[Printing-architecture] Right place to put the code: label size protocol for Brother QL720NW label printer

Hello.

I have reverse-engineered the protocol Brother QL720NW networked label 
printer (and similar)
use to report the size of installed labels reel (it's a custom SNMP 
attribute, heh).

I'd like to add this support to the corresponding driver, however I'm at 
loss
where the corresponding driver is.

Could you please guide me to the proper place?

Best,
Misha.