samples/bpf: Use recvfrom() in xdpsock/rxdrop

Start using recvfrom() the rxdrop scenario.
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
Link: https://lore.kernel.org/bpf/20201130185205.196029-8-bjorn.topel@gmail.com

samples/bpf/xdpsock_user.c

@@ -1170,7 +1170,7 @@ static inline void complete_tx_only(struct xsk_socket_info *xsk,
 	}
 }
 
-static void rx_drop(struct xsk_socket_info *xsk, struct pollfd *fds)
+static void rx_drop(struct xsk_socket_info *xsk)
 {
 	unsigned int rcvd, i;
 	u32 idx_rx = 0, idx_fq = 0;
@@ -1180,7 +1180,7 @@ static void rx_drop(struct xsk_socket_info *xsk, struct pollfd *fds)
 	if (!rcvd) {
 		if (xsk_ring_prod__needs_wakeup(&xsk->umem->fq)) {
 			xsk->app_stats.rx_empty_polls++;
-			ret = poll(fds, num_socks, opt_timeout);
+			recvfrom(xsk_socket__fd(xsk->xsk), NULL, 0, MSG_DONTWAIT, NULL, NULL);
 		}
 		return;
 	}
@@ -1191,7 +1191,7 @@ static void rx_drop(struct xsk_socket_info *xsk, struct pollfd *fds)
 			exit_with_error(-ret);
 		if (xsk_ring_prod__needs_wakeup(&xsk->umem->fq)) {
 			xsk->app_stats.fill_fail_polls++;
-			ret = poll(fds, num_socks, opt_timeout);
+			recvfrom(xsk_socket__fd(xsk->xsk), NULL, 0, MSG_DONTWAIT, NULL, NULL);
 		}
 		ret = xsk_ring_prod__reserve(&xsk->umem->fq, rcvd, &idx_fq);
 	}
@@ -1233,7 +1233,7 @@ static void rx_drop_all(void)
 		}
 
 		for (i = 0; i < num_socks; i++)
-			rx_drop(xsks[i], fds);
+			rx_drop(xsks[i]);
 
 		if (benchmark_done)
 			break;