armsr: preserve configuration during sysupgrade

Copy configuration to boot partition (partition 1) instead of root
partition (partition 2) because the root partition is not writable if
it's a suqashfs image.
Move configuration back to root during preinit.

Fixes: openwrt#13695
Signed-off-by: Christian Buschau <cbuschau@d00t.de>

target/linux/armsr/base-files/lib/preinit/79_move_config

@@ -0,0 +1,19 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+move_config() {
+	local partdev parttype=ext4
+
+	. /lib/upgrade/common.sh
+
+	if export_bootdevice && export_partdevice partdev 1; then
+		part_magic_fat "/dev/$partdev" && parttype=vfat
+		if mount -t $parttype -o rw,noatime "/dev/$partdev" /mnt; then
+			if [ -f "/mnt/$BACKUP_FILE" ]; then
+				mv -f "/mnt/$BACKUP_FILE" /
+			fi
+			umount /mnt
+		fi
+	fi
+}
+
+boot_hook_add preinit_mount_root move_config

target/linux/armsr/base-files/lib/upgrade/platform.sh

@@ -36,7 +36,8 @@ platform_check_image() {
 platform_copy_config() {
 	local partdev parttype=ext4
 
-	if export_partdevice partdev 2; then
+	if export_partdevice partdev 1; then
+		part_magic_fat "/dev/$partdev" && parttype=vfat
 		mount -t $parttype -o rw,noatime "/dev/$partdev" /mnt
 		cp -af "$UPGRADE_BACKUP" "/mnt/$BACKUP_FILE"
 		umount /mnt