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

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

> 	I said, "scan the bus *after* initializing the hot plugging
> support and deal with devices that are already plugged in [...]"
> You may process a device twice this way, but user level software
> can detect this and synchronize when this is really necessary.  In
> most cases, you just want to modprobe a module, which can safely be
> done multiple times, so it is not necessary to bother checking.

The problem is that may try to configure a device that's no longer there,
or worse a device that is being replaced this way. You need to tell the 
kernel that it must cease processing events on a bus that you are scanning.

> 	In cases where you really need to avoid doing something twice
> (such as spawning a dhcp client on an ethernet port), you can do your
> synchronization at user level, by something like:
>
> 	# "insert" script
> 	netif=$1   # For example "eth0"
> 	# /var/run was previous cleared earlier in the boot process, so
> 	# we know that if this directory exists, we have been called
> 	# twice.
> 	if mkdir /var/run/$netif ; then
> 		dhclient -pf /var/run/$netif/pid $netif &
> 	fi
>
> 	# "remove" script
> 	netif=$1   # For example "eth0"
> 	kill $(cat /var/run/netif/$netif/pid)
> 	rm -rf /var/run/$netif

That's the problem. You compute $1 and then you configure it without a 
guarantee that $1 is still the interface you thought it to be.
It is a very small window, but I feel that we shouldn't design something 
which works only in most cases.

	Regards
		Oliver

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