On Mon, Apr 12, 2021 at 03:42:23PM -0700, Jiang Wang . wrote:
> On Mon, Apr 12, 2021 at 7:21 AM Stefano Garzarella <sgarz...@redhat.com>
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.w...@bytedance.com>
> > >> ---
> > >> 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.
>
The important thing I think is to have a single flag in virtio-vsock that
identifies pretty much the same thing: this is the last fragment of a series
to rebuild a packet.
We should reuse the same flag for DGRAM and SEQPACKET.
Thanks,
Stefano