selftests/bpf: Add BPF-helper test for CLOCK_TAI access

Add BPF-helper test case for CLOCK_TAI access. The added test verifies that:

 * Timestamps are generated
 * Timestamps are moving forward
 * Timestamps are reasonable
Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Link: https://lore.kernel.org/r/20220809060803.5773-3-kurt@linutronix.deSigned-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/prog_tests/time_tai.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) 2022 Linutronix GmbH */
+
+#include <test_progs.h>
+#include <network_helpers.h>
+
+#include "test_time_tai.skel.h"
+
+#include <time.h>
+#include <stdint.h>
+
+#define TAI_THRESHOLD	1000000000ULL /* 1s */
+#define NSEC_PER_SEC	1000000000ULL
+
+static __u64 ts_to_ns(const struct timespec *ts)
+{
+	return ts->tv_sec * NSEC_PER_SEC + ts->tv_nsec;
+}
+
+void test_time_tai(void)
+{
+	struct __sk_buff skb = {
+		.cb[0] = 0,
+		.cb[1] = 0,
+		.tstamp = 0,
+	};
+	LIBBPF_OPTS(bpf_test_run_opts, topts,
+		.data_in = &pkt_v4,
+		.data_size_in = sizeof(pkt_v4),
+		.ctx_in = &skb,
+		.ctx_size_in = sizeof(skb),
+		.ctx_out = &skb,
+		.ctx_size_out = sizeof(skb),
+	);
+	struct test_time_tai *skel;
+	struct timespec now_tai;
+	__u64 ts1, ts2, now;
+	int ret, prog_fd;
+
+	/* Open and load */
+	skel = test_time_tai__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "tai_open"))
+		return;
+
+	/* Run test program */
+	prog_fd = bpf_program__fd(skel->progs.time_tai);
+	ret = bpf_prog_test_run_opts(prog_fd, &topts);
+	ASSERT_OK(ret, "test_run");
+
+	/* Retrieve generated TAI timestamps */
+	ts1 = skb.tstamp;
+	ts2 = skb.cb[0] | ((__u64)skb.cb[1] << 32);
+
+	/* TAI != 0 */
+	ASSERT_NEQ(ts1, 0, "tai_ts1");
+	ASSERT_NEQ(ts2, 0, "tai_ts2");
+
+	/* TAI is moving forward only */
+	ASSERT_GT(ts2, ts1, "tai_forward");
+
+	/* Check for future */
+	ret = clock_gettime(CLOCK_TAI, &now_tai);
+	ASSERT_EQ(ret, 0, "tai_gettime");
+	now = ts_to_ns(&now_tai);
+
+	ASSERT_TRUE(now > ts1, "tai_future_ts1");
+	ASSERT_TRUE(now > ts2, "tai_future_ts2");
+
+	/* Check for reasonable range */
+	ASSERT_TRUE(now - ts1 < TAI_THRESHOLD, "tai_range_ts1");
+	ASSERT_TRUE(now - ts2 < TAI_THRESHOLD, "tai_range_ts2");
+
+	test_time_tai__destroy(skel);
+}

tools/testing/selftests/bpf/progs/test_time_tai.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) 2022 Linutronix GmbH */
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+
+SEC("tc")
+int time_tai(struct __sk_buff *skb)
+{
+	__u64 ts1, ts2;
+
+	/* Get TAI timestamps */
+	ts1 = bpf_ktime_get_tai_ns();
+	ts2 = bpf_ktime_get_tai_ns();
+
+	/* Save TAI timestamps (Note: skb->hwtstamp is read-only) */
+	skb->tstamp = ts1;
+	skb->cb[0] = ts2 & 0xffffffff;
+	skb->cb[1] = ts2 >> 32;
+
+	return 0;
+}