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

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Message-ID: <20110125052902.GC7850@core.coreip.homeip.net>
Date:	Mon, 24 Jan 2011 21:29:02 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Mark Lord <kernel@...savvy.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 Tue, Jan 25, 2011 at 12:04:10AM -0500, Mark Lord wrote:
> 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.

You are inventing rules.  You are requesting a scancode->keycode
mapping. If scancode is unknown/invalid for the device ioctl returns
-EINVAL.

> 
> 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.

For unmapped - yes, either KEY_RESERVED or KEY_UNKNOWN should be
returned. For invalid scancodes -EINVAL shoudl be returned. Scancodes
are not guaranteed to be continuous (and never have been for all devices
although there are still plenty of devices with continuous scancodes,
like atkbd).

> 
> 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.  :)
> 

-- 
Dmitry
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