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

From: "Durrant, Paul" <pdurrant@amazon.com>
To: "Jürgen Groß" <jgross@suse.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"xen-devel@lists.xenproject.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
Date: Mon, 9 Dec 2019 14:01:43 +0000	[thread overview]
Message-ID: <158cb2845bec457fa54c6dfbd5a9efac@EX13D32EUC003.ant.amazon.com> (raw)
In-Reply-To: <bbf958af-d435-3a56-1e91-e068125a9ce7@suse.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