Here are a few tips and notes that might be useful if you are interested in modifying samba source code and getting it into samba's main branch.
In order to contribute code to samba, make sure you have the latest source. Retrieving the samba source code from CVS is documented in the appendix of the Samba HOWTO Collection.
Please discuss large modifications you are going to make with members of the samba team. Some parts of the samba code have one or more 'owners' - samba developers who wrote most of the code and maintain it.
This way you can avoid spending your time and effort on something that is not going to make it into the main samba branch because someone else was working on the same thing or because your implementation is not the correct one.
Patches to the samba tree should be in unified diff format, e.g. files generated by diff -u.
If you are modifying a copy of samba you retrieved from CVS, you can easily generate a diff file of these changes by running cvs diff -u.
Don't simply copy code from other places and modify it until it works. Code needs to be clean and logical. Duplicate code is to be avoided.
Test your patch. It might take a while before one of us looks at your patch so it will take longer before your patch when your patch needs to go thru the review cycle again.
Don't put separate patches in one large diff file. This makes it harder to read, understand and test the patch. You might also risk not getting a good patch committed because you mixed it with one that had issues.
Make sure your patch complies to the samba coding style as suggested in the coding-suggestions chapter.
Bugfixes to bugs in samba should be submitted to samba's bugzilla system, along with a description of the bug.
Send feature patches along with a description of what the patch is supposed to do to the Samba-technical mailinglist and possibly to a samba team member who is (one of the) 'owners' of the code you made modifications to. We are all busy people so everybody tends to 'let one of the others handle it'. If nobody responded to your patch for a week, try to send it again until you get a response from one of us.
One of the team members will look at your patch and either commit your patch or give comments why he won't apply it. In the latter case you can fix your patch and re-send it until your patch is approved.