Merging using only fast-forward

Hi,


I have a work flow where A is only allowed to rebase and B is only allowed to
fast-forward.  They both fetch from each other and rebase/merge using pull.  On
A I can use the configuration branch.<name>.rebase but it does not seem to be an
option to enforce a fast-forward on B.

If there are changes on both A and B that have not yet been integrated (by A
doing a pull (fetch/rebase)) I want a pull (fetch/merge) on B to fail.

It would be useful with a configuration ala branch.<name>.fast-forward or an
option --ff-only to git-merge so I could use the configuration
branch.<name>.mergeoptions.

Is there any other way to achieve this?

Thanks for a great tool.  I am using git with accurev where B is the integrator
between git and accurev (commits flow in both directions).  I imagine this could
be useful in other environments as well.

-- 
Sverre Hvammen Johansen