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Subject: Re: [PATCH 4/4] xen-blkback: support dynamic unbind/bind
To:     Paul Durrant <pdurrant@amazon.com>, linux-kernel@vger.kernel.org,
        xen-devel@lists.xenproject.org
Cc:     Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= <roger.pau@citrix.com>,
        Jens Axboe <axboe@kernel.dk>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Stefano Stabellini <sstabellini@kernel.org>
References: <20191205140123.3817-1-pdurrant@amazon.com>
 <20191205140123.3817-5-pdurrant@amazon.com>
From:   =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>
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Date:   Mon, 9 Dec 2019 14:57:49 +0100
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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.

I'm fine with the general approach, though.


Juergen