xdp-trafficgen: Output helpful suggestions if interface probing fails

In some cases we can say something more about why probing for XDP
feature support for an interface fails (because of particular driver
quirks). Add output to the 'probe' command for these cases.

Signed-off-by: Toke Høiland-Jørgensen <[email protected]>

Author: tohojo

xdp-trafficgen/xdp-trafficgen.c

@@ -1038,8 +1038,23 @@ int do_probe(const void *opt, __unused const char *pin_root_path)
 	const struct probeopt *cfg = opt;
 	int err1 = 0, err2;
 
-	if (cfg->iface.ifindex)
+	if (cfg->iface.ifindex) {
 		err1 = check_iface_support(&cfg->iface);
+		if (err1) {
+			const char *name = get_driver_name(cfg->iface.ifindex);
+			if (driver_needs_xdp_pass(&cfg->iface)) {
+				pr_info(" Note that this driver (%s) needs an XDP program "
+					"loaded to use XDP_REDIRECT.\n"
+					" Loading a dummy XDP program on the interface "
+					"may enable support.\n", name);
+			} else {
+
+				if (!strcmp(name, "veth"))
+					pr_info(" Note that enabling GRO on both ends of a "
+						"veth pair may enable XDP support\n");
+			}
+		}
+	}
 
 	err2 = probe_kernel_support();
 	if (!err2)