Re: Question to recent xentools3 update

[Juergen Hannken-Illjes <hannken%eis.cs.tu-bs.de@localhost>]

On Thu, Mar 27, 2008 at 08:12:30PM +0100, Christoph Egger wrote:
> Manuel Bouyer wrote:
> >On Thu, Mar 27, 2008 at 07:05:04PM +0100, Christoph Egger wrote:
> >>>If a Xen config with "disk = [ 'phy:/dev/rraid0f,0x1,w' ]" works and no 
> >>>other
> >>>Xen component opens the corresponding block device this could work.  As 
> >>>my
> >>>Xen machine is in production now, I cannot test it.
> >>When you create two new guests (for testing purpose) both with
> >>"disk = [ 'phy:/dev/cd0a,0x1,r' ]" do you get an EBUSY when you start 
> >>the second guest?
> >
> >yes.
> >
> >>I think, trying to start two guests from the same 
> >>(Live-)CD shouldn't hurt.
> >
> >I think this behavior changed recently in current. I've not investigated
> >this yet. 
> 
> What I want to know is what happens when two guests open the same
> block device. /dev/cd0a is a harmless test candidate. Do you mean, cd0a 
> is an exception now?
> 
> Christoph

No exception -- this behaviour is the same for all block devices.  It is the
result of the second item of:

date: 2008/01/24 17:32:54;  author: ad;  state: Exp;  lines: +56 -213
specfs changes for PR kern/37717 (raidclose() is no longer called on
shutdown). There are still problems with device access and a PR will be
filed.

- Kill checkalias(). Allow multiple vnodes to reference a single device.

- Don't play dangerous tricks with block vnodes to ensure that only one
  vnode can describe a block device. Instead, prohibit concurrent opens of
  block devices. As a bonus remove the unreliable code that prevents
  multiple file system mounts on the same device. It's no longer needed.

- Track opens by vnode and by device. Issue cdev_close() when the last open
  goes away, instead of abusing vnode::v_usecount to tell if the device is
  open.

-- 
Juergen Hannken-Illjes - hannken%eis.cs.tu-bs.de@localhost - TU Braunschweig 
(Germany)