Re: [PATCH v6 00/11] xfs: widen timestamps to deal with y2038

[Dave Chinner <david@fromorbit.com>]

On Tue, Sep 01, 2020 at 07:56:27PM -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.
> 
> On a current V5 filesystem, inodes timestamps are a signed 32-bit
> seconds counter, with 0 being the Unix epoch.  Quota timers are an
> unsigned 32-bit seconds counter, with 0 also being the Unix epoch.
> 
> This means that inode timestamps can range from:
> -(2^31-1) (13 Dec 1901) through (2^31-1) (19 Jan 2038).
> 
> And quota timers can range from:
> 0 (1 Jan 1970) through (2^32-1) (7 Feb 2106).
> 
> With the bigtime encoding turned on, inode timestamps are an unsigned
> 64-bit nanoseconds counter, with 0 being the 1901 epoch.  Quota timers
> are a 34-bit unsigned second counter right shifted two bits, with 0
> being the Unix epoch, and capped at the maximum inode timestamp value.
> 
> This means that inode timestamps can range from:
> 0 (13 Dec 1901) through (2^64-1 / 1e9) (2 Jul 2486)
> 
> Quota timers could theoretically range from:
> 0 (1 Jan 1970) through (((2^34-1) + (2^31-1)) & ~3) (16 Jun 2582).
> 
> But with the capping in place, the quota timers maximum is:
> max((2^64-1 / 1e9) - (2^31-1), (((2^34-1) + (2^31-1)) & ~3) (2 Jul 2486).
> 
> v2: rebase to 5.9, having landed the quota refactoring
> v3: various suggestions by Amir and Dave
> v4: drop the timestamp unions, add "is bigtime?" predicates everywhere
> v5: reintroduce timestamp unions as *legacy* timestamp unions
> v6: minor stylistic changes
> 
> If you're going to start using this mess, you probably ought to just
> pull from my git trees, which are linked below.
> 
> This is an extraordinary way to destroy everything.  Enjoy!
> Comments and questions are, as always, welcome.

The whole series looks good to me now.

Reviewed-by: Dave Chinner <dchinner@redhat.com>

-- 
Dave Chinner
david@fromorbit.com