execdriver: Make GetPidsForContainer() a driver call

The current implementation is lxc specific.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)

cgroups/cgroups.go

@@ -5,10 +5,7 @@ import (
 	"fmt"
 	"github.com/dotcloud/docker/pkg/mount"
 	"io"
-	"io/ioutil"
 	"os"
-	"path/filepath"
-	"strconv"
 	"strings"
 )
 
@@ -33,7 +30,7 @@ func FindCgroupMountpoint(subsystem string) (string, error) {
 }
 
 // Returns the relative path to the cgroup docker is running in.
-func getThisCgroupDir(subsystem string) (string, error) {
+func GetThisCgroupDir(subsystem string) (string, error) {
 	f, err := os.Open("/proc/self/cgroup")
 	if err != nil {
 		return "", err
@@ -58,43 +55,3 @@ func parseCgroupFile(subsystem string, r io.Reader) (string, error) {
 	}
 	return "", fmt.Errorf("cgroup '%s' not found in /proc/self/cgroup", subsystem)
 }
-
-// Returns a list of pids for the given container.
-func GetPidsForContainer(id string) ([]int, error) {
-	pids := []int{}
-
-	// memory is chosen randomly, any cgroup used by docker works
-	subsystem := "memory"
-
-	cgroupRoot, err := FindCgroupMountpoint(subsystem)
-	if err != nil {
-		return pids, err
-	}
-
-	cgroupDir, err := getThisCgroupDir(subsystem)
-	if err != nil {
-		return pids, err
-	}
-
-	filename := filepath.Join(cgroupRoot, cgroupDir, id, "tasks")
-	if _, err := os.Stat(filename); os.IsNotExist(err) {
-		// With more recent lxc versions use, cgroup will be in lxc/
-		filename = filepath.Join(cgroupRoot, cgroupDir, "lxc", id, "tasks")
-	}
-
-	output, err := ioutil.ReadFile(filename)
-	if err != nil {
-		return pids, err
-	}
-	for _, p := range strings.Split(string(output), "\n") {
-		if len(p) == 0 {
-			continue
-		}
-		pid, err := strconv.Atoi(p)
-		if err != nil {
-			return pids, fmt.Errorf("Invalid pid '%s': %s", p, err)
-		}
-		pids = append(pids, pid)
-	}
-	return pids, nil
-}