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Message-ID: <CACGkMEs4Ps6Jnbzrx+4Zju7SUfgu0aTACrLyqpqBcxsZP7YOkQ@mail.gmail.com>
Date: Tue, 28 Jun 2022 14:12:13 +0800
From: Jason Wang <jasowang@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
virtualization <virtualization@...ts.linux-foundation.org>,
Richard Weinberger <richard@....at>,
Anton Ivanov <anton.ivanov@...bridgegreys.com>,
Johannes Berg <johannes@...solutions.net>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Hans de Goede <hdegoede@...hat.com>,
Mark Gross <markgross@...nel.org>,
Vadim Pasternak <vadimp@...dia.com>,
Bjorn Andersson <bjorn.andersson@...aro.org>,
Mathieu Poirier <mathieu.poirier@...aro.org>,
Cornelia Huck <cohuck@...hat.com>,
Halil Pasic <pasic@...ux.ibm.com>,
Eric Farman <farman@...ux.ibm.com>,
Heiko Carstens <hca@...ux.ibm.com>,
Vasily Gorbik <gor@...ux.ibm.com>,
Alexander Gordeev <agordeev@...ux.ibm.com>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Sven Schnelle <svens@...ux.ibm.com>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Jesper Dangaard Brouer <hawk@...nel.org>,
John Fastabend <john.fastabend@...il.com>,
Vincent Whitchurch <vincent.whitchurch@...s.com>,
linux-um@...ts.infradead.org, netdev <netdev@...r.kernel.org>,
platform-driver-x86@...r.kernel.org,
linux-remoteproc@...r.kernel.org, linux-s390@...r.kernel.org,
kvm <kvm@...r.kernel.org>,
"open list:XDP (eXpress Data Path)" <bpf@...r.kernel.org>,
kangjie.xu@...ux.alibaba.com
Subject: Re: [PATCH v10 25/41] virtio_pci: struct virtio_pci_common_cfg add queue_notify_data
On Tue, Jun 28, 2022 at 2:10 PM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Tue, Jun 28, 2022 at 02:07:28PM +0800, Jason Wang wrote:
> > On Tue, Jun 28, 2022 at 1:46 PM Michael S. Tsirkin <mst@...hat.com> wrote:
> > >
> > > On Tue, Jun 28, 2022 at 11:50:37AM +0800, Jason Wang wrote:
> > > > On Mon, Jun 27, 2022 at 7:53 PM Michael S. Tsirkin <mst@...hat.com> wrote:
> > > > >
> > > > > On Mon, Jun 27, 2022 at 04:14:20PM +0800, Jason Wang wrote:
> > > > > > On Mon, Jun 27, 2022 at 3:58 PM Michael S. Tsirkin <mst@...hat.com> wrote:
> > > > > > >
> > > > > > > On Mon, Jun 27, 2022 at 03:45:30PM +0800, Jason Wang wrote:
> > > > > > > > On Mon, Jun 27, 2022 at 2:39 PM Michael S. Tsirkin <mst@...hat.com> 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@...hat.com> 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
> > > > > > >
> > > > > > > Hmm I guess there's risk... but then how are we going to maintain this
> > > > > > > going forward? Add a new struct on any change?
> > > > > >
> > > > > > This is the way we have used it for the past 5 or more years. I don't
> > > > > > see why this must be handled in the vq reset feature.
> > > > > >
> > > > > > >Can we at least
> > > > > > > prevent this going forward somehow?
> > > > > >
> > > > > > Like have some padding?
> > > > > >
> > > > > > Thanks
> > > > >
> > > > > Maybe - this is what QEMU does ...
> > > >
> > > > Do you want this to be addressed in this series (it's already very huge anyhow)?
> > > >
> > > > Thanks
> > >
> > > Let's come up with a solution at least. QEMU does not seem to need the struct.
> >
> > If we want to implement it in Qemu we need that:
> >
> > https://github.com/fengidri/qemu/commit/39b79335cb55144d11a3b01f93d46cc73342c6bb
> >
> > > Let's just put
> > > it in virtio_pci_modern.h for now then?
> >
> > Does this mean userspace needs to define the struct by their own
> > instead of depending on the uapi in the future?
> >
> > Thanks
>
>
> $ git grep 'struct virtio_pci_common_cfg'
> include/standard-headers/linux/virtio_pci.h:struct virtio_pci_common_cfg {
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg,
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg, device_feature));
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg,
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg, device_feature));
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg,
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg,
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg,
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg,
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg,
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg, guest_feature));
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg,
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg, guest_feature));
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg,
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg,
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg, queue_select),
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg, queue_size));
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg, queue_desc_lo),
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg, queue_desc_hi),
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg, queue_avail_lo),
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg, queue_avail_hi),
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg, queue_used_lo),
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg, queue_used_hi),
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg,
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg, queue_enable), 1);
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg, msix_config), entry);
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg,
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg, queue_msix_vector),
> tests/qtest/libqos/virtio-pci-modern.c: offsetof(struct virtio_pci_common_cfg,
>
>
> The only user of the struct is libqos and it just wants
> the offsets so can use macros just as well.
Yes, so this way should be fine.
Thanks
>
>
> > >
> > > > >
> > > > > > >
> > > > > > >
> > > > > > > > >
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > > > Since I want to add queue_reset after queue_notify_data, I submitted
> > > > > > > > > > > > this patch first.
> > > > > > > > > > > >
> > > > > > > > > > > > Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > > > > > > > > > > > Acked-by: Jason Wang <jasowang@...hat.com>
> > > > > > > > > > > > ---
> > > > > > > > > > > > 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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