Re: [PATCH 2/2] virtio-balloon: Reject qmp_balloon during hot-unplug

[Julia Suvorova]

On Thu, Jan 16, 2020 at 1:36 PM David Hildenbrand <address@hidden> wrote:
>
> On 15.01.20 23:40, Julia Suvorova wrote:
> > Hot-unplug takes some time due to communication with the guest.
> > Do not change the device while freeing up resources.
> >
> > Signed-off-by: Julia Suvorova <address@hidden>
> > ---
> >  balloon.c                  | 2 +-
> >  hw/virtio/virtio-balloon.c | 9 ++++++++-
> >  include/sysemu/balloon.h   | 2 +-
> >  3 files changed, 10 insertions(+), 3 deletions(-)
> >
> > diff --git a/balloon.c b/balloon.c
> > index f104b42961..998ec53a0f 100644
> > --- a/balloon.c
> > +++ b/balloon.c
> > @@ -119,5 +119,5 @@ void qmp_balloon(int64_t target, Error **errp)
> >      }
> >
> >      trace_balloon_event(balloon_opaque, target);
> > -    balloon_event_fn(balloon_opaque, target);
> > +    balloon_event_fn(balloon_opaque, target, errp);
> >  }
> > diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> > index 57f3b9f22d..0fa4e4454b 100644
> > --- a/hw/virtio/virtio-balloon.c
> > +++ b/hw/virtio/virtio-balloon.c
> > @@ -717,12 +717,19 @@ static void virtio_balloon_stat(void *opaque, 
> > BalloonInfo *info)
> >                                               VIRTIO_BALLOON_PFN_SHIFT);
> >  }
> >
> > -static void virtio_balloon_to_target(void *opaque, ram_addr_t target)
> > +static void virtio_balloon_to_target(void *opaque, ram_addr_t target,
> > +                                     Error **errp)
> >  {
> > +    DeviceState *bus_dev = qdev_get_bus_device(DEVICE(opaque));
> >      VirtIOBalloon *dev = VIRTIO_BALLOON(opaque);
> >      VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> >      ram_addr_t vm_ram_size = get_current_ram_size();
> >
> > +    if (bus_dev && bus_dev->pending_deleted_event) {
> > +        error_setg(errp, "Hot-unplug of %s is in progress", vdev->name);
> > +        return;
> > +    }
> > +
>
> How exactly does this help? The guest is free to inflate/deflate
> whenever it wants.

Guest is aware of hot-unplug start, and virtio driver should not
initiate any operations. This patch just restricts issuing commands
from qmp monitor.

Best regards, Julia Suvorova.