On Fri, Oct 04, 2013 at 09:32:23AM +1000, Peter Hutterer wrote:
> On Thu, Oct 03, 2013 at 12:10:36AM +0200, David Herrmann wrote:
> > As we painfully noticed during the 3.12 merge-window our
> > EVIOCGABS/EVIOCSABS API is limited to ABS_MAX<=0x3f. We tried several
> > hacks to work around it but if we ever decide to increase ABS_MAX, the
> > EVIOCSABS ioctl ABI might overflow into the next byte causing horrible
> > misinterpretations in the kernel that we cannot catch.
> >
> > Therefore, we decided to go with ABS_MAX2/CNT2 and introduce two new
> > ioctls to get/set abs-params. They no longer encode the ABS code in the
> > ioctl number and thus allow up to 4 billion ABS codes.
> >
> > Unfortunately, the uinput API also hard-coded the ABS_CNT value in its
> > ABI. To avoid any hacks in uinput, we simply introduce a new
> > uinput_user_dev2 to replace the old one. The new API allows growing
> > ABS_CNT2 values without any API changes.
> >
> > Signed-off-by: David Herrmann <dh.herrm...@gmail.com>
> > ---
> > Hi
> >
> > This is only compile-tested but I wanted to get a first revision out to let
> > people know what we're working on. Unfortunately, the ABS API has this
> > horribly
> > low ABS_MAX limit and we couldn't figure out a way to increase it while
> > keeping
> > ABI compatibility.
> >
> > Any feedback and review is welcome. And if anyone spots ABI breakage by this
> > patch, please let me know. If nothing comes up I will patch libevdev to use
> > the
> > new API, write some extensive test-cases and push this forward.
> >
> > As a sidenote: I didn't modify joydev to use the new values. Fortunately,
> > the
> > joydev API would allow switching to ABS_CNT2 without breaking API, but it
> > would
> > limit the new ABS_CNT2 to 16k. This is quite high but nothing compared to
> > the
> > 2^32 that we can theoretically support now. If you think 16k ought to be
> > enough
> > (probably?) I can adjust the joydev API, too.
> > All other kernel users were converted to the new values. Nothing left
> > behind..
>
>
> just a comment from skimming the patch:
> if you need a new uinput abi anyway, can we add the resolution here? it's
> sorely needed for some tests. see also the patch Benjamin sent a while ago
> ("input/uinput: support abs resolution", July 15 2013)
Indeed. Also, while we are at it, would it make sense to allow
requesting a range of ABS infos at once?
--
Dmitry
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