Re: cold plugging

[Aras Vaichas <arasv@magellan-technology.com>]

Alexander E. Patrakov wrote:
> Thanks, but you probably missed the point. Your loop does NOT wait for 
> all events. I think that in my case the following happens:
> 
> 1) The script creates an empty /dev/.udev/queue directory
> 2) The script causes the kernel to emit uevents
> 3) udevd gets those uevents, and reacts upon them. This reaction 
> involves, among other things, making device nodes and calling 
> /sbin/modprobe to load new drivers.
> 4) Those drivers are bound to devices by the kernel, this produces new 
> uevents, go to (3).
> 5) When the internal queue of udevd becomes empty, it removes the 
> /dev/.udev/queue directory and the loop exits.
> 
> The problem is that some modules take longer than 0.1s to detect their 
> hardware, so there is a period of time longer than 0.1s with the empty 
> udevd queue, after which new uevents arrive.
>
> 6) such late uevents reach udevd after the loop ends, and then it may be 
> too late (but it is OK for me to ignore this for my scanner).

I had a similar problem with a USB Flash drive that had a delay in the driver 
for it to "warm up". I just had a larger delay (and less cycles) in my queue 
polling script and it works OK. The worst case scenario is that this loop 
delays the boot for 1 second, which I can live with.

mkdir -p /dev/.udev/queue
udevsynthesize
udevd_timeout\x10
while [ -d /dev/.udev/queue/ ]; do
         /usr/bin/sleep 1
         udevd_timeout=$(($udevd_timeout - 1))
         if [ $udevd_timeout -eq 0 ]; then
                 echo "timeout"
                 break
         fi
done
echo "coldplug complete"

regards,

Aras Vaichas


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