Merge pull request #2604 from kolyshkin/fscommon-I

libct/cgroups/fscommon: nits

libcontainer/cgroups/fs2/hugetlb.go

@@ -43,7 +43,7 @@ func statHugeTlb(dirPath string, stats *cgroups.Stats) error {
 		usage := strings.Join([]string{"hugetlb", pagesize, "current"}, ".")
 		value, err := fscommon.GetCgroupParamUint(dirPath, usage)
 		if err != nil {
-			return errors.Wrapf(err, "failed to parse hugetlb.%s.current file", pagesize)
+			return err
 		}
 		hugetlbStats.Usage = value
 
@@ -51,11 +51,11 @@ func statHugeTlb(dirPath string, stats *cgroups.Stats) error {
 		filePath := filepath.Join(dirPath, fileName)
 		contents, err := ioutil.ReadFile(filePath)
 		if err != nil {
-			return errors.Wrapf(err, "failed to parse hugetlb.%s.events file", pagesize)
+			return errors.Wrap(err, "failed to read stats")
 		}
 		_, value, err = fscommon.GetCgroupParamKeyValue(string(contents))
 		if err != nil {
-			return errors.Wrapf(err, "failed to parse hugetlb.%s.events file", pagesize)
+			return errors.Wrap(err, "failed to parse "+fileName)
 		}
 		hugetlbStats.Failcnt = value
 

libcontainer/cgroups/fscommon/fscommon.go

@@ -12,6 +12,8 @@ import (
 	"golang.org/x/sys/unix"
 )
 
+// WriteFile writes data to a cgroup file in dir.
+// It is supposed to be used for cgroup files only.
 func WriteFile(dir, file, data string) error {
 	if dir == "" {
 		return errors.Errorf("no directory specified for %s", file)
@@ -26,6 +28,8 @@ func WriteFile(dir, file, data string) error {
 	return nil
 }
 
+// ReadFile reads data from a cgroup file in dir.
+// It is supposed to be used for cgroup files only.
 func ReadFile(dir, file string) (string, error) {
 	if dir == "" {
 		return "", errors.Errorf("no directory specified for %s", file)

libcontainer/cgroups/fscommon/utils.go

@@ -5,9 +5,7 @@ package fscommon
 import (
 	"errors"
 	"fmt"
-	"io/ioutil"
 	"math"
-	"path/filepath"
 	"strconv"
 	"strings"
 )
@@ -16,8 +14,9 @@ var (
 	ErrNotValidFormat = errors.New("line is not a valid key value format")
 )
 
-// Saturates negative values at zero and returns a uint64.
-// Due to kernel bugs, some of the memory cgroup stats can be negative.
+// ParseUint converts a string to an uint64 integer.
+// Negative values are returned at zero as, due to kernel bugs,
+// some of the memory cgroup stats can be negative.
 func ParseUint(s string, base, bitSize int) (uint64, error) {
 	value, err := strconv.ParseUint(s, base, bitSize)
 	if err != nil {
@@ -36,15 +35,16 @@ func ParseUint(s string, base, bitSize int) (uint64, error) {
 	return value, nil
 }
 
-// Parses a cgroup param and returns as name, value
-//  i.e. "io_service_bytes 1234" will return as io_service_bytes, 1234
+// 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 param value (%q) to uint64: %v", parts[1], err)
+			return "", 0, fmt.Errorf("unable to convert to uint64: %v", err)
 		}
 
 		return parts[0], value, nil
@@ -53,28 +53,28 @@ func GetCgroupParamKeyValue(t string) (string, uint64, error) {
 	}
 }
 
-// Gets a single uint64 value from the specified cgroup file.
-func GetCgroupParamUint(cgroupPath, cgroupFile string) (uint64, error) {
-	fileName := filepath.Join(cgroupPath, cgroupFile)
-	contents, err := ioutil.ReadFile(fileName)
+// GetCgroupParamUint reads a single uint64 value from the specified cgroup file.
+// If the value read is "max", the math.MaxUint64 is returned.
+func GetCgroupParamUint(path, file string) (uint64, error) {
+	contents, err := GetCgroupParamString(path, file)
 	if err != nil {
 		return 0, err
 	}
-	trimmed := strings.TrimSpace(string(contents))
-	if trimmed == "max" {
+	contents = strings.TrimSpace(contents)
+	if contents == "max" {
 		return math.MaxUint64, nil
 	}
 
-	res, err := ParseUint(trimmed, 10, 64)
+	res, err := ParseUint(contents, 10, 64)
 	if err != nil {
-		return res, fmt.Errorf("unable to parse %q as a uint from Cgroup file %q", string(contents), fileName)
+		return res, fmt.Errorf("unable to parse file %q", path+"/"+file)
 	}
 	return res, nil
 }
 
-// Gets a string value from the specified cgroup file
-func GetCgroupParamString(cgroupPath, cgroupFile string) (string, error) {
-	contents, err := ioutil.ReadFile(filepath.Join(cgroupPath, cgroupFile))
+// GetCgroupParamString reads a string from the specified cgroup file.
+func GetCgroupParamString(path, file string) (string, error) {
+	contents, err := ReadFile(path, file)
 	if err != nil {
 		return "", err
 	}