51ec1eb70d
Linux and Solaris (at least OpenSolaris) has PF_PACKET socket families to send raw ethernet frames. The only FreeBSD interface that can be used to send raw frames is BPF. As a result, many programs like cdpd, lldpd, various dhcp stuff uses BPF only to send data. This leads us to the situation when software like cdpd, being run on high-traffic-volume interface significantly reduces overall performance since we have to acquire additional locks for every packet. Here we add sysctl that changes BPF behavior in the following way: If program came and opens BPF socket without explicitly specifyin read filter we assume it to be write-only and add it to special writer-only per-interface list. This makes bpf_peers_present() return 0, so no additional overhead is introduced. After filter is supplied, descriptor is added to original per-interface list permitting packets to be captured. Unfortunately, pcap_open_live() sets catch-all filter itself for the purpose of setting snap length. Fortunately, most programs explicitly sets (event catch-all) filter after that. tcpdump(1) is a good example. So a bit hackis approach is taken: we upgrade description only after second BIOCSETF is received. Sysctl is named net.bpf.optimize_writers and is turned off by default. - While here, document all sysctl variables in bpf.4 Sponsored by Yandex LLC Reviewed by: glebius (previous version) Reviewed by: silence on -net@ Approved by: (mentor) MFC after: 4 weeks |
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