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Wed, 16 Sep 2020 14:27:05 -0700 (PDT) Received: from alrua-x1.borgediget.toke.dk ([2a0c:4d80:42:443::2]) by smtp.gmail.com with ESMTPSA id t22sm8919184wmt.1.2020.09.16.14.27.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 16 Sep 2020 14:27:04 -0700 (PDT) Received: by alrua-x1.borgediget.toke.dk (Postfix, from userid 1000) id 86742183A90; Wed, 16 Sep 2020 23:27:04 +0200 (CEST) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= To: Andrii Nakryiko Cc: Alexei Starovoitov , Daniel Borkmann , Martin KaFai Lau , Song Liu , Yonghong Song , Andrii Nakryiko , John Fastabend , Jiri Olsa , Eelco Chaudron , KP Singh , Networking , bpf Subject: Re: [PATCH bpf-next v5 4/8] bpf: support attaching freplace programs to multiple attach points In-Reply-To: References: <160017005691.98230.13648200635390228683.stgit@toke.dk> <160017006133.98230.8867570651560085505.stgit@toke.dk> <87r1r1pgr5.fsf@toke.dk> X-Clacks-Overhead: GNU Terry Pratchett Date: Wed, 16 Sep 2020 23:27:04 +0200 Message-ID: <87een1pg47.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Andrii Nakryiko writes: > On Wed, Sep 16, 2020 at 2:13 PM Toke H=C3=B8iland-J=C3=B8rgensen wrote: >> >> >> [ will fix all your comments above ] >> >> >> @@ -3924,10 +3983,16 @@ static int tracing_bpf_link_attach(const unio= n bpf_attr *attr, struct bpf_prog * >> >> prog->expected_attach_type =3D=3D BPF_TRACE_ITER) >> >> return bpf_iter_link_attach(attr, prog); >> >> >> >> + if (attr->link_create.attach_type =3D=3D BPF_TRACE_FREPLACE && >> >> + !prog->expected_attach_type) >> >> + return bpf_tracing_prog_attach(prog, >> >> + attr->link_create.targ= et_fd, >> >> + attr->link_create.targ= et_btf_id); >> > >> > Hm.. so you added a "fake" BPF_TRACE_FREPLACE attach_type, which is >> > not really set with BPF_PROG_TYPE_EXT and is only specified for the >> > LINK_CREATE command. Are you just trying to satisfy the link_create >> > flow of going from attach_type to program type? If that's the only >> > reason, I think we can adjust link_create code to handle this more >> > flexibly. >> > >> > I need to think a bit more whether we want BPF_TRACE_FREPLACE at all, >> > but if we do, whether we should make it an expected_attach_type for >> > BPF_PROG_TYPE_EXT then... >> >> Yeah, wasn't too sure about this. But attach_type seemed to be the only >> way to disambiguate between the different link types in the LINK_CREATE >> command, so went with that. Didn't think too much about it, TBH :) > > having extra attach types has real costs in terms of memory (in cgroup > land), which no one ever got to fixing yet. And then > prog->expected_attach_type !=3D link's expected_attach_type looks weird > and wrong and who knows which bugs we'll get later because of this. > >> >> I guess an alternative could be to just enforce attach_type=3D=3D0 and l= ook >> at prog->type? Or if you have any other ideas, I'm all ears! > > Right, we have prog fd, so can get it (regardless of type), then do > switch by type, then translate expected attach type to prog type and > see if it matches, but only for program types that care (which right > now is all but tracing, where it's obvious from prog_type alone, I > think). Right, makes sense; will do that in the next version! -Toke