Re: [RFC] Pushing device/driver binding decisions to userspace

[Kay Sievers]

On 11/23/06, Greg KH <greg@xxxxxxxxx> wrote:
> On Sun, Nov 12, 2006 at 09:22:44PM -0800, Ben Collins wrote:
> > On Sun, 2006-11-12 at 17:47 -0800, Nicholas Miell wrote:
> > > On Sun, 2006-11-12 at 17:24 -0800, Ben Collins wrote:
> > > > On Sun, 2006-11-12 at 16:49 -0800, Nicholas Miell wrote:
> > > > > On Sun, 2006-11-12 at 15:39 -0800, Ben Collins wrote:
> > > > >
> > > > > What's wrong with making udev or whatever unbind driver A and then bind
> > > > > driver B if the driver bound by the kernel ends up being the wrong
> > > > > choice? (Besides the inelegance of the kernel choosing one and then
> > > > > userspace immediately choosing the other, of course.)
> > > > >
> > > > > I'd argue that having multiple drivers for the same hardware is a bit
> > > > > strange to begin with, but that's another issue entirely.
> > > >
> > > > If two drivers are loaded for the same device, there's no way for udev
> > > > to tell the kernel which driver to use for a device, that I know of.
> > >
> > > /sys/bus/*/drivers/*/{bind,unbind}
> >
> > "bind" does not tell the driver core to "bind this device with this
> > driver", it tells it to "bind this driver to whatever devices we match
> > that aren't already bound".
>
> No it does not, it tells the driver core to "bind this device with this
> driver, _if_ the driver will accept it".
>
> > That doesn't solve my use case.
>
> Yes it does:
>         echo -n BUS_ID > /sys/bus/foo_bus/drivers/foo_driver/unbind
>         echo -n BUS_ID > /sys/bus/foo_bus/drivers/baz_driver/bind
>
> and you are set.  That's the way other distros use this functionality :)

Right, I currently port that part of SUSE's sysconfig's per-device
configuration to udev, and udev-rules will be able to specify what
driver to use for a device, including driver-unbinding/binding.

Also modprobe will be built into udev to solve the
performance-problems we see with parsing the modprobe-files for every
device with a modalias.

Kay
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