Re: future of sysctls?

[Ludwig Nussel <ludwig.nussel@suse.de>]

Lennart Poettering wrote:
> On Thu, 12.05.11 17:41, Ludwig Nussel (ludwig.nussel@suse.de) wrote:
> > I'm currently struggling to find a sane way to set
> > net.ipv6.conf.default.use_tempaddr.
> > Traditionally at some point during boot "sysctl -e -q -p /etc/sysctl.conf" is
> > called. That doesn't really work out anymore. The aforementioned setting needs
> > to be applied after the ipv6 module is loaded (could be compiled into the
> > kernel too though) otherwise it wouldn't apply. It needs to be set before a
> > network driver is loaded though as the default value is copied to
> > interfaces specific settings at interface creation time. On top of
> > that there are also network interface specific sysctls that need to
> > be applied after an interface is created (e.g.
> > net.ipv6.conf.eth0.use_tempaddr).
> 
> Something like this is kinda broken anyway, since it is racy: you can
> apply the sysctl only after the interface is already available.

Exactly.

> Might be a good idea to just ignore these kinds of settings. Or if this
> is not possible, then set them from NM or whatever controls the network.

That's that hack that's currently in place. Network scripts grep
/etc/sysctl.conf for interface specific settings...

> > Are there any plans to better deal with that?
> > Like e.g. emitting events when some part of the kernel registers a sysctl so
> > userspace can override the compiled in default value?
> > Or just offer sysfs attributes instead of sysctls?
> 
> In a systemd world the ipv6 module is loaded very early and hence the
> sysctl should always be available, no special setup needed. If the same
> problem appears in real life with other modules too, then we could order
> sysctl setting after module loading and fix things by this.

Grepping for register_sysctl in the kernel sources shows quite a few modules
that use sysctls. A prominent one is nfs.
If you apply sysctl setttings after module loading, specifically network
drivers, the ipv6 setting won't have any effect anymore though.

cu
Ludwig

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