I want to create a mavros plugin for the FENCE_STATUS MAVLink common message (https://mavlink.io/en/messages/common.html#FENCE_STATUS), but I am very new and do not know where to start or what the process is. It seems that I need to create a fence_status.msg file and add it to /mavros/mavros_msgs/msg folder. What do I do after that to create the plugin?
Uploading/downloading a geofence is done with the same protocol as mission upload. I would suggest you modify the mission plugin to allow sending geofences (I think it currently hardcodes that the waypoints you send to mavros using the waypoint service are mission waypoints). That way you don’t have to re-implement the protocol.