Re: [RFC PATCH] docs/interop: define STANDALONE protocol feature for vhost-user

[Stefan Hajnoczi <stefanha@redhat.com>]

On Tue, Jul 04, 2023 at 01:36:00PM +0100, Alex Bennée wrote:
> Currently QEMU has to know some details about the back-end to be able
> to setup the guest. While various parts of the setup can be delegated
> to the backend (for example config handling) this is a very piecemeal
> approach.
> 
> This patch suggests a new feature flag (VHOST_USER_PROTOCOL_F_STANDALONE)
> which the back-end can advertise which allows a probe message to be
> sent to get all the details QEMU needs to know in one message.
> 
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> 
> ---
> Initial RFC for discussion. I intend to prototype this work with QEMU
> and one of the rust-vmm vhost-user daemons.
> ---
>  docs/interop/vhost-user.rst | 37 +++++++++++++++++++++++++++++++++++++
>  hw/virtio/vhost-user.c      |  8 ++++++++
>  2 files changed, 45 insertions(+)
> 
> diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
> index 5a070adbc1..85b1b1583a 100644
> --- a/docs/interop/vhost-user.rst
> +++ b/docs/interop/vhost-user.rst
> @@ -275,6 +275,21 @@ Inflight description
>  
>  :queue size: a 16-bit size of virtqueues
>  
> +Backend specifications
> +^^^^^^^^^^^^^^^^^^^^^^
> +
> ++-----------+-------------+------------+------------+
> +| device id | config size |   min_vqs  |   max_vqs  |
> ++-----------+-------------+------------+------------+
> +
> +:device id: a 32-bit value holding the VirtIO device ID
> +
> +:config size: a 32-bit value holding the config size (see ``VHOST_USER_GET_CONFIG``)
> +
> +:min_vqs: a 32-bit value holding the minimum number of vqs supported

What is the purpose of min_vqs? I'm not sure why the front-end needs to
know this.

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