Re: Which node has the device been bound to?

[Greg KH <greg@kroah.com>]

On Tue, Jun 04, 2002 at 01:37:13AM +0200, Oliver Neukum wrote:
> Am Dienstag, 4. Juni 2002 01:16 schrieb Greg KH:
> > On Tue, Jun 04, 2002 at 01:05:09AM +0200, Oliver Neukum wrote:
> > > > > I can't come up with anything better than a set of ioctls that
> > > > > return the contents of the individual files. And I know that this
> > > > > is ugly. I don't claim that this is a good solution, just that
> > > > > it's the only solution I have and that there's a race otherwise.
> > > > > You simply cannot use names, thus parsing files for the name of
> > > > > the node won't work.
> > > >
> > > > Or we could just drop the whole idea of using ioctl() and live with
> > > > the "instability" of parsing a filesystem :)
> > >
> > > There is no such thing is an acceptable race condition.
> >
> > Then use the device tree in driverfs as a "hint" as to where you might
> > find your device.  Then rely on other things (fs labels, usb serial
> > numbers, ethernet mac addresses, etc.) to verify if the device you are
> > talking to really is the one you think it is.
> 
> The project started out to solve the problem once and forever and now we 
> are back at several heuristics.

Wait, what project?  linux-hotplug was created to "solve" the initial
problem of people calling /sbin/hotplug in different ways, which broke
userspace tools.  It then became a forum for the linux-hotplug package,
and general hotplugging issues.

It was never created to solve "the hotplugging/device naming/persistent
path/fish slicing and dicing" problem.

> IMHO this defeats the purpose.

What purpose?  driverfs?  driverfs is for a system-wide driver topology,
and to provide a driver specific place for driver specific interface
files (instead of /proc).  And it meets that purpose quite well.

Just because we can't uniquely, and race-free identify a device node
with a physical device (either mapping, you choose) doesn't mean all is
lost.  We've never been able to do that :)

thanks,

greg k-h

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