Subject: Re: [PATCH v10 25/41] virtio_pci: struct virtio_pci_common_cfg add queue_notify_data

From: "Michael S. Tsirkin" <[email-masked]>
Date: Mon, 27 Jun 2022 02:39:41 -0400

On Mon, Jun 27, 2022 at 10:30:42AM +0800, Jason Wang wrote:
> On Fri, Jun 24, 2022 at 2:59 PM Michael S. Tsirkin <[email-masked]> wrote:
> >
> > On Fri, Jun 24, 2022 at 10:56:05AM +0800, Xuan Zhuo wrote:
> > > Add queue_notify_data in struct virtio_pci_common_cfg, which comes from
> > > here https://github.com/oasis-tcs/virtio-spec/issues/89
> > >
> > > For not breaks uABI, add a new struct virtio_pci_common_cfg_notify.
> >
> > What exactly is meant by not breaking uABI?
> > Users are supposed to be prepared for struct size to change ... no?
> 
> Not sure, any doc for this?
> 
> Thanks

Well we have this:

        The drivers SHOULD only map part of configuration structure
        large enough for device operation.  The drivers MUST handle
        an unexpectedly large \field{length}, but MAY check that \field{length}
        is large enough for device operation.

> 
> >
> >
> > > Since I want to add queue_reset after queue_notify_data, I submitted
> > > this patch first.
> > >
> > > Signed-off-by: Xuan Zhuo <[email-masked]>
> > > Acked-by: Jason Wang <[email-masked]>
> > > ---
> > >  include/uapi/linux/virtio_pci.h | 7 +++++++
> > >  1 file changed, 7 insertions(+)
> > >
> > > diff --git a/include/uapi/linux/virtio_pci.h b/include/uapi/linux/virtio_pci.h
> > > index 3a86f36d7e3d..22bec9bd0dfc 100644
> > > --- a/include/uapi/linux/virtio_pci.h
> > > +++ b/include/uapi/linux/virtio_pci.h
> > > @@ -166,6 +166,13 @@ struct virtio_pci_common_cfg {
> > >       __le32 queue_used_hi;           /* read-write */
> > >  };
> > >
> > > +struct virtio_pci_common_cfg_notify {
> > > +     struct virtio_pci_common_cfg cfg;
> > > +
> > > +     __le16 queue_notify_data;       /* read-write */
> > > +     __le16 padding;
> > > +};
> > > +
> > >  /* Fields in VIRTIO_PCI_CAP_PCI_CFG: */
> > >  struct virtio_pci_cfg_cap {
> > >       struct virtio_pci_cap cap;
> > > --
> > > 2.31.0
> >