bcachefs docs: SubmittingPatches.rst

Add an (initial?) patch submission checklist, focusing mainly on
testing.

Yes, all patches must be tested, and that starts (but does not end) with
the patch author.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Documentation/filesystems/bcachefs/SubmittingPatches.rst

@@ -0,0 +1,98 @@
+Submitting patches to bcachefs:
+===============================
+
+Patches must be tested before being submitted, either with the xfstests suite
+[0], or the full bcachefs test suite in ktest [1], depending on what's being
+touched. Note that ktest wraps xfstests and will be an easier method to running
+it for most users; it includes single-command wrappers for all the mainstream
+in-kernel local filesystems.
+
+Patches will undergo more testing after being merged (including
+lockdep/kasan/preempt/etc. variants), these are not generally required to be
+run by the submitter - but do put some thought into what you're changing and
+which tests might be relevant, e.g. are you dealing with tricky memory layout
+work? kasan, are you doing locking work? then lockdep; and ktest includes
+single-command variants for the debug build types you'll most likely need.
+
+The exception to this rule is incomplete WIP/RFC patches: if you're working on
+something nontrivial, it's encouraged to send out a WIP patch to let people
+know what you're doing and make sure you're on the right track. Just make sure
+it includes a brief note as to what's done and what's incomplete, to avoid
+confusion.
+
+Rigorous checkpatch.pl adherence is not required (many of its warnings are
+considered out of date), but try not to deviate too much without reason.
+
+Focus on writing code that reads well and is organized well; code should be
+aesthetically pleasing.
+
+CI:
+===
+
+Instead of running your tests locally, when running the full test suite it's
+prefereable to let a server farm do it in parallel, and then have the results
+in a nice test dashboard (which can tell you which failures are new, and
+presents results in a git log view, avoiding the need for most bisecting).
+
+That exists [2], and community members may request an account. If you work for
+a big tech company, you'll need to help out with server costs to get access -
+but the CI is not restricted to running bcachefs tests: it runs any ktest test
+(which generally makes it easy to wrap other tests that can run in qemu).
+
+Other things to think about:
+============================
+
+- How will we debug this code? Is there sufficient introspection to diagnose
+  when something starts acting wonky on a user machine?
+
+  We don't necessarily need every single field of every data structure visible
+  with introspection, but having the important fields of all the core data
+  types wired up makes debugging drastically easier - a bit of thoughtful
+  foresight greatly reduces the need to have people build custom kernels with
+  debug patches.
+
+  More broadly, think about all the debug tooling that might be needed.
+
+- Does it make the codebase more or less of a mess? Can we also try to do some
+  organizing, too?
+
+- Do new tests need to be written? New assertions? How do we know and verify
+  that the code is correct, and what happens if something goes wrong?
+
+  We don't yet have automated code coverage analysis or easy fault injection -
+  but for now, pretend we did and ask what they might tell us.
+
+  Assertions are hugely important, given that we don't yet have a systems
+  language that can do ergonomic embedded correctness proofs. Hitting an assert
+  in testing is much better than wandering off into undefined behaviour la-la
+  land - use them. Use them judiciously, and not as a replacement for proper
+  error handling, but use them.
+
+- Does it need to be performance tested? Should we add new peformance counters?
+
+  bcachefs has a set of persistent runtime counters which can be viewed with
+  the 'bcachefs fs top' command; this should give users a basic idea of what
+  their filesystem is currently doing. If you're doing a new feature or looking
+  at old code, think if anything should be added.
+
+- If it's a new on disk format feature - have upgrades and downgrades been
+  tested? (Automated tests exists but aren't in the CI, due to the hassle of
+  disk image management; coordinate to have them run.)
+
+Mailing list, IRC:
+==================
+
+Patches should hit the list [3], but much discussion and code review happens on
+IRC as well [4]; many people appreciate the more conversational approach and
+quicker feedback.
+
+Additionally, we have a lively user community doing excellent QA work, which
+exists primarily on IRC. Please make use of that resource; user feedback is
+important for any nontrivial feature, and documenting it in commit messages
+would be a good idea.
+
+[0]: git://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git
+[1]: https://evilpiepirate.org/git/ktest.git/
+[2]: https://evilpiepirate.org/~testdashboard/ci/
+[3]: linux-bcachefs@vger.kernel.org
+[4]: irc.oftc.net#bcache, #bcachefs-dev

Documentation/filesystems/bcachefs/index.rst

@@ -9,4 +9,5 @@ bcachefs Documentation
    :numbered:
 
    CodingStyle
+   SubmittingPatches
    errorcodes

MAINTAINERS

@@ -3955,6 +3955,7 @@ M:	Kent Overstreet <kent.overstreet@linux.dev>
 L:	linux-bcachefs@vger.kernel.org
 S:	Supported
 C:	irc://irc.oftc.net/bcache
+P:      Documentation/filesystems/bcachefs/SubmittingPatches.rst
 T:	git https://evilpiepirate.org/git/bcachefs.git
 F:	fs/bcachefs/
 F:	Documentation/filesystems/bcachefs/