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

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On Mon, Jun 27, 2022 at 2:39 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
>
> 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 <mst@xxxxxxxxxx> 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.

Yes, but that's the device/driver interface. What's done here is the
userspace/kernel.

Userspace may break if it uses e.g sizeof(struct virtio_pci_common_cfg)?

Thanks

>
>
>
> >
> > >
> > >
> > > > Since I want to add queue_reset after queue_notify_data, I submitted
> > > > this patch first.
> > > >
> > > > Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> > > > Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
> > > > ---
> > > >  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
> > >
>




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