container: GetCgroupSubsystems: simplify

Instead of creating an intermediate map to remove specific mounts based
on MetricSet, amend the supportedSubsystems map to have information
about which subsystem reports which metrics.

Based on that info, the check whether the subsystem is needed or not
becomes much simpler.

Signed-off-by: Kir Kolyshkin <[email protected]>

Author: kolyshkin

container/libcontainer/helpers.go

@@ -39,38 +39,7 @@ func GetCgroupSubsystems(includedMetrics container.MetricSet) (map[string]string
 		return nil, err
 	}
 
-	disableCgroups := map[string]struct{}{}
-
-	if !includedMetrics.Has(container.DiskIOMetrics) {
-		disableCgroups["blkio"] = struct{}{}
-		disableCgroups["io"] = struct{}{}
-	}
-
-	if !includedMetrics.Has(container.CpuUsageMetrics) {
-		disableCgroups["cpu"] = struct{}{}
-	}
-
-	if !includedMetrics.Has(container.CPUSetMetrics) {
-		disableCgroups["cpuset"] = struct{}{}
-	}
-
-	if !includedMetrics.Has(container.HugetlbUsageMetrics) {
-		disableCgroups["hugetlb"] = struct{}{}
-	}
-
-	if !includedMetrics.Has(container.MemoryUsageMetrics) {
-		disableCgroups["memory"] = struct{}{}
-	}
-
-	if !includedMetrics.Has(container.PerfMetrics) {
-		disableCgroups["perf_event"] = struct{}{}
-	}
-
-	if !includedMetrics.Has(container.ProcessMetrics) {
-		disableCgroups["pids"] = struct{}{}
-	}
-
-	return getCgroupSubsystemsHelper(allCgroups, disableCgroups)
+	return getCgroupSubsystemsHelper(allCgroups, includedMetrics)
 }
 
 // Get information about all the cgroup subsystems.
@@ -81,11 +50,10 @@ func GetAllCgroupSubsystems() (map[string]string, error) {
 		return nil, err
 	}
 
-	emptyDisableCgroups := map[string]struct{}{}
-	return getCgroupSubsystemsHelper(allCgroups, emptyDisableCgroups)
+	return getCgroupSubsystemsHelper(allCgroups, nil)
 }
 
-func getCgroupSubsystemsHelper(allCgroups []cgroups.Mount, disableCgroups map[string]struct{}) (map[string]string, error) {
+func getCgroupSubsystemsHelper(allCgroups []cgroups.Mount, includedMetrics container.MetricSet) (map[string]string, error) {
 	if len(allCgroups) == 0 {
 		return nil, fmt.Errorf("failed to find cgroup mounts")
 	}
@@ -94,11 +62,7 @@ func getCgroupSubsystemsHelper(allCgroups []cgroups.Mount, disableCgroups map[st
 	mountPoints := make(map[string]string, len(allCgroups))
 	for _, mount := range allCgroups {
 		for _, subsystem := range mount.Subsystems {
-			if _, exists := disableCgroups[subsystem]; exists {
-				continue
-			}
-			if _, ok := supportedSubsystems[subsystem]; !ok {
-				// Unsupported subsystem
+			if !needSubsys(subsystem, includedMetrics) {
 				continue
 			}
 			if _, ok := mountPoints[subsystem]; ok {
@@ -113,18 +77,34 @@ func getCgroupSubsystemsHelper(allCgroups []cgroups.Mount, disableCgroups map[st
 	return mountPoints, nil
 }
 
-// Cgroup subsystems we support listing (should be the minimal set we need stats from).
-var supportedSubsystems map[string]struct{} = map[string]struct{}{
-	"cpu":        {},
-	"cpuacct":    {},
-	"memory":     {},
-	"hugetlb":    {},
-	"pids":       {},
-	"cpuset":     {},
-	"blkio":      {},
-	"io":         {},
-	"devices":    {},
-	"perf_event": {},
+// A map of cgroup subsystems we support listing (should be the minimal set
+// we need stats from) to a respective MetricKind.
+var supportedSubsystems = map[string]container.MetricKind{
+	"cpu":        container.CpuUsageMetrics,
+	"cpuacct":    container.CpuUsageMetrics,
+	"memory":     container.MemoryUsageMetrics,
+	"hugetlb":    container.HugetlbUsageMetrics,
+	"pids":       container.ProcessMetrics,
+	"cpuset":     container.CPUSetMetrics,
+	"blkio":      container.DiskIOMetrics,
+	"io":         container.DiskIOMetrics,
+	"devices":    "",
+	"perf_event": container.PerfMetrics,
+}
+
+// Check if this cgroup subsystem/controller is of use.
+func needSubsys(name string, metrics container.MetricSet) bool {
+	// Check if supported.
+	metric, supported := supportedSubsystems[name]
+	if !supported {
+		return false
+	}
+	// Check if needed.
+	if metrics == nil || metric == "" {
+		return true
+	}
+
+	return metrics.Has(metric)
 }
 
 func diskStatsCopy0(major, minor uint64) *info.PerDiskStats {

container/libcontainer/helpers_test.go

@@ -90,7 +90,7 @@ func TestGetCgroupSubsystems(t *testing.T) {
 	}
 
 	for i, testCase := range testCases {
-		subSystems, err := getCgroupSubsystemsHelper(testCase.mounts, map[string]struct{}{})
+		subSystems, err := getCgroupSubsystemsHelper(testCase.mounts, nil)
 		if testCase.err {
 			if err == nil {
 				t.Fatalf("[case %d] Expected error but didn't get one", i)