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

[Vojtech Pavlik <vojtech@suse.cz>]

On Fri, Feb 09, 2001 at 02:09:39PM +0100, Oliver Neukum wrote:
> > > 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.
> 
> This would work provided that the lock is taken atomically with binding to 
> the name.

Yep, that's what I intended.

> > > 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.
> 
> Why is that ? Even if you assign numbers by the agent you would take them out 
> of a pool of numbers the kernel could also use.
> In both cases it would seem that devices use the same amount of numbers.

Actually, you're right. For some reason I was assuming the symlinks
would have to point to stable names - unique at least for each topology path.
This is not completely necessary, though.

> > > 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.
> 
> I can see devfs helping tremendously with providing stable names, but why is 
> it necessary ?

It isn't needed - I was assuming the symlinks would have to point to
stable names.

-- 
Vojtech Pavlik
SuSE Labs

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