Replace pid and started file with State type

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

namespaces/exec.go

@@ -56,12 +56,18 @@ func Exec(container *libcontainer.Config, term Terminal, rootfs, dataPath string
 	if err != nil {
 		return -1, err
 	}
-	if err := WritePid(dataPath, command.Process.Pid, started); err != nil {
+
+	state := &libcontainer.State{
+		Pid1:          command.Process.Pid,
+		Pid1StartTime: started,
+	}
+
+	if err := libcontainer.WriteState(dataPath, state); err != nil {
 		command.Process.Kill()
 		command.Wait()
 		return -1, err
 	}
-	defer DeletePid(dataPath)
+	defer libcontainer.DeleteState(dataPath)
 
 	// Do this before syncing with child so that no children
 	// can escape the cgroup

namespaces/execin.go

@@ -13,7 +13,7 @@ import (
 )
 
 // ExecIn uses an existing pid and joins the pid's namespaces with the new command.
-func ExecIn(container *libcontainer.Config, nspid int, args []string) error {
+func ExecIn(container *libcontainer.Config, state *libcontainer.State, args []string) error {
 	// TODO(vmarmol): If this gets too long, send it over a pipe to the child.
 	// Marshall the container into JSON since it won't be available in the namespace.
 	containerJson, err := json.Marshal(container)
@@ -22,7 +22,7 @@ func ExecIn(container *libcontainer.Config, nspid int, args []string) error {
 	}
 
 	// Enter the namespace and then finish setup
-	finalArgs := []string{os.Args[0], "nsenter", "--nspid", strconv.Itoa(nspid), "--containerjson", string(containerJson), "--"}
+	finalArgs := []string{os.Args[0], "nsenter", "--nspid", strconv.Itoa(state.Pid1), "--containerjson", string(containerJson), "--"}
 	finalArgs = append(finalArgs, args...)
 	if err := system.Execv(finalArgs[0], finalArgs[0:], os.Environ()); err != nil {
 		return err

namespaces/pid.go

@@ -1,28 +0,0 @@
-package namespaces
-
-import (
-	"fmt"
-	"io/ioutil"
-	"os"
-	"path/filepath"
-)
-
-// WritePid writes the namespaced processes pid to pid and it's start time
-// to the path specified
-func WritePid(path string, pid int, startTime string) error {
-	err := ioutil.WriteFile(filepath.Join(path, "pid"), []byte(fmt.Sprint(pid)), 0655)
-	if err != nil {
-		return err
-	}
-	return ioutil.WriteFile(filepath.Join(path, "start"), []byte(startTime), 0655)
-}
-
-// DeletePid removes the pid and started file from disk when the container's process
-// dies and the container is cleanly removed
-func DeletePid(path string) error {
-	err := os.Remove(filepath.Join(path, "pid"))
-	if serr := os.Remove(filepath.Join(path, "start")); err == nil {
-		err = serr
-	}
-	return err
-}

nsinit/exec.go

@@ -19,19 +19,20 @@ var execCommand = cli.Command{
 }
 
 func execAction(context *cli.Context) {
-	var nspid, exitCode int
+	var exitCode int
 
 	container, err := loadContainer()
 	if err != nil {
 		log.Fatal(err)
 	}
 
-	if nspid, err = readPid(); err != nil && !os.IsNotExist(err) {
-		log.Fatalf("unable to read pid: %s", err)
+	state, err := libcontainer.LoadState(dataPath)
+	if err != nil && !os.IsNotExist(err) {
+		log.Fatalf("unable to read state.json: %s", err)
 	}
 
-	if nspid > 0 {
-		err = namespaces.ExecIn(container, nspid, []string(context.Args()))
+	if state != nil {
+		err = namespaces.ExecIn(container, state, []string(context.Args()))
 	} else {
 		term := namespaces.NewTerminal(os.Stdin, os.Stdout, os.Stderr, container.Tty)
 		exitCode, err = startContainer(container, term, dataPath, []string(context.Args()))

nsinit/utils.go

@@ -2,11 +2,9 @@ package main
 
 import (
 	"encoding/json"
-	"io/ioutil"
 	"log"
 	"os"
 	"path/filepath"
-	"strconv"
 
 	"github.com/docker/libcontainer"
 )
@@ -26,20 +24,6 @@ func loadContainer() (*libcontainer.Config, error) {
 	return container, nil
 }
 
-func readPid() (int, error) {
-	data, err := ioutil.ReadFile(filepath.Join(dataPath, "pid"))
-	if err != nil {
-		return -1, err
-	}
-
-	pid, err := strconv.Atoi(string(data))
-	if err != nil {
-		return -1, err
-	}
-
-	return pid, nil
-}
-
 func openLog(name string) error {
 	f, err := os.OpenFile(name, os.O_CREATE|os.O_RDWR|os.O_APPEND, 0755)
 	if err != nil {

state.go

@@ -0,0 +1,48 @@
+package libcontainer
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+)
+
+// State represents a running container's state
+type State struct {
+	// Pid1 is the process id for the container's pid 1 in it's parent namespace
+	Pid1 int `json:"pid1,omitempty"`
+	// Pid1StartTime is the process start time for the container's pid 1
+	Pid1StartTime string `json:"pid1_start_time,omitempty"`
+}
+
+// WriteState writes the container's runtime state to a state.json file
+// in the specified path
+func WriteState(basePath string, state *State) error {
+	f, err := os.Create(filepath.Join(basePath, "state.json"))
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	return json.NewEncoder(f).Encode(state)
+}
+
+// LoadState reads the state.json file for a running container
+func LoadState(basePath string) (*State, error) {
+	f, err := os.Open(filepath.Join(basePath, "state.json"))
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	var state *State
+	if err := json.NewDecoder(f).Decode(&state); err != nil {
+		return nil, err
+	}
+
+	return state, nil
+}
+
+// DeleteState deletes the state.json file
+func DeleteState(basePath string) error {
+	return os.Remove(filepath.Join(basePath, "state.json"))
+}