_EXPLICIT treated as EXPLICIT_DELALLOC which may be changed
in future. Let's fix it now.

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 639613f..db4be39 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1516,8 +1516,12 @@
 		return -1;
 	if (args->from && (m->flags & MOPT_GTE0) && (arg < 0))
 		return -1;
-	if (m->flags & MOPT_EXPLICIT)
-		set_opt2(sb, EXPLICIT_DELALLOC);
+	if (m->flags & MOPT_EXPLICIT) {
+		if (m->mount_opt & EXT4_MOUNT_DELALLOC) {
+			set_opt2(sb, EXPLICIT_DELALLOC);
+		} else
+			return -1;
+	}
 	if (m->flags & MOPT_CLEAR_ERR)
 		clear_opt(sb, ERRORS_MASK);
 	if (token == Opt_noquota && sb_any_quota_loaded(sb)) {