Basic implementation of TCP over XDP for Knot server

including connection handling for kxdpgun in TCP mode.

The implementation is not perfect!! But the interface with other Knot parts is stable.

src/knot/server/udp-handler.c

@@ -113,8 +113,15 @@ typedef struct {
 	int (*udp_recv)(int, void *, void *);
 	int (*udp_handle)(udp_context_t *, void *, void *);
 	int (*udp_send)(void *, void *);
+	int (*udp_tick)(void *, void *);
 } udp_api_t;
 
+static int udp_noop(void *unused1, void *unused2) {
+	UNUSED(unused1);
+	UNUSED(unused2);
+	return KNOT_EOK;
+}
+
 /*! \brief Control message to fit IP_PKTINFO or IPv6_RECVPKTINFO. */
 typedef union {
 	struct cmsghdr cmsg;
@@ -245,7 +252,8 @@ static udp_api_t udp_recvfrom_api = {
 	udp_recvfrom_deinit,
 	udp_recvfrom_recv,
 	udp_recvfrom_handle,
-	udp_recvfrom_send
+	udp_recvfrom_send,
+	udp_noop
 };
 
 #ifdef ENABLE_RECVMMSG
@@ -362,7 +370,8 @@ static udp_api_t udp_recvmmsg_api = {
 	udp_recvmmsg_deinit,
 	udp_recvmmsg_recv,
 	udp_recvmmsg_handle,
-	udp_recvmmsg_send
+	udp_recvmmsg_send,
+	udp_noop
 };
 #endif /* ENABLE_RECVMMSG */
 
@@ -394,12 +403,18 @@ static int xdp_recvmmsg_send(void *d, void *xdp_sock)
 	return xdp_handle_send(d, xdp_sock);
 }
 
+static int xdp_recvmmsg_tick(void *d, void *xdp_sock)
+{
+	return xdp_handle_timeout(d, xdp_sock);
+}
+
 static udp_api_t xdp_recvmmsg_api = {
 	xdp_recvmmsg_init,
 	xdp_recvmmsg_deinit,
 	xdp_recvmmsg_recv,
 	xdp_recvmmsg_handle,
-	xdp_recvmmsg_send
+	xdp_recvmmsg_send,
+	xdp_recvmmsg_tick
 };
 #endif /* ENABLE_XDP */
 
@@ -535,7 +550,7 @@ int udp_master(dthread_t *thread)
 
 		/* Wait for events. */
 		fdset_it_t it;
-		(void)fdset_poll(&fds, &it, 0, -1);
+		(void)fdset_poll(&fds, &it, 0, 1000);
 
 		/* Process the events. */
 		for (; !fdset_it_is_done(&it); fdset_it_next(&it)) {
@@ -547,6 +562,9 @@ int udp_master(dthread_t *thread)
 				api->udp_send(rq, xdp_socket);
 			}
 		}
+
+		/* Regular maintenance (XDP-TCP only). */
+		api->udp_tick(rq, xdp_socket);
 	}
 
 finish: