Re: [PATCH v2] ipv6: default IPV6_SIT to m

Fernando Fernandez Mancera
2026-05-04T15:02:03Z

On 5/4/26 4:30 PM, Alyssa Ross wrote:
> Fernando Fernandez Mancera <fmancera@suse.de> writes:
>
>> On 5/3/26 9:25 PM, Alyssa Ross wrote:
>>> This basically defaulted to m until recently, since IPV6 defaulted to
>>> m. Since IPV6 was changed to a boolean with a default of y, IPV6_SIT
>>> started defaulting to built-in as well. This results in a surprise
>>> sit0 device by default for defconfig (and defconfig-derived config)
>>> users at boot. For me, this broke an (admittedly non-robust) script.
>>> Preserve the behaviour of most configs by avoiding building this
>>> module, that's probably overall seldom used compared to IPv6 as a
>>> whole, into the kernel.
>>>
>>> Fixes: 309b905deee59 ("ipv6: convert CONFIG_IPV6 to built-in only and clean up Kconfigs")
>>> Signed-off-by: Alyssa Ross <hi@alyssa.is>
>>
>> Hi, I am not sure about this. IPV6_SIT was already defaulting to 'y' for
>> most distributions (except for ARM). Sure, if you had CONFIG_IPV6=m then
>> CONFIG_IPV6_SIT was defaulting to 'm'.
>>
>> Hm. Maybe we can aim this for net-next tree instead of net? I just don't
>> think this is a fix but a change in behavior. FWIW, it makes sense to me
>> to have this as a module by default.
>>
>> Let's see what do others think.
>
> Yes, it appears you're right. I had only tested on ARM. In that case,
> perhaps it make sense to instead set this to m in the arm64 defconfig, to
> preserve the previous situation, but I can also see the value in
> reducing platform discongruity by letting it change to y on arm64 too.

Changing it on arm64 defconfig would make sense to me too. We should
probably visit other configs that might be in the same situation. That
in my opinion would qualify a net tree fix as you proposed initially.