Differentiate ErrNoData and other errors (#1323, #1723)

Signed-off-by: Li Ling <liiling@google.com>

collector/pressure_linux.go

@@ -16,7 +16,9 @@
 package collector
 
 import (
+	"errors"
 	"fmt"
+	"os"
 
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
@@ -88,9 +90,12 @@ func (c *pressureStatsCollector) Update(ch chan<- prometheus.Metric) error {
 		level.Debug(c.logger).Log("msg", "collecting statistics for resource", "resource", res)
 		vals, err := c.fs.PSIStatsForResource(res)
 		if err != nil {
+			if errors.Is(err, os.ErrNotExist) {
 				level.Debug(c.logger).Log("msg", "pressure information is unavailable, you need a Linux kernel >= 4.20 and/or CONFIG_PSI enabled for your kernel")
 				return ErrNoData
 			}
+			return fmt.Errorf("failed to retrieve pressure stats: %w", err)
+		}
 		switch res {
 		case "cpu":
 			ch <- prometheus.MustNewConstMetric(c.cpu, prometheus.CounterValue, float64(vals.Some.Total)/1000.0/1000.0)

collector/rapl_linux.go

@@ -16,15 +16,20 @@
 package collector
 
 import (
+	"errors"
+	"fmt"
+	"os"
 	"strconv"
 
 	"github.com/go-kit/kit/log"
+	"github.com/go-kit/kit/log/level"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/procfs/sysfs"
 )
 
 type raplCollector struct {
 	fs     sysfs.FS
+	logger log.Logger
 }
 
 func init() {
@@ -41,6 +46,7 @@ func NewRaplCollector(logger log.Logger) (Collector, error) {
 
 	collector := raplCollector{
 		fs:     fs,
+		logger: logger,
 	}
 	return &collector, nil
 }
@@ -50,8 +56,12 @@ func (c *raplCollector) Update(ch chan<- prometheus.Metric) error {
 	// nil zones are fine when platform doesn't have powercap files present.
 	zones, err := sysfs.GetRaplZones(c.fs)
 	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			level.Debug(c.logger).Log("msg", "Platform doesn't have powercap files present", "err", err)
 			return ErrNoData
 		}
+		return fmt.Errorf("failed to retrieve rapl stats: %w", err)
+	}
 
 	for _, rz := range zones {
 		newMicrojoules, err := rz.GetEnergyMicrojoules()