Commit 2ae19aca authored by Theodore Ts'o's avatar Theodore Ts'o Committed by Jonathan Corbet
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Documentation: Add "how to write a good patch summary" to SubmittingPatches

Unfortunately many patch submissions are arriving with painfully poor
patch descriptions.   As a result of the discussion on LKML:

      http://lkml.org/lkml/2009/4/15/296



explain how to submit a better patch description, in the (perhaps
vain) hope that maintainers won't end up having to rewrite the git
commit logs as often as they do today.
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent 5801da1b
......@@ -91,6 +91,10 @@ Be as specific as possible. The WORST descriptions possible include
things like "update driver X", "bug fix for driver X", or "this patch
includes updates for subsystem X. Please apply."
The maintainer will thank you if you write your patch description in a
form which can be easily pulled into Linux's source code management
system, git, as a "commit log". See #15, below.
If your description starts to get long, that's a sign that you probably
need to split up your patch. See #3, next.
......@@ -492,12 +496,33 @@ phrase" should not be a filename. Do not use the same "summary
phrase" for every patch in a whole patch series (where a "patch
series" is an ordered sequence of multiple, related patches).
Bear in mind that the "summary phrase" of your email becomes
a globally-unique identifier for that patch. It propagates
all the way into the git changelog. The "summary phrase" may
later be used in developer discussions which refer to the patch.
People will want to google for the "summary phrase" to read
discussion regarding that patch.
Bear in mind that the "summary phrase" of your email becomes a
globally-unique identifier for that patch. It propagates all the way
into the git changelog. The "summary phrase" may later be used in
developer discussions which refer to the patch. People will want to
google for the "summary phrase" to read discussion regarding that
patch. It will also be the only thing that people may quickly see
when, two or three months later, they are going through perhaps
thousands of patches using tools such as "gitk" or "git log
--oneline".
For these reasons, the "summary" must be no more than 70-75
characters, and it must describe both what the patch changes, as well
as why the patch might be necessary. It is challenging to be both
succinct and descriptive, but that is what a well-written summary
should do.
The "summary phrase" may be prefixed by tags enclosed in square
brackets: "Subject: [PATCH tag] <summary phrase>". The tags are not
considered part of the summary phrase, but describe how the patch
should be treated. Common tags might include a version descriptor if
the multiple versions of the patch have been sent out in response to
comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
comments. If there are four patches in a patch series the individual
patches may be numbered like this: 1/4, 2/4, 3/4, 4/4. This assures
that developers understand the order in which the patches should be
applied and that they have reviewed or applied all of the patches in
the patch series.
A couple of example Subjects:
......@@ -517,19 +542,31 @@ the patch author in the changelog.
The explanation body will be committed to the permanent source
changelog, so should make sense to a competent reader who has long
since forgotten the immediate details of the discussion that might
have led to this patch.
have led to this patch. Including symptoms of the failure which the
patch addresses (kernel log messages, oops messages, etc.) is
especially useful for people who might be searching the commit logs
looking for the applicable patch. If a patch fixes a compile failure,
it may not be necessary to include _all_ of the compile failures; just
enough that it is likely that someone searching for the patch can find
it. As in the "summary phrase", it is important to be both succinct as
well as descriptive.
The "---" marker line serves the essential purpose of marking for patch
handling tools where the changelog message ends.
One good use for the additional comments after the "---" marker is for
a diffstat, to show what files have changed, and the number of inserted
and deleted lines per file. A diffstat is especially useful on bigger
patches. Other comments relevant only to the moment or the maintainer,
not suitable for the permanent changelog, should also go here.
Use diffstat options "-p 1 -w 70" so that filenames are listed from the
top of the kernel source tree and don't use too much horizontal space
(easily fit in 80 columns, maybe with some indentation).
a diffstat, to show what files have changed, and the number of
inserted and deleted lines per file. A diffstat is especially useful
on bigger patches. Other comments relevant only to the moment or the
maintainer, not suitable for the permanent changelog, should also go
here. A good example of such comments might be "patch changelogs"
which describe what has changed between the v1 and v2 version of the
patch.
If you are going to include a diffstat after the "---" marker, please
use diffstat options "-p 1 -w 70" so that filenames are listed from
the top of the kernel source tree and don't use too much horizontal
space (easily fit in 80 columns, maybe with some indentation).
See more details on the proper patch format in the following
references.
......
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