When a filesystem is shared with Samba, SMB clients may request to change the timestamps on files. This often happens when a user uses the "robocopy" windows utility to synchronize a directory on a windows computer to a FreeBSD samba server. Due to some quirks of how robocopy works, it first sends a request to set the modify time to a date in 1980 and then after that succeeds, the client sends a second request to set the btime, mtime, and atime to the correct values to preserve what is on the original file.
Unfortunately, the current mechanism for modifying birthtime does not allow us to go forward in time. Moreover, Windows clients often request to set a btime that is more recent than the mtime, and if we don't honor this unfortunate abuse of timestamps, many backup utilities will keep trying to re-sync timestamps with us.
Proposal is to add a new syscall that allows setting btime, mtime, and atime simultaneously.