Re: [virtio-comment] [PATCH] Update VIRTIO_F_EVENT_IDX throughout

[Cornelia Huck <cohuck@redhat.com>]

On Thu, 29 Apr 2021 16:10:16 -0700
Joel Nider <joel@nider.org> wrote:

> This flag has been called by many names in the past
> (VIRTIO_RING_F_EVENT_IDX, VIRTIO_F_RING_EVENT_IDX) and there are
> just a few stragglers left to clean up.
> 
> Signed-off-by: Joel Nider <joel@nider.org>
> ---
>  content.tex     | 2 +-
>  packed-ring.tex | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/content.tex b/content.tex
> index 9232d5c..5a803dc 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -6581,7 +6581,7 @@ \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
>  Descriptors}~\nameref{sec:Basic Facilities of a Virtio Device /
>  Virtqueues / The Virtqueue Descriptor Table / Indirect
>  Descriptors} and \ref{sec:Packed Virtqueues / Indirect Flag: Scatter-Gather Support}~\nameref{sec:Packed Virtqueues / Indirect Flag: Scatter-Gather Support}.
> -  \item[VIRTIO_F_RING_EVENT_IDX(29)] This feature enables the \field{used_event}
> +  \item[VIRTIO_F_EVENT_IDX(29)] This feature enables the \field{used_event}

Hm. The VIRTIO_F_RING_ version actually matches well with
VIRTIO_F_RING_INDIRECT_DESC and VIRTIO_F_RING_PACKED. While the latter
is used consistently throughout the spec, we seem to use
VIRTIO_F_INDIRECT_DESC in other places. For added variety, Linux and
QEMU use VIRTIO_RING_F_INDIRECT_DESC and VIRTIO_RING_F_EVENT_IDX (but
VIRTIO_F_RING_PACKED.)

We should be consistent within the spec, so I'd vote for using the
VIRTIO_F_RING_ versions everywhere here. (The Linux/QEMU variants are
still easily recognizable, so there's actually not much potential for
confusion.) The only downside is that this would mean more changes.

Opinions?

>    and the \field{avail_event} fields as described in
>  \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Used Buffer Notification Suppression}, \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / The Virtqueue Used Ring} and \ref{sec:Packed Virtqueues / Driver and Device Event Suppression}.
>  
> diff --git a/packed-ring.tex b/packed-ring.tex
> index ea92543..a9e6c16 100644
> --- a/packed-ring.tex
> +++ b/packed-ring.tex
> @@ -336,7 +336,7 @@ \subsection{Driver and Device Event Suppression}
>  /*
>   * Enable events for a specific descriptor
>   * (as specified by Descriptor Ring Change Event Offset/Wrap Counter).
> - * Only valid if VIRTIO_F_RING_EVENT_IDX has been negotiated.
> + * Only valid if VIRTIO_F_EVENT_IDX has been negotiated.
>   */
>  #define RING_EVENT_FLAGS_DESC 0x2
>  /* The value 0x3 is reserved */
> @@ -597,7 +597,7 @@ \subsubsection{Implementation Example}\label{sec:Basic Facilities of a Virtio De
>  
>  Below is a driver code example. It does not attempt to reduce
>  the number of available buffer notifications, neither does it support
> -the VIRTIO_F_RING_EVENT_IDX feature.
> +the VIRTIO_F_EVENT_IDX feature.
>  
>  \begin{lstlisting}
>  /* Note: vq->avail_wrap_count is initialized to 1 */