Linux Virtualization - Jun 2021 - [PATCH v5] virtio-vsock: add description for datagram type

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 at bytedance.com>
---

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

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 at 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.
> ---
> 
> 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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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 at bytedance.com>
> ---
Overall this looks good. The tricky thing will be implementing dgram
sockets in a way that minimizes dropped packets and provides some degree
of fairness between senders. Those are implementation issues though and
not visible at the device specification level.
> 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.
s/as the following/as follows:/
> +
> +\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.
Is this really bit 2 or did you mean bit 1 (value 0x2)?

What happens to the virtqueue layout when VIRTIO_VSOCK_F_DGRAM is
present and VIRTIO_VSOCK_F_STREAM is absent? The virtqueue section above
implies that VIRTIO_VSOCK_F_STREAM is always present.
> +\end{description}
> +
> +If no feature bits are defined, assume device only supports stream socket
type.
It's cleaner to define VIRTIO_VSOCK_F_NO_STREAM (0) instead. When the
bit is set the stream socket type is not available and the stream_rx/tx
virtqueues are absent.

This way it's not necessary to define special behavior depending on
certain combinations of feature bits.
>  \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:
This change seems unrelated to dgram sockets. I don't think adding the
word "allocates" makes things clearer or more precise. The driver may
reuse receive buffers rather than allocating fresh buffers. I suggest
dropping this change.
>  
>  \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.
>  
Unnecessary whitespace change. Please drop.
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