Optimize file system device filtering for simple case

receiver/hostmetricsreceiver/internal/scraper/filesystemscraper/filesystem_scraper.go

@@ -98,18 +98,13 @@ func (s *scraper) ScrapeMetrics(_ context.Context) (pdata.MetricSlice, error) {
 	}
 
 	// filter devices by name
-	filteredUsages := make([]*deviceUsage, 0, len(usages))
-	for _, usage := range usages {
-		if s.includeDevice(usage.deviceName) {
-			filteredUsages = append(filteredUsages, usage)
-		}
-	}
+	usages = s.filterByDevice(usages)
 
-	if len(filteredUsages) > 0 {
+	if len(usages) > 0 {
 		metrics.Resize(1 + systemSpecificMetricsLen)
 
-		initializeFileSystemUsageMetric(metrics.At(0), filteredUsages)
-		appendSystemSpecificMetrics(metrics, 1, filteredUsages)
+		initializeFileSystemUsageMetric(metrics.At(0), usages)
+		appendSystemSpecificMetrics(metrics, 1, usages)
 	}
 
 	if len(errors) > 0 {
@@ -137,6 +132,20 @@ func initializeFileSystemUsageDataPoint(dataPoint pdata.Int64DataPoint, deviceLa
 	dataPoint.SetValue(value)
 }
 
+func (s *scraper) filterByDevice(usages []*deviceUsage) []*deviceUsage {
+	if s.includeFS == nil && s.excludeFS == nil {
+		return usages
+	}
+
+	filteredUsages := make([]*deviceUsage, 0, len(usages))
+	for _, usage := range usages {
+		if s.includeDevice(usage.deviceName) {
+			filteredUsages = append(filteredUsages, usage)
+		}
+	}
+	return filteredUsages
+}
+
 func (s *scraper) includeDevice(deviceName string) bool {
 	return (s.includeFS == nil || s.includeFS.Matches(deviceName)) &&
 		(s.excludeFS == nil || !s.excludeFS.Matches(deviceName))

receiver/hostmetricsreceiver/internal/scraper/filesystemscraper/filesystem_scraper_test.go

@@ -31,20 +31,33 @@ import (
 
 func TestScrapeMetrics(t *testing.T) {
 	type testCase struct {
-		name           string
-		config         Config
-		partitionsFunc func(bool) ([]disk.PartitionStat, error)
-		usageFunc      func(string) (*disk.UsageStat, error)
-		expectMetrics  bool
-		newErrRegex    string
-		expectedErr    string
+		name                     string
+		config                   Config
+		partitionsFunc           func(bool) ([]disk.PartitionStat, error)
+		usageFunc                func(string) (*disk.UsageStat, error)
+		expectMetrics            bool
+		expectedDeviceDataPoints int
+		newErrRegex              string
+		expectedErr              string
 	}
 
 	testCases := []testCase{
 		{
 			name:          "Standard",
 			expectMetrics: true,
 		},
+		{
+			name:   "Include single process filter",
+			config: Config{Include: MatchConfig{filterset.Config{MatchType: "strict"}, []string{"a"}}},
+			partitionsFunc: func(bool) ([]disk.PartitionStat, error) {
+				return []disk.PartitionStat{{Device: "a"}, {Device: "b"}}, nil
+			},
+			usageFunc: func(string) (*disk.UsageStat, error) {
+				return &disk.UsageStat{}, nil
+			},
+			expectMetrics:            true,
+			expectedDeviceDataPoints: 1,
+		},
 		{
 			name:          "Include Filter that matches nothing",
 			config:        Config{Include: MatchConfig{filterset.Config{MatchType: "strict"}, []string{"@*^#&*$^#)"}}},
@@ -107,19 +120,23 @@ func TestScrapeMetrics(t *testing.T) {
 
 			assert.GreaterOrEqual(t, metrics.Len(), 1)
 
-			assertFileSystemUsageMetricValid(t, metrics.At(0), fileSystemUsageDescriptor)
+			assertFileSystemUsageMetricValid(t, metrics.At(0), fileSystemUsageDescriptor, test.expectedDeviceDataPoints*fileSystemStatesLen)
 
 			if isUnix() {
 				assertFileSystemUsageMetricHasUnixSpecificStateLabels(t, metrics.At(0))
-				assertFileSystemUsageMetricValid(t, metrics.At(1), fileSystemINodesUsageDescriptor)
+				assertFileSystemUsageMetricValid(t, metrics.At(1), fileSystemINodesUsageDescriptor, test.expectedDeviceDataPoints*2)
 			}
 		})
 	}
 }
 
-func assertFileSystemUsageMetricValid(t *testing.T, metric pdata.Metric, descriptor pdata.MetricDescriptor) {
+func assertFileSystemUsageMetricValid(t *testing.T, metric pdata.Metric, descriptor pdata.MetricDescriptor, expectedDeviceDataPoints int) {
 	internal.AssertDescriptorEqual(t, descriptor, metric.MetricDescriptor())
-	assert.GreaterOrEqual(t, metric.Int64DataPoints().Len(), 2)
+	if expectedDeviceDataPoints > 0 {
+		assert.Equal(t, expectedDeviceDataPoints, metric.Int64DataPoints().Len())
+	} else {
+		assert.GreaterOrEqual(t, metric.Int64DataPoints().Len(), fileSystemStatesLen)
+	}
 	internal.AssertInt64MetricLabelHasValue(t, metric, 0, stateLabelName, usedLabelValue)
 	internal.AssertInt64MetricLabelHasValue(t, metric, 1, stateLabelName, freeLabelValue)
 }