Re: [virtio-comment] Re: [RFC PATCH v5 2/2] virtio-vsock: SOCK_SEQPACKET description

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

On Wed, Apr 21, 2021 at 09:45:23AM +0200, Stefano Garzarella wrote:
> On Wed, Apr 14, 2021 at 09:04:47AM +0300, Arseny Krasnov wrote:
> > 
> > On 13.04.2021 22:55, Michael S. Tsirkin wrote:
> > > On Tue, Apr 13, 2021 at 05:22:44PM +0300, Arseny Krasnov wrote:
> > > > On 13.04.2021 16:10, Michael S. Tsirkin wrote:
> > > > > On Tue, Apr 13, 2021 at 03:53:29PM +0300, Arseny Krasnov wrote:
> > > > > > This adds description of SOCK_SEQPACKET socket type
> > > > > > support for virtio-vsock.
> > > > > > 
> > > > > > Signed-off-by: Arseny Krasnov <arseny.krasnov@kaspersky.com>
> > > > > > ---
> > > > > >  virtio-vsock.tex | 26 +++++++++++++++++++++-----
> > > > > >  1 file changed, 21 insertions(+), 5 deletions(-)
> > > > > > 
> > > > > > diff --git a/virtio-vsock.tex b/virtio-vsock.tex
> > > > > > index ad57f9d..00e59cc 100644
> > > > > > --- a/virtio-vsock.tex
> > > > > > +++ b/virtio-vsock.tex
> > > > > > @@ -16,7 +16,10 @@ \subsection{Virtqueues}\label{sec:Device Types / Socket Device / 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_SEQPACKET (0) SOCK_SEQPACKET socket type is
> > > > > > +    supported.
> > > > > Does it make sense to only support seqpacket and not stream?
> > > > > I am guessing not since seqpacket is more or less
> > > > > a superset ...
> > > > You mean, this sentence must be "Both SOCK_SEQPACKET and SOCK_STREAM types
> > > > 
> > > > are supported"?
> > > 
> > > No. I am asking whether we want a feature bit for SOCK_STREAM too?
> > 
> > I think  there is no practical sense in SOCK_STREAM bit, because SOCK_SEQPACKET
> > 
> > is stream + message boundaries and potential DGRAM is completely different
> > 
> > thing. Of course i can implement it in my patches and also add it to spec patch, but  i see only
> > 
> > esthetic in this: all three socket types have own feature bits.
> > 
> 
> I agree that it may make sense to have a bit for SOCK_STREAM. For example we
> may have devices in the future that want to implement only DGRAM for
> simplicity.
> 
> I'm just worried about backwards compatibility with current devices where we
> don't have any feature bit.
> 
> Should we add a negative feature flag? (e.g. VIRTIO_VSOCK_F_NO_STREAM)
> I don't like it much, but I can't think of anything better.
> 
> Thanks,
> Stefano

We can simply specify that if there are no feature bits at all then
stream is assumed supported.


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