Test functionality of BPF filters with SO_REUSEPORT and SO_ATTACH_REUSEPORT_CBPF.

This test creates an SO_REUSEPORT receiver group containing one socket per CPU core.

It then creates a BPF program that will select a socket from this group based on the core id that receives the packet.

The sending code artificially moves itself to run on different core ids and sends one message from each core. Since these packets are delivered over loopback, they should arrive on the same core that sent them.

The receiving code then ensures that the packet was received on the socket for the corresponding core id.

var rawSMPProcessorID = SKF_AD_OFF + SKF_AD_CPU

var code = [...]unix.SockFilter{
	{unix.BPF_LD | unix.BPF_W | unix.BPF_ABS, 0, 0, uint32(rawSMPProcessorID)}, // A = raw_smp_processor_id()
	{unix.BPF_RET | unix.BPF_A, 0, 0, 0},                                       // return A
}

var prog = unix.SockFprog{
	Len:    uint16(len(code)),
	Filter: &code[0],
}

err = unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_REUSEPORT, 1)
if err != nil {
  return
}

err = unix.SetsockoptSockFprog(int(fd), unix.SOL_SOCKET, unix.SO_ATTACH_REUSEPORT_CBPF, &prog)
if err != nil {
  return
}