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

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Date:   Mon, 9 Dec 2019 14:01:43 +0000
From:   "Durrant, Paul" <pdurrant@...zon.com>
To:     Jürgen Groß <jgross@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>
CC:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Roger Pau Monné <roger.pau@...rix.com>,
        Jens Axboe <axboe@...nel.dk>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        "Stefano Stabellini" <sstabellini@...nel.org>
Subject: RE: [PATCH 4/4] xen-blkback: support dynamic unbind/bind

> -----Original Message-----
> From: Jürgen Groß <jgross@...e.com>
> Sent: 09 December 2019 13:58
> To: Durrant, Paul <pdurrant@...zon.com>; linux-kernel@...r.kernel.org;
> xen-devel@...ts.xenproject.org
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>; Roger Pau Monné
> <roger.pau@...rix.com>; Jens Axboe <axboe@...nel.dk>; Boris Ostrovsky
> <boris.ostrovsky@...cle.com>; Stefano Stabellini <sstabellini@...nel.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