Re: [PATCH 2/9 v7] V4L: add two new ioctl()s for multi-size videobuffer management

[Guennadi Liakhovetski <g.liakhovetski@gmx.de>]

Hi Hans

On Tue, 27 Sep 2011, Hans Verkuil wrote:

> On Thursday, September 08, 2011 09:45:15 Guennadi Liakhovetski wrote:
> > A possibility to preallocate and initialise buffers of different sizes
> > in V4L2 is required for an efficient implementation of a snapshot
> > mode. This patch adds two new ioctl()s: VIDIOC_CREATE_BUFS and
> > VIDIOC_PREPARE_BUF and defines respective data structures.
> > 
> > Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
> > ---
> > 
> > v7: added the "experimental" comment, as suggested by Sakari - thanks.
> > 
> >  drivers/media/video/v4l2-compat-ioctl32.c |   67 +++++++++++++++++++++++++---
> >  drivers/media/video/v4l2-ioctl.c          |   29 ++++++++++++
> >  include/linux/videodev2.h                 |   17 +++++++
> >  include/media/v4l2-ioctl.h                |    2 +
> >  4 files changed, 107 insertions(+), 8 deletions(-)

[snip]

> > diff --git a/include/linux/videodev2.h b/include/linux/videodev2.h
> > index a5359c6..6e87ea9 100644
> > --- a/include/linux/videodev2.h
> > +++ b/include/linux/videodev2.h
> > @@ -653,6 +653,9 @@ struct v4l2_buffer {
> >  #define V4L2_BUF_FLAG_ERROR	0x0040
> >  #define V4L2_BUF_FLAG_TIMECODE	0x0100	/* timecode field is valid */
> >  #define V4L2_BUF_FLAG_INPUT     0x0200  /* input field is valid */
> > +/* Cache handling flags */
> > +#define V4L2_BUF_FLAG_NO_CACHE_INVALIDATE	0x0400
> > +#define V4L2_BUF_FLAG_NO_CACHE_CLEAN		0x0800
> >  
> >  /*
> >   *	O V E R L A Y   P R E V I E W
> > @@ -2098,6 +2101,15 @@ struct v4l2_dbg_chip_ident {
> >  	__u32 revision;    /* chip revision, chip specific */
> >  } __attribute__ ((packed));
> >  
> > +/* VIDIOC_CREATE_BUFS */
> > +struct v4l2_create_buffers {
> > +	__u32			index;		/* output: buffers index...index + count - 1 have been created */
> > +	__u32			count;
> > +	enum v4l2_memory        memory;
> > +	struct v4l2_format	format;		/* "type" is used always, the rest if sizeimage == 0 */
> > +	__u32			reserved[8];
> > +};
> > +
> >  /*
> >   *	I O C T L   C O D E S   F O R   V I D E O   D E V I C E S
> >   *
> > @@ -2188,6 +2200,11 @@ struct v4l2_dbg_chip_ident {
> >  #define	VIDIOC_SUBSCRIBE_EVENT	 _IOW('V', 90, struct v4l2_event_subscription)
> >  #define	VIDIOC_UNSUBSCRIBE_EVENT _IOW('V', 91, struct v4l2_event_subscription)
> >  
> > +/* Experimental, the below two ioctls may change over the next couple of kernel
> > +   versions */
> > +#define VIDIOC_CREATE_BUFS	_IOWR('V', 92, struct v4l2_create_buffers)
> > +#define VIDIOC_PREPARE_BUF	 _IOW('V', 93, struct v4l2_buffer)
> 
> I think I would prefer _IOWR here. QBUF etc. also use IOWR and you never know
> what you might return in the future. At the very least using IOWR allows us
> to update the state field, which would be a perfectly reasonable thing to do.

Sorry, which state field do you mean? We have already marked these ioctl() 
as experimental, isn't this enough?

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/