On 09/18/15 11:43, Arnd Bergmann wrote:
On Friday 18 September 2015 11:27:40 Hans Verkuil wrote:
Ah, OK. Got it.
I think this is dependent on the upcoming media workshop next month. If we decide to redesign v4l2_buffer anyway, then we can avoid timeval completely. And the only place where we would need to convert it in the compat code hidden in the v4l2 core (likely v4l2-ioctl.c).
Ah, I think I understood the idea now, I missed that earlier when you mention the idea.
So what you are saying here is that you could come up with a new unambiguous (using only __u32 and __u64 types and no pointers) format that gets exposed to a new set of ioctls, and then change the handling of the existing three formats (native 64-bit, traditional 32-bit, and 32-bit with 64-bit time_t) so they get converted into the new format by the common ioctl handling code?
Right. Drivers only see the new struct, and only v4l2-ioctl.c (and possible v4l2-compat-ioctl32.c) see the old ones.
BTW, I will probably pick up patches 4 and 6 for 4.4. That should help a bit.
Regards,
Hans
I am not really keen on having v4l2_timeval in all these drivers. I would have to check them anyway since I suspect that in several drivers the local timeval variable can be avoided by rewriting that part of the driver.
I've tried to do that for all the drivers where I could find an easy solution in patch 6/9, but I'm sure you can do it for a couple more.
We could also do a lightweight redesign and use 'timespec64' internally in all the drivers and then convert that to 'timeval' or the 64-bit format of that in the ioctl handler. This is also something I tried at some point but then found it a bit more intuitive to leave the normal ioctl path alone and have an explicit type.
Personally I am in favor of a redesigned v4l2_buffer: it's awkward to use with multiplanar formats, there is cruft in there that can be removed (timecode), and there is little space for additions (HW-specific timecodes, more buffer meta data, etc).
We'll see.
Ok.
Arnd