fix: handle nat66 prefix and unsupported opts in --vmnet-disable-dhcp

Follow-up to Copilot review on the macOS 26 --vmnet-disable-dhcp path:

- Apply --vmnet-nat66-prefix via vmnet_network_configuration_set_ipv6_prefix
  (parsed with inet_pton, /64), mirroring the legacy vmnet_nat66_prefix_key.
- Warn that --vmnet-interface-id, --vmnet-network-identifier and
  --vmnet-dhcp-end are ignored on this path: the macOS 26 vmnet network
  configuration API has no setter for the network identifier,
  vmnet_interface_start_with_network assigns its own interface id (verified
  empirically on macOS 26.4), and no DHCP server is started.
- Validate --vmnet-gateway / --vmnet-mask separately and print the offending
  value instead of relying on errno (inet_aton does not set errno on failure).
- Tighten the disable-dhcp test assertion and PID handling.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: fpolica91 <fabriciopolicarpo0@gmail.com>

Author: fpolica91

cli.c

@@ -139,6 +139,7 @@ struct cli_options *cli_options_parse(int argc, char *argv[]) {
       break;
     case CLI_OPT_VMNET_DHCP_END:
       res->vmnet_dhcp_end = strdup(optarg);
+      res->vmnet_dhcp_end_specified = true;
       break;
     case CLI_OPT_VMNET_MASK:
       res->vmnet_mask = strdup(optarg);

cli.h

@@ -16,6 +16,7 @@ struct cli_options {
   char *vmnet_gateway;
   // --vmnet-dhcp-end, corresponds to vmnet_end_address_key
   char *vmnet_dhcp_end;
+  bool vmnet_dhcp_end_specified;
   // --vmnet-mask, corresponds to vmnet_subnet_mask_key
   char *vmnet_mask;
   // --vmnet-interface-id, corresponds to vmnet_interface_id_key

main.c

@@ -253,6 +253,10 @@ static interface_ref start(struct state *state, struct cli_options *cliopt) {
         WARN("--vmnet-network-identifier is ignored with --vmnet-disable-dhcp: "
              "the macOS 26 vmnet network configuration API has no equivalent");
       }
+      if (cliopt->vmnet_dhcp_end_specified) {
+        WARN("--vmnet-dhcp-end is ignored with --vmnet-disable-dhcp: "
+             "no DHCP server is started");
+      }
       vmnet_return_t st = VMNET_FAILURE;
       vmnet_network_configuration_ref cfg =
           vmnet_network_configuration_create(cliopt->vmnet_mode, &st);
@@ -271,8 +275,12 @@ static interface_ref start(struct state *state, struct cli_options *cliopt) {
       }
       if (cliopt->vmnet_gateway != NULL) {
         struct in_addr gateway, subnet, mask;
-        if (!inet_aton(cliopt->vmnet_gateway, &gateway) || !inet_aton(cliopt->vmnet_mask, &mask)) {
-          ERRORN("inet_aton");
+        if (!inet_aton(cliopt->vmnet_gateway, &gateway)) {
+          ERRORF("invalid address \"%s\" was specified for --vmnet-gateway", cliopt->vmnet_gateway);
+          return NULL;
+        }
+        if (!inet_aton(cliopt->vmnet_mask, &mask)) {
+          ERRORF("invalid address \"%s\" was specified for --vmnet-mask", cliopt->vmnet_mask);
           return NULL;
         }
         subnet = gateway;

test/test-disable-dhcp.sh

@@ -15,11 +15,15 @@ if [ ! -f ipxe.lkrn ]; then
 	curl -fSL -O https://boot.ipxe.org/ipxe.lkrn
 fi
 
-sudo /opt/socket_vmnet/bin/socket_vmnet --vmnet-disable-dhcp \
+PIDFILE="$(mktemp -t socket_vmnet.pid.XXXXXX)"
+
+sudo /opt/socket_vmnet/bin/socket_vmnet --pidfile "${PIDFILE}" --vmnet-disable-dhcp \
 	--vmnet-gateway="${GATEWAY}" --socket-group=staff "${SOCKET}" &
-socket_vmnet_pid=$!
 cleanup() {
-	sudo kill "${socket_vmnet_pid}" 2>/dev/null || true
+	if [ -f "${PIDFILE}" ]; then
+		sudo kill "$(cat "${PIDFILE}")" 2>/dev/null || true
+		rm -f "${PIDFILE}"
+	fi
 	sudo rm -f "${SOCKET}"
 }
 trap cleanup EXIT