Re: [PATCH] scripts/setlocalversion: make git describe output more reliable

[Brian Norris]

On Thu, Sep 10, 2020 at 7:35 AM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote:
> On Thu, Sep 10, 2020 at 8:57 PM Rasmus Villemoes
> <linux@xxxxxxxxxxxxxxxxxx> wrote:
> > So in order to avoid `uname -a` output relying on such random details
> > of the build environment which are rather hard to ensure are
> > consistent between developers and buildbots, use an explicit
> > --abbrev=15 option (and for consistency, also use rev-parse --short=15
> > for the unlikely case of no signed tags being usable).

For the patch:

Reviewed-by: Brian Norris <briannorris@xxxxxxxxxxxx>

> I agree that any randomness should be avoided.
>
> My question is, do we need 15-digits?
...
> So, I think the conflict happens
> only when we have two commits that start with the same 7-digits
> in the _same_ release. Is this correct?

For the rev-parse usage ("unlikely case where we have no signed tag"),
the total number of objects is definitely relevant, and the man-page
says:
"unique prefix with at least length characters"
i.e., it might be longer, if needed for uniqueness.

For git-describe (the case where we have a tag to base off):
"use <n> digits, or as many digits as needed to form a unique object name"
I'm not quite sure whether the uniqueness is including anything about
the tag-relative prefix, but if not, then we have the same problem.

At least, that's my reading of the situation.

Brian