RE: [RFC qemu 2/4] virtio-balloon: Add a new feature to balloon device

[Li, Liang Z]

> On Thu,  3 Mar 2016 18:44:26 +0800
> Liang Li <liang.z.li@xxxxxxxxx> wrote:
> 
> > Extend the virtio balloon device to support a new feature, this new
> > feature can help to get guest's free pages information, which can be
> > used for live migration optimzation.
> 
> Do you have a spec for this, e.g. as a patch to the virtio spec?

Not yet.
> 
> >
> > Signed-off-by: Liang Li <liang.z.li@xxxxxxxxx>
> > ---
> >  balloon.c                                       | 30 ++++++++-
> >  hw/virtio/virtio-balloon.c                      | 81 ++++++++++++++++++++++++-
> >  include/hw/virtio/virtio-balloon.h              | 17 +++++-
> >  include/standard-headers/linux/virtio_balloon.h |  1 +
> >  include/sysemu/balloon.h                        | 10 ++-
> >  5 files changed, 134 insertions(+), 5 deletions(-)
> 
> > +static int virtio_balloon_free_pages(void *opaque,
> > +                                     unsigned long *free_pages_bitmap,
> > +                                     unsigned long *free_pages_count)
> > +{
> > +    VirtIOBalloon *s = opaque;
> > +    VirtIODevice *vdev = VIRTIO_DEVICE(s);
> > +    VirtQueueElement *elem = s->free_pages_vq_elem;
> > +    int len;
> > +
> > +    if (!balloon_free_pages_supported(s)) {
> > +        return -1;
> > +    }
> > +
> > +    if (s->req_status == NOT_STARTED) {
> > +        s->free_pages_bitmap = free_pages_bitmap;
> > +        s->req_status = STARTED;
> > +        s->mem_layout.low_mem =
> > + pc_get_lowmem(PC_MACHINE(current_machine));
> 
> Please don't leak pc-specific information into generic code.

I have already notice that and just leave it here in this  initial RFC version,  
the hard part of this solution is how to handle different architecture ...

Thanks!

Liang