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

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Message-ID: <20200512230600.dxuvhy6cvwpkvlc5@ast-mbp>
Date:   Tue, 12 May 2020 16:06:00 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.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

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.