Re: [RFC v5 07/11] [media] vb2: add in-fence support to QBUF

[Brian Starkey]

On Fri, Nov 17, 2017 at 11:19:05AM -0200, Mauro Carvalho Chehab wrote:
> Em Fri, 17 Nov 2017 11:08:01 -0200
> Gustavo Padovan <gustavo@xxxxxxxxxxx> escreveu:
>
> > 2017-11-17 Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxx>:
> >
> > > Em Fri, 17 Nov 2017 15:49:23 +0900
> > > Alexandre Courbot <acourbot@xxxxxxxxxxxx> escreveu:
> > >
> > > > > @@ -178,6 +179,12 @@ static int vb2_queue_or_prepare_buf(struct
> > > > > vb2_queue *q, struct v4l2_buffer *b,
> > > > >  		return -EINVAL;
> > > > >  	}
> > > > >
> > > > > +	if ((b->fence_fd != 0 && b->fence_fd != -1) &&
> > > >
> > > > Why do we need to consider both values invalid? Can 0 ever be a valid fence
> > > > fd?
> > >
> > > Programs that don't use fences will initialize reserved2/fence_fd field
> > > at the uAPI call to zero.
> > >
> > > So, I guess using fd=0 here could be a problem. Anyway, I would, instead,
> > > do:
> > >
> > > 	if ((b->fence_fd < 1) &&
> > > 		...
> > >
> > > as other negative values are likely invalid as well.
> >
> > We are checking when the fence_fd is set but the flag wasn't. Checking
> > for < 1 is exactly the opposite. so we keep as is or do it fence_fd > 0.
>
> Ah, yes. Anyway, I would stick with:
> 	if ((b->fence_fd > 0) &&
> 		...

0 is a valid fence_fd right? If I close stdin, and create a sync_file,
couldn't I get a fence with fd zero?

-Brian

> > Gustavo
>
>
> --
> Thanks,
> Mauro