dhcp: support prefix delegation hint

Support the prefix delegation hint in the DHCP client.

dhclient only supports a prefix length, emit a warning if the user set
a non-zero prefix.

src/core/devices/nm-device.c

@@ -10631,6 +10631,7 @@ _dev_ipdhcpx_start(NMDevice *self, int addr_family)
         gboolean               iaid_explicit;
         guint32                iaid;
         NMDhcpClientConfig     config;
+        const char            *pd_hint;
 
         iaid = _prop_get_ipvx_dhcp_iaid(self, AF_INET6, connection, FALSE, &iaid_explicit);
         duid = _prop_get_ipv6_dhcp_duid(self, connection, hwaddr, &enforce_duid);
@@ -10657,6 +10658,21 @@ _dev_ipdhcpx_start(NMDevice *self, int addr_family)
                 },
         };
 
+        pd_hint = nm_setting_ip6_config_get_dhcp_pd_hint(NM_SETTING_IP6_CONFIG(s_ip));
+        if (pd_hint) {
+            int      pd_hint_length;
+            gboolean res;
+
+            res = nm_inet_parse_with_prefix_bin(AF_INET6,
+                                                pd_hint,
+                                                NULL,
+                                                &config.v6.pd_hint_addr,
+                                                &pd_hint_length);
+            nm_assert(res);
+            nm_assert(pd_hint_length > 0 || pd_hint_length <= 128);
+            config.v6.pd_hint_length = pd_hint_length;
+        }
+
         priv->ipdhcp_data_6.client =
             nm_dhcp_manager_start_client(nm_dhcp_manager_get(), &config, &error);
     }

src/core/dhcp/nm-dhcp-client.h

@@ -174,6 +174,10 @@ typedef struct {
             /* Number to prefixes (IA_PD) to request */
             guint needed_prefixes;
 
+            /* A hint to send to server for prefix delegation (IA_PD). */
+            struct in6_addr pd_hint_addr;
+            guint8          pd_hint_length;
+
             /* Use Information-request to get stateless configuration
              * parameters (don't request a IA_NA) */
             bool info_only : 1;

src/core/dhcp/nm-dhcp-dhclient.c

@@ -356,6 +356,7 @@ dhclient_start(NMDhcpClient *client,
     gs_free char                *preferred_leasefile_path = NULL;
     int                          addr_family;
     const NMDhcpClientConfig    *client_config;
+    char                         pd_length_str[16];
 
     g_return_val_if_fail(!priv->pid_file, FALSE);
     client_config = nm_dhcp_client_get_config(client);
@@ -463,6 +464,17 @@ dhclient_start(NMDhcpClient *client,
 
         if (mode_opt)
             g_ptr_array_add(argv, (gpointer) mode_opt);
+
+        if (prefixes > 0 && client_config->v6.pd_hint_length > 0) {
+            if (!IN6_IS_ADDR_UNSPECIFIED(&client_config->v6.pd_hint_addr)) {
+                _LOGW("dhclient only supports a length as prefix delegation hint, not a prefix");
+            }
+
+            nm_sprintf_buf(pd_length_str, "%u", client_config->v6.pd_hint_length);
+            g_ptr_array_add(argv, "--prefix-len-hint");
+            g_ptr_array_add(argv, pd_length_str);
+        }
+
         while (prefixes--)
             g_ptr_array_add(argv, (gpointer) "-P");
     }

src/core/dhcp/nm-dhcp-systemd.c

@@ -366,6 +366,15 @@ ip6_start(NMDhcpClient *client, const struct in6_addr *ll_addr, GError **error)
             _LOGW("dhcp-client6: only one prefix request is supported");
         }
         prefix_delegation = TRUE;
+        if (client_config->v6.pd_hint_length > 0) {
+            r = sd_dhcp6_client_set_prefix_delegation_hint(sd_client,
+                                                           client_config->v6.pd_hint_length,
+                                                           &client_config->v6.pd_hint_addr);
+            if (r < 0) {
+                nm_utils_error_set_errno(error, r, "failed to set prefix delegation hint: %s");
+                return FALSE;
+            }
+        }
     }
     r = sd_dhcp6_client_set_prefix_delegation(sd_client, prefix_delegation);
     if (r < 0) {