Re: hotplugd - event serializer and multiplexer

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

On Mon, 2004-03-08 at 18:06, Patrick Mansfield wrote:
> On Sun, Mar 07, 2004 at 10:37:57PM +0100, Kay Sievers wrote:

> > The programs are executed in the background, but only _one_ program runs
> > at any time for a single DEVPATH. No longer need for the various 'sleep 2'
> > all over the scripts. It's possible now to order the programs, so that
> > udev has already created all nodes, before the scripts are called.
> > udevd is no longer neccessary, we can call udev directly.
> 
> How does serializing these avoid kernel races in creating attributes after
> the hotplug has been sent?

Basically it's just udevd moved to /sbin/hotplug with the ability to run
more programs than the single udev. If udev is the first program which
is executed with a hotplug event, all other programs wait until udev is
ready waiting for the attibutes and creating the nodes. So any program
that run _after_ udev can be sure that everything is in place.

Maybe we need some more folders in /etc/hotplug.d/. One with programs
executed anytime before the /etc/hotplug.d/<subsys>/ scripts and 
default/ only if no <subsys>/ is found?

> > It doesn't depend on any shell and therefore should be very fast for
> > a lot of devices connected at once. Hmm, I have only 4 :)
> 
> Use scsi_debug. Build it as a module and load it via:
> 
> /sbin/modprobe scsi_debug num_tgts=X max_luns=Y delay=T
> 
> Where X * Y is the number of disks that will get created. The delay T
> defaults to 1 milliseconds, changing this to 0 does not help as much as
> you would think (probably because we have to wake up ksoftirqd to handle
> the phony IO completions, rather than run them off of a timeout).
> 
> The sysfs entries can use up quite a bit of memory.

Nice, I will give it a try later tonight.

thanks,
Kay



-------------------------------------------------------
This SF.Net email is sponsored by: IBM Linux Tutorials
Free Linux tutorial presented by Daniel Robbins, President and CEO of
GenToo technologies. Learn everything from fundamentals to system
administration.http://ads.osdn.com/?ad_id\x1470&alloc_id638&op=click
_______________________________________________
Linux-hotplug-devel mailing list  http://linux-hotplug.sourceforge.net
Linux-hotplug-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-hotplug-devel