Simplify codes on calculating shutdown timeout

Signed-off-by: Allen Sun <shlallen1990@gmail.com>
Signed-off-by: Vincent Demeester <vincent@sbr.pm>

daemon/daemon.go

@@ -949,27 +949,32 @@ func (daemon *Daemon) shutdownContainer(c *container.Container) error {
 	return nil
 }
 
-// ShutdownTimeout returns the shutdown timeout based on the max stopTimeout of the containers,
+// ShutdownTimeout returns the timeout (in seconds) before containers are forcibly
-// and is limited by daemon's ShutdownTimeout.
+// killed during shutdown. The default timeout can be configured both on the daemon
+// and per container, and the longest timeout will be used. A grace-period of
+// 5 seconds is added to the configured timeout.
+//
+// A negative (-1) timeout means "indefinitely", which means that containers
+// are not forcibly killed, and the daemon shuts down after all containers exit.
 func (daemon *Daemon) ShutdownTimeout() int {
-	// By default we use daemon's ShutdownTimeout.
 	shutdownTimeout := daemon.configStore.ShutdownTimeout
+	if shutdownTimeout < 0 {
+		return -1
+	}
+	if daemon.containers == nil {
+		return shutdownTimeout
+	}
 
 	graceTimeout := 5
-	if daemon.containers != nil {
 	for _, c := range daemon.containers.List() {
-			if shutdownTimeout >= 0 {
 		stopTimeout := c.StopTimeout()
 		if stopTimeout < 0 {
-					shutdownTimeout = -1
+			return -1
-				} else {
+		}
 		if stopTimeout+graceTimeout > shutdownTimeout {
 			shutdownTimeout = stopTimeout + graceTimeout
 		}
 	}
-			}
-		}
-	}
 	return shutdownTimeout
 }