Jakub Kicinski [off-list ref] wrote:

On Wed, 10 Jun 2026 19:58:43 +0200 Florian Westphal wrote:

quoted

@@ -73,7 +86,10 @@ nsim_setup_tc(struct net_device *dev, enum tc_setup_type type, void *type_data)
 						  &nsim_block_cb_list,
 						  nsim_setup_tc_block_cb,
 						  ns, ns, true);
+	case TC_SETUP_FT:
+		return 0;
 	default:
 		return -EOPNOTSUPP;
 	}
 }
+ALLOW_ERROR_INJECTION(nsim_setup_tc, ERRNO);

As you probably seen other netdevsim offloads use explicit debugfs 
files to "fail operation X". Slightly easier to deal with, and
netdevsim is a test harness anyway. But entirely up to you.

I'd rather not reimplement the '30% failure rate' and the 'make-it-fail'
logic (allows to have restrict the error injection to selected
processed), so I would prefer to give fuzzers more rope.

I'll fix up the sashiko hints in v2.