gbmc-bridge: Fix RWFS check

Some platforms mount the RWFS as mtd:rwfs instead of /dev/mtdblock<N>,
this breaks the check in the purge script and causes it to overwrite the
JFFS2 while it's still mounted during netboot.

Tested: Manually reran the hook to verify that it's following the
correct path on the known problematic platform.

Google-Bug-Id: 526772581
Google-Bug-Id: 532737092
Change-Id: I35eba8636e661318bd8c7882dbf6685a051cfa13
Signed-off-by: William A. Kennington III <wak@google.com>

recipes-google/networking/gbmc-bridge/49-purge-rwfs.sh

diff --git a/recipes-google/networking/gbmc-bridge/49-purge-rwfs.sh b/recipes-google/networking/gbmc-bridge/49-purge-rwfs.sh
index 7ba5597..7346a2e 100644
--- a/recipes-google/networking/gbmc-bridge/49-purge-rwfs.sh
+++ b/recipes-google/networking/gbmc-bridge/49-purge-rwfs.sh
@@ -16,11 +16,11 @@
 [ -z "${gbmc_purge_rwfs-}" ] || return
 
 # fs util functions from obmc-init.sh
-findmtd() {
+findmtdnum() {
   local m
   m=$(grep -xl "$1" /sys/class/mtd/*/name)
   m=${m%/name}
-  m=${m##*/}
+  m=${m##*/mtd}
   echo "$m"
 }
 
@@ -58,23 +58,23 @@
   update_netboot_status "rwfs_check" "RWFS purge needed" "SUCCESS"
   update_netboot_status "rwfs_set" "Setting RWFS purge flag" "START"
 
-  local google_dir rwfs rwdev rwfst
+  local mtd_num
+  if ! mtd_num=$(findmtdnum rwfs) || [ -z "$mtd_num" ]; then
+    update_netboot_status "rwfs_check" "Finding RWFS MTD number failed" "FAIL"
+    return 1
+  fi
 
-  rwfs=$(findmtd rwfs)
-  rwdev="/dev/mtdblock${rwfs#mtd}"
-  rwfst="jffs2"
-
-  google_dir="/var/google"
-  if ! grep -q "$rwdev" /proc/mounts; then
+  local google_dir="/var/google"
+  if ! grep -qE "^(mtd:rwfs|/dev/mtdblock${mtd_num}|/dev/mtd${mtd_num}) " /proc/mounts; then
     update_netboot_status "rwfs_mfg_clear" "Erasing RWFS for manufacture image" "START"
 
-    flash_eraseall "/dev/$rwfs" || true
+    flash_eraseall "/dev/mtd${mtd_num}" || true
 
     update_netboot_status "rwfs_mfg_clear" "Erasing RWFS passed" "SUCCESS"
     update_netboot_status "rwfs_mfg_mount" "Mouting RWFS started" "START"
 
     mkdir -p /run/rwfsdir || return
-    if mount "$rwdev" /run/rwfsdir -t "$rwfst" -o rw; then
+    if mount mtd:rwfs /run/rwfsdir -t jffs2 -o rw; then
       google_dir="/run/rwfsdir/cow/var/google"
       update_netboot_status "rwfs_mfg_mount" "RWFS mounted" "SUCCESS"
     else