git-p4 -- any great explanations for how it works

If you use perforce remotely and desire to have the awesome speed of git for tracking diffs, here is the solution: http://kb.perforce.com/article/1417/git-p4

However, I've noticed the following:

1. Follow the instructions exactly
2. It can take a while to import a large tree without getting history
3. On a large tree, the first commit will take a long time as this command will sync the whole tree.
4. If you do a commit that you do not want to send to perforce, you have to do a "git rebase -i" and remove the offending commit record. You cannot do a "git p4 submit" and then "p4 revert" the file you don't want to send.
5. If you mess something up, things can get really confusing.

How does git-p4 uses the remote repositories?

git-p4 is not for the faint-at-heart. I'm learning that you really need to understand git well in order to use it well.

There is some more information in Documentation/git-p4.txt in the git project source code.

git-p4 maintains a refs/remotes/p4 branch to mirror the remote Perforce server. By default git-p4 clone and git-p4 sync update this remote and you rebase your master against it.

git-p4 submit requires configuring an additional local directory as the Perforce client root for use by p4 submit.

git-p4 sync/clone will record each Perforce changelist number in the corresponding git commit message. For example:

[git-p4: depot-paths = "//depot/test/": change = 51]

Using these changelist notations, git-p4 sync acquires changelists on the Perforce server not yet committed to git, adding changelist notations to each new git commit message.

git-p4 submit begins by identifying new local git commits - those without [git-p4: ...]. Using the Perforce client local workspace, it syncs down the Perforce files, and with git apply applies the patches gotten from git format-patch on the unsubmitted git commits before calling p4 submit.

Then git-p4 submit calls git-p4 sync to update the ref/remotes/p4 branch against the just updated Perforce remote.

Finally git-p4 submit will call git rebase on the master branch against the updated remote. This results in the same git tree which was submitted, but with edited commit messages containing the [git-p4...] changelist notations.

How does one keep a few files modified in git without ever sending them to p4?

git-p4 submit will submit all branch commits. Use the usual git tools to organize changes into and out of the branch you choose to submit to Perforce.