XDP chain using tail calls

XDP chain using tail calls

[Radu Stoenescu]

Hello

I was recently reading through the XDP documentation from Cilium[1]
and I couldn't really wrap my head around the tail cal section.

Is there any tutorial/code example of using this feature with XDP?

Regards
-- 
Radu Stoenescu

[1]: https://docs.cilium.io/en/v1.4/bpf/

Re: XDP chain using tail calls

[Taeung Song]

Hi Radu Stoenescu,

You can run 'BPF tail call' examples at samples/bpf of kernel source
That are sockex3_kern.c or tracex5_kern.c
I think it'd be better to understand it if running tracex5
that just uses bpf_tail_call() helper function for a BPF prog
depending on syscall number.

Thanks,
Taeung

On 4/17/19 10:11 PM, Radu Stoenescu wrote:
> Hello
> 
> I was recently reading through the XDP documentation from Cilium[1]
> and I couldn't really wrap my head around the tail cal section.
> 
> Is there any tutorial/code example of using this feature with XDP?
> 
> Regards
> 

Re: XDP chain using tail calls

[Toke Høiland-Jørgensen]

Taeung Song <treeze.taeung@gmail.com> writes:

> Hi Radu Stoenescu,
>
> You can run 'BPF tail call' examples at samples/bpf of kernel source
> That are sockex3_kern.c or tracex5_kern.c
> I think it'd be better to understand it if running tracex5
> that just uses bpf_tail_call() helper function for a BPF prog
> depending on syscall number.

Oh, there are actually some of the samples that include tail calls.
Guess my grepping foo failed me... Cool :)

-Toke

Re: XDP chain using tail calls

[Radu Stoenescu]

Thank you!

If you think this might be useful, I could bring it to the xdp-tutorial repo.

It's a bit tricky to find those, I did managed to find the in the
meantime via the kernel commit that introduced them:
https://lwn.net/Articles/645169/

Best,
Radu

On Wed, Apr 17, 2019 at 4:27 PM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> Taeung Song <treeze.taeung@gmail.com> writes:
>
> > Hi Radu Stoenescu,
> >
> > You can run 'BPF tail call' examples at samples/bpf of kernel source
> > That are sockex3_kern.c or tracex5_kern.c
> > I think it'd be better to understand it if running tracex5
> > that just uses bpf_tail_call() helper function for a BPF prog
> > depending on syscall number.
>
> Oh, there are actually some of the samples that include tail calls.
> Guess my grepping foo failed me... Cool :)
>
> -Toke



-- 
Radu Stoenescu

Re: XDP chain using tail calls

[Toke Høiland-Jørgensen]

Radu Stoenescu <radu.stoe@gmail.com> writes:

> Thank you!
>
> If you think this might be useful, I could bring it to the
> xdp-tutorial repo.

Please do! This is definitely something we should cover :)

-Toke

Re: XDP chain using tail calls

[Toke Høiland-Jørgensen]

Radu Stoenescu <radu.stoe@gmail.com> writes:

> Hello
>
> I was recently reading through the XDP documentation from Cilium[1]
> and I couldn't really wrap my head around the tail cal section.
>
> Is there any tutorial/code example of using this feature with XDP?

Hmm, I'm not sure there are any current examples. But you make a good
point, we should probably have one. We're building an interactive
tutorial here: https://github.com/xdp-project/xdp-tutorial - please feel
free to open an issue here requesting it to be added! :)

-Toke

Re: XDP chain using tail calls

[Daniel Borkmann]

On 04/17/2019 03:26 PM, Toke Høiland-Jørgensen wrote:
> Radu Stoenescu <radu.stoe@gmail.com> writes:
> 
>> Hello
>>
>> I was recently reading through the XDP documentation from Cilium[1]
>> and I couldn't really wrap my head around the tail cal section.
>>
>> Is there any tutorial/code example of using this feature with XDP?
> 
> Hmm, I'm not sure there are any current examples. But you make a good
> point, we should probably have one. We're building an interactive
> tutorial here: https://github.com/xdp-project/xdp-tutorial - please feel
> free to open an issue here requesting it to be added! :)

Wrt iproute2, there's some simple examples to start here:

  https://git.kernel.org/pub/scm/network/iproute2/iproute2.git/tree/examples/bpf

If you need more elaborate ones, you might want to check out:

  https://github.com/cilium/cilium/tree/master/bpf

Cheers,
Daniel