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

From: JÃrgen GroÃ
Date: Mon Dec 09 2019 - 08:57:53 EST

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;

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

I'm fine with the general approach, though.