tetragon: Add missed stats to kprobemetrics package

Add tetragon_missed_probes_total metric to kprobemetrics package and
logic to store and collect missed stats.

The missed stats are supported for kprobes and stored per function
and policy name, like for generic kprobes:

  tetragon_missed_probes_total{attach="__x64_sys_close",policy="syswritefollowfdpsswd"} 453
  tetragon_missed_probes_total{attach="__x64_sys_write",policy="syswritefollowfdpsswd"} 455
  tetragon_missed_probes_total{attach="fd_install",policy="syswritefollowfdpsswd"} 451

and multi kprobes:

  tetragon_missed_probes_total{attach="kprobe_multi (3 functions)",policy="syswritefollowfdpsswd"} 41

Signed-off-by: Jiri Olsa <jolsa@kernel.org>

pkg/metrics/kprobemetrics/collector.go

@@ -0,0 +1,87 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright Authors of Tetragon
+
+package kprobemetrics
+
+import (
+	"github.com/cilium/ebpf/link"
+	"github.com/cilium/tetragon/pkg/bpf"
+	"github.com/cilium/tetragon/pkg/sensors"
+	"github.com/cilium/tetragon/pkg/sensors/base"
+	"github.com/prometheus/client_golang/prometheus"
+	"golang.org/x/sys/unix"
+)
+
+// bpfCollector implements prometheus.Collector. It collects metrics directly from BPF maps.
+type bpfCollector struct{}
+
+func NewBPFCollector() prometheus.Collector {
+	return &bpfCollector{}
+}
+
+func (c *bpfCollector) Describe(ch chan<- *prometheus.Desc) {
+	ch <- MissedProbes.Desc()
+}
+
+func (c *bpfCollector) Collect(ch chan<- prometheus.Metric) {
+	allPrograms := sensors.AllPrograms()
+	for _, prog := range allPrograms {
+
+		if prog.Link == nil {
+			continue
+		}
+
+		info, err := prog.Link.Info()
+		if err != nil {
+			continue
+		}
+
+		missed := uint64(0)
+
+		switch info.Type {
+		case link.PerfEventType:
+			if bpf.HasMissedStatsPerfEvent() {
+				pevent := info.PerfEvent()
+				switch pevent.Type {
+				case unix.BPF_PERF_EVENT_KPROBE, unix.BPF_PERF_EVENT_KRETPROBE:
+					kprobe := pevent.Kprobe()
+					missed, _ = kprobe.Missed()
+				}
+			} else {
+				missed = base.GetKprobeMissed(prog.Link)
+
+			}
+		case link.KprobeMultiType:
+			if bpf.HasMissedStatsKprobeMulti() {
+				kmulti := info.KprobeMulti()
+				missed, _ = kmulti.Missed()
+			} else {
+				// warn
+			}
+		default:
+		}
+
+		ch <- MissedProbes.MustMetric(float64(missed), prog.Policy, prog.Attach)
+	}
+}
+
+// bpfZeroCollector implements prometheus.Collector. It collects "zero" metrics.
+// It's intended to be used when BPF metrics are not collected, but we still want
+// Prometheus metrics to be exposed.
+type bpfZeroCollector struct {
+	bpfCollector
+}
+
+func NewBPFZeroCollector() prometheus.Collector {
+	return &bpfZeroCollector{
+		bpfCollector: bpfCollector{},
+	}
+}
+
+func (c *bpfZeroCollector) Describe(ch chan<- *prometheus.Desc) {
+	c.bpfCollector.Describe(ch)
+}
+
+func (c *bpfZeroCollector) Collect(ch chan<- prometheus.Metric) {
+	ch <- MissedProbes.MustMetric(0, "policy", "attach")
+}

pkg/metrics/kprobemetrics/missed.go

@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright Authors of Tetragon
+
+package kprobemetrics
+
+import (
+	"github.com/cilium/tetragon/pkg/metrics"
+	"github.com/cilium/tetragon/pkg/metrics/consts"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+var (
+	MissedProbes = metrics.NewBPFCounter(prometheus.NewDesc(
+		prometheus.BuildFQName(consts.MetricsNamespace, "", "missed_probes_total"),
+		"The total number of Tetragon probe missed per program.",
+		[]string{"policy", "attach"}, nil,
+	))
+)

pkg/metrics/metricsconfig/initmetrics.go

@@ -59,6 +59,7 @@ func initAllHealthMetrics(registry *prometheus.Registry) {
 	// register custom collectors
 	registry.MustRegister(observer.NewBPFCollector())
 	registry.MustRegister(eventmetrics.NewBPFCollector())
+	registry.MustRegister(kprobemetrics.NewBPFCollector())
 }
 
 func InitHealthMetricsForDocs(registry *prometheus.Registry) {
@@ -70,6 +71,7 @@ func InitHealthMetricsForDocs(registry *prometheus.Registry) {
 	// register custom zero collectors
 	registry.MustRegister(observer.NewBPFZeroCollector())
 	registry.MustRegister(eventmetrics.NewBPFZeroCollector())
+	registry.MustRegister(kprobemetrics.NewBPFZeroCollector())
 }
 
 func initResourcesMetrics(registry *prometheus.Registry) {