From mboxrd@z Thu Jan 1 00:00:00 1970 From: Willem de Bruijn Subject: Re: [PATCH net-next v3 3/4] net: use skb->priority for overloading skb->dropcount and skb->reserved_tailroom instead of skb->mark Date: Wed, 25 Feb 2015 15:49:40 -0500 Message-ID: References: <1424713924-6821-2-git-send-email-eyal.birger@gmail.com> <1424713924-6821-4-git-send-email-eyal.birger@gmail.com> <20150223205633.7fbd08d4@halley> <20150223.164801.842537100812023841.davem@davemloft.net> <1424783915.5565.74.camel@edumazet-glaptop2.roam.corp.google.com> <1424788868.5565.81.camel@edumazet-glaptop2.roam.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: Eric Dumazet , David Miller , Shmulik Ladkani , Eric Dumazet , Network Development To: Eyal Birger Return-path: Received: from mail-ob0-f177.google.com ([209.85.214.177]:39455 "EHLO mail-ob0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753323AbbBYUuM (ORCPT ); Wed, 25 Feb 2015 15:50:12 -0500 Received: by mail-ob0-f177.google.com with SMTP id wp18so6385724obc.8 for ; Wed, 25 Feb 2015 12:50:12 -0800 (PST) In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: >> We have to be a bit creative/hacky to keep skb size small. >> > > I agree. I don't think these feature deserve an skb size increase, so > some hackery is required. > > Though, as skb->cb[] is somewhat 'owned' by the protocol families on > socket enqueue > I tend to find aliasing skb->priority with skb->dropcount "a lesser > evil" as compared with > partitioning the skb->cb[] space. Please consider another field than priority. There are use cases that want to receive priority, similar to reading mark. Indeed, I have a draft packet auxdata patch for one user who wants to see the iptables changes (and infer tc effects) on egress packets. Fwiw, that patch also exposes mark, and runs into exactly this issue that you're fixing, so thanks :) Fields that are consistently NULL on enqueue, such as the dev field that Eric proposed, do not have this drawback.