Re: xbd0: WARNING: cache flush not supported by backend

[Thor Lancelot Simon <tls%panix.com@localhost>]

On Sat, Sep 25, 2010 at 12:22:39AM +0200, Manuel Bouyer wrote:
> On Fri, Sep 24, 2010 at 05:39:56PM -0400, Thor Lancelot Simon wrote:
> > 
> > I have wondered about this.  Linux guests hosted on NetBSD dom0 complain
> > that they cannot do flushes or write barriers.  Hosted on Linux Dom0,
> > they work fine.
> > 
> > So I have to conclude that we just implement cache flushes in a different
> > way than they do, not that they don't implement them.  Why?
> 
> I guess this is something that showed up in a later version of Xen then.
> When I wrote the cache flush I'm almost sure nothing related was
> present in the public interface.
> 
> With what linux guest do you see this ? I'm not seeing any warning
> with the linux guests I use (RHEL5 like)

Here's what I get from gentoo with XFS.  I don't get these warnings with
a Linux dom0 (I checked very carefully about six months ago but do not
have a Linux dom0 to confirm again now):

[    0.413403] Filesystem "xvda1": Disabling barriers, trial barrier write
failed
[    0.414310] XFS mounting filesystem xvda1

Thor