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From: Nicolas Pitre <nicolas.pitre@linaro.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Dave Chinner <david@fromorbit.com>,
	hch@infradead.org, linux-mtd@lists.infradead.org,
	"H. Peter Anvin" <hpa@zytor.com>,
	logfs@logfs.org, linux-afs@lists.infradead.org,
	"Joseph S. Myers" <joseph@codesourcery.com>,
	linux-arch@vger.kernel.org, linux-cifs@vger.kernel.org,
	linux-scsi@vger.kernel.org, ceph-devel@vger.kernel.org,
	cluster-devel@redhat.com, coda@cs.cmu.edu, geert@linux-m68k.org,
	linux-ext4@vger.kernel.org, codalist@telemann.coda.cs.cmu.edu,
	fuse-devel@lists.sourceforge.net, reiserfs-devel@vger.kernel.org,
	xfs@oss.sgi.com, john.stultz@linaro.org, tglx@linutronix.de,
	linux-nfs@vger.kernel.org, linux-ntfs-dev@lists.sourceforge.net,
	samba-technical@lists.samba.org, linux-kernel@vger.kernel.org,
	linux-f2fs-devel@lists.sourceforge.net,
	ocfs2-devel@oss.oracle.com, linux-fsdevel@vger.kernel.org,
	lftan@altera.com, linux-btrfs@vger.kernel.org
Subject: Re: [RFC 00/32] making inode time stamps y2038 ready
Date: Wed, 4 Jun 2014 13:30:32 -0400 (EDT)
Message-ID: <alpine.LFD.2.11.1406041308300.17310@knanqh.ubzr> (raw)
In-Reply-To: <201406041703.47592.arnd@arndb.de>

On Wed, 4 Jun 2014, Arnd Bergmann wrote:

> On Tuesday 03 June 2014, Dave Chinner wrote:
> > Just ot be pedantic, inodes don't need 96 bit timestamps - some
> > filesystems can *support up to* 96 bit timestamps. If the kernel
> > only supports 64 bit timestamps and that's all the kernel can
> > represent, then the upper bits of the 96 bit on-disk inode
> > timestamps simply remain zero.
> 
> I meant the reverse: since we have file systems that can store
> 96-bit timestamps when using 64-bit kernels, we need to extend
> 32-bit kernels to have the same internal representation so we
> can actually read those file systems correctly.
> 
> > If you move the filesystem between kernels with different time
> > ranges, then the filesystem needs to be able to tell the kernel what
> > it's supported range is.  This is where having the VFS limit the
> > range of supported timestamps is important: the limit is the
> > min(kernel range, filesystem range). This allows the filesystems
> > to be indepenent of the kernel time representation, and the kernel
> > to be independent of the physical filesystem time encoding....
> 
> I agree it makes sense to let the kernel know about the limits
> of the file system it accesses, but for the reverse, we're probably
> better off just making the kernel representation large enough (i.e.
> 96 bits) so it can work with any known file system.

Depends...  96 bit handling may get prohibitive on 32-bit archs.

The important point here is for the kernel to be able to represent the 
time _range_ used by any known filesystem, not necessarily the time 
_precision_.

For example, a 64 bit representation can be made of 40 bits for seconds 
spanning 34865 years, and 24 bits for fractional seconds providing 
precision down to 60 nanosecs.  That ought to be plenty good on 32 bit 
systems while still being cheap to handle.


Nicolas

  reply index

Thread overview: 124+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-05-30 20:01 Arnd Bergmann
2014-05-30 20:01 ` [RFC 01/32] fs: introduce new 'struct inode_time' Arnd Bergmann
2014-05-31  7:56   ` Geert Uytterhoeven
2014-05-31  8:39     ` Andreas Schwab
2014-05-31 13:19       ` Geert Uytterhoeven
2014-05-31 13:46         ` Andreas Schwab
2014-05-31 14:54       ` Arnd Bergmann
2014-05-31 16:15         ` Geert Uytterhoeven
2014-05-31  9:03   ` H. Peter Anvin
2014-05-31 14:53     ` Arnd Bergmann
2014-05-31 14:55       ` H. Peter Anvin
2014-05-30 20:01 ` [RFC 02/32] uapi: add struct __kernel_timespec{32,64} Arnd Bergmann
2014-05-30 20:18   ` H. Peter Anvin
2014-05-31 15:09     ` Arnd Bergmann
2014-05-30 20:01 ` [RFC 03/32] fs: introduce sys_utimens64at Arnd Bergmann
2014-05-31  9:22   ` Andreas Schwab
2014-05-31 14:55     ` Arnd Bergmann
2014-05-30 20:01 ` [RFC 04/32] fs: introduce sys_newfstat64/sys_newfstatat64 Arnd Bergmann
2014-05-30 20:01 ` [RFC 05/32] arch: hook up new stat and utimes syscalls Arnd Bergmann
2014-05-30 20:01 ` [RFC 06/32] isofs: fix timestamps beyond 2027 Arnd Bergmann
2014-05-31  7:59   ` Geert Uytterhoeven
2014-05-31  8:47     ` H. Peter Anvin
2014-05-30 20:01 ` [RFC 07/32] fs/nfs: convert to struct inode_time Arnd Bergmann
2014-05-30 20:01 ` [RFC 08/32] fs/ceph: convert to 'struct inode_time' Arnd Bergmann
2014-05-30 20:01 ` [RFC 09/32] fs/pstore: convert to struct inode_time Arnd Bergmann
2014-05-30 21:14   ` Kees Cook
2014-05-30 20:01 ` [RFC 10/32] fs/coda: " Arnd Bergmann
2014-05-30 20:01 ` [RFC 11/32] xfs: " Arnd Bergmann
2014-05-31  0:37   ` Dave Chinner
2014-05-31  0:41     ` H. Peter Anvin
2014-05-31  1:14       ` Dave Chinner
2014-05-31  1:22         ` H. Peter Anvin
2014-05-31  5:54           ` Dave Chinner
2014-05-31  8:41             ` H. Peter Anvin
2014-05-31 15:46               ` Nicolas Pitre
2014-06-01 19:56                 ` Arnd Bergmann
2014-06-01 20:26                   ` H. Peter Anvin
2014-06-02 11:02                     ` Arnd Bergmann
2014-06-02  1:36                   ` Nicolas Pitre
2014-06-02  2:22                     ` Dave Chinner
2014-06-02  7:09                       ` Geert Uytterhoeven
2014-06-02 10:56                     ` Arnd Bergmann
2014-06-02 11:57                       ` Theodore Ts'o
2014-06-02 12:38                         ` Arnd Bergmann
2014-06-02 13:15                           ` Theodore Ts'o
2014-06-02 12:52                         ` Arnd Bergmann
2014-06-02 13:07                           ` Theodore Ts'o
2014-06-02 15:01                             ` Arnd Bergmann
2014-06-02 14:52                         ` H. Peter Anvin
2014-06-02 15:04                       ` Chuck Lever
2014-06-02 15:31                         ` Theodore Ts'o
2014-06-02 17:12                           ` H. Peter Anvin
2014-06-02 18:50                             ` Arnd Bergmann
2014-06-02 22:29                             ` Theodore Ts'o
2014-06-02 22:32                               ` H. Peter Anvin
2014-06-02 23:32                                 ` Theodore Ts'o
2014-06-02 23:33                                   ` H. Peter Anvin
2014-06-03 13:09                                   ` Roger Willcocks
2014-06-02 18:52                         ` Arnd Bergmann
2014-06-02 18:58                         ` Roger Willcocks
2014-06-02 19:04                           ` Chuck Lever
2014-06-02 19:10                             ` Arnd Bergmann
2014-06-01  0:39               ` Dave Chinner
2014-06-02 14:00             ` Joseph S. Myers
2014-05-31 15:37         ` Arnd Bergmann
2014-06-01  0:24           ` Dave Chinner
2014-06-02  0:28             ` Dave Chinner
2014-06-02 11:35               ` Roger Willcocks
2014-06-02 11:43               ` Arnd Bergmann
2014-06-03  0:32                 ` Dave Chinner
2014-06-03  7:33                   ` Arnd Bergmann
2014-06-03  8:41                     ` Dave Chinner
2014-06-03  9:16                       ` Arnd Bergmann
2014-05-30 20:01 ` [RFC 12/32] btrfs: " Arnd Bergmann
2014-05-30 20:01 ` [RFC 13/32] ext3: " Arnd Bergmann
2014-05-31  9:10   ` H. Peter Anvin
2014-05-31 14:32     ` Arnd Bergmann
2014-05-30 20:01 ` [RFC 14/32] ext4: " Arnd Bergmann
2014-05-30 20:01 ` [RFC 15/32] cifs: " Arnd Bergmann
2014-05-30 20:01 ` [RFC 16/32] ntfs: " Arnd Bergmann
2014-05-30 20:01 ` [RFC 17/32] ubifs: " Arnd Bergmann
2014-06-02  7:54   ` Artem Bityutskiy
2014-05-30 20:01 ` [RFC 18/32] ocfs2: " Arnd Bergmann
2014-05-30 20:01 ` [RFC 19/32] fs/fat: " Arnd Bergmann
2014-05-30 20:01 ` [RFC 20/32] afs: " Arnd Bergmann
2014-05-30 20:01 ` [RFC 21/32] udf: " Arnd Bergmann
2014-05-30 20:01 ` [RFC 22/32] fs: convert simple fs to inode_time Arnd Bergmann
2014-05-30 23:06   ` Greg Kroah-Hartman
2014-05-30 20:01 ` [RFC 23/32] logfs: convert to struct inode_time Arnd Bergmann
2014-05-30 20:01 ` [RFC 24/32] hfs, hfsplus: " Arnd Bergmann
2014-05-31 14:23   ` Vyacheslav Dubeyko
2014-05-30 20:01 ` [RFC 25/32] gfs2: " Arnd Bergmann
2014-06-02  9:52   ` Steven Whitehouse
2014-05-30 20:01 ` [RFC 26/32] reiserfs: " Arnd Bergmann
2014-05-30 20:01 ` [RFC 27/32] jffs2: " Arnd Bergmann
2014-05-30 20:01 ` [RFC 28/32] adfs: " Arnd Bergmann
2014-05-30 20:01 ` [RFC 29/32] f2fs: " Arnd Bergmann
2014-05-30 20:01 ` [RFC 30/32] fuse: " Arnd Bergmann
2014-05-30 20:01 ` [RFC 31/32] scsi: fnic: use current_kernel_time() for timestamp Arnd Bergmann
2014-05-30 20:01 ` [RFC 32/32] fs: use new inode_time definition unconditionally Arnd Bergmann
2014-05-31 14:30 ` [RFC 00/32] making inode time stamps y2038 ready Vyacheslav Dubeyko
2014-06-03 12:21   ` Arnd Bergmann
2014-05-31 14:51 ` Richard Cochran
2014-05-31 15:23   ` Arnd Bergmann
2014-05-31 18:22     ` Richard Cochran
2014-05-31 19:34       ` H. Peter Anvin
2014-06-01  4:46         ` Richard Cochran
2014-06-01  4:44     ` Richard Cochran
2014-06-02 13:52 ` Joseph S. Myers
2014-06-02 19:19   ` Arnd Bergmann
2014-06-02 19:26     ` H. Peter Anvin
2014-06-02 19:55       ` Arnd Bergmann
2014-06-02 21:57         ` H. Peter Anvin
2014-06-03 14:22           ` Arnd Bergmann
2014-06-03 14:33             ` Joseph S. Myers
2014-06-03 14:37               ` Arnd Bergmann
2014-06-03 21:38             ` Dave Chinner
2014-06-04 15:03               ` Arnd Bergmann
2014-06-04 17:30                 ` Nicolas Pitre [this message]
2014-06-04 19:24                   ` Arnd Bergmann
2014-06-05  0:10                     ` H. Peter Anvin
2014-06-10  9:54                       ` Arnd Bergmann
2014-06-02 21:02     ` Joseph S. Myers
2014-06-04 15:05       ` Arnd Bergmann

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