On Tue, Dec 17, 2013 at 04:48:52PM +0100, 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.
>
> The new API also allows to query multiple ABS values with one call. To
> allow EVIOCSABS2(code = 0, cnt = ABS_CNT2) we need to silently ignore
> writes to ABS_MT_SLOT. Furthermore, for better compatibility with
> newer user-space, we ignore writes to unknown codes. Hence, if we ever
> increase ABS_MAX2, new user-space will work with code=0,cnt=ABS_CNT2 just
> fine even on old kernels.
>
> Note that we also need to increase EV_VERSION so user-space can reliably
> know whether ABS2 is supported. Unfortunately, we return EINVAL instead of
> ENOSYS for unknown evdev ioctls so it's nearly impossible to catch
> reliably without EVIOCGVERSION.
>
> Signed-off-by: David Herrmann <dh.herrmann@xxxxxxxxx>
> ---
> drivers/hid/hid-debug.c | 2 +-
> drivers/hid/hid-input.c | 2 +-
> drivers/input/evdev.c | 95 +++++++++++++++++++++++++++++++-
> drivers/input/input.c | 14 ++---
> drivers/input/keyboard/goldfish_events.c | 6 +-
> drivers/input/keyboard/hil_kbd.c | 2 +-
> drivers/input/misc/uinput.c | 6 +-
> include/linux/hid.h | 2 +-
> include/linux/input.h | 6 +-
> include/uapi/linux/input.h | 42 +++++++++++++-
> include/uapi/linux/uinput.h | 2 +-
> 11 files changed, 155 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/hid/hid-debug.c b/drivers/hid/hid-debug.c
> index 8453214..d32fa30 100644
> --- a/drivers/hid/hid-debug.c
> +++ b/drivers/hid/hid-debug.c
> @@ -862,7 +862,7 @@ static const char *relatives[REL_MAX + 1] = {
> [REL_WHEEL] = "Wheel", [REL_MISC] = "Misc",
> };
>
> -static const char *absolutes[ABS_CNT] = {
> +static const char *absolutes[ABS_CNT2] = {
> [ABS_X] = "X", [ABS_Y] = "Y",
> [ABS_Z] = "Z", [ABS_RX] = "Rx",
> [ABS_RY] = "Ry", [ABS_RZ] = "Rz",
> diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
> index d97f232..a02721c 100644
> --- a/drivers/hid/hid-input.c
> +++ b/drivers/hid/hid-input.c
> @@ -1300,7 +1300,7 @@ static bool hidinput_has_been_populated(struct hid_input *hidinput)
> for (i = 0; i < BITS_TO_LONGS(REL_CNT); i++)
> r |= hidinput->input->relbit[i];
>
> - for (i = 0; i < BITS_TO_LONGS(ABS_CNT); i++)
> + for (i = 0; i < BITS_TO_LONGS(ABS_CNT2); i++)
> r |= hidinput->input->absbit[i];
I wonder if kittens will die if we do:
in include/uapi/linux/input:
#define ABS_MAX1 0x3f
#define ABS_MAX2 0xYY
/*
* Keep old value of ABS_MAX exported to userspace. Users ready to
* handle bigger range will have to use ABS_MAX2 explicitly.
*/
#define ABS_MAX ABS_MAX1
in include/linux/input.h
...
/* Kernel should use the new ABS range by default */
#undef ABS_MAX
#define ABS_MAX ABS_MAX2
Thanks.
--
Dmitry
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