networkd: add DHCPServer PoolSize and PoolOffset DBus properties

Closes https://github.com/systemd/systemd/issues/30011

man/org.freedesktop.network1.xml

@@ -458,6 +458,10 @@ node /org/freedesktop/network1/link/_1 {
   interface org.freedesktop.network1.DHCPServer {
     properties:
       readonly a(uayayayayt) Leases = [...];
+      @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
+      readonly u PoolSize = ...;
+      @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
+      readonly u PoolOffset = ...;
   };
   interface org.freedesktop.DBus.Peer { ... };
   interface org.freedesktop.DBus.Introspectable { ... };
@@ -466,8 +470,6 @@ node /org/freedesktop/network1/link/_1 {
 };
 </programlisting>
 
-    <!--property Leases is not documented!-->
-
     <!--Autogenerated cross-references for systemd.directives, do not edit-->
 
     <variablelist class="dbus-interface" generated="True" extra-ref="org.freedesktop.network1.Link"/>
@@ -480,10 +482,23 @@ node /org/freedesktop/network1/link/_1 {
 
     <variablelist class="dbus-property" generated="True" extra-ref="Leases"/>
 
+    <variablelist class="dbus-property" generated="True" extra-ref="PoolSize"/>
+
+    <variablelist class="dbus-property" generated="True" extra-ref="PoolOffset"/>
+
     <!--End of Autogenerated section-->
 
     <para>
-      Provides information about leases.
+      Provides information about the DHCP server. The <varname>Leases</varname> property contains
+      the currently active leases. The <varname>PoolSize</varname> property contains the total number
+      of addresses in the dynamic address pool. The <varname>PoolOffset</varname> property contains
+      the offset from the subnet base address where the pool starts. These correspond to the
+      <varname>PoolSize=</varname> and <varname>PoolOffset=</varname> settings in
+      <citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
+      <constant>UINT32_MAX</constant> is used as a sentinel value for <varname>PoolSize</varname>
+      and <varname>PoolOffset</varname> to indicate that the information is unavailable (i.e. no
+      DHCP server is configured or the link is in relay mode), rather than a valid pool size or
+      offset.
     </para>
   </refsect1>
 
@@ -589,6 +604,10 @@ $ gdbus introspect --system \
 
   <refsect1>
     <title>History</title>
+    <refsect2>
+      <title>DHCP Server Object</title>
+      <para><varname>PoolSize</varname> and <varname>PoolOffset</varname> were added in version 261.</para>
+    </refsect2>
     <refsect2>
       <title>DHCPv4 Client Object</title>
       <para><varname>State</varname> was added in version 255.</para>

src/network/networkd-dhcp-server-bus.c

@@ -74,6 +74,46 @@ static int property_get_leases(
         return sd_bus_message_close_container(reply);
 }
 
+static int property_get_pool_size(
+                sd_bus *bus,
+                const char *path,
+                const char *interface,
+                const char *property,
+                sd_bus_message *reply,
+                void *userdata,
+                sd_bus_error *error) {
+        Link *l = ASSERT_PTR(userdata);
+        sd_dhcp_server *s;
+        uint32_t v;
+
+        assert(reply);
+
+        s = l->dhcp_server;
+        v = s && !sd_dhcp_server_is_in_relay_mode(s) ? s->pool_size : UINT32_MAX;
+
+        return sd_bus_message_append_basic(reply, 'u', &v);
+}
+
+static int property_get_pool_offset(
+                sd_bus *bus,
+                const char *path,
+                const char *interface,
+                const char *property,
+                sd_bus_message *reply,
+                void *userdata,
+                sd_bus_error *error) {
+        Link *l = ASSERT_PTR(userdata);
+        sd_dhcp_server *s;
+        uint32_t v;
+
+        assert(reply);
+
+        s = l->dhcp_server;
+        v = s && !sd_dhcp_server_is_in_relay_mode(s) ? s->pool_offset : UINT32_MAX;
+
+        return sd_bus_message_append_basic(reply, 'u', &v);
+}
+
 static int dhcp_server_emit_changed_strv(Link *link, char **properties) {
         _cleanup_free_ char *path = NULL;
 
@@ -104,6 +144,8 @@ static const sd_bus_vtable dhcp_server_vtable[] = {
         SD_BUS_VTABLE_START(0),
 
         SD_BUS_PROPERTY("Leases", "a(uayayayayt)", property_get_leases, 0, SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
+        SD_BUS_PROPERTY("PoolSize", "u", property_get_pool_size, 0, SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("PoolOffset", "u", property_get_pool_offset, 0, SD_BUS_VTABLE_PROPERTY_CONST),
 
         SD_BUS_VTABLE_END
 };