00-rootdev.sh: always use the blkid detected fstype unless rootfstype= is passed

defaults/initrd.d/00-rootdev.sh

@@ -69,11 +69,14 @@ _rootdev_mount() {
     local mount_opts=ro
     local mount_fstype="${ROOTFSTYPE}"
     local fstype=$(get_device_fstype "${REAL_ROOT}")
+
     if is_zfs_fstype "${fstype}"; then
-        mount_fstype=zfs
+        [ -z "${mount_fstype}" ] && mount_fstype=zfs
         mount_opts=$(zfs_get_real_root_mount_flags)
     fi
 
+    [ -z "${mount_fstype}" ] && mount_fstype="${fstype}"
+
     good_msg "Detected fstype: ${fstype}"
     good_msg "Using mount fstype: ${mount_fstype}"
     _fstype_init "${fstype}"
@@ -84,8 +87,15 @@ _rootdev_mount() {
     good_msg "Using mount opts: -o ${mopts}"
 
     mount -t "${mount_fstype}" -o "${mopts}" \
-        "${REAL_ROOT}" "${NEW_ROOT}" || return 1
-    return 0
+        "${REAL_ROOT}" "${NEW_ROOT}" && return 0
+
+    bad_msg "Cannot mount ${REAL_ROOT}, trying with -t auto"
+    mount -t "auto" -o "${mopts}" \
+        "${REAL_ROOT}" "${NEW_ROOT}" && return 0
+
+    bad_msg "Cannot mount ${REAL_ROOT} with -t auto, giving up"
+
+    return 1
 }
 
 _get_mounts_list() {

defaults/linuxrc

@@ -34,7 +34,6 @@ FAKE_INIT=""
 REAL_INIT="/sbin/init"
 FAKE_ROOTFLAGS=""
 INIT_OPTS=""
-ROOTFSTYPE="auto"
 CRYPT_SILENT=0
 QUIET=""