Move get pid into cgroup implementation

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)

libcontainer/cgroups/fs/apply_raw.go

@@ -103,6 +103,36 @@ func GetStats(c *cgroups.Cgroup, subsystem string, pid int) (map[string]float64,
 	return sys.Stats(d)
 }
 
+func GetPids(c *cgroups.Cgroup) ([]int, error) {
+	cgroupRoot, err := cgroups.FindCgroupMountpoint("cpu")
+	if err != nil {
+		return nil, err
+	}
+	cgroupRoot = filepath.Dir(cgroupRoot)
+
+	if _, err := os.Stat(cgroupRoot); err != nil {
+		return nil, fmt.Errorf("cgroup root %s not found", cgroupRoot)
+	}
+
+	cgroup := c.Name
+	if c.Parent != "" {
+		cgroup = filepath.Join(c.Parent, cgroup)
+	}
+
+	d := &data{
+		root:   cgroupRoot,
+		cgroup: cgroup,
+		c:      c,
+	}
+
+	dir, err := d.path("devices")
+	if err != nil {
+		return nil, err
+	}
+
+	return cgroups.ReadProcsFile(dir)
+}
+
 func (raw *data) parent(subsystem string) (string, error) {
 	initPath, err := cgroups.GetInitCgroupDir(subsystem)
 	if err != nil {

libcontainer/cgroups/fs/devices.go

@@ -1,9 +1,5 @@
 package fs
 
-import (
-	"os"
-)
-
 type devicesGroup struct {
 }
 
@@ -12,11 +8,6 @@ func (s *devicesGroup) Set(d *data) error {
 	if err != nil {
 		return err
 	}
-	defer func() {
-		if err != nil {
-			os.RemoveAll(dir)
-		}
-	}()
 
 	if !d.c.DeviceAccess {
 		if err := writeFile(dir, "devices.deny", "a"); err != nil {