persistent-vars-storage-ubootenv: adds a uboot-env compatible persistent storage utility

The Morse Micro persistent-vars-storage package is used to load and store certain device
parameters or configuration from non-volatile storage on a device. This is useful for a
more persistent configuration than what is offered by UCI. Typically used for dpp keys.

The uboot-env version targets any device which can allocate a uboot-env style partition
in flash dedicated for this purpose. It is recommended to not use the actual uboot-env
partition, but rather create a new partition using the uboot-env format.

utils/persistent-vars-storage-ubootenv/Makefile

@@ -0,0 +1,36 @@
+#
+# Copyright 2024 Morse Micro
+#
+# This is free software, licensed under the GNU General Public License v2.
+# See /LICENSE for more information.
+#
+
+include $(TOPDIR)/rules.mk
+
+
+PKG_NAME:=persistent-vars-storage-ubootenv
+PKG_RELEASE=1
+
+PKG_MAINTAINER:=Morse Micro
+
+include $(INCLUDE_DIR)/package.mk
+
+define Package/persistent-vars-storage-ubootenv
+  SECTION:=Utilities
+  CATEGORY:=Utilities
+  PROVIDES:=persistent-vars-storage
+  TITLE:=Reads or writes key-value vars from/into the persistent storage (u-boot-env)
+  DEPENDS:= uboot-envtools
+endef
+
+define Build/Compile
+
+endef
+
+define Package/persistent-vars-storage-ubootenv/install
+	$(INSTALL_DIR) $(1)/sbin
+	$(INSTALL_BIN) ./files/sbin/persistent_vars_storage.sh $(1)/sbin/persistent_vars_storage.sh
+	$(INSTALL_DIR) $(1)/etc
+endef
+
+$(eval $(call BuildPackage,persistent-vars-storage-ubootenv))

utils/persistent-vars-storage-ubootenv/files/sbin/persistent_vars_storage.sh

@@ -0,0 +1,74 @@
+#!/bin/sh
+#
+# Copyright (C) 2023 MorseMicro
+#
+
+set -eu
+trap exit_handler EXIT
+
+exit_handler()
+{
+	if [ "$?" -ne 0 ]; then
+		echo "Usage: $0 OPERATION(READ|WRITE|ERASE) KEY [VALUE]" 1>&2
+		exit 1
+	fi
+}
+
+# We don't use OpenWrt's find_mtd_part here because we want to write a script
+# that exploits 'set -eu'.
+find_mtd_partition()
+{
+	local name="$1"
+
+	for partition in /sys/class/mtd/mtd*; do
+		if [ "$(cat "$partition/name" 2> /dev/null)" = "$name" ]; then
+			echo "/dev/$(basename "$partition")"
+			return
+		fi
+	done
+
+	1>&2 echo "Internal error: can't find $name partition"
+	exit 1
+}
+
+show_raw_partition_data()
+{
+	local partition="$1" skip="$2" count="$3"
+
+	# Running this through shell/echo strips the nulls and puts a newline in (consistent with fw_printenv)
+	echo "$(dd if="$(find_mtd_partition "$partition")" bs=1  skip=$(($skip)) count="$count" 2> /dev/null)"
+}
+
+# Use secondary uboot env in preference
+# (this one is less likely to be the 'real' uboot env).
+# The disadvantage of using the real uboot env is that if it's empty/fails the CRC
+# uboot-envtools decides to write the 'default' environment that it understands.
+# Unfortunately, this is very unlikely to be consistent with the default environment
+# compiled into the uboot, so it causes issues.
+if [ -e /etc/fw_sys.config ]; then
+	conffile=/etc/fw_sys.config
+else
+	conffile=/etc/fw_env.config
+fi
+
+operation="$1"
+key="$2"
+
+case "$operation" in
+	READ)
+		fw_printenv -n -c "$conffile" "$key" 2> /dev/null
+	;;
+
+	WRITE)
+		value="$3"
+		fw_setenv -c "$conffile" "$key" "$value"
+	;;
+
+	ERASE)
+		fw_setenv -c "$conffile" "$key"
+	;;
+
+	*)
+		exit 1
+	;;
+esac