Re: [Xen-devel] [PATCH v10] xen: add para-virtual sound interface header file

[Julien Grall <julien.grall@xxxxxxx>]

Hi Oleksandr,

On 24/11/16 18:04, Oleksandr Andrushchenko wrote:
> > > > > > > +struct xensnd_close_req {
> > > > > > > +};
> > > > > >
> > > > > >
> > > > > > I'm afraid structures without any members aren't permitted by C89.
> > > > > There are 2 options I see:
> > > > > 1. Remove empty structures
> > > > > 2. Leave them in, but add a comment and add a dummy place holder
> > > > > I would prefer option 1 as this way the interface seems to be clearer,
> > > > > like all requests are defined etc.
> > > Typo: I would prefer option 2 with placeholders and comments
> > > > > > > +struct xensnd_request {
> > > > > > > +     uint8_t raw[64];
> > > > > > > +};
> > > > > > > +
> > > > > > > +struct xensnd_response {
> > > > > > > +     uint8_t raw[64];
> > > > > > > +};
> > > > > >
> > > > > >
> > > > > > What are these two needed for now? If you want to enforce a
> > > > > > minimum size, that would better go ...
> > > > > That is because we want to be cache line aligned.
> > > >
> > > >
> > > > But this is only accurate to your platform. There is HW available with
> > > > 128
> > > > bytes.
> > > >
> > > > For instance on Xen ARM, all the structures are aligned to 128 bytes in
> > > > order to fit in most of cache line. Although technically it would be
> > > > possible have bigger one (see the definition of CSSIDR).
> > > So, then I will align to 32
> >
> > To confirm, you don't plan to reduce the size of the command packet to 32
> > octet?
> Well, actually this is what I was going to do...
> So, what is the correct value to be used here?
I don't know. What is the expected maximum size of a command?

Regards,

--
Julien Grall

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