support for multiple and dynamic addition of ebpf prog to xdp

[Sats]

Hi All,

I am looking to plug in multiple ebpf programs on xdp hook, so is there any support for it.
a. Adding multiple ebpf programs at xdp, apart from baf tail calls any other way to do?
b. Adding a program as bpf tail call dynamically to an already attached ebpf program on xdp.
I am using kernel version 5.8.0-43

Thanks,
Sachin

[Toke Høiland-Jørgensen]

sachints123 <[e-mail]> writes:

Hi All, I am looking to plug in multiple ebpf programs on xdp hook, so is there any support for it. a. Adding multiple ebpf programs at xdp, apart from baf tail calls any other way to do?

Yes! That's what libxdp does: https://github.com/xdp-project/xdp-tools You can use the command line xdp-loader utility to load programs this way, or the libxdp library to do so from an application. See the libxdp documentation (also the man page) for how to use this: https://github.com/xdp-project/xdp-tools/blob/master/lib/libxdp/README.org or this document for an explanation of how it works under the hood: https://github.com/xdp-project/xdp-tools/blob/master/lib/libxdp/protocol.org

b. Adding a program as bpf tail call dynamically to an already attached ebpf program on xdp.

This is not possible in general, but see above :)

I am using kernel version 5.8.0-43

One caveat is that with kernel 5.8, while you can attach multiple programs using libxdp as explained above, you can only do so if you attach all of them at once. The kernel support for attaching them incrementally (i.e., attach one, then later attach another) wasn't merged until 5.10. So with 5.8 you can do load(prog1, prog2), but not load(prog1), load(prog2). Also, you need to use libxdp to attach from the get-go, you can't "promote" an XDP program attached in the traditional way to one that supports multi-program, sadly. However, I've tried hard to make libxdp seamless to use so that this should be a huge barrier in practice. Please don't hesitate to open issues if you run into any problems!

[Sats]

Okay. I will go through libxdp. In this case I will upgrade to 5.10 and try.

1. Currently I am using python for user space program and loading xdp programs, looks like there is no libxdp support in python.
   With kernel 5.10, can I load existing xdp program from python and can I write one more user space prog in C to load and attach another xdp program dynamically?.
   How the sequence of xdp progs is decided? Is it in the order of loading?

2. In one of the previous issues you mentioned xdp support for multicast and cloning is under dev. is it available in 5.10 ?

[Toke Høiland-Jørgensen]

sachints123 <[e-mail]> writes:

Okay. I will go through libxdp. In this case I will upgrade to 5.10 and try.

Yeah, that'll probably give you the best experience :)

1. Currently I am using python for user space program and loading xdp programs, looks like there is no libxdp support in python. With kernel 5.10, can I load existing xdp program from python and can I write one more user space prog in C to load and attach another xdp program dynamically?.

No, that's what I meant with "we can't promote existing programs" - everything has to go through libxdp from the get-go. It would in principle be possible to add Python bindings to libxdp, but I have no idea how difficult it is to do in practice; feel free to open an issue in the xdp-tools repository for this (or even better, contribute patches ;)). Until then, I think the easiest thing to do from Python would be to shell out to the command-line xdp-loader.

How the sequence of xdp progs is decided? Is it in the order of loading?

Programs are sorted by priority. The priority can be specified in the object file at compile time, and overridden from libxdp at load time. See the libxdp man page for details.

2. In one of the previous issues you mentioned xdp support for multicast and cloning is under dev. is it available in 5.10 ?

Nope. It's very close to done, but the patches just missed the 5.12 merge window; so I guess this will land in 5.13...

[Sats]

ok, thank you.
I will explore command line tool.
Yeah, i will open an issue and also try to look into the existing python binding implementation of libbpf, to know the complexity of it.