Michael S. Tsirkin
2023-Sep-06 08:17 UTC
[PATCH] virtio-vsock: add VIRTIO_VSOCK_F_DGRAM feature bit
On Sat, Sep 02, 2023 at 09:24:26AM +0000, Bobby Eshleman wrote:> On Sat, Sep 02, 2023 at 04:41:28AM -0400, Michael S. Tsirkin wrote: > > On Sat, Sep 02, 2023 at 04:37:19AM +0000, Bobby Eshleman wrote: > > > On Fri, Sep 01, 2023 at 09:31:03AM -0400, Michael S. Tsirkin wrote: > > > > On Wed, Aug 30, 2023 at 12:43:03AM +0000, Bobby Eshleman wrote: > > > > > On Tue, Aug 29, 2023 at 06:21:35PM -0400, Michael S. Tsirkin wrote: > > > > > > On Tue, Aug 29, 2023 at 09:29:45PM +0000, Bobby Eshleman wrote: > > > > > > > This adds support for datagrams to the virtio-vsock device. > > > > > > > > > > > > > > virtio-vsock already supports stream and seqpacket types. The existing > > > > > > > message types and header fields are extended to support datagrams. > > > > > > > Semantic differences between the flow types are stated, as well as any > > > > > > > additional requirements for devices and drivers implementing this > > > > > > > feature. > > > > > > > > > > > > > > Signed-off-by: Bobby Eshleman <bobby.eshleman at bytedance.com> > > > > > > > --- > > > > > > > device-types/vsock/description.tex | 95 +++++++++++++++++++++++++++--- > > > > > > > 1 file changed, 88 insertions(+), 7 deletions(-) > > > > > > > > > > > > > > diff --git a/device-types/vsock/description.tex b/device-types/vsock/description.tex > > > > > > > index 7d91d159872f..638dca8e5da1 100644 > > > > > > > --- a/device-types/vsock/description.tex > > > > > > > +++ b/device-types/vsock/description.tex > > > > > > > @@ -20,6 +20,7 @@ \subsection{Feature bits}\label{sec:Device Types / Socket Device / Feature bits} > > > > > > > \item[VIRTIO_VSOCK_F_STREAM (0)] stream socket type is supported. > > > > > > > \item[VIRTIO_VSOCK_F_SEQPACKET (1)] seqpacket socket type is supported. > > > > > > > \item[VIRTIO_VSOCK_F_NO_IMPLIED_STREAM (2)] stream socket type is not implied. > > > > > > > +\item[VIRTIO_VSOCK_F_DGRAM (3)] datagram socket type is supported. > > > > > > > \end{description} > > > > > > > > > > > > > > \drivernormative{\subsubsection}{Feature bits}{Device Types / Socket Device / Feature bits} > > > > > > > @@ -167,17 +168,22 @@ \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 stream and seqpacket sockets are supported. \field{type} is 1 (VIRTIO_VSOCK_TYPE_STREAM) > > > > > > > -for stream socket types, and 2 (VIRTIO_VSOCK_TYPE_SEQPACKET) for seqpacket socket types. > > > > > > > + > > > > > > > +Currently stream, seqpacket, and datagram sockets are supported. \field{type} is > > > > > > > +1 (VIRTIO_VSOCK_TYPE_STREAM) for stream socket types, 2 (VIRTIO_VSOCK_TYPE_SEQPACKET) for > > > > > > > +seqpacket socket types, and 3 (VIRTIO_VSOCK_TYPE_DGRAM) for datagram socket types. > > > > > > > > > > > > > > \begin{lstlisting} > > > > > > > #define VIRTIO_VSOCK_TYPE_STREAM 1 > > > > > > > #define VIRTIO_VSOCK_TYPE_SEQPACKET 2 > > > > > > > +#define VIRTIO_VSOCK_TYPE_DGRAM 3 > > > > > > > \end{lstlisting} > > > > > > > > > > > > > > Stream sockets provide in-order, guaranteed, connection-oriented delivery > > > > > > > without message boundaries. Seqpacket sockets provide in-order, guaranteed, > > > > > > > -connection-oriented delivery with message and record boundaries. > > > > > > > +connection-oriented delivery with message and record boundaries. Datagram > > > > > > > +sockets provide connection-less, best-effort delivery of messages, with no > > > > > > > +order or reliability guarantees. > > > > > > > > > > > > > > \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 > > > > > > > @@ -203,16 +209,19 @@ \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. > > > > > > > > > > > > > > +\field{buf_alloc} and \field{fwd_cnt} are reserved for future use by datagram > > > > > > > +sockets. These fields are not used for datagram buffer space management. > > > > > > > > > > > > no limits on datagram size? > > > > > > > > > > > > > > > > In the Linux proof-of-concept, it is 64KB. I can add that here too. > > > > > > > > or device driven maybe ... > > > > > > > > > > Ah yes, I think Stefano was suggesting something like Laura's proposal: > > > https://lists.oasis-open.org/archives/virtio-comment/202206/msg00093.html > > > > > > > > > also with no flow control at all there's a performance problem: > > > > > > imagine queue gets full. now buffers begin to be dropped. > > > > > > problem is, dropping is faster than delivering to application. > > > > > > so now application sees its packets consumed super quickly > > > > > > and starts sending even faster. > > > > > > not good for performance. > > > > > > > > > > > > yes datagram expects some way to drop packets but just disabling flow > > > > > > control completely is not the right thing to do I think. > > > > > > > > > > > > > > > > On the LKML I discussed using congestion notification as a way to handle > > > > > this situation, but deferred it to a future feature bit. I can build > > > > > it in from the beginning though. > > > > > > > > as in messages to stop/start transmission? might work. > > > > > > > > > > Yes, say for example that a flow is sending a large number of packets > > > and the destination socket's receive queue becomes full. The destination > > > sends a "stop" message with the destination address. More packets are > > > likely to continue trailing in, and they may be dropped. The source > > > device or driver will use the destination address to throttle further > > > attempts of sockets to transmit to that destination, and the flow will > > > stop. > > > > > > After the socket's receive queue is no longer full, it may notify the > > > device/driver which can then send a "start" message with the destination > > > address to any previously "stopped" sources. The sources can then > > > reenable flows to that destination. > > > > Ah so control is actually per socket. Another idea is that does not have > > to be completely full - we can start suppressing a bit before it's full > > to reduce packet drops. > > > > Totally, yes that makes sense.I don't know how we prevent blocking traffic to unrelated destinations in this case though. Do we have to?> > > > > > The other alternative I evaluated was using a single "stop for some > > > time" message with an exponential or fibonacci backoff with a ceiling, > > > but the downside is that a congested queue could block the "stop" > > > message from reaching the source and eventually the source would become > > > unthrottled even though the destination is *trying* to throttle it. I > > > think this is bad for some pretty abusable cases, such as creating a > > > socket that has no receiver. A stop/start message pair doesn't have this > > > issue. > > > > > > > > > > > > > + > > > > > > > \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 and seqpacket flows, VIRTIO_VSOCK_OP_RW data packets MUST only be > > > > > > > +transmitted when the peer has sufficient free buffer space for the payload. > > > > > > > > > > > > > > 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 and seqpacket flows, VIRTIO_VSOCK_OP_RW data packets MUST only be > > > > > > > +transmitted when the peer has sufficient free buffer space for the payload. > > > > > > > > > > > > > > All packets associated with a stream flow MUST contain valid information in > > > > > > > \field{buf_alloc} and \field{fwd_cnt} fields. > > > > > > > @@ -299,6 +308,78 @@ \subsubsection{Seqpacket Sockets}\label{sec:Device Types / Socket Device / Devic > > > > > > > #define VIRTIO_VSOCK_SEQ_EOR (1 << 1) > > > > > > > \end{lstlisting} > > > > > > > > > > > > > > +\subsubsection{Datagram Sockets}\label{sec:Device Types / Socket Device / Device Operation / Datagram Sockets} > > > > > > > + > > > > > > > +\drivernormative{\paragraph}{Device Operation: Packet Fragmentation}{Device Types / Socket Device / Datagram Sockets / Fragmentation} > > > > > > > + > > > > > > > +Drivers MAY disassemble packets into smaller fragments. If drivers fragment a > > > > > > > +packet, they MUST follow the fragmentation rules described in section > > > > > > > +\ref{sec:Device Types / Socket Device / Device Operation / Datagram Sockets / Fragmentation}. > > > > > > > + > > > > > > > +Drivers MUST support assembly of received packet fragments according to the > > > > > > > +fragmentation rules described in section > > > > > > > +\ref{sec:Device Types / Socket Device / Device Operation / Datagram Sockets / Fragmentation}. > > > > > > > + > > > > > > > +\devicenormative{\paragraph}{Device Operation: Packet Fragmentation}{Device Types / Socket Device / Datagram Sockets / Fragmentation} > > > > > > > + > > > > > > > +Devices MAY disassemble packets into smaller fragments. If devices fragment a > > > > > > > +packet, they MUST follow the fragmentation rules described in section > > > > > > > +\ref{sec:Device Types / Socket Device / Device Operation / Datagram Sockets / Fragmentation}. > > > > > > > + > > > > > > > +Devices MUST support assembly of received packet fragments according to the > > > > > > > +fragmentation rules described in section > > > > > > > +\ref{sec:Device Types / Socket Device / Device Operation / Datagram Sockets / Fragmentation}. > > > > > > > + > > > > > > > +\drivernormative{\paragraph}{Device Operation: Packet Dropping}{Device Types / Socket Device / Datagram Sockets / Dropping} > > > > > > > + > > > > > > > +The driver MAY drop received packets with no notification to the device. This > > > > > > > +can happen if, for example, there are insufficient resources or no socket > > > > > > > +exists for the destination address. > > > > > > > + > > > > > > > +\devicenormative{\paragraph}{Device Operation: Packet Dropping}{Device Types / Socket Device / Datagram Sockets / Dropping} > > > > > > > + > > > > > > > +The device MAY drop received packets with no notification to the driver. This > > > > > > > +can happen if, for example, there are insufficient resources or no socket > > > > > > > +exists for the destination address. > > > > > > > + > > > > > > > +\paragraph{Datagram Fragmentation}\label{sec:Device Types / Socket Device / Device Operation / Datagram Sockets / Fragmentation} > > > > > > > + > > > > > > > +\field{flags} may have the following bit set: > > > > > > > + > > > > > > > +\begin{lstlisting} > > > > > > > +#define VIRTIO_VSOCK_DGRAM_EOM (1 << 0) > > > > > > > +\end{lstlisting} > > > > > > > + > > > > > > > +When the header \field{flags} field bit VIRTIO_VSOCK_DGRAM_EOM (bit 0) is set, > > > > > > > +it indicates that the current payload is the end of a datagram fragment OR that > > > > > > > +the current payload is an entire datagram packet. > > > > > > > + > > > > > > > +Datagram fragmentation is subject to the following rules: > > > > > > > + > > > > > > > +The fragments for a datagram packet MUST be added to the virtqueue in > > > > > > > +sequential order. > > > > > > > + > > > > > > > +If a packet is not a fragment, then the VIRTIO_VSOCK_DGRAM_EOM bit (bit 0) of > > > > > > > +\field{flags} MUST be set. > > > > > > > + > > > > > > > +If a packet is the last fragment of a fragment sequence, then the > > > > > > > +VIRTIO_VSOCK_DGRAM_EOM bit (bit 0) of \field{flags} MUST be set. > > > > > > > + > > > > > > > +If a packet is any fragment except the last fragment of a fragment sequence, > > > > > > > +then the VIRTIO_VSOCK_DGRAM_EOM bit (bit 0) of \field{flags} MUST NOT be set. > > > > > > > + > > > > > > > +If a driver or device has already placed a fragment of a packet on the > > > > > > > +virtqueue, it MUST add the remaining fragments of the packet to the virtqueue > > > > > > > +before adding any additional packets or fragments to the virtqueue. > > > > > > > + > > > > > > > +If fragments for a packet are only partially received after an > > > > > > > +implementation-specific amount of time, then the destination device or driver > > > > > > > +MAY drop the fragments. > > > > > > > > > > > > and how to detect this partial situation? > > > > > > > > > > > > and if not then what happens? > > > > > > > > > > All packets with EOM=0 should be added into a per-flow fragment list. > > > > > > > > > > Once a packet with EOM=1 is received, they can all be concatenated and > > > > > delivered to the destination socket. > > > > > > > > > > If after X time no packet with EOM=1 is received, then we have detected > > > > > this partial situation. The "then what happens part" is that the > > > > > fragment list can be dropped and freed. Because the peer must send the > > > > > remaining fragments, they will also be dropped and freed until EOM=1 is > > > > > received. > > > > > > > > aha. worth mentioning. > > > > > > > > also all the must/may/should really belong in conformance > > > > sections. > > > > > > > > > > Got it, will do. > > > > > > > > > > > > > > > > > > > > +Each buffer containing a fragment MUST begin with a valid struct > > > > > > > +virtio_vsock_hdr. \field{len} MUST equal the length of the fragment payload > > > > > > > +only. > > > > > > > > > > > > what does this mean exactly? > > > > > > > > > > > > > > > > It means that len only accounts for the fragment and not the whole > > > > > (fragmented) packet. The second sentence means that the virtqueue buffer > > > > > starts with the header. > > > > > > > > > > For virtio-net mergable RX buffers the header is only in the first > > > > > buffer and the length field accounts for the entire fragmented packet > > > > > (that spans multiple bufers), so I suspected the specification was > > > > > needed here too. > > > > > > > > > > I'm happy to omit it. > > > > > > > \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 > > > > > > > -- > > > > > > > 2.20.1 > > > > > > > > > > > > _______________________________________________ > > > > > > Virtualization mailing list > > > > > > Virtualization at lists.linux-foundation.org > > > > > > https://lists.linuxfoundation.org/mailman/listinfo/virtualization > > > > > > > > _______________________________________________ > > > > Virtualization mailing list > > > > Virtualization at lists.linux-foundation.org > > > > https://lists.linuxfoundation.org/mailman/listinfo/virtualization > > > > _______________________________________________ > > Virtualization mailing list > > Virtualization at lists.linux-foundation.org > > https://lists.linuxfoundation.org/mailman/listinfo/virtualization