[ovs-dev] [PATCH] netdev-afxdp: Add pcap dump support.

[William Tu]

On Mon, Dec 16, 2019 at 9:47 AM Ilya Maximets <i.maximets at ovn.org> wrote:
>
> On 16.12.2019 18:23, William Tu wrote:
> > On Mon, Dec 16, 2019 at 7:27 AM Ilya Maximets <i.maximets at ovn.org> wrote:
> >>
> >> On 16.12.2019 15:27, William Tu wrote:
> >>> On Mon, Dec 16, 2019 at 5:57 AM Ilya Maximets <i.maximets at ovn.org> wrote:
> >>>>
> >>>> On 16.12.2019 14:43, William Tu wrote:
> >>>>> On Mon, Dec 16, 2019 at 1:41 AM Ilya Maximets <i.maximets at ovn.org> wrote:
> >>>>>>
> >>>>>> On 13.12.2019 21:59, William Tu wrote:
> >>>>>>> Debugging netdev-afxdp is hard because tcpdump does not work
> >>>>>>> at all, even for generic mode.  ovs-tcpdump which uses port
> >>>>>>> mirroring also does not work for netdev-afxdp.
> >>>>>>
> >>>>>> Hmm.  Why ovs-tcpdump doesn't work for you?  It should not depend
> >>>>>> on port type.  If it doesn't work we need to investigate this
> >>>>>> case and fix it because it's a very important tool.
> >>>>>
> >>>>> Because ovs-tcpdump still uses 'tcpdump' tool to capture packets,
> >>>>> (dump-cmd=tcpdump) and forward to mirror port.  Since tcpdump
> >>>>> sees no packet at all when type=afxdp, there is no packets to mirror.
> >>>>
> >>>> ovs-tcpdump creates simple tap interface and mirrors all the traffic
> >>>> to it.  tcpdump command is started on that tap interface (no xdp here).
> >>>> There is no difference from which port types you're mirroring the traffic.
> >>>> It works for DPDK based ports and should work for afxdp.
> >>>
> >>> I got it working using ovs-tcpdump now, thanks!
> >>> ex: ovs-tcpdump -i afxdp-p0 -n -l -w /tmp/p0.pcap
> >>
> >> OK.  So, this patch is not needed.
> >
> > I think this patch is still useful, because using 'options:pcap'
> > is much easier than ovs-tcpdump (which requires python libs,
> > creates tap, etc).
> > Another use case is for testsuite, we can compare the packet
> > content by dumpling the pcap file.
> >
> > But this patch might have performance impact even
> > when not enabling it?
>
> Yes, it will have performance impact since you're calling it from
> the hot path.
>
> Also, current version will not work correctly.  clang build fails.
> (your travis link in commit-message is not correct).
> To implement the functionality properly you need to protect pcap
> streams by rcu.

Thanks, I paste the wrong link
The error was here:
https://travis-ci.org/williamtu/ovs-travis/builds/624759289

>
> I don't think that it's hard to use ovs-tcpdump.  Not harder than
> usual tcpdump.  All the additional ports and mirroring are created
> and configured automatically.
>
> Best regards, Ilya Maximets.

OK, make sense. I will use ovs-tcpdump.
William