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

[Qingshuang Fu]

在 2026/9/17 08:40, Jakub Kicinski 写道:
> 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?

I noticed it reading the script, then reproduced it on 6.8.0-138-generic.
This Ubuntu kernel ships with CONFIG_NET_FOU=m by default. Without the fou
module loaded, tunnel creation fails with "RTNETLINK answers: Invalid 
argument"
and the test reports a false failure at 0/100 packets. After applying 
the patch
the subtest skips cleanly.

For FOU this was the only gap. The two other net/ tests that use it
(pmtu.sh, rtnetlink.sh) already load the module.

v2 sent: drop Fixes tag and the in‑script comment as requested. Thanks 
for the review.

Regards,
Qingshuang Fu