List all RPC services exported by device

mos call RPC.List
[
  "FS.Umount",
  ...

You can see see what arguments an RPC service expects by calling an RPC.Describe, which provides a simple introspection:

mos call RPC.Describe '{"name": "Config.Set"}'
{
  "name": "Config.Set",
  "args_fmt": "{config: %M}"
}

It works because C API for registering an RPC service has JSON format specification for the input arguments. That's why Mongoose OS knows about JSON formats for all registered RPC services.