remove files in /boot at preinst when bootfs is vfat (#4886)

* remove files in /boot at preinst when bootfs is vfat

* use findmnt to get /boot source device

lib/functions/compilation/kernel-debs.sh

@@ -235,6 +235,19 @@ function kernel_package_callback_linux_image() {
 				test -d ${debian_kernel_hook_dir}/${script}.d && run-parts --arg="${kernel_version_family}" --arg="/${installed_image_path}" ${debian_kernel_hook_dir}/${script}.d
 			KERNEL_HOOK_DELEGATION
 
+			if [[ "${script}" == "preinst" ]]; then
+				cat <<- HOOK_FOR_REMOVE_VFAT_BOOT_FILES
+					check_boot_dev (){
+						boot_partition=\$(findmnt -n -o SOURCE /boot)
+						bootfstype=\$(blkid -s TYPE -o value \$boot_partition)
+						if [ "\$bootfstype" = "vfat" ]; then
+							rm -f /boot/System.map* /boot/config* /boot/vmlinuz* /boot/$image_name /boot/uImage
+						fi
+					}
+					mountpoint -q /boot && check_boot_dev
+				HOOK_FOR_REMOVE_VFAT_BOOT_FILES
+			fi
+
 			# @TODO: only if u-boot, only for postinst. Gotta find a hook scheme for these...
 			if [[ "${script}" == "postinst" ]]; then
 				cat <<- HOOK_FOR_LINK_TO_LAST_INSTALLED_KERNEL