networkd: generate resolv.conf

This adds support to generate a basic resolv.conf in /run/systemd/network.
This file will not take any effect unless a symlink is created from
/etc/resolv.conf.

Nameservers received over DHCP takes precedence over statically configured ones.

Note: /etc/resolv.conf is severely limited, so in the future we will likely
rather provide a much more powerfull nss plugin (or something to that effect),
but this should allow current users to function without any loss of
functionality.

1 files changed, 8 insertions, 0 deletions

diff --git a/src/network/networkd-link.c b/src/network/networkd-link.c
index 25d92c8aa4..5dd8e91007 100644
--- a/src/network/networkd-link.c
+++ b/src/network/networkd-link.c
@@ -378,6 +378,7 @@ static void dhcp_handler(sd_dhcp_client *client, int event, void *userdata) {
         if (event == DHCP_EVENT_IP_CHANGE || event == DHCP_EVENT_IP_ACQUIRE) {
                 _cleanup_address_free_ Address *addr = NULL;
                 _cleanup_route_free_ Route *rt = NULL;
+                struct in_addr **nameservers;
 
                 log_struct_link(LOG_INFO, link,
                                 "MESSAGE=%s: DHCPv4 address %u.%u.%u.%u/%u via %u.%u.%u.%u",
@@ -420,6 +421,13 @@ static void dhcp_handler(sd_dhcp_client *client, int event, void *userdata) {
                 addr = NULL;
                 rt = NULL;
 
+                r = sd_dhcp_client_get_dns(client, &nameservers);
+                if (r >= 0) {
+                        r = manager_update_resolv_conf(link->manager);
+                        if (r < 0)
+                                log_error("Failed to update resolv.conf");
+                }
+
                 link_enter_set_addresses(link);
         }