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

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On Tuesday, September 27, 2011 13:00:24 Guennadi Liakhovetski wrote:
> 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@xxxxxx>
> > > ---
> > > 
> > > 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?

The state field in the v4l2_buffer argument.

The experimental tag allows for changes, that's true. So this is my proposed
change :-)

Regards,

	Hans

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