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

[Oliver Neukum <Oliver.Neukum@lrz.uni-muenchen.de>]

> > a) How do you operate during system start ?
>
> 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, ...

> > 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. 

> > 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 ?

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

	Regards
		Oliver

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