Subject: Re: [PATCH 31/33] sctp: add sctp_sock_set_nodelay

From: Marcelo Ricardo Leitner <[email-masked]>
Date: Wed, 20 May 2020 20:10:01 -0300

On Wed, May 20, 2020 at 09:55:07PM +0200, Christoph Hellwig wrote:
> Add a helper to directly set the SCTP_NODELAY sockopt from kernel space
> without going through a fake uaccess.
> 
> Signed-off-by: Christoph Hellwig <[email-masked]>
> ---
>  fs/dlm/lowcomms.c       | 10 ++--------
>  include/net/sctp/sctp.h |  7 +++++++
>  2 files changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/dlm/lowcomms.c b/fs/dlm/lowcomms.c
> index 69333728d871b..9f1c3cdc9d653 100644
> --- a/fs/dlm/lowcomms.c
> +++ b/fs/dlm/lowcomms.c
> @@ -914,7 +914,6 @@ static int sctp_bind_addrs(struct connection *con, uint16_t port)
>  static void sctp_connect_to_sock(struct connection *con)
>  {
>  	struct sockaddr_storage daddr;
> -	int one = 1;
>  	int result;
>  	int addr_len;
>  	struct socket *sock;
> @@ -961,8 +960,7 @@ static void sctp_connect_to_sock(struct connection *con)
>  	log_print("connecting to %d", con->nodeid);
>  
>  	/* Turn off Nagle's algorithm */
> -	kernel_setsockopt(sock, SOL_SCTP, SCTP_NODELAY, (char *)&one,
> -			  sizeof(one));
> +	sctp_sock_set_nodelay(sock->sk);
>  
>  	/*
>  	 * Make sock->ops->connect() function return in specified time,
> @@ -1176,7 +1174,6 @@ static int sctp_listen_for_all(void)
>  	struct socket *sock = NULL;
>  	int result = -EINVAL;
>  	struct connection *con = nodeid2con(0, GFP_NOFS);
> -	int one = 1;
>  
>  	if (!con)
>  		return -ENOMEM;
> @@ -1191,10 +1188,7 @@ static int sctp_listen_for_all(void)
>  	}
>  
>  	sock_set_rcvbuf(sock->sk, NEEDED_RMEM);
> -	result = kernel_setsockopt(sock, SOL_SCTP, SCTP_NODELAY, (char *)&one,
> -				   sizeof(one));
> -	if (result < 0)
> -		log_print("Could not set SCTP NODELAY error %d\n", result);
> +	sctp_sock_set_nodelay(sock->sk);
>  
>  	write_lock_bh(&sock->sk->sk_callback_lock);
>  	/* Init con struct */
> diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
> index 3ab5c6bbb90bd..f8bcb75bb0448 100644
> --- a/include/net/sctp/sctp.h
> +++ b/include/net/sctp/sctp.h
> @@ -615,4 +615,11 @@ static inline bool sctp_newsk_ready(const struct sock *sk)
>  	return sock_flag(sk, SOCK_DEAD) || sk->sk_socket;
>  }
>  
> +static inline void sctp_sock_set_nodelay(struct sock *sk)
> +{
> +	lock_sock(sk);
> +	sctp_sk(sk)->nodelay = true;
> +	release_sock(sk);
> +}
> +

The duplication with sctp_setsockopt_nodelay() is quite silly/bad.
Also, why have the 'true' hardcoded? It's what dlm uses, yes, but the
API could be a bit more complete than that.

Like for the other patch, this one could build on David's patch, do
the ternary check before calling sctp_setsockopt_nodelay and then move
sctp_setsockopt_nodelay to the header, or something like that.