tcpdump mailing list archives
Re: BPF_COP support for libpcap
From: Mindaugas Rasiukevicius <rmind () noxt eu>
Date: Mon, 18 May 2015 00:31:47 +0100
Michael Richardson <mcr () sandelman ca> wrote:
Mindaugas Rasiukevicius <rmind () noxt eu> wrote: > A while ago NetBSD gained support for BPF_COP instruction, see [1] > for more details. However, now there are use cases of it outside > the NetBSD kernel, e.g. standalone NPF packet filter running as a > program on Linux. Hence I would like to add the support for the > BPF_COP instruction to the pcap_compile() and pcap_dump() of the > libpcap library. It seems like a good thing to have to evolve BPF forward, particularly in light of more and more complex 802.1q and "metro-ethernet" ring layer-2 formats, and walking IPv6 header chains. It seems that we really wind up needing a registry of co-processor function indexes... which begin to seem like new instructions in some sense. Perhaps the difference is that they are better defined, and more dynamic.
Well, the patch just provides the capability to invoke the coprocessor. The benefit of BPF_COP approach is that the vendors can implement their custom coprocessor and use through libpcap/tcpdump without polluting the instruction space. I think the RISC-like coprocessor approach (think of MIPS) is both clean and powerful compared to adding complex instructions. It would be good to have some general purpose coprocessor (for walking IPv6 header chain and other operations), but that would probably be difficult to agree and standardise amongst the vendors. Speaking of evolving BPF, I would love to see Linux eBPF support (except the new instructions). That is a separate discussion though.
- As there are users who want to pcap_compile() an expression with BPF_COP on Linux, can we expose BPF_COP or make it otherwise available for the systems where this instruction would not be in the net/bpf.h header?instructions currently live in pcap/bpf.h in the libpcap directory.
Will move it to the pcap/bpf.h file. The question is whether #ifndef approach on BPF_COP is fine? Also, any comment on opt_stmt() change in optimize.c? It is somewhat convoluted code and I might have missed some edge case. If the patch looks fine, should I make a github pullup request? -- Mindaugas _______________________________________________ tcpdump-workers mailing list tcpdump-workers () lists tcpdump org https://lists.sandelman.ca/mailman/listinfo/tcpdump-workers
Current thread:
- BPF_COP support for libpcap Mindaugas Rasiukevicius (May 12)
- Message not available
- Re: BPF_COP support for libpcap Mindaugas Rasiukevicius (May 17)
- Re: BPF_COP support for libpcap Darren Reed (May 19)
- Re: BPF_COP support for libpcap Paul "LeoNerd" Evans (May 20)
- Re: BPF_COP support for libpcap Mindaugas Rasiukevicius (May 25)
- Message not available
- Re: BPF_COP support for libpcap Mindaugas Rasiukevicius (Jun 10)
- Re: BPF_COP support for libpcap Mindaugas Rasiukevicius (May 17)
- Message not available