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)

execdriver/chroot/driver.go

@@ -85,3 +85,7 @@ func (d *driver) Info(id string) execdriver.Info {
 func (d *driver) Name() string {
 	return fmt.Sprintf("%s-%s", DriverName, Version)
 }
+
+func (d *driver) GetPidsForContainer(id string) ([]int, error) {
+	return nil, fmt.Errorf("Not supported")
+}

execdriver/driver.go

@@ -61,9 +61,10 @@ type Info interface {
 type Driver interface {
 	Run(c *Command, startCallback StartCallback) (int, error) // Run executes the process and blocks until the process exits and returns the exit code
 	Kill(c *Command, sig int) error
-	Restore(c *Command) error // Wait and try to re-attach on an out of process command
-	Name() string             // Driver name
-	Info(id string) Info      // "temporary" hack (until we move state from core to plugins)
+	Restore(c *Command) error                     // Wait and try to re-attach on an out of process command
+	Name() string                                 // Driver name
+	Info(id string) Info                          // "temporary" hack (until we move state from core to plugins)
+	GetPidsForContainer(id string) ([]int, error) // Returns a list of pids for the given container.
 }
 
 // Network settings of the container

execdriver/lxc/driver.go

@@ -3,12 +3,14 @@ package lxc
 import (
 	"fmt"
 	"github.com/dotcloud/docker/execdriver"
+	"github.com/dotcloud/docker/pkg/cgroups"
 	"github.com/dotcloud/docker/utils"
 	"io/ioutil"
 	"log"
 	"os"
 	"os/exec"
 	"path"
+	"path/filepath"
 	"strconv"
 	"strings"
 	"syscall"
@@ -272,6 +274,45 @@ func (d *driver) Info(id string) execdriver.Info {
 	}
 }
 
+func (d *driver) GetPidsForContainer(id string) ([]int, error) {
+	pids := []int{}
+
+	// memory is chosen randomly, any cgroup used by docker works
+	subsystem := "memory"
+
+	cgroupRoot, err := cgroups.FindCgroupMountpoint(subsystem)
+	if err != nil {
+		return pids, err
+	}
+
+	cgroupDir, err := cgroups.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
+}
+
 func linkLxcStart(root string) error {
 	sourcePath, err := exec.LookPath("lxc-start")
 	if err != nil {

pkg/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
-}

server.go

@@ -7,7 +7,6 @@ import (
 	"github.com/dotcloud/docker/archive"
 	"github.com/dotcloud/docker/auth"
 	"github.com/dotcloud/docker/engine"
-	"github.com/dotcloud/docker/pkg/cgroups"
 	"github.com/dotcloud/docker/pkg/graphdb"
 	"github.com/dotcloud/docker/registry"
 	"github.com/dotcloud/docker/utils"
@@ -980,7 +979,7 @@ func (srv *Server) ContainerTop(job *engine.Job) engine.Status {
 			job.Errorf("Container %s is not running", name)
 			return engine.StatusErr
 		}
-		pids, err := cgroups.GetPidsForContainer(container.ID)
+		pids, err := srv.runtime.execDriver.GetPidsForContainer(container.ID)
 		if err != nil {
 			job.Error(err)
 			return engine.StatusErr