Add load process.json for exec command

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

exec.go

@@ -3,6 +3,7 @@
 package main
 
 import (
+	"encoding/json"
 	"fmt"
 	"os"
 	"path"
@@ -11,6 +12,7 @@ import (
 
 	"github.com/Sirupsen/logrus"
 	"github.com/codegangsta/cli"
+	"github.com/opencontainers/specs"
 )
 
 var execCommand = cli.Command{
@@ -37,15 +39,16 @@ var execCommand = cli.Command{
 			Name:  "user, u",
 			Usage: "UID (format: <uid>[:<gid>])",
 		},
+		cli.StringFlag{
+			Name:  "process,p",
+			Usage: "path to the process.json",
+		},
 	},
 	Action: func(context *cli.Context) {
-		if len(context.Args()) == 0 {
-			logrus.Fatal("pass the command")
-		}
 		if os.Geteuid() != 0 {
 			logrus.Fatal("runc should be run as root")
 		}
-		status, err := execProcess(context, context.Args())
+		status, err := execProcess(context)
 		if err != nil {
 			logrus.Fatalf("exec failed: %v", err)
 		}
@@ -53,72 +56,83 @@ var execCommand = cli.Command{
 	},
 }
 
-func execProcess(context *cli.Context, args []string) (int, error) {
+func execProcess(context *cli.Context) (int, error) {
 	container, err := getContainer(context)
 	if err != nil {
 		return -1, err
 	}
-
 	bundle := container.Config().Rootfs
-	if err := os.Chdir(path.Dir(bundle)); err != nil {
-		return -1, err
-	}
-	spec, _, err := loadSpec(specConfig, runtimeConfig)
+	rootuid, err := container.Config().HostUID()
 	if err != nil {
 		return -1, err
 	}
+	p, err := getProcess(context, path.Dir(bundle))
+	if err != nil {
+		return -1, err
+	}
+	process := newProcess(*p)
+	tty, err := newTty(p.Terminal, process, rootuid, context.String("console"))
+	if err != nil {
+		return -1, err
+	}
+	handler := newSignalHandler(tty)
+	defer handler.Close()
+	if err := container.Start(process); err != nil {
+		return -1, err
+	}
+	return handler.forward(process)
+}
 
+func getProcess(context *cli.Context, bundle string) (*specs.Process, error) {
+	if path := context.String("process"); path != "" {
+		f, err := os.Open(path)
+		if err != nil {
+			return nil, err
+		}
+		defer f.Close()
+		var p specs.Process
+		if err := json.NewDecoder(f).Decode(&p); err != nil {
+			return nil, err
+		}
+		return &p, nil
+	}
+	// process via cli flags
+	if err := os.Chdir(bundle); err != nil {
+		return nil, err
+	}
+	spec, _, err := loadSpec(specConfig, runtimeConfig)
+	if err != nil {
+		return nil, err
+	}
 	p := spec.Process
-
+	p.Args = context.Args()
 	// override the cwd, if passed
 	if context.String("cwd") != "" {
 		p.Cwd = context.String("cwd")
 	}
-
 	// append the passed env variables
 	for _, e := range context.StringSlice("env") {
 		p.Env = append(p.Env, e)
 	}
-
 	// set the tty
 	if context.IsSet("tty") {
 		p.Terminal = context.Bool("tty")
 	}
-
 	// override the user, if passed
 	if context.String("user") != "" {
 		u := strings.SplitN(context.String("user"), ":", 2)
 		if len(u) > 1 {
 			gid, err := strconv.Atoi(u[1])
 			if err != nil {
-				return -1, fmt.Errorf("parsing %s as int for gid failed: %v", u[1], err)
+				return nil, fmt.Errorf("parsing %s as int for gid failed: %v", u[1], err)
 			}
 			p.User.GID = uint32(gid)
 		}
 		uid, err := strconv.Atoi(u[0])
 		if err != nil {
-			return -1, fmt.Errorf("parsing %s as int for uid failed: %v", u[0], err)
+			return nil, fmt.Errorf("parsing %s as int for uid failed: %v", u[0], err)
 		}
 		p.User.UID = uint32(uid)
 	}
-
-	process := newProcess(p)
-	process.Args = args
-	rootuid, err := container.Config().HostUID()
-	if err != nil {
-		return -1, err
-	}
-
-	tty, err := newTty(p.Terminal, process, rootuid, context.String("console"))
-	if err != nil {
-		return -1, err
-	}
-
-	handler := newSignalHandler(tty)
-	defer handler.Close()
-	if err := container.Start(process); err != nil {
-		return -1, err
-	}
-
-	return handler.forward(process)
+	return &p, nil
 }