netdev - Re: [PATCH bpf-next v4 09/27] bpf: Add support to load multi func tracing program

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Date:   Wed, 1 Sep 2021 13:32:43 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>, Daniel Xu <dxu@...uu.xyz>,
        Viktor Malik <vmalik@...hat.com>
Subject: Re: [PATCH bpf-next v4 09/27] bpf: Add support to load multi func
 tracing program

On Tue, Aug 31, 2021 at 04:17:33PM -0700, Andrii Nakryiko wrote:
> On Thu, Aug 26, 2021 at 12:40 PM Jiri Olsa <jolsa@...hat.com> wrote:
> >
> > Adding support to load tracing program with new BPF_F_MULTI_FUNC flag,
> > that allows the program to be loaded without specific function to be
> > attached to.
> 
> Are there any benefits to using a new load flag vs having separate
> expected attach types like FENTRY_MULTI/FEXIT_MULTI? I find load flags
> a bigger pain to work with compared to expected attach type (and
> expected attach type should be more apparent in BPF link info, bpftool
> output, etc).

it means more of the additional code, with the flag we just reuse
BPF_TRACE_FENTRY/BPF_TRACE_FEXIT related code because we use
current trampoline paths

I recall trying that approach while back, but ended up with bigger
changes that seemed unnecessary, I can dig it up to get more
details

jirka

> 
> >
> > Such program will be allowed to be attached to multiple functions
> > in following patches.
> >
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> >  include/linux/bpf.h            |  1 +
> >  include/uapi/linux/bpf.h       |  7 +++++++
> >  kernel/bpf/syscall.c           | 35 +++++++++++++++++++++++++++++-----
> >  kernel/bpf/verifier.c          |  3 ++-
> >  tools/include/uapi/linux/bpf.h |  7 +++++++
> >  5 files changed, 47 insertions(+), 6 deletions(-)
> >
> 
> [...]
>