postmarketos-update-kernel: support A/B devices (MR 2214)

Add support for detecting A/B devices and cleanup the script a bit.

main/postmarketos-update-kernel/APKBUILD

 pkgname=postmarketos-update-kernel
-pkgver=0.0.4
+pkgver=0.0.5
 pkgrel=0
 pkgdesc="kernel updater script for postmarketOS"
 url="https://postmarketos.org"
@@ -12,4 +12,7 @@ package() {
 	install -Dm755 "$srcdir/update-kernel.sh" \
 		"$pkgdir/sbin/pmos-update-kernel"
 }
-sha512sums="17de682e88fec2632cb51c6b034e7b9c27e77736d5943906a57e276fb4c594af7af93e411e8cdb1ea2aeefb8d7f231408195102b02af3e8e55d594d1c812ff16  update-kernel.sh"
+
+sha512sums="
+256892629581fb9813ef9e7aa5bc18e7c1b80c88b97baeb96d7d432418f4cba79e0687193d7eca48bb3dba1543a3b7d1685f686206497c82df2e1ef80e026eb1  update-kernel.sh
+"

main/postmarketos-update-kernel/update-kernel.sh

@@ -15,28 +15,47 @@ deviceinfo_append_dtb=""
 # shellcheck disable=SC1091
 . /etc/deviceinfo
 
+# On A/B devices with bootloader cmdline ON this will return the slot suffix
+# if booting with an alternate method which erases the stock bootloader cmdline
+# this will be empty and the update will fail.
+# https://source.android.com/devices/bootloader/updating#slots
+# On non-A/B devices this will be empty
+ab_get_slot() {
+	ab_slot_suffix=$(grep -o 'androidboot\.slot_suffix=..' /proc/cmdline |  cut -d "=" -f2) || :
+	echo "$ab_slot_suffix"
+}
+
+update_android_fastboot() {
+	BOOT_PART_SUFFIX=$(ab_get_slot) # Empty for non-A/B devices
+	BOOT_PARTITION=$(findfs PARTLABEL="boot${BOOT_PART_SUFFIX}")
+	echo "Flashing boot.img to 'boot${BOOT_PART_SUFFIX}'"
+	dd if=/boot/boot.img-"$FLAVOR" of="$BOOT_PARTITION" bs=1M
+}
+
+update_android_split_kernel_initfs() {
+	KERNEL_PARTITION=$(findfs PARTLABEL="${deviceinfo_flash_heimdall_partition_kernel:?}")
+	INITFS_PARTITION=$(findfs PARTLABEL="${deviceinfo_flash_heimdall_partition_initfs:?}")
+
+	KERNEL="vmlinuz-$FLAVOR"
+	if [ "${deviceinfo_append_dtb}" = "true" ]; then
+		KERNEL="$KERNEL-dtb"
+	fi
+
+	echo "Flashing kernel ($KERNEL)..."
+	dd if=/boot/"$KERNEL" of="$KERNEL_PARTITION" bs=1M
+
+	echo "Flashing initramfs..."
+	gunzip -c /boot/initramfs-"$FLAVOR" | lzop | dd of="$INITFS_PARTITION" bs=1M
+}
+
 FLAVOR=$1
 METHOD=${deviceinfo_flash_method:?}
 case $METHOD in
 	fastboot|heimdall-bootimg)
-		BOOT_PARTITION=$(findfs PARTLABEL="boot")
-		echo "Flashing boot.img..."
-		dd if=/boot/boot.img-"$FLAVOR" of="$BOOT_PARTITION" bs=1M
+		update_android_fastboot
 		;;
 	heimdall-isorec)
-		KERNEL_PARTITION=$(findfs PARTLABEL="${deviceinfo_flash_heimdall_partition_kernel:?}")
-		INITFS_PARTITION=$(findfs PARTLABEL="${deviceinfo_flash_heimdall_partition_initfs:?}")
-
-		KERNEL="vmlinuz-$FLAVOR"
-		if [ "${deviceinfo_append_dtb}" = "true" ]; then
-			KERNEL="$KERNEL-dtb"
-		fi
-
-		echo "Flashing kernel ($KERNEL)..."
-		dd if=/boot/"$KERNEL" of="$KERNEL_PARTITION" bs=1M
-
-		echo "Flashing initramfs..."
-		gunzip -c /boot/initramfs-"$FLAVOR" | lzop | dd of="$INITFS_PARTITION" bs=1M
+		update_android_split_kernel_initfs
 		;;
 	0xffff)
 		echo -n "No need to use this utility, since uboot loads the kernel directly from"