On Thursday 29 April 2010 09:10:42 Laurent Pinchart wrote: > Hi Hans, > > On Thursday 29 April 2010 08:44:29 Hans Verkuil wrote: > > On Thursday 29 April 2010 05:42:39 Frederic Weisbecker wrote: > > > Hi, > > > > > > Linus suggested to rename struct v4l2_file_operations::ioctl > > > into bkl_ioctl to eventually get something greppable and make > > > its background explicit. > > > > > > While at it I thought it could be a good idea to just pushdown > > > the bkl to every v4l drivers that have an .ioctl, so that we > > > actually remove struct v4l2_file_operations::ioctl for good. > > > > > > It passed make allyesconfig on sparc. > > > Please tell me what you think. > > > > I much prefer to keep the bkl inside the v4l2 core. One reason is that I > > think that we can replace the bkl in the core with a mutex. Still not > > ideal of course, so the next step will be to implement proper locking in > > each driver. For this some additional v4l infrastructure work needs to be > > done. I couldn't proceed with that until the v4l events API patches went > > in, and that happened yesterday. > > > > So from my point of view the timeline is this: > > > > 1) I do the infrastructure work this weekend. This will make it much easier > > to convert drivers to do proper locking. And it will also simplify > > v4l2_priority handling, so I'm killing two birds with one stone :-) > > > > 2) Wait until Arnd's patch gets merged that pushes the bkl down to > > v4l2-dev.c > > > > 3) Investigate what needs to be done to replace the bkl with a v4l2-dev.c > > global mutex. Those drivers that call the bkl themselves should probably be > > converted to do proper locking, but there are only about 14 drivers that do > > this. The other 60 or so drivers should work fine if a v4l2-dev global lock > > is used. At this point the bkl is effectively removed from the v4l > > subsystem. > > > > 4) Work on the remaining 60 drivers to do proper locking and get rid of the > > v4l2-dev global lock. This is probably less work than it sounds. > > > > Since your patch moves everything down to the driver level it will actually > > make this work harder rather than easier. And it touches almost all drivers > > as well. > > Every driver will need to be carefully checked to make sure the BKL can be > replaced by a v4l2-dev global mutex. Why would it be more difficult to do so > if the BKL is pushed down to the drivers ? The main reason is really that pushing the bkl into the v4l core makes it easier to review. I noticed for example that this patch series forgot to change the video_ioctl2 call in ivtv-ioctl.c to video_ioctl2_unlocked. And there may be other places as well that were missed. Having so many drivers changed also means a lot of careful reviewing. But I will not block this change. However, I do think it would be better to create a video_ioctl2_bkl rather than add a video_ioctl2_unlocked. The current video_ioctl2 function *is* already unlocked. So you are subtle changing the behavior of video_ioctl2. Not a good idea IMHO. And yes, grepping for video_ioctl2_bkl is also easy to do and makes it more obvious that the BKL is used in drivers that call this. Regards, Hans -- Hans Verkuil - video4linux developer - sponsored by TANDBERG, part of Cisco -- 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
