On Monday 30 April 2012 16:06:16 Sakari Ailus wrote:
> Hi Hans,
>
> Thanks for your comments.
>
> On Mon, Apr 30, 2012 at 03:48:14PM +0200, Hans Verkuil wrote:
> > On Monday 30 April 2012 15:34:58 Sakari Ailus wrote:
> > > Remove input field in struct v4l2_buffer and flag V4L2_BUF_FLAG_INPUT
> > > which tells the former is valid. The flag is used by no driver
> > > currently.
> > >
> > > Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxx>
> > > ---
> > > Hi all,
> > >
> > > I thought this would be a good time to get rid of the input field in
> > > v4l2_buffer to avoid writing more useless compat code for it --- the
> > > enum compat code.
> > >
> > > Comments are welcome. This patch is compile tested on videobuf and
> > > videobuf2.
> >
> > I'm all in favor of this. Don't forget to update the documentation as
> > well, though!
>
> Good point. I'll go through that next.
>
> > What would the impact be on applications, though? Any app that currently
> > does 'reserved = 0' would fail to compile after this change.
>
> I had a bit of that in drivers and videobuf(2), too.
>
> Is there a known good practice of dealing with this? The reserved fields
> are supposed to be set to zero by applications but the reserved fields may
> even vanish over time from some structs.
We never ran out of reserved fields before (at least to my knowledge), so
there is no known good practice.
> One option is to keep the reserved fields as array even there was just one
> of them or if it no longer was there. If so, reserved should have been
> reserved[1] in the first place. This would make it easier to deal with
> the changing size of the reserved field.
Definitely. But I think struct v4l2_buffer has been like this for a long time
(Laurent would know when the input field was added).
Regards,
Hans
>
> > Perhaps rather than removing 'input' and changing 'reserved' to
> > 'reserved[2]' we should do something like this:
> >
> > union {
> >
> > u32 input;
> > u32 reserved2;
> >
> > };
> > u32 reserved;
> >
> > Or perhaps leave out the union and just replace 'input' by 'reserved2'.
>
> That sounds like a good option to me, too.
>
> Kind regards,
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