Re: strange delays in vc class

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

On Fri, Oct 15, 2004 at 11:59:35AM -0700, Greg KH wrote:
> On Fri, Oct 15, 2004 at 08:48:39PM +0200, Kay Sievers wrote:
> > On Fri, Oct 15, 2004 at 11:34:33AM -0700, Greg KH wrote:
> > > On Fri, Oct 15, 2004 at 02:23:53AM +0200, Kay Sievers wrote:
> > > > On Fri, Oct 15, 2004 at 02:04:46AM +0200, Kay Sievers wrote:
> > > > > I've some debug output from a patched wait_for_sysfs. But no idea,
> > > > > what's going wrong here:
> > > > 
> > > > Ok, there is a pattern. Seems pretty strange to get _two_ hotplug events
> > > > for the same device. Only the second event will create the "dev" file we're
> > > > looking for. So the first event will spin until the second arrives with the file.
> > > 
> > > Is this with the -mm tree?  or a "clean" 2.6.9-rc4 kernel?
> > 
> > It happens with a 2.6.8 kernel.
> 
> 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...

I'm getting closer:
This is the sequence I get on bootup:

  SUBSYSTEM=net
  DEVPATH=/class/net/sit0
  SEQNUM&0
  ACTION­d

  SUBSYSTEM=vc
  DEVPATH=/class/vc/vcs4
  SEQNUM&1
  ACTION­d

  SUBSYSTEM=vc
  DEVPATH=/class/vc/vcsa4
  SEQNUM&2
  ACTION­d

  SUBSYSTEM=vc
  DEVPATH=/class/vc/vcs4
  SEQNUM&3
  ACTION=remove

  SUBSYSTEM=vc
  DEVPATH=/class/vc/vcsa4
  SEQNUM&4
  ACTION=remove

  SUBSYSTEM=vc
  DEVPATH=/class/vc/vcs4
  SEQNUM&5
  ACTION­d

  SUBSYSTEM=vc
  DEVPATH=/class/vc/vcsa4
  SEQNUM&6
  ACTION­d

According to the kernel code the vc is created on open() and destroyed
on close() which causes hotplug events.  Seems like the bootup opens and
closes a vc two times for every device.
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.

Kay


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