Zero-copy BPF update (was: Re: Aggregating many ports into one
for tcpdump server.)
rwatson at FreeBSD.org
Mon Dec 24 16:40:12 PST 2007
On Mon, 24 Dec 2007, Robert Watson wrote:
> I've put up an updated tarball based on some recent changes here:
Unfortunately, there was a problem with a change I made to the kernel check
for a userspace notification that a buffer was available via shared memory, so
I have updated the tarball. While there, I've made the following further
- bpf.4 has been updated to reflect the shared memory interface.
- I've eliminated the BPF_ZEROCOPY environmental variable in libpcap; libpcap
will try to use zero-copy BPF if it is compiled into the kernel and enabled.
- The kernel now has a net.bpf.zerocopy_enable sysctl, set to 1 by default,
which controls whether the kernel will allow new zero-copy BPF sessions to
- Memory barriers and atomic operations have been introduced on the shared
memory interface to improve correctness on platforms with weaker memory
Robert N M Watson
University of Cambridge
> The main changes since this last drop are:
> - BPF_ZERO_COPY environmental variable renamed to BPF_ZEROCOPY to match
> option name.
> - libpcap support for zero-copy BPF buffers reworked to avoid unconditional
> call to select() for each buffer when there's already a pending buffer
> available to use; in general, avoid system calls entirely when there's data
> already waiting, only use system calls when there isn't a completed buffer
> to work on next.
> - Comments cleanup and some code cleanup.
> - A README to provide a little more guidance on getting it working. :-)
> You will need to "make clean ; make ; make install" in the modified libpcap
> against, as the size of pcap_t has changed. In principle "make ; make
> install" should DTRT, but it appears not to for me.
> Robert N M Watson
> Computer Laboratory
> University of Cambridge
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