Add pid file support

README.md

@@ -83,6 +83,13 @@ The main magic of how this works is that the container processes are moved from
 
 The above will use the `name=systemd` and `cpu` cgroups of systemd but then use Docker's cgroups for all the others, like the freezer cgroup.
 
+Pid File
+--------
+
+If for whatever reason you want to create a pid file for the container PID, you can.  Just add `--pid-file` as below
+
+`ExecStart=/opt/bin/systemd-docker --pid-file=/var/run/%n.pid --env run --rm --name %n nginx`
+
 systemd-notify support
 ----------------------
 

main.go

@@ -41,6 +41,7 @@ type Context struct {
 	NotifySocket string
 	Cmd          *exec.Cmd
 	Pid          int
+	PidFile      string
 	Client       *dockerClient.Client
 }
 
@@ -72,10 +73,11 @@ func parseContext(args []string) (*Context, error) {
 		AllCgroups: false,
 	}
 
-	flags := flag.NewFlagSet("run", flag.ContinueOnError)
+	flags := flag.NewFlagSet("systemd-docker", flag.ContinueOnError)
 
 	var flCgroups opts.ListOpts
 
+	flags.StringVar(&c.PidFile, []string{"p", "-pid-file"}, "", "pipe file")
 	flags.BoolVar(&c.Logs, []string{"l", "-logs"}, true, "pipe logs")
 	flags.BoolVar(&c.Notify, []string{"n", "-notify"}, false, "setup systemd notify for container")
 	flags.BoolVar(&c.Env, []string{"e", "-env"}, false, "inherit environment variable")
@@ -443,6 +445,19 @@ func notify(c *Context) error {
 	return nil
 }
 
+func pidFile(c *Context) error {
+	if len(c.PidFile) == 0 || c.Pid <= 0 {
+		return nil
+	}
+
+	err := ioutil.WriteFile(c.PidFile, []byte(strconv.Itoa(c.Pid)), 0644)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
 func pipeLogs(c *Context) error {
 	if !c.Logs {
 		return nil
@@ -527,6 +542,11 @@ func mainWithArgs(args []string) (*Context, error) {
 		return c, err
 	}
 
+	err = pidFile(c)
+	if err != nil {
+		return c, err
+	}
+
 	go pipeLogs(c)
 
 	err = keepAlive(c)

main_test.go

@@ -1,10 +1,12 @@
 package main
 
 import (
+	"io/ioutil"
 	"log"
 	"os"
 	"os/exec"
 	"path"
+	"strconv"
 	"syscall"
 	"testing"
 
@@ -452,3 +454,40 @@ func TestNamedContainerAttach(t *testing.T) {
 
 	deleteTestContainer(t)
 }
+
+func Exist(path string) bool {
+	_, err := os.Stat(path)
+	return os.IsExist(err)
+}
+
+func TestPidFile(t *testing.T) {
+	client, err := getClient(&Context{})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	pidFileName := "./pid-file"
+
+	os.Remove(pidFileName)
+
+	c, err := mainWithArgs([]string{"--logs=false", "--pid-file", "./pid-file", "run", "--rm", "busybox", "echo", "hi"})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = client.InspectContainer(c.Id)
+	if err == nil {
+		t.Fatal("Container should not exist")
+	}
+
+	bytes, err := ioutil.ReadFile(pidFileName)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if string(bytes) != strconv.Itoa(c.Pid) {
+		t.Fatal("Failed to write pid file")
+	}
+
+	os.Remove(pidFileName)
+}