optimize check in port-allocation code

Hi,

In the 2.6.11 code, I found this:
static int tcp_v6_get_port(struct sock *sk, unsigned short snum) also in:
static int tcp_v4_get_port(struct sock *sk, unsigned short snum) {
...

        if (snum == 0) {
                int low = sysctl_local_port_range[0];
                int high = sysctl_local_port_range[1];

                spin_lock(&tcp_portalloc_lock);
		rover = tcp_port_rover;
                do {    rover++;
                        if ((rover < low) || (rover > high))
                                rover = low;

That 'rover < low' check is redundant?
ints are bigger then the maximum portnumber (65535) so when rover++ gets too high, the check for 'rover > high' will truncate it to low (in the next line) waaay before the int itself wraps. It is needed because tcp_port_rover might be < low before the function starts, in that case the check for <low can be taken out of the loop.

Patch:

diff -uNr net/ipv4/tcp_ipv4.c.org net/ipv4/tcp_ipv4.c
@@ -222,10 +222,13 @@
                int rover;
 
                spin_lock(&tcp_portalloc_lock);
-               rover = tcp_port_rover;
+               if (tcp_port_rover < low)
+                       rover = low;
+               else
+                       rover = tcp_port_rover;
                do {
                        rover++;
-                       if (rover < low || rover > high)
+                       if (rover > high)
                                rover = low;
                        head = &tcp_bhash[tcp_bhashfn(rover)];
                        spin_lock(&head->lock);

diff -uNr net/ipv6/tcp_ipv6.c.org net/ipv6/tcp_ipv6.c
@@ -139,9 +139,12 @@
                int rover;
 
                spin_lock(&tcp_portalloc_lock);
-               rover = tcp_port_rover;
+               if (tcp_port_rover < low)
+                       rover = low;
+               else
+                       rover = tcp_port_rover;
                do {    rover++;
-                       if ((rover < low) || (rover > high))
+                       if (rover > high)
                                rover = low;
                        head = &tcp_bhash[tcp_bhashfn(rover)];
                        spin_lock(&head->lock);

Folkert van Heusden

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