Problem relating to modprobe not applying a modules kernel parameters at load time

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Hi,

I've been investigating an issue in Ubuntu [1] which nominally relates to sysctl. After analysing
the problem [2], it appears that the real problem is that although modprobe allows a modules _module
parameters_ to be set at load time, it does not provide a way to set a modules sysfs _kernel
parameters_ at load time.

So, modules that specify kernel parameters but *not* module parameters, such as the 'bridge' module,
do not get the correct values set when modprobe loads.

The reason is that in Ubuntu we run 'sysctl -ep' as early as possible (for options like
kernel.printk). Any settings in /etc/sysctl.* relating to modules that haven't yet been loaded
cannot of course be applied. Later, the bridge module is loaded via modprobe. However, the bridges
fail to start since their settings are incorrect (as the required settings are in /etc/sysctl.*, but
sysctl has now finished).

One possible solution to the problem would be to mandate that all modules which have configurable
kernel parameters also provide equivalent module parameters to allow those values to be set at load
time.

Another possible solution might be for modprobe to extract the relevant bits from sysctl and apply
them somehow(?)

The approach adopted for Ubuntu currently is to simply call sysctl *twice* - once as early as
possible, and again after all network interfaces are up. This seems like the best we can do
currently, but it isn't perfect since it only fixes the problem for network devices.

I'd be interested in your thoughts on a holistic solution to this issue.

Kind regards,

James.

[1] - https://bugs.launchpad.net/ubuntu/+source/procps/+bug/771372
[2] - https://bugs.launchpad.net/ubuntu/+source/procps/+bug/771372/comments/4

--
James Hunt
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