networkd: Allow DHCP servers to be re-configured on carrier gain

In normal operation this would trigger an assertion
when a DHCP server is configured every time the link goes up.

This change makes sd_dhcp_server_configure_pool idempotent
and stops the DHCP server when the link loses carrier.

In addition to this stopping the assertion being triggered,
this has the useful side-effect of allowing the link to be taken down
and then brought back up as a way to have it use DNS from an "upstream"
interface that got its DNS configuration via DHCP
after the downstream link was configured.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/network/networkd-link.c b/src/network/networkd-link.c
index 4af61df7ff..4c57fa1793 100644
--- a/src/network/networkd-link.c
+++ b/src/network/networkd-link.c
@@ -3060,6 +3060,8 @@ static int link_carrier_lost(Link *link) {
                 return r;
         }
 
+        (void) sd_dhcp_server_stop(link->dhcp_server);
+
         r = link_drop_config(link);
         if (r < 0)
                 return r;