Date: Sun, 20 Nov 2011 23:02:24 -0800 From: Garrett Cooper <yanegomi@gmail.com> To: Julien Ridoux <jrid@cubinlab.ee.unimelb.edu.au> Cc: svn-src-head@freebsd.org, Lawrence Stewart <lstewart@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: <CAGH67wQsOesjobdrUC03WgkC-VZgCCOLJe-8_ROyv_80LMKRsQ@mail.gmail.com> In-Reply-To: <648D11A8-3636-49E5-BF20-83E4EA87242C@cubinlab.ee.unimelb.edu.au> References: <201111210417.pAL4HOdi023556@svn.freebsd.org> <CAK2BMK4DP=japDufnbMUgqMgmL7rRye4wMrwqzHePyreNwiu-Q@mail.gmail.com> <4EC9E408.9000304@freebsd.org> <648D11A8-3636-49E5-BF20-83E4EA87242C@cubinlab.ee.unimelb.edu.au>
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On Sun, Nov 20, 2011 at 10:18 PM, Julien Ridoux <jrid@cubinlab.ee.unimelb.edu.au> wrote: > > 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= > =A0wrote: >>>> Author: lstewart >>>> Date: Mon Nov 21 04:17:24 2011 >>>> New Revision: 227778 >>>> URL: http://svn.freebsd.org/changeset/base/227778 >>>> >>>> Log: >>>> =A0- When feed-forward clock support is compiled in, change the BPF he= ader to >>>> =A0 =A0contain both a regular timestamp obtained from the system clock= and the >>>> =A0 =A0current feed-forward ffcounter value. This enables new possibil= ities including >>> >>> Is it really necessary to make the ABI dependent on a kernel >>> configuration option? =A0This 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. >> >> Fair question. Julien, if pcap and other consumers will happily ignore t= he new ffcount_stamp member in the bpf header, is there any reason to condi= tionally 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 pr= esence of this sysctl, it will know if the ffcount_stamp member is availabl= e. Is it too much of a hack? > > Alternatively, if the ffcounter is added to the bpf header unconditionall= y, 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? struct inaddr, etc withstood sizing restrictions by adjusting the sin_family / sin_len values appropriate to how large the payload was made.. Could something similar be done for the ffcounter work (obscure behind a void* pointer, use a proper bitwise ORed value for the sin_len and sin_family, etc)? Thanks, -Garrett
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