Implement L2 learning to avoid flooding

[AkihiroSuda]

socket_vmnet should learn the MAC addresses of the VMs, set the MAC addresses to the struct conn objects, and avoid flooding when possible.

socket_vmnet/main.c

Lines 85 to 89 in 8b16e51

	struct conn {
	// TODO: uint8_t mac[6];
	int socket_fd;
	struct conn *next;
	} _conn;

socket_vmnet/main.c

Lines 180 to 205 in 8b16e51

	for (struct conn *conn = conns; conn != NULL; conn = conn->next) {
	// FIXME: avoid flooding
	DEBUGF("[Handler i=%d] Sending to the socket %d: 4 + %ld bytes [Dest "
	"%02X:%02X:%02X:%02X:%02X:%02X]",
	i, conn->socket_fd, pdv[i].vm_pkt_size, dest_mac[0], dest_mac[1],
	dest_mac[2], dest_mac[3], dest_mac[4], dest_mac[5]);
	uint32_t header_be = htonl(pdv[i].vm_pkt_size);
	struct iovec iov[2] = {
	{
	.iov_base = &header_be,
	.iov_len = 4,
	},
	{
	.iov_base = pdv[i].vm_pkt_iov[0].iov_base,
	.iov_len = pdv[i].vm_pkt_size, // not vm_pkt_iov[0].iov_len
	},
	};
	ssize_t written = writev(conn->socket_fd, iov, 2);
	DEBUGF("[Handler i=%d] Sent to the socket: %ld bytes (including uint32be "
	"header)",
	i, written);
	if (written < 0) {
	perror("writev");
	goto done;
	}
	}

socket_vmnet/main.c

Lines 512 to 542 in 8b16e51

	// Flood the packet to other VMs in the same network too.
	// (Not handled by vmnet)
	// FIXME: avoid flooding
	dispatch_semaphore_wait(state->sem, DISPATCH_TIME_FOREVER);
	struct conn *conns = state->conns;
	dispatch_semaphore_signal(state->sem);
	for (struct conn *conn = conns; conn != NULL; conn = conn->next) {
	if (conn->socket_fd == accept_fd)
	continue;
	DEBUGF("[Socket-to-Socket i=%lld] Sending from socket %d to socket %d: "
	"4 + %d bytes",
	i, accept_fd, conn->socket_fd, header);
	struct iovec iov[2] = {
	{
	.iov_base = &header_be,
	.iov_len = 4,
	},
	{
	.iov_base = buf,
	.iov_len = header,
	},
	};
	ssize_t written = writev(conn->socket_fd, iov, 2);
	DEBUGF("[Socket-to-Socket i=%lld] Sent from socket %d to socket %d: %ld "
	"bytes (including uint32be header)",
	i, accept_fd, conn->socket_fd, written);
	if (written < 0) {
	perror("writev");
	continue;
	}
	}