On Sat, May 01, 2010 at 11:55:37AM +0200, Hans Verkuil wrote: > 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. Indeed, that's because I did it in a half automated way and my script didn't took the direct calls to video_ioctl2() into account, so I had to check them manually and probably missed a few, I will fix this one and double check. > > 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. Totally agreed, will respin with this rename. Thanks. -- 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
