Re: [PATCH 00/10 net-next] Convert CONFIG_IPV6 to built-in and remove stubs

[Daniel Borkmann]

On 3/9/26 1:43 PM, Krzysztof Kozlowski wrote:
> On 09/03/2026 12:38, Fernando Fernandez Mancera wrote:
> > On 3/9/26 11:22 AM, Krzysztof Kozlowski wrote:
> > > On 09/03/2026 03:19, Fernando Fernandez Mancera wrote:
> > > > Historically, the Linux kernel has supported compiling the IPv6 stack as
> > > > a loadable module. While this made sense in the early days of IPv6
> > > > adoption, modern deployments and distributions overwhelmingly either
> > > > build IPv6 directly into the kernel (CONFIG_IPV6=y) or disable it
> > > > entirely (CONFIG_IPV6=n). The modular IPv6 use-case provides little to
> > > > no practical benefit today.
> > >
> > > It does. We all use generic kernels, thus it is one configuration for
> > > all boards and some setups have IPv6 and some not. The ones without IPv6
> > > just don't use that module.
> >
> > While I understand this, I would like to clarify that IMHO IPv6 isn't a
> > secondary protocol and it is fundamental to modern networking. This is
>
> Not for end user devices. None of my devices - neither routers, nor
> embedded boards, nor mobile phone from 5G provider - receive IPv6
> address, thus for them it is not fundamental.

If that is the case for them, then they should just CONFIG_IPV6=n.

> I agree it is fundamental for your cloud machines and network backbone
> which you are targeting, but this patchset completely ignores other
> users calling their use-cases "little practical benefit"! Try running
> Amiga machine...

Are you talking about [0]? That's legacy hardware and in this case just
disable IPv6 altogether, why would you still prefer to have it as a module?

  [0] https://en.wikipedia.org/wiki/Amiga

> There is no even bloatometer stats for these defconfigs so we can see
> the impact.
>
> > why I believe it should be built-in by default. Currently OpenWRT,
> > Debian ARM and others already ships the kernel with CONFIG_IPV6=y. I
> > know that Alpine and Yocto doesn't do that for arm64.
>
> Maybe there are other reasons why distro should not choose it as module
> (like module load calls on ipv6 packets) but that was not explained here.
>
> Arch Linux Rpi kernel on arm64 has IPV6=6 and the module itself is 650
> kB. That's noticeable for smaller arm64 boards.
>
> For arm it would be even more noticeable as some have 256 MB RAM like
> first Rpi.

You are arguing that these will never be able to migrate to an IPv6 world
given their memory is too small?

> > I guess the most critical one here is Yocto but if the developer of the
> > embedded device is sure they won't use IPv6 at all, they should turn it off.
> >
> > At the same time, Alpine ships software that enable IPV6 and is
> > frequently loaded as a module. So the only remaining concern would be
> > the boot partition size. I don't really have a solution for that problem.
> >
> > I think that the infrastructure for allowing IPV6=m is bug-prone and it
> > impacts performance. Forcing the use of indirect function calls in core
> > networking, Netfilter or BPF datapaths seems like a heavy tax to me.
> >
> > > Also, with these generic kernels (so again all machines are using same
> > > ones, e.g. distro) users can easily blacklist the module.
> >
> > FWIW; users can still boot with kernel command line parameter
> > ipv6.disable=1 and then IPV6 will be administratively disabled.
>
> It's not the same. You enabled it on amiga_defconfig and do you
> understand what sort of machine is that? The newest have 16 MB RAM, many
> much less like 2 MB, and ipv6 module on m68k is 400 kB, so pretty
> significant change.

If IPv6 is not relevant for amiga_defconfig presumably it should just be
set to CONFIG_IPV6=n?

Thanks,
Daniel