Re: [PATCH 1/2] tcp, tcp_splice: Make helper for setting SO_LINGER socket option

[Jon Maloy <jmaloy@redhat.com>]

On 2026-05-13 03:18, David Gibson wrote:
 > Both spliced and non-spliced TCP in some cases set the SO_LINGER socket
 > option in order to to force a TCP RST on a socket side connection. 
In eachs/to to/to> case we open code the setsockopt() logic.  We're 
shortly going to add
 > another place that needs this, so move the setsockopt() and error 
handling
 > logic into a shared helper.
 >
 > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Jon Maloy <jmaloy@redhat.com>


On 2026-05-13 03:18, David Gibson wrote:
> Both spliced and non-spliced TCP in some cases set the SO_LINGER socket
> option in order to to force a TCP RST on a socket side connection.  In each

s/to to/to/
> case we open code the setsockopt() logic.  We're shortly going to add
> another place that needs this, so move the setsockopt() and error handling
> logic into a shared helper.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

Reviewed-by: Jon Maloy <jmaloy@redhat.com>

>   tcp.c        | 33 ++++++++++++++++++++-------------
>   tcp_conn.h   |  3 +++
>   tcp_splice.c | 20 +++-----------------
>   3 files changed, 26 insertions(+), 30 deletions(-)
> 
> diff --git a/tcp.c b/tcp.c
> index d6a9ba28..1078bdc3 100644
> --- a/tcp.c
> +++ b/tcp.c
> @@ -1395,29 +1395,36 @@ static int tcp_send_flag(const struct ctx *c, struct tcp_tap_conn *conn,
>   }
>   
>   /**
> - * tcp_sock_rst() - Close TCP connection forcing RST on socket side
> - * @c:		Execution context
> - * @conn:	Connection pointer
> + * tcp_linger0_() - Set SO_LINGER with 0 timeout on socket
> + * @f:		Flow header (only for debug logging)
> + * @s:		Socket to modify
>    */
> -static void tcp_sock_rst(const struct ctx *c, struct tcp_tap_conn *conn)
> +void tcp_linger0_(const struct flow_common *f, int s)
>   {
>   	const struct linger linger0 = {
>   		.l_onoff = 1,
>   		.l_linger = 0,
>   	};
>   
> -	/* Force RST on socket to inform the peer
> -	 *
> -	 * We do this by setting SO_LINGER with 0 timeout, which means that
> -	 * close() will send an RST (unless the connection is already closed in
> -	 * both directions).
> +	/* Setting SO_LINGER with 0 timeout, means that close() will send an RST
> +	 * (unless the connection is already closed in both directions).
>   	 */
> -	if (setsockopt(conn->sock, SOL_SOCKET,
> -		       SO_LINGER, &linger0, sizeof(linger0)) < 0) {
> -		flow_dbg_perror(conn,
> -				"SO_LINGER failed, may not send RST to peer");
> +	if (setsockopt(s, SOL_SOCKET, SO_LINGER,
> +		       &linger0, sizeof(linger0)) < 0) {
> +		flow_log_perror_(f, LOG_DEBUG,
> +				 "SO_LINGER failed, may not send RST to peer");
>   	}
> +}
>   
> +/**
> + * tcp_sock_rst() - Close TCP connection forcing RST on socket side
> + * @c:		Execution context
> + * @conn:	Connection pointer
> + */
> +static void tcp_sock_rst(const struct ctx *c, struct tcp_tap_conn *conn)
> +{
> +	/* Force RST on socket to inform the peer */
> +	tcp_linger0(conn, conn->sock);
>   	conn_event(c, conn, CLOSED);
>   }
>   
> diff --git a/tcp_conn.h b/tcp_conn.h
> index 9f5bee03..5f7af240 100644
> --- a/tcp_conn.h
> +++ b/tcp_conn.h
> @@ -241,6 +241,9 @@ struct tcp_splice_conn {
>   extern int init_sock_pool4	[TCP_SOCK_POOL_SIZE];
>   extern int init_sock_pool6	[TCP_SOCK_POOL_SIZE];
>   
> +void tcp_linger0_(const struct flow_common *f, int s);
> +#define tcp_linger0(flow_, s_)	tcp_linger0_(&(flow_)->f, (s_))
> +
>   bool tcp_flow_defer(const struct tcp_tap_conn *conn);
>   
>   int tcp_flow_repair_on(struct ctx *c, const struct tcp_tap_conn *conn);
> diff --git a/tcp_splice.c b/tcp_splice.c
> index 42ee8abc..4c18f0c4 100644
> --- a/tcp_splice.c
> +++ b/tcp_splice.c
> @@ -240,28 +240,14 @@ static void conn_event_do(struct tcp_splice_conn *conn, unsigned long event)
>    */
>   static void tcp_splice_rst(struct tcp_splice_conn *conn)
>   {
> -	const struct linger linger0 = {
> -		.l_onoff = 1,
> -		.l_linger = 0,
> -	};
>   	unsigned sidei;
>   
>   	if (conn->flags & CLOSING)
>   		return; /* Nothing to do */
>   
> -	/* Force RST on sockets to inform the peer
> -	 *
> -	 * We do this by setting SO_LINGER with 0 timeout, which means that
> -	 * close() will send an RST (unless the connection is already closed in
> -	 * both directions).
> -	 */
> -	flow_foreach_sidei(sidei) {
> -		if (setsockopt(conn->s[sidei], SOL_SOCKET,
> -			       SO_LINGER, &linger0, sizeof(linger0)) < 0) {
> -			flow_dbg_perror(conn,
> -"SO_LINGER failed, may not send RST to peer");
> -		}
> -	}
> +	/* Force RST on sockets to inform the peer */
> +	flow_foreach_sidei(sidei)
> +		tcp_linger0(conn, conn->s[sidei]);
>   
>   	conn_flag(conn, CLOSING);
>   }