Q：Why does the bindresvport_sa function use ports 600 ~ 1023?

[Haroldll]

When ganesha tries to connect to other services, such as rpcbind, the ports 600~1023 are used when calling the bindresvport_sa interface(assuming that AF_LOCAL is not used), is there any particular reason for this, can't we just have the system assign a random source port?

code see:

#ifdef __linux__
#define STARTPORT 600
#define LOWPORT 512
#define ENDPORT (IPPORT_RESERVED - 1)
#define NPORTS  (ENDPORT - STARTPORT + 1)
int
bindresvport_sa(int sd, struct sockaddr *sa)
{
............
	u_int16_t *portp;
	static u_int16_t port;
	static short startport = STARTPORT;
	socklen_t salen;
	int nports = ENDPORT - startport + 1;
	int endport = ENDPORT;
	int i;
............

	if (port == 0)
		port = (getpid() % NPORTS) + STARTPORT;

	res = -1;
	errno = EADDRINUSE;
 again:
	for (i = 0; i < nports; ++i) {
		*portp = htons(port++);
		if (port > endport)
			port = startport;
		res = bind(sd, sa, salen);
		if (res >= 0 || errno != EADDRINUSE)
			break;
	}
	if (i == nports && startport != LOWPORT) {
		startport = LOWPORT;
		endport = STARTPORT - 1;
		nports = STARTPORT - LOWPORT;
		port = LOWPORT + port % (STARTPORT - LOWPORT);
		goto again;
	}
	return (res);
}

Ganesha uses a lot of ports in this segment when it starts up, binds one for every request, and then releases it, but there is a time_wait time, and the next time it picks a new port, all of which occupy a lot of ports. This time may cause the bind port to fail for application services that use this port.

So can just set port to 0 and let the system assign a port, like this:

    sin->sin_port = 0;
    sa->sa_family = AF_INET;
    res = bind(sd, sa, salen);

Or is there some kind of restriction that the ports here must be 600~1023?