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

[Mauro Carvalho Chehab <mchehab@redhat.com>]

Em 25-01-2011 03:31, Dmitry Torokhov escreveu:
> On Tue, Jan 25, 2011 at 12:07:29AM -0500, Mark Lord wrote:
>> On 11-01-25 12:04 AM, 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.
>>>
>>> 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.  :)
>>
>> Note that this device DOES have "flat scancode space",
>> and the kernel is now incorrectly signalling an error (-EINVAL)
>> in response to a perfectly valid query of a VALID (and mappable)
>> keycode on the remote control
>>
>> The code really is a valid button, it just doesn't have a default mapping
>> set by the kernel (I can set a mapping for that code from userspace and it works).
>>
> 
> OK, in this case let's ping Mauro - I think he done the adjustments to
> IR keymap hanlding.

I lost part of the thread, but a quick search via the Internet showed that you're using
the input tools to work with a Remote Controller, right? Are you using a vanilla
kernel, or are you using the media_build backports? There are some distros that are
using those backports also like Fedora 14.

In the latter case, I found the reason why the backports were not working and I fixed
it a couple days ago:
	http://git.linuxtv.org/media_build.git?a=commit;h=b83dc3e49d90527d8e1016d09e06f4842a6a847a

The issue is simple, and it is related on how the input.c used to handle EVIOSGKEYCODE.
Basically, before allowing you to change a key, it used to call EVIOCGKEYCODE to check
it that key exists. However, when you're creating a new association, the key didn't
exist, and, to be strict with input rules, EVIOCGKEYCODE should return -EINVAL.
To circumvent that behaviour, old versions were returning 0, and associating unmapped
scancodes to KEY_RESERVED. We used this workaround for a few kernel versions, while
we were discussing the improvements so support larger scancodes.

Yet, on all vanilla kernels, changing the keycode association works fine.

However, the backport patch at media_build were not taking this workaround into account,
and were just returning -EINVAL. So, the backported media drivers stopped allowing
some keytable changes. The patch above fixes it.

Cheers,
Mauro