Re: [PATCH 1/3] tcp_splice: Register fds with epoll at flow creation

[David Gibson <david@gibson.dropbear.id.au>]

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On Fri, Jan 16, 2026 at 04:52:21PM +0100, Laurent Vivier wrote:
> Register both splice connection sockets with epoll using empty events
> (events=0) in tcp_splice_connect(), before initiating the connection.
> 
> This allows tcp_splice_epoll_ctl() to always use EPOLL_CTL_MOD, removing
> the need to check whether fds are already registered. As a result, the
> conditional ADD/MOD logic is no longer needed, simplifying the function.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>

Nice!  One query below.

> ---
>  tcp_splice.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/tcp_splice.c b/tcp_splice.c
> index a7c04ca8652a..cb81e012ee4b 100644
> --- a/tcp_splice.c
> +++ b/tcp_splice.c
> @@ -142,20 +142,12 @@ static uint32_t tcp_splice_conn_epoll_events(uint16_t events, unsigned sidei)
>  static int tcp_splice_epoll_ctl(struct tcp_splice_conn *conn)
>  {
>  	uint32_t events[2];
> -	int m;
> -
> -	if (flow_in_epoll(&conn->f)) {
> -		m = EPOLL_CTL_MOD;
> -	} else {
> -		flow_epollid_set(&conn->f, EPOLLFD_ID_DEFAULT);
> -		m = EPOLL_CTL_ADD;
> -	}
>  
>  	events[0] = tcp_splice_conn_epoll_events(conn->events, 0);
>  	events[1] = tcp_splice_conn_epoll_events(conn->events, 1);
>  
> -	if (flow_epoll_set(&conn->f, m, events[0], conn->s[0], 0) ||
> -	    flow_epoll_set(&conn->f, m, events[1], conn->s[1], 1)) {
> +	if (flow_epoll_set(&conn->f, EPOLL_CTL_MOD, events[0], conn->s[0], 0) ||
> +	    flow_epoll_set(&conn->f, EPOLL_CTL_MOD, events[1], conn->s[1], 1)) {
>  		int ret = -errno;
>  		flow_perror(conn, "ERROR on epoll_ctl()");
>  		return ret;
> @@ -368,6 +360,14 @@ static int tcp_splice_connect(const struct ctx *c, struct tcp_splice_conn *conn)
>  
>  	pif_sockaddr(c, &sa, tgtpif, &tgt->eaddr, tgt->eport);
>  
> +	flow_epollid_set(&conn->f, EPOLLFD_ID_DEFAULT);
> +	if (flow_epoll_set(&conn->f, EPOLL_CTL_ADD, 0, conn->s[0], 0) ||
> +	    flow_epoll_set(&conn->f, EPOLL_CTL_ADD, 0, conn->s[1], 1)) {
> +		int ret = -errno;
> +		flow_perror(conn, "Cannot register to epollfd");
> +		return ret;

Do we need to worry about rollback here, if the first one succeeds,
but the second one fails?

> +	}
> +
>  	conn_event(conn, SPLICE_CONNECT);
>  
>  	if (connect(conn->s[1], &sa.sa, socklen_inany(&sa))) {
> -- 
> 2.52.0
> 

-- 
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

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