Use strings.Cut where possible

exec.go

@@ -124,20 +124,17 @@ func getSubCgroupPaths(args []string) (map[string]string, error) {
 	paths := make(map[string]string, len(args))
 	for _, c := range args {
 		// Split into controller:path.
-		cs := strings.SplitN(c, ":", 3)
-		if len(cs) > 2 {
-			return nil, fmt.Errorf("invalid --cgroup argument: %s", c)
-		}
-		if len(cs) == 1 { // no controller: prefix
+		if ctr, path, ok := strings.Cut(c, ":"); ok {
+			// There may be a few comma-separated controllers.
+			for _, ctrl := range strings.Split(ctr, ",") {
+				paths[ctrl] = path
+			}
+		} else {
+			// No controller: prefix.
 			if len(args) != 1 {
 				return nil, fmt.Errorf("invalid --cgroup argument: %s (missing <controller>: prefix)", c)
 			}
 			paths[""] = c
-		} else {
-			// There may be a few comma-separated controllers.
-			for _, ctrl := range strings.Split(cs[0], ",") {
-				paths[ctrl] = cs[1]
-			}
 		}
 	}
 	return paths, nil

libcontainer/cgroups/fs/cpuacct.go

@@ -12,14 +12,7 @@ import (
 )
 
 const (
-	cgroupCpuacctStat     = "cpuacct.stat"
-	cgroupCpuacctUsageAll = "cpuacct.usage_all"
-
-	nanosecondsInSecond = 1000000000
-
-	userModeColumn              = 1
-	kernelModeColumn            = 2
-	cuacctUsageAllColumnsNumber = 3
+	nsInSec = 1000000000
 
 	// The value comes from `C.sysconf(C._SC_CLK_TCK)`, and
 	// on Linux it's a constant which is safe to be hard coded,
@@ -81,7 +74,7 @@ func getCpuUsageBreakdown(path string) (uint64, uint64, error) {
 	const (
 		userField   = "user"
 		systemField = "system"
-		file        = cgroupCpuacctStat
+		file        = "cpuacct.stat"
 	)
 
 	// Expected format:
@@ -103,7 +96,7 @@ func getCpuUsageBreakdown(path string) (uint64, uint64, error) {
 		return 0, 0, &parseError{Path: path, File: file, Err: err}
 	}
 
-	return (userModeUsage * nanosecondsInSecond) / clockTicks, (kernelModeUsage * nanosecondsInSecond) / clockTicks, nil
+	return (userModeUsage * nsInSec) / clockTicks, (kernelModeUsage * nsInSec) / clockTicks, nil
 }
 
 func getPercpuUsage(path string) ([]uint64, error) {
@@ -113,7 +106,6 @@ func getPercpuUsage(path string) ([]uint64, error) {
 	if err != nil {
 		return percpuUsage, err
 	}
-	// TODO: use strings.SplitN instead.
 	for _, value := range strings.Fields(data) {
 		value, err := strconv.ParseUint(value, 10, 64)
 		if err != nil {
@@ -127,7 +119,7 @@ func getPercpuUsage(path string) ([]uint64, error) {
 func getPercpuUsageInModes(path string) ([]uint64, []uint64, error) {
 	usageKernelMode := []uint64{}
 	usageUserMode := []uint64{}
-	const file = cgroupCpuacctUsageAll
+	const file = "cpuacct.usage_all"
 
 	fd, err := cgroups.OpenFile(path, file, os.O_RDONLY)
 	if os.IsNotExist(err) {
@@ -141,22 +133,24 @@ func getPercpuUsageInModes(path string) ([]uint64, []uint64, error) {
 	scanner.Scan() // skipping header line
 
 	for scanner.Scan() {
-		lineFields := strings.SplitN(scanner.Text(), " ", cuacctUsageAllColumnsNumber+1)
-		if len(lineFields) != cuacctUsageAllColumnsNumber {
+		// Each line is: cpu user system
+		fields := strings.SplitN(scanner.Text(), " ", 3)
+		if len(fields) != 3 {
 			continue
 		}
 
-		usageInKernelMode, err := strconv.ParseUint(lineFields[kernelModeColumn], 10, 64)
+		user, err := strconv.ParseUint(fields[1], 10, 64)
 		if err != nil {
 			return nil, nil, &parseError{Path: path, File: file, Err: err}
 		}
-		usageKernelMode = append(usageKernelMode, usageInKernelMode)
+		usageUserMode = append(usageUserMode, user)
 
-		usageInUserMode, err := strconv.ParseUint(lineFields[userModeColumn], 10, 64)
+		kernel, err := strconv.ParseUint(fields[2], 10, 64)
 		if err != nil {
 			return nil, nil, &parseError{Path: path, File: file, Err: err}
 		}
-		usageUserMode = append(usageUserMode, usageInUserMode)
+		usageKernelMode = append(usageKernelMode, kernel)
+
 	}
 	if err := scanner.Err(); err != nil {
 		return nil, nil, &parseError{Path: path, File: file, Err: err}

libcontainer/cgroups/fs/cpuacct_test.go

@@ -53,8 +53,8 @@ func TestCpuacctStats(t *testing.T) {
 			962250696038415, 981956408513304, 1002658817529022, 994937703492523,
 			874843781648690, 872544369885276, 870104915696359, 870202363887496,
 		},
-		UsageInKernelmode: (uint64(291429664) * nanosecondsInSecond) / clockTicks,
-		UsageInUsermode:   (uint64(452278264) * nanosecondsInSecond) / clockTicks,
+		UsageInKernelmode: (uint64(291429664) * nsInSec) / clockTicks,
+		UsageInUsermode:   (uint64(452278264) * nsInSec) / clockTicks,
 	}
 
 	if !reflect.DeepEqual(expectedStats, actualStats.CpuStats.CpuUsage) {
@@ -86,8 +86,8 @@ func TestCpuacctStatsWithoutUsageAll(t *testing.T) {
 		},
 		PercpuUsageInKernelmode: []uint64{},
 		PercpuUsageInUsermode:   []uint64{},
-		UsageInKernelmode:       (uint64(291429664) * nanosecondsInSecond) / clockTicks,
-		UsageInUsermode:         (uint64(452278264) * nanosecondsInSecond) / clockTicks,
+		UsageInKernelmode:       (uint64(291429664) * nsInSec) / clockTicks,
+		UsageInUsermode:         (uint64(452278264) * nsInSec) / clockTicks,
 	}
 
 	if !reflect.DeepEqual(expectedStats, actualStats.CpuStats.CpuUsage) {

libcontainer/cgroups/fs/cpuset.go

@@ -49,26 +49,23 @@ func getCpusetStat(path string, file string) ([]uint16, error) {
 	}
 
 	for _, s := range strings.Split(fileContent, ",") {
-		sp := strings.SplitN(s, "-", 3)
-		switch len(sp) {
-		case 3:
-			return extracted, &parseError{Path: path, File: file, Err: errors.New("extra dash")}
-		case 2:
-			min, err := strconv.ParseUint(sp[0], 10, 16)
+		fromStr, toStr, ok := strings.Cut(s, "-")
+		if ok {
+			from, err := strconv.ParseUint(fromStr, 10, 16)
 			if err != nil {
 				return extracted, &parseError{Path: path, File: file, Err: err}
 			}
-			max, err := strconv.ParseUint(sp[1], 10, 16)
+			to, err := strconv.ParseUint(toStr, 10, 16)
 			if err != nil {
 				return extracted, &parseError{Path: path, File: file, Err: err}
 			}
-			if min > max {
-				return extracted, &parseError{Path: path, File: file, Err: errors.New("invalid values, min > max")}
+			if from > to {
+				return extracted, &parseError{Path: path, File: file, Err: errors.New("invalid values, from > to")}
 			}
-			for i := min; i <= max; i++ {
+			for i := from; i <= to; i++ {
 				extracted = append(extracted, uint16(i))
 			}
-		case 1:
+		} else {
 			value, err := strconv.ParseUint(s, 10, 16)
 			if err != nil {
 				return extracted, &parseError{Path: path, File: file, Err: err}

libcontainer/cgroups/fs2/defaultpath.go

@@ -83,16 +83,9 @@ func parseCgroupFile(path string) (string, error) {
 func parseCgroupFromReader(r io.Reader) (string, error) {
 	s := bufio.NewScanner(r)
 	for s.Scan() {
-		var (
-			text  = s.Text()
-			parts = strings.SplitN(text, ":", 3)
-		)
-		if len(parts) < 3 {
-			return "", fmt.Errorf("invalid cgroup entry: %q", text)
-		}
-		// text is like "0::/user.slice/user-1001.slice/session-1.scope"
-		if parts[0] == "0" && parts[1] == "" {
-			return parts[2], nil
+		// "0::/user.slice/user-1001.slice/session-1.scope"
+		if path, ok := strings.CutPrefix(s.Text(), "0::"); ok {
+			return path, nil
 		}
 	}
 	if err := s.Err(); err != nil {

libcontainer/cgroups/fs2/fs2.go

@@ -238,11 +238,10 @@ func (m *Manager) setUnified(res map[string]string) error {
 			if errors.Is(err, os.ErrPermission) || errors.Is(err, os.ErrNotExist) {
 				// Check if a controller is available,
 				// to give more specific error if not.
-				sk := strings.SplitN(k, ".", 2)
-				if len(sk) != 2 {
+				c, _, ok := strings.Cut(k, ".")
+				if !ok {
 					return fmt.Errorf("unified resource %q must be in the form CONTROLLER.PARAMETER", k)
 				}
-				c := sk[0]
 				if _, ok := m.controllers[c]; !ok && c != "cgroup" {
 					return fmt.Errorf("unified resource %q can't be set: controller %q not available", k, c)
 				}

libcontainer/cgroups/fs2/psi.go

@@ -58,29 +58,29 @@ func statPSI(dirPath string, file string) (*cgroups.PSIStats, error) {
 func parsePSIData(psi []string) (cgroups.PSIData, error) {
 	data := cgroups.PSIData{}
 	for _, f := range psi {
-		kv := strings.SplitN(f, "=", 2)
-		if len(kv) != 2 {
+		key, val, ok := strings.Cut(f, "=")
+		if !ok {
 			return data, fmt.Errorf("invalid psi data: %q", f)
 		}
 		var pv *float64
-		switch kv[0] {
+		switch key {
 		case "avg10":
 			pv = &data.Avg10
 		case "avg60":
 			pv = &data.Avg60
 		case "avg300":
 			pv = &data.Avg300
 		case "total":
-			v, err := strconv.ParseUint(kv[1], 10, 64)
+			v, err := strconv.ParseUint(val, 10, 64)
 			if err != nil {
-				return data, fmt.Errorf("invalid %s PSI value: %w", kv[0], err)
+				return data, fmt.Errorf("invalid %s PSI value: %w", key, err)
 			}
 			data.Total = v
 		}
 		if pv != nil {
-			v, err := strconv.ParseFloat(kv[1], 64)
+			v, err := strconv.ParseFloat(val, 64)
 			if err != nil {
-				return data, fmt.Errorf("invalid %s PSI value: %w", kv[0], err)
+				return data, fmt.Errorf("invalid %s PSI value: %w", key, err)
 			}
 			*pv = v
 		}

libcontainer/cgroups/fscommon/rdma.go

@@ -17,14 +17,12 @@ import (
 func parseRdmaKV(raw string, entry *cgroups.RdmaEntry) error {
 	var value uint32
 
-	parts := strings.SplitN(raw, "=", 3)
+	k, v, ok := strings.Cut(raw, "=")
 
-	if len(parts) != 2 {
+	if !ok {
 		return errors.New("Unable to parse RDMA entry")
 	}
 
-	k, v := parts[0], parts[1]
-
 	if v == "max" {
 		value = math.MaxUint32
 	} else {
@@ -34,9 +32,10 @@ func parseRdmaKV(raw string, entry *cgroups.RdmaEntry) error {
 		}
 		value = uint32(val64)
 	}
-	if k == "hca_handle" {
+	switch k {
+	case "hca_handle":
 		entry.HcaHandles = value
-	} else if k == "hca_object" {
+	case "hca_object":
 		entry.HcaObjects = value
 	}
 

libcontainer/cgroups/fscommon/utils.go

@@ -56,24 +56,24 @@ func ParseUint(s string, base, bitSize int) (uint64, error) {
 
 // ParseKeyValue parses a space-separated "name value" kind of cgroup
 // parameter and returns its key as a string, and its value as uint64
-// (ParseUint is used to convert the value). For example,
+// (using [ParseUint] to convert the value). For example,
 // "io_service_bytes 1234" will be returned as "io_service_bytes", 1234.
 func ParseKeyValue(t string) (string, uint64, error) {
-	parts := strings.SplitN(t, " ", 3)
-	if len(parts) != 2 {
+	key, val, ok := strings.Cut(t, " ")
+	if !ok {
 		return "", 0, fmt.Errorf("line %q is not in key value format", t)
 	}
 
-	value, err := ParseUint(parts[1], 10, 64)
+	value, err := ParseUint(val, 10, 64)
 	if err != nil {
 		return "", 0, err
 	}
 
-	return parts[0], value, nil
+	return key, value, nil
 }
 
 // GetValueByKey reads a key-value pairs from the specified cgroup file,
-// and returns a value of the specified key. ParseUint is used for value
+// and returns a value of the specified key. [ParseUint] is used for value
 // conversion.
 func GetValueByKey(path, file, key string) (uint64, error) {
 	content, err := cgroups.ReadFile(path, file)
@@ -83,9 +83,9 @@ func GetValueByKey(path, file, key string) (uint64, error) {
 
 	lines := strings.Split(content, "\n")
 	for _, line := range lines {
-		arr := strings.Split(line, " ")
-		if len(arr) == 2 && arr[0] == key {
-			val, err := ParseUint(arr[1], 10, 64)
+		k, v, ok := strings.Cut(line, " ")
+		if ok && k == key {
+			val, err := ParseUint(v, 10, 64)
 			if err != nil {
 				err = &ParseError{Path: path, File: file, Err: err}
 			}