daemon: Daemon.containerStart(): add comment to clarify error-type

Any error that occurs while creating the spec, even if it's the
result of an invalid container config, must be considered a System
error (internal server error), as it's not an error with the request
to start the container.

Invalid configuration in the config itself must be validated when
creating the container (creating its config), but some errors are
dependent on the current state, for example when starting a container
that shares a namespace with another container, and that container
is not running (or missing).

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

daemon/start.go

@@ -154,6 +154,16 @@ func (daemon *Daemon) containerStart(ctx context.Context, daemonCfg *configStore
 
 	spec, err := daemon.createSpec(ctx, daemonCfg, container)
 	if err != nil {
+		// Any error that occurs while creating the spec, even if it's the
+		// result of an invalid container config, must be considered a System
+		// error (internal server error), as it's not an error with the request
+		// to start the container.
+		//
+		// Invalid configuration in the config itself must be validated when
+		// creating the container (creating its config), but some errors are
+		// dependent on the current state, for example when starting a container
+		// that shares a namespace with another container, and that container
+		// is not running (or missing).
 		return errdefs.System(err)
 	}