netdev - Re: [PATCH 08/13] bpf: Add kprobe link for attaching raw kprobes

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Date:   Thu, 6 Jan 2022 08:32:18 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        lkml <linux-kernel@...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>,
        Steven Rostedt <rostedt@...dmis.org>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 08/13] bpf: Add kprobe link for attaching raw kprobes

On Thu, Jan 6, 2022 at 12:41 AM Jiri Olsa <jolsa@...hat.com> wrote:
>
> On Wed, Jan 05, 2022 at 08:30:56PM -0800, Andrii Nakryiko wrote:
> > On Tue, Jan 4, 2022 at 12:10 AM Jiri Olsa <jolsa@...hat.com> wrote:
> > >
> > > Adding new link type BPF_LINK_TYPE_KPROBE to attach kprobes
> > > directly through register_kprobe/kretprobe API.
> > >
> > > Adding new attach type BPF_TRACE_RAW_KPROBE that enables
> > > such link for kprobe program.
> > >
> > > The new link allows to create multiple kprobes link by using
> > > new link_create interface:
> > >
> > >   struct {
> > >     __aligned_u64   addrs;
> > >     __u32           cnt;
> > >     __u64           bpf_cookie;
> >
> > I'm afraid bpf_cookie has to be different for each addr, otherwise
> > it's severely limiting. So it would be an array of cookies alongside
> > an array of addresses
>
> ok
>
> >
> > >   } kprobe;
> > >
> > > Plus new flag BPF_F_KPROBE_RETURN for link_create.flags to
> > > create return probe.
> > >
> > > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > > ---
> > >  include/linux/bpf_types.h      |   1 +
> > >  include/uapi/linux/bpf.h       |  12 +++
> > >  kernel/bpf/syscall.c           | 191 ++++++++++++++++++++++++++++++++-
> > >  tools/include/uapi/linux/bpf.h |  12 +++
> > >  4 files changed, 211 insertions(+), 5 deletions(-)
> > >
> >
> > [...]
> >
> > > @@ -1111,6 +1113,11 @@ enum bpf_link_type {
> > >   */
> > >  #define BPF_F_SLEEPABLE                (1U << 4)
> > >
> > > +/* link_create flags used in LINK_CREATE command for BPF_TRACE_RAW_KPROBE
> > > + * attach type.
> > > + */
> > > +#define BPF_F_KPROBE_RETURN    (1U << 0)
> > > +
> >
> > we have plenty of flexibility to have per-link type fields, so why not
> > add `bool is_retprobe` next to addrs and cnt?
>
> well I thought if I do that, people would suggest to use the empty
> flags field instead ;-)
>
> we can move it there as you suggest, but I wonder it's good idea to
> use bool in uapi headers, because the bool size definition is vague

Good point. No 'bool' please.
grep bool include/uapi/linux/
Only gives openvswitch.h and it's guarded by ifdef KERNEL
So not a single uapi header has bool in it.