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From: Dave Chinner <david@fromorbit.com>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: linux-xfs@vger.kernel.org, amir73il@gmail.com, sandeen@sandeen.net
Subject: Re: [PATCH v2 00/11] xfs: widen timestamps to deal with y2038
Date: Wed, 19 Aug 2020 09:41:52 +1000	[thread overview]
Message-ID: <20200818234152.GE21744@dread.disaster.area> (raw)
In-Reply-To: <20200818231033.GO6096@magnolia>

On Tue, Aug 18, 2020 at 04:10:33PM -0700, Darrick J. Wong wrote:
> On Wed, Aug 19, 2020 at 09:01:21AM +1000, Dave Chinner wrote:
> > On Mon, Aug 17, 2020 at 03:56:48PM -0700, Darrick J. Wong wrote:
> > > Hi all,
> > > 
> > > This series performs some refactoring of our timestamp and inode
> > > encoding functions, then retrofits the timestamp union to handle
> > > timestamps as a 64-bit nanosecond counter.  Next, it adds bit shifting
> > > to the non-root dquot timer fields to boost their effective size to 34
> > > bits.  These two changes enable correct time handling on XFS through the
> > > year 2486.
> > 
> > A bit more detail would be nice :)
> 
> Heh, ok.
> 
> > Like, the inode timestamp has a range of slightly greater than 2^34
> > because 10^9 < 2^30. i.e.
> > 
> > Inode timestamp range in days:
> > 
> > $ echo $(((2**62 / (1000*1000*1000) / 86400) * 2**2))
> > 213500
> > $
> > 
> > While the quota timer range in days is:
> > $ echo $(((2**34 / 86400)))
> > 198841
> > $
> > 
> > There's ~15,000 days difference in range here, which in years is
> > about 40 years. Hence the inodes have a timestamp range out to
> > ~2485 from the 1901 epoch start, while quota timers have a range
> > out to only 2445 from the epoch start.
> 
> Quota timers have always treated the d_{b,i,rtb}timer value as an
> unsigned 32-bit integer, which means that it has /never/ been possible
> to set a timer expiration before 1/1/1970.  The quota timer range is
> therefore 198,841 days *after* 1970, not after 1901.
> 
> Therefore, the quota timer range in days is:
> 
> $ echo $(( ((2**34) + (2**31)) / 86400) ))
> 223696
> 
> So, technically speaking, the quota timers could go beyond 2486, but the
> current patchset clamps the quota counters to the same max as the
> inodes.  I guess I just proved the need for more details upfront.

Yeah, little things like quota timers and inode timestamps having a
different epoch value are kinda important to understand. :)

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

      reply	other threads:[~2020-08-18 23:42 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-17 22:56 [PATCH v2 00/11] xfs: widen timestamps to deal with y2038 Darrick J. Wong
2020-08-17 22:56 ` [PATCH 01/11] xfs: explicitly define inode timestamp range Darrick J. Wong
2020-08-18  6:25   ` Amir Goldstein
2020-08-17 22:57 ` [PATCH 02/11] xfs: refactor quota expiration timer modification Darrick J. Wong
2020-08-18  6:48   ` Amir Goldstein
2020-08-18 15:40     ` Darrick J. Wong
2020-08-17 22:57 ` [PATCH 03/11] xfs: refactor default quota grace period setting code Darrick J. Wong
2020-08-18 10:46   ` Amir Goldstein
2020-08-17 22:57 ` [PATCH 04/11] xfs: remove xfs_timestamp_t Darrick J. Wong
2020-08-18 10:50   ` Amir Goldstein
2020-08-17 22:57 ` [PATCH 05/11] xfs: move xfs_log_dinode_to_disk to the log code Darrick J. Wong
2020-08-18 10:51   ` Amir Goldstein
2020-08-17 22:57 ` [PATCH 06/11] xfs: refactor inode timestamp coding Darrick J. Wong
2020-08-18 11:20   ` Amir Goldstein
2020-08-18 15:42     ` Darrick J. Wong
2020-08-17 22:57 ` [PATCH 07/11] xfs: convert struct xfs_timestamp to union Darrick J. Wong
2020-08-18 11:24   ` Amir Goldstein
2020-08-17 22:57 ` [PATCH 08/11] xfs: widen ondisk timestamps to deal with y2038 problem Darrick J. Wong
2020-08-18 12:00   ` Amir Goldstein
2020-08-18 12:53     ` Amir Goldstein
2020-08-18 15:53       ` Darrick J. Wong
2020-08-18 20:52         ` Darrick J. Wong
2020-08-18 15:44     ` Darrick J. Wong
2020-08-18 23:35   ` Dave Chinner
2020-08-19 21:43     ` Darrick J. Wong
2020-08-19 23:58       ` Dave Chinner
2020-08-20  0:01       ` Darrick J. Wong
2020-08-20  4:42         ` griffin tucker
2020-08-20 16:23           ` Darrick J. Wong
2020-08-21  5:02             ` griffin tucker
2020-08-21 15:31               ` Mike Fleetwood
2020-08-20  5:11         ` Amir Goldstein
2020-08-20 22:47           ` Dave Chinner
2020-08-17 22:57 ` [PATCH 09/11] xfs: refactor quota timestamp coding Darrick J. Wong
2020-08-18 12:25   ` Amir Goldstein
2020-08-17 22:57 ` [PATCH 10/11] xfs: enable bigtime for quota timers Darrick J. Wong
2020-08-18 13:58   ` Amir Goldstein
2020-08-18 15:59     ` Darrick J. Wong
2020-08-17 22:57 ` [PATCH 11/11] xfs: enable big timestamps Darrick J. Wong
2020-08-18 14:04   ` Amir Goldstein
2020-08-18 23:01 ` [PATCH v2 00/11] xfs: widen timestamps to deal with y2038 Dave Chinner
2020-08-18 23:10   ` Darrick J. Wong
2020-08-18 23:41     ` Dave Chinner [this message]

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