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+.. _modifyingpatches:
+
+Modifying Patches
+=================
+
+If you are a subsystem or branch maintainer, sometimes you need to slightly
+modify patches you receive in order to merge them, because the code is not
+exactly the same in your tree and the submitters'. If you stick strictly to
+rule (c) of the developers certificate of origin, you should ask the submitter
+to rediff, but this is a totally counter-productive waste of time and energy.
+Rule (b) allows you to adjust the code, but then it is very impolite to change
+one submitters code and make him endorse your bugs. To solve this problem, it
+is recommended that you add a line between the last Signed-off-by header and
+yours, indicating the nature of your changes. While there is nothing mandatory
+about this, it seems like prepending the description with your mail and/or
+name, all enclosed in square brackets, is noticeable enough to make it obvious
+that you are responsible for last-minute changes. Example::
+
+       Signed-off-by: Random J Developer <random@developer.example.org>
+       [lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
+       Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
+
+This practice is particularly helpful if you maintain a stable branch and
+want at the same time to credit the author, track changes, merge the fix,
+and protect the submitter from complaints. Note that under no circumstances
+can you change the author's identity (the From header), as it is the one
+which appears in the changelog.
+
+Special note to back-porters: It seems to be a common and useful practice
+to insert an indication of the origin of a patch at the top of the commit
+message (just after the subject line) to facilitate tracking. For instance,
+here's what we see in a 3.x-stable release::
+
+  Date:   Tue Oct 7 07:26:38 2014 -0400
+
+    libata: Un-break ATA blacklist
+
+    commit 1c40279960bcd7d52dbdf1d466b20d24b99176c8 upstream.
+
+And here's what might appear in an older kernel once a patch is backported::
+
+    Date:   Tue May 13 22:12:27 2008 +0200
+
+        wireless, airo: waitbusy() won't delay
+
+        [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
+
+Whatever the format, this information provides a valuable help to people
+tracking your trees, and to people trying to troubleshoot bugs in your
+tree.