[PATCH bpf-next 3/6] selftests/xsk: Add testapp_xdp_adjust_tail function to userspace for packet tail adjustment

[Tushar Vyavahare <tushar.vyavahare@xxxxxxxxx>]

This commit adds the testapp_xdp_adjust_tail function in the userspace
code. The function is responsible for adjusting the tail of packets using
the xsk_xdp_adjust_tail XDP program.

The function performs the following tasks:
1. Retrieves the XDP program objects (skel_rx and skel_tx) from the
   test_spec structure.
2. Finds the bpf_map for the XDP program's bss section.
3. Updates the 'count' variable in the XDP program's bss section with the
   provided adjust_value.
4. Sets the XDP program (xsk_xdp_adjust_tail) for both RX and TX
   interfaces using test_spec_set_xdp_prog.
5. Calls testapp_validate_traffic to validate the traffic after adjusting
   the packet tail.

This function allows testing and validating the XDP program's behavior when
adjusting the packet tail using the bpf_xdp_adjust_tail helper function.

Signed-off-by: Tushar Vyavahare <tushar.vyavahare@xxxxxxxxx>
---
 tools/testing/selftests/bpf/xskxceiver.c | 25 ++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/tools/testing/selftests/bpf/xskxceiver.c b/tools/testing/selftests/bpf/xskxceiver.c
index 1d9b03666ee6..ff3316f6174e 100644
--- a/tools/testing/selftests/bpf/xskxceiver.c
+++ b/tools/testing/selftests/bpf/xskxceiver.c
@@ -2518,6 +2518,31 @@ static int testapp_hw_sw_max_ring_size(struct test_spec *test)
 	return testapp_validate_traffic(test);
 }
 
+static int testapp_xdp_adjust_tail(struct test_spec *test, int count)
+{
+	struct xsk_xdp_progs *skel_rx = test->ifobj_rx->xdp_progs;
+	struct xsk_xdp_progs *skel_tx = test->ifobj_tx->xdp_progs;
+	struct bpf_map *data_map;
+	int key = 0;
+
+	test_spec_set_xdp_prog(test, skel_rx->progs.xsk_xdp_adjust_tail,
+			       skel_tx->progs.xsk_xdp_adjust_tail,
+			       skel_rx->maps.xsk, skel_tx->maps.xsk);
+
+	data_map = bpf_object__find_map_by_name(skel_rx->obj, "xsk_xdp_.bss");
+	if (!data_map || !bpf_map__is_internal(data_map)) {
+		ksft_print_msg("Error: could not find bss section of XDP program\n");
+		return TEST_FAILURE;
+	}
+
+	if (bpf_map_update_elem(bpf_map__fd(data_map), &key, &count, BPF_ANY)) {
+		ksft_print_msg("Error: could not update count element\n");
+		return TEST_FAILURE;
+	}
+
+	return testapp_validate_traffic(test);
+}
+
 static void run_pkt_test(struct test_spec *test)
 {
 	int ret;
-- 
2.34.1