linux-kernel - Re: support autofocus / autogain in libv4l2

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Message-ID: <1493139207.19105.16.camel@ndufresne.ca>
Date:   Tue, 25 Apr 2017 12:53:27 -0400
From:   Nicolas Dufresne <nicolas@...fresne.ca>
To:     Pavel Machek <pavel@....cz>,
        Mauro Carvalho Chehab <mchehab@...pensource.com>
Cc:     pali.rohar@...il.com, sre@...nel.org,
        kernel list <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-omap@...r.kernel.org, tony@...mide.com, khilman@...nel.org,
        aaro.koskinen@....fi, ivo.g.dimitrov.75@...il.com,
        patrikbachan@...il.com, serge@...lyn.com, abcloriens@...il.com,
        Sakari Ailus <sakari.ailus@....fi>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        linux-media@...r.kernel.org
Subject: Re: support autofocus / autogain in libv4l2

Le mardi 25 avril 2017 à 10:05 +0200, Pavel Machek a écrit :
> Well, fd's are hard, because application can do fork() and now
> interesting stuff happens. Threads are tricky, because now you have
> locking etc.
> 
> libv4l2 is designed to be LD_PRELOADED. That is not really feasible
> with "complex" library.

That is incorrect. The library propose an API where you simply replace
certain low level calls, like ioctl -> v4l2_ioctl, open -> v4l2_open().
You have to do that explicitly in your existing code. It does not
abstract the API itself unlike libdrm.

Nicolas
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