Re: [PATCH 01/13 RFC net-next] net: ipv4: introduce CONFIG_IPV4 to decouple the IPv4 stack

["Arnd Bergmann" <arnd@xxxxxxxx>]

On Mon, Jul 13, 2026, at 16:00, Fernando Fernandez Mancera wrote:
> On 7/12/26 1:01 PM, Arnd Bergmann wrote:
>> On Sun, Jul 12, 2026, at 03:38, Fernando Fernandez Mancera wrote:
>>> Historically, the IPv4 protocol has been linked to the core INET
>>> subsystem. Because shared infrastructure like the TCP/UDP engine,
>>> routing or INET hashtables live inside net/ipv4/, it has been impossible
>>> to compile a kernel with only IPv6 support.
>>>
>>> This patch introduces the CONFIG_IPV4 Kconfig symbol, which is set to
>>> 'def_bool y' for now. This does not allow to completely disable the
>>> IPv4 stack yet but it lays the necessary build-system work for that
>>> goal.
>> 
>> I expect this will cause additional (trivial) build regression in the
>> next step when randconfig builds run into obscure corner cases, either
>> with INET=y IPV4=n IPV6=y or with INET=y IPV4=n IPV6=n.
>> 
>> I can probably give your patch (with IPV4 visible or disabled) an
>> early go on the randconfig tree to find these more quickly.
>> If I run into regressions, should I just add more 'depends on IPV4',
>> or do you have other plans?
>> 
>
> Yes, I have a job running randconfig and verifying nothing breaks. If 
> something breaks and it isn't core networking stack I would just make 
> the Kconfig symbol depend on IPv4.
>
> Then later we will have more time to write a dedicate patch so it does 
> not depend on IPv4.

Ok

>> Should we have some logic to ensure that at least one of IPV4 or
>> IPV6 is enabled? I think this would work
>> 
>> config IPV4
>>        bool "The IPv4 protocol" if IPV6
>>        default INET
>> 
>> which only allows turning IPV4 off if IPV6 has enabled.
>> 
>
> I do wonder, should we? I mean, I didn't try it off but I don't see why 
> we should not allow a pure L2 system..

I expected a pure L2 system to be CONFIG_ETHERNET=y CONFIG_INET=n.

Which user-visible parts of CONFIG_INET would you want keep working
when both v4 and v6 are disabled?

     Arnd