linux-kernel - Re: [PATCH] staging: android: uapi: drop definitions of removed ION_IOC

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Date:   Wed, 14 Jun 2017 18:48:03 +0300
From:   "Dmitry V. Levin" <ldv@...linux.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Gleb Fotengauer-Malinovskiy <glebfm@...linux.org>,
        Laura Abbott <labbott@...hat.com>,
        linux-kernel@...r.kernel.org,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Riley Andrews <riandrews@...roid.com>,
        devel@...verdev.osuosl.org
Subject: Re: [PATCH] staging: android: uapi: drop definitions of removed
 ION_IOC_{FREE,SHARE} ioctls

On Wed, Jun 14, 2017 at 07:08:39AM +0200, Greg Kroah-Hartman wrote:
> On Tue, Jun 13, 2017 at 09:17:05PM +0300, Gleb Fotengauer-Malinovskiy wrote:
> > On Tue, May 30, 2017 at 04:33:57PM -0700, Laura Abbott wrote:
> > > On 05/30/2017 07:11 AM, Gleb Fotengauer-Malinovskiy wrote:
> > > > This problem was found by strace ioctl list generator.
> > > > 
> > > > Fixes: 15c6098cfec5 ("staging: android: ion: Remove ion_handle and ion_client")
> > 
> > As this commit fixes a regression, please apply it to the tree which will
> > be merged before 4.12 release, too.
> 
> What "regression" is there?  The fact that a staging driver has a few
> spare ioctls floating around in a header file?  How is that bad?

I thought it was pretty obvious.
OK, here is a bit more detailed explanation.

There is an uapi header that after commit 15c6098cfec5 provides
definitions of ioctl macros that do not compile when used.

Imagine a userspace code that does something as harmless as
#ifdef ION_IOC_FREE
	use(ION_IOC_FREE);
#endif
This simple code is broken by commit 15c6098cfec5.

The regression is not a pure virtual one, there is a quite real userspace
(strace ioctl list generator) broken by the change.


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