Laszlo's unkempt git guide for edk2 contributors and maintainers

Disclaimer

This is a quick and dirty, simplified and slightly modified description of my own edk2 workflow with git. It expressly defers to the EDK II Development Process article on the TianoCore wiki. It doesn't try to be generic, focuses only on GNU/Linux (that's what I use). It will not go into many details about git; if you are interested, you'll have to research those concepts on the web yourself.

Also, this is very specific to edk2. Other projects have different workflows.

Contributor workflow

§ Create an account on GitHub.
§ Enable SSH authentication for your account.

https://help.github.com/articles/generating-an-ssh-key/

When completing this step, you should end up with a new keypair under ~/.ssh/, for example:
```
id_rsa_for_github
id_rsa_for_github.pub
```
and the following stanza in your ~/.ssh/config:
```
Host github.com
  User          git
  IdentityFile  ~/.ssh/id_rsa_for_github
```
§ Fork the following repository on GitHub into your own GitHub account, using the GitHub web GUI:

https://github.com/tianocore/edk2/

(My personal fork is at https://github.com/lersek/edk2/)

§ Clone the official edk2 repository to your local computer:

cd some-appropriate-directory
git clone https://github.com/tianocore/edk2.git

§ Implement the following git settings for your local clone, i.e., while standing in your local edk2 directory (these steps don't need customization):

git config am.keepcr              true
git config am.signoff             true
git config cherry-pick.signoff    true
git config color.diff             true
git config color.grep             auto
git config commit.signoff         true
git config core.abbrev            12
git config core.pager             cat
git config core.whitespace        cr-at-eol
git config diff.algorithm         patience
git config diff.ini.xfuncname     '^\[[A-Za-z0-9_., ]+]'
git config diff.renames           copies
git config format.coverletter     true
git config format.numbered        true
git config format.signoff         false
git config notes.rewriteRef       refs/notes/commits
git config sendemail.chainreplyto false
git config sendemail.thread       true
git config sendemail.to           [email protected]

§ Also implement the following -- they need customization:

git config sendemail.smtpserver FQDN_OF_YOUR_LOCAL_SMTP_SERVER
git config user.email           "Your Email Address"
git config user.name            "Your Name"

§ Create a file called tianocore.template somewhere outside your edk2 clone, with the following contents. Note that the last line requires customization.
```
[empty line]
[empty line]
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Your Name <Your Email Address>
```

§ Standing in your edk2 clone, implement the following setting (requires customization):

git config commit.template                   \
  FULL_PATHNAME_OF_FILE_CREATED_IN_LAST_STEP

§ Open the file

.git/info/attributes

(create it if it doesn't exist), and add the following contents:

*.efi     -diff
*.EFI     -diff
*.bin     -diff
*.BIN     -diff
*.raw     -diff
*.RAW     -diff
*.bmp     -diff
*.BMP     -diff
*.dec     diff=ini
*.dsc     diff=ini
*.dsc.inc diff=ini
*.fdf     diff=ini
*.fdf.inc diff=ini
*.inf     diff=ini

§ Create a file called edk2.diff.order somewhere outside your local clone, with the following contents:
```
*.dec
*.dsc.inc
*.dsc
*.fdf
*.inf
*.h
*.vfr
*.c
```

§ Add your own fork of edk2 that lives on GitHub as a remote to your local clone:

git remote add -f --no-tags              \
  YOUR_GITHUB_ID                         \
  [email protected]:YOUR_GITHUB_ID/edk2.git

§ At this point you are ready to start developing. Refresh your local master branch from the upstream master branch:
```
git checkout master
git pull
```
The first command is extremely important. You should only run git pull while you are standing on your local master branch that tracks (and never diverges from) the upstream master branch.

These commands will fetch any new commits from upstream master, and fast-forward your local tracking branch to the new HEAD.
§ Create and check out a topic branch for the feature or bugfix that you would like to work on. The topic branch name requires customization of course.
```
git checkout -b implement_foo_for_bar_v1 master
```
§ Make sure you have the build environment set up:
```
source edksetup.sh
make -C "$EDK_TOOLS_PATH"
```
§ Implement the next atomic, logical step in your feature or bugfix. Test that it builds and works. You should not cross module (driver, library class, library instance) boundaries within a single patch, if possible.
§ Add your changes gradually to the staging area of git (it is called the "index"):
```
git add -p
```
This command will ask you interactively about staging each separate hunk, for files that git already tracks. In order to stage the addition of a new file, use
```
git add pathname
```
Finally, for staging the removal of a file that git has been tracking, issue
```
git rm pathname
```
§ When done, you can run
```
git status
```
This will list the files with staged and unstaged changes. You can show the diff that is staged for commit:
```
git diff --staged
```
and also the diff that is not staged yet:
```
git diff
```
§ If you are happy with the staged changes, run:
```
git commit
```
This will commit the staged changes to your local branch called implement_foo_for_bar_v1. You created this branch in step 13.

Before the commit occurs, git will fire up your preferred editor (from the EDITOR environment variable) for you to edit the commit message. The commit message will be primed from the template created in step 7 and configured in step 8.

Above the template, you should add:
- a subject line, no longer than 74-76 characters, consisting of
```
PackageName: ModuleName: summary of changes
```
- an empty line
- one or more paragraphs that describe the changes in the patch. No line should be longer than 74 characters.
- an empty line
- One or more tags directly above the Contributed-under line (which comes from the template) that CC the package maintainers that are relevant for this specific patch. Consult the Maintainers.txt file. For example, if you wrote a patch for OvmfPkg, add:
```
Cc: Jordan Justen <[email protected]>
Cc: Laszlo Ersek <[email protected]>
```
§ When you have committed the patch, it is best to confirm it adheres to the edk2 coding style. Run:
```
python BaseTools/Scripts/PatchCheck.py -1
```
§ If the command in step 19 reports problems, modify the source code accordingly, then go back to step 16 and continue from there. However, as a small but important change for step 18, run git commit with the --amend option:
```
git commit --amend
```
This will squash your fixups into the last commit, and it will also let you re-edit the commit message (the PatchCheck.py script can also find problems with the commit message format).

Re-run step 19 as well, to see if your patch is now solid.
§ Write your next patch. That is, repeat this procedure (goto step 15) until you are happy with the series -- each single one of your patches builds and runs (implementing the next atomic, logical step in the bugfix or feature), and at the last patch, the feature / bugfix is complete.
§ It is now time to publish your changes for review.

(At this point, at the latest, it is important to review your full series using a git GUI; for example gitk. Practically, any time you are in doubt, and especially before publishing patches, run git status and gitk (or another GUI tool) and go over your series.)

First, we'll push your local branch to your personal repository on GitHub, under the same branch name.
```
git push YOUR_GITHUB_ID master implement_foo_for_bar_v1
```
This command will connect to github using your remote configuration added in step 11, employing the SSH authentication configured in step 2.

It will update the master branch in your personal repo on GitHub to your local master branch (which in turn follows the official master branch, see step 12).

It will also push the topic branch you created under step 13.
§ Now we'll format the patches as email messages, and send them to the list. Standing in the root of your edk2 directory, run the following (note that the -O option needs customization: please update the pathname to the file created in step 10):
```
rm -f -- *.patch

git format-patch                               \
  --notes                                      \
  -O"/fully/qualified/path/to/edk2.diff.order" \
  --subject-prefix="PATCH v1"                  \
  --stat=1000                                  \
  --stat-graph-width=20                        \
  master..implement_foo_for_bar_v1
```
This command will generate an email file for each one of your commits. The patch files will be numbered. The file numbered 0000 is a cover letter, which you should edit in-place:
- in the Subject: line, summarize the goal of your series,
- in the message body, describe the changes on a broad level,
- reference, by complete URL, the implement_foo_for_bar_v1 branch in your personal GitHub repo -- the one that you pushed in step 22,
- finally, add all of the Cc: tags to the cover letter that you used across all of the patches. This will ensure that even if a maintainer is involved in reviewing one or two of your patches across the series, he or she will get a copy of your cover letter, which outlines the full feature or bugfix.
§ Time to mail-bomb the list! Do the following:
```
git send-email         \
  --suppress-cc=author \
  --suppress-cc=self   \
  --suppress-cc=cc     \
  --suppress-cc=sob    \
  *.patch
```
This command might ask you about sending the messages in response to another message (identified by Message-Id). Just press Enter without entering anything.

You might want to run the command first with the --dry-run parameter prepended.

The messages will be posted to the list only, and to the maintainers that you CC'd explicitly in the commit messages.

Once the messages are sent, you can remove the local patch files with:
```
rm -f -- *.patch
```
§ On the list, you will get feedback. In the optimal case, each patch will get a Reviewed-by tag (or an Acked-by tag) from at least one maintainer that is responsible for the package being touched by that patch. If you are lucky, you will also get Tested-by tags from some of them.

Once all tags are in place, one of the maintainers will pick up the entire series, update the commit messages to include the above tags (Reviewed-by, Acked-by, Tested-by) at the bottom, and commit and push your patches to upstream master. If this happens, pop the champagne, and goto step 12.
§ More frequently though, you will get requests for changes for some of your patches, while others of your patches will be fine, and garner Reviewed-by, Acked-by, and Tested-by tags. What you need to do in this case is:
- create the next version of your local branch
- pick up the tags that you got on the list
- implement the requested changes
- mark the v2 changes on each patch outside of the commit message
- push the next version to your personal repo again
- post the next version to the list

In the following steps, we'll go through each of these in more detail.

§ Create the next version of your local branch. Run the following commands in your edk2 tree:
```
git checkout master
git pull

git checkout                  \
  -b implement_foo_for_bar_v2 \
  implement_foo_for_bar_v1

git rebase master implement_foo_for_bar_v2
```
These commands do the following: first they refresh (fast forward) your local master branch to the current upstream master.

Then they fork version 2 of your topic branch off of version 1 of the same. Finally version 2 of the topic branch is rebased, non-interactively, on top of the refreshed master branch.

The upshot is that at this point, you have an identical version of your series on top of refreshed master, under a name that states v2, without touching the original v1 series.

Theoretically the last command could run into conflicts, but those are unlikely for a low-churn project like edk2, and if you get those, you should ask for help on the list. Conflict resolution is outside of the scope of this writeup. For now we'll assume that your last command completes without errors.
§ Pick up the tags that you got on the list. Run the following command:
```
git rebase -i master implement_foo_for_bar_v2
```
This will open your EDITOR with a list of your patches, identified by commit hash and subject line, each prefixed with a rebase action. By default, the rebase action will be pick.

You should carefully go through the feedback you received on the list for the v1 posting. (An email client that supports threading is a hard requirement for this.) For each v1 patch where you received a tag (Reviewed-by, Tested-by, Acked-by), replace the pick action with reword. Be sure not to modify anything else in the rebase action list.

Once you modified these actions, save the file, and quit the editor. Git will now rebase your patches again (to the same refreshed local master branch), but now it will also stop at each patch that you marked reword, and will let you edit the commit message for the patch. This is when you append the tags from the mailing list feedback to the very end of the commit message, underneath your own Signed-off-by tag. Save the updated commit message and quit the editor; git will continue the rebase.

Important: when you append the Reviewed-by, Tested-by, Acked-by tags from the mailing list feedback to the very end of a given commit message, never retype those tags. Always cut and paste them with the clipboard instead. You have to treat those tags as opaque.

If you mess up a commit message, don't panic. There are two options to bail out. First, you can update the next commit message to an empty text file. Git rebase will then stop and expect you to issue further commands at the normal shell prompt. This is when you run
```
git rebase --abort
```
and everything will be exactly like at the end of step 27.

The second option if you mess up a commit message (and you notice too late, i.e., the rebase finishes), is just to repeat step 28, and fix up the commit message.

(There is a third option: the branch can be forcibly reset to a chronologically earlier HEAD, which you can collect from the reflog. But that is a very sharp tool and not recommended for now.)

At the end of this step, you will have picked up the feedback tags from the list, for each affected patch individually.
§ Implement the requested changes. For this you run again
```
git rebase -i master implement_foo_for_bar_v2
```
but this time, you replace the pick actions of the affected (= to be modified) patches with edit. My strong recommendation is to set the edit action for exactly one patch in the series, and let the rest remain pick. (There are cases when this is not the best advice, but once you get in those situations, you won't need this guide.)

Okay then, git will start the rebase, and it will stop right after the patch you marked as edit is committed. Your working tree will be clean (no changes relative to the staging index), your staging index will also be clean (no changes staged relative to the last commit -- which is the patch you marked as edit).

At this point you modify the code as necessary, and build it and test it. Once satisfied, you run step 16 and step 17. After those steps, your working tree will be clean relative to the staging index, and the index will have all the necessary changes staged relative to the last commit (which you marked as edit in the rebase action list).

Now, if you ran
```
git commit
```
at this point (i.e., step 18 verbatim), then git would insert the staged changes as a separate patch into your series, so don't do that; that's most likely not your intent. Instead, run
```
git commit --amend
```
which will squash your staged changes into the patch-to-be-edited.

Then see step 19 and step 20.

(I am leaving out some editing action types here, such as: dropping a patch entirely, inserting a new patch, reordering patches, squashing patches together, and especially splitting up patches into smaller patches, and moving hunks between patches. Those are completely doable, and constitute the absolute power that git has over subversion, but they are definitely beyond these basics.)

Okay, your patch is fixed up now as the reviewer(s) requested; it builds, it runs (at the level expected at this stage into your series); PatchCheck.py is happy with it; and you have it committed. Time to run:
```
git rebase --continue
```
This will complete the rebase.

You can repeat this step (step 29) as many times as necessary. Again, I recommend to run a full rebase per each patch that needs an edit.

A small caveat: if you significantly edit a patch, say, for the v3 posting, for which you have received a Reviewed-by or Tested-by earlier, you are supposed to drop these tags, because your significant edits render them stale.
§ Mark the v2 changes on each patch outside of the commit message. This step is not strictly required, but it is a huge help for reviewers and maintainers.

Each time you finish a full rebase (an iteration of step 29), you should run your git GUI (gitk or anything else), and locate the patch (by subject) that you just edited in step 29.

Grab the SHA1 commit hash of that patch, and run:
```
git notes edit COMMIT_HASH_OF_THAT_PATCH
```
Git will again fire up your text editor, and allow you to attach notes to the commit. The distinction between a commit message and commit notes is that the notes are ephemeral. They will be included in a special section of the patch email, but they will never be included in the commit message itself, on the upstream master branch. They are perfect for communicating v1 -> v2 -> v3 changes, per patch, during the evolution of a given patch series.

So, please format the notes as follows:
```
v2:
- frobnicate quux [Jordan]
- perturb xizzy [Laszlo]
```
No line should be longer than 72 characters in the notes, and each entry should preferably mark who suggested that specific change for the patch.

Save the notes file and quit your editor, git will apply the changes. If you need to reedit the note, just repeat this step (step 30).

Very importantly, every time you complete a rebase, your notes are preserved, even if you edit the patch itself (code or commit message) during the rebase. This is very important for v2 -> v3 updates, because in that case you can add the v3 section on top of v2 in the notes!
§ Push the next version to your personal repo again.

Practically, repeat step 22, but using the branch name implement_foo_for_bar_v2.

(It is very important that you never ever modify implement_foo_for_bar_v1 after you push it to your personal github repo. Namely, this feature_branch_vN kind of branch is supposed to reflect your vN mailing list posting precisely. Since your mailing list posting is read only (you cannot modify emails you sent), you must not modify the corresponding branches in your github repo either. If a new version is necessary, you'll post a new version, and you'll push a new branch too.)
§ Post the next version to the list.

In practice, repeat step 23, with the following modifications:
- The subject prefix should state
```
--subject-prefix="PATCH v2"
```
- The commit range given should be
```
master..implement_foo_for_bar_v2
```
- The cover letter should reference the v2 branch pushed in step 31.
- The cover letter should include or reference (with an URL to the mailing list archive) the cover letter of the v1 posting, and also summarize the v1->v2 changes.
Then repeat step 24.

This is it, more or less, for a contributor. Nonetheless, I recommend reading the rest even to contributors, because it will help them understand how maintainers are supposed to operate, and how their actions above assist maintainers in doing their work.

Maintainer workflow

§ You need the same settings in your edk2 clone as a contributor. This includes contributor step 1 through contributor step 11.
§ You get patches to review, either by CC, or you notice them on the list.

If you can immediately point out problems with (some of) the patches, do so. If you are pleased with (some of) the patches, respond with your Reviewed-by, per patch. (Or, well, if you like it all, to the cover letter.)

If you agree with a patch, more or less, but lack the expertise to review it in depth (possible for patches that target a package that you don't maintain), respond with your Acked-by.
§ When reviewing a v2, v3, ... posting of a series, focus on the changes. The contributor is expected to support you in this with:
- Picking up your Reviewed-by and Acked-by tags from your v1 review. You can skip re-reviewing those patches in v2, especially because contributor step 29 instructs the contributor to drop your earlier Reviewed-by or Acked-by if he or she reworks the patch significantly.
- Listing the relative changes per patch, in the git-notes section. Refer to contributor step 30.
- Summarizing the changes in the v2, v3, ... cover letters. Refer to contributor step 32.
§ Assuming the series has converged (i.e., all patches have gained the necessary Reviewed-by and/or Acked-by tags), plus you have been "elected" as the lucky maintainer to apply and push the series, read on.

(The following steps are also relevant if you would like to test the series, or if you would like to review each patch in the series against a fully up-to-date, complete codebase, with all the precursor patches from the series applied.)
§ The first attempt at applying the contributor's series is directly from emails. For this, you absolutely need a mail user agent (MUA) that allows you to save patch emails intact.

So save all the patch emails into a dedicated, new folder.
§ Refresh your local master branch.
```
git checkout master
git pull
```
Note that it is extremely important to switch to the master branch, with the checkout command above, before you run git pull.
§ Create an application/testing/review branch, and apply the patches from the files you saved in maintainer step 5, from within your MUA:
```
git checkout -b REVIEW_implement_foo_for_bar_vN master

git am dedicated_directory/*.eml
```
Now, this step can genuinely fail for two reasons. The first reason is very obscure and I'm sharing it only for completeness.

So the first reason is that the patch may create or delete files, which implies /dev/null filenames in the git diff hunk headers. Because of the core.whitespace setting in contributor step 5 -- which we absolutely need due to the source files using CRLF line terminators in the internal git representation --, git-am might choke on those /dev/null lines. This depends on the Content-transfer-encoding of the email that is saved in maintainer step 5.

The second reason is that the master branch may have genuinely diverged from where it was when the contributor prepared his or her patches, on top of then-master. And the patches may no longer apply with git-am on top of current master.

If git am above fails for any reason at all, immediately issue
```
git am --abort
```
and proceed to the next step, maintainer step 8. Otherwise, if git am succeeds, skip forward to maintainer step 11.
§ As an alternative to maintainer step 7, here we'll grab the contributor's patches from his or her personal GitHub repo.

First add his or her personal repo as a remote to your local clone (this step only needs to be done once, during all of the collaboration with a given contributor):
```
git remote add --no-tags                           \
  HIS_OR_HER_GITHUB_ID                             \
  https://github.com/HIS_OR_HER_GITHUB_ID/edk2.git
```
At this point you should of course use the repo URL that the contributor shared in his or her cover letter, in contributor step 23 or -- for a v2, v3, ... post -- in contributor step 32.
§ Fetch any new commits and branches from the contributor's repo:
```
git fetch HIS_OR_HER_GITHUB_ID
```
§ Now, set up a local, non-tracking branch off of the contributor's relevant remote branch. You know about the relevant branch again from contributor step 23 or contributor step 32, i.e., the cover letter.
```
git checkout --no-track                         \
  -b REVIEW_implement_foo_for_bar_vN            \
  HIS_OR_HER_GITHUB_ID/implement_foo_for_bar_vN
```
§ Rebase the contributor's series -- using your local branch that you created either in maintainer step 7 or in maintainer step 10 -- to the local master branch (which you refreshed from upstream master in maintainer step 6):
```
git rebase -i master REVIEW_implement_foo_for_bar_vN
```
Here you should mark those patches with reword that have received Reviewed-by, Acked-by, Tested-by tags on the mailing list after the contributor's last posting. (Patches that garnered such tags in earlier versions are supposed to carry those tags already, due to contributor step 28.)

When rewording the relevant patches, simply append the relevant Reviewed-by, Acked-by, Tested-by tags from the mailing list feedback. (Refer to contributor step 28.)

Now, this rebase has a much better chance to succeed than git am in maintainer step 7, for two reasons again. The first reason is that the problem with the /dev/null headers just doesn't exist. The second reason is that git rebase, unlike git am, knows whence you are rebasing, which helps it immensely in calculating conflict resolutions automatically.

Nonetheless, the rebase might still fail, if meanwhile there have been intrusive / conflicting changes on the upstream master branch. If that happens, you can try to resolve the conflicts yourself, or you can ask the contributor to rebase his or her work on current upstream master, and to post it as the next version.
§ Okay, now you have the contributor's patches on top of your local master branch, with all the tags added from the mailing list. Time to build-test it! If the build fails, report it to the list, and ask the contributor for a new version.

(The OCD variant of this step is to build-test the contributor's series at each constituting patch, to enforce bisectability.)
§ Okay, the build test passes! Maybe you want to runtime test it as well. If you do, and it works, you can respond with a Tested-by to the entire series on the list, and immediately add your own Tested-by to the patches as well. Employ maintainer step 11 accordingly.
§ Time to push the patches to upstream master. Take a big breath :), and run
```
git push origin REVIEW_implement_foo_for_bar_vN:master
```
This will attempt to push the commits from your local REVIEW_implement_foo_for_bar_vN branch -- which is based off of your local master branch -- to the main github repo, and move the upstream master branch forward to the final commit among those.

If it succeeds, you deserve an alcoholic (or non-alcoholic) drink of your choice, you're done.

If it fails, then the reason is that another maintainer executed these steps in parallel, and moved forward the upstream master branch after your maintainer step 6, but before your maintainer step 14. If github accepted your push in this case, that would cause the other maintainer's push to go lost. So, proceed to the next step.
§ Repeat the following steps:
- maintainer step 6 -- Refresh your local master branch.
  
  Do not forget the git checkout master part in that step!
- maintainer step 11 -- Rebase the contributor's series.
  
  No changes should be necessary, but if conflicts are found, those are due to the fresh commits pushed by the other maintainer, mentioned in maintainer step 14. The possible remedies are discussed in maintainer step 11 -- fix up the conflicts yourself, or ask the contributor to rebase and post a new version.
- maintainer step 12 through maintainer step 14 -- rebuild, optionally retest, try pushing again.

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