Re: [PATCH] inet: add bound ports statistic

[Eric Dumazet <eric.dumazet@gmail.com>]

On Wed, 2018-02-28 at 18:01 -0800, Stephen Hemminger wrote:
> This adds a number of bound ports in a network namespace which is
> a useful for socket summary (ss) command. It adds one additional
> field onto /proc/net/sockstat.
> 
> Since collecting these kind of counters can be sensitive for large
> machines, the impact is placed on the reading side which will be
> much rarer.
> 
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
>  include/net/inet_connection_sock.h |  2 +-
>  net/ipv4/inet_connection_sock.c    | 22 ++++++++++++++++++++++
>  net/ipv4/proc.c                    |  5 +++--
>  3 files changed, 26 insertions(+), 3 deletions(-)
> 
> diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
> index c1a93ce35e62..3044deec73ce 100644
> --- a/include/net/inet_connection_sock.h
> +++ b/include/net/inet_connection_sock.h
> @@ -265,7 +265,7 @@ inet_csk_rto_backoff(const struct inet_connection_sock *icsk,
>  }
>  
>  struct sock *inet_csk_accept(struct sock *sk, int flags, int *err, bool kern);
> -
> +unsigned int inet_csk_count_ports(struct net *net, struct proto *prot);
>  int inet_csk_get_port(struct sock *sk, unsigned short snum);
>  
>  struct dst_entry *inet_csk_route_req(const struct sock *sk, struct flowi4 *fl4,
> diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
> index 881ac6d046f2..2418abce4d50 100644
> --- a/net/ipv4/inet_connection_sock.c
> +++ b/net/ipv4/inet_connection_sock.c
> @@ -424,6 +424,28 @@ static int inet_csk_wait_for_connect(struct sock *sk, long timeo)
>  	return err;
>  }
>  
> +/* Count how many any entries are in the bind hash table */

How useful it is to report this information ?

Given REUSEADDR and REUSEPORT, I really wonder what can be derived from
this counter.

It seems its semantic is weak.