From: Daniel Borkmann <daniel@iogearbox•net>
To: Jesper Dangaard Brouer <brouer@redhat•com>,
John Fastabend <john.fastabend@gmail•com>
Cc: Daniel Borkmann <borkmann@iogearbox•net>,
Alexei Starovoitov <alexei.starovoitov@gmail•com>,
Alexei Starovoitov <ast@fb•com>,
"netdev@vger•kernel.org" <netdev@vger•kernel.org>,
"xdp-newbies@vger•kernel.org" <xdp-newbies@vger•kernel.org>
Subject: Re: XDP question: best API for returning/setting egress port?
Date: Wed, 19 Apr 2017 14:33:27 +0200 [thread overview]
Message-ID: <58F75917.1050409@iogearbox.net> (raw)
In-Reply-To: <20170419140019.366fb1fb@redhat.com>
On 04/19/2017 02:00 PM, Jesper Dangaard Brouer wrote:
> On Tue, 18 Apr 2017 13:54:45 -0700
> John Fastabend <john.fastabend@gmail•com> wrote:
>> On 17-04-18 12:58 PM, Jesper Dangaard Brouer wrote:
>>>
>>> As I argued in NetConf presentation[1] (from slide #9) we need a port
>>> mapping table (instead of using ifindex'es). Both for supporting
>>> other "port" types than net_devices (think sockets), and for
>>> sandboxing what XDP can bypass.
>>>
>>> I want to create a new XDP action called XDP_REDIRECT, that instruct
>>> XDP to send the xdp_buff to another "port" (get translated into a
>>> net_device, or something else depending on internal port type).
>>>
>>> Looking at the userspace/eBPF interface, I'm wondering what is the
>>> best API for "returning" this port number from eBPF?
>>>
>>> The options I see is:
>>>
>>> 1) Split-up the u32 action code, and e.g let the high-16-bit be the
>>> port number and lower-16bit the (existing) action verdict.
>>>
>>> Pros: Simple API
>>> Cons: Number of ports limited to 64K
>>>
>>> 2) Extend both xdp_buff + xdp_md to contain a (u32) port number, allow
>>> eBPF to update xdp_md->port.
>>>
>>> Pros: Larger number of ports.
>>> Cons: This require some ebpf translation steps between xdp_buff <-> xdp_md.
>>> (see xdp_convert_ctx_access)
>>>
>>> 3) Extend only xdp_buff and create bpf_helper that set port in xdp_buff.
>>>
>>> Pros: Hides impl details, and allows helper to give eBPF code feedback
>>> (on e.g. if port doesn't exist any longer)
>>> Cons: Helper function call likely slower?
>>
>> How about doing this the same way redirect is done in the tc case? I have this
>> patch under test,
>>
>> https://github.com/jrfastab/linux/commit/e78f5425d5e3c305b4170ddd85c61c2e15359fee
>
> I have been looking at this approach, which is close to option #3 above.
>
> The problem with your implementation that you use a per-cpu store.
> This creates the problem of storing state between packets. First packet
> can call helper bpf_xdp_redirect() setting an ifindex, but program can
> still return XDP_PASS. Next packet can call XDP_REDIRECT and use the
> ifindex set from the first packet. IMHO this is a problematic API to
> expose.
>
> I do see that the TC interface that uses the same approach, via helper
> bpf_redirect(). Maybe it have the same API problem? Looking at
> sch_handle_ingress() I don't see this is handled (e.g. by always
> clearing this_cpu_ptr(redirect_info)->ifindex = 0).
It's cleared in {skb,xdp}_do_redirect() right after fetching the
ifindex. I think this approach is just fine. The example described
above is a misuse of the API by a buggy program calling bpf_xdp_redirect()
and returning XDP_PASS while another time it returns XDP_REDIRECT
without the bpf_xdp_redirect() helper, sounds very exotic, but it's
as buggy as, say, a program doing the csum update wrong, a program
writing the wrong data to the packet, doing adjust head on the wrong
header offset, jumping into the wrong tail call entry and other things.
I think encoding this into an action code is rather limiting, f.e.
where would we place a flags argument if needed in future? Would
that mean, we need a XDP_REDIRECT2 return code that also allows for
encoding flags?
Thanks,
Daniel
next prev parent reply other threads:[~2017-04-19 12:33 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-18 19:58 XDP question: best API for returning/setting egress port? Jesper Dangaard Brouer
2017-04-18 20:54 ` John Fastabend
2017-04-19 12:00 ` Jesper Dangaard Brouer
2017-04-19 12:33 ` Daniel Borkmann [this message]
2017-04-19 15:24 ` Jesper Dangaard Brouer
2017-04-19 12:25 ` Hannes Frederic Sowa
2017-04-19 20:02 ` Andy Gospodarek
2017-04-19 21:42 ` Daniel Borkmann
2017-04-20 17:12 ` Andy Gospodarek
2017-04-19 22:51 ` Daniel Borkmann
2017-04-20 2:56 ` xdp_redirect ifindex vs port. Was: " Alexei Starovoitov
2017-04-20 4:38 ` John Fastabend
2017-04-20 4:58 ` Alexei Starovoitov
2017-04-20 5:14 ` John Fastabend
2017-04-20 6:10 ` Jesper Dangaard Brouer
2017-04-20 17:10 ` Alexei Starovoitov
2017-04-25 9:34 ` Jesper Dangaard Brouer
2017-04-26 0:26 ` Alexei Starovoitov
2017-04-26 3:07 ` John Fastabend
2017-04-26 9:11 ` Jesper Dangaard Brouer
2017-04-26 16:35 ` John Fastabend
2017-04-26 17:58 ` Alexei Starovoitov
2017-04-26 20:55 ` Andy Gospodarek
2017-04-27 8:41 ` Jesper Dangaard Brouer
2017-04-27 23:31 ` Alexei Starovoitov
2017-04-28 5:06 ` John Fastabend
2017-04-28 5:30 ` Alexei Starovoitov
2017-04-28 19:43 ` Hannes Frederic Sowa
2017-04-30 1:35 ` Alexei Starovoitov
2017-04-28 10:58 ` Jesper Dangaard Brouer
2017-04-30 1:04 ` Alexei Starovoitov
2017-04-30 22:55 ` John Fastabend
2017-04-20 6:39 ` XDP question: " Jesper Dangaard Brouer
2017-04-20 4:43 ` John Fastabend
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