tag name | bigtime_2020-09-14 (580b00df04b65de77b0d4f8abc10e8a4dde5e76c) |
tag date | 2020-09-14 19:11:46 -0700 |
tagged by | Darrick J. Wong <darrick.wong@oracle.com> |
tagged object | commit e11a82ba00... |
xfs: widen timestamps to deal with y2038
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