libct/cg/fscommon: add GetValueByKey

Generalize the libct/getValueFromCgroup() as fscommon.GetValueByKey(),
and document it.

No changes other than using fscommon.ParseUint to convert the value.

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

libcontainer/cgroups/fscommon/utils.go

@@ -53,6 +53,26 @@ func ParseKeyValue(t string) (string, uint64, error) {
 	return parts[0], 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
+// conversion.
+func GetValueByKey(path, file, key string) (uint64, error) {
+	content, err := ReadFile(path, file)
+	if err != nil {
+		return 0, err
+	}
+
+	lines := strings.Split(string(content), "\n")
+	for _, line := range lines {
+		arr := strings.Split(line, " ")
+		if len(arr) == 2 && arr[0] == key {
+			return ParseUint(arr[1], 10, 64)
+		}
+	}
+
+	return 0, nil
+}
+
 // 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) {

libcontainer/notify_linux_v2.go

@@ -4,8 +4,6 @@ package libcontainer
 
 import (
 	"path/filepath"
-	"strconv"
-	"strings"
 	"unsafe"
 
 	"github.com/opencontainers/runc/libcontainer/cgroups/fscommon"
@@ -14,22 +12,6 @@ import (
 	"golang.org/x/sys/unix"
 )
 
-func getValueFromCgroup(path, file, key string) (int, error) {
-	content, err := fscommon.ReadFile(path, file)
-	if err != nil {
-		return 0, err
-	}
-
-	lines := strings.Split(string(content), "\n")
-	for _, line := range lines {
-		arr := strings.Split(line, " ")
-		if len(arr) == 2 && arr[0] == key {
-			return strconv.Atoi(arr[1])
-		}
-	}
-	return 0, nil
-}
-
 func registerMemoryEventV2(cgDir, evName, cgEvName string) (<-chan struct{}, error) {
 	fd, err := unix.InotifyInit()
 	if err != nil {
@@ -77,12 +59,12 @@ func registerMemoryEventV2(cgDir, evName, cgEvName string) (<-chan struct{}, err
 				}
 				switch int(rawEvent.Wd) {
 				case evFd:
-					oom, err := getValueFromCgroup(cgDir, evName, "oom_kill")
+					oom, err := fscommon.GetValueByKey(cgDir, evName, "oom_kill")
 					if err != nil || oom > 0 {
 						ch <- struct{}{}
 					}
 				case cgFd:
-					pids, err := getValueFromCgroup(cgDir, cgEvName, "populated")
+					pids, err := fscommon.GetValueByKey(cgDir, cgEvName, "populated")
 					if err != nil || pids == 0 {
 						return
 					}