Inequality constraint in dolfin adjoint

I need to add an inequality constraint of my control function
in PDE-constrained optimisation problem. This constraint is
L2 norm of the control function <= some constant.

Is there a way to include this constraint in adjoint?
I come up with such class
class dolfin_adjoint.InequalityConstraint
in documentation, but I don't know how to use it.
Thanks in advance