Re: [PATCH 19/22] conf, fwd: Split notion of gateway/router from guest-visible host address

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

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On Tue, Aug 20, 2024 at 09:56:31PM +0200, Stefano Brivio wrote:
> On Fri, 16 Aug 2024 15:40:00 +1000
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > The @gw fields in the ip4_ctx and ip6_ctx give the (host's) default
> > gateway.  We use this for two quite distinct things: advertising the
> > gateway that the guest should use (via DHCP, NDP and/or --config-net)
> > and for a limited form of NAT.  So that the guest can access services
> > on the host, we map the gateway address within the guest to the
> > loopback address on the host.
> > 
> > Using the gateway address for this isn't necessarily the best choice
> > for this purpose, certainly not for all circumstances.  So, start off
> > by splitting the notion of these into two different values: @guest_gw
> > which is the gateway address the guest should use and @nat_host_loopback,
> > which is the guest visible address to remap to the host's loopback.
> > 
> > Usually nat_host_loopback will have the same value as guest_gw.  However
> > when --no-map-gw is specified we leave them unspecified instead.  This
> > means when we use nat_host_loopback, we don't need to separately check
> > c->no_map_gw to see if it's relevant.
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  conf.c  | 60 +++++++++++++++++++++++++++++----------------------------
> >  dhcp.c  | 10 ++++++----
> >  fwd.c   |  4 ++--
> >  passt.h | 16 +++++++++------
> >  pasta.c |  6 ++++--
> >  5 files changed, 53 insertions(+), 43 deletions(-)
> > 
> > diff --git a/conf.c b/conf.c
> > index b1c58d5b..26373584 100644
> > --- a/conf.c
> > +++ b/conf.c
> > @@ -410,12 +410,12 @@ static void add_dns_resolv(struct ctx *c, const char *nameserver,
> >  		 * redirect
> >  		 */
> >  		if (IN4_IS_ADDR_LOOPBACK(&ns4)) {
> > -			if (c->no_map_gw)
> > +			if (IN4_IS_ADDR_UNSPECIFIED(&c->ip4.nat_host_loopback))
> 
> If you change the command-line option name to use "map", it would be
> good to also change these names.

Will do.

-- 
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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