[systemd-devel] how to bind to other drivers using systemd

[Panu Matilainen]

On 10/13/2015 03:24 PM, Harald Hoyer wrote:
> On 13.10.2015 14:08, Panu Matilainen wrote:
>> On 09/30/2015 08:43 PM, Flavio Leitner wrote:
>>> On Tue, Sep 29, 2015 at 12:30:54AM +0300, Mantas Mikulėnas wrote:
>>>> I wonder if this could be handled with a generic Type=oneshot,
>>>> ExecStart=driverctl bind foo...
>>>
>>> Could you elaborate more on that?
>>>
>>> If driverctl is an utility, we could use scripts, yeah.  The issue
>>> is how to identify the device. We probably would need some sort
>>> matching mechanism like udev does.
>>
>> Since the silence is deafening, and since its usually easier to poke holes in
>> something concrete no matter how incomplete and/or broken, here's a beginning
>> of an approach to alternative driver assignment in the udev realm:
>> http://laiskiainen.org/udev/driverctl/
>>
>> # <copy/patch the bits to their places>
>> # echo vfio-pci > /etc/driverctl.d/0000:01:00.0
>> # echo 1 > /sys/bus/pci/devices/0000:01:00.0/remove
>> # echo 1 > /sys/bus/pci/rescan
>>
>> ...and there you go, udev vfio-pci is forced for that device on the rescan, and
>> a real hotplug is handled similarly.
>>
>> Since normally the device probing occurs early in the boot, these things also
>> need to go to initramfs so a dracut module/patch is needed, and dracut needs to
>> be run after adding devices here, ie
>>
>> # echo vfio-pci > /etc/driverctl.d/0000:01:00.0
>> # dracut -f
>> # reboot
>>
>> Having to mess with initramfs is a bit of a PITA but at least some of that
>> could be hidden in the driverctl utility, and then overriding the default
>> driver early in the boot means we get none of the side-effects with interfaces
>> coming and going, possibly wrestling with NetworkManager over it etc.
>>
>> For a real-world implementation there are tons of TODOs like
>> - support non-pci buses
>> - support direct bind/unbind in driverctl
>> - million errors situations to check
>> - vfio & uio -bound devices disappear from systemd, we'd probably want them
>> there in some form to be able to depend on them
>> - etc...
>>
>>      - Panu -
>>
>
> I don't know nothing about driver binding/unbinding,

Neither do I, that's why I'm asking here ;)

> but what happens if the
> initial driver binding (with the wrong driver) happens in-between these lines?
>
>      if [ -L /sys/$DEVPATH/driver ]; then
> 	echo "$DEV" > /sys/$DEVPATH/driver/unbind
>      fi
>      […]
>
> --->> HERE the other driver binds to the device <<<----
>
>      […]
>     echo "$DRV" > /sys/$DEVPATH/driver_override

The wrong thing probably... The unbind probably doesn't belong there at 
all, I added it there for the wrong reason and forgot to remove.

Thanks for pointing that out though.

	- Panu -


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