Em 16-11-2010 14:01, Arnd Bergmann escreveu: > On Tuesday 16 November 2010, Hans Verkuil wrote: >>> I think there is a misunderstanding. One V4L device (e.g. a TV capture >>> card, a webcam, etc.) has one v4l2_device struct. But it can have multiple >>> V4L device nodes (/dev/video0, /dev/radio0, etc.), each represented by a >>> struct video_device (and I really hope I can rename that to v4l2_devnode >>> soon since that's a very confusing name). >>> >>> You typically need to serialize between all the device nodes belonging to >>> the same video hardware. A mutex in struct video_device doesn't do that, >>> that just serializes access to that single device node. But a mutex in >>> v4l2_device is at the right level. > > Ok, got it now. > >> A quick follow-up as I saw I didn't fully answer your question: to my >> knowledge there are no per-driver data structures that need a BKL for >> protection. It's definitely not something I am worried about. > > Good. Are you preparing a patch for a per-v4l2_device then? This sounds > like the right place with your explanation. I would not put in the > CONFIG_BKL switch, because I tried that for two other subsystems and got > called back, but I'm not going to stop you. > > As for the fallback to a global mutex, I guess you can set the > videodev->lock pointer and use unlocked_ioctl for those drivers > that do not use a v4l2_device yet, if there are only a handful of them. Hans, FYI, Linus already pull Arnd patch that removed BKL on -rc2 (commit 0edf2e5e2bd0ae7689ce8a57ae3c87cc1f0c6548). I've pulled back from -rc2 into linux-media.git tree. So, the patch is now visible on our main tree. Cheers, Mauro -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
