Where are these function definition

Hi,
 
I cd into pppd directory in folder /usr/src and found
the following functions declared in the pppd.h header
 file, but I couldn't found where these APIs are
defined.
 
/* Procedures exported from demand.c */
void demand_conf __P((void)); /* config interface(s)
for demand-dial */
void demand_block __P((void)); /* set all NPs to queue
up packets */
void demand_unblock __P((void)); /* set all NPs to
pass packets */
void demand_discard __P((void)); /* set all NPs to
discard packets */
void demand_rexmit __P((int)); /* retransmit saved
frames for an NP */
int loop_chars __P((unsigned char *, int)); /* process
chars from loopback */
int loop_frame __P((unsigned char *, int)); /* process
frame from loopback */
 
/* Procedures exported from sys-*.c */
void sys_init __P((void)); /* Do system-dependent
initialization */
void sys_cleanup __P((void)); /* Restore system state
before exiting */
void sys_check_options __P((void)); /* Check options
specified */
void sys_close __P((void)); /* Clean up in a child
before execing */
int ppp_available __P((void)); /* Test whether ppp
kernel support exists */
void open_ppp_loopback __P((void)); /* Open loopback
for demand-dialling */
void establish_ppp __P((int)); /* Turn serial port
into a ppp interface */
void restore_loop __P((void)); /* Transfer ppp unit
back to loopback */
void disestablish_ppp __P((int)); /* Restore port to
normal operation */
void clean_check __P((void)); /* Check if line was
8-bit clean */
void set_up_tty __P((int, int)); /* Set up port's
speed, parameters, etc. */
void restore_tty __P((int)); /* Restore port's
original parameters */
void setdtr __P((int, int)); /* Raise or lower port's
DTR line */
void output __P((int, u_char *, int)); /* Output a PPP
packet */
void wait_input __P((struct timeval *));
 
Can anyone please tell me how to find out where these
APIs are defined in freebsd src?
 
Thanks
Sam


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