base-files,procd: add generic service status

Adds a default status action for init.d scripts.

procd "service status" will return:

 0) for loaded services (even if disabled by conf or dead)
 3) for inactive services
 4) when filtering a non-existing instance

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
[rebased, cleaned up]
Signed-off-by: Petr Štetiar <ynezz@true.cz>

package/system/procd/files/procd.sh

@@ -443,6 +443,31 @@ _procd_send_signal() {
 	_procd_ubus_call signal
 }
 
+_procd_status() {
+	local service="$1"
+	local instance="$2"
+	local data
+
+	json_init
+	[ -n "$service" ] && json_add_string name "$service"
+
+	data=$(_procd_ubus_call list | jsonfilter -e '@["'"$service"'"]')
+	[ -z "$data" ] && { echo "inactive"; return 3; }
+
+	data=$(echo "$data" | jsonfilter -e '$.instances')
+	if [ -z "$data" ]; then
+		[ -z "$instance" ] && { echo "active with no instances"; return 0; }
+		data="[]"
+	fi
+
+	[ -n "$instance" ] && instance="\"$instance\"" || instance='*'
+	if [ -z "$(echo "$data" | jsonfilter -e '$['"$instance"']')" ]; then
+		echo "unknown instance $instance"; return 4
+	else
+		echo "running"; return 0
+	fi
+}
+
 procd_open_data() {
 	local name="$1"
 	json_set_namespace procd __procd_old_cb