networkd: Add support to configure IPv6 preferred lifetime (#3102)

Closes #2166.

We only allow 0, infinity and forever.
infinity and forever is same.

man/systemd.network.xml

@@ -652,6 +652,18 @@
             <para>An address label.</para>
           </listitem>
         </varlistentry>
+        <varlistentry>
+          <term><varname>PreferredLifetime=</varname></term>
+          <listitem>
+            <para>Allows the default "preferred lifetime" of the address to be overridden.
+            Only three settings are accepted: <literal>forever</literal> or <literal>infinity</literal>
+            which is the default and means that the address never expires, and <literal>0</literal> which means
+            that the address is considered immediately "expired" and will not be used,
+            unless explicitly requested. A setting of PreferredLifetime=0 is useful for
+            addresses which are added to be used only by a specific application,
+            which is then configured to use them explicitly.</para>
+          </listitem>
+        </varlistentry>
       </variablelist>
   </refsect1>
 

src/network/networkd-address.c

@@ -774,6 +774,54 @@ int config_parse_label(const char *unit,
         return 0;
 }
 
+int config_parse_lifetime(const char *unit,
+                          const char *filename,
+                          unsigned line,
+                          const char *section,
+                          unsigned section_line,
+                          const char *lvalue,
+                          int ltype,
+                          const char *rvalue,
+                          void *data,
+                          void *userdata) {
+        Network *network = userdata;
+        _cleanup_address_free_ Address *n = NULL;
+        unsigned k;
+        int r;
+
+        assert(filename);
+        assert(section);
+        assert(lvalue);
+        assert(rvalue);
+        assert(data);
+
+        r = address_new_static(network, section_line, &n);
+        if (r < 0)
+                return r;
+
+        if (STR_IN_SET(rvalue, "forever", "infinity")) {
+                n->cinfo.ifa_prefered = CACHE_INFO_INFINITY_LIFE_TIME;
+                n = NULL;
+
+                return 0;
+        }
+
+        r = safe_atou(rvalue, &k);
+        if (r < 0) {
+                log_syntax(unit, LOG_ERR, filename, line, r, "Failed to parse PreferredLifetime, ignoring: %s", rvalue);
+                return 0;
+        }
+
+        if (k != 0)
+                log_syntax(unit, LOG_ERR, filename, line, 0, "Invalid PreferredLifetime value, ignoring: %d", k);
+        else {
+                n->cinfo.ifa_prefered = k;
+                n = NULL;
+        }
+
+        return 0;
+}
+
 bool address_is_ready(const Address *a) {
         assert(a);
 

src/network/networkd-address.h

@@ -74,3 +74,4 @@ DEFINE_TRIVIAL_CLEANUP_FUNC(Address*, address_free);
 int config_parse_address(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 int config_parse_broadcast(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 int config_parse_label(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
+int config_parse_lifetime(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);

src/network/networkd-network-gperf.gperf

@@ -65,6 +65,7 @@ Address.Address,                        config_parse_address,
 Address.Peer,                           config_parse_address,                           0,                             0
 Address.Broadcast,                      config_parse_broadcast,                         0,                             0
 Address.Label,                          config_parse_label,                             0,                             0
+Address.PreferredLifetime,              config_parse_lifetime,                          0,                             0
 Route.Gateway,                          config_parse_gateway,                           0,                             0
 Route.Destination,                      config_parse_destination,                       0,                             0
 Route.Source,                           config_parse_destination,                       0,                             0