netdev - Re: [PATCH bpf-next] bpf: support SO_DEBUG in bpf

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Date:   Tue, 5 Feb 2019 23:44:21 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     kafai@...com, brakmo@...com, ast@...nel.org, daniel@...earbox.net,
        netdev <netdev@...r.kernel.org>, shaoyafang@...iglobal.com
Subject: Re: [PATCH bpf-next] bpf: support SO_DEBUG in bpf_setsockopt()

On Tue, Feb 5, 2019 at 1:35 AM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Sun, Feb 03, 2019 at 04:15:07PM +0800, Yafang Shao wrote:
> > Then we can enable/disable socket debugging without modifying user code.
> > That is more convenient for debugging.
> >
> > Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> > ---
> >  include/net/sock.h | 8 ++++++++
> >  net/core/filter.c  | 3 +++
> >  net/core/sock.c    | 8 --------
> >  3 files changed, 11 insertions(+), 8 deletions(-)
> >
> > diff --git a/include/net/sock.h b/include/net/sock.h
> > index 2b229f7..8decee9 100644
> > --- a/include/net/sock.h
> > +++ b/include/net/sock.h
> > @@ -1935,6 +1935,14 @@ static inline void sock_confirm_neigh(struct sk_buff *skb, struct neighbour *n)
> >       }
> >  }
> >
> > +static inline void sock_valbool_flag(struct sock *sk, int bit, int valbool)
> > +{
> > +     if (valbool)
> > +             sock_set_flag(sk, bit);
> > +     else
> > +             sock_reset_flag(sk, bit);
> > +}
> > +
> >  bool sk_mc_loop(struct sock *sk);
> >
> >  static inline bool sk_can_gso(const struct sock *sk)
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index 3a49f68..ce5da57 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -4111,6 +4111,9 @@ static unsigned long bpf_xdp_copy(void *dst_buff, const void *src_buff,
> >
> >               /* Only some socketops are supported */
> >               switch (optname) {
> > +             case SO_DEBUG:
> > +                     sock_valbool_flag(sk, SOCK_DBG, val);
> > +                     break;
>
> I'm missing the point here.
> This flag has any effect only when SOCK_DEBUGGING is set.
> But it is off in distros.

It's not off in distros. At least it is set in RHEL.
Pls. see the comment in include/net/sock.h,
    /* Define this to get the SOCK_DBG debugging facility. */
    #define SOCK_DEBUGGING

> Since it's for custom debug kernel only why bother with
> setting the flag via bpf prog?
>