Re: [Qemu-devel] [PATCH 2/3] virtio-9p: add unrealize handler

[Greg Kurz <gkurz@linux.vnet.ibm.com>]

On Fri, 9 Oct 2015 10:36:56 +0300
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Fri, Oct 09, 2015 at 09:23:49AM +0200, Greg Kurz wrote:
> > On Wed, 07 Oct 2015 14:20:28 +0530
> > "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> wrote:
> > 
> > > Stefan Hajnoczi <stefanha@gmail.com> writes:
> > > 
> > > > On Mon, Oct 05, 2015 at 11:07:23AM +0200, Greg Kurz wrote:
> > > >> If the user tries to hot unplug a virtio-9p device, it seems to succeed but
> > > >> in fact:
> > > >> - virtio-9p coroutines thread pool and async queue are leaked
> > > >> - QEMU crashes in virtio_vmstate_change() if the user tries to live migrate
> > > >> 
> > > >> This patch brings hot unplug support to virtio-9p-device. It fixes both
> > > >> above issues.
> > > >> 
> > > >> Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> > > >> ---
> > > >>  hw/9pfs/virtio-9p-device.c |   12 ++++++++++++
> > > >>  1 file changed, 12 insertions(+)
> > > >
> > > > What happens to in-flight I/O requests?  We cannot assume that the guest
> > > > driver quiesces the device.
> > > 
> > > We enable migration blocker when we have an active mount. So if we get
> > > here, that should indicate no active 9p mounts.
> > > 
> > > -aneesh
> > 
> > Oops.. Stefan is talking about hot-unplug versus in-flight requests... not
> > about migration. And there is no such thing as a hot-unplug blocker...
> 
> If unplug request fails, that should be enough.
> 

Like setting @hotpluggable to false for the virtio-9p-pci class ? I see no
other way for the unplug request to fail... but I will happily accept all
suggestions :)

--
Greg