# Re: \[virtio-comment\] \[RFC PATCH v1 1/1\] virtio-vsock: add SOCK\_SEQPACKET description

- From: Stefano Garzarella \<sgarzare@redhat.com\>
- Date: 2021-02-24 09:32:10 
- List: virtualization
- Page: https://ratatoskr.run/virtualization/2021/02/14539300
- Thread: https://ratatoskr.run/virtio-comment/2021/02/14539298/t.md

```text
On Thu, Feb 18, 2021 at 09:08:23AM +0300, Arseny Krasnov wrote:
>Signed-off-by: Arseny Krasnov <redacted>
>---
> 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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