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

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Date:   Thu, 10 Sep 2020 12:05:51 -0700
From:   Brian Norris <briannorris@...omium.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Randy Dunlap <rdunlap@...radead.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Bhaskar Chowdhury <unixbhaskar@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] scripts/setlocalversion: make git describe output more reliable

On Thu, Sep 10, 2020 at 7:35 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
> On Thu, Sep 10, 2020 at 8:57 PM Rasmus Villemoes
> <linux@...musvillemoes.dk> 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@...omium.org>

> 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