Make exec driver run a blocking command

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

execdriver/chroot/driver.go

@@ -17,7 +17,7 @@ func (d *driver) String() string {
 	return "chroot"
 }
 
-func (d *driver) Start(c *execdriver.Process) error {
+func (d *driver) Run(c *execdriver.Process, startCallback execdriver.StartCallback) (int, error) {
 	params := []string{
 		"chroot",
 		c.Rootfs,
@@ -40,17 +40,27 @@ func (d *driver) Start(c *execdriver.Process) error {
 	c.Args = append([]string{name}, arg...)
 
 	if err := c.Start(); err != nil {
-		return err
+		return -1, err
 	}
 
+	var (
+		waitErr  error
+		waitLock = make(chan struct{})
+	)
 	go func() {
 		if err := c.Wait(); err != nil {
-			c.WaitError = err
+			waitErr = err
 		}
-		close(c.WaitLock)
+		close(waitLock)
 	}()
 
-	return nil
+	if startCallback != nil {
+		startCallback(c)
+	}
+
+	<-waitLock
+
+	return c.GetExitCode(), waitErr
 }
 
 func (d *driver) Kill(p *execdriver.Process, sig int) error {

execdriver/driver.go

@@ -6,10 +6,13 @@ import (
 	"time"
 )
 
+type StartCallback func(*Process)
+
 type Driver interface {
-	Start(c *Process) error
+	Run(c *Process, startCallback StartCallback) (int, error) // Run executes the process and blocks until the process exits and returns the exit code
 	Kill(c *Process, sig int) error
-	Wait(id string, duration time.Duration) error // Wait on an out of process option - lxc ghosts
+	// TODO: @crosbymichael @creack wait should probably return the exit code
+	Wait(id string, duration time.Duration) error // Wait on an out of process...process - lxc ghosts
 	Version() string
 	String() string
 }
@@ -38,8 +41,6 @@ type Process struct {
 	Tty         bool
 	Network     *Network // if network is nil then networking is disabled
 	SysInitPath string
-	WaitLock    chan struct{}
-	WaitError   error
 }
 
 func (c *Process) Pid() int {

execdriver/lxc/driver.go

@@ -45,7 +45,7 @@ func (d *driver) String() string {
 	return "lxc"
 }
 
-func (d *driver) Start(c *execdriver.Process) error {
+func (d *driver) Run(c *execdriver.Process, startCallback execdriver.StartCallback) (int, error) {
 	params := []string{
 		startPath,
 		"-n", c.ID,
@@ -111,21 +111,32 @@ func (d *driver) Start(c *execdriver.Process) error {
 	c.Args = append([]string{name}, arg...)
 
 	if err := c.Start(); err != nil {
-		return err
+		return -1, err
 	}
 
+	var (
+		waitErr  error
+		waitLock = make(chan struct{})
+	)
 	go func() {
 		if err := c.Wait(); err != nil {
-			c.WaitError = err
+			waitErr = err
 		}
-		close(c.WaitLock)
+		close(waitLock)
 	}()
 
-	// Poll for running
-	if err := d.waitForStart(c); err != nil {
-		return err
+	// Poll lxc for RUNNING status
+	if err := d.waitForStart(c, waitLock); err != nil {
+		return -1, err
 	}
-	return nil
+
+	if startCallback != nil {
+		startCallback(c)
+	}
+
+	<-waitLock
+
+	return c.GetExitCode(), waitErr
 }
 
 func (d *driver) Kill(c *execdriver.Process, sig int) error {
@@ -171,7 +182,7 @@ func (d *driver) kill(c *execdriver.Process, sig int) error {
 	return nil
 }
 
-func (d *driver) waitForStart(c *execdriver.Process) error {
+func (d *driver) waitForStart(c *execdriver.Process, waitLock chan struct{}) error {
 	var (
 		err    error
 		output []byte
@@ -182,7 +193,7 @@ func (d *driver) waitForStart(c *execdriver.Process) error {
 	// the end of this loop
 	for now := time.Now(); time.Since(now) < 5*time.Second; {
 		select {
-		case <-c.WaitLock:
+		case <-waitLock:
 			// If the process dies while waiting for it, just return
 			if c.ProcessState != nil && c.ProcessState.Exited() {
 				return nil