From mboxrd@z Thu Jan 1 00:00:00 1970 From: Octavian Purdila Subject: Re: [net-next PATCH v4 3/3] net: reserve ports for applications using fixed port numbers Date: Tue, 16 Feb 2010 16:25:22 +0200 Message-ID: <201002161625.22495.opurdila@ixiacom.com> References: <1266271241-6293-1-git-send-email-opurdila@ixiacom.com> <201002161306.29708.opurdila@ixiacom.com> <4B7A9852.5020105@redhat.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: David Miller , Linux Kernel Network Developers , Linux Kernel Developers , Neil Horman , Eric Dumazet To: Cong Wang Return-path: In-Reply-To: <4B7A9852.5020105@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Tuesday 16 February 2010 15:06:26 you wrote: > Octavian Purdila wrote: > > On Tuesday 16 February 2010 11:37:04 you wrote: > >>> BUILD_BUG_ON(sizeof(struct inet_skb_parm) > sizeof(dummy_skb->cb)); > >>> > >>> + sysctl_local_reserved_ports = kzalloc(65536 / 8, GFP_KERNEL); > >>> + if (!sysctl_local_reserved_ports) > >>> + goto out; > >>> + > >> > >> I think we should also consider the ports in ip_local_port_range, > >> since we can only reserve the ports in that range. > > > > That is subject to changes at runtime, which means we will have to > > readjust the bitmap at runtime which introduces the need for additional > > synchronization operations which I would rather avoid. > > Why? As long as the bitmap is global, this will not be hard. > For the more important point see bellow, but with regard to reallocation, this means we need to at least use rcu_read_lock() in the fast path to avoid races between freeing the old bitmap and doing a read in progress. Granted, that is a light operation, but would it makes things so much more complicated just so that we save one memory page (assuming the range is the default [32000 64000] one). > Consider that if one user writes a port number which is beyond > the ip_local_port_range into ip_local_reserved_ports, we should > not accept this, because it doesn't make any sense. But with your > patch, we do. > I think it should be allowed. I see ip_local_reserved_ports and ip_local_range as independent settings that can be change at any time. That way I can flag port 8080 even if the current range is [32000, 64000] and then later I can expand the range to [1024, 64000] without loosing the 8080 reservation.