From owner-svn-src-head@FreeBSD.ORG Mon Nov 21 06:37:20 2011 Return-Path: Delivered-To: svn-src-head@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id C5004106564A; Mon, 21 Nov 2011 06:37:20 +0000 (UTC) (envelope-from jrid@cubinlab.ee.unimelb.edu.au) Received: from mail-gw2.its.unimelb.edu.au (mail-gw2.its.unimelb.edu.au [128.250.5.151]) by mx1.freebsd.org (Postfix) with ESMTP id 7F6A08FC0A; Mon, 21 Nov 2011 06:37:20 +0000 (UTC) Received: from emu.cubinlab.ee.unimelb.edu.au (cubinlab.ee.unimelb.edu.au [128.250.80.33]) by mail-gw2.its.unimelb.edu.au (Postfix) with ESMTPS id 8AE80541; Mon, 21 Nov 2011 17:18:52 +1100 (EST) Received: from jrid.cubinlab.ee.unimelb.edu.au (jrid.cubinlab.ee.unimelb.edu.au [10.0.1.128]) (authenticated bits=0) by emu.cubinlab.ee.unimelb.edu.au (8.14.4/8.14.4) with ESMTP id pAL6In3I005096 (version=TLSv1/SSLv3 cipher=DHE-DSS-AES128-SHA bits=128 verify=NO); Mon, 21 Nov 2011 17:18:50 +1100 (EST) (envelope-from jrid@cubinlab.ee.unimelb.edu.au) Mime-Version: 1.0 (Apple Message framework v1084) Content-Type: text/plain; charset=us-ascii From: Julien Ridoux In-Reply-To: <4EC9E408.9000304@freebsd.org> Date: Mon, 21 Nov 2011 17:18:48 +1100 Content-Transfer-Encoding: quoted-printable Message-Id: <648D11A8-3636-49E5-BF20-83E4EA87242C@cubinlab.ee.unimelb.edu.au> References: <201111210417.pAL4HOdi023556@svn.freebsd.org> <4EC9E408.9000304@freebsd.org> To: Lawrence Stewart X-Mailer: Apple Mail (2.1084) Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Ben Kaduk Subject: Re: svn commit: r227778 - head/sys/net X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 21 Nov 2011 06:37:20 -0000 On 21/11/2011, at 4:39 PM, Lawrence Stewart wrote: > On 11/21/11 16:12, Ben Kaduk wrote: >> On Sun, Nov 20, 2011 at 11:17 PM, Lawrence = Stewart wrote: >>> Author: lstewart >>> Date: Mon Nov 21 04:17:24 2011 >>> New Revision: 227778 >>> URL: http://svn.freebsd.org/changeset/base/227778 >>>=20 >>> Log: >>> - When feed-forward clock support is compiled in, change the BPF = header to >>> contain both a regular timestamp obtained from the system clock = and the >>> current feed-forward ffcounter value. This enables new = possibilities including >>=20 >> Is it really necessary to make the ABI dependent on a kernel >> configuration option? This causes all sorts of headaches if loadable >> modules ever want to use that ABI, something that we just ran into >> with vm_page_t and friends and had a long thread on -current about. >=20 > Fair question. Julien, if pcap and other consumers will happily ignore = the new ffcount_stamp member in the bpf header, is there any reason to = conditionally add the ffcounter into the header struct? It is a valid question indeed. The feedback I have received so far was = to not have the feed-forward clock support be a default kernel = configuration option. What follows is based on this assumption. The commit (r227747) introduces sysctl that are conditioned by the same = "FFCLOCK" kernel configuration option. If a loadable module tests for = the presence of this sysctl, it will know if the ffcount_stamp member is = available. Is it too much of a hack? Alternatively, if the ffcounter is added to the bpf header = unconditionally, the ffcount_stamp member can be set to 0. Loadable = modules will then see a consistent ABI but will retrieve a meaningless = value. I am not sure which option makes more sense, any preference? Cheers, Julien=