docs: Encourage better changelogs in the development process document
Add a couple of paragraphs to the "patch formatting" section on how patches
should be described. This text is shamelessly cribbed from suggestions
posted by Rusty Russell.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/Documentation/development-process/5.Posting b/Documentation/development-process/5.Posting
index dd48132..f622c1e 100644
--- a/Documentation/development-process/5.Posting
+++ b/Documentation/development-process/5.Posting
@@ -119,7 +119,7 @@
done. When done properly, though, it is time well spent.
-5.4: PATCH FORMATTING
+5.4: PATCH FORMATTING AND CHANGELOGS
So now you have a perfect series of patches for posting, but the work is
not done quite yet. Each patch needs to be formatted into a message which
@@ -146,8 +146,33 @@
- One or more tag lines, with, at a minimum, one Signed-off-by: line from
the author of the patch. Tags will be described in more detail below.
-The above three items should, normally, be the text used when committing
-the change to a revision control system. They are followed by:
+The items above, together, form the changelog for the patch. Writing good
+changelogs is a crucial but often-neglected art; it's worth spending
+another moment discussing this issue. When writing a changelog, you should
+bear in mind that a number of different people will be reading your words.
+These include subsystem maintainers and reviewers who need to decide
+whether the patch should be included, distributors and other maintainers
+trying to decide whether a patch should be backported to other kernels, bug
+hunters wondering whether the patch is responsible for a problem they are
+chasing, users who want to know how the kernel has changed, and more. A
+good changelog conveys the needed information to all of these people in the
+most direct and concise way possible.
+
+To that end, the summary line should describe the effects of and motivation
+for the change as well as possible given the one-line constraint. The
+detailed description can then amplify on those topics and provide any
+needed additional information. If the patch fixes a bug, cite the commit
+which introduced the bug if possible. If a problem is associated with
+specific log or compiler output, include that output to help others
+searching for a solution to the same problem. If the change is meant to
+support other changes coming in later patch, say so. If internal APIs are
+changed, detail those changes and how other developers should respond. In
+general, the more you can put yourself into the shoes of everybody who will
+be reading your changelog, the better that changelog (and the kernel as a
+whole) will be.
+
+Needless to say, the changelog should be the text used when committing the
+change to a revision control system. It will be followed by:
- The patch itself, in the unified ("-u") patch format. Using the "-p"
option to diff will associate function names with changes, making the