Re: [PATCH 2/3] docs: vhost-user: rewrite section on ring state machine

[Stefan Hajnoczi]

On Fri, Feb 26, 2021 at 09:34:12AM -0500, Paolo Bonzini wrote:
> This section is using the word "back-end" to refer to the
> "slave's back-end", and talking about the "client" for
> what the rest of the document calls the "slave".
> 
> Rework it to free the use of the term "back-end", which in
> the next patch will replace "slave".
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  docs/interop/vhost-user.rst | 46 +++++++++++++++++--------------------
>  1 file changed, 21 insertions(+), 25 deletions(-)
> 
> diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
> index 6bbc092958..028ff98eac 100644
> --- a/docs/interop/vhost-user.rst
> +++ b/docs/interop/vhost-user.rst
> @@ -307,40 +307,36 @@ bit was dedicated for this purpose::
>  
>    #define VHOST_USER_F_PROTOCOL_FEATURES 30
>  
> -Starting and stopping rings
> ----------------------------
> +Ring states
> +-----------
>  
> -Client must only process each ring when it is started.
> +Rings can be in one of three states:
>  
> -Client must only pass data between the ring and the backend, when the
> -ring is enabled.
> +* stopped: the slave must not process the ring at all.
>  
> -If ring is started but disabled, client must process the ring without
> -talking to the backend.
> +* started but disabled: the slave must process the ring without
> +  causing any side effects.  For example, for a networking device,
> +  in the disabled state the slave must not supply any new RX packets,
> +  but must process and discard any TX packets.
>  
> -For example, for a networking device, in the disabled state client
> -must not supply any new RX packets, but must process and discard any
> -TX packets.
> +* started and enabled.
>  
> -If ``VHOST_USER_F_PROTOCOL_FEATURES`` has not been negotiated, the
> -ring is initialized in an enabled state.
> +Each ring is initialized in a stopped state.  The slave must start
> +ring upon receiving a kick (that is, detecting that file descriptor is

s/ring/the ring/

> +readable) on the descriptor specified by ``VHOST_USER_SET_VRING_KICK``
> +or receiving the in-band message ``VHOST_USER_VRING_KICK`` if negotiated,
> +and stop ring upon receiving ``VHOST_USER_GET_VRING_BASE``.

s/ring/the ring/

>  
> -If ``VHOST_USER_F_PROTOCOL_FEATURES`` has been negotiated, the ring is
> -initialized in a disabled state. Client must not pass data to/from the
> -backend until ring is enabled by ``VHOST_USER_SET_VRING_ENABLE`` with
> -parameter 1, or after it has been disabled by
> -``VHOST_USER_SET_VRING_ENABLE`` with parameter 0.
> +Rings can be enabled or disabled by ``VHOST_USER_SET_VRING_ENABLE``.
>  
> -Each ring is initialized in a stopped state, client must not process
> -it until ring is started, or after it has been stopped.
> +If ``VHOST_USER_F_PROTOCOL_FEATURES`` has not been negotiated, the
> +ring starts directly in the enabled state.

"starts" can be confused with the started ring state but is used to mean
"initialized" above. The following is clearer:
"ring is initialized to the stopped but enabled state"

>  
> -Client must start ring upon receiving a kick (that is, detecting that
> -file descriptor is readable) on the descriptor specified by
> -``VHOST_USER_SET_VRING_KICK`` or receiving the in-band message
> -``VHOST_USER_VRING_KICK`` if negotiated, and stop ring upon receiving
> -``VHOST_USER_GET_VRING_BASE``.
> +If ``VHOST_USER_F_PROTOCOL_FEATURES`` has been negotiated, the ring is
> +initialized in a disabled state and is enabled by
> +``VHOST_USER_SET_VRING_ENABLE`` with parameter 1.
>  
> -While processing the rings (whether they are enabled or not), client
> +While processing the rings (whether they are enabled or not), the slave
>  must support changing some configuration aspects on the fly.
>  
>  Multiple queue support
> -- 
> 2.26.2
> 
>

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