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

["Adam J. Richter" <adam@yggdrasil.com>]

>>  = Andrew Morton <morton@nortelnetworks.com>
>   = Oliver Neukum <Oliver.Neukum@lrz.uni-muenchen.de>

>> You're right, it _can_ be done by synthesizing hotpluf
>> events from the initscripts.  In fact, that's how it
>> must be done.
>
>I am afraid it cannot be simply done from the init scripts.
>Simply parsing proc has an unavoidable race condition.
>You need to lock it.
>
>        HTH
>                Oliver

	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.

	Also, since the races are done once the init script completes
(before any user logs in), you can safely do things like load the
saved device settings without worrying about clobbering any work done
before.

	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


Adam J. Richter     __     ______________   4880 Stevens Creek Blvd, Suite 104
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