selftests: xsk: Add single packet test

Add a test where a single packet is sent and received. This might
sound like a silly test, but since many of the interfaces in xsk are
batched, it is important to be able to validate that we did not break
something as fundamental as just receiving single packets, instead of
batches of packets at high speed.

Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210922075613.12186-12-magnus.karlsson@gmail.com

tools/testing/selftests/bpf/xdpxceiver.c

@@ -1217,6 +1217,15 @@ static bool testapp_unaligned(struct test_spec *test)
 	return true;
 }
 
+static void testapp_single_pkt(struct test_spec *test)
+{
+	struct pkt pkts[] = {{0x1000, PKT_SIZE, 0, true}};
+
+	pkt_stream_generate_custom(test, pkts, ARRAY_SIZE(pkts));
+	testapp_validate_traffic(test);
+	pkt_stream_restore_default(test);
+}
+
 static void testapp_invalid_desc(struct test_spec *test)
 {
 	struct pkt pkts[] = {
@@ -1298,6 +1307,10 @@ static void run_pkt_test(struct test_spec *test, enum test_mode mode, enum test_
 		test_spec_set_name(test, "RUN_TO_COMPLETION");
 		testapp_validate_traffic(test);
 		break;
+	case TEST_TYPE_RUN_TO_COMPLETION_SINGLE_PKT:
+		test_spec_set_name(test, "RUN_TO_COMPLETION_SINGLE_PKT");
+		testapp_single_pkt(test);
+		break;
 	case TEST_TYPE_RUN_TO_COMPLETION_2K_FRAME:
 		test_spec_set_name(test, "RUN_TO_COMPLETION_2K_FRAME_SIZE");
 		test->ifobj_tx->umem->frame_size = 2048;

tools/testing/selftests/bpf/xdpxceiver.h

@@ -55,6 +55,7 @@ enum test_mode {
 enum test_type {
 	TEST_TYPE_RUN_TO_COMPLETION,
 	TEST_TYPE_RUN_TO_COMPLETION_2K_FRAME,
+	TEST_TYPE_RUN_TO_COMPLETION_SINGLE_PKT,
 	TEST_TYPE_POLL,
 	TEST_TYPE_UNALIGNED,
 	TEST_TYPE_ALIGNED_INV_DESC,