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Date:   Wed, 13 May 2020 12:25:09 +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:

> On Tue, May 12, 2020 at 10:34:58AM +0200, Toke Høiland-Jørgensen wrote:
>> 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? :)
>
> On my priority list it's after cap_bpf and sleepable.
> If it's urgent for you please start hacking.

OK, ACK. Not extremely urgent right now, just wanted to check in with
what your plans were. Thanks for letting me know!

-Toke

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