[PATCH 1/2] docs: introduce dedicated page about code provenance / sign-off

["Daniel P. Berrangé" <berrange@redhat.com>]

Currently we have a short paragraph saying that patches must include
a Signed-off-by line, and merely link to the kernel documentation.
The linked kernel docs have alot of content beyond the part about
sign-off an thus is misleading/distracting to QEMU contributors.

This introduces a dedicated 'code-provenance' page in QEMU talking
about why we require sign-off, explaining the other tags we commonly
use, and what to do in some edge cases.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 docs/devel/code-provenance.rst    | 197 ++++++++++++++++++++++++++++++
 docs/devel/index-process.rst      |   1 +
 docs/devel/submitting-a-patch.rst |  18 +--
 3 files changed, 201 insertions(+), 15 deletions(-)
 create mode 100644 docs/devel/code-provenance.rst

diff --git a/docs/devel/code-provenance.rst b/docs/devel/code-provenance.rst
new file mode 100644
index 0000000000..b4591a2dec
--- /dev/null
+++ b/docs/devel/code-provenance.rst
@@ -0,0 +1,197 @@
+.. _code-provenance:
+
+Code provenance
+===============
+
+Certifying patch submissions
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The QEMU community **mandates** all contributors to certify provenance
+of patch submissions they make to the project. To put it another way,
+contributors must indicate that they are legally permitted to contribute
+to the project.
+
+Certification is achieved with a low overhead by adding a single line
+to the bottom of every git commit::
+
+   Signed-off-by: YOUR NAME <YOUR@EMAIL>
+
+This existence of this line asserts that the author of the patch is
+contributing in accordance with the `Developer's Certificate of
+Origin <https://developercertifcate.org>`__:
+
+.. _dco:
+
+::
+  Developer's Certificate of Origin 1.1
+
+  By making a contribution to this project, I certify that:
+
+  (a) The contribution was created in whole or in part by me and I
+      have the right to submit it under the open source license
+      indicated in the file; or
+
+  (b) The contribution is based upon previous work that, to the best
+      of my knowledge, is covered under an appropriate open source
+      license and I have the right under that license to submit that
+      work with modifications, whether created in whole or in part
+      by me, under the same open source license (unless I am
+      permitted to submit under a different license), as indicated
+      in the file; or
+
+  (c) The contribution was provided directly to me by some other
+      person who certified (a), (b) or (c) and I have not modified
+      it.
+
+  (d) I understand and agree that this project and the contribution
+      are public and that a record of the contribution (including all
+      personal information I submit with it, including my sign-off) is
+      maintained indefinitely and may be redistributed consistent with
+      this project or the open source license(s) involved.
+
+It is generally expected that the name and email addresses used in one
+of the ``Signed-off-by`` lines, matches that of the git commit ``Author``
+field. If the person sending the mail is also one of the patch authors,
+it is further expected that the mail ``From:`` line name & address match
+one of the ``Signed-off-by`` lines. 
+
+Multiple authorship
+~~~~~~~~~~~~~~~~~~~
+
+It is not uncommon for a patch to have contributions from multiple
+authors. In such a scenario, a git commit will usually be expected
+to have a ``Signed-off-by`` line for each contributor involved in
+creatin of the patch. Some edge cases:
+
+  * The non-primary author's contributions were so trivial that
+    they can be considered not subject to copyright. In this case
+    the secondary authors need not include a ``Signed-off-by``.
+
+    This case most commonly applies where QEMU reviewers give short
+    snippets of code as suggested fixes to a patch. The reviewers
+    don't need to have their own ``Signed-off-by`` added unless
+    their code suggestion was unusually large.
+
+  * Both contributors work for the same employer and the employer
+    requires copyright assignment.
+
+    It can be said that in this case a ``Signed-off-by`` is indicating
+    that the person has permission to contributeo from their employer
+    who is the copyright holder. It is none the less still preferrable
+    to include a ``Signed-off-by`` for each contributor, as in some
+    countries employees are not able to assign copyright to their
+    employer, and it also covers any time invested outside working
+    hours.
+
+Other commit tags
+~~~~~~~~~~~~~~~~~
+
+While the ``Signed-off-by`` tag is mandatory, there are a number of
+other tags that are commonly used during QEMU development
+
+ * **``Reviewed-by``**: when a QEMU community member reviews a patch
+   on the mailing list, if they consider the patch acceptable, they
+   should send an email reply containing a ``Reviewed-by`` tag.
+
+   NB: a subsystem maintainer sending a pull request would replace
+   their own ``Reviewed-by`` with another ``Signed-off-by``
+
+ * **``Acked-by``**: when a QEMU subsystem maintainer approves a patch
+   that touches their subsystem, but intends to allow a different
+   maintainer to queue it and send a pull request, they would send
+   a mail containing a ``Acked-by`` tag.
+   
+ * **``Tested-by``**: when a QEMU community member has functionally
+   tested the behaviour of the patch in some manner, they should
+   send an email reply conmtaning a ``Tested-by`` tag.
+
+ * **``Reported-by``**: when a QEMU community member reports a problem
+   via the mailing list, or some other informal channel that is not
+   the issue tracker, it is good practice to credit them by including
+   a ``Reported-by`` tag on any patch fixing the issue. When the
+   problem is reported via the GitLab issue tracker, however, it is
+   sufficient to just include a link to the issue.
+
+Subsystem maintainer requirements
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When a subsystem maintainer accepts a patch from a contributor, in
+addition to the normal code review points, they are expected to validate
+the presence of suitable ``Signed-off-by`` tags.
+
+At the time they queue the patch in their subsystem tree, the maintainer
+**MUST** also then add their own ``Signed-off-by`` to indicate that they
+have done the aforementioned validation.
+
+The subsystem maintainer submitting a pull request is **NOT** expected to
+have a ``Reviewed-by`` tag on the patch, since this is implied by their
+own ``Signed-off-by``.
+  
+Tools for adding ``Signed-of-by``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There are a variety of ways tools can support adding ``Signed-off-by``
+tags for patches, avoiding the need for contributors to manually
+type in this repetitive text each time.
+
+git commands
+^^^^^^^^^^^^
+
+When creating, or amending, a commit the ``-s`` flag to ``git commit``
+will append a suitable line matching the configuring git author
+details.
+
+If preparing patches using the ``git format-patch`` tool, the ``-s``
+flag can be used to append a suitable line in the emails it creates,
+without modifying the local commits. Alternatively to modify the
+local commits on a branch en-mass::
+
+  git rebase master -x 'git commit --amend --no-edit -s'
+
+emacs
+^^^^^
+
+In the file ``$HOME/.emacs.d/abbrev_defs`` add::
+
+  (define-abbrev-table 'global-abbrev-table
+    '(
+      ("8rev" "Reviewed-by: YOUR NAME <your@email.addr>" nil 1)
+      ("8ack" "Acked-by: YOUR NAME <your@email.addr>" nil 1)
+      ("8test" "Tested-by: YOUR NAME <your@email.addr>" nil 1)
+      ("8sob" "Signed-off-by: YOUR NAME <your@email.addr>" nil 1)
+     ))
+
+with this change, if you type (for example) ``8rev`` followed
+by ``<space>`` or ``<enter>`` it will expand to the whole phrase. 
+
+vim
+^^^
+
+In the file ``$HOME/.vimrc`` add::
+
+  iabbrev 8rev Reviewed-by: YOUR NAME <your@email.addr>
+  iabbrev 8ack Acked-by: YOUR NAME <your@email.addr>
+  iabbrev 8test Tested-by: YOUR NAME <your@email.addr>
+  iabbrev 8sob Signed-off-by: YOUR NAME <your@email.addr>
+
+with this change, if you type (for example) ``8rev`` followed
+by ``<space>`` or ``<enter>`` it will expand to the whole phrase. 
+
+Re-starting abandoned work
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+For a variety of reasons there are some patches that get submitted to
+QEMU but never merged. An unrelated contributor may decide (months or
+years later) to continue working from the abandoned patch and re-submit
+it with extra changes.
+
+If the abandoned patch already had a ``Signed-off-by`` from the original
+author this **must** be preserved. The new contributor **must** then add
+their own ``Signed-off-by`` after the original one if they made any
+further changes to it. It is common to include a comment just prior to
+the new ``Signed-off-by`` indicating what extra changes were made. For
+example::
+
+  Signed-off-by: Some Person <some.person@example.com>
+  [Rebased and added support for 'foo']
+  Signed-off-by: New Person <new.person@example.com>
diff --git a/docs/devel/index-process.rst b/docs/devel/index-process.rst
index 362f97ee30..b54e58105e 100644
--- a/docs/devel/index-process.rst
+++ b/docs/devel/index-process.rst
@@ -13,6 +13,7 @@ Notes about how to interact with the community and how and where to submit patch
    maintainers
    style
    submitting-a-patch
+   code-provenance
    trivial-patches
    stable-process
    submitting-a-pull-request
diff --git a/docs/devel/submitting-a-patch.rst b/docs/devel/submitting-a-patch.rst
index c641d948f1..ec541b3d15 100644
--- a/docs/devel/submitting-a-patch.rst
+++ b/docs/devel/submitting-a-patch.rst
@@ -322,21 +322,9 @@ Patch emails must include a ``Signed-off-by:`` line
 
 Your patches **must** include a Signed-off-by: line. This is a hard
 requirement because it's how you say "I'm legally okay to contribute
-this and happy for it to go into QEMU". The process is modelled after
-the `Linux kernel
-<http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/SubmittingPatches?id=f6f94e2ab1b33f0082ac22d71f66385a60d8157f#n297>`__
-policy.
-
-If you wrote the patch, make sure your "From:" and "Signed-off-by:"
-lines use the same spelling. It's okay if you subscribe or contribute to
-the list via more than one address, but using multiple addresses in one
-commit just confuses things. If someone else wrote the patch, git will
-include a "From:" line in the body of the email (different from your
-envelope From:) that will give credit to the correct author; but again,
-that author's Signed-off-by: line is mandatory, with the same spelling.
-
-There are various tooling options for automatically adding these tags
-include using ``git commit -s`` or ``git format-patch -s``. For more
+this and happy for it to go into QEMU". For full guidance, read the
+:ref:`code-provenance` documentation.
+
 information see `SubmittingPatches 1.12
 <http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/SubmittingPatches?id=f6f94e2ab1b33f0082ac22d71f66385a60d8157f#n297>`__.
 
-- 
2.41.0