Re: [External] Re: [virtio-comment] [PATCH v5] virtio-vsock: add description for datagram type

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

On Tue, Aug 31, 2021 at 06:24:34PM -0700, Jiang Wang . wrote:
> On Tue, Aug 31, 2021 at 6:13 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Thu, Jun 10, 2021 at 06:12:03PM +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@bytedance.com>
> >
> > Is this going anywhere? Linux with this included was just released but
> > if no one has the cycles to work on the spec then it's not too late to
> > disable the guest code in a stable@ patch.
> >
> 
> Hi Michael,
> 
> I am still working on this (fixing the migration issue), but would
> like to know if there are any more
> comments or not.  I did not notice any commits related to vsock
> dgram merged to Linux kernel, could you show me the commit link?
> 
> Thanks and regards,
> 
> Jiang

My bad I was thinking of seqpacket. I see that description
was not posted as well, so all is well.

> > > ---
> > >
> > > V2: addressed the comments for the previous version.
> > > V3: add description for the mergeable receive buffer.
> > > V4: add a feature bit for stream and reserver a bit for seqpacket.
> > > Fix mrg_rxbuf related sentences.
> > > V5: removed mergeable rx buffer part. It will go to a
> > > separate patch. Fixed comments about tx, rx, feature bit etc.
> > >
> > >  virtio-vsock.tex | 71 +++++++++++++++++++++++++++++++++++++++++++++++---------
> > >  1 file changed, 60 insertions(+), 11 deletions(-)
> > >
> > > diff --git a/virtio-vsock.tex b/virtio-vsock.tex
> > > index da7e641..26a62ac 100644
> > > --- a/virtio-vsock.tex
> > > +++ b/virtio-vsock.tex
> > > @@ -9,14 +9,37 @@ \subsection{Device ID}\label{sec:Device Types / Socket Device / Device ID}
> > >
> > >  \subsection{Virtqueues}\label{sec:Device Types / Socket Device / Virtqueues}
> > >  \begin{description}
> > > -\item[0] rx
> > > -\item[1] tx
> > > +\item[0] stream rx
> > > +\item[1] stream 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.
> > > +
> > > +\begin{description}
> > > +\item[0] stream rx
> > > +\item[1] stream tx
> > >  \item[2] event
> > >  \end{description}
> > >
> > > +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.
> > > +
> > >  \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_STREAM (0)] Device has support for stream socket type.
> > > +\end{description}
> > > +
> > > +\begin{description}
> > > +\item[VIRTIO_VSOCK_F_DGRAM (2)] Device has support for datagram socket type.
> > > +\end{description}
> > > +
> > > +If no feature bits are defined, assume device only supports stream socket type.
> > >
> > >  \subsection{Device configuration layout}\label{sec:Device Types / Socket Device / Device configuration layout}
> > >
> > > @@ -107,6 +130,9 @@ \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 +166,15 @@ \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 unordered, unreliable, connectionless messages
> > > +with message boundaries and a maximum length.
> > > +
> > >  \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
> > >  stream sockets. The guest and the device publish how much buffer space is
> > > @@ -162,7 +191,7 @@ \subsubsection{Buffer Space Management}\label{sec:Device Types / Socket Device /
> > >  u32 peer_free = peer_buf_alloc - (tx_cnt - peer_fwd_cnt);
> > >  \end{lstlisting}
> > >
> > > -If there is insufficient buffer space, the sender waits until virtqueue buffers
> > > +For stream sockets, if there is insufficient buffer space, the sender waits until virtqueue buffers
> > >  are returned and checks \field{buf_alloc} and \field{fwd_cnt} again. Sending
> > >  the VIRTIO_VSOCK_OP_CREDIT_REQUEST packet queries how much buffer space is
> > >  available. The reply to this query is a VIRTIO_VSOCK_OP_CREDIT_UPDATE packet.
> > > @@ -170,22 +199,33 @@ \subsubsection{Buffer Space Management}\label{sec:Device Types / Socket Device /
> > >  previously receiving a VIRTIO_VSOCK_OP_CREDIT_REQUEST packet. This allows
> > >  communicating updates any time a change in buffer space occurs.
> > >
> > > +Unlike stream sockets, dgram sockets do not use VIRTIO_VSOCK_OP_CREDIT_UPDATE or
> > > +VIRTIO_VSOCK_OP_CREDIT_REQUEST packets. The dgram buffer management
> > > +is split to two parts: sender side and receiver side. For the sender side, if the
> > > +virtqueue is full, the packet will be dropped.
> > > +For the receiver side, the packet is dropped by the receiver if there is no space in the
> > > +receive buffer.
> > > +
> > >  \drivernormative{\paragraph}{Device Operation: Buffer Space Management}{Device Types / Socket Device / Device Operation / Buffer Space Management}
> > > -VIRTIO_VSOCK_OP_RW data packets MUST only be transmitted when the peer has
> > > -sufficient free buffer space for the payload.
> > > +For stream sockets, VIRTIO_VSOCK_OP_RW data packets MUST only be transmitted when the peer has
> > > +sufficient free buffer space for the payload. For dgram sockets, VIRTIO_VSOCK_OP_RW data packets
> > > +MAY be transmitted when the peer rx buffer is full. Then the packet will be dropped by the peer,
> > > +and driver will not get any notification.
> > >
> > >  All packets associated with a stream flow MUST contain valid information in
> > >  \field{buf_alloc} and \field{fwd_cnt} fields.
> > >
> > >  \devicenormative{\paragraph}{Device Operation: Buffer Space Management}{Device Types / Socket Device / Device Operation / Buffer Space Management}
> > > -VIRTIO_VSOCK_OP_RW data packets MUST only be transmitted when the peer has
> > > -sufficient free buffer space for the payload.
> > > +For stream sockets, VIRTIO_VSOCK_OP_RW data packets MUST only be transmitted when the peer has
> > > +sufficient free buffer space for the payload. For dgram sockets, VIRTIO_VSOCK_OP_RW data packets
> > > +MAY be transmitted when the peer rx buffer is full. Then the packet will be dropped by the peer,
> > > +and the device will not get any notification.
> > >
> > >  All packets associated with a stream flow MUST contain valid information in
> > >  \field{buf_alloc} and \field{fwd_cnt} fields.
> > >
> > >  \subsubsection{Receive and Transmit}\label{sec:Device Types / Socket Device / Device Operation / Receive and Transmit}
> > > -The driver queues outgoing packets on the tx virtqueue and incoming packet
> > > +The driver queues outgoing packets on the tx virtqueue and allocates incoming packet
> > >  receive buffers on the rx virtqueue. Packets are of the following form:
> > >
> > >  \begin{lstlisting}
> > > @@ -195,6 +235,7 @@ \subsubsection{Receive and Transmit}\label{sec:Device Types / Socket Device / De
> > >  };
> > >  \end{lstlisting}
> > >
> > > +
> > >  Virtqueue buffers for outgoing packets are read-only. Virtqueue buffers for
> > >  incoming packets are write-only.
> > >
> > > @@ -240,6 +281,14 @@ \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{Datagram Sockets}\label{sec:Device Types / Socket Device / Device Operation / Datagram Sockets}
> > > +
> > > +Datagram (dgram) sockets are connectionless and unreliable. The sender just sends
> > > +a message to the peer and hopes it will be delivered. A VIRTIO_VSOCK_OP_RST reply is sent if
> > > +a receiving socket does not exist on the destination.
> > > +If the transmission or receiving buffers are full, the packets
> > > +are dropped.
> > > +
> > >  \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
> > > --
> > > 2.11.0
> > >
> > >
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