Since v6.3, checkpatch.pl now complains about the use of "Closes:" tags
followed by a link [1].  It also complains if a "Reported-by:" tag is
followed by a "Closes:" one [2].

As detailed in the first patch, this "Closes:" tag is used for a bit of
time, mainly by DRM and MPTCP subsystems.  It is used by some bug trackers
to automate the closure of issues when a patch is accepted.  It is even
planned to use this tag with bugzilla.kernel.org [3].

The first patch updates the documentation to explain what is this
"Closes:" tag and how/when to use it.  The second patch modifies
checkpatch.pl to stop complaining about it.

The DRM maintainers and their mailing list have been added in Cc as they
are probably interested by these two patches as well.

[1] https://lore.kernel.org/all/3b036087d80b8c0e07a46a1dbaaf4ad0d018f8d5.1674217480.git.linux@leemhuis.info/
[2] https://lore.kernel.org/all/bb5dfd55ea2026303ab2296f4a6df3da7dd64006.1674217480.git.linux@leemhuis.info/
[3] https://lore.kernel.org/linux-doc/20230315181205.f3av7h6owqzzw64p@meerkat.local/


This patch (of 5):

Making sure a bug tracker is up to date is not an easy task.  For example,
a first version of a patch fixing a tracked issue can be sent a long time
after having created the issue.  But also, it can take some time to have
this patch accepted upstream in its final form.  When it is done, someone
-- probably not the person who accepted the patch -- has to remember about
closing the corresponding issue.

This task of closing and tracking the patch can be done automatically by
bug trackers like GitLab [1], GitHub [2] and hopefully soon [3]
bugzilla.kernel.org when the appropriated tag is used.  The two first ones
accept multiple tags but it is probably better to pick one.

According to commit 76f381bb ("checkpatch: warn when unknown tags are used for links"),
the "Closes" tag seems to have been used in the past by a few people and
it is supported by popular bug trackers. Here is how it has been used in
the past:

 $ git log --no-merges --format=email -P --grep='^Closes: http' | \
       grep '^Closes: http' | cut -d/ -f3-5 | sort | uniq -c | sort -rn
    391 gitlab.freedesktop.org/drm/intel
     79 github.com/multipath-tcp/mptcp_net-next
      8 gitlab.freedesktop.org/drm/msm
      3 gitlab.freedesktop.org/drm/amd
      2 gitlab.freedesktop.org/mesa/mesa
      1 patchwork.freedesktop.org/series/73320
      1 gitlab.freedesktop.org/lima/linux
      1 gitlab.freedesktop.org/drm/nouveau
      1 github.com/ClangBuiltLinux/linux
      1 bugzilla.netfilter.org/show_bug.cgi?id=1579
      1 bugzilla.netfilter.org/show_bug.cgi?id=1543
      1 bugzilla.netfilter.org/show_bug.cgi?id=1436
      1 bugzilla.netfilter.org/show_bug.cgi?id=1427
      1 bugs.debian.org/625804

Likely here, the "Closes" tag was only properly used with GitLab and
GitHub.  We can also see that it has been used quite a few times (and
still used recently) and this is then not a "random tag that makes no
sense" like it was the case with "BugLink" recently [4].  It has also been
misused but that was a long time ago, when it was common to use many
different random tags.

checkpatch.pl script should then stop complaining about this "Closes" tag.
As suggested by Thorsten [5], if this tag is accepted, it should first be
described in the documentation.  This is what is done here in this patch.

To avoid confusion, the "Closes" should be used with any public bug
report.  No need to check if the underlying bug tracker supports
automations.  Having this tag with any kind of public bug reports allows
bots like regzbot to clearly identify patches fixing a specific bug and
avoid false-positives, e.g.  patches mentioning it is related to an issue
but not fixing it.  As suggested by Thorsten [6] again, if we follow the
same logic, the "Closes" tag should then be used after a "Reported-by"
one.

Note that thanks to this "Closes" tag, the mentioned bug trackers can also
locate where a patch has been applied in different branches and
repositories.  If only the "Link" tag is used, the tracking can also be
done but the ticket will not be closed and a manual operation will be
needed.  Also, these bug trackers have some safeguards: the closure is
only done if a commit having the "Closes:" tag is applied in a specific
branch.  It will then not be closed if a random commit having the same tag
is published elsewhere.  Also in case of closure, a notification is sent
to the owners.

Link: https://lkml.kernel.org/r/20230314-doc-checkpatch-closes-tag-v4-0-d26d1fa66f9f@tessares.net
Link: https://docs.gitlab.com/ee/user/project/issues/managing_issues.html#default-closing-pattern [1]
Link: https://docs.github.com/en/get-started/writing-on-github/working-with-advanced-formatting/using-keywords-in-issues-and-pull-requests [2]
Link: https://lore.kernel.org/linux-doc/20230315181205.f3av7h6owqzzw64p@meerkat.local/ [3]
Link: https://lore.kernel.org/all/CAHk-=wgs38ZrfPvy=nOwVkVzjpM3VFU1zobP37Fwd_h9iAD5JQ@mail.gmail.com/ [4]
Link: https://lore.kernel.org/all/688cd6cb-90ab-6834-a6f5-97080e39ca8e@leemhuis.info/ [5]
Link: https://lore.kernel.org/linux-doc/2194d19d-f195-1a1e-41fc-7827ae569351@leemhuis.info/ [6]
Link: https://github.com/multipath-tcp/mptcp_net-next/issues/373
Link: https://lkml.kernel.org/r/20230314-doc-checkpatch-closes-tag-v4-1-d26d1fa66f9f@tessares.netSigned-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Suggested-by: Thorsten Leemhuis <linux@leemhuis.info>
Acked-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>
Acked-by: Joe Perches <joe@perches.com>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: Bagas Sanjaya <bagasdotme@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@gmail.com>
Cc: Dwaipayan Ray <dwaipayanray1@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kai Wasserbäch <kai@dev.carbon-project.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>