1.. _modifyingpatches: 2 3Modifying Patches 4================= 5 6If you are a subsystem or branch maintainer, sometimes you need to slightly 7modify patches you receive in order to merge them, because the code is not 8exactly the same in your tree and the submitters'. If you stick strictly to 9rule (c) of the developers certificate of origin, you should ask the submitter 10to rediff, but this is a totally counter-productive waste of time and energy. 11Rule (b) allows you to adjust the code, but then it is very impolite to change 12one submitters code and make him endorse your bugs. To solve this problem, it 13is recommended that you add a line between the last Signed-off-by header and 14yours, indicating the nature of your changes. While there is nothing mandatory 15about this, it seems like prepending the description with your mail and/or 16name, all enclosed in square brackets, is noticeable enough to make it obvious 17that you are responsible for last-minute changes. Example:: 18 19 Signed-off-by: Random J Developer <random@developer.example.org> 20 [lucky@maintainer.example.org: struct foo moved from foo.c to foo.h] 21 Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org> 22 23This practice is particularly helpful if you maintain a stable branch and 24want at the same time to credit the author, track changes, merge the fix, 25and protect the submitter from complaints. Note that under no circumstances 26can you change the author's identity (the From header), as it is the one 27which appears in the changelog. 28 29Special note to back-porters: It seems to be a common and useful practice 30to insert an indication of the origin of a patch at the top of the commit 31message (just after the subject line) to facilitate tracking. For instance, 32here's what we see in a 3.x-stable release:: 33 34 Date: Tue Oct 7 07:26:38 2014 -0400 35 36 libata: Un-break ATA blacklist 37 38 commit 1c40279960bcd7d52dbdf1d466b20d24b99176c8 upstream. 39 40And here's what might appear in an older kernel once a patch is backported:: 41 42 Date: Tue May 13 22:12:27 2008 +0200 43 44 wireless, airo: waitbusy() won't delay 45 46 [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a] 47 48Whatever the format, this information provides a valuable help to people 49tracking your trees, and to people trying to troubleshoot bugs in your 50tree. 51