https://docs.oracle.com/cd/E88353_01/html/E37855/bcanputnext-9f.html
bcanputnext - man pages section 9: DDI and DKI Kernel Functions
canputnext , bcanputnext - test for room in next module's message queue Architecture independent level 1 (DDI/DKI).
man pagessectionddidkikernel