metrics: Do not return when we cannot find a _stats map

In Tetragon, we have maps ending with _stats that contain metadata about
the main maps. An example is that we have execve_map and
execve_map_stats that contains errors and other information related to
execve_map map.

Now when we fail to open the _stats map, we just stop the loop and we
can possibly miss to check for other maps. This patch change that and
tries for the next map.

Additionally we do not try to collect stats for maps that already end up
with _stats as this would result in _stats_stats map names.

Signed-off-by: Anastasios Papagiannis <tasos.papagiannnis@gmail.com>

pkg/observer/observer_stats.go

@@ -6,12 +6,15 @@ package observer
 import (
 	"fmt"
 	"path/filepath"
+	"strings"
 
 	"github.com/cilium/ebpf"
+	"github.com/cilium/tetragon/pkg/logger"
 	"github.com/cilium/tetragon/pkg/metrics/mapmetrics"
 	"github.com/cilium/tetragon/pkg/option"
 	"github.com/cilium/tetragon/pkg/sensors"
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/sirupsen/logrus"
 )
 
 // bpfCollector implements prometheus.Collector. It collects metrics directly from BPF maps.
@@ -27,19 +30,33 @@ func (c *bpfCollector) Describe(ch chan<- *prometheus.Desc) {
 }
 
 func (c *bpfCollector) Collect(ch chan<- prometheus.Metric) {
+	statsSuffix := "_stats"
 	for _, m := range sensors.AllMaps {
 		name := m.Name
 		pin := filepath.Join(option.Config.MapDir, name)
-		pinStats := pin + "_stats"
+		// Skip map names that end up with _stats.
+		// This will result in _stats_stats suffixes that we don't care about
+		if strings.HasSuffix(pin, statsSuffix) {
+			continue
+		}
+		pinStats := pin + statsSuffix
 
 		mapLinkStats, err := ebpf.LoadPinnedMap(pinStats, nil)
 		if err != nil {
-			return
+			// If we fail to open the map with _stats suffix
+			// continue to the next map.
+			continue
 		}
 		defer mapLinkStats.Close()
 		mapLink, err := ebpf.LoadPinnedMap(pin, nil)
 		if err != nil {
-			return
+			// We have already opened the map with _stats suffix
+			// so we don't expect that to fail.
+			logger.GetLogger().WithFields(logrus.Fields{
+				"MapName":      pin,
+				"StatsMapName": pinStats,
+			}).Warn("Failed to open the corresponding map for an existing stats map.")
+			continue
 		}
 		defer mapLink.Close()