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

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

> > These are not enough. You must ensure that "remove" has finished before
> > you start anything that reuses the device node.
>
> I was assuming something that I suspect we should be considering
> as a goal (an "architectural" one?): names passed by hotplug agents
> must be stable.

Good idea.

> I'll have to think more about Vojtech's comments.  I think I will
> likely want the kernel to guarantee some stable name (is that a
> place where devfs could really help?) and let all the mappings
> to "virtual" names (like "eth0") be managed separately.

For SCSI devfs does that. About other subsystems I don't know enough.

But stable names don't save you from a need to serialise due to reuse.
In fact a stable name implies reuse, as it depends on bus location.
Either you get unique or you get stable names.

> > You see, changing the order of events 2 and 3 is wrong.
> > You'd have the wrong interfaces in printcap.
>
> Couldn't matter if the agent were passing the right stable names
> though, right?

Right, except for true reuse. See above.

> > Then you'd need to have a stable name provided to the hotplug script.
>
> Yes ...
>
> > This is difficult, for several reasons.
> > a) You need devfs (which is not PC)
>
> "devfsd" is not PC for me, but I'm less clear why a "/devfs" wouldn't be
> fine. Anyone care to start a separate thread on such topics?
>
> > b) You know that name only after the driver is loaded. (You don't even
> > know the number of names, multifunction devices and bridges)
>
> Device drivers can be viewed as adapters between namespaces:
> loading a device driver may cause entries in other namespaces.

This is the most theoretical way I have ever heard device drivers described 
:-)

> USB device "/proc/bus/usb/002/031" may be network interface "usb0".
> The lower level name (USB) is known before "usbnet" is loaded,
> but "usb0" isn't known till afterwards ... but then, USB hotplugging
> sees the USB name, and network hotplugging is what sees "usb0".

True, but there's no equivalent for network hotplugging for other subsystems.

> > c) You'd need to call after drivers have bound to interfaces.
>
> USB hotplug is called after the kernel gives drivers a chance to
> bind to interfaces.

That's not enough.
The mapping between devices and nodes isn't 1:1 but 1:0-n
You need an agent run for every node and an agent for the device (to load the 
driver)

> > These are conflicting requirements. In fact you'd need _two_ scripts. One
> > to load the driver, a second to configure the device the driver has bound
> > to.
>
> You mean like the difference between /etc/hotplug/*.agent (load driver FOO)
> and /etc/hotplug/*/FOO (configure each new device)?  :-)

I am not sure. I think you need to call them independently.

	Regards
		Oliver

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