rtl-sdr: Add start script file for rtl-tcp

One of the most common uses of the rtl-sdr suite on OpenWrt is to stream
data to a remote analyzer. This commit creates a /etc/init.d/ and
/etc/config entry for rtl-tcp, so that it can automatically launch on
startup.

Signed-off-by: Mike Miller <github@mikeage.net>

utils/rtl-sdr/files/rtl_tcp.init

@@ -0,0 +1,64 @@
+#!/bin/sh /etc/rc.common
+# Copyright (C) 2016 OpenWrt.org
+
+START=90
+STOP=10
+USE_PROCD=1
+
+append_arg() {
+	local cfg="$1"
+	local var="$2"
+	local opt="$3"
+	local def="$4"
+	local val
+
+	config_get val "$cfg" "$var"
+	[ -n "$val" -o -n "$def" ] && procd_append_param command $opt "${val:-$def}"
+}
+
+append_bool() {
+	local cfg="$1"
+	local var="$2"
+	local opt="$3"
+	local def="$4"
+	local val
+
+	config_get_bool val "$cfg" "$var" "$def"
+	[ "$val" = 1 ] && procd_append_param command "$opt"
+}
+
+
+start_instance() {
+	local cfg="$1"
+	local aux
+
+	config_get_bool aux "$cfg" 'disabled' '0'
+	[ "$aux" = 1 ] && return 1
+
+	procd_open_instance
+
+	procd_set_param command /usr/bin/rtl_tcp
+	append_arg "$cfg" device_index "-d"
+	append_arg "$cfg" address "-a"
+	append_arg "$cfg" port "-p"
+	append_arg "$cfg" frequency "-f"
+	append_arg "$cfg" gain "-g"
+	append_arg "$cfg" samplerate "-s"
+	append_arg "$cfg" buffers "-b"
+	append_arg "$cfg" num_linked_lists "-n"
+	append_arg "$cfg" ppm_error "-P"
+
+	config_get_bool aux "$cfg" 'respawn' '0'
+	[ "$aux" = 1 ] && procd_set_param respawn
+
+	procd_close_instance
+}
+
+service_triggers() {
+	procd_add_reload_trigger "rtl_tcp"
+}
+
+start_service() {
+	config_load rtl_tcp
+	config_foreach start_instance rtl_tcp
+}