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Subject: Re: [virtio-dev] [PATCH 09/14] legacy feature bits: confirmance statements


On Tue, Feb 25, 2014 at 01:07:40PM +1030, Rusty Russell wrote:
> "Michael S. Tsirkin" <mst@redhat.com> writes:
> > ---
> >  content.tex | 15 ++++++++++-----
> >  1 file changed, 10 insertions(+), 5 deletions(-)
> >
> > diff --git a/content.tex b/content.tex
> > index 2de0644..58402f3 100644
> > --- a/content.tex
> > +++ b/content.tex
> > @@ -4352,20 +4352,25 @@ and should not be used.
> >  
> >  \section{Legacy Interface: Reserved Feature Bits}\label{sec:Reserved Feature Bits / Legacy Interface: Reserved Feature Bits}
> >  
> > -Legacy or transitional devices may offer the following:
> > -
> > +Transitional devices MAY offer the following:
> >  \begin{description}
> > -\item[VIRTIO_F_NOTIFY_ON_EMPTY (24)] Negotiating this feature
> > -  indicates that the driver wants an interrupt if the device runs
> > +\item[VIRTIO_F_NOTIFY_ON_EMPTY (24)] If this feature
> > +  has been negotiated by driver, the device MUST issue
> > +  an interrupt if the device runs
> >    out of available descriptors on a virtqueue, even though
> >    interrupts are suppressed using the VRING_AVAIL_F_NO_INTERRUPT
> > -  flag or the \field{used_event} field. An example of this is the
> > +  flag or the \field{used_event} field. An example of a driver
> > +  using this feature is the legacy
> >    networking driver: it doesn't need to know every time a packet
> >    is transmitted, but it does need to free the transmitted
> >    packets a finite time after they are transmitted. It can avoid
> >    using a timer if the device interrupts it when all the packets
> >    are transmitted.
> > +\end{description}
> 
> Move the example into a \note{} so it's clearly separated from
> the normative section.  Actually, move the normative requirements into
> their own section, so this has to be split.
> 
> > +Transitional devices MUST offer, and if offered by the device
> > +traditional drivers MUST negotiate the following:
> > +\begin{description}
> >  \item[VIRTIO_F_ANY_LAYOUT (27)] This feature indicates that the device
> >    accepts arbitrary descriptor layouts, as described in Section
> >    \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Message Framing / Legacy Interface: Message Framing}~\nameref{sec:Basic Facilities of a Virtio Device / Virtqueues / Message Framing / Legacy Interface: Message Framing}.
> 
> s/traditional/transitional/
> 
> s/if offered by the device traditional drivers MUST negotiate/
> transitional drivers MUST accept/ ?
> 
> This requirement seems like a SHOULD, not a MUST to me though.
> 
> Cheers,
> Rusty.

I made it a MUST because it creates a way for device to detect
that driver is new and might use arbitrary layout.
I'm worried that since everything seems to work without it,
people will ignore the SHOULD requirement.


> 
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