On 7/13/26 4:22 PM, Arnd Bergmann wrote:

On Mon, Jul 13, 2026, at 16:00, Fernando Fernandez Mancera wrote:

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On 7/12/26 1:01 PM, Arnd Bergmann wrote:

quoted

On Sun, Jul 12, 2026, at 03:38, Fernando Fernandez Mancera wrote:

quoted

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

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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?

Yes, you are right. So I think introducing something as you proposed 
makes sense. Right now I cannot think about something needed from INET 
for pure L2.

Thank you!
Fernando.