Subject: Re: [PATCH RFC] Userspace library for handling multiple XDP programs on an interface

From: Toke Høiland-Jørgensen <[email-masked]>
Date: Tue, 03 Mar 2020 17:27:34 +0100

Alexei Starovoitov <[email-masked]> writes:

> On Tue, Mar 3, 2020 at 1:50 AM Toke Høiland-Jørgensen <[email-masked]> wrote:
>>
>> This is the reason why I think the 'link' between the main program and
>> the replacement program is in the "wrong direction". Instead I want to
>> introduce a new attachment API that can be used instead of
>> bpf_raw_tracepoint_open() - something like:
>>
>> prog_fd = sys_bpf(BPF_PROG_LOAD, ...); // dispatcher
>> func_fd = sys_bpf(BPF_PROG_LOAD, ...); // replacement func
>> err = sys_bpf(BPF_PROG_REPLACE_FUNC, prog_fd, btf_id, func_fd); // does *not* return an fd
>>
>> When using this, the kernel will flip the direction of the reference
>> between BPF programs, so it goes main_prog -> replacement_prog. And
>> instead of getting an fd back, this will make the replacement prog share
>> its lifecycle with the main program, so that when the main program is
>> released, so is the replacement (absent other references, of course).
>> There could be an explicit 'release' command as well, of course, and a
>> way to list all replacements on a program.
>
> Nack to such api.
> We hit this opposite direction issue with xdp and tc in the past.
> Not going to repeat the same mistake again.

Care to elaborate? What mistake, and what was the issue?

-Toke