Re: [virtio-comment] Re: [PATCH v5] virtio-vsock: add description for datagram type
On Fri, Sep 03, 2021 at 03:57:24AM -0400, Michael S. Tsirkin wrote:
On Fri, Sep 03, 2021 at 09:22:24AM +0200, Stefano Garzarella wrote:
On Thu, Sep 02, 2021 at 05:08:01PM -0700, Jiang Wang . wrote:
> On Thu, Sep 2, 2021 at 7:07 AM Stefan Hajnoczi wrote:
> > On Thu, Jun 10, 2021 at 06:12:03PM +, Jiang Wang wrote:
[...]
> > >
> > > -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)?
> >
> I left bit 1 for SEQPACKET feature bit. That will probably merge
> before this patch.
Yep, SEQPACKET implementation is also merged in the linux kernel using the
feature bit 1 (0x2), bit 0 (0x1) was left free for stream.
>
> > 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.
> >
> yeah, good question. I think then it means the first two queues will be used
> for dgram?
>
> > > +\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.
> >
> Agree. I went back and read old emails again and found I missed the
> negative bit part. So repeating the previous question, if
> VIRTIO_VSOCK_F_NO_STREAM and VIRTIO_VSOCK_F_DGRAM
> present, then we will only have 3 queues and the first two are for dgram,
right?
>
> Also, I am wondering what if an implementation only sets
> VIRTIO_VSOCK_F_NO_STREAM bit, but somehow forgot (or for whatever
> reason) to set VIRTIO_VSOCK_F_DGRAM bit? Does that mean there will
> be no virtqueues? The implementation is a mistake? Because it will not
> do anything.
> Do we need to explicitly add a sentence in the spec to say something like
> "Don't set VIRTIO_VSOCK_F_NO_STREAM alone" etc?
Good point.
IIRC we thought to add F_STREAM to allow devices for example that support
only DGRAM, but we said to consider stream supported if no feature was set
for backward compatibility.
With F_NO_STREAM we can do the same, but actually we could have this strange
case. I don't think it's a big problem, in the end it's a configuration
error. Maybe F_NO_STREMA is clearer since the original device spec supports
streams without any feature bit defined.
Stefano
How about that instead of VIRTIO_VSOCK_F_NO_STREAM we do
VIRTIO_VSOCK_F_TYPE /* device supports multiple socket types */
then with VIRTIO_VSOCK_F_TYPE clear we only have stream.
For SEQPACKET it should be okay, since it depends on stream queues, but
DGRAM will have its own queues, so with F_TYPE it seems to me more
difficult to handle the case in which a device supports DGRAM but not
STREAM.
We should also make SEQPACKET depend on this VIRTIO_VSOCK_F_TYPE -
linux guests do not validate that right now but
it's probably not too late to add such a patch to linux
as a bugfix.
Yep, also with F_NO_STREAM we should do a validation, since F_SEQPACKET
depends on !F_NO_STREAM.
I'll take care of this when we decide what flag to use.
Stefano
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Re: [virtio-comment] Re: [PATCH v5] virtio-vsock: add description for datagram type
On Fri, Sep 03, 2021 at 09:22:24AM +0200, Stefano Garzarella wrote:
> On Thu, Sep 02, 2021 at 05:08:01PM -0700, Jiang Wang . wrote:
> > On Thu, Sep 2, 2021 at 7:07 AM Stefan Hajnoczi wrote:
> > >
> > > On Thu, Jun 10, 2021 at 06:12:03PM +, 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
> > > > ---
> > >
> > > 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:/
> > >
> > Will do.
> >
> > > > +
> > > > +\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)?
> > >
> > I left bit 1 for SEQPACKET feature bit. That will probably merge
> > before this patch.
>
> Yep, SEQPACKET implementation is also merged in the linux kernel using the
> feature bit 1 (0x2), bit 0 (0x1) was left free for stream.
>
> >
> > > 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.
> > >
> > yeah, good question. I think then it means the first two queues will be
> > used
> > for dgram?
> >
> > > > +\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.
> > >
> > Agree. I went back and read old emails again and found I missed the
> > negative bit part. So repeating the previous question, if
> > VIRTIO_VSOCK_F_NO_STREAM and VIRTIO_VSOCK_F_DGRAM
> > present, then we will only have 3 queues and the first two are for dgram,
> > right?
> >
> > Also, I am wondering what if an implementation only sets
> > VIRTIO_VSOCK_F_NO_STREAM bit, but somehow forgot (or for whatever
> > reason) to set VIRTIO_VSOCK_F_DGRAM bit? Does that mean there will
> > be no virtqueues? The implementation is a mistake? Because it will not
> > do anything.
> > Do we need to explicitly add a sentence in the spec to say something like
> > "Don't set VIRTIO_VSOCK_F_NO_STREAM alone" etc?
>
> Good point.
>
> IIRC we thought to add F_STREAM to allow devices for example that support
> only DGRAM, but we said to consider stream supported if no feature was set
> for backward compatibility.
> With F_NO_STREAM we can do the same, but actually we could have this strange
> case. I don't think it's a big problem, in the end it's a configuration
> error. Maybe F_NO_STREMA is clearer since
Re: [virtio-comment] Re: [PATCH v5] virtio-vsock: add description for datagram type
On Thu, Sep 02, 2021 at 05:08:01PM -0700, Jiang Wang . wrote:
On Thu, Sep 2, 2021 at 7:07 AM Stefan Hajnoczi wrote:
On Thu, Jun 10, 2021 at 06:12:03PM +, 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
> ---
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:/
Will do.
> +
> +\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)?
I left bit 1 for SEQPACKET feature bit. That will probably merge
before this patch.
Yep, SEQPACKET implementation is also merged in the linux kernel using
the feature bit 1 (0x2), bit 0 (0x1) was left free for stream.
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.
yeah, good question. I think then it means the first two queues will be used
for dgram?
> +\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.
Agree. I went back and read old emails again and found I missed the
negative bit part. So repeating the previous question, if
VIRTIO_VSOCK_F_NO_STREAM and VIRTIO_VSOCK_F_DGRAM
present, then we will only have 3 queues and the first two are for dgram, right?
Also, I am wondering what if an implementation only sets
VIRTIO_VSOCK_F_NO_STREAM bit, but somehow forgot (or for whatever
reason) to set VIRTIO_VSOCK_F_DGRAM bit? Does that mean there will
be no virtqueues? The implementation is a mistake? Because it will not
do anything.
Do we need to explicitly add a sentence in the spec to say something like
"Don't set VIRTIO_VSOCK_F_NO_STREAM alone" etc?
Good point.
IIRC we thought to add F_STREAM to allow devices for example that
support only DGRAM, but we said to consider stream supported if no
feature was set for backward compatibility.
With F_NO_STREAM we can do the same, but actually we could have this
strange case. I don't think it's a big problem, in the end it's a
configuration error. Maybe F_NO_STREMA is clearer since the original
device spec supports streams without any feature bit defined.
Stefano
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Re: [virtio-comment] Re: [PATCH v5] virtio-vsock: add description for datagram type
On Thu, Sep 2, 2021 at 7:07 AM Stefan Hajnoczi wrote:
>
> On Thu, Jun 10, 2021 at 06:12:03PM +, 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
> > ---
>
> 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:/
>
Will do.
> > +
> > +\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)?
>
I left bit 1 for SEQPACKET feature bit. That will probably merge
before this patch.
> 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.
>
yeah, good question. I think then it means the first two queues will be used
for dgram?
> > +\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.
>
Agree. I went back and read old emails again and found I missed the
negative bit part. So repeating the previous question, if
VIRTIO_VSOCK_F_NO_STREAM and VIRTIO_VSOCK_F_DGRAM
present, then we will only have 3 queues and the first two are for dgram, right?
Also, I am wondering what if an implementation only sets
VIRTIO_VSOCK_F_NO_STREAM bit, but somehow forgot (or for whatever
reason) to set VIRTIO_VSOCK_F_DGRAM bit? Does that mean there will
be no virtqueues? The implementation is a mistake? Because it will not
do anything.
Do we need to explicitly add a sentence in the spec to say something like
"Don't set VIRTIO_VSOCK_F_NO_STREAM alone" etc?
> > \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.
>
Got it. Will do.
> >
> > \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.
Sure.
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