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

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Date:   Mon, 4 Feb 2019 09:35:22 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     kafai@...com, brakmo@...com, ast@...nel.org, daniel@...earbox.net,
        netdev@...r.kernel.org, shaoyafang@...iglobal.com
Subject: Re: [PATCH bpf-next] bpf: support SO_DEBUG in bpf_setsockopt()

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