On Tue, May 12, 2020 at 10:34:58AM +0200, Toke Høiland-Jørgensen wrote:

Alexei Starovoitov [off-list ref] writes:

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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.