base-files: functions: introduce new helper functions

Introduce cmdline_get_var() to /lib/function.sh and make use of it in
export_rootdev() in /lib/upgrade/common.sh, making the code more
simple and removing one level of indentation.
Introduce get_partition_by_name() to /lib/upgrade/common.sh which is
useful on non-EFI GPT platforms like mt7622.
Remove some dead-code while at it.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

package/base-files/files/lib/functions.sh

@@ -384,4 +384,14 @@ board_name() {
 	[ -e /tmp/sysinfo/board_name ] && cat /tmp/sysinfo/board_name || echo "generic"
 }
 
+cmdline_get_var() {
+	local var=$1
+	local cmdlinevar tmp
+
+	for cmdlinevar in $(cat /proc/cmdline); do
+		tmp=${cmdlinevar##${var}}
+		[ "=" = "${tmp:0:1}" ] && echo ${tmp:1}
+	done
+}
+
 [ -z "$IPKG_INSTROOT" ] && [ -f /lib/config/uci.sh ] && . /lib/config/uci.sh

package/base-files/files/lib/upgrade/common.sh

@@ -147,22 +147,9 @@ part_magic_fat() {
 }
 
 export_bootdevice() {
-	local cmdline bootdisk rootpart uuid blockdev uevent line class
+	local cmdline uuid blockdev uevent line class
 	local MAJOR MINOR DEVNAME DEVTYPE
-
-	if read cmdline < /proc/cmdline; then
-		case "$cmdline" in
-			*root=*)
-				rootpart="${cmdline##*root=}"
-				rootpart="${rootpart%% *}"
-			;;
-		esac
-
-		case "$bootdisk" in
-			/dev/*)
-				uevent="/sys/class/block/${bootdisk##*/}/uevent"
-			;;
-		esac
+	local rootpart="$(cmdline_get_var root)"
 
 	case "$rootpart" in
 		PARTUUID=[a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9]-[a-f0-9][a-f0-9])
@@ -212,7 +199,6 @@ export_bootdevice() {
 		export BOOTDEV_MINOR=$MINOR
 		return 0
 	fi
-	fi
 
 	return 1
 }
@@ -242,6 +228,15 @@ hex_le32_to_cpu() {
 	echo "$@"
 }
 
+get_partition_by_name() {
+	for partname in /sys/class/block/$1/*/name; do
+		[ "$(cat ${partname})" = "$2" ] && {
+			basename ${partname%%/name}
+			break
+		}
+	done
+}
+
 get_partitions() { # <device> <filename>
 	local disk="$1"
 	local filename="$2"