Ignore not exist errors for joining default subsystems

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

pkg/cgroups/apply_raw.go

@@ -135,6 +135,7 @@ func (raw *rawCgroup) setupDevices(c *Cgroup, pid int) (err error) {
 
 func (raw *rawCgroup) setupMemory(c *Cgroup, pid int) (err error) {
 	dir, err := raw.join("memory", pid)
+	// only return an error for memory if it was not specified
 	if err != nil && (c.Memory != 0 || c.MemorySwap != 0) {
 		return err
 	}
@@ -145,7 +146,6 @@ func (raw *rawCgroup) setupMemory(c *Cgroup, pid int) (err error) {
 	}()
 
 	if c.Memory != 0 || c.MemorySwap != 0 {
-
 		if c.Memory != 0 {
 			if err := writeFile(dir, "memory.limit_in_bytes", strconv.FormatInt(c.Memory, 10)); err != nil {
 				return err
@@ -202,26 +202,34 @@ func (raw *rawCgroup) setupCpuset(c *Cgroup, pid int) (err error) {
 
 func (raw *rawCgroup) setupCpuacct(c *Cgroup, pid int) error {
 	// we just want to join this group even though we don't set anything
-	_, err := raw.join("cpuacct", pid)
-	return err
+	if _, err := raw.join("cpuacct", pid); err != nil && err != ErrNotFound {
+		return err
+	}
+	return nil
 }
 
 func (raw *rawCgroup) setupBlkio(c *Cgroup, pid int) error {
 	// we just want to join this group even though we don't set anything
-	_, err := raw.join("blkio", pid)
-	return err
+	if _, err := raw.join("blkio", pid); err != nil && err != ErrNotFound {
+		return err
+	}
+	return nil
 }
 
 func (raw *rawCgroup) setupPerfevent(c *Cgroup, pid int) error {
 	// we just want to join this group even though we don't set anything
-	_, err := raw.join("perf_event", pid)
-	return err
+	if _, err := raw.join("perf_event", pid); err != nil && err != ErrNotFound {
+		return err
+	}
+	return nil
 }
 
 func (raw *rawCgroup) setupFreezer(c *Cgroup, pid int) error {
 	// we just want to join this group even though we don't set anything
-	_, err := raw.join("freezer", pid)
-	return err
+	if _, err := raw.join("freezer", pid); err != nil && err != ErrNotFound {
+		return err
+	}
+	return nil
 }
 
 func (raw *rawCgroup) Cleanup() error {

pkg/cgroups/cgroups.go

@@ -2,7 +2,7 @@ package cgroups
 
 import (
 	"bufio"
-	"fmt"
+	"errors"
 	"github.com/dotcloud/docker/pkg/mount"
 	"io"
 	"io/ioutil"
@@ -11,6 +11,10 @@ import (
 	"strings"
 )
 
+var (
+	ErrNotFound = errors.New("mountpoint not found")
+)
+
 type Cgroup struct {
 	Name   string `json:"name,omitempty"`
 	Parent string `json:"parent,omitempty"`
@@ -44,7 +48,7 @@ func FindCgroupMountpoint(subsystem string) (string, error) {
 			}
 		}
 	}
-	return "", fmt.Errorf("cgroup mountpoint not found for %s", subsystem)
+	return "", ErrNotFound
 }
 
 // Returns the relative path to the cgroup docker is running in.
@@ -82,7 +86,7 @@ func parseCgroupFile(subsystem string, r io.Reader) (string, error) {
 			}
 		}
 	}
-	return "", fmt.Errorf("cgroup '%s' not found in /proc/self/cgroup", subsystem)
+	return "", ErrNotFound
 }
 
 func writeFile(dir, file, data string) error {