update_kernel: fix to be not rely on kernel command-line

update_kernel.sh

 #!/bin/bash
 
 # Copyright (c) 2009-2010 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Script to update the kernel on a live running ChromiumOS instance.
 
 # --- BEGIN COMMON.SH BOILERPLATE ---
 # Load common CrOS utilities.  Inside the chroot this file is installed in
@@ skipping 44 matching lines @@
 function learn_device() {
   [ -n "${FLAGS_device}" ] && return
   remote_sh df /mnt/stateful_partition
   FLAGS_device=$(echo "${REMOTE_OUT}" | awk '/dev/ {print $1}' | sed s/1\$//)
   info "Target reports root device is ${FLAGS_device}"
 }
 
 # Ask the target what the kernel partition is
 function learn_partition() {
   [ -n "${FLAGS_partition}" ] && return
-  remote_sh cat /proc/cmdline
-  if echo "${REMOTE_OUT}" | egrep -q "${FLAGS_device}3"; then
+  ! remote_sh rootdev
+  if [ "${REMOTE_OUT}" == "/dev/dm-0" ]; then
+    remote_sh ls /sys/block/dm-0/slaves
+    REMOTE_OUT="/dev/${REMOTE_OUT}"
+  fi
+  if [ "${REMOTE_OUT}" == "${FLAGS_device}3" ]; then
     FLAGS_partition="${FLAGS_device}2"
   else
     FLAGS_partition="${FLAGS_device}4"
   fi
   if [ -z "${FLAGS_partition}" ]; then
     error "Partition required"
     exit 1
   fi
   info "Target reports kernel partition is ${FLAGS_partition}"
 }
@@ skipping 61 matching lines @@
   fi
 
   remote_reboot
 
   remote_sh uname -r -v
   info "old kernel: ${old_kernel}"
   info "new kernel: ${REMOTE_OUT}"
 }
 
 main "$@"