[PATCH] optimize check in port-allocation code

[folkert@vanheusden.com (Folkert van Heusden)]

[-- Attachment #1: Type: text/plain, Size: 3096 bytes --]

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
--- net/ipv4/tcp_ipv4.c.org     2005-03-04 22:39:37.340950747 +0100
+++ net/ipv4/tcp_ipv4.c 2005-03-04 22:40:35.570059217 +0100
@@ -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
--- net/ipv6/tcp_ipv6.c.org     2005-03-04 22:41:44.043007791 +0100
+++ net/ipv6/tcp_ipv6.c 2005-03-04 22:42:17.604728073 +0100
@@ -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);


Signed-off-by: Folkert van Heusden <folkert@vanheusden.com>


Folkert van Heusden

Auto te koop! Zie: http://www.vanheusden.com/daihatsu.php
Op zoek naar een IT of Finance baan? Mail me voor de mogelijkheden!
+------------------------------------------------------------------+
|UNIX admin? Then give MultiTail (http://vanheusden.com/multitail/)|
|a try, it brings monitoring logfiles to a different level! See    |
|http://vanheusden.com/multitail/features.html for a feature list. |
+------------------------------------------= www.unixsoftware.nl =-+
Phone: +31-6-41278122, PGP-key: 1F28D8AE
Get your PGP/GPG key signed at www.biglumber.com!

[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 189 bytes --]