Re: [PATCHv2] ipv6: Create module parameter for use_tempaddr

On Tue, Sep 13, 2011 at 11:39 AM, Bjørn Mork [off-list ref] wrote:

Paul Stewart [off-list ref] writes:

quoted

When ipv6 is used as a module, there is no good place to set
the default value for use_tempaddr.  Using sysctl.conf will
set this parameter too early -- before the module is loaded.
To solve this, create a module parameter that will set the
default value of use_tempaddr for all devices.

How is use_tempaddr any different from the other /proc/sys/net/ipv6/*
variables?  Do you want to add a module parameter for all of them?

With use_tempaddr and ipv6 loaded as a module, there is a gap of time
between addrconf starting up and whatever configuration one would use
to set use_tempaddr (you can't use sysctl.conf since module-load time
might be much later).  By the time boot scripts (or whatever you'd
use) are able to tweak use_tempaddr, it might be too late and the
global-trackable address (related to the MAC address) might end up in
use.  This negates the entire point of use_tempaddr.  If any of the
other flags suffer this badly at module-load time, I'd be happy to add
module parameters for them, but this is the only one that I've come to
be aware of.

Why can't you run sysctl with an ipv6-specific sysctl.conf at a time
fitting your boot sequence?  Or load the ipv6 module before sysctl is
loads the default sysctl.conf if that is what you want?  Or just set the
variables in your network configuration scripts, prior to bringing the
interfaces up?

Or do as most people do nowadays:  Forget that ipv6 can be built as a
module, and just use it builtin.  It's not like it can be unloaded
anyway, so building it as a module does not give you anything.

All helpful suggestions.  However, I'm not yet willing to accept the
claim that ipv6 cannot be used as a module unless the rest of the
system is painstakingly crafted to close any races between addrconf,
sysctl and other IPv6-using processes.  That strikes me as far too
brittle.

--
Paul