timeutil/ptp: fix conversion from seconds to Time

Epic: none
Release note (bug fix): since 22.2.0, using a PTP clock device (enabled by the
--clock-device flag) would generate timestamps in the far future. It now
generates the correct time. This could cause nodes to crash due to incorrect
timestamps, or in the worst case irreversibly advance the cluster's HLC clock
into the far future.

pkg/BUILD.bazel

@@ -694,6 +694,7 @@ ALL_TESTS = [
     "//pkg/util/timeofday:timeofday_test",
     "//pkg/util/timetz:timetz_test",
     "//pkg/util/timeutil/pgdate:pgdate_test",
+    "//pkg/util/timeutil/ptp:ptp_test",
     "//pkg/util/timeutil:timeutil_test",
     "//pkg/util/tochar:tochar_test",
     "//pkg/util/tracing/collector:collector_test",
@@ -2416,6 +2417,7 @@ GO_TARGETS = [
     "//pkg/util/timeutil/pgdate:pgdate",
     "//pkg/util/timeutil/pgdate:pgdate_test",
     "//pkg/util/timeutil/ptp:ptp",
+    "//pkg/util/timeutil/ptp:ptp_test",
     "//pkg/util/timeutil:timeutil",
     "//pkg/util/timeutil:timeutil_test",
     "//pkg/util/tochar:tochar",

pkg/util/timeutil/ptp/BUILD.bazel

@@ -1,4 +1,4 @@
-load("@io_bazel_rules_go//go:def.bzl", "go_library")
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
 
 go_library(
     name = "ptp",
@@ -59,3 +59,19 @@ go_library(
         "//conditions:default": [],
     }),
 )
+
+go_test(
+    name = "ptp_test",
+    srcs = ["ptp_clock_linux_test.go"],
+    args = ["-test.timeout=295s"],
+    embed = [":ptp"],
+    deps = select({
+        "@io_bazel_rules_go//go/platform:android": [
+            "//pkg/util/timeutil",
+        ],
+        "@io_bazel_rules_go//go/platform:linux": [
+            "//pkg/util/timeutil",
+        ],
+        "//conditions:default": [],
+    }),
+)

pkg/util/timeutil/ptp/ptp_clock_linux.go

@@ -79,5 +79,10 @@ func (p Clock) Now() time.Time {
 		panic(err)
 	}
 
-	return timeutil.Unix(int64(ts.tv_sec)*1e9, int64(ts.tv_nsec))
+	return timeutil.Unix(int64(ts.tv_sec), int64(ts.tv_nsec))
+}
+
+// realtime returns a clock using the system CLOCK_REALTIME device. For testing.
+func realtime() Clock {
+	return Clock{clockDeviceID: uintptr(C.CLOCK_REALTIME)}
 }

pkg/util/timeutil/ptp/ptp_clock_linux_test.go

@@ -0,0 +1,30 @@
+// Copyright 2023 The Cockroach Authors.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+//go:build linux
+// +build linux
+
+package ptp
+
+import (
+	"testing"
+	"time"
+
+	"github.com/cockroachdb/cockroach/pkg/util/timeutil"
+)
+
+// TestClockNow sanity checks that Clock.Now() sourced from the CLOCK_REALTIME
+// device returns time close to timeutil.Now(). This ensures that the conversion
+// from the time returned by a clock device to Go's time.Time is correct.
+func TestClockNow(t *testing.T) {
+	if got, want := realtime().Now(), timeutil.Now(); want.Sub(got).Abs() > 10*time.Second {
+		t.Errorf("clock mismatch: got %v; timeutil says %v", got, want)
+	}
+}