Reacting to new commits in a poll-mirror

Folks,

I am trying to set up Patchwork-Git integration on host A for
a project whose Git repo is on host B. I thought I could use
a mirror (git clone --mirror) on A and regularly fetch from B, but
I cannot find a way (hook) to make Git on A react to new commits it
fetched from B.

I can probably hack something up, e.g. store refs before a fetch and
then iterate the refs between the stored refs and the HEAD, but this
seems exceedingly hackish and I'd much rather have this information
from git-fetch (like git-push calls post-receive).

Is this at all possible?
Would it be possible?
Where would this be done?

-- 
martin | http://madduck.net/ | http://two.sentenc.es/
 
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