On Fri, Dec 19, 2025 at 05:45:14PM +0100, Laurent Vivier wrote:
> The function tcp_splice_conn_epoll_events() currently takes an array of
> struct epoll_event and fills in the .events field for both sides using
> flow_foreach_sidei() loops.
> 
> This works, but the function is doing two conceptually separate things
> at once: computing events for side 0 and computing events for side 1.
> The OUT_WAIT handling is particularly subtle, as it has cross-side
> effects: when OUT_WAIT(sidei) is set, we add EPOLLOUT to ev[sidei] but
> also remove EPOLLIN from ev[!sidei].
> 
> Refactor to make the function compute events for a single side at a
> time, taking sidei as a parameter and returning uint32_t. This makes
> the logic more focused and easier to follow. The cross-side effects of
> OUT_WAIT are preserved by checking both OUT_WAIT(sidei) and
> OUT_WAIT(!sidei) within each call.
> 
> The caller tcp_splice_epoll_ctl() now invokes the function twice, once
> for each side, making the two-sided nature of the operation explicit.
> 
> No functional change.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  tcp_splice.c | 33 ++++++++++++++-------------------
>  1 file changed, 14 insertions(+), 19 deletions(-)
> 
> diff --git a/tcp_splice.c b/tcp_splice.c
> index 440522449c13..bf4ff466de07 100644
> --- a/tcp_splice.c
> +++ b/tcp_splice.c
> @@ -114,29 +114,23 @@ static struct tcp_splice_conn *conn_at_sidx(flow_sidx_t sidx)
>   * @events:	Connection event flags
>   * @ev:		Events to fill in, 0 is accepted socket, 1 is connecting socket
>   */
> -static void tcp_splice_conn_epoll_events(uint16_t events,
> -					 struct epoll_event ev[])
> +static uint32_t tcp_splice_conn_epoll_events(uint16_t events, unsigned sidei)
>  {
> -	unsigned sidei;
> -
> -	flow_foreach_sidei(sidei)
> -		ev[sidei].events = 0;
> +	uint32_t e = 0;
>  
>  	if (events & SPLICE_ESTABLISHED) {
> -		flow_foreach_sidei(sidei) {
> -			if (!(events & FIN_SENT(!sidei)))
> -				ev[sidei].events = EPOLLIN | EPOLLRDHUP;
> -		}
> -	} else if (events & SPLICE_CONNECT) {
> -		ev[1].events = EPOLLOUT;
> +		if (!(events & FIN_SENT(!sidei)))
> +			e = EPOLLIN | EPOLLRDHUP;
> +	} else if (sidei == 1 && events & SPLICE_CONNECT) {
> +		e = EPOLLOUT;
>  	}
>  
> -	flow_foreach_sidei(sidei) {
> -		if (events & OUT_WAIT(sidei)) {
> -			ev[sidei].events |= EPOLLOUT;
> -			ev[!sidei].events &= ~EPOLLIN;
> -		}
> -	}
> +	if (events & OUT_WAIT(sidei))
> +		e |= EPOLLOUT;
> +	if (events & OUT_WAIT(!sidei))
> +		e &= ~EPOLLIN;
> +
> +	return e;
>  }
>  
>  /**
> @@ -161,7 +155,8 @@ static int tcp_splice_epoll_ctl(const struct ctx *c,
>  	struct epoll_event ev[SIDES] = { { .data.u64 = ref[0].u64 },
>  					 { .data.u64 = ref[1].u64 } };
>  
> -	tcp_splice_conn_epoll_events(conn->events, ev);
> +	ev[0].events = tcp_splice_conn_epoll_events(conn->events, 0);
> +	ev[1].events = tcp_splice_conn_epoll_events(conn->events, 1);
>  
>  
>  	if (epoll_ctl(epollfd, m, conn->s[0], &ev[0]) ||
> -- 
> 2.51.1
> 

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson