Re: [PATCH v2] virtio-vsock: add VIRTIO_VSOCK_F_NO_IMPLIED_STREAM feature bit

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jul 18, 2022 at 04:26:53PM +0200, Stefano Garzarella wrote:
> Initially virtio-vsock only supported the stream type, which is why
> there was no feature. Later we added the seqpacket type and in the future
> we may have other types (e.g. datagram).
> 
> seqpacket is an extension of stream, so it might be implied that if
> seqpacket is supported, stream is too, but this might not be true for
> other types.
> 
> As we discussed here [1] should be better to add a new
> VIRTIO_VSOCK_F_NO_IMPLIED_STREAM feature bit to avoid this implication.
> 
> Let's also add normative sections to better define the behavior when
> VIRTIO_VSOCK_F_NO_IMPLIED_STREAM is negotiated or not.
> 
> [1] http://markmail.org/message/2s3qd74drgjxkvte
> 
> Suggested-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

> ---
> v2:
> - rewrote better normative statements [Cornelia]
> - updated conformance.tex with the new sections [Cornelia]
> 
> v1: https://markmail.org/message/ybtl4trifrhjnkfe
> ---
>  conformance.tex  |  2 ++
>  virtio-vsock.tex | 28 ++++++++++++++++++++++++----
>  2 files changed, 26 insertions(+), 4 deletions(-)
> 
> diff --git a/conformance.tex b/conformance.tex
> index 663e7c3..98626ba 100644
> --- a/conformance.tex
> +++ b/conformance.tex
> @@ -229,6 +229,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
>  A socket driver MUST conform to the following normative statements:
>  
>  \begin{itemize}
> +\item \ref{drivernormative:Device Types / Socket Device / Feature bits}
>  \item \ref{drivernormative:Device Types / Socket Device / Device Operation / Buffer Space Management}
>  \item \ref{drivernormative:Device Types / Socket Device / Device Operation / Receive and Transmit}
>  \item \ref{drivernormative:Device Types / Socket Device / Device Operation / Device Events}
> @@ -500,6 +501,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
>  A socket device MUST conform to the following normative statements:
>  
>  \begin{itemize}
> +\item \ref{devicenormative:Device Types / Socket Device / Feature bits}
>  \item \ref{devicenormative:Device Types / Socket Device / Device Operation / Buffer Space Management}
>  \item \ref{devicenormative:Device Types / Socket Device / Device Operation / Receive and Transmit}
>  \end{itemize}
> diff --git a/virtio-vsock.tex b/virtio-vsock.tex
> index d79984d..b3ff45a 100644
> --- a/virtio-vsock.tex
> +++ b/virtio-vsock.tex
> @@ -16,15 +16,35 @@ \subsection{Virtqueues}\label{sec:Device Types / Socket Device / Virtqueues}
>  
>  \subsection{Feature bits}\label{sec:Device Types / Socket Device / Feature bits}
>  
> -If no feature bit is set, only stream socket type is supported.
> -If VIRTIO_VSOCK_F_SEQPACKET has been negotiated, the device MAY act
> -as if VIRTIO_VSOCK_F_STREAM has also been negotiated.
> -
>  \begin{description}
>  \item[VIRTIO_VSOCK_F_STREAM (0)] stream socket type is supported.
>  \item[VIRTIO_VSOCK_F_SEQPACKET (1)] seqpacket socket type is supported.
> +\item[VIRTIO_VSOCK_F_NO_IMPLIED_STREAM (2)] stream socket type is not implied.
>  \end{description}
>  
> +\drivernormative{\subsubsection}{Feature bits}{Device Types / Socket Device / Feature bits}
> +
> +The driver SHOULD accept the VIRTIO_VSOCK_F_NO_IMPLIED_STREAM feature if
> +offered by the device.
> +
> +If no feature bit has been negotiated, the driver SHOULD act as if
> +VIRTIO_VSOCK_F_STREAM has been negotiated.
> +
> +If VIRTIO_VSOCK_F_SEQPACKET has been negotiated, but not
> +VIRTIO_VSOCK_F_NO_IMPLIED_STREAM, the driver MAY act as if
> +VIRTIO_VSOCK_F_STREAM has also been negotiated.
> +
> +\devicenormative{\subsubsection}{Feature bits}{Device Types / Socket Device / Feature bits}
> +
> +The device SHOULD offer the VIRTIO_VSOCK_F_NO_IMPLIED_STREAM feature.
> +
> +If no feature bit has been negotiated, the device SHOULD act as if
> +VIRTIO_VSOCK_F_STREAM has been negotiated.
> +
> +If VIRTIO_VSOCK_F_SEQPACKET has been negotiated, but not
> +VIRTIO_VSOCK_F_NO_IMPLIED_STREAM, the device MAY act as if
> +VIRTIO_VSOCK_F_STREAM has also been negotiated.
> +
>  \subsection{Device configuration layout}\label{sec:Device Types / Socket Device / Device configuration layout}
>  
>  Socket device configuration uses the following layout structure:
> -- 
> 2.36.1