linux-kernel - Re: [PATCH 00/25] Change time_t and clock

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Date:	Wed, 14 May 2014 13:00:21 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ley Foon Tan <lftan@...era.com>,
	Linux-Arch <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	LeyFoon Tan <lftan.linux@...il.com>,
	Chung-Lin Tang <cltang@...esourcery.com>
Subject: Re: [PATCH 00/25] Change time_t and clock_t to 64 bit

On Tuesday 13 May 2014 22:35:08 Geert Uytterhoeven wrote:
> 
> On Tue, May 13, 2014 at 9:32 PM, Arnd Bergmann <arnd@...db.de> wrote:
> > I think we have three categories:
> 
> Thanks for the list!
> 
> > a) interfaces that uses relative time_t/timespec/timeval:
> > b) interfaces that don't make sense for times in the past:
> 
> > c) interfaces that require absolute times:
> >    - stat/lstat/fstatat/
> >    - utime/utimes/futimesat
> >
> > These absolutely have to use something better than time_t
> > both in user space and in the kernel so we can deal with
> > old files. A lot of file systems need to be fixed as well so
> > we can actually store the times, regardless of whether we
> > are running a 32 or 64 bit kernel.
> 
> So these are the ones we have to worry about.
> It looks like they all involve I/O? Apart from the case of using block data
> from the buffer cache, the 64-bit operations should disappear in the
> actual I/O noise, right?

Right. Also there have been proposals for a better 'stat' replacement
for years, which would solve half of the interface problem for the
file system interfaces.

However, we also need to find a solution for category b), I only put
them into a different category above because we can treat them
differently in the kernel. For instance, we could use ktime_t for
the kernel code in category b) and a new struct timespec64 for
the times in struct inode.
On the user interface side, using timespec64 would be a reasonable
choice for both categories, because we already have two implementations
of all those syscalls in order to handle 32-on-64 compat tasks,
and we could use the same set of syscall implementations for time64-on-32.

	Arnd
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