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

[Kay Sievers <kay.sievers@vrfy.org>]

On Mon, Nov 21, 2005 at 01:01:54AM +0100, Marco d'Itri wrote:
> On Nov 21, Kay Sievers <kay.sievers@vrfy.org> wrote:
> 
> > > I still see a problem with this design: there is a period (which may be
> > > easy to hit if the udevd is spawning the maximum allowed number of
> > > children), between when events are sent to udevd and when it starts
> > > processing them, when the on-disk queue is empty.
> > It's the received event queue, which is exported, not the processes
> > currently running. What problem do you see related to the maximum number
> > of childs?
> Nevermind, this makes the race much shorter but it's still there.
> 
> > There is still a small theorethical window between the module load
> > and the first event for a device created by that module, but it's unlikely
> > to hit that and it should be easy to work around that, if necessary.
> Yes, this is what I meant (in the context of boot-time events synthesis)
> and I do not like taking this risk.

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.

Kay


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