container_exec: use process file with runc exec

Signed-off-by: Antonio Murdaca <runcom@redhat.com>

server/container_exec.go

@@ -1,8 +1,10 @@
 package server
 
 import (
+	"encoding/json"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"os"
 	"os/exec"
 	"time"
@@ -53,12 +55,29 @@ func (ss streamService) Exec(containerID string, cmd []string, stdin io.Reader,
 		return fmt.Errorf("container is not created or running")
 	}
 
+	f, err := ioutil.TempFile("", "exec-process")
+	if err != nil {
+		return err
+	}
+	defer os.RemoveAll(f.Name())
+
+	pspec := c.Spec().Process
+	pspec.Args = cmd
+	processJSON, err := json.Marshal(pspec)
+	if err != nil {
+		return err
+	}
+
+	if err := ioutil.WriteFile(f.Name(), processJSON, 0644); err != nil {
+		return err
+	}
+
 	args := []string{"exec"}
 	if tty {
 		args = append(args, "-t")
 	}
+	args = append(args, "-p", f.Name())
 	args = append(args, c.ID())
-	args = append(args, cmd...)
 	execCmd := exec.Command(ss.runtimeServer.Runtime().Path(c), args...)
 	var cmdErr error
 	if tty {