networkd: support proxy_arp_pvlan sysctl

The proxy ARP private VLAN sysctl is useful for VLAN aggregation, see
https://sysctl-explorer.net/net/ipv4/proxy_arp_pvlan/ for details.

src/network/networkd-network-gperf.gperf

@@ -138,6 +138,7 @@ Network.IPv4RouteLocalnet,                   config_parse_tristate,
 Network.ActiveSlave,                         config_parse_bool,                                        0,                             offsetof(Network, active_slave)
 Network.PrimarySlave,                        config_parse_bool,                                        0,                             offsetof(Network, primary_slave)
 Network.IPv4ProxyARP,                        config_parse_tristate,                                    0,                             offsetof(Network, proxy_arp)
+Network.IPv4ProxyARPPrivateVLAN,             config_parse_tristate,                                    0,                             offsetof(Network, proxy_arp_pvlan)
 Network.ProxyARP,                            config_parse_tristate,                                    0,                             offsetof(Network, proxy_arp)
 Network.IPv6ProxyNDPAddress,                 config_parse_ipv6_proxy_ndp_address,                      0,                             0
 Network.IPv4ReversePathFilter,               config_parse_ip_reverse_path_filter,                      0,                             offsetof(Network, ipv4_rp_filter)

src/network/networkd-network.c

@@ -473,6 +473,7 @@ int network_load_one(Manager *manager, OrderedHashmap **networks, const char *fi
                 .ipv6_dad_transmits = -1,
                 .ipv6_proxy_ndp = -1,
                 .proxy_arp = -1,
+                .proxy_arp_pvlan = -1,
                 .ipv4_rp_filter = _IP_REVERSE_PATH_FILTER_INVALID,
 
                 .ipv6_accept_ra = -1,

src/network/networkd-network.h

@@ -325,6 +325,7 @@ struct Network {
         int ipv6_dad_transmits;
         uint8_t ipv6_hop_limit;
         int proxy_arp;
+        int proxy_arp_pvlan;
         uint32_t ipv6_mtu;
         IPv6PrivacyExtensions ipv6_privacy_extensions;
         IPReversePathFilter ipv4_rp_filter;

src/network/networkd-sysctl.c

@@ -58,6 +58,18 @@ static int link_set_proxy_arp(Link *link) {
         return sysctl_write_ip_property_boolean(AF_INET, link->ifname, "proxy_arp", link->network->proxy_arp > 0);
 }
 
+static int link_set_proxy_arp_pvlan(Link *link) {
+        assert(link);
+
+        if (!link_is_configured_for_family(link, AF_INET))
+                return 0;
+
+        if (link->network->proxy_arp_pvlan < 0)
+                return 0;
+
+        return sysctl_write_ip_property_boolean(AF_INET, link->ifname, "proxy_arp_pvlan", link->network->proxy_arp_pvlan > 0);
+}
+
 static bool link_ip_forward_enabled(Link *link, int family) {
         assert(link);
         assert(IN_SET(family, AF_INET, AF_INET6));
@@ -257,6 +269,10 @@ int link_set_sysctl(Link *link) {
         if (r < 0)
                log_link_warning_errno(link, r, "Cannot configure proxy ARP for interface, ignoring: %m");
 
+        r = link_set_proxy_arp_pvlan(link);
+        if (r < 0)
+                log_link_warning_errno(link, r, "Cannot configure proxy ARP private VLAN for interface, ignoring: %m");
+
         r = link_set_ipv4_forward(link);
         if (r < 0)
                 log_link_warning_errno(link, r, "Cannot turn on IPv4 packet forwarding, ignoring: %m");