netdevice problem

[Andrew Morton <andrewm@uow.edu.au>]

As far as I know, the "vision" is that the hotplug
architecture can be used at boot time.  We identify
all the ISA/PCI/whatever devices and create hotplug
insertion events for them, and just let the hotplug
magic happen.

There are several ways of doing this, most notably:

a) Buffer the results of the bootup PCI scan and
   spit out hotplug events after filesystems have
   been mounted, etc.

b) Scan the buses from initscripts, synthesise hotplug
   events from userspace.

Both approaches are broken, because we'll end up
running /sbin/hotplug N times concurrently.  The
assignment of eth0, eth1, eth2, etc will be totally
random and people will hate us.

The fixes appear to be:

1: Funky hard-wired delay in the hotplug synthesiser.  (cs89x0
   will require five seconds, please...)

2: Funky userland locking which blocks each hotplug synthesis
   until the previous one has completed its `ifconfig up',
   if it indeed did it.  This is crap.

3: Stick with modutils.conf to drive the bootup process,
   switch to hotplug scripts for post-boot insert/remove.
   This is a sad mix.

4: Rework call_usermodehelper for synchronous (or completion
   callback) semantics.  So the pci layer's callout doesn't
   return until both 'hotplug pci' and its child, 
   'hotplug net' have terminated.

Option 4 is of course the patch-which-didn't-make-it.  I haven't
resubmitted because the jury is still out on whether it's
still needed.  If the current setup can be reasonably used
from userspace then let's not hassle Linus.

But I now feel it's needed.  Any clever ideas out there?

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