From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-return-3580-cohuck=redhat.com@lists.oasis-open.org Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Date: Thu, 8 Apr 2021 22:18:13 +0200 From: Halil Pasic Message-ID: <20210408221813.7796697c.pasic@linux.ibm.com> In-Reply-To: <20210318182314.163060-1-mst@redhat.com> References: <20210318182314.163060-1-mst@redhat.com> MIME-Version: 1.0 Subject: [virtio] Re: [virtio-comment] [PATCH v2] introduction: document #define syntax Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable To: "Michael S. Tsirkin" Cc: virtio-comment@lists.oasis-open.org, virtio-dev@lists.oasis-open.org, virtio@lists.oasis-open.org List-ID: On Thu, 18 Mar 2021 14:23:33 -0400 "Michael S. Tsirkin" wrote: > We use the C #define syntax to refer to numeric values. > Let's document that. >=20 > Signed-off-by: Michael S. Tsirkin > --- >=20 > changes from v1: > address Cornelia's comments >=20 >=20 > introduction.tex | 23 +++++++++++++++++++++++ > 1 file changed, 23 insertions(+) >=20 > diff --git a/introduction.tex b/introduction.tex > index cc38e29..47bebf5 100644 > --- a/introduction.tex > +++ b/introduction.tex > @@ -210,6 +210,29 @@ \section{Structure Specifications} > \begin{lstlisting} > CPU_TO_BE16(B << 15 | A) > \end{lstlisting} > +\section{Constant Specifications} > + > +In many cases, numeric values used in the interface between the device > +and the driver are documented using the C #define and /* */ > +comment syntax. Multiple related values are grouped together with > +a common name as a prefix, using _ as a separator. > +Using _XXX as a suffix refers to all values in a group. > +For example: > + > +\begin{lstlisting} > +/* Field Fld value A description */ > +#define VIRTIO_FLD_A (1 << 0) > +/* Field Fld value B description */ > +#define VIRTIO_FLD_B (1 << 1) > +\end{lstlisting} > +documents two numeric values for a field \field{Fld}, with > +\field{Fld} having value 1 referring to \field{A} and \field{Fld} > +having value 2 referring to \field{B}. > +Note that $<<$ refers to the shift-left operation. > + > +Further, in this case VIRTIO_FLD_A and VIRTIO_FLD_B > +refer to values 1 and 2 of Fld respectively. Further, VIRTIO_FLD_XXX ref= ers to > +either VIRTIO_FLD_A or VIRTIO_FLD_B. IMHO we also use the define stuff to do flags, and that does not match nicely with the above sentence, since VIRTIO_FLD_F_A does not mean that the FLD_F field has value A if we are trying to specify a flag or a feature bit. And the left-shift is actually most common in these cases. I'm not opposed to this change. In the virtio spec we tend to not be very rigorous about formalism, and I came to accept that as a given. Just wanted to point it out. Sorry for not commenting on this sooner. Regards, Halil > =20 > \newpage > =20 --------------------------------------------------------------------- To unsubscribe from this mail list, you must leave the OASIS TC that=20 generates this mail. Follow this link to all your TCs in OASIS at: https://www.oasis-open.org/apps/org/workgroup/portal/my_workgroups.php=20