[systemd-devel] Loading Kernel Modules

[Kay Sievers]

On Mon, Mar 19, 2012 at 16:02, Pawel Pastuszak <pawelpastuszak at gmail.com> wrote:
> I am not sure if i made my self clear, what i am doing is and custom distro
> for an custom embedded device, which i want to have the ability to upgrade
> the system in runtime, which i need to ability to to stop my custom driver
> modules for the upgrade. So this is why i was asking what is the best way of
> starting and stop modules.
>
> Unless what your saying is replace the file and just reboot, instead of stop
> the service and replace then start it again.

Oh, there is no general advice in the systemd context, I guess. It's
also not systemd specific, and mostly handled inside the kernel. As
mentioned, we generally do not support at all any kernel-module
unloading with systemd-native infrastructure, but that should be no
reason for custom logic inside a service to do that.

Usually you need to stop the service/application using the device, and
then you can unload the driver module. Most modules can only be
unloaded when they are not in use. The most common exception is
network driver modules, which for historic reasons do not pin the
modules in use. This can either be managed by completely stopping and
restarting the service, or by sending specific commands to a service
to release the open()ed devices.

Alternatively, if the service/app can handle hot-device removal, you
can just unbind the driver from the device in
/sys/bus/*/drivers/*/{bind,unbind}, and after that unload the module.
But the service/app needs to be able to cope with devices
disappearing; many services/apps don't.

Kay