What does undocumented "proto" command line argument do in auditdistd on FreeBSD?

As you might know there is an auditdistd(8) daemon available on FreeBSD. It has some documented command line arguments like -c, -d, etc. (see more here (link) ). I was trying to learn how it works when I stumbled upon a code handling an undocumented command line argument, proto: - Apparently, proto_exec is called when you execute /usr/sbin/auditdistd proto foo bar baz and foo bar baz are passed to the function as its arguments. > /* > * We are executed from proto to create sandbox. > */ > if (argc > 1 && strcmp(argv, "proto") == 0) { > argc -= 2; > argv += 2; > if (proto_exec(argc, argv) == -1) > err(EX_USAGE, "Unable to execute proto"); > } > _(See /contrib/openbsm/bin/auditdistd/auditdistd.c:main() (link) for more details.)_ - Here's the proto_exec function: > int > proto_exec(int argc, char *argv[]) > { > struct proto *proto; > int error; > > if (argc == 0) { > errno = EINVAL; > return (-1); > } > TAILQ_FOREACH(proto, &protos, prt_next) { > if (strcmp(proto->prt_name, argv) == 0) > break; > } > if (proto == NULL) { > errno = EINVAL; > return (-1); > } > if (proto->prt_exec == NULL) { > errno = EOPNOTSUPP; > return (-1); > } > error = proto->prt_exec(argc, argv); > if (error != 0) { > errno = error; > return (-1); > } > /* NOTREACHED */ > return (0); > } > _(See /contrib/openbsm/bin/auditdistd/proto.c:proto_exec() (link) for more details.)_ Honestly, I cannot figure out what is happening here. - The protos variable is initialized like this: > static TAILQ_HEAD(, proto) protos = TAILQ_HEAD_INITIALIZER(protos); > _(See /contrib/openbsm/bin/auditdistd/proto.c (link) for more details.)_ - When /usr/sbin/auditdistd proto foo is called it just says: > auditdistd: Unable to execute proto: Invalid argument Does anyone know what is this option and how to use it?