bf_logon() is used by eth_init(), psip_init(), ip_init(), icmp_init(), tcp_init(), and udp_init() to register their functions for freeing buffers. For example, eth_init() calls bf_logon() with an argument of eth_buffree().
After bf_logon() is finished, freereq[] is configured as follows:
freereq[0]=eth_buffree
freereq[1]=psip_buffree
freereq[2]=ip_buffree
freereq[3]=icmp_buffree
freereq[4]=tcp_buffree
freereq[5]=udp_buffree