Amongst the new IPC primitives in Minix 3 is 'echo' (see
/usr/src/kernel/ipc.h), which according to comments in the source code
(c.f. /usr/src/kernel/proc.c) just returns the message back to the
caller. I can't find any instances of this being used anywhere in the
Minix 3 sources, and am wondering what its purpose is. Is it a
left-over from testing or early development?

[Just for the record, Minix 3 also adds non-blocking variants of send
and receive, appropriately called nb_send and nb_receive. These each
get used just once each: see /usr/src/servers/pm/utility.c:anic(),
and /usr/src/drivers/tty/keyboard.c::do_panic_dumps(). The other new
primitive is notify, which is used extensively in the device drivers
and system servers.]

Kind Regards,

Michael