Extract cgroups pkg.

Initial move before enhancing cgroups package.

Docker-DCO-1.1-Signed-off-by: Paul Nasrat <pnasrat@gmail.com> (github: pnasrat)

cgroups/MAINTAINERS

@@ -0,0 +1 @@
+Michael Crosby <michael@crosbymichael.com> (@crosbymichael)

cgroups/cgroups.go

@@ -0,0 +1,106 @@
+package cgroups
+
+import (
+	"bufio"
+	"fmt"
+	"github.com/dotcloud/docker/pkg/mount"
+	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+)
+
+type Values struct {
+	Memory     int64 `json:"memory"`
+	MemorySwap int64 `json:"memory_swap"`
+	CpuShares  int64 `json:"cpu_shares"`
+}
+
+// https://www.kernel.org/doc/Documentation/cgroups/cgroups.txt
+func FindCgroupMountpoint(subsystem string) (string, error) {
+	mounts, err := mount.GetMounts()
+	if err != nil {
+		return "", err
+	}
+
+	for _, mount := range mounts {
+		if mount.Fstype == "cgroup" {
+			for _, opt := range strings.Split(mount.VfsOpts, ",") {
+				if opt == subsystem {
+					return mount.Mountpoint, nil
+				}
+			}
+		}
+	}
+
+	return "", fmt.Errorf("cgroup mountpoint not found for %s", subsystem)
+}
+
+// Returns the relative path to the cgroup docker is running in.
+func getThisCgroupDir(subsystem string) (string, error) {
+	f, err := os.Open("/proc/self/cgroup")
+	if err != nil {
+		return "", err
+	}
+	defer f.Close()
+
+	return parseCgroupFile(subsystem, f)
+}
+
+func parseCgroupFile(subsystem string, r io.Reader) (string, error) {
+	s := bufio.NewScanner(r)
+
+	for s.Scan() {
+		if err := s.Err(); err != nil {
+			return "", err
+		}
+		text := s.Text()
+		parts := strings.Split(text, ":")
+		if parts[1] == subsystem {
+			return parts[2], nil
+		}
+	}
+	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
+}

cgroups/cgroups_test.go

@@ -0,0 +1,27 @@
+package cgroups
+
+import (
+	"bytes"
+	"testing"
+)
+
+const (
+	cgroupsContents = `11:hugetlb:/
+10:perf_event:/
+9:blkio:/
+8:net_cls:/
+7:freezer:/
+6:devices:/
+5:memory:/
+4:cpuacct,cpu:/
+3:cpuset:/
+2:name=systemd:/user.slice/user-1000.slice/session-16.scope`
+)
+
+func TestParseCgroups(t *testing.T) {
+	r := bytes.NewBuffer([]byte(cgroupsContents))
+	_, err := parseCgroupFile("blkio", r)
+	if err != nil {
+		t.Fatal(err)
+	}
+}

sysinfo/sysinfo.go

@@ -1,7 +1,7 @@
 package sysinfo
 
 import (
-	"github.com/dotcloud/docker/cgroups" // FIXME: move cgroups in pkg
+	"github.com/dotcloud/docker/pkg/cgroups"
 	"io/ioutil"
 	"log"
 	"os"