[PATCH net 6/7] selftests/xsk: fix too-many-frags multi-buffer Tx test

[Maciej Fijalkowski <maciej.fijalkowski@intel.com>]

The too-many-frags test describes a packet that is valid from the Tx
ring ownership point of view, but invalid for transmission because it
exceeds the supported number of fragments.

Keep the generated Tx descriptors valid so that __send_pkts() accounts
them as outstanding descriptors that must be reclaimed through the CQ.
Then mark the corresponding Rx packet invalid so the test still does
not expect the oversized packet to appear on the receive side.

Add a valid synchronization packet after the oversized packet so the
test can verify that the Tx path drains the bad packet and resumes at
the next packet boundary.

Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
---
 .../selftests/bpf/prog_tests/test_xsk.c       | 20 +++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/test_xsk.c b/tools/testing/selftests/bpf/prog_tests/test_xsk.c
index 72875071d4f1..de1e63c3fdf6 100644
--- a/tools/testing/selftests/bpf/prog_tests/test_xsk.c
+++ b/tools/testing/selftests/bpf/prog_tests/test_xsk.c
@@ -2258,7 +2258,7 @@ int testapp_too_many_frags(struct test_spec *test)
 		max_frags += 1;
 	}
 
-	pkts = calloc(2 * max_frags + 2, sizeof(struct pkt));
+	pkts = calloc(2 * max_frags + 3, sizeof(struct pkt));
 	if (!pkts)
 		return TEST_FAILURE;
 
@@ -2279,21 +2279,29 @@ int testapp_too_many_frags(struct test_spec *test)
 	/* An invalid packet with the max amount of frags but signals packet
 	 * continues on the last frag
 	 */
-	for (i = max_frags + 1; i < 2 * max_frags + 1; i++) {
+	for (i = max_frags + 1; i < 2 * max_frags + 2; i++) {
 		pkts[i].len = MIN_PKT_SIZE;
 		pkts[i].options = XDP_PKT_CONTD;
-		pkts[i].valid = false;
+		pkts[i].valid = true;
 	}
+	pkts[2 * max_frags + 1].options = 0;
 
 	/* Valid packet for synch */
-	pkts[2 * max_frags + 1].len = MIN_PKT_SIZE;
-	pkts[2 * max_frags + 1].valid = true;
+	pkts[2 * max_frags + 2].len = MIN_PKT_SIZE;
+	pkts[2 * max_frags + 2].valid = true;
 
-	if (pkt_stream_generate_custom(test, pkts, 2 * max_frags + 2)) {
+	if (pkt_stream_generate_custom(test, pkts, 2 * max_frags + 3)) {
 		free(pkts);
 		return TEST_FAILURE;
 	}
 
+	/* The generated Tx stream must keep the too-big packet valid so that
+	 * __send_pkts() accounts its descriptors in outstanding_tx. The Rx
+	 * stream, however, must not expect this packet on the wire.
+	 */
+	test->ifobj_rx->xsk->pkt_stream->pkts[2].valid = false;
+	test->ifobj_rx->xsk->pkt_stream->nb_valid_entries--;
+
 	ret = testapp_validate_traffic(test);
 	free(pkts);
 	return ret;
-- 
2.43.0