git log for a merged branch

[Stephen Bash <bash@genarts.com>]

Hi everyone-

A coworker asked me a Git question yesterday that I can't answer, so I thought I'd pass it along:

Assume I have a release branch with bug fixes that is tagged at the end of the release cycle (let's call the tag tagFoo).  The release branch then gets merged back into mainline development (call the branch mainline), and the release branch is deleted.  If I want to see the commits (bug fixes) performed on the release branch, how do I do it?

I don't think
   git log mainline..tagFoo
works because all the commits of tagFoo are now reachable by mainline thanks to the merge.  Is there a simple way to express this concept?

Obviously in a pinch a simple
   git log tagFoo
will give you everything back to the beginning of time, but I think that's suboptimal...

To complicate things a bit more, in the real world there may be multiple merges from the release branch to mainline during the life of the release branch, so any solution that also deals with that would be outstanding (probably at the cost of additional complexity?)

Thanks,
Stephen