On Mon, Apr 12, 2021 at 7:21 AM Stefano Garzarella <sgarzare@xxxxxxxxxx> wrote:
>
> On Mon, Apr 12, 2021 at 02:50:17PM +0100, Stefan Hajnoczi wrote:
> >On Thu, Apr 01, 2021 at 04:36:02AM +0000, jiang.wang wrote:
> >> Add supports for datagram type for virtio-vsock. Datagram
> >> sockets are connectionless and unreliable. To avoid contention
> >> with stream and other sockets, add two more virtqueues and
> >> a new feature bit to identify if those two new queues exist or not.
> >>
> >> Also add descriptions for resource management of datagram, which
> >> does not use the existing credit update mechanism associated with
> >> stream sockets.
> >>
> >> Signed-off-by: Jiang Wang <jiang.wang@xxxxxxxxxxxxx>
> >> ---
> >> V2 addressed the comments for the previous version.
> >>
> >> virtio-vsock.tex | 62 +++++++++++++++++++++++++++++++++++++++++++++++---------
> >> 1 file changed, 52 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/virtio-vsock.tex b/virtio-vsock.tex
> >> index da7e641..62c12e0 100644
> >> --- a/virtio-vsock.tex
> >> +++ b/virtio-vsock.tex
> >> @@ -11,12 +11,25 @@ \subsection{Virtqueues}\label{sec:Device Types / Socket Device / Virtqueues}
> >> \begin{description}
> >> \item[0] rx
> >> \item[1] tx
> >> +\item[2] datagram rx
> >> +\item[3] datagram tx
> >> +\item[4] event
> >> +\end{description}
> >> +The virtio socket device uses 5 queues if feature bit VIRTIO_VSOCK_F_DRGAM is set. Otherwise, it
> >> +only uses 3 queues, as the following. Rx and tx queues are always used for stream sockets.
> >> +
> >> +\begin{description}
> >> +\item[0] rx
> >> +\item[1] tx
> >> \item[2] event
> >> \end{description}
> >>
> >
> >I suggest renaming "rx" and "tx" to "stream rx" and "stream tx"
> >virtqueues and also adding this:
> >
> > When behavior differs between stream and datagram rx/tx virtqueues
> > their full names are used. Common behavior is simply described in
> > terms of rx/tx virtqueues and applies to both stream and datagram
> > virtqueues.
> >
> >This way you won't need to duplicate portions of the spec that deal with
> >populating the virtqueues, for example.
> >
> >It's also clearer to use a full name for stream rx/tx virtqueues instead
> >of calling them rx/tx virtqueues now that we have datagram rx/tx
> >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_DGRAM (0)] Device has support for datagram socket type.
> >> +\end{description}
> >>
> >> \subsection{Device configuration layout}\label{sec:Device Types / Socket Device / Device configuration layout}
> >>
> >> @@ -107,6 +120,9 @@ \subsection{Device Operation}\label{sec:Device Types / Socket Device / Device Op
> >>
> >> \subsubsection{Virtqueue Flow Control}\label{sec:Device Types / Socket Device / Device Operation / Virtqueue Flow Control}
> >>
> >> +Flow control applies to stream sockets; datagram sockets do not have
> >> +flow control.
> >> +
> >> The tx virtqueue carries packets initiated by applications and replies to
> >> received packets. The rx virtqueue carries packets initiated by the device and
> >> replies to previously transmitted packets.
> >> @@ -140,12 +156,15 @@ \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 datagram (dgram) sockets are supported. \field{type} is 1 for stream
> >> +socket types. \field{type} is 3 for dgram socket types.
> >>
> >> Stream sockets provide in-order, guaranteed, connection-oriented delivery
> >> without message boundaries.
> >>
> >> +Datagram sockets provide connectionless unreliable messages of
> >> +a fixed maximum length.
> >
> >Plus unordered (?) and with message boundaries. In other words:
> >
> > Datagram sockets provide unordered, unreliable, connectionless message
> > with message boundaries and a fixed maximum length.
> >
> >I didn't think of the fixed maximum length aspect before. I guess the
> >intention is that the rx buffer size is the message size limit? That's
> >different from UDP messages, which can be fragmented into multiple IP
> >packets and can be larger than 64KiB:
> >https://en.wikipedia.org/wiki/User_Datagram_Protocol#UDP_datagram_structure
> >
> >Is it possible to support large datagram messages in vsock? I'm a little
> >concerned that applications that run successfully over UDP will not be
> >portable if vsock has this limitation because it would impose extra
> >message boundaries that the application protocol might not tolerate.
>
> Maybe we can reuse the same approach Arseny is using for SEQPACKET.
> Fragment the packets according to the buffers in the virtqueue and set
> the EOR flag to indicate the last packet in the message.
>
Agree. Another option is to use the ones for skb since we may need to
use skbs for multiple transport support anyway.
> Thanks,
> Stefano
>
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