libct/cg: improve GetAllPids and readProcsFile

Since every cgroup directory is guaranteed to have cgroup.procs file,
we don't have to do filename comparison in GetAllPids() and just read
cgroup.procs in every directory.

While at it, switch readProcsFile to use our own OpenFile.

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

Author: kolyshkin

libcontainer/cgroups/getallpids.go

@@ -16,7 +16,7 @@ func GetAllPids(path string) ([]int, error) {
 		if iErr != nil {
 			return iErr
 		}
-		if info.IsDir() || info.Name() != CgroupProcesses {
+		if !info.IsDir() {
 			return nil
 		}
 		cPids, err := readProcsFile(p)

libcontainer/cgroups/utils.go

@@ -118,8 +118,8 @@ func GetAllSubsystems() ([]string, error) {
 	return subsystems, nil
 }
 
-func readProcsFile(file string) ([]int, error) {
-	f, err := os.Open(file)
+func readProcsFile(dir string) ([]int, error) {
+	f, err := OpenFile(dir, CgroupProcesses, os.O_RDONLY)
 	if err != nil {
 		return nil, err
 	}
@@ -336,7 +336,7 @@ func getHugePageSizeFromFilenames(fileNames []string) ([]string, error) {
 
 // GetPids returns all pids, that were added to cgroup at path.
 func GetPids(dir string) ([]int, error) {
-	return readProcsFile(filepath.Join(dir, CgroupProcesses))
+	return readProcsFile(dir)
 }
 
 // WriteCgroupProc writes the specified pid into the cgroup's cgroup.procs file