Just out of curiosity, does this enable 64-bit timestamps for everything by default? I see that ext4 later sets its own values in fill_super; what about things like XFS that really only have 32-bit seconds fields?
This is just initializing limits for each filesystem. Filesystems then override these limits with the actual limits they support. This is what ext4 patch in the series is doing. As the cover letter says, I will be submitting patches for all filesystems to update limits.
This is no different than what is happening right now. Right now, on 64 bit systems, VFS assumes timestamps to be 64 bits long for all filesystems.
On 32 bit systems, the series only effects handling of dates beyond the year 2038. This is until vfs is transitioned to support 64 bit times. At which point, the behavior on these will also be similar to 64 bit machines.
-Deepa