xdr_string_encode
if (xdr_string_encode(&send_tail, hostname, hostnamelen)) {
if (xdr_string_encode(&send_tail, key, strlen(key))) {
int xdr_string_encode(char **p, char *str, int len);
struct mbuf *xdr_string_encode(char *, int);
m = xdr_string_encode(hostname, hostnamelen);
m->m_next = xdr_string_encode(key, strlen(key));
m = xdr_string_encode(path, strlen(path));