Re: strange delays in vc class

[Greg KH <greg@kroah.com>]

On Fri, Oct 15, 2004 at 10:09:25PM +0200, Kay Sievers wrote:
> 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?

I think it's a big rewrite from what we have working today :)

Although some of the benifits you list might be nice to have. I don't
know how well we could get rid of the dev.d/ stuff, as we still can't
map hotplug events to dev.d/ events without running through udev (so a
hotplug.d script would know where to be placed.)

thanks,

greg k-h


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