[tz] Version identification (was Re: Downstream use of 2021c)

[Paul Eggert]

On 10/7/21 15:54, Alan Mintz via tz wrote:

> there are "fifteen bytes containing zeros reserved for 
> future use" starting at the 6th byte of the tzfile(5) binary format. 
> Perhaps some of that could be used to carry the version of the source 
> data? If downstream mods add their own suffix,

That's been proposed before. Unfortunately, it's likely that version 
strings would exceed 15 bytes in length, given downstream needs. For 
example, the tzdata package on my workstation is named 
"tzdata-2021b-1.fc34.noarch" and I've seen longer.

Also, as a rule I've found that putting a version number into every file 
(or every line of every file) to be overkill. It's generally better to 
have at most one version number per thing versioned.