Re: [PATCH v14 02/10] passt: add no_map_gw flag to struct ctx

[Stefano Brivio <sbrivio@redhat.com>]

On Tue, 14 Oct 2025 22:55:13 -0400
Jon Maloy <jmaloy@redhat.com> wrote:

> Later in this series we will introduce a new initialization function
> which needs access to the 'no_map_gw' flag. This flag is currently
> a local variable inside the conf() call, where it is too early to
> call the new function. The new function needs both ctx->hash_secret
> and a valid ctx->fd_tap to be set, neither of which are initialized
> at that point.
> 
> We therefore add the 'no_map_gw' flag to struct ctx, so it can be
> carried along and used by later functions.
> 
> Signed-off-by: Jon Maloy <jmaloy@redhat.com>
> Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
> 
> ---
> v14: Fixed typo in commit log
> ---
>  conf.c  | 10 +++++-----
>  passt.h |  1 +
>  2 files changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/conf.c b/conf.c
> index 66b9e63..6143b54 100644
> --- a/conf.c
> +++ b/conf.c
> @@ -1410,7 +1410,7 @@ fail:
>   */
>  void conf(struct ctx *c, int argc, char **argv)
>  {
> -	int netns_only = 0, no_map_gw = 0;
> +	int netns_only = 0;
>  	const struct option options[] = {
>  		{"debug",	no_argument,		NULL,		'd' },
>  		{"quiet",	no_argument,		NULL,		'q' },
> @@ -1442,7 +1442,7 @@ void conf(struct ctx *c, int argc, char **argv)
>  		{"no-ra",	no_argument,		&c->no_ra,	1 },
>  		{"no-splice",	no_argument,		&c->no_splice,	1 },
>  		{"freebind",	no_argument,		&c->freebind,	1 },
> -		{"no-map-gw",	no_argument,		&no_map_gw,	1 },
> +		{"no-map-gw",	no_argument,		&c->no_map_gw,	1 },
>  		{"ipv4-only",	no_argument,		NULL,		'4' },
>  		{"ipv6-only",	no_argument,		NULL,		'6' },
>  		{"one-off",	no_argument,		NULL,		'1' },
> @@ -1656,7 +1656,7 @@ void conf(struct ctx *c, int argc, char **argv)
>  			break;
>  		case 21:
>  			conf_nat(optarg, &c->ip4.map_host_loopback,
> -				 &c->ip6.map_host_loopback, &no_map_gw);
> +				 &c->ip6.map_host_loopback, &c->no_map_gw);

This is by the way what causes the pre-existing issue you reported in
fee75072-42c9-4bc6-959d-9641f0b27ebd@redhat.com as we should process
the no_map_gw in a separate argument parsing loop first, and only then
we can call conf_nat().

>  			break;
>  		case 22:
>  			conf_nat(optarg, &c->ip4.map_guest_addr,
> @@ -2005,11 +2005,11 @@ void conf(struct ctx *c, int argc, char **argv)
>  		}
>  	}
>  
> -	if (c->ifi4 && !no_map_gw &&
> +	if (c->ifi4 && !c->no_map_gw &&
>  	    IN4_IS_ADDR_UNSPECIFIED(&c->ip4.map_host_loopback))
>  		c->ip4.map_host_loopback = c->ip4.guest_gw;
>  
> -	if (c->ifi6 && !no_map_gw &&
> +	if (c->ifi6 && !c->no_map_gw &&
>  	    IN6_IS_ADDR_UNSPECIFIED(&c->ip6.map_host_loopback))
>  		c->ip6.map_host_loopback = c->ip6.guest_gw;
>  
> diff --git a/passt.h b/passt.h
> index 0075eb4..830bc36 100644
> --- a/passt.h
> +++ b/passt.h
> @@ -310,6 +310,7 @@ struct ctx {
>  	int no_ndp;
>  	int no_ra;
>  	int no_splice;
> +	int no_map_gw;

This is now undocumented. See 935bd81936cf ("conf, fwd: Split notion of
gateway/router from guest-visible host address") for the hunk you're
reverting here.

>  	int host_lo_to_ns_lo;
>  	int freebind;
>  

-- 
Stefano