xfs: widen timestamps to deal with y2038

XFS is a high performance filesystem often found in Enterprise Linux installations.

On 20 Aug 2020, Darrick J. Wong released a set of patches that extend the XFS on-disk file format so that the filesystem correctly handles dates beyond 2038. The new configuration will "enable correct time handling on XFS through the year 2486." These changes were incorporated into the Linux 5.10 kernel.

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.

https://lwn.net/Articles/829314/

https://www.phoronix.com/news/XFS-Linux-5.10

Note that some Enterprise Linux distributions had to backport support for these newly created "bigtime" filesystems, resulting in bugs like this in SUSE Linux Enterprise Server SLES12 SP5, addressed in "Enhancements to support filesystems created with bigtime and inobtcount", SUSE KB 000020881

https://www.suse.com/support/kb/doc/?id=000020881

Later versions of xfs (5.13.x) provide for the creation of filesystems with additional functionality and attributes. The filesystems that could not be mounted, had been created with attribute support that is not present in the xfs versions used in SLES12 SP5 (xfs 4.15.x) and no kernel or grub2 support for these enhancements existed in SLES12 SP5.