linux-kernel - Re: 2.6.36/2.6.37: broken compatibility with userspace input-utils ?

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Message-ID: <4D3E59CA.6070107@teksavvy.com>
Date:	Tue, 25 Jan 2011 00:04:10 -0500
From:	Mark Lord <kernel@...savvy.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
CC:	Linux Kernel <linux-kernel@...r.kernel.org>,
	linux-input@...r.kernel.org
Subject: Re: 2.6.36/2.6.37: broken compatibility with userspace input-utils
 ?

On 11-01-24 11:55 PM, Dmitry Torokhov wrote:
> On Mon, Jan 24, 2011 at 11:37:06PM -0500, Mark Lord wrote:
..
>> This results in (map->size==10) for 2.6.36+ (wrong),
>> and a much larger map->size for 2.6.35 and earlier.
>>
>> So perhaps EVIOCGKEYCODE has changed?
>>
> 
> So the utility expects that all devices have flat scancode space and
> driver might have changed so it does not recognize scancode 10 as valid
> scancode anymore.
> 
> The options are:
> 
> 1. Convert to EVIOCGKEYCODE2
> 2. Ignore errors from EVIOCGKEYCODE and go through all 65536 iterations.

or 3. Revert/fix the in-kernel regression.

The EVIOCGKEYCODE ioctl is supposed to return KEY_RESERVED for unmapped
(but value) keycodes, and only return -EINVAL when the keycode itself
is out of range.

That's how it worked in all kernels prior to 2.6.36,
and now it is broken.  It now returns -EINVAL for any unmapped keycode,
even though keycodes higher than that still have mappings.

This is a bug, a regression, and breaks userspace.
I haven't identified *where* in the kernel the breakage happened,
though.. that code confuses me.  :)

Thanks.
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