The Mesa 3D Graphics Library

# Submitting Patches

- Basic guidelines
- Patch formatting
- Testing Patches
- Submitting Patches
- Reviewing Patches
- Nominating a commit for a stable branch
- Criteria for accepting patches to the stable branch
- Sending backports for the stable branch
- Git tips

## Basic guidelines

- Patches should not mix code changes with code formatting changes (except, perhaps, in very trivial cases.)
- Code patches should follow Mesa coding conventions.
- Whenever possible, patches should only affect individual Mesa/Gallium components.
- Patches should never introduce build breaks and should be bisectable (see `git bisect`.)
- Patches should be properly formatted.
- Patches should be sufficiently tested before submitting.
- Patches should be submitted via a merge request for review.

## Patch formatting

- Lines should be limited to 75 characters or less so that git logs displayed in 80-column terminals avoid line wrapping. Note that git log uses 4 spaces of indentation (4 + 75 < 80).
- The first line should be a short, concise summary of the change prefixed with a module name. Examples:

      mesa: Add support for querying GL_VERTEX_ATTRIB_ARRAY_LONG

      gallium: add PIPE_CAP_DEVICE_RESET_STATUS_QUERY

      i965: Fix missing type in local variable declaration.

- Subsequent patch comments should describe the change in more detail, if needed. For example:

      i965: Remove end-of-thread SEND alignment code.

      This was present in Eric's initial implementation of the compaction code
      for Sandybridge (commit 077d01b6). There is no documentation saying this
      is necessary, and removing it causes no regressions in piglit on any
      platform.

- A "Signed-off-by:" line is not required, but not discouraged either.
- If a patch addresses an issue in gitlab, use the Closes: tag For example:

      Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/1

  Prefer the full url to just `Closes: #1`, since the url makes it easier to get to the bug page from `git log`

  Do not use the Fixes: tag for this! Mesa already uses Fixes for something else.
- If a patch addresses a issue introduced with earlier commit, that should be noted in the patch comment. For example:

      Fixes: d7b3707c612 "util/disk_cache: use stat() to check if entry is a directory"

- You can produce those fixes lines by running

      git config --global alias.fixes "show -s --pretty='format:Fixes: %h (\"%s\")'"

  once and then using

      git fixes <sha1>

- If there have been several revisions to a patch during the review process, they should be noted such as in this example:

      st/mesa: add ARB_texture_stencil8 support (v4)

      if we support stencil texturing, enable texture_stencil8
      there is no requirement to support native S8 for this,
      the texture can be converted to x24s8 fine.

      v2: fold fixes from Marek in:
         a) put S8 last in the list
         b) fix renderable to always test for d/s renderable
           fixup the texture case to use a stencil only format
           for picking the format for the texture view.
      v3: hit fallback for getteximage
      v4: put s8 back in front, it shouldn't get picked now (Ilia)

- If someone tested your patch, document it with a line like this:

      Tested-by: Joe Hacker <jhacker@foo.com>

- If the patch was reviewed (usually the case) or acked by someone, that should be documented with:

      Reviewed-by: Joe Hacker <jhacker@foo.com>
      Acked-by: Joe Hacker <jhacker@foo.com>

- If sending later revision of a patch, add all the tags - ack, r-b, Cc: mesa-stable and/or other. This provides reviewers with quick feedback if the patch has already been reviewed.

## Testing Patches

It should go without saying that patches must be tested. In general, do whatever testing is prudent.

You should always run the Mesa test suite before submitting patches. The test suite can be run using the 'meson test' command. All tests must pass before patches will be accepted, this may mean you have to update the tests themselves.

Whenever possible and applicable, test the patch with Piglit and/or dEQP to check for regressions.

As mentioned at the beginning, patches should be bisectable. A good way to test this is to make use of the `git rebase` command, to run your tests on each commit. Assuming your branch is based off `origin/master`, you can run:

    $ git rebase --interactive --exec "meson test -C build/" origin/master

replacing `"meson test"` with whatever other test you want to run.

## Submitting Patches

Patches are submitted to the Mesa project via a GitLab Merge Request.

Add labels to your MR to help reviewers find it. For example:

- Mesa changes affecting all drivers: mesa
- Hardware vendor specific code: amd, intel, nvidia, ...
- Driver specific code: anvil, freedreno, i965, iris, radeonsi, radv, vc4, ...
- Other tag examples: gallium, util

Tick the following when creating the MR. It allows developers to rebase your work on top of master.

    Allow commits from members who can merge to the target branch

If you revise your patches based on code review and push an update to your branch, you should maintain a clean history in your patches. There should not be "fixup" patches in the history. The series should be buildable and functional after every commit whenever you push the branch.

It is your responsibility to keep the MR alive and making progress, as there are no guarantees that a Mesa dev will independently take interest in it.

Some other notes:

- Make changes and update your branch based on feedback
- After an update, for the feedback you handled, close the feedback discussion with the "Resolve Discussion" button. This way the reviewers know which feedback got handled and which didn't.
- Old, stale MR may be closed, but you can reopen it if you still want to pursue the changes
- You should periodically check to see if your MR needs to be rebased
- Make sure your MR is closed if your patches get pushed outside of GitLab
- Please send MRs from a personal fork rather than from the main Mesa repository, as it clutters it unnecessarily.

## Reviewing Patches

To participate in code review, you can monitor the GitLab Mesa Merge Requests page, and/or register for notifications in your gitlab settings.

When you've reviewed a patch, please be unambiguous about your review. That is, state either

    Reviewed-by: Joe Hacker <jhacker@foo.com>

or

    Acked-by: Joe Hacker <jhacker@foo.com>

Rather than saying just "LGTM" or "Seems OK".

If small changes are suggested, it's OK to say something like:

    With the above fixes, Reviewed-by: Joe Hacker <jhacker@foo.com>

which tells the patch author that the patch can be committed, as long as the issues are resolved first.

These Reviewed-by, Acked-by, and Tested-by tags should also be amended into commits in a MR before it is merged.

When providing a Reviewed-by, Acked-by, or Tested-by tag in a gitlab MR, enclose the tag in backticks:

    `Reviewed-by: Joe Hacker <jhacker@example.com>`

This is the markdown format for literal, and will prevent gitlab from hiding the < and > symbols.

Review by non-experts is encouraged. Understanding how someone else goes about solving a problem is a great way to learn your way around the project. The submitter is expected to evaluate whether they have an appropriate amount of review feedback from people who also understand the code before merging their patches.

## Nominating a commit for a stable branch

There are three ways to nominate a patch for inclusion in the stable branch and release.

- By adding the Cc: mesa-stable@ tag as described below.
- By adding the fixes: tag as described below.
- By submitting a merge request against the "staging/year.quarter" branch on gitlab.

Please DO NOT send patches to mesa-stable@lists.freedesktop.org, it is not monitored actively and is a historical artifact.

If you are not the author of the original patch, please Cc: them in your nomination request.

The current patch status can be observed in the staging branch.

### The stable tag

If you want a commit to be applied to a stable branch, you should add an appropriate note to the commit message.

Using a "fixes tag" as described in Patch formatting is the preferred way to nominate a commit that you know ahead of time should be backported. There are scripts that will figure out which releases to apply the patch to automatically, so you don't need to figure it out.

Alternatively, you may use a "CC:" tag. Here are some examples of such a note:

    CC: 20.0 19.3 <mesa-stable@lists.freedesktop.org>

Using the CC tag should include the stable branches you want to nominate the patch to. If you do not provide any version it is nominated to all active stable branches.

## Criteria for accepting patches to the stable branch

Mesa has a designated release manager for each stable branch, and the release manager is the only developer that should be pushing changes to these branches. Everyone else should nominate patches using the mechanism described above. The following rules define which patches are accepted and which are not. The stable-release manager is also given broad discretion in rejecting patches that have been nominated.

- Patch must conform with the Basic guidelines
- Patch must have landed in master first. In case where the original patch is too large and/or otherwise contradicts with the rules set within, a backport is appropriate.
- It must not introduce a regression - be that build or runtime wise. Note: If the regression is due to faulty piglit/dEQP/CTS/other test the latter must be fixed first. A reference to the offending test(s) and respective fix(es) should be provided in the nominated patch.
- Patch cannot be larger than 100 lines.
- Patches that move code around with no functional change should be rejected.
- Patch must be a bug fix and not a new feature. Note: An exception to this rule, are hardware-enabling "features". For example, backports of new code to support a newly-developed hardware product can be accepted if they can be reasonably determined not to have effects on other hardware.
- Patch must be reviewed, For example, the commit message has Reviewed-by, Signed-off-by, or Tested-by tags from someone but the author.
- Performance patches are considered only if they provide information about the hardware, program in question and observed improvement. Use numbers to represent your measurements.

If the patch complies with the rules it will be cherry-picked. Alternatively the release manager will reply to the patch in question stating why the patch has been rejected or would request a backport. The stable-release manager may at times need to force-push changes to the stable branches, for example, to drop a previously-picked patch that was later identified as causing a regression). These force-pushes may cause changes to be lost from the stable branch if developers push things directly. Consider yourself warned.

## Sending backports for the stable branch

By default merge conflicts are resolved by the stable-release manager. The release maintainer should resolve trivial conflicts, but for complex conflicts they should ask the original author to provide a backport or de-nominate the patch.

For patches that either need to be nominated after they've landed in master, or that are known ahead of time to not not apply cleanly to a stable branch (such as due to a rename), using a gitlab MR is most appropriate. The MR should be based on and target the staging/year.quarter branch, not on the year.quarter branch, per the stable branch policy. Assigning the MR to release maintainer for said branch or mentioning them is helpful, but not required.

## Git tips

- `git rebase -i ...` is your friend. Don't be afraid to use it.
- Apply a fixup to commit FOO.

      git add ...
      git commit --fixup=FOO
      git rebase -i --autosquash ...

- Test for build breakage between patches e.g last 8 commits.

      git rebase -i --exec="ninja -C build/" HEAD~8

- Sets the default mailing address for your repo.

      git config --local sendemail.to mesa-dev@lists.freedesktop.org

- Add version to subject line of patch series in this case for the last 8 commits before sending.

      git send-email --subject-prefix="PATCH v4" HEAD~8
      git send-email -v4 @~8 # shorter version, inherited from git format-patch