Jiang Wang .
2021-Apr-12 22:42 UTC
[RFC v2] virtio-vsock: add description for datagram type
On Mon, Apr 12, 2021 at 7:21 AM Stefano Garzarella <sgarzare at 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.wang at 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.> Thanks, > Stefano >
Stefano Garzarella
2021-Apr-13 12:58 UTC
[RFC v2] virtio-vsock: add description for datagram type
On Mon, Apr 12, 2021 at 03:42:23PM -0700, Jiang Wang . wrote:>On Mon, Apr 12, 2021 at 7:21 AM Stefano Garzarella <sgarzare at 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.wang at 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