On Thu, Sep 06, 2012 at 09:46:50AM +0200, Paolo Bonzini wrote: > VIRTIO_BALLOON_F_MUST_TELL_HOST cannot be used properly because it is a > "negative" feature: it tells you that silent defalte is not supported. > Right now, QEMU refuses migration if the target does not support all the > features that were negotiated. But then: > > - a migration from non-MUST_TELL_HOST to MUST_TELL_HOST will succeed, > which is wrong; > > - a migration from MUST_TELL_HOST to non-MUST_TELL_HOST will fail, which > is useless. > > Add instead a new feature VIRTIO_BALLOON_F_SILENT_DEFLATE, and deprecate > VIRTIO_BALLOON_F_MUST_TELL_HOST since it is never actually used. > > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Frankly I think it's a qemu migration bug. I don't see why we need to tweak spec: just teach qemu to be smarter during migration. Can you show a scenario with old driver/new hypervisor or new driver/old hypervisor that fails? > --- > virtio-spec.lyx | 36 +++++++++++++++++++++++++++++++++--- > 1 file modificato, 33 inserzioni(+), 3 rimozioni(-) > > diff --git a/virtio-spec.lyx b/virtio-spec.lyx > index 7a073f4..1a25a18 100644 > --- a/virtio-spec.lyx > +++ b/virtio-spec.lyx > @@ -6238,6 +6238,8 @@ bits > > \begin_deeper > \begin_layout Description > + > +\change_deleted 1531152142 1346917221 > VIRTIO_BALLOON_F_MUST_TELL_HOST > \begin_inset space ~ > \end_inset > @@ -6251,6 +6253,20 @@ VIRTIO_BALLOON_F_STATS_VQ > \end_inset > > (1) A virtqueue for reporting guest memory statistics is present. > +\change_inserted 1531152142 1346917193 > + > +\end_layout > + > +\begin_layout Description > + > +\change_inserted 1531152142 1346917219 > +VIRTIO_BALLOON_F_SILENT_DEFLATE > +\begin_inset space ~ > +\end_inset > + > +(2) Host does not need to be told before pages from the balloon are used. > +\change_unchanged > + > \end_layout > > \end_deeper > @@ -6401,9 +6417,23 @@ The driver constructs an array of addresses of memory pages it has previously > \end_layout > > \begin_layout Enumerate > -If the VIRTIO_BALLOON_F_MUST_TELL_HOST feature is set, the guest may not > - use these requested pages until that descriptor in the deflateq has been > - used by the device. > +If the VIRTIO_BALLOON_F_ > +\change_deleted 1531152142 1346917234 > +MUST_TELL_HOST > +\change_inserted 1531152142 1346917237 > +SILENT_DEFLATE > +\change_unchanged > + feature is > +\change_inserted 1531152142 1346917241 > +not > +\change_unchanged > +set, the guest may not use these requested pages until that descriptor in > + the deflateq has been used by the device. > + > +\change_inserted 1531152142 1346917253 > + If it is set, the guest may choose to not use the deflateq at all. > +\change_unchanged > + > \end_layout > > \begin_layout Enumerate > -- > 1.7.11.2 _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
