send file descriptor via ipc

[Yan Yu]

Hello, there,
  I am looking for the function that handle send/recv file descriptors
through sendmsg/recvmsg?
by looking through source files,
unp_internalize/unp_externalize in kern/uipc-usrreq.c seems relevant..

but i am not sure since i could not guess the meaning of the function
name..  (btw, what is "unp", the prefix in the function name stands for?)
Can someone please confirm if it is the right function or point
me to the right one i should look at?

many thanks,
yan