Re: [PATCH 3/3] tcp, udp: Make {tcp,udp}_listen() return socket fds

[Stefano Brivio <sbrivio@redhat.com>]

On Mon,  5 Jan 2026 19:28:50 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> {tcp,udp}_listen() currently return 0 on success, rather than the socket
> fd they created.  Historically, that was because these functions could
> sometimes create multiple sockets.  We've now refactored things to avoid
> that, so it makes more sense for them to return the socket on success.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  conf.c | 14 +++++++-------
>  tcp.c  |  7 ++-----
>  udp.c  |  4 ++--
>  3 files changed, 11 insertions(+), 14 deletions(-)
> 
> diff --git a/conf.c b/conf.c
> index cc3c20a9..5db49653 100644
> --- a/conf.c
> +++ b/conf.c
> @@ -149,7 +149,7 @@ static void conf_ports_range_except(const struct ctx *c, char optname,
>  {
>  	bool bound_one = false;
>  	unsigned i;
> -	int ret;
> +	int fd;
>  
>  	if (first == 0) {
>  		die("Can't forward port 0 for option '-%c %s'",
> @@ -185,23 +185,23 @@ static void conf_ports_range_except(const struct ctx *c, char optname,
>  		fwd->delta[i] = to - first;
>  
>  		if (optname == 't')
> -			ret = tcp_listen(c, PIF_HOST, addr, ifname, i);
> +			fd = tcp_listen(c, PIF_HOST, addr, ifname, i);
>  		else if (optname == 'u')
> -			ret = udp_listen(c, PIF_HOST, addr, ifname, i);
> +			fd = udp_listen(c, PIF_HOST, addr, ifname, i);
>  		else
>  			/* No way to check in advance for -T and -U */
> -			ret = 0;
> +			fd = 0;
>  
> -		if (ret == -ENFILE || ret == -EMFILE) {
> +		if (fd == -ENFILE || fd == -EMFILE) {
>  			die("Can't open enough sockets for port specifier: %s",
>  			    optarg);
>  		}
>  
> -		if (!ret) {
> +		if (fd >= 0) {
>  			bound_one = true;
>  		} else if (!weak) {
>  			die("Failed to bind port %u (%s) for option '-%c %s'",
> -			    i, strerror_(-ret), optname, optarg);
> +			    i, strerror_(-fd), optname, optarg);
>  		}
>  	}
>  
> diff --git a/tcp.c b/tcp.c
> index 67007c05..80b47f3c 100644
> --- a/tcp.c
> +++ b/tcp.c
> @@ -2680,7 +2680,7 @@ void tcp_sock_handler(const struct ctx *c, union epoll_ref ref,
>   * @ifname:	Name of interface to bind to, NULL for any
>   * @port:	Port, host order
>   *
> - * Return: 0 on success, negative error code on failure
> + * Return: Socket fd on success, negative error code on failure

Nit, here and on udp_listen(): "socket". See also 9e0423e13541 ("style:
Fix 'Return' comment style").

>   */
>  int tcp_listen(const struct ctx *c, uint8_t pif,
>  	       const union inany_addr *addr, const char *ifname, in_port_t port)
> @@ -2729,10 +2729,7 @@ int tcp_listen(const struct ctx *c, uint8_t pif,
>  			socks[port][V6] = s < 0 ? -1 : s;
>  	}
>  
> -	if (s < 0)
> -		return s;
> -
> -	return 0;
> +	return s;
>  }
>  
>  /**
> diff --git a/udp.c b/udp.c
> index 8cfa1e1f..63dc7c25 100644
> --- a/udp.c
> +++ b/udp.c
> @@ -1136,7 +1136,7 @@ int udp_tap_handler(const struct ctx *c, uint8_t pif,
>   * @ifname:	Name of interface to bind to, NULL if not configured
>   * @port:	Port, host order
>   *
> - * Return: 0 on success, negative error code on failure
> + * Return: Socket fd on success, negative error code on failure
>   */
>  int udp_listen(const struct ctx *c, uint8_t pif,
>  	       const union inany_addr *addr, const char *ifname, in_port_t port)
> @@ -1180,7 +1180,7 @@ int udp_listen(const struct ctx *c, uint8_t pif,
>  	if (!addr || !inany_v4(addr))
>  		socks[V6][port] = s < 0 ? -1 : s;
>  
> -	return s < 0 ? s : 0;
> +	return s;
>  }
>  
>  /**

-- 
Stefano