Re: [PATCH 02/18] conf: Simplify handling of default forwarding mode

[Stefano Brivio <sbrivio@redhat.com>]

On Tue,  7 Apr 2026 13:16:14 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> For passt, the default forwarding mode is "none", which falls out naturally
> from the other handling: if we don't get any options, we get empty
> forwarding tables, which corresponds to "none" behaviour.  However, for
> pasta the default is "auto".  This is handled a bit oddly: in conf_ports()
> we set the mode variable, but don't set up the rules we need for "auto"
> mode.  Instead we want until nearly the end of conf() and if the mode is
> FWD_MODE_AUTO or unset, we make conf_ports_range_except() calls to set up
> the "auto" rules.
> 
> Simplify this a bit, by creating the rules within conf_ports() itself when
> we parse -[tuTU] auto.  For the case of no forwarding options we call
> into conf_ports() itself with synthetic arguments.  As well as making the
> code a little shorter, this makes it more obvious that giving no arguments
> really is equivalent to -[tuTU] auto.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  conf.c | 54 ++++++++++++++++++++++--------------------------------
>  1 file changed, 22 insertions(+), 32 deletions(-)
> 
> diff --git a/conf.c b/conf.c
> index c515480b..7d718f91 100644
> --- a/conf.c
> +++ b/conf.c
> @@ -345,6 +345,10 @@ static void conf_ports(const struct ctx *c, char optname, const char *optarg,
>  			die("'auto' port forwarding is only allowed for pasta");
>  
>  		*mode = FWD_MODE_AUTO;
> +
> +		conf_ports_range_except(c, optname, optarg, fwd, NULL, NULL,
> +					1, NUM_PORTS - 1, NULL, 1, FWD_SCAN);
> +
>  		return;
>  	}

Pre-existing, it goes away in 12/18 of the current series, and it's
harmless unless somebody should ever touch 'enum fwd_mode' in a rather
unlikely way: the code here checks:

		if (*mode)
			...

relying on the fact that FWD_MODE_UNSPEC is 0 (and we also have a _NONE
value, which makes it somewhat risky) instead of directly checking if
(*mode == FWD_MODE_UNSPEC).

I thought I would note it here in the unlikely case we'd need to back to
mode constants for whatever reason.

-- 
Stefano