Re: [PATCH] selftests: net: fou_mcast_encap: conditionally load fou module and skip IPv4 case

[Jakub Kicinski <kuba@kernel.org>]

On Fri, 11 Sep 2026 18:01:58 +0800 Qingshuang Fu wrote:
> Fixes: e5382133c51c ("selftests: net: add FOU multicast encapsulation resubmit test")

No fixes tag, please, this is barely worth applying at all, let along
as a fix.

> diff --git a/tools/testing/selftests/net/fou_mcast_encap.sh b/tools/testing/selftests/net/fou_mcast_encap.sh
> index 70210d39fba3..d94c19237daf 100755
> --- a/tools/testing/selftests/net/fou_mcast_encap.sh
> +++ b/tools/testing/selftests/net/fou_mcast_encap.sh
> @@ -51,8 +51,6 @@ setup_common() {
>  }
>  
>  setup_ipv4() {
> -	# IPv4 FOU (CONFIG_NET_FOU) is built in on kernels configured for
> -	# these tests, so no module load is needed here.
>  	ip -n "$NSENDER" addr add 10.0.0.1/24 dev veth_s
>  	ip -n "$NRECV" addr add 10.0.0.2/24 dev veth_r
>  
> @@ -160,8 +158,17 @@ run_ping_test() {
>  }
>  
>  setup_common
> -setup_ipv4
> -run_ping_test -4 eoudp4 "$TUN4_R" "FOU/GRETAP IPv4 multicast encap resubmit"
> +
> +# The fou module registers both the tunnel encap ops used by "encap fou"
> +# and the FOU genetlink family used by "ip fou add", and neither of them
> +# is auto-loaded. modprobe succeeds as a no-op when CONFIG_NET_FOU=y.
> +# Keep any other setup error as a test failure rather than a skip.

Drop this comment please, its obvious. Well, to people with basic
kernel familiarity it is.

> +if modprobe -q fou; then
> +	setup_ipv4
> +	run_ping_test -4 eoudp4 "$TUN4_R" "FOU/GRETAP IPv4 multicast encap resubmit"
> +else
> +	log_test_skip "FOU/GRETAP IPv4 multicast encap resubmit"
> +fi

Two very important questions you must answer before posting v2 or any
other similar fix:

Have you actually run into this or it's a result of an LLM scan?

How many of such fixes would we need to make all the net/ tests 
clean from similar issues?