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

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
+\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
+\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.


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