+# probe filesystem metadata of optical drives which have a media inserted
+KERNEL=="sr*", ENV{ID_CDROM_MEDIA_TRACK_COUNT_DATA}=="?*", ENV{ID_CDROM_MEDIA_SESSION_LAST_OFFSET}=="?*", IMPORT{program}="/sbin/blkid -o udev -p -u noraid -O $env{ID_CDROM_MEDIA_SESSION_LAST_OFFSET} $tempnode"
+# single-session CDs do not have ID_CDROM_MEDIA_SESSION_LAST_OFFSET
+KERNEL=="sr*", ENV{ID_CDROM_MEDIA_TRACK_COUNT_DATA}=="?*", ENV{ID_CDROM_MEDIA_SESSION_LAST_OFFSET}=="", IMPORT{program}="/sbin/blkid -o udev -p -u noraid $tempnode"
+
+# probe filesystem metadata of disks
+KERNEL!="sr*", IMPORT{program}="/sbin/blkid -o udev -p $tempnode"
+
+# watch for future changes
+KERNEL!="sr*", OPTIONS+="watch"