Re: strange delays in vc class

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

On Fri, Oct 15, 2004 at 09:18:26PM +0200, Kay Sievers wrote:
> On Fri, Oct 15, 2004 at 11:59:35AM -0700, Greg KH wrote:
> > 
> > Ugh.  In looking at the kernel code, I don't see how it could be doing
> > this.  But the console startup code is a strange beast...
> 
> The close will remove the "dev" file and the wait_for_sysfs from the
> add-hotplug will spin and fail or at best will recover with the next
> hotplug-add. The "remove" event beats the "add"! We have the same event
> serializing problem here, we solved with udevd for udev.

I may reactivate my old hotplugd work to address this?

We merge udev and udevd. We parse the config and rules once on startup and
then wait for events as udevd does today.

On a kernel event udevd does a fork() but _no_ exec(). This will create a
new instance of the same code with the already parsed config in memory.

The forked udevd instance will:
  o wait for sysfs internally
  o if needed create the node and set the environment
  o execute /etc/hotplug.d/ scripts (with DEVPATH in the environment)

This leads to:
  o complete serialized hotplug sequence handling
  o hotplug.d/ execution with sane sysfs state and created node
  o no more dev.d/ (can just live in hotplug.d/)
  o no udev disk activity (with nodes and db on tmpfs)
  o only one process fork() for every event (besides possible callouts)

It is a bit far from the current model but we already rely on a running
daemon. I've had something like this in mind with all my recent work.
In the very long run we may even set /proc/sys/kernel/hotplug to "" after
bootup and udevd(hotplugd) can get the hotplug-events over netlink :)

What do you think?

Kay


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