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From:   "Durrant, Paul" <pdurrant@amazon.com>
To:     =?iso-8859-1?Q?Roger_Pau_Monn=E9?= <roger.pau@citrix.com>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
        "Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
        Jens Axboe <axboe@kernel.dk>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        Stefano Stabellini <sstabellini@kernel.org>
Subject: RE: [PATCH 4/4] xen-blkback: support dynamic unbind/bind
Thread-Topic: [PATCH 4/4] xen-blkback: support dynamic unbind/bind
Thread-Index: AQHVq3SGozEa3lNeXkCoixgttFczb6exvlMAgAABmYA=
Date:   Mon, 9 Dec 2019 12:24:49 +0000
Message-ID: <215c57c1096548769aeaaeaa76e7c73b@EX13D32EUC003.ant.amazon.com>
References: <20191205140123.3817-1-pdurrant@amazon.com>
 <20191205140123.3817-5-pdurrant@amazon.com>
 <20191209121726.GU980@Air-de-Roger>
In-Reply-To: <20191209121726.GU980@Air-de-Roger>
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> -----Original Message-----
> From: Roger Pau Monn=E9 <roger.pau@citrix.com>
> Sent: 09 December 2019 12:17
> To: Durrant, Paul <pdurrant@amazon.com>
> Cc: linux-kernel@vger.kernel.org; xen-devel@lists.xenproject.org; Konrad
> Rzeszutek Wilk <konrad.wilk@oracle.com>; Jens Axboe <axboe@kernel.dk>;
> Boris Ostrovsky <boris.ostrovsky@oracle.com>; Juergen Gross
> <jgross@suse.com>; Stefano Stabellini <sstabellini@kernel.org>
> Subject: Re: [PATCH 4/4] xen-blkback: support dynamic unbind/bind
>=20
> On Thu, Dec 05, 2019 at 02:01:23PM +0000, Paul Durrant wrote:
> > By simply re-attaching to shared rings during connect_ring() rather tha=
n
> > 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=3D/dev/urandom of=3Dtest.img bs=3D1M count=3D1024;=
 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
>=20
> So this does unbind blkback while leaving the PV interface as
> connected?
>=20

Yes, everything is left in place in the frontend. The backend detaches from=
 the ring, closes its end of the event channels, etc. but the guest can sti=
ll send requests which will get serviced when the new backend attaches.

  Paul