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Re: [RFC 11/32] xfs: convert to struct inode_time

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [RFC 11/32] xfs: convert to struct inode_time
From: "Joseph S. Myers" <joseph@xxxxxxxxxxxxxxxx>
Date: Mon, 2 Jun 2014 14:00:11 +0000
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>, Arnd Bergmann <arnd@xxxxxxxx>, <linux-kernel@xxxxxxxxxxxxxxx>, <linux-arch@xxxxxxxxxxxxxxx>, <john.stultz@xxxxxxxxxx>, <hch@xxxxxxxxxxxxx>, <tglx@xxxxxxxxxxxxx>, <geert@xxxxxxxxxxxxxx>, <lftan@xxxxxxxxxx>, <linux-fsdevel@xxxxxxxxxxxxxxx>, <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20140531055457.GK14410@dastard>
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Sender: Joseph Myers <joseph@xxxxxxxxxxxxxxxx>
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

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