Re: [virtio-dev] Re: [PATCH v8 08/16] packed virtqueues: more efficient virtqueue layout

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

On Mon, Feb 26, 2018 at 06:51:11PM +0800, Tiwei Bie wrote:
> On Sun, Feb 25, 2018 at 08:49:10PM +0200, Michael S. Tsirkin wrote:
> > On Sat, Feb 24, 2018 at 01:17:08PM +0800, Tiwei Bie wrote:
> > > On Fri, Feb 16, 2018 at 09:24:12AM +0200, Michael S. Tsirkin wrote:
> [...]
> > > > +\subsection{Event Suppression Structure Format}\label{sec:Basic
> > > > +Facilities of a Virtio Device / Packed Virtqueues / Event Suppression Structure
> > > > +Format}
> > > > +
> > > > +The following structure is used to reduce the number of
> > > > +notifications sent between driver and device.
> > > > +
> > > > +\begin{lstlisting}
> > > > +__le16 desc_event_off : 15; /* Descriptor Event Offset */
> > > > +int    desc_event_wrap : 1; /* Descriptor Event Wrap Counter */
> > > 
> > > Is this `int` a typo?
> > 
> > It's a single bit so I think it does not matter.
> > What type would you like me to use instead?
> 
> It looks a bit strange to use different types here, and
> that's why I asked. If there is no particular reason to
> use `int` here, maybe it's better to keep using __le16.
> 
> Besides, just for fun. For C language, I checked gcc and
> clang. It seems that `int desc_event_wrap:1;` is a signed
> type. So, e.g. `p->desc_event_wrap == 1` is always false.
> 
> Best regards,
> Tiwei Bie

I'll switch to u8 here, IMHO le16 for a single bit
is really confusing. There's no byte order for a single byte.

> > 
> > > > +__le16 desc_event_flags : 2; /* Descriptor Event Flags */
> > > > +\end{lstlisting}
> [...]