In addition to sending data, processes may send file descriptors across a Unix domain socket connection using the sendmsg() and recvmsg() system calls. This allows the sending processes to grant the receiving process access to a file descriptor for which the receiving process otherwise does not have access.
From: Unix domain socket - Wikipedia
As this happens entirely through system calls, I’m not sure you can get around calling the appropriate functions via ccall. As far as I’m aware, it’s not possible to do syscalls directly through julia, but I may be wrong about that.
Wayland is very Unix specific though, so relying on C for this is not unreasonable.