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 {

libcontainer/cgroups/systemd/apply_nosystemd.go

@@ -12,6 +12,10 @@ func UseSystemd() bool {
 	return false
 }
 
-func Apply(c *Cgroup, pid int) (cgroups.ActiveCgroup, error) {
+func Apply(c *cgroups.Cgroup, pid int) (cgroups.ActiveCgroup, error) {
+	return nil, fmt.Errorf("Systemd not supported")
+}
+
+func GetPids(c *cgroups.Cgroup) ([]int, error) {
 	return nil, fmt.Errorf("Systemd not supported")
 }

libcontainer/cgroups/systemd/apply_systemd.go

@@ -3,6 +3,7 @@
 package systemd
 
 import (
+	"fmt"
 	"io/ioutil"
 	"os"
 	"path/filepath"
@@ -78,7 +79,7 @@ type cgroupArg struct {
 
 func Apply(c *cgroups.Cgroup, pid int) (cgroups.ActiveCgroup, error) {
 	var (
-		unitName   = c.Parent + "-" + c.Name + ".scope"
+		unitName   = getUnitName(c)
 		slice      = "system.slice"
 		properties []systemd1.Property
 		cpuArgs    []cgroupArg
@@ -303,3 +304,24 @@ func (c *systemdCgroup) Cleanup() error {
 
 	return nil
 }
+
+func GetPids(c *cgroups.Cgroup) ([]int, error) {
+	unitName := getUnitName(c)
+
+	mountpoint, err := cgroups.FindCgroupMountpoint("cpu")
+	if err != nil {
+		return nil, err
+	}
+
+	props, err := theConn.GetUnitTypeProperties(unitName, getIfaceForUnit(unitName))
+	if err != nil {
+		return nil, err
+	}
+	cgroup := props["ControlGroup"].(string)
+
+	return cgroups.ReadProcsFile(filepath.Join(mountpoint, cgroup))
+}
+
+func getUnitName(c *cgroups.Cgroup) string {
+	return fmt.Sprintf("%s-%s.scope", c.Parent, c.Name)
+}

libcontainer/cgroups/utils.go

@@ -4,6 +4,8 @@ import (
 	"bufio"
 	"io"
 	"os"
+	"path/filepath"
+	"strconv"
 	"strings"
 
 	"github.com/dotcloud/docker/pkg/mount"
@@ -49,6 +51,30 @@ func GetInitCgroupDir(subsystem string) (string, error) {
 	return parseCgroupFile(subsystem, f)
 }
 
+func ReadProcsFile(dir string) ([]int, error) {
+	f, err := os.Open(filepath.Join(dir, "cgroup.procs"))
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	var (
+		s   = bufio.NewScanner(f)
+		out = []int{}
+	)
+
+	for s.Scan() {
+		if t := s.Text(); t != "" {
+			pid, err := strconv.Atoi(t)
+			if err != nil {
+				return nil, err
+			}
+			out = append(out, pid)
+		}
+	}
+	return out, nil
+}
+
 func parseCgroupFile(subsystem string, r io.Reader) (string, error) {
 	s := bufio.NewScanner(r)
 	for s.Scan() {