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SubjectRe: [PATCH v3 4/4] xen-blkback: support dynamic unbind/bind
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@amazon.com>

Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

Thanks!

Juergen: I guess you will also pick this series and merge it from the
Xen tree instead of the block one?

Roger.

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