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

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Message-ID: <20110125210153.GB19896@core.coreip.homeip.net>
Date:	Tue, 25 Jan 2011 13:01:54 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Mauro Carvalho Chehab <mchehab@...hat.com>,
	Mark Lord <kernel@...savvy.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	linux-input@...r.kernel.org, linux-media@...r.kernel.org
Subject: Re: 2.6.36/2.6.37: broken compatibility with userspace input-utils ?

On Tue, Jan 25, 2011 at 12:54:53PM -0800, Dmitry Torokhov wrote:
> On Wed, Jan 26, 2011 at 06:09:45AM +1000, Linus Torvalds wrote:
> > On Wed, Jan 26, 2011 at 2:48 AM, Dmitry Torokhov
> > <dmitry.torokhov@...il.com> wrote:
> > >
> > > We should be able to handle the case where scancode is valid even though
> > > it might be unmapped yet. This is regardless of what version of
> > > EVIOCGKEYCODE we use, 1 or 2, and whether it is sparse keymap or not.
> > >
> > > Is it possible to validate the scancode by driver?
> > 
> > More appropriately, why not just revert the thing? The version change
> 
> Well, then we'll break Ubuntu again as they recompiled their input-utils
> package (without fixing the check). And the rest of distros do not seem
> to be using that package...
> 
> > and the buggy EINVAL return both.
> 
> I believe that -EINVAL thing only affects RC devices that Mauro switched
> to the new rc-core; input core in itself should be ABI compatible. Thus
> I'll leave the decision to him whether he wants to revert or fix
> compatibility issue.
> 
> > 
> > As Mark said, breaking user space simply isn't acceptable. And since
> > breaking user space isn't acceptable, then incrementing the version is
> > stupid too.
> 
> It might not have been the best idea to increment, however I maintain
> that if there exists version is can be changed. Otherwise there is no
> point in having version at all.
> 
> As I said, reverting the version bump will cause yet another wave of
> breakages so I propose leaving version as is.
> 
> > 
> > The way we add new ioctl's is not by incrementing some "ABI version"
> > crap. It's by adding new ioctl's or system calls or whatever that
> > simply used to return -ENOSYS or other error before, while preserving
> > the old ABI. That way old binaries don't break (for _ANY_ reason), and
> > new binaries can see "oh, this doesn't support the new thing".
> 
> That has been done as well; we have 2 new ioctls and kept 2 old ioctls.
> 

BTW, another issue is that evdev's ioctl returns -EINVAL for unknown
ioctls so applications would have hard time figuring out whether error
returned because of kernel being too old or because they are trying to
retrieve/establish invalid mapping if they had to go only by the error
code.

As far as I can see EINVAL is a proper error for unknown ioctls:

[dtor@...mer work]$ man 2 ioctl | grep EINVAL
       EINVAL Request or argp is not valid.
[dtor@...mer work]$

-- 
Dmitry
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