understanding index

Hey list.

I'm having some understanding trouble with git index. As I understand, 'git rm --cached' is not strictly the opposite of 'git add'. It's a little embarrassing in this particular case : what if you want to commit and did a wrong 'git add -u' command ?

Here's a minimalist sample :

% ls foo bar

[ hack, hack, hack on both files ]

% git status
[...]
	modified: foo
	modified: bar
[...]
% git add -u foo bar

[ optional hack on foo ] [ damn, you realize you don't want to commit changes on foo at all ]

% git rm --cached foo
% git status
[...]
	deleted: foo
	modified: bar
[...]

If committed as is, foo will be marked as deleted (in 'git log --name-status' at least, which is not wanted).

How to retrieve the state before the wrong 'git add -u' command _and_ keep the working tree as well (including last hacks) ? Is there any command which is the exact opposite of 'git add -u' ?

Cheers,