Date: Mon, 21 Nov 2011 17:18:48 +1100 From: Julien Ridoux <jrid@cubinlab.ee.unimelb.edu.au> To: Lawrence Stewart <lstewart@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Ben Kaduk <minimarmot@gmail.com> Subject: Re: svn commit: r227778 - head/sys/net Message-ID: <648D11A8-3636-49E5-BF20-83E4EA87242C@cubinlab.ee.unimelb.edu.au> In-Reply-To: <4EC9E408.9000304@freebsd.org> References: <201111210417.pAL4HOdi023556@svn.freebsd.org> <CAK2BMK4DP=japDufnbMUgqMgmL7rRye4wMrwqzHePyreNwiu-Q@mail.gmail.com> <4EC9E408.9000304@freebsd.org>
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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<lstewart@freebsd.org> 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=
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