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Subject: Re: tip: New "Link:" tag to replace "LKML-Reference:"
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        LKML <linux-kernel@vger.kernel.org>
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Date: Thu, 07 Apr 2011 16:54:10 +0200
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On Thu, 2011-04-07 at 07:43 -0700, H. Peter Anvin wrote:
> On 04/07/2011 07:08 AM, Peter Zijlstra wrote:
> > 
> > OK, so I fixed my scripts to match this and it all seems to work, except
> > for the:
> > 
> >  LKML-Reference: <new-submission>
> > 
> > case, where the tip-bot would mail it out for me. While I try not to use
> > it too much its convenient for quick fixes etc. Will the absence of a
> > Link tag suffice or is there more to it?
> > 
> 
> OK, I have asked for a long time that we do not use <new-submission>.
> 
> The recommended pattern has been:
> 
> LKML-Reference: <tip-*@git.kernel.org>
> 
> ... which at least indicates to the user how the message-ID is to be
> generated (* being a placeholder for the commit SHA1).

Oh, I never heard of that, it would've been easy to make my scripts do
that if that were the preferred form, a well.

> The only think I can think of for how to make Link: work would be to
> recognize a pattern that the tip-bot would use as its own Message-ID
> *instead* of the commit SHA1 pattern that it would normally use.  There
> are disadvantages to every approach, of course.
> 
> We have a couple of alternatives:
> 
> a) Continue to use "LKML-Reference: <tip-*@git.kernel.org>"
>    + At least gives a hint how to find the newly-formed LKML thread
>    - Not a clickable link
>    - Somewhat noisy
> b) Just Cc: everything to LKML regardless of tag
>    + Easy
>    - No way to *not* post everything to LKML
>    - No way to locate the thread without knowing the magic
> c) A recognizable pattern with a unique pattern *generated by the
>    committer*, something like:
>    Link: http://lkml.kernel.org/r/tip-`uuidgen -r`@git.kernel.org
>    + Clickable link
>    - Long (the above is 86 characters wide)
>    - Message-IDs of a nonstandard form
>    - Bad things will happen if someone re-uses an identifier
>    - String has to be generated by machine at commit time
> 
> [Using ranpwd instead of uuidgen allows for a more compact random string
> by using a wider character set.  For example:
> 
> Link: http://lkml.kernel.org/r/tip-`ranpwd -l 24`@git.kernel.org
> 
> ... has the same entropy but is 74 characters wide.]

Can't we use a prepare-commit-msg or commit-msg hook to re-write the
commit message to include a Link tag when one is missing, using
something like:

Link: http://lkml.kernel.org/r/tip-$SHA@git.kernel.org

And have the post-commit hook that sends the messages recognize this
form and send the message using the correct msgid.

That way the commit includes a correct and clickable link, doesn't
require magic knowledge and doesn't need the committer to do extra work.
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