Re: [virtio-comment] [PATCH v2 01/11] transport-fabrics: introduce Virtio Over Fabrics overview

[Parav Pandit <parav@nvidia.com>]

On 5/4/2023 4:19 AM, zhenwei pi wrote:
> In the past years, virtio supports lots of device specifications by
> PCI/MMIO/CCW. These devices work fine in the virtualization environment.
>
> Introduce Virtio Over Fabrics transport to support "network defined
> peripheral devices". With this transport, Many Virtio based devices
> transparently work over fabrics. Note that the balloon device may not
> make sense. Shared memory regions won't work.
>
> Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
> ---
>   content.tex           |  1 +
>   transport-fabrics.tex | 31 +++++++++++++++++++++++++++++++
>   2 files changed, 32 insertions(+)
>   create mode 100644 transport-fabrics.tex
>
> diff --git a/content.tex b/content.tex
> index cff548a..f899c3a 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -582,6 +582,7 @@ \chapter{Virtio Transport Options}\label{sec:Virtio Transport Options}
>   \input{transport-pci.tex}
>   \input{transport-mmio.tex}
>   \input{transport-ccw.tex}
> +\input{transport-fabrics.tex}
>   
>   \chapter{Device Types}\label{sec:Device Types}
>   
> diff --git a/transport-fabrics.tex b/transport-fabrics.tex
> new file mode 100644
> index 0000000..0dc031b
> --- /dev/null
> +++ b/transport-fabrics.tex
> @@ -0,0 +1,31 @@
> +\section{Virtio Over Fabrics}\label{sec:Virtio Transport Options / Virtio Over Fabrics}
> +
> +This section defines specification to Virtio that enables operation over other
"other" is contextual given the current spec definition.
And once this change is merged its not any "other" transport.

We can probably write it without referring to the PCI transport.

> +interconnects. A central goal of Virtio Over Fabrics is to maintain consistency
> +with the PCI device, so Virtio based devices transparently work over PCI or
> +fabrics.
> +

> +Virtio Over Fabrics uses reliable connection to transmit data, the reliable
> +connection betweens two rules:
> +
between
> +\begin{itemize}
> +\item An initiator functions as an Virtio Over Fabrics client. An initiator
> +typically serves the same purpose to a machine as a Virtio device, issues
> +commands to remote side.
> +\item A target functions as an Virtio Over Fabrics server. An target typically
> +handles commands from the initiator side and responses completions.
> +\end{itemize}
> +
> +Virtio Over Fabrics has the following differences from the PCI based
> +specification:
> +
> +\begin{itemize}
> +\item Instead of memory sharing mechanism of virtqueue, there is a one-to-one
> +mapping between virtqueue and the reliable connection which executes the vring
> +data transmission.
There is no concept of vring in virtio specification beyond 0.9.5 citations.
I guess to say "reliable connection that transports virtio command, 
status and associated data".

> +\item An additional control connection is required to execute control commands
> +which is similar to read/write register on a PCI device.
> +\item Virtio Over Fabrics does not define an interrupt mechanism that allows an
> +initiator to generate a host interrupt. It is the responsibility of the host
> +fabric interface to generate host interrupts.
> +\end{itemize}
In context of fabrics "host" to be replaced with "client" or "initiator".