netdev - Re: [PATCH bpf-next 1/3] bpf: preserve command of the process that loaded the program

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Date:   Fri, 11 Oct 2019 17:38:19 -0700
From:   Stanislav Fomichev <sdf@...ichev.me>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Stanislav Fomichev <sdf@...gle.com>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH bpf-next 1/3] bpf: preserve command of the process that
 loaded the program

On 10/11, Alexei Starovoitov wrote:
> On Fri, Oct 11, 2019 at 9:21 AM Stanislav Fomichev <sdf@...gle.com> wrote:
> >
> > Even though we have the pointer to user_struct and can recover
> > uid of the user who has created the program, it usually contains
> > 0 (root) which is not very informative. Let's store the comm of the
> > calling process and export it via bpf_prog_info. This should help
> > answer the question "which process loaded this particular program".
> >
> > Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> > ---
> >  include/linux/bpf.h      | 1 +
> >  include/uapi/linux/bpf.h | 2 ++
> >  kernel/bpf/syscall.c     | 4 ++++
> >  3 files changed, 7 insertions(+)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index 5b9d22338606..b03ea396afe5 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -421,6 +421,7 @@ struct bpf_prog_aux {
> >                 struct work_struct work;
> >                 struct rcu_head rcu;
> >         };
> > +       char created_by_comm[BPF_CREATED_COMM_LEN];
> >  };
> >
> >  struct bpf_array {
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index a65c3b0c6935..4e883ecbba1e 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -326,6 +326,7 @@ enum bpf_attach_type {
> >  #define BPF_F_NUMA_NODE                (1U << 2)
> >
> >  #define BPF_OBJ_NAME_LEN 16U
> > +#define BPF_CREATED_COMM_LEN   16U
> 
> Nack.
> 16 bytes is going to be useless.
> We found it the hard way with prog_name.
> If you want to embed additional debug information
> please use BTF for that.
BTF was my natural choice initially, but then I saw created_by_uid and
thought created_by_comm might have a chance :-)

To clarify, by BTF you mean creating some unused global variable
and use its name as the debugging info? Or there is some better way?