networkd: merge ll addressing fallback modes into normal "boolean" values

They are not really boolean, because we have both ipv4 and ipv6, but
for each protocol we have either unset, no, and yes.

From https://github.com/systemd/systemd/issues/13316#issuecomment-582906817:
LinkLocalAddressing must be a boolean option, at least for ipv4:
- LinkLocalAddressing=no => no LL at all.

- LinkLocalAddressing=yes + Static Address => invalid configuration, warn and
  interpret as LinkLocalAddressing=no, no LL at all.

(we check that during parsing and reject)

- LinkLocalAddressing=yes + DHCP => LL process should be subordinated to the
  DHCP one, an LL address must be acquired at start or after a short N
  unsuccessful DHCP attemps, and must not stop DHCP to keeping trying. When a
  DHCP address is acquired, drop the LL address. If the DHCP address is lost,
  re-adquire a new LL address.

(next patch will move in this direction)

- LinkLocalAddressing=fallback has no reason to exist, because LL address must
  always be allocated as a fallback option when using DHCP. Having both DHCP
  and LL address at the same time is an RFC violation, so
  LinkLocalAdressing=yes correctly implemented is already the "fallback"
  behavior. The fallback option must be deprecated and if present in older
  configs must be interpreted as LinkLocalAddressing=yes.

(removed)

- And for IPv6, the LinkLocalAddress option has any sense at all? IPv6-LL
  address aren't required to be always set for every IPv6 enabled interface (in
  this case, coexisting with static or dynamic address if any)? Shouldn't be
  always =yes?

(good question)

This effectively reverts 29e81083bd. There is no
special "fallback" mode now, so the check doesn't make sense anymore.

man/systemd.network.xml

@@ -364,17 +364,13 @@
         <varlistentry>
           <term><varname>LinkLocalAddressing=</varname></term>
           <listitem>
-            <para>Enables link-local address autoconfiguration. Accepts <literal>yes</literal>,
+            <para>Enables link-local address autoconfiguration. Accepts <option>yes</option>,
-            <literal>no</literal>, <literal>ipv4</literal>, <literal>ipv6</literal>,
+            <option>no</option>, <option>ipv4</option>, and <option>ipv6</option>. An IPv6 link-local address
-            <literal>fallback</literal>, or <literal>ipv4-fallback</literal>. If
+            is configured when <option>yes</option> or <option>ipv6</option>. An IPv4 link-local address is
-            <literal>fallback</literal> or <literal>ipv4-fallback</literal> is specified, then an IPv4
+            configured when <option>yes</option> or <option>ipv4</option>.</para>
-            link-local address is configured only when DHCPv4 fails. If <literal>fallback</literal>,
+
-            an IPv6 link-local address is always configured, and if <literal>ipv4-fallback</literal>,
+            <para>Defaults to <option>no</option> when <varname>Bridge=yes</varname> is set, and
-            the address is not configured. Note that, the fallback mechanism works only when DHCPv4
+            <option>ipv6</option> otherwise.</para>
-            client is enabled, that is, it requires <literal>DHCP=yes</literal> or
-            <literal>DHCP=ipv4</literal>. If <varname>Bridge=</varname> is set, defaults to
-            <literal>no</literal>, and if not, defaults to <literal>ipv6</literal>.
-            </para>
           </listitem>
         </varlistentry>
         <varlistentry>

src/basic/string-table.h

@@ -28,13 +28,12 @@ ssize_t string_table_lookup(const char * const *table, size_t len, const char *k
 
 #define _DEFINE_STRING_TABLE_LOOKUP_FROM_STRING_WITH_BOOLEAN(name,type,yes,scope) \
         scope type name##_from_string(const char *s) {                  \
-                int b;                                                  \
                 if (!s)                                                 \
                         return -1;                                      \
-                b = parse_boolean(s);                                   \
+                int b = parse_boolean(s);                               \
                 if (b == 0)                                             \
                         return (type) 0;                                \
-                else if (b > 0)                                         \
+                if (b > 0)                                              \
                         return yes;                                     \
                 return (type) string_table_lookup(name##_table, ELEMENTSOF(name##_table), s); \
         }

src/network/networkd-dhcp4.c

@@ -1048,8 +1048,7 @@ static int dhcp4_handler(sd_dhcp_client *client, int event, void *userdata) {
 
         switch (event) {
                 case SD_DHCP_CLIENT_EVENT_STOP:
-
+                        if (link_ipv4ll_enabled(link)) {
-                        if (link_ipv4ll_enabled(link, ADDRESS_FAMILY_FALLBACK_IPV4)) {
                                 assert(link->ipv4ll);
 
                                 log_link_debug(link, "DHCP client is stopped. Acquiring IPv4 link-local address");

src/network/networkd-ipv4ll.c

@@ -148,7 +148,7 @@ int ipv4ll_configure(Link *link) {
 
         assert(link);
 
-        if (!link_ipv4ll_enabled(link, ADDRESS_FAMILY_IPV4 | ADDRESS_FAMILY_FALLBACK_IPV4))
+        if (!link_ipv4ll_enabled(link))
                 return 0;
 
         if (!link->ipv4ll) {

src/network/networkd-link.c

@@ -55,9 +55,8 @@
 #include "util.h"
 #include "vrf.h"
 
-bool link_ipv4ll_enabled(Link *link, AddressFamily mask) {
+bool link_ipv4ll_enabled(Link *link) {
         assert(link);
-        assert((mask & ~(ADDRESS_FAMILY_IPV4 | ADDRESS_FAMILY_FALLBACK_IPV4)) == 0);
 
         if (link->flags & IFF_LOOPBACK)
                 return false;
@@ -80,7 +79,7 @@ bool link_ipv4ll_enabled(Link *link, AddressFamily mask) {
         if (link->network->bond)
                 return false;
 
-        return link->network->link_local & mask;
+        return link->network->link_local & ADDRESS_FAMILY_IPV4;
 }
 
 bool link_ipv6ll_enabled(Link *link) {
@@ -795,7 +794,7 @@ void link_check_ready(Link *link) {
                 bool has_ndisc_address = false;
                 NDiscAddress *n;
 
-                if (link_ipv4ll_enabled(link, ADDRESS_FAMILY_IPV4) && !link->ipv4ll_address_configured) {
+                if (link_ipv4ll_enabled(link) && !link->ipv4ll_address_configured) {
                         log_link_debug(link, "%s(): IPv4LL is not configured.", __func__);
                         return;
                 }
@@ -814,7 +813,7 @@ void link_check_ready(Link *link) {
 
                 if ((link_dhcp4_enabled(link) || link_dhcp6_enabled(link)) &&
                     !link->dhcp_address && set_isempty(link->dhcp6_addresses) && !has_ndisc_address &&
-                    !(link_ipv4ll_enabled(link, ADDRESS_FAMILY_FALLBACK_IPV4) && link->ipv4ll_address_configured)) {
+                    !(link_ipv4ll_enabled(link) && link->ipv4ll_address_configured)) {
                         log_link_debug(link, "%s(): DHCP4 or DHCP6 is enabled but no dynamic address is assigned yet.", __func__);
                         return;
                 }
@@ -824,7 +823,7 @@ void link_check_ready(Link *link) {
                             !(link->dhcp6_address_configured && link->dhcp6_route_configured) &&
                             !(link->dhcp6_pd_address_configured && link->dhcp6_pd_route_configured) &&
                             !(link->ndisc_addresses_configured && link->ndisc_routes_configured) &&
-                            !(link_ipv4ll_enabled(link, ADDRESS_FAMILY_FALLBACK_IPV4) && link->ipv4ll_address_configured)) {
+                            !(link_ipv4ll_enabled(link) && link->ipv4ll_address_configured)) {
                                 /* When DHCP or RA is enabled, at least one protocol must provide an address, or
                                  * an IPv4ll fallback address must be configured. */
                                 log_link_debug(link, "%s(): dynamic addresses or routes are not configured.", __func__);
@@ -1230,7 +1229,7 @@ static int link_acquire_ipv4_conf(Link *link) {
         assert(link->manager);
         assert(link->manager->event);
 
-        if (link_ipv4ll_enabled(link, ADDRESS_FAMILY_IPV4)) {
+        if (link_ipv4ll_enabled(link)) {
                 assert(link->ipv4ll);
 
                 log_link_debug(link, "Acquiring IPv4 link-local address");

src/network/networkd-link.h

@@ -231,7 +231,7 @@ int link_ipv6ll_gained(Link *link, const struct in6_addr *address);
 
 int link_set_mtu(Link *link, uint32_t mtu);
 
-bool link_ipv4ll_enabled(Link *link, AddressFamily mask);
+bool link_ipv4ll_enabled(Link *link);
 
 int link_stop_engines(Link *link, bool may_keep_dhcp);
 

src/network/networkd-network.c

@@ -210,13 +210,6 @@ int network_verify(Network *network) {
         if (network->link_local < 0)
                 network->link_local = network->bridge ? ADDRESS_FAMILY_NO : ADDRESS_FAMILY_IPV6;
 
-        if (FLAGS_SET(network->link_local, ADDRESS_FAMILY_FALLBACK_IPV4) &&
-            !FLAGS_SET(network->dhcp, ADDRESS_FAMILY_IPV4)) {
-                log_warning("%s: fallback assignment of IPv4 link local address is enabled but DHCPv4 is disabled. "
-                            "Disabling the fallback assignment.", network->filename);
-                SET_FLAG(network->link_local, ADDRESS_FAMILY_FALLBACK_IPV4, false);
-        }
-
         /* IPMasquerade=yes implies IPForward=yes */
         if (network->ip_masquerade)
                 network->ip_forward |= ADDRESS_FAMILY_IPV4;

src/network/networkd-util.c

@@ -15,15 +15,6 @@ static const char* const address_family_table[_ADDRESS_FAMILY_MAX] = {
         [ADDRESS_FAMILY_IPV6]          = "ipv6",
 };
 
-static const char* const link_local_address_family_table[_ADDRESS_FAMILY_MAX] = {
-        [ADDRESS_FAMILY_NO]            = "no",
-        [ADDRESS_FAMILY_YES]           = "yes",
-        [ADDRESS_FAMILY_IPV4]          = "ipv4",
-        [ADDRESS_FAMILY_IPV6]          = "ipv6",
-        [ADDRESS_FAMILY_FALLBACK]      = "fallback",
-        [ADDRESS_FAMILY_FALLBACK_IPV4] = "ipv4-fallback",
-};
-
 static const char* const routing_policy_rule_address_family_table[_ADDRESS_FAMILY_MAX] = {
         [ADDRESS_FAMILY_YES]           = "both",
         [ADDRESS_FAMILY_IPV4]          = "ipv4",
@@ -47,7 +38,15 @@ static const char* const dhcp_lease_server_type_table[_SD_DHCP_LEASE_SERVER_TYPE
 };
 
 DEFINE_STRING_TABLE_LOOKUP_WITH_BOOLEAN(address_family, AddressFamily, ADDRESS_FAMILY_YES);
-DEFINE_STRING_TABLE_LOOKUP_WITH_BOOLEAN(link_local_address_family, AddressFamily, ADDRESS_FAMILY_YES);
+
+AddressFamily link_local_address_family_from_string(const char *s) {
+        if (streq_ptr(s, "fallback"))         /* compat name */
+                return ADDRESS_FAMILY_YES;
+        if (streq_ptr(s, "fallback-ipv4"))    /* compat name */
+                return ADDRESS_FAMILY_IPV4;
+        return address_family_from_string(s);
+}
+
 DEFINE_STRING_TABLE_LOOKUP(routing_policy_rule_address_family, AddressFamily);
 DEFINE_STRING_TABLE_LOOKUP(duplicate_address_detection_address_family, AddressFamily);
 DEFINE_CONFIG_PARSE_ENUM(config_parse_link_local_address_family, link_local_address_family,

src/network/networkd-util.h

@@ -16,8 +16,6 @@ typedef enum AddressFamily {
         ADDRESS_FAMILY_IPV4           = 1 << 0,
         ADDRESS_FAMILY_IPV6           = 1 << 1,
         ADDRESS_FAMILY_YES            = ADDRESS_FAMILY_IPV4 | ADDRESS_FAMILY_IPV6,
-        ADDRESS_FAMILY_FALLBACK_IPV4  = 1 << 2,
-        ADDRESS_FAMILY_FALLBACK       = ADDRESS_FAMILY_FALLBACK_IPV4 | ADDRESS_FAMILY_IPV6,
         _ADDRESS_FAMILY_MAX,
         _ADDRESS_FAMILY_INVALID = -1,
 } AddressFamily;
@@ -34,7 +32,6 @@ CONFIG_PARSER_PROTOTYPE(config_parse_address_family_with_kernel);
 const char *address_family_to_string(AddressFamily b) _const_;
 AddressFamily address_family_from_string(const char *s) _pure_;
 
-const char *link_local_address_family_to_string(AddressFamily b) _const_;
 AddressFamily link_local_address_family_from_string(const char *s) _pure_;
 
 const char *routing_policy_rule_address_family_to_string(AddressFamily b) _const_;

test/test-network/conf/dhcp-client-with-ipv4ll-with-dhcp-server.network

@@ -3,5 +3,5 @@ Name=veth99
 
 [Network]
 DHCP=ipv4
-LinkLocalAddressing=fallback
+LinkLocalAddressing=yes
 IPv6AcceptRA=no

test/test-network/conf/dhcp-client-with-ipv4ll-without-dhcp-server.network

@@ -3,7 +3,7 @@ Name=veth99
 
 [Network]
 DHCP=ipv4
-LinkLocalAddressing=fallback
+LinkLocalAddressing=yes
 IPv6AcceptRA=no
 
 [DHCPv4]

test/test-network/systemd-networkd-tests.py

@@ -3428,8 +3428,8 @@ class NetworkdDHCPClientTests(unittest.TestCase, Utilities):
         'dhcp-client-use-dns-yes.network',
         'dhcp-client-use-domains.network',
         'dhcp-client-vrf.network',
-        'dhcp-client-with-ipv4ll-fallback-with-dhcp-server.network',
+        'dhcp-client-with-ipv4ll-with-dhcp-server.network',
-        'dhcp-client-with-ipv4ll-fallback-without-dhcp-server.network',
+        'dhcp-client-with-ipv4ll-without-dhcp-server.network',
         'dhcp-client-with-static-address.network',
         'dhcp-client.network',
         'dhcp-server-decline.network',
@@ -3995,9 +3995,9 @@ class NetworkdDHCPClientTests(unittest.TestCase, Utilities):
         print(output)
         self.assertRegex(output, 'onlink')
 
-    def test_dhcp_client_with_ipv4ll_fallback_with_dhcp_server(self):
+    def test_dhcp_client_with_ipv4ll_with_dhcp_server(self):
         copy_unit_to_networkd_unit_path('25-veth.netdev', 'dhcp-server-veth-peer.network',
-                                        'dhcp-client-with-ipv4ll-fallback-with-dhcp-server.network')
+                                        'dhcp-client-with-ipv4ll-with-dhcp-server.network')
         start_networkd()
         self.wait_online(['veth-peer:carrier'])
         start_dnsmasq(lease_time='2m')
@@ -4032,9 +4032,9 @@ class NetworkdDHCPClientTests(unittest.TestCase, Utilities):
 
         search_words_in_dnsmasq_log('DHCPOFFER', show_all=True)
 
-    def test_dhcp_client_with_ipv4ll_fallback_without_dhcp_server(self):
+    def test_dhcp_client_with_ipv4ll_without_dhcp_server(self):
         copy_unit_to_networkd_unit_path('25-veth.netdev', 'dhcp-server-veth-peer.network',
-                                        'dhcp-client-with-ipv4ll-fallback-without-dhcp-server.network')
+                                        'dhcp-client-with-ipv4ll-without-dhcp-server.network')
         start_networkd()
         self.wait_online(['veth99:degraded', 'veth-peer:routable'])