docs: process: allow Closes tags with links

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 76f381bb77 ("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.net
Signed-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>

Documentation/process/5.Posting.rst

@@ -207,8 +207,8 @@ the patch::
 	Fixes: 1f2e3d4c5b6a ("The first line of the commit specified by the first 12 characters of its SHA-1 ID")
 
 Another tag is used for linking web pages with additional backgrounds or
-details, for example a report about a bug fixed by the patch or a document
-with a specification implemented by the patch::
+details, for example an earlier discussion which leads to the patch or a
+document with a specification implemented by the patch::
 
 	Link: https://example.com/somewhere.html  optional-other-stuff
 
@@ -217,7 +217,17 @@ latest public review posting of the patch; often this is automatically done
 by tools like b4 or a git hook like the one described in
 'Documentation/maintainer/configure-git.rst'.
 
-A third kind of tag is used to document who was involved in the development of
+If the URL points to a public bug report being fixed by the patch, use the
+"Closes:" tag instead::
+
+	Closes: https://example.com/issues/1234  optional-other-stuff
+
+Some bug trackers have the ability to close issues automatically when a
+commit with such a tag is applied. Some bots monitoring mailing lists can
+also track such tags and take certain actions. Private bug trackers and
+invalid URLs are forbidden.
+
+Another kind of tag is used to document who was involved in the development of
 the patch. Each of these uses this format::
 
 	tag: Full Name <email address>  optional-other-stuff
@@ -251,8 +261,10 @@ The tags in common use are:
  - Reported-by: names a user who reported a problem which is fixed by this
    patch; this tag is used to give credit to the (often underappreciated)
    people who test our code and let us know when things do not work
-   correctly. Note, this tag should be followed by a Link: tag pointing to the
-   report, unless the report is not available on the web.
+   correctly. Note, this tag should be followed by a Closes: tag pointing to
+   the report, unless the report is not available on the web. The Link: tag
+   can be used instead of Closes: if the patch fixes a part of the issue(s)
+   being reported.
 
  - Cc: the named person received a copy of the patch and had the
    opportunity to comment on it.

Documentation/process/submitting-patches.rst

@@ -113,11 +113,9 @@ there is no collision with your six-character ID now, that condition may
 change five years from now.
 
 If related discussions or any other background information behind the change
-can be found on the web, add 'Link:' tags pointing to it. In case your patch
-fixes a bug, for example, add a tag with a URL referencing the report in the
-mailing list archives or a bug tracker; if the patch is a result of some
-earlier mailing list discussion or something documented on the web, point to
-it.
+can be found on the web, add 'Link:' tags pointing to it. If the patch is a
+result of some earlier mailing list discussions or something documented on the
+web, point to it.
 
 When linking to mailing list archives, preferably use the lore.kernel.org
 message archiver service. To create the link URL, use the contents of the
@@ -134,6 +132,16 @@ resources. In addition to giving a URL to a mailing list archive or bug,
 summarize the relevant points of the discussion that led to the
 patch as submitted.
 
+In case your patch fixes a bug, use the 'Closes:' tag with a URL referencing
+the report in the mailing list archives or a public bug tracker. For example::
+
+	Closes: https://example.com/issues/1234
+
+Some bug trackers have the ability to close issues automatically when a
+commit with such a tag is applied. Some bots monitoring mailing lists can
+also track such tags and take certain actions. Private bug trackers and
+invalid URLs are forbidden.
+
 If your patch fixes a bug in a specific commit, e.g. you found an issue using
 ``git bisect``, please use the 'Fixes:' tag with the first 12 characters of
 the SHA-1 ID, and the one line summary.  Do not split the tag across multiple
@@ -498,9 +506,11 @@ Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
 The Reported-by tag gives credit to people who find bugs and report them and it
 hopefully inspires them to help us again in the future. The tag is intended for
 bugs; please do not use it to credit feature requests. The tag should be
-followed by a Link: tag pointing to the report, unless the report is not
-available on the web. Please note that if the bug was reported in private, then
-ask for permission first before using the Reported-by tag.
+followed by a Closes: tag pointing to the report, unless the report is not
+available on the web. The Link: tag can be used instead of Closes: if the patch
+fixes a part of the issue(s) being reported. Please note that if the bug was
+reported in private, then ask for permission first before using the Reported-by
+tag.
 
 A Tested-by: tag indicates that the patch has been successfully tested (in
 some environment) by the person named.  This tag informs maintainers that