overlay: avoid to use NULL OVL_BASE_FSTYP for mounting

Generally, FSTYP is used to specify OVL_BASE_FSTYP. When we specify FSTYP
through an environment variable, it is not converted to OVL_BASE_FSTYP.
In addition, sometimes we do not even specify the file type. For example,
we only use `./check -n -overlay -g auto` to list overlay-related cases.
If OVL_BASE_FSTYP is NULL, mounting fails and the test fails.

To solve this problem, try to assign a value to OVL_BASE_FSTYP when
specifying -overlay. In addition, in the _overlay_base_mount function,
the basic file system type of the overlay is specified only when
OVL_BASE_FSTYP is not NULL.

Reported-by: Murphy Zhou <jencce.kernel@gmail.com>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/check b/check
index 1ff0f44a..22062935 100755
--- a/check
+++ b/check
@@ -283,6 +283,7 @@ while [ $# -gt 0 ]; do
 		FSTYP="${1:1}"
 		;;
 	-overlay)
+		[ "$FSTYP" == overlay ] || export OVL_BASE_FSTYP="$FSTYP"
 		FSTYP=overlay
 		export OVERLAY=true
 		;;