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

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Message-ID: <20171117110025.2a49db49@vento.lan>
Date:   Fri, 17 Nov 2017 11:00:25 -0200
From:   Mauro Carvalho Chehab <mchehab@....samsung.com>
To:     Alexandre Courbot <acourbot@...omium.org>
Cc:     Gustavo Padovan <gustavo@...ovan.org>,
        <linux-media@...r.kernel.org>, Hans Verkuil <hverkuil@...all.nl>,
        Shuah Khan <shuahkh@....samsung.com>,
        Pawel Osciak <pawel@...iak.com>,
        Sakari Ailus <sakari.ailus@....fi>,
        Brian Starkey <brian.starkey@....com>,
        Thierry Escande <thierry.escande@...labora.com>,
        <linux-kernel@...r.kernel.org>,
        Gustavo Padovan <gustavo.padovan@...labora.com>
Subject: Re: [RFC v5 07/11] [media] vb2: add in-fence support to QBUF

Em Fri, 17 Nov 2017 15:49:23 +0900
Alexandre Courbot <acourbot@...omium.org> 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.

-- 
Thanks,
Mauro