linux-kernel - Re: linux-next: unnecessary merge in the v4l-dvb tree

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Date:   Mon, 12 Feb 2018 19:36:17 -0200
From:   Mauro Carvalho Chehab <mchehab@....samsung.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Junio C Hamano <gitster@...ox.com>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Git Mailing List <git@...r.kernel.org>
Subject: Re: linux-next: unnecessary merge in the v4l-dvb tree

Em Mon, 12 Feb 2018 13:15:04 -0800
Linus Torvalds <torvalds@...ux-foundation.org> escreveu:

> On Mon, Feb 12, 2018 at 1:00 PM, Stephen Rothwell <sfr@...b.auug.org.au> wrote:
> >
> > Linus, this happens a bit after the merge window, so I am wondering
> > about the rational of not doing a fast forward merge when merging a
> > signed tag (I forget the reasoning).  
> 
> The reasoning is to avoid losing the signature from the tag (when
> merging a signed tag, the signature gets inserted into the merge
> commit itself - use "git log --show-signature" to see them).
> 
> So when I merge a signed tag, I do *not* want to fast-forward to the
> top commit, because then I'd lose the signature from the tag. Thus the
> "merging signed tags are non-fast-forward by default" reasoning.
> 
> But, yes, that reasoning is really only valid for proper merges of new
> features, not for back-merges.
> 
> The problem, of course, is that since git is distributed, git doesn't
> know who is "upstream" and who is "downstream", so there's no
> _technical_ difference between merging a development tree, and a
> development tree doing a back-merge of the upstream tree.
> 
> Maybe it was a mistake to make signed tag merges non-fast-forward,
> since they cause these kinds of issues with people who use "pull" to
> update their otherwise unmodified trees.
> 
> I can always teach myself to just use --no-ff, since I end up doing
> things like verifying at the signatures anyway.

Hmm... at least at git version 2.14.3, git documentation doesn't
mention that signed pull requests won't do fast forward. Instead,
it says that --ff is the default behavior:


       --ff
           When the merge resolves as a fast-forward, only update the branch pointer, without creating a merge commit. This is the
           default behavior.

Btw, even doing:

	$ git merge -ff v4.16-rc1

it will still produce a git commit for the merge.


-- 
Thanks,
Mauro