Re: [virtio-comment] [PATCH] virtio-net: introduce admin control virtqueue

[Jason Wang <jasowang@redhat.com>]

On 2021/1/22 äå6:11, Cornelia Huck wrote:
> On Fri, 22 Jan 2021 16:23:25 +0800
> Jason Wang<jasowang@redhat.com>  wrote:
>
> > When implementing multiple (sub)functions virtio device like SRIOV or
> > sub-function. We're suffering from several issues:
> >
> > - There's no management interface for management function (PF) to
> >    configure features, attributes for a (sub)function
> > - Per (sub)function control virtqueue could be too expensive as the
> >    number of (sub)functions could be very large
> > - Virtualize per (sub)function control virtqueue could be very
> >    challenge as we need the support of DMA isolation at queue level
> >
> > So this patch introduces the feature of VIRTIO_NET_CTRL_ADMIN_VQ. This
> > allows the device to implement a single admin control virtqueue to
> > manage per (sub)function features and attributes.
> >
> > The idea is simple, a new function id is introduced on top of the
> > exist virtio_net_ctrl structure. This id is transport or device
> > specific to uniquely identify a (sub)function.
> >
> > With this, we get a way of using management function (PF) to configure
> > per (sub)function features and attributes. And since the admin control
> > virtqueue belongs to management function (PF), the DMA is naturally
> > isolated at (sub)function level instead of the queue level for per
> > (sub)function control vq.
> >
> > Signed-off-by: Jason Wang<jasowang@redhat.com>
> > ---
> >   content.tex | 23 +++++++++++++++++++++++
> >   1 file changed, 23 insertions(+)
> >
> > diff --git a/content.tex b/content.tex
> > index 620c0e2..98592a4 100644
> > --- a/content.tex
> > +++ b/content.tex
> > @@ -2940,6 +2940,9 @@ \subsection{Feature bits}\label{sec:Device Types / Network Device / Feature bits
> >   \item[VIRTIO_NET_F_CTRL_MAC_ADDR(23)] Set MAC address through control
> >       channel.
> >   
> > +\item[VIRTIO_NET_F_ADMIN_CTRL_VQ(56)] Admin control channel is
> > +    available.
> > +
> >   \item[VIRTIO_NET_F_HASH_REPORT(57)] Device can report per-packet hash
> >       value and a type of calculated hash.
> >   
> > @@ -3864,6 +3867,26 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi
> >   do except issue a diagnostic if \field{ack} is not
> >   VIRTIO_NET_OK.
> >   
> > +\subsubsection{Admin Control Virtqueue}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue}
> > +
> > +When VIRTIO_NET_F_ADMIN_CTRL_VQ is negotiated, the driver can use the
> > +control virtqueue to manipulate features of individual function where
> > +the control virtqueues is not easily implemented in each function.
> What is a 'function' in the context of the virtio-net device? I don't
> think that this term is universal across transports.


Good point. It might have well definition only in PCI.

I wonder whether we can use "virtual device" here? It avoids transport 
specific terminology. And we can explain "virtual device" in one or two 
sentences here.

Thanks


>