The bindresvport and bindresvport_sa functions are used to bind a socket descriptor to a privileged IP port, that is, a port number in the range 0-1023.
If sin is a pointer to a "struct sockaddr_in" then the appropriate fields in the structure should be defined. Note that sin->sin_family must be initialized to the address family of the socket, passed by sd. If sin->sin_port is '0' then an anonymous port (in the range 600-1023) will be chosen, and if bind(2) is successful, the sin->sin_port will be updated to contain the allocated port.
If sin is the NULL pointer, an anonymous port will be allocated (as above). However, there is no way for bindresvport to return the allocated port in this case.
Only root can bind to a privileged port; this call will fail for any other users.
Function prototype of bindresvport is biased to AF_INET socket. The bindresvport_sa function acts exactly the same, with more neutral function prototype. Note that both functions behave exactly the same, and both support AF_INET6 sockets as well as AF_INET sockets.
.Rv -std bindresvport