[PATCH] conf: Warn if we can't advertise any nameserver via DHCP, NDP, or DHCPv6

[Stefano Brivio <sbrivio@redhat.com>]

We might have read from resolv.conf, or from the command line, a
resolver that's reachable via loopback address, but that doesn't mean
we can offer that via DHCP, NDP or DHCPv6: warn if there are no
resolvers we can offer for a given IP version.

Suggested-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 conf.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/conf.c b/conf.c
index 17c667a..ac9fb34 100644
--- a/conf.c
+++ b/conf.c
@@ -464,8 +464,21 @@ static void get_dns(struct ctx *c)
 	close(fd);
 
 out:
-	if (!dns_set && !added)
-		warn("Couldn't get any nameserver address");
+	if (!dns_set) {
+		if (!added)
+			warn("Couldn't get any nameserver address");
+
+		if (c->no_dhcp_dns)
+			return;
+
+		if (c->ifi4 && !c->no_dhcp &&
+		    IN4_IS_ADDR_UNSPECIFIED(&c->ip4.dns[0]))
+			warn("No IPv4 nameserver available for DHCP");
+
+		if (c->ifi6 && ((!c->no_ndp && !c->no_ra) || !c->no_dhcpv6) &&
+		    IN6_IS_ADDR_UNSPECIFIED(&c->ip6.dns[0]))
+			warn("No IPv6 nameserver available for NDP/DHCPv6");
+	}
 }
 
 /**
-- 
@@ -464,8 +464,21 @@ static void get_dns(struct ctx *c)
 	close(fd);
 
 out:
-	if (!dns_set && !added)
-		warn("Couldn't get any nameserver address");
+	if (!dns_set) {
+		if (!added)
+			warn("Couldn't get any nameserver address");
+
+		if (c->no_dhcp_dns)
+			return;
+
+		if (c->ifi4 && !c->no_dhcp &&
+		    IN4_IS_ADDR_UNSPECIFIED(&c->ip4.dns[0]))
+			warn("No IPv4 nameserver available for DHCP");
+
+		if (c->ifi6 && ((!c->no_ndp && !c->no_ra) || !c->no_dhcpv6) &&
+		    IN6_IS_ADDR_UNSPECIFIED(&c->ip6.dns[0]))
+			warn("No IPv6 nameserver available for NDP/DHCPv6");
+	}
 }
 
 /**
-- 
2.39.2