[PATCH] virtio-net: introduce admin control virtqueue

[Jason Wang <jasowang@redhat.com>]

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.
+
+All commands are of the following form:
+
+\begin{lstlisting}
+struct virtio_net_admin_ctrl {
+        u32 function_id;
+        struct virtio_net_ctrl ctrl;
+};
+
+\end{lstlisting}
+
+The \field{function_id} is an unique transport or device specific
+identifier for a function. E.g for the case of PCI SRIOV, it's the id
+of PCI function.
+
 \paragraph{Packet Receive Filtering}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Packet Receive Filtering}
 \label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Setting Promiscuous Mode}%old label for latexdiff
 
-- 
2.25.1