Merge pull request #32195 from yuwata/network-ndisc-mtu

network: several cleanups for IPv6 MTU

src/network/networkd-link.c

@@ -1881,7 +1881,7 @@ static int link_admin_state_up(Link *link) {
 
         /* We set the ipv6 mtu after the device mtu, but the kernel resets
          * ipv6 mtu on NETDEV_UP, so we need to reset it. */
-        r = link_set_ipv6_mtu(link);
+        r = link_set_ipv6_mtu(link, LOG_INFO);
         if (r < 0)
                 log_link_warning_errno(link, r, "Cannot set IPv6 MTU, ignoring: %m");
 
@@ -2434,6 +2434,13 @@ static int link_update_mtu(Link *link, sd_netlink_message *message) {
 
         link->mtu = mtu;
 
+        if (IN_SET(link->state, LINK_STATE_CONFIGURING, LINK_STATE_CONFIGURED)) {
+                /* The kernel resets IPv6 MTU after changing device MTU. So, we need to re-set IPv6 MTU again. */
+                r = link_set_ipv6_mtu(link, LOG_INFO);
+                if (r < 0)
+                        log_link_warning_errno(link, r, "Failed to set IPv6 MTU, ignoring: %m");
+        }
+
         if (link->dhcp_client) {
                 r = sd_dhcp_client_set_mtu(link->dhcp_client, link->mtu);
                 if (r < 0)

src/network/networkd-link.h

@@ -167,6 +167,7 @@ typedef struct Link {
         Set *ndisc_captive_portals;
         Set *ndisc_pref64;
         Set *ndisc_redirects;
+        uint32_t ndisc_mtu;
         unsigned ndisc_messages;
         bool ndisc_configured:1;
 

src/network/networkd-ndisc.c

@@ -1048,6 +1048,37 @@ static int ndisc_router_process_hop_limit(Link *link, sd_ndisc_router *rt) {
         return 0;
 }
 
+static int ndisc_router_process_mtu(Link *link, sd_ndisc_router *rt) {
+        uint32_t mtu;
+        int r;
+
+        assert(link);
+        assert(link->network);
+        assert(rt);
+
+        if (!link->network->ndisc_use_mtu)
+                return 0;
+
+        /* Ignore the MTU option if the lifetime is zero. */
+        r = sd_ndisc_router_get_lifetime(rt, NULL);
+        if (r <= 0)
+                return r;
+
+        r = sd_ndisc_router_get_mtu(rt, &mtu);
+        if (r == -ENODATA)
+                return 0;
+        if (r < 0)
+                return log_link_warning_errno(link, r, "Failed to get MTU from RA: %m");
+
+        link->ndisc_mtu = mtu;
+
+        r = link_set_ipv6_mtu(link, LOG_DEBUG);
+        if (r < 0)
+                log_link_warning_errno(link, r, "Failed to apply IPv6 MTU (%"PRIu32"), ignoring: %m", mtu);
+
+        return 0;
+}
+
 static int ndisc_router_process_autonomous_prefix(Link *link, sd_ndisc_router *rt) {
         usec_t lifetime_valid_usec, lifetime_preferred_usec;
         struct in6_addr prefix;
@@ -2122,6 +2153,10 @@ static int ndisc_router_handler(Link *link, sd_ndisc_router *rt) {
         if (r < 0)
                 return r;
 
+        r = ndisc_router_process_mtu(link, rt);
+        if (r < 0)
+                return r;
+
         r = ndisc_router_process_options(link, rt);
         if (r < 0)
                 return r;
@@ -2456,6 +2491,7 @@ void ndisc_flush(Link *link) {
         link->ndisc_captive_portals = set_free(link->ndisc_captive_portals);
         link->ndisc_pref64 = set_free(link->ndisc_pref64);
         link->ndisc_redirects = set_free(link->ndisc_redirects);
+        link->ndisc_mtu = 0;
 }
 
 static const char* const ndisc_start_dhcp6_client_table[_IPV6_ACCEPT_RA_START_DHCP6_CLIENT_MAX] = {

src/network/networkd-setlink.c

@@ -173,19 +173,7 @@ static int link_unset_master_handler(sd_netlink *rtnl, sd_netlink_message *m, Re
 }
 
 static int link_set_mtu_handler(sd_netlink *rtnl, sd_netlink_message *m, Request *req, Link *link, void *userdata) {
-        int r;
+        return set_link_handler_internal(rtnl, m, req, link, /* ignore = */ true, get_link_default_handler);
-
-        r = set_link_handler_internal(rtnl, m, req, link, /* ignore = */ true, get_link_default_handler);
-        if (r <= 0)
-                return r;
-
-        /* The kernel resets ipv6 mtu after changing device mtu;
-         * we must set this here, after we've set device mtu */
-        r = link_set_ipv6_mtu(link);
-        if (r < 0)
-                log_link_warning_errno(link, r, "Failed to set IPv6 MTU, ignoring: %m");
-
-        return 0;
 }
 
 static int link_configure_fill_message(
@@ -453,6 +441,43 @@ static bool netdev_is_ready(NetDev *netdev) {
         return true;
 }
 
+static uint32_t link_adjust_mtu(Link *link, uint32_t mtu) {
+        const char *origin;
+        uint32_t min_mtu;
+
+        assert(link);
+        assert(link->network);
+
+        min_mtu = link->min_mtu;
+        origin = "the minimum MTU of the interface";
+        if (link_ipv6_enabled(link)) {
+                /* IPv6 protocol requires a minimum MTU of IPV6_MTU_MIN(1280) bytes on the interface. Bump up
+                 * MTU bytes to IPV6_MTU_MIN. */
+                if (min_mtu < IPV6_MIN_MTU) {
+                        min_mtu = IPV6_MIN_MTU;
+                        origin = "the minimum IPv6 MTU";
+                }
+                if (min_mtu < link->network->ipv6_mtu) {
+                        min_mtu = link->network->ipv6_mtu;
+                        origin = "the requested IPv6 MTU in IPv6MTUBytes=";
+                }
+        }
+
+        if (mtu < min_mtu) {
+                log_link_warning(link, "Bumping the requested MTU %"PRIu32" to %s (%"PRIu32")",
+                                 mtu, origin, min_mtu);
+                mtu = min_mtu;
+        }
+
+        if (mtu > link->max_mtu) {
+                log_link_warning(link, "Reducing the requested MTU %"PRIu32" to the interface's maximum MTU %"PRIu32".",
+                                 mtu, link->max_mtu);
+                mtu = link->max_mtu;
+        }
+
+        return mtu;
+}
+
 static int link_is_ready_to_set_link(Link *link, Request *req) {
         int r;
 
@@ -570,13 +595,24 @@ static int link_is_ready_to_set_link(Link *link, Request *req) {
                                          }))
                         return false;
 
-                /* Changing FD mode may affect MTU. */
+                /* Changing FD mode may affect MTU.
+                 * See https://docs.kernel.org/networking/can.html#can-fd-flexible-data-rate-driver-support
+                 *   MTU = 16 (CAN_MTU)   => Classical CAN device
+                 *   MTU = 72 (CANFD_MTU) => CAN FD capable device */
                 if (ordered_set_contains(link->manager->request_queue,
                                          &(const Request) {
                                                  .link = link,
                                                  .type = REQUEST_TYPE_SET_LINK_CAN,
                                          }))
                         return false;
+
+                /* Now, it is ready to set MTU, but before setting, adjust requested MTU. */
+                uint32_t mtu = link_adjust_mtu(link, PTR_TO_UINT32(req->userdata));
+                if (mtu == link->mtu)
+                        return -EALREADY; /* Not necessary to set the same value. */
+
+                req->userdata = UINT32_TO_PTR(mtu);
+                return true;
         }
         default:
                 break;
@@ -865,51 +901,12 @@ int link_request_to_set_master(Link *link) {
 }
 
 int link_request_to_set_mtu(Link *link, uint32_t mtu) {
-        const char *origin;
-        uint32_t min_mtu, max_mtu;
         Request *req;
         int r;
 
         assert(link);
-        assert(link->network);
 
-        min_mtu = link->min_mtu;
+        if (mtu == 0)
-        origin = "the minimum MTU of the interface";
-        if (link_ipv6_enabled(link)) {
-                /* IPv6 protocol requires a minimum MTU of IPV6_MTU_MIN(1280) bytes on the interface. Bump up
-                 * MTU bytes to IPV6_MTU_MIN. */
-                if (min_mtu < IPV6_MIN_MTU) {
-                        min_mtu = IPV6_MIN_MTU;
-                        origin = "the minimum IPv6 MTU";
-                }
-                if (min_mtu < link->network->ipv6_mtu) {
-                        min_mtu = link->network->ipv6_mtu;
-                        origin = "the requested IPv6 MTU in IPv6MTUBytes=";
-                }
-        }
-
-        if (mtu < min_mtu) {
-                log_link_warning(link, "Bumping the requested MTU %"PRIu32" to %s (%"PRIu32")",
-                                 mtu, origin, min_mtu);
-                mtu = min_mtu;
-        }
-
-        max_mtu = link->max_mtu;
-        if (link->iftype == ARPHRD_CAN)
-                /* The maximum MTU may be changed when FD mode is changed.
-                 * See https://docs.kernel.org/networking/can.html#can-fd-flexible-data-rate-driver-support
-                 *   MTU = 16 (CAN_MTU)   => Classical CAN device
-                 *   MTU = 72 (CANFD_MTU) => CAN FD capable device
-                 * So, even if the current maximum is 16, we should not reduce the requested value now. */
-                max_mtu = MAX(max_mtu, 72u);
-
-        if (mtu > max_mtu) {
-                log_link_warning(link, "Reducing the requested MTU %"PRIu32" to the interface's maximum MTU %"PRIu32".",
-                                 mtu, max_mtu);
-                mtu = max_mtu;
-        }
-
-        if (link->mtu == mtu)
                 return 0;
 
         r = link_request_set_link(link, REQUEST_TYPE_SET_LINK_MTU,

src/network/networkd-sysctl.c

@@ -250,22 +250,28 @@ static int link_set_ipv6_proxy_ndp(Link *link) {
         return sysctl_write_ip_property_boolean(AF_INET6, link->ifname, "proxy_ndp", v);
 }
 
-int link_set_ipv6_mtu(Link *link) {
+int link_set_ipv6_mtu(Link *link, int log_level) {
-        uint32_t mtu;
+        uint32_t mtu = 0;
 
         assert(link);
 
         if (!link_is_configured_for_family(link, AF_INET6))
                 return 0;
 
-        if (link->network->ipv6_mtu == 0)
+        assert(link->network);
+
+        if (link->network->ndisc_use_mtu)
+                mtu = link->ndisc_mtu;
+        if (mtu == 0)
+                mtu = link->network->ipv6_mtu;
+        if (mtu == 0)
                 return 0;
 
-        mtu = link->network->ipv6_mtu;
+        if (mtu > link->mtu) {
-        if (mtu > link->max_mtu) {
+                log_link_full(link, log_level,
-                log_link_warning(link, "Reducing requested IPv6 MTU %"PRIu32" to the interface's maximum MTU %"PRIu32".",
+                              "Reducing requested IPv6 MTU %"PRIu32" to the interface's maximum MTU %"PRIu32".",
-                                 mtu, link->max_mtu);
+                              mtu, link->mtu);
-                mtu = link->max_mtu;
+                mtu = link->mtu;
         }
 
         return sysctl_write_ip_property_uint32(AF_INET6, link->ifname, "mtu", mtu);
@@ -355,7 +361,7 @@ int link_set_sysctl(Link *link) {
         if (r < 0)
                 log_link_warning_errno(link, r, "Cannot set IPv6 proxy NDP, ignoring: %m");
 
-        r = link_set_ipv6_mtu(link);
+        r = link_set_ipv6_mtu(link, LOG_INFO);
         if (r < 0)
                 log_link_warning_errno(link, r, "Cannot set IPv6 MTU, ignoring: %m");
 

src/network/networkd-sysctl.h

@@ -31,7 +31,7 @@ void manager_set_sysctl(Manager *manager);
 
 int link_get_ip_forwarding(Link *link, int family);
 int link_set_sysctl(Link *link);
-int link_set_ipv6_mtu(Link *link);
+int link_set_ipv6_mtu(Link *link, int log_level);
 
 const char* ipv6_privacy_extensions_to_string(IPv6PrivacyExtensions i) _const_;
 IPv6PrivacyExtensions ipv6_privacy_extensions_from_string(const char *s) _pure_;

test/test-network/conf/25-veth-peer-no-address.network

@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: LGPL-2.1-or-later
+[Match]
+Name=veth-peer
+
+[Network]
+IPv6AcceptRA=no

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

@@ -5572,6 +5572,48 @@ class NetworkdRATests(unittest.TestCase, Utilities):
         self.wait_route_dropped('veth99', 'proto redirect', ipv='-6', timeout_sec=10)
         self.wait_route_dropped('veth99', 'proto ra', ipv='-6', timeout_sec=10)
 
+    def check_ndisc_mtu(self, mtu):
+        for _ in range(20):
+            output = read_ipv6_sysctl_attr('veth99', 'mtu')
+            if output == f'{mtu}':
+                break
+            time.sleep(0.5)
+        else:
+            self.fail(f'IPv6 MTU does not matches: value={output}, expected={mtu}')
+
+    def test_ndisc_mtu(self):
+        if not os.path.exists(test_ndisc_send):
+            self.skipTest(f"{test_ndisc_send} does not exist.")
+
+        copy_network_unit('25-veth.netdev',
+                          '25-veth-peer-no-address.network',
+                          '25-ipv6-prefix-veth-token-static.network')
+        start_networkd()
+        self.wait_online('veth-peer:degraded')
+
+        for _ in range(20):
+            output = read_networkd_log()
+            if 'veth99: NDISC: Started IPv6 Router Solicitation client' in output:
+                break
+            time.sleep(0.5)
+        else:
+            self.fail('sd-ndisc does not started on veth99.')
+
+        check_output(f'{test_ndisc_send} --interface veth-peer --type ra --lifetime 1hour --mtu 1400')
+        self.check_ndisc_mtu(1400)
+
+        check_output(f'{test_ndisc_send} --interface veth-peer --type ra --lifetime 1hour --mtu 1410')
+        self.check_ndisc_mtu(1410)
+
+        check_output('ip link set dev veth99 mtu 1600')
+        self.check_ndisc_mtu(1410)
+
+        check_output(f'{test_ndisc_send} --interface veth-peer --type ra --lifetime 1hour --mtu 1700')
+        self.check_ndisc_mtu(1600)
+
+        check_output('ip link set dev veth99 mtu 1800')
+        self.check_ndisc_mtu(1700)
+
     def test_ipv6_token_prefixstable(self):
         copy_network_unit('25-veth.netdev', '25-ipv6-prefix.network', '25-ipv6-prefix-veth-token-prefixstable.network')
         start_networkd()