libct/cg/fscommon: rename/facelift GetCgroupParamKeyValue

1. This is the only function in the package with Get prefix
   that does not read a file (but parses a string). Rename
   accordingly, and convert the callers.

	GetCgroupParamKeyValue -> ParseKeyValue

2. Use strings.Split rather than strings.Fields. Split by a space
   is 2x faster, plus we can limit the splitting. The downside is
   we have to strip a newline in one of the callers.

3. Improve the doc and the code flow.

4. Fix a test case with invalid data (spaces at BOL).

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/cgroups/fs/cpu.go

@@ -97,7 +97,7 @@ func (s *CpuGroup) GetStats(path string, stats *cgroups.Stats) error {
 
 	sc := bufio.NewScanner(f)
 	for sc.Scan() {
-		t, v, err := fscommon.GetCgroupParamKeyValue(sc.Text())
+		t, v, err := fscommon.ParseKeyValue(sc.Text())
 		if err != nil {
 			return err
 		}

libcontainer/cgroups/fs/cpu_test.go

@@ -112,7 +112,7 @@ func TestCpuStats(t *testing.T) {
 		throttledTime = uint64(18446744073709551615)
 	)
 
-	cpuStatContent := fmt.Sprintf("nr_periods %d\n nr_throttled %d\n throttled_time %d\n",
+	cpuStatContent := fmt.Sprintf("nr_periods %d\nnr_throttled %d\nthrottled_time %d\n",
 		nrPeriods, nrThrottled, throttledTime)
 	helper.writeFileContents(map[string]string{
 		"cpu.stat": cpuStatContent,

libcontainer/cgroups/fs/memory.go

@@ -188,7 +188,7 @@ func (s *MemoryGroup) GetStats(path string, stats *cgroups.Stats) error {
 
 	sc := bufio.NewScanner(statsFile)
 	for sc.Scan() {
-		t, v, err := fscommon.GetCgroupParamKeyValue(sc.Text())
+		t, v, err := fscommon.ParseKeyValue(sc.Text())
 		if err != nil {
 			return fmt.Errorf("failed to parse memory.stat (%q) - %v", sc.Text(), err)
 		}

libcontainer/cgroups/fs2/cpu.go

@@ -57,7 +57,7 @@ func statCpu(dirPath string, stats *cgroups.Stats) error {
 
 	sc := bufio.NewScanner(f)
 	for sc.Scan() {
-		t, v, err := fscommon.GetCgroupParamKeyValue(sc.Text())
+		t, v, err := fscommon.ParseKeyValue(sc.Text())
 		if err != nil {
 			return err
 		}

libcontainer/cgroups/fs2/hugetlb.go

@@ -4,6 +4,7 @@ package fs2
 
 import (
 	"strconv"
+	"strings"
 
 	"github.com/pkg/errors"
 
@@ -48,7 +49,7 @@ func statHugeTlb(dirPath string, stats *cgroups.Stats) error {
 		if err != nil {
 			return errors.Wrap(err, "failed to read stats")
 		}
-		_, value, err = fscommon.GetCgroupParamKeyValue(contents)
+		_, value, err = fscommon.ParseKeyValue(strings.TrimSuffix(contents, "\n"))
 		if err != nil {
 			return errors.Wrap(err, "failed to parse "+fileName)
 		}

libcontainer/cgroups/fs2/memory.go

@@ -82,7 +82,7 @@ func statMemory(dirPath string, stats *cgroups.Stats) error {
 
 	sc := bufio.NewScanner(statsFile)
 	for sc.Scan() {
-		t, v, err := fscommon.GetCgroupParamKeyValue(sc.Text())
+		t, v, err := fscommon.ParseKeyValue(sc.Text())
 		if err != nil {
 			return errors.Wrapf(err, "failed to parse memory.stat (%q)", sc.Text())
 		}

libcontainer/cgroups/fscommon/utils.go

@@ -35,22 +35,22 @@ func ParseUint(s string, base, bitSize int) (uint64, error) {
 	return value, nil
 }
 
-// GetCgroupParamKeyValue parses a space-separated "name value" kind of cgroup
-// parameter and returns its components. For example, "io_service_bytes 1234"
-// will return as "io_service_bytes", 1234.
-func GetCgroupParamKeyValue(t string) (string, uint64, error) {
-	parts := strings.Fields(t)
-	switch len(parts) {
-	case 2:
-		value, err := ParseUint(parts[1], 10, 64)
-		if err != nil {
-			return "", 0, fmt.Errorf("unable to convert to uint64: %v", err)
-		}
-
-		return parts[0], value, nil
-	default:
-		return "", 0, ErrNotValidFormat
+// 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,
+// "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 {
+		return "", 0, fmt.Errorf("line %q is not in key value format", t)
 	}
+
+	value, err := ParseUint(parts[1], 10, 64)
+	if err != nil {
+		return "", 0, fmt.Errorf("unable to convert to uint64: %v", err)
+	}
+
+	return parts[0], value, nil
 }
 
 // GetCgroupParamUint reads a single uint64 value from the specified cgroup file.