Out-of-band UDP support

The EVL network stack implements the UDP protocol over IPv4 as specified by RFC768. This is the EVL equivalent of the AF_INET protocol family using datagram sockets (SOCK_DGRAM) available wih the in-band network stack. Using out-of-band datagram sockets with EVL is very similar to using its in-band counterpart, as illustrated by the oob-net-udp demo program. This boils down to:

  1. creating a socket with the SOCK_OOB flag set, which extends the associated protocol support to out-of-band handling, in this case AF_PACKET.
#include <sys/socket.h>

	/* Get a datagram socket in the IPv4 domain with out-of-band capabilities. */
	s = socket(AF_INET, SOCK_DGRAM | SOCK_OOB, 0);
  1. binding an address to the socket on the RX side (binding is optional on the TX side):
#include <sys/socket.h>
#include <arpa/inet.h>

	struct sockaddr_in addr;

	memset(&addr, 0, sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_port = htons(udp_port_number);
    if (!inet_pton(AF_INET, ip_address_as_string, &addr.sin_addr))
          error(1, EINVAL, "invalid IPv4 address");
  1. solicit the peer host for obtaining its address for the TX side prior to sending. The reasoning behind this aspect is detailed in this document.
		int ret = evl_net_solicit(s, (const struct sockaddr *)&addr, EVL_NEIGH_PERMANENT);
		if (ret)
			  error(1, -ret, "evl_net_solicit()");
  1. sending and/or receiving datagrams via the socket using the oob_recvmsg() and oob_sendmsg() calls respectively.
	struct oob_msghdr msghdr;
	struct sockaddr_in addr;
	struct iovec iov;
	ssize_t count;

	/* INPUT */
	iov.iov_base = input_datagram;
	iov.iov_len = sizeof(input_datagram);
	msghdr.msg_iov = &iov;
	msghdr.msg_iovlen = 1;
	msghdr.msg_control = NULL;
	msghdr.msg_controllen = 0;
	msghdr.msg_name = &addr;	/* or NULL, optional */
	msghdr.msg_namelen = sizeof(addr); /* or zero, optional */
	msghdr.msg_flags = 0;
	count = oob_recvmsg(s, &msghdr, NULL, 0);
	if (count < 0)
		  error(1, errno, "oob_recvmsg() failed");

	/* OUTPUT */
	iov.iov_base = output_datagram;
	iov.iov_len = sizeof(output_datagram);
	msghdr.msg_iov = &iov;
	msghdr.msg_iovlen = 1;
	msghdr.msg_control = NULL;
	msghdr.msg_controllen = 0;
	msghdr.msg_name = NULL; /* Optional, use bound device if NULL. */
	msghdr.msg_namelen = 0;
	msghdr.msg_flags = 0;
	count = oob_sendmsg(s, &msghdr, NULL, 0);
	if (count < 0)
	      error(1, errno, "oob_sendmsg() failed");

Threads issuing the oob_recvmsg() and/or oob_sendmsg() calls must be attached to the EVL core.

Last modified: Thu, 03 Jul 2025 16:39:27 +0200