Re: waiting for an unknown set of udev /dev entries to complete

[Scott James Remnant <scott@ubuntu.com>]

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On Wed, 2005-11-23 at 00:13 +0100, Kay Sievers wrote:

> Scott sent a nice patch to remove the /dev/.udev.queue directory if it's
> empty. That makes it pretty easy to work around this:
>   start udevd
>   mkdir -p /dev/.udev/queue
>   trigger uevent's in /sys
>   while test -d /dev/.udev/queue; do sleep 0.1; done
> 
> The last event will just rmdir() the created queue directory.
> 
There's still a potential race here: if an event arrives after you've
created the queue directory and finishes just as you finish triggering
the uevents, but before the first triggered event gets queued, the queue
directory will be removed and the script won't wait.  

Looking through the kernel code it does look like it's almost
impossible, as the triggering of a uevent seems to not complete the
write() call until it's been posted down the netlink socket.

Almost isn't totally though; so it's there ... but it's such a remote
chance that I think it's fine for now, and the only real way to avoid
race conditions is just not to wait and arrange your entire boot
sequence to be event-driven rather than serial.

Scott
-- 
Scott James Remnant
scott@ubuntu.com

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