Re: [PATCH bpf-next v4 0/2] libbpf: adding AF_XDP support

[Magnus Karlsson <magnus.karlsson@gmail.com>]

On Mon, Feb 11, 2019 at 9:44 PM Jonathan Lemon <jonathan.lemon@gmail.com> wrote:
>
> On 8 Feb 2019, at 5:05, Magnus Karlsson wrote:
>
> > This patch proposes to add AF_XDP support to libbpf. The main reason
> > for this is to facilitate writing applications that use AF_XDP by
> > offering higher-level APIs that hide many of the details of the AF_XDP
> > uapi. This is in the same vein as libbpf facilitates XDP adoption by
> > offering easy-to-use higher level interfaces of XDP
> > functionality. Hopefully this will facilitate adoption of AF_XDP, make
> > applications using it simpler and smaller, and finally also make it
> > possible for applications to benefit from optimizations in the AF_XDP
> > user space access code. Previously, people just copied and pasted the
> > code from the sample application into their application, which is not
> > desirable.
>
> I like the idea of encapsulating the boilerplate logic in a library.
>
> I do think there is an important missing piece though - there should be
> some code which queries the netdev for how many queues are attached, and
> create the appropriate number of umem/AF_XDP sockets.
>
> I ran into this issue when testing the current AF_XDP code - on my test
> boxes, the mlx5 card has 55 channels (aka queues), so when the test program
> binds only to channel 0, nothing works as expected, since not all traffic
> is being intercepted.  While obvious in hindsight, this took a while to
> track down.

Yes, agreed. You are not the first one to stumble upon this problem
:-). Let me think a little bit on how to solve this in a good way. We
need this to be simple and intuitive, as you say.

/Magnus

> --
> Jonathan