[Xcb] [PATCH proto 1/2] Add sizeof tag to struct

[Daniel Martin]

On Thu, Jan 03, 2013 at 12:46:06PM +1000, Peter Hutterer wrote:
> On Sun, Dec 23, 2012 at 03:29:23PM +0100, Daniel Martin wrote:
> > If a struct provides all necessary informations to calculate it's
> > size, i.e. an explicit length field, this sizeof tag makes it possible
> > to reference to the length field with an expression (known from lists).
> > This makes further iterations over these structs very easy, as we don't
> > have to sum up all field lengths, lists and may add padding.
> > 
> > structs with such a length field can be found in the XInput extension.
> > For example the device classes (xXIButtonInfo, xXIKeyInfo, ...):
> >   http://cgit.freedesktop.org/xorg/proto/inputproto/tree/XI2proto.h#n136
> > 
> > Signed-off-by: Daniel Martin <consume.noise at gmail.com>
> 
> I don't know enough about xcb's internals but the approach seems sensible.
> two typos pointed out below.
...
> > +  If the optional sizeof element is present it provides a simple way to
> > +  compute the struct size at runtime. This is usefull if the struct itself
> 
> useful
> 
> > +  contains a length field referencing the whole struct. With that given it's
> > +  not necessary to sum up all fields, lists and pads of the struct.
> > +  DO NOT use it the work around alignmend issues. Use the packed attribute
> 
> alignment

Thanks, changes applied.