Re: Adding PCMCIA support to the kernel tree -- developers needed.

[Vojtech Pavlik <vojtech@suse.cz>]

On Fri, Feb 09, 2001 at 12:48:59PM +0100, Oliver Neukum wrote:

> > Either assign the numbers by detection order or not at all and assume
> > the hotplug agent is started early from the root partition - then when
> > it starts, it'll see the unhandled (new) devices.. Can't do much else
> > anyway.
> 
> By detection order, else good bye to booting from PCMCIA, firewire, FC-AL, ...

Ok.

> > > c) How do you handle locking ? You need total mutual exclusion.
> >
> > Uh, mutual exclusion of what? I can't handle a device in the bus path
> > that's and one below/above it simultaneously. I can handle devices on
> > different branches simultaneously. It's possible that the hotplug agent
> > will want the same minor number for two different devices, one of these
> > calls will fail and will have to be retried with a different number by
> > the hotplug agent.
> 
> You can retry, you are right. I failed to see that.
> But you seem to suffer from the name reuse race.
> 
> reality			task A			task B
> plug in dev A
> 			bind dev A to name 0
> unplug dev A
> 						unbind name 0
> plug in dev B
> 						bind dev B to name 0
> 			do something arbitrary
> 			to the dev associated
> 			with name 0
> 
> If the kernel would select name 0, it could lock on name 0.
> With your scheme this is hard to do. 

Unbind on name 0 should block until task A finishes the arbitrary stuff.
Is there any problem with that? We could even have a 'setup finished'
ioctl for this, though I think I'd prefer just having one task per action.

> > > e) What other algorithmus that couldn't be trivially implemented in
> > > kernel do you want to use ?
> >
> > I want a config file, where the user can specify that:
> >
> > a) The ethercard with MAC 00:06:08:fa:9c:dd is to be registered always
> >    as eth0
> >
> > b) Any USB mouse that's connected to a hub connected to the first port
> >    of the USB card in first PCI slot is to be /dev/input/mouse2
> >
> > c) Any IDE drive with serial number 8937298A is to be /dev/hdf
> >
> > d) et similar.
> >
> > You can't do this sanely in the kernel.
> 
> Nor do you absolutely need to.
> You can already rename network devices by ioctl.
> For everything else a humble symlink should do the job, shouldn't it ?

Yes, but with humble symlinks you will run out of minor/major numbers soon.

> Else you introduce complexity without much gain.
> And you need renaming in any case, as device names may have been assigned
> during boot.

Yes. Symlinks would help here, however, you'd probably need devfs in
that case.

-- 
Vojtech Pavlik
SuSE Labs

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