How to make a Samba .distversion file

[Steve French]

If trying to get Samba to build with a version tag that includes the
git hash (trailing string), it looks like it can already do this if
you have a ".distversion" file in the root directory of the build
(since with rpmbuild you won't be in the git tree at that point, as
you have created a tar.gz) - but how is a valid .distversion file
generated.  "make dist" didn't seem to do what I expected (built a lot
of documents, and an invalid .distversion).

What is the format of .distversion and is there a script which
trivially generates it?

-- 
Thanks,

Steve