Re: [Linaro-mm-sig] [RFCv2 PATCH 4/9] v4l: add buffer exporting via dmabuf

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

On Thursday 22 March 2012 15:26:08 Daniel Vetter wrote:
> On Thu, Mar 22, 2012 at 03:07:18PM +0100, Laurent Pinchart wrote:
> > > >> + * Contains data used for exporting a video buffer as DMABUF file
> > > >> + * descriptor. Uses the same 'cookie' as mmap() syscall. All
> > > >> reserved
> > > >> fields
> > > >> + * must be set to zero.
> > > >> + */
> > > >> +struct v4l2_exportbuffer {
> > > >> +	__u32		fd;
> > > >> +	__u32		reserved0;
> > > > 
> > > > Why is there a reserved field here ?
> > > 
> > > +1 to Laurent. Any particular need for reserved0 and reserved[13] below?
> > > I think one void user pointer is sufficient even for future need.
> > 
> > I'd rather have more than one void user pointer, just in case. A couple of
> > bytes won't be expensive, and they will save lots of hassle in the future
> > if we need to add a couple of fields. I was just wondering why there was
> > a reserved field between fd and mem_offset.
> 
> Quick comment from a random bystander: __u32 is not big enough for a void*
> pointer from userspace ...

That's why I'm happy with 14 reserved __u32. That should be enough for 
userspace pointers in the foreseable future :-)

-- 
Regards,

Laurent Pinchart