linux-kernel - Re: [RFC, PATCH] HSI: cmt_speech: fix timestamp interface

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Date:	Fri, 10 Apr 2015 22:11:43 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Sebastian Reichel <sre@...nel.org>
Cc:	Kai Vehmanen <kvehmanen@...ignal.fi>,
	Aaro Koskinen <aaro.koskinen@....fi>,
	Pavel Machek <pavel@....cz>, linux-kernel@...r.kernel.org
Subject: Re: [RFC, PATCH] HSI: cmt_speech: fix timestamp interface

On Friday 10 April 2015 15:36:10 Sebastian Reichel wrote:
> 
> > - The layout is incompatible between 32-bit and 64-bit user
> >   space, because of the size differences in 'struct timespec'.
> >   This means that the driver can not work when used with 32-bit
> >   user space on a 64-bit kernel.
> > 
> > - As there are plans to change 32-bit user space to use
> >   a 64-bit time_t type in the future, it will also be
> >   incompatible with new 32-bit user space.
> > 
> > As the driver is not yet widely used, now would be a good time
> > to change it to just use a 64-bit nanosecond value, which also
> > happens to be more efficient. In order to make the layout
> > non-ambiguous, we have to also add extra padding so the 64-bit
> > value is naturally aligned.
> > 
> > The change requires the respective update to user space tools
> > using it. If that is for some reason not possible any more,
> > another solution would be to replace the timespec structure
> > with two __u32 values to avoid incompatibilities later.
> >
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> 
> I think updating to two __u32 values is the better solution here.
> While the driver is new in the mainline kernel it has been used
> for multiple years downstream in the Maemo/MeeGo/Mer communities
> and I would prefer to keep userspace compatibility.

Ok. You still need to update that userspace to the new ABI in order
to support compiling on 64-bit machines and on future arm32 with
64-bit time_t, but existing binaries will continue to run.

Can you (or someone on Cc) prepare a patch for this?

	Arnd
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