linux-kernel - Re: [PATCH v3 4/4] xen-blkback: support dynamic unbind/bind

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Date:   Thu, 12 Dec 2019 13:04:04 +0100
From:   Jürgen Groß <jgross@...e.com>
To:     Roger Pau Monné <roger.pau@...rix.com>,
        Paul Durrant <pdurrant@...zon.com>
Cc:     xen-devel@...ts.xenproject.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Jens Axboe <axboe@...nel.dk>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>
Subject: Re: [PATCH v3 4/4] xen-blkback: support dynamic unbind/bind

On 12.12.19 12:46, Roger Pau Monné wrote:
> On Wed, Dec 11, 2019 at 03:29:56PM +0000, 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 fio --name=randwrite --ioengine=libaio --iodepth=16 \
>>    --rw=randwrite --bs=4k --direct=1 --size=1G --verify=crc32;
>>    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.
>>
>> This is a highly useful feature for a backend module as it allows it to be
>> unloaded and re-loaded (i.e. updated) without requiring domUs to be halted.
>> This was also tested by running:
>>
>> while true;
>>    do echo vbd-$DOMID-$VBD >unbind;
>>    echo unbound;
>>    sleep 5;
>>    rmmod xen-blkback;
>>    echo unloaded;
>>    sleep 1;
>>    modprobe xen-blkback;
>>    echo bound;
>>    cd $(pwd);
>>    sleep 3;
>>    done
>>
>> in dom0 whilst running the same loop as above in the (single) PV guest.
>>
>> Some (less stressful) testing has also been done using a Windows HVM guest
>> with the latest 9.0 PV drivers installed.
>>
>> Signed-off-by: Paul Durrant <pdurrant@...zon.com>
> 
> Reviewed-by: Roger Pau Monné <roger.pau@...rix.com>
> 
> Thanks!
> 
> Juergen: I guess you will also pick this series and merge it from the
> Xen tree instead of the block one?

Yes.


Juergen