Override phase function for a volume shader

[timothee.chabatFS8S2]

[Arnold 6.0.1.0 ; Maya 2019 ; MtoA 4.0.1.0]

I'm writing in C++ my own volume shader and since I have specifics needs I wanted to change the phase function, thus I can't call AiClosureVolumeHenyeyGreenstein.

As far as my understanding goes, I should precise the absorption, emission and the scattering at some point. AiClosureVolumeEmission and AiClosureVolumeAbsorption are indeed defined but I can't find the scattering closure, even though it is mentioned in "ai_closure.h" l.38 .

Also in the API ref here, they mention a scattering_coefficient but they do not precise where it is possible to set it. Any leads or workaround would be very usefull.