On Fri, Dec 05, 2025 at 01:51:26AM +0100, Stefano Brivio wrote:
> This fixes an issue and introduces a feature:
> 
> - in local mode, we accidentally ignored the -4 / --ipv4-only and
>   -6 / --ipv6-only command line options
> 
> - if no template interface is available for a given IP version,
>   instead of disabling that IP version, use local mode, separately,
>   for it
> 
> Link: https://bugs.passt.top/show_bug.cgi?id=129
> Link: https://bugs.passt.top/show_bug.cgi?id=128
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

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

> ---
>  conf.c  | 19 +++++++++++--------
>  passt.1 | 15 ++++++++-------
>  2 files changed, 19 insertions(+), 15 deletions(-)
> 
> diff --git a/conf.c b/conf.c
> index 02a4b65..fdc19e8 100644
> --- a/conf.c
> +++ b/conf.c
> @@ -1109,7 +1109,7 @@ static void conf_print(const struct ctx *c)
>  		info("Template interface: %s%s%s%s%s",
>  		     c->ifi4 > 0 ? if_indextoname(c->ifi4, ifn) : "",
>  		     c->ifi4 > 0 ? " (IPv4)" : "",
> -		     (c->ifi4 && c->ifi6) ? ", " : "",
> +		     (c->ifi4 > 0 && c->ifi6 > 0) ? ", " : "",
>  		     c->ifi6 > 0 ? if_indextoname(c->ifi6, ifn) : "",
>  		     c->ifi6 > 0 ? " (IPv6)" : "");
>  	}
> @@ -2001,20 +2001,23 @@ void conf(struct ctx *c, int argc, char **argv)
>  	    (*c->ip6.ifname_out && !c->ifi6))
>  		die("External interface not usable");
>  
> +	if (!c->ifi4 && !c->ifi6 && !*c->pasta_ifn) {
> +		strncpy(c->pasta_ifn, pasta_default_ifn,
> +			sizeof(c->pasta_ifn) - 1);
> +	}
>  
> -	if (!c->ifi4 && !c->ifi6) {
> -		info("No external interface as template, switch to local mode");
> +	if (!c->ifi4 && !v6_only) {
> +		info("IPv4: no external interface as template, use local mode");
>  
>  		conf_ip4_local(&c->ip4);
>  		c->ifi4 = -1;
> +	}
> +
> +	if (!c->ifi6 && !v4_only) {
> +		info("IPv6: no external interface as template, use local mode");
>  
>  		conf_ip6_local(&c->ip6);
>  		c->ifi6 = -1;
> -
> -		if (!*c->pasta_ifn) {
> -			strncpy(c->pasta_ifn, pasta_default_ifn,
> -				sizeof(c->pasta_ifn) - 1);
> -		}
>  	}
>  
>  	if (c->ifi4 && !no_map_gw &&
> diff --git a/passt.1 b/passt.1
> index 0c17454..db0d662 100644
> --- a/passt.1
> +++ b/passt.1
> @@ -166,8 +166,8 @@ By default, assigned IPv4 and IPv6 addresses are taken from the host interfaces
>  with the first default route, if any, for the corresponding IP version. If no
>  default routes are available and there is any interface with any route for a
>  given IP version, the first of these interfaces will be chosen instead. If no
> -such interface exists, the link-local address 169.254.2.1 is assigned for IPv4,
> -and no additional address will be assigned for IPv6.
> +such interface exists for a given IP version, the link-local address 169.254.2.1
> +is assigned for IPv4, and no additional address will be assigned for IPv6.
>  
>  .TP
>  .BR \-n ", " \-\-netmask " " \fImask
> @@ -194,9 +194,9 @@ first default route, if any, for the corresponding IP version. If the default
>  route is a multipath one, the gateway is the first nexthop router returned by
>  the kernel which has the highest weight in the set of paths. If no default
>  routes are available and there is just one interface with any route, that
> -interface will be chosen instead. If no such interface exists, the link-local
> -address 169.254.2.2 is used for IPv4, and the link-local address fe80::1 is used
> -for IPv6.
> +interface will be chosen instead. If no such interface exists for a given IP
> +version, the link-local address 169.254.2.2 is used for IPv4, and the link-local
> +address fe80::1 is used for IPv6.
>  
>  Note: these addresses are also used as source address for packets directed to
>  the guest or to the target namespace having a loopback or local source address,
> @@ -1117,8 +1117,9 @@ throughput of TCP connections.
>  .SS Local mode for disconnected setups
>  
>  If \fBpasst\fR and \fBpasta\fR fail to find a host interface with a configured
> -address, other than loopback addresses, they will, obviously, not attempt to
> -source addresses or routes from the host.
> +address for a given IP version, other than loopback addresses, they will,
> +obviously, not attempt to source addresses or routes from the host, for that
> +IP version.
>  
>  In this case, unless configured otherwise, they will assign the IPv4 link-local
>  address 169.254.2.1 to the guest or target namespace, and no IPv6 address. The
> -- 
> 2.43.0
> 

-- 
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