Re: [PATCH] Input: uinput - Add UI_SET_UNIQ ioctl handler

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

Hi Pali,

On Sun, Dec 01, 2019 at 03:53:57PM +0100, Pali Rohár wrote:
> Hello!
> 
> On Wednesday 27 November 2019 10:51:39 Abhishek Pandit-Subedi wrote:
> > Support setting the uniq attribute of the input device. The uniq
> > attribute is used as a unique identifier for the connected device.
> > 
> > For example, uinput devices created by BlueZ will store the address of
> > the connected device as the uniq property.
> > 
> > Signed-off-by: Abhishek Pandit-Subedi <abhishekpandit@chromium.org>
> 
> ...
> 
> > diff --git a/include/uapi/linux/uinput.h b/include/uapi/linux/uinput.h
> > index c9e677e3af1d..d5b7767c1b02 100644
> > --- a/include/uapi/linux/uinput.h
> > +++ b/include/uapi/linux/uinput.h
> > @@ -145,6 +145,7 @@ struct uinput_abs_setup {
> >  #define UI_SET_PHYS		_IOW(UINPUT_IOCTL_BASE, 108, char*)
> >  #define UI_SET_SWBIT		_IOW(UINPUT_IOCTL_BASE, 109, int)
> >  #define UI_SET_PROPBIT		_IOW(UINPUT_IOCTL_BASE, 110, int)
> > +#define UI_SET_UNIQ		_IOW(UINPUT_IOCTL_BASE, 111, char*)
> 
> I think that usage of char* as type in _IOW would cause compatibility
> problems like it is for UI_SET_PHYS (there is UI_SET_PHYS_COMPAT). Size
> of char* pointer depends on userspace (32 vs 64bit), so 32bit process on
> 64bit kernel would not be able to call this new UI_SET_UNIQ ioctl.
> 
> I would suggest to define this ioctl as e.g.:
> 
>   #define UI_SET_UNIQ		_IOW(_IOC_WRITE, UINPUT_IOCTL_BASE, 111, 0)
> 
> And then in uinput.c code handle it as:
> 
>   case UI_SET_UNIQ & ~IOCSIZE_MASK:
> 
> as part of section /* Now check variable-length commands */

If we did not have UI_SET_PHYS in its current form, I'd agree with you,
but I think there is benefit in having UI_SET_UNIQ be similar to
UI_SET_PHYS.

But you are absolutely correct that in current form the patch is
deficient on 64/32 systems, and the compat handling needs to be added
before it can be accepted.

Thanks.

-- 
Dmitry