From: "Toke Høiland-Jørgensen" <toke@redhat•com>
To: Daniel Borkmann <daniel@iogearbox•net>,
Magnus Karlsson <magnus.karlsson@gmail•com>,
Jesper Dangaard Brouer <brouer@redhat•com>
Cc: "Xuan Zhuo" <xuanzhuo@linux•alibaba.com>,
"Eelco Chaudron" <echaudro@redhat•com>,
"Lorenzo Bianconi" <lorenzo.bianconi@redhat•com>,
"Björn Töpel" <bjorn@kernel•org>,
"Magnus Karlsson" <magnus.karlsson@intel•com>,
"Jonathan Lemon" <jonathan.lemon@gmail•com>,
"David S. Miller" <davem@davemloft•net>,
"Jakub Kicinski" <kuba@kernel•org>,
"Alexei Starovoitov" <ast@kernel•org>,
"John Fastabend" <john.fastabend@gmail•com>,
"Andrii Nakryiko" <andrii@kernel•org>,
"Martin KaFai Lau" <kafai@fb•com>,
"Song Liu" <songliubraving@fb•com>, "Yonghong Song" <yhs@fb•com>,
"KP Singh" <kpsingh@kernel•org>,
"Willem de Bruijn" <willemb@google•com>,
"Xie He" <xie.he.0141@gmail•com>,
"Eric Dumazet" <edumazet@google•com>,
"John Ogness" <john.ogness@linutronix•de>,
"Wang Hai" <wanghai38@huawei•com>,
"Tanner Love" <tannerlove@google•com>,
"Eyal Birger" <eyal.birger@gmail•com>,
"Menglong Dong" <dong.menglong@zte•com.cn>,
"Network Development" <netdev@vger•kernel.org>,
bpf <bpf@vger•kernel.org>
Subject: Re: [PATCH bpf-next] xsk: support AF_PACKET
Date: Fri, 28 May 2021 12:54:49 +0200 [thread overview]
Message-ID: <87a6ofgmbq.fsf@toke.dk> (raw)
In-Reply-To: <f90b1066-a962-ba38-a5b5-ac59a13d4dd1@iogearbox.net>
Daniel Borkmann <daniel@iogearbox•net> writes:
> On 5/28/21 12:00 PM, Magnus Karlsson wrote:
>> On Fri, May 28, 2021 at 11:52 AM Jesper Dangaard Brouer
>> <brouer@redhat•com> wrote:
>>> On Fri, 28 May 2021 17:02:01 +0800
>>> Xuan Zhuo <xuanzhuo@linux•alibaba.com> wrote:
>>>> On Fri, 28 May 2021 10:55:58 +0200, Toke Høiland-Jørgensen <toke@redhat•com> wrote:
>>>>> Xuan Zhuo <xuanzhuo@linux•alibaba.com> writes:
>>>>>
>>>>>> In xsk mode, users cannot use AF_PACKET(tcpdump) to observe the current
>>>>>> rx/tx data packets. This feature is very important in many cases. So
>>>>>> this patch allows AF_PACKET to obtain xsk packages.
>>>>>
>>>>> You can use xdpdump to dump the packets from the XDP program before it
>>>>> gets redirected into the XSK:
>>>>> https://github.com/xdp-project/xdp-tools/tree/master/xdp-dump
>>>>
>>>> Wow, this is a good idea.
>>>
>>> Yes, it is rather cool (credit to Eelco). Notice the extra info you
>>> can capture from 'exit', like XDP return codes, if_index, rx_queue.
>>>
>>> The tool uses the perf ring-buffer to send/copy data to userspace.
>>> This is actually surprisingly fast, but I still think AF_XDP will be
>>> faster (but it usually 'steals' the packet).
>>>
>>> Another (crazy?) idea is to extend this (and xdpdump), is to leverage
>>> Hangbin's recent XDP_REDIRECT extension e624d4ed4aa8 ("xdp: Extend
>>> xdp_redirect_map with broadcast support"). We now have a
>>> xdp_redirect_map flag BPF_F_BROADCAST, what if we create a
>>> BPF_F_CLONE_PASS flag?
>>>
>>> The semantic meaning of BPF_F_CLONE_PASS flag is to copy/clone the
>>> packet for the specified map target index (e.g AF_XDP map), but
>>> afterwards it does like veth/cpumap and creates an SKB from the
>>> xdp_frame (see __xdp_build_skb_from_frame()) and send to netstack.
>>> (Feel free to kick me if this doesn't make any sense)
>>
>> This would be a smooth way to implement clone support for AF_XDP. If
>> we had this and someone added AF_XDP support to libpcap, we could both
>> capture AF_XDP traffic with tcpdump (using this clone functionality in
>> the XDP program) and speed up tcpdump for dumping traffic destined for
>> regular sockets. Would that solve your use case Xuan? Note that I have
>> not looked into the BPF_F_CLONE_PASS code, so do not know at this
>> point what it would take to support this for XSKMAPs.
>
> Recently also ended up with something similar for our XDP LB to record pcaps [0] ;)
> My question is.. tcpdump doesn't really care where the packet data comes from,
> so why not extending libpcap's Linux-related internals to either capture from
> perf RB or BPF ringbuf rather than AF_PACKET sockets? Cloning is slow, and if
> you need to end up creating an skb which is then cloned once again inside AF_PACKET
> it's even worse. Just relying and reading out, say, perf RB you don't need any
> clones at all.
We discussed this when creating xdpdump and decided to keep it as a
separate tool for the time being. I forget the details of the
discussion, maybe Eelco remembers.
Anyway, xdpdump does have a "pipe pcap to stdout" feature so you can do
`xdpdump | tcpdump` and get the interactive output; and it will also
save pcap information to disk, of course (using pcap-ng so it can also
save metadata like XDP program name and return code).
-Toke
next prev parent reply other threads:[~2021-05-28 10:54 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-28 6:08 [PATCH bpf-next] xsk: support AF_PACKET Xuan Zhuo
2021-05-28 8:27 ` kernel test robot
2021-05-28 8:34 ` kernel test robot
2021-05-28 8:55 ` Toke Høiland-Jørgensen
[not found] ` <1622192521.5931044-1-xuanzhuo@linux.alibaba.com>
2021-05-28 9:25 ` Toke Høiland-Jørgensen
2021-05-28 9:32 ` Maciej Fijalkowski
2021-05-28 9:50 ` Jesper Dangaard Brouer
2021-05-28 10:00 ` Magnus Karlsson
2021-05-28 10:22 ` Daniel Borkmann
2021-05-28 10:54 ` Toke Høiland-Jørgensen [this message]
2021-05-28 11:29 ` Daniel Borkmann
2021-05-28 12:35 ` Toke Høiland-Jørgensen
2021-05-28 12:23 ` Jesper Dangaard Brouer
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