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

[Qingshuang Fu <fuqingshuang@kylinos.cn>]

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