Submitting patches

# The Mesa 3D Graphics Library

# Submitting patches

- Basic guidelines
- Patch formatting
- Testing Patches
- Mailing Patches
- Reviewing Patches
- Nominating a commit for a stable branch
- Criteria for accepting patches to 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 effect 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 to mesa-dev for review using `git send-email`.

## 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 address a bugzilla issue, that should be noted in the patch comment. For example:

         Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89689

- 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.
- In order for your patch to reach the prospective reviewer easier/faster, use the script scripts/get_reviewer.pl to get a list of individuals and include them in the CC list.
  Please use common sense and do not blindly add everyone.

          $ scripts/get_reviewer.pl --help # to get the the help screen
          $ scripts/get_reviewer.pl -f src/egl/drivers/dri2/platform_android.c
          Rob Herring  (reviewer:ANDROID EGL SUPPORT,added_lines:188/700=27%,removed_lines:58/283=20%)
          Tomasz Figa  (reviewer:ANDROID EGL SUPPORT,authored:12/41=29%,added_lines:308/700=44%,removed_lines:115/283=41%)
          Emil Velikov  (authored:13/41=32%,removed_lines:76/283=27%)

## 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 'make check' 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.

## Mailing Patches

Patches should be sent to the mesa-dev mailing list for review: mesa-dev@lists.freedesktop.org. When submitting a patch make sure to use git send-email rather than attaching patches to emails. Sending patches as attachments prevents people from being able to provide in-line review comments.

When submitting follow-up patches you can use --in-reply-to to make v2, v3, etc patches show up as replies to the originals. This usually works well when you're sending out updates to individual patches (as opposed to re-sending the whole series). Using --in-reply-to makes it harder for reviewers to accidentally review old patches.

When submitting follow-up patches you should also login to patchwork and change the state of your old patches to Superseded.

## Reviewing Patches

When you've reviewed a patch on the mailing list, 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.

## Nominating a commit for a stable branch

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

- By adding the Cc: mesa-stable@ tag as described below.
- Sending the commit ID (as seen in master branch) to the mesa-stable@ mailing list.
- Forwarding the patch from the mesa-dev@ mailing list.

Note: resending patch identical to one on mesa-dev@ or one that differs only by the extra mesa-stable@ tag is not recommended.

### 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.

Here are some examples of such a note:

- CC: <mesa-stable@lists.freedesktop.org>
- CC: "9.2 10.0" <mesa-stable@lists.freedesktop.org>
- CC: "10.0" <mesa-stable@lists.freedesktop.org>

Simply adding the CC to the mesa-stable list address is adequate to nominate the commit for the most-recently-created stable branch. It is only necessary to specify a specific branch name, (such as "9.2 10.0" or "10.0" in the examples above), if you want to nominate the commit for an older stable branch. And, as in these examples, you can nominate the commit for the older branch in addition to the more recent branch, or nominate the commit exclusively for the older branch. This "CC" syntax for patch nomination will cause patches to automatically be copied to the mesa-stable@ mailing list when you use "git send-email" to send patches to the mesa-dev@ mailing list. If you prefer using --suppress-cc that won't have any effect negative effect on the patch nomination.

Note: by removing the tag [as the commit is pushed] the patch is explicitly rejected from inclusion in the stable branch(es).
Thus, drop the line only if you want to cancel the nomination.

## 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 simply nominate patches using the mechanism described above. The stable-release manager will work with the list of nominated patches, and for each patch that meets the criteria below will cherry-pick the patch with: `git cherry-pick -x <commit>`. The `-x` option is important so that the picked patch references the commit ID of the original patch. 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. The stable-release manager is also given broad discretion in rejecting patches that have been nominated for the stable branch. The most basic rule is that the stable branch is for bug fixes only, (no new features, no regressions). Here is a non-exhaustive list of some reasons that a patch may be rejected:

- Patch introduces a regression. Any reported build breakage or other regression caused by a particular patch, (game no longer work, piglit test changes from PASS to FAIL), is justification for rejecting a patch.
- Patch is too large, (say, larger than 100 lines)
- Patch is not a fix. For example, a commit that moves code around with no functional change should be rejected.
- Patch fix is not clearly described. For example, a commit message of only a single line, no description of the bug, no mention of bugzilla, etc.
- Patch has not obviously been reviewed, For example, the commit message has no Reviewed-by, Signed-off-by, nor Tested-by tags from anyone but the author.
- Patch has not already been merged to the master branch. As a rule, bug fixes should never be applied first to a stable branch. Patches should land first on the master branch and then be cherry-picked to a stable branch. (This is to avoid future releases causing regressions if the patch is not also applied to master.) The only things that might look like exceptions would be backports of patches from master that happen to look significantly different.
- Patch depends on too many other patches. Ideally, all stable-branch patches should be self-contained. It sometimes occurs that a single, logical bug-fix occurs as two separate patches on master, (such as an original patch, then a subsequent fix-up to that patch). In such a case, these two patches should be squashed into a single, self-contained patch for the stable branch. (Of course, if the squashing makes the patch too large, then that could be a reason to reject the patch.)
- Patch includes new feature development, not bug fixes. New OpenGL features, extensions, etc. should be applied to Mesa master and included in the next major release. Stable releases are intended only for bug fixes. Note: As an exception to this rule, the stable-release manager may accept 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 to not have effects on other hardware.
- Patch is a performance optimization. As a rule, performance patches are not candidates for the stable branch. The only exception might be a case where an application's performance was recently severely impacted so as to become unusable. The fix for this performance regression could then be considered for a stable branch. The optimization must also be non-controversial and the patches still need to meet the other criteria of being simple and self-contained
- Patch introduces a new failure mode (such as an assert). While the new assert might technically be correct, for example to make Mesa more conformant, this is not the kind of "bug fix" we want in a stable release. The potential problem here is that an OpenGL program that was previously working, (even if technically non-compliant with the specification), could stop working after this patch. So that would be a regression that is unacceptable for the stable branch.

## 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="make -j4" 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

- Configure git to use the get_reviewer.pl script interactively. Thus you can avoid adding the world to the CC list.

          git config sendemail.cccmd "./scripts/get_reviewer.pl -i"