RE: [PATCH 4/4] xen-blkback: support dynamic unbind/bind

["Durrant, Paul" <pdurrant@amazon.com>]

> -----Original Message-----
> From: Jürgen Groß <jgross@suse.com>
> Sent: 09 December 2019 13:58
> To: Durrant, Paul <pdurrant@amazon.com>; linux-kernel@vger.kernel.org;
> xen-devel@lists.xenproject.org
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>; Roger Pau Monné
> <roger.pau@citrix.com>; Jens Axboe <axboe@kernel.dk>; Boris Ostrovsky
> <boris.ostrovsky@oracle.com>; Stefano Stabellini <sstabellini@kernel.org>
> Subject: Re: [PATCH 4/4] xen-blkback: support dynamic unbind/bind
> 
> On 05.12.19 15:01, Paul Durrant wrote:
> > By simply re-attaching to shared rings during connect_ring() rather than
> > assuming they are freshly allocated (i.e assuming the counters are zero)
> > it is possible for vbd instances to be unbound and re-bound from and to
> > (respectively) a running guest.
> >
> > This has been tested by running:
> >
> > while true; do dd if=/dev/urandom of=test.img bs=1M count=1024; done
> >
> > in a PV guest whilst running:
> >
> > while true;
> >    do echo vbd-$DOMID-$VBD >unbind;
> >    echo unbound;
> >    sleep 5;
> >    echo vbd-$DOMID-$VBD >bind;
> >    echo bound;
> >    sleep 3;
> >    done
> >
> > in dom0 from /sys/bus/xen-backend/drivers/vbd to continuously unbind and
> > re-bind its system disk image.
> 
> Could you do the same test with mixed reads/writes and verification of
> the read/written data, please? A write-only test is not _that_
> convincing regarding correctness. It only proves the guest is not
> crashing.

Sure. I'll find something that will verify content.

> 
> I'm fine with the general approach, though.
> 

Cool, thanks,

  Paul

> 
> Juergen