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

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

On Fri, Sep 24, 2010 at 07:58:08PM +0200, Manuel Bouyer wrote:
> 
> I guess this is because you're using -o log on the filesystems ?
> In order to work reliably, NetBSD needs to be able to flush the underlying's
> disk cache. This needs support in the backed driver, but this was not
> provisionned by the Xen peoples (I'm not sure how or if linux manages
> to run reliably a journaled filesystem without it) so it's a NetBSD
> extention to the Xen block device protocol.

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?

Thor