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

From: "Pali Rohár" <pali.rohar@gmail.com>
To: Abhishek Pandit-Subedi <abhishekpandit@chromium.org>
Cc: linux-input@vger.kernel.org, linux-bluetooth@vger.kernel.org,
	Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
	Enric Balletbo i Serra <enric.balletbo@collabora.com>,
	linux-kernel@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Logan Gunthorpe <logang@deltatee.com>,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	Andrey Smirnov <andrew.smirnov@gmail.com>,
	Kirill Smelkov <kirr@nexedi.com>
Subject: Re: [PATCH] Input: uinput - Add UI_SET_UNIQ ioctl handler
Date: Sun, 1 Dec 2019 15:53:57 +0100	[thread overview]
Message-ID: <20191201145357.ybq5gfty4ulnfasq@pali> (raw)
In-Reply-To: <20191127185139.65048-1-abhishekpandit@chromium.org>

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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 */

-- 
Pali Rohár
pali.rohar@gmail.com

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