Re: [RFC PATCH v5 2/2] virtio-vsock: SOCK_SEQPACKET description

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

On Tue, Apr 13, 2021 at 03:53:29PM +0300, Arseny Krasnov wrote:
> This adds description of SOCK_SEQPACKET socket type
> support for virtio-vsock.
> 
> Signed-off-by: Arseny Krasnov <arseny.krasnov@kaspersky.com>
> ---
>  virtio-vsock.tex | 26 +++++++++++++++++++++-----
>  1 file changed, 21 insertions(+), 5 deletions(-)
> 
> diff --git a/virtio-vsock.tex b/virtio-vsock.tex
> index ad57f9d..00e59cc 100644
> --- a/virtio-vsock.tex
> +++ b/virtio-vsock.tex
> @@ -16,7 +16,10 @@ \subsection{Virtqueues}\label{sec:Device Types / Socket Device / Virtqueues}
>  
>  \subsection{Feature bits}\label{sec:Device Types / Socket Device / Feature bits}
>  
> -There are currently no feature bits defined for this device.
> +\begin{description}
> +\item VIRTIO_VSOCK_F_SEQPACKET (0) SOCK_SEQPACKET socket type is
> +    supported.

Does it make sense to only support seqpacket and not stream?
I am guessing not since seqpacket is more or less
a superset ...

> +\end{description}
>  
>  \subsection{Device configuration layout}\label{sec:Device Types / Socket Device / Device configuration layout}
>  
> @@ -135,15 +138,17 @@ \subsubsection{Addressing}\label{sec:Device Types / Socket Device / Device Opera
>  consists of a (cid, port number) tuple. The header fields used for this are
>  \field{src_cid}, \field{src_port}, \field{dst_cid}, and \field{dst_port}.
>  
> -Currently only stream sockets are supported. \field{type} is 1 (VIRTIO_VSOCK_TYPE_STREAM)
> -for stream socket types.
> +Currently stream and seqpacket sockets are supported. \field{type} is 1 (VIRTIO_VSOCK_TYPE_STREAM)
> +for stream socket types, and 2 (VIRTIO_VSOCK_TYPE_SEQPACKET) for seqpacket socket types.
>  
>  \begin{lstlisting}
> -#define VIRTIO_VSOCK_TYPE_STREAM 1
> +#define VIRTIO_VSOCK_TYPE_STREAM    1
> +#define VIRTIO_VSOCK_TYPE_SEQPACKET 2
>  \end{lstlisting}
>  
>  Stream sockets provide in-order, guaranteed, connection-oriented delivery
> -without message boundaries.
> +without message boundaries. Seqpacket sockets provide in-order, guaranteed,
> +connection-oriented delivery with message boundaries.
>  
>  \subsubsection{Buffer Space Management}\label{sec:Device Types / Socket Device / Device Operation / Buffer Space Management}
>  \field{buf_alloc} and \field{fwd_cnt} are used for buffer space management of
> @@ -244,6 +249,17 @@ \subsubsection{Stream Sockets}\label{sec:Device Types / Socket Device / Device O
>  destination) address tuple for a new connection while the other peer is still
>  processing the old connection.
>  
> +\subsubsection{Seqpacket Sockets}\label{sec:Device Types / Socket Device / Device Operation / Seqpacket Sockets}
> +
> +\paragraph{Message boundaries}\label{sec:Device Types / Socket Device / Device Operation / Seqpacket Sockets / Message boundaries}
> +
> +To provide message boundaries, last RW packet of each message has VIRTIO_VSOCK_SEQ_EOR
> +bit set in the \field{flags} of packet's header.
> +
> +\begin{lstlisting}
> +#define VIRTIO_VSOCK_SEQ_EOR 1
> +\end{lstlisting}


Problem is, where is device going to hold this boundary?
Currently device discards the header just keeping the payload
around.
I suspect we need to have some kind of header per message
maintained by the device and
accounted for as part of the the credit accounting.


> +
>  \subsubsection{Device Events}\label{sec:Device Types / Socket Device / Device Operation / Device Events}
>  
>  Certain events are communicated by the device to the driver using the event
> -- 
> 2.25.1

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