SHARED_UMEM creation

[jaydizz]

Hi all,
currently I am writing a pure golang library for using AF_XDP sockets. Little heads up: I do not want or need any support in my go code :)
I rather have a question regarding the creation of multiple sockets sharing UMEM. I have been reading the source-code of the tutorials here as well as the source of libxdp and I am none the wiser.
If I understand correctly, to create multiple XSKs with a single shared UMEM you would go along the lines of this:
For the first socket:

1. Create the first socket.
2. MMAP Umem, FR/CR RX/TX-Rings.
3. Register them.
4. Bind to the socket.

For all further sockets:

1. Create the socket.
2. MMAP RX/TX-Ring.
3. Register RX/TX.
4. Register shared UMEM from first socket, as well as FR/CR
5. Bind with flags |= XDP_SHARED_UMEM and set the shared_umem_fd to the fd of the first socket.

If I do that, the bind-syscall returns "EINVAL" and after countless hours of debugging I am out of options of what values are considered invalid. Right now I am questioning if I am understanding this procedure correctly of if I am missing something.
Maybe someone here can help me.

Much appreciated!