Re: [PATCHv3 net-next] sctp: add support for SCTP_REUSE_PORT sockopt

[David Miller <davem@davemloft.net>]

From: Xin Long <lucien.xin@gmail.com>
Date: Thu, 28 Jun 2018 15:31:00 +0800

> This feature is actually already supported by sk->sk_reuse which can be
> set by socket level opt SO_REUSEADDR. But it's not working exactly as
> RFC6458 demands in section 8.1.27, like:
> 
>   - This option only supports one-to-one style SCTP sockets
>   - This socket option must not be used after calling bind()
>     or sctp_bindx().
> 
> Besides, SCTP_REUSE_PORT sockopt should be provided for user's programs.
> Otherwise, the programs with SCTP_REUSE_PORT from other systems will not
> work in linux.
> 
> To separate it from the socket level version, this patch adds 'reuse' in
> sctp_sock and it works pretty much as sk->sk_reuse, but with some extra
> setup limitations that are needed when it is being enabled.
> 
> "It should be noted that the behavior of the socket-level socket option
> to reuse ports and/or addresses for SCTP sockets is unspecified", so it
> leaves SO_REUSEADDR as is for the compatibility.
> 
> Note that the name SCTP_REUSE_PORT is somewhat confusing, as its
> functionality is nearly identical to SO_REUSEADDR, but with some
> extra restrictions. Here it uses 'reuse' in sctp_sock instead of
> 'reuseport'. As for sk->sk_reuseport support for SCTP, it will be
> added in another patch.
> 
> Thanks to Neil to make this clear.
> 
> v1->v2:
>   - add sctp_sk->reuse to separate it from the socket level version.
> v2->v3:
>   - improve changelog according to Marcelo's suggestion.
> 
> Acked-by: Neil Horman <nhorman@tuxdriver.com>
> Signed-off-by: Xin Long <lucien.xin@gmail.com>

Applied, thanks for working on getting the semantics right.