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<lstew...@freebsd.org> >> wrote: >>> Author: lstewart >>> Date: Mon Nov 21 04:17:24 2011 >>> New Revision: 227778 >>> URL: http://svn.freebsd.org/changeset/base/227778 >>> >>> 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 >> >> 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. > > 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_______________________________________________ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
