overlay: fix _scratch_remount with xfs_info 5.0.0

xfs_info version 5.0.0 started using findmnt to find the filesystem to query. This change resulted in a regression of _scratch_remount when testing overlay over xfs. For example, test overlay/035, started to report:
[not run] overlay/035 -- upper fs needs to support d_type

Internally, '_overlay_scratch_mount -o remount' calls '_supports_filetype $OVL_BASE_SCRATCH_MNT -o remount' and with the following example mounts:

/dev/vdf /vdf xfs rw,relatime,attr2,inode64,noquota 0 0
/vdf /vdf/ovl-mnt overlay rw,lowerdir=/vdf/lower,upperdir=/vdf/upper...

'_supports_filetype /vdf' returns false and reports:
"/vdf/ovl-mnt: Not on a mounted XFS filesystem".

Regardless of the change in xfs_info, which I proposed a fix for, there is no reason to test d_type support on remount. Therefore, fix the regression by skipping unneeded overlayfs mount logic on remount.

---

Eryu,

I think this fix is desired regardless of the proposed xfs_info fix [1].

Thanks,
Amir.

[1] https://marc.info/?l=linux-xfs&m=156077152313826&w=2

 common/overlay | 5 +++++
 1 file changed, 5 insertions(+)

index 00946a94..65c639e9 100644
@@ -105,6 +105,11 @@ _overlay_base_scratch_mount()
 
 _overlay_scratch_mount()
 {
+	if echo "$*" | grep -q remount; then
+		$MOUNT_PROG $SCRATCH_MNT $*
+		return
+	fi
+
 	_overlay_base_scratch_mount && \
 		_overlay_mount $OVL_BASE_SCRATCH_MNT $SCRATCH_MNT $*
 }

2.17.1