All the Qubes code is kept in GIT repositories. We divided the project into several components, each of which has its own separate repository, some of them:
1. Make all the changes in your working directory, i.e. edit files, move them around (you can use 'git mv' for this), etc.
2. Add the changes and commit them (git add, git commit). Never mix different changes into one commit! Write a good description of the commit. The first line should contain a short summary, and then, if you feel like more explanations are needed, enter an empty new line, and then start the long, detailed description (optional).
3. Test your changes NOW: check if RPMs build fine, etc.
4. Create the patch using 'git format-patch'. This has an advantage over 'git diff', because the former will also include your commit message, your name and email, so that \*your\* name will be used as a commit's author.
5. Send your patch to qubes-devel. Start the message subject with the '[PATCH]' string.
