Re: Question to recent xentools3 update

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Thu, Mar 27, 2008 at 08:42:36PM +0100, Juergen Hannken-Illjes wrote:
> 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:

Hum, I remember someone saying it would still work with vnd0d.

> 
> 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.

it should be possible to open the same block device multiple times, if it's
open read-only. I don't know if it can be easily be done in the current
world.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--