netdev - Re: bpf: ability to attach freplace to multiple parents

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Message-ID: <87h7wlwnyl.fsf@toke.dk>
Date:   Tue, 12 May 2020 10:34:58 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Andrey Ignatov <rdna@...com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: bpf: ability to attach freplace to multiple parents

Alexei Starovoitov <alexei.starovoitov@...il.com> writes:

>> > Currently fentry/fexit/freplace progs have single prog->aux->linked_prog pointer.
>> > It just needs to become a linked list.
>> > The api extension could be like this:
>> > bpf_raw_tp_open(prog_fd, attach_prog_fd, attach_btf_id);
>> > (currently it's just bpf_raw_tp_open(prog_fd))
>> > The same pair of (attach_prog_fd, attach_btf_id) is already passed into prog_load
>> > to hold the linked_prog and its corresponding btf_id.
>> > I'm proposing to extend raw_tp_open with this pair as well to
>> > attach existing fentry/fexit/freplace prog to another target.
>> > Internally the kernel verify that btf of current linked_prog
>> > exactly matches to btf of another requested linked_prog and
>> > if they match it will attach the same prog to two target programs (in case of freplace)
>> > or two kernel functions (in case of fentry/fexit).
>> 
>> API-wise this was exactly what I had in mind as well.
>
> perfect!

Hi Alexei

I don't suppose you've had a chance to whip up a patch for this, have
you? :)

-Toke