New to git

Jordan Justen edited this page Feb 12, 2016 · 4 revisions

New to git? The git site has some great documentation:

And, if you've worked with svn in the past, this page might be helpful:

EDK II git workflows

See EDK II Development Process

Some Potentially Dangerous Commands

Similar to using the dangerous rm -rf or del /s commands, there are some aspects of git usage you should be careful with. Here are a few commands to be careful with.

  • git reset --hard

    • This command takes your current branch (head) and sets it to another revision. By default, it sets it to the last commit on the current branch.

    • Why it is potentially dangerous:

      • It will overwrite any change in files that you have not committed.

      • It can move your branch to somewhere else, and make you lose commits.

    • Ways to recover:

      • Uncommitted changes in files: NONE. There is no way to recover these lost changes!

      • Lost commits: There is a good chance you can recover the commits with the git reflog command.

  • git clean

    • This command deletes files in your local tree that are not tracked in your git repository.

    • Why it is potentially dangerous:

      • It can delete files for new features that you have not yet added to git.
    • Ways to recover:

      • NONE. There is no way to recover the deleted files!
    • Tip:

      • Use the --dry-run parameter to see what will be deleted.
  • git merge

    • This command joins together the histories of two branches.

    • For now, EDK II is choosing to maintain a linear history, and not use merges.

    • Why it is potentially dangerous:

      • It is occasionally possible for git to choose the wrong action when auto-merging the two branches. Although rare, this can lead to some changes getting dropped in the latest tree.
    • Ways to recover:

      • If the merge has not be pushed upstream, there are a few ways to recover.

        • The best guaranteed way to fix things is to look through the history to find the tree version before your merge. (Helpful tools: gitk, tig, or git log --oneline --graph)

        • Now, use git reset --hard <good-version>

          • This will force your branch back to the state before the merge. Be sure to understand the dangers of git reset --hard as documented above.
        • You might also be able to simply use git rebase origin/master to remove the merge commit.

      • If the merged commit is pushed upstream, then unfortunately it will persist in history. This is not really a big deal, but just be sure that the merge worked correctly. If you find that changes were actually lost then add new commits to re-apply the changes.

  • git pull

    • By default, the git pull command is a git fetch followed by a git merge. Therefore it has the same concerns as the git merge command documented above.

    • Tip:

      • You can also run git config pull.rebase true to set your edk2 tree up so that git pull will be a git fetch followed by a git rebase (rather than git merge)
  • git push -f

    • This command 'force' pushes a branch. This potentially can force the remote branch to rewrite its history.

    • Note: The main edk2 tree is protected from force pushes, and you can setup your github branches to be similarly protected:

    • Why it is potentially dangerous:

      • If you 'rewrite' the history of a tree, then people will be suspicious that bad changes have been snuck into the tree.

      • This is generally only considered bad for 'upstream' branches that many people are basing their work off of.

    • Ways to recover:

      • You might be able to force push the old version back if you can find out its version.
    • It's sometimes okay to force push

      • For your personal development branches where no one is depending on the branch, it is okay to force push. In fact, most people will eventually find that force pushing is a good way to backup the currect state of their development work on a remote server.
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