Re: [virtio-comment] [RFC PATCH v1 1/1] virtio-vsock: add SOCK_SEQPACKET description

[Stefano Garzarella <sgarzare@redhat.com>]

On Thu, Feb 18, 2021 at 09:08:23AM +0300, Arseny Krasnov wrote:
> Signed-off-by: Arseny Krasnov <arseny.krasnov@kaspersky.com>
> ---
> virtio-vsock.tex | 40 +++++++++++++++++++++++++++++++++++++---
> 1 file changed, 37 insertions(+), 3 deletions(-)
>
> diff --git a/virtio-vsock.tex b/virtio-vsock.tex
> index da7e641..1ee8f99 100644
> --- a/virtio-vsock.tex
> +++ b/virtio-vsock.tex
> @@ -102,6 +102,11 @@ \subsection{Device Operation}\label{sec:Device Types / Socket Device / Device Op
> 	VIRTIO_VSOCK_OP_CREDIT_UPDATE = 6,
> 	/* Request the peer to send the credit info to us */
> 	VIRTIO_VSOCK_OP_CREDIT_REQUEST = 7,
> +
> +	/* Message begin for SOCK_SEQPACKET */
> +	VIRTIO_VSOCK_OP_SEQ_BEGIN = 8,
> +	/* Message end for SOCK_SEQPACKET */
> +	VIRTIO_VSOCK_OP_SEQ_END = 9,
> };
> \end{lstlisting}
>
> @@ -140,11 +145,11 @@ \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 for stream
> -socket types.
> +Currently stream and seqpacket sockets are supported. \field{type} is 1 for
> +stream socket types. \field{type} is 2 for seqpacket socket types.
>
> Stream sockets provide in-order, guaranteed, connection-oriented delivery
> -without message boundaries.
> +without message boundaries. Seqpacket sockets also provide 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
> @@ -240,6 +245,35 @@ \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}
> +
> +Seqpacket sockets differ from stream sockets only in data transmission way: in
> +stream sockets all data is sent using only VIRTIO_VSOCK_OP_RW packets. In
> +seqpacket sockets, to provide message boundaries, every sequence of
> +VIRTIO_VSOCK_OP_RW packets of each message is headed with
                                             ^
Since this is a spec, I think we should use MUST when something must be 
respected by the peer, for example here we can say "MUST be headed"

> +VIRTIO_VSOCK_OP_SEQ_BEGIN and tailed with VIRTIO_VSOCK_OP_SEQ_END packets.
> +Both VIRTIO_VSOCK_OP_SEQ_BEGIN and VIRTIO_VSOCK_OP_SEQ_END packets carry
                                                                     ^
Same here "MUST carry" and in the rest of the patch.

> +special header in payload:
> +
> +\begin{lstlisting}
> +struct virtio_vsock_seq_hdr {
> +	__le32  msg_cnt;
> +	__le32  msg_len;
> +};
> +\end{lstlisting}
> +
> +\field{msg_cnt} is per socket and incremented by 1 on every send of
> +VIRTIO_VSOCK_OP_SEQ_BEGIN or VIRTIO_VSOCK_OP_SEQ_END. \field{msg_len} contains
> +message length. This header is used to check integrity of each message: message
> +is valid if length of data in VIRTIO_VSOCK_OP_RW packets is equal to
> +\field{msg_len} of prepending VIRTIO_VSOCK_OP_SEQ_BEGIN and \field{msg_cnt} of
> +VIRTIO_VSOCK_OP_SEQ_END differs from \field{msg_cnt} of
> +VIRTIO_VSOCK_OP_SEQ_BEGIN by 1.

If we replace msg_cnt with msg_id, I think we should have the same 
'msg_id' for VIRTIO_VSOCK_OP_SEQ_BEGIN or VIRTIO_VSOCK_OP_SEQ_END. If 
you want to use 'msg_cnt' and you increment it between BEGIN and END, we 
should consider the overflow case.

> +
> +POSIX MSG_EOR flag is supported by special value of \field{flags} in packet's
> +header. If this flag is set for message, then all VIRTIO_VSOCK_OP_RW packets
> +of this message have bit 0 is set to 1 in \field{flags}.

Maybe we need to define what MSG_EOR means.

Thanks,
Stefano

> +
> \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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