linux-kernel - Re: [RFC 11/32] xfs: convert to struct inode

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Message-ID: <Pine.LNX.4.64.1406021355230.19591@digraph.polyomino.org.uk>
Date:	Mon, 2 Jun 2014 14:00:11 +0000
From:	"Joseph S. Myers" <joseph@...esourcery.com>
To:	Dave Chinner <david@...morbit.com>
CC:	"H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
	<linux-kernel@...r.kernel.org>, <linux-arch@...r.kernel.org>,
	<john.stultz@...aro.org>, <hch@...radead.org>,
	<tglx@...utronix.de>, <geert@...ux-m68k.org>, <lftan@...era.com>,
	<linux-fsdevel@...r.kernel.org>, <xfs@....sgi.com>
Subject: Re: [RFC 11/32] xfs: convert to struct inode_time

On Sat, 31 May 2014, Dave Chinner wrote:

> If we are changing the in-kernel timestamp to have a greater dynamic
> range that anything we current support on disk, then we need support
> for all filesystems for similar translation and constraint. The
> filesystems need to be able to tell the kernel what they timestamp
> range they support, and then the kernel needs to follow those
> guidelines. And if the filesystem is mounted on a kernel that
> doesn't support the current filesystem's timestamp format, then at
> minimum that filesystem cannot do anything that writes a
> timestamp....
> 
> Put simply: the filesystem defines the timestamp range that can be
> used safely, not the userspace API. If the filesystem can't support
> the date it is handed then that is an out-of-range error. Since
> when have we accepted that it's OK to handle out-of-range data with
> silent overflows or corruption of the data that we are attempting to
> store? We're defining a new API to support a wider date range -
> there is nothing that prevents us from saying ERANGE can be returned
> to a timestamp that the file cannot store correctly....

I don't see anything new about this issue.  All problems that could arise 
from the kernel being able to represent a timestamp some filesystems can't 
are problems that already apply with 64-bit kernels using 64-bit time_t 
internally.  So while as part of Y2038-preparedness we do need a clear 
understanding of which filesystems have what timestamp limits and what 
happens with timestamps beyond those limits, I think this is a separate 
strand of the problem - one that applies to both 32-bit and 64-bit systems 
- from the more general issue for 32-bit systems.

-- 
Joseph S. Myers
joseph@...esourcery.com
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