feat: Allow specifying vmnet network UUID to disable DHCP (on vmnet.host network only)

This commit introduces a new `--vmnet-network-uuid` command-line option to allow
setting the `vmnet_network_identifier_key` for vmnet.

This property is only applicable to a vmnet_interface in
VMNET_HOST_MODE.

If this property is set, the vmnet_interface is added to an isolated
network with the specified identifier.

No DHCP service is provided on this network.

This is useful for certain applications where the users need an isolated
network and are running their own dhcp to assign IPs in such network.

See issue [#139](#139)

```
❯ sudo ./socket_vmnet "/opt/homebrew/var/run/socket_vmnet" --vmnet-mode=host --vmnet-gateway=192.168.100.1 --vmnet-network-uuid=99eddb74-3193-48e3-bafb-b3ca99e949c1
Password:                                                                                                                                                           INFO | Initializing vmnet.framework (mode 1000)
INFO | * vmnet_write_max_packets: 256
INFO | * vmnet_read_max_packets: 256
INFO | * vmnet_subnet_mask: 0.0.0.0
INFO | * vmnet_mtu: 1500
INFO | * vmnet_end_address: 255.255.255.254
INFO | * vmnet_start_address: 0.0.0.0
INFO | * vmnet_interface_id: 0E21C1D4-43D9-4363-B767-A64FE591EA7D
INFO | * vmnet_max_packet_size: 1514
INFO | * vmnet_mac_address: 66:77:98:e1:52:9c
```

I could run my LAB vms, I saw no DHCP been handed over by MacOS/bootp,
my Lab runs a special VM with DHCPD and I saw that not colliding.

```
❯ sudo ./socket_vmnet "/opt/homebrew/var/run/socket_vmnet" --vmnet-gateway=192.168.100.1 --vmnet-network-uuid=99eddb74-3193-48e3-bafb-b3ca99e949c1
INFO | Initializing vmnet.framework (mode 1001)
INFO | * vmnet_write_max_packets: 256                                                                                                                               INFO | * vmnet_read_max_packets: 256
INFO | * vmnet_subnet_mask: 255.255.255.0
INFO | * vmnet_mtu: 1500
INFO | * vmnet_end_address: 192.168.100.254
INFO | * vmnet_start_address: 192.168.100.1
INFO | * vmnet_interface_id: 99AC02F6-59D3-4192-820B-C8DAED0F2B81
INFO | * vmnet_max_packet_size: 1514
INFO | * vmnet_nat66_prefix: fd86:9a96:2682:1344::
INFO | * vmnet_mac_address: 3a:be:d4:0d:33:11
```

Signed-off-by: Angelo Failla <[email protected]>

Author: pallotron

README.md

@@ -351,6 +351,12 @@ sudo launchctl bootout system /Library/LaunchDaemons/io.github.lima-vm.socket_vm
 sudo rm /Library/LaunchDaemons/io.github.lima-vm.socket_vmnet.bridged.${BRIDGED}.plist
 ```
 
+### No DHCP mode
+
+By passing `--vmnet-mode=host` without `--vmnet-gateway` to `socket_vmnet`, the internal DHCP will be disabled.
+This is useful for situations where the users want to create a network with statically assigned IP addresses or where another VMs is running its own DHCP server.
+This mode does not come with a launchd service.
+
 ## FAQs
 
 ### Why does `socket_vmnet` require root?
@@ -430,6 +436,15 @@ sudo /usr/libexec/ApplicationFirewall/socketfilterfw --add /usr/libexec/bootpd
 /usr/libexec/ApplicationFirewall/socketfilterfw --unblock /usr/libexec/bootpd
 ```
 
+### How to setup a vmnet host network without DHCP
+
+You may need to disable the vmnet framework's DHCP to:
+- Create a host network where all VMs have static IPs.
+- Run a custom DHCP server on one VM to assign IPs to others on the same network.
+
+To disable the internal DHCP, use `--vmnet-mode=host` without `--vmnet-gateway`. This allows you to use static IP addresses for your VMs.
+You can optionally provide a `--vmnet-network-uuid`.
+
 ## Links
 
 - https://developer.apple.com/documentation/vmnet

cli.c

@@ -48,6 +48,8 @@ static void print_usage(const char *argv0) {
          "specified\n");
   printf("--vmnet-interface-id=UUID           vmnet interface ID (default: "
          "random)\n");
+  printf("--vmnet-network-uuid=UUID           vmnet network UUID, if provided in \"host\" vmnet mode withouht --vmnet-gateway, the\n"
+         "                                    internal DHCP will be disabled (default: " "random)\n");
   printf("--vmnet-nat66-prefix=PREFIX::       The IPv6 prefix to use with "
          "shared mode.\n");
   printf("                                    The prefix must be a ULA i.e. "
@@ -72,6 +74,7 @@ enum {
   CLI_OPT_VMNET_MASK,
   CLI_OPT_VMNET_INTERFACE_ID,
   CLI_OPT_VMNET_NAT66_PREFIX,
+  CLI_OPT_VMNET_NETWORK_UUID,
 };
 
 struct cli_options *cli_options_parse(int argc, char *argv[]) {
@@ -80,6 +83,7 @@ struct cli_options *cli_options_parse(int argc, char *argv[]) {
     ERRORN("calloc");
     exit(EXIT_FAILURE);
   }
+  uuid_clear(res->vmnet_network_uuid);
 
   const struct option longopts[] = {
       {"socket-group",       required_argument, NULL, CLI_OPT_SOCKET_GROUP      },
@@ -90,6 +94,7 @@ struct cli_options *cli_options_parse(int argc, char *argv[]) {
       {"vmnet-mask",         required_argument, NULL, CLI_OPT_VMNET_MASK        },
       {"vmnet-interface-id", required_argument, NULL, CLI_OPT_VMNET_INTERFACE_ID},
       {"vmnet-nat66-prefix", required_argument, NULL, CLI_OPT_VMNET_NAT66_PREFIX},
+      {"vmnet-network-uuid", required_argument, NULL, CLI_OPT_VMNET_NETWORK_UUID},
       {"pidfile",            required_argument, NULL, 'p'                       },
       {"help",               no_argument,       NULL, 'h'                       },
       {"version",            no_argument,       NULL, 'v'                       },
@@ -134,6 +139,12 @@ struct cli_options *cli_options_parse(int argc, char *argv[]) {
     case CLI_OPT_VMNET_NAT66_PREFIX:
       res->vmnet_nat66_prefix = strdup(optarg);
       break;
+    case CLI_OPT_VMNET_NETWORK_UUID:
+      if (uuid_parse(optarg, res->vmnet_network_uuid) < 0) {
+        ERRORF("Failed to parse UUID \"%s\"", optarg);
+        goto error;
+      }
+      break;
     case 'p':
       res->pidfile = strdup(optarg);
       break;
@@ -184,14 +195,17 @@ struct cli_options *cli_options_parse(int argc, char *argv[]) {
   if (uuid_is_null(res->vmnet_interface_id)) {
     uuid_generate_random(res->vmnet_interface_id);
   }
+  if (uuid_is_null(res->vmnet_network_uuid)) {
+    uuid_generate_random(res->vmnet_network_uuid);
+  }
 
   /* validate */
   if (res->vmnet_mode == VMNET_BRIDGED_MODE && res->vmnet_interface == NULL) {
     ERROR("vmnet mode \"bridged\" require --vmnet-interface to be specified");
     goto error;
   }
   if (res->vmnet_gateway == NULL) {
-    if (res->vmnet_mode != VMNET_BRIDGED_MODE) {
+    if (res->vmnet_mode != VMNET_BRIDGED_MODE && res->vmnet_mode != VMNET_HOST_MODE) {
       WARN("--vmnet-gateway=IP should be explicitly specified to "
            "avoid conflicting with other applications");
     }

cli.h

@@ -20,6 +20,8 @@ struct cli_options {
   char *vmnet_mask;
   // --vmnet-interface-id, corresponds to vmnet_interface_id_key
   uuid_t vmnet_interface_id;
+  // --vmnet-network-uuid, corresponds to vmnet_network_identifier_key
+  uuid_t vmnet_network_uuid;
   // --vmnet-nat66-prefix, corresponds to vmnet_nat66_prefix_key
   char *vmnet_nat66_prefix;
   // -p, --pidfile; writes pidfile using permissions of socket_vmnet

main.c

@@ -230,10 +230,19 @@ static interface_ref start(struct state *state, struct cli_options *cliopt) {
     INFOF("Using network interface \"%s\"", cliopt->vmnet_interface);
     xpc_dictionary_set_string(dict, vmnet_shared_interface_name_key, cliopt->vmnet_interface);
   }
-  if (cliopt->vmnet_gateway != NULL) {
-    xpc_dictionary_set_string(dict, vmnet_start_address_key, cliopt->vmnet_gateway);
-    xpc_dictionary_set_string(dict, vmnet_end_address_key, cliopt->vmnet_dhcp_end);
-    xpc_dictionary_set_string(dict, vmnet_subnet_mask_key, cliopt->vmnet_mask);
+
+  // no dhcp
+  if (cliopt->vmnet_mode == VMNET_HOST_MODE && cliopt->vmnet_gateway == NULL) {
+    xpc_dictionary_set_uuid(dict, vmnet_network_identifier_key, cliopt->vmnet_network_uuid);
+    uuid_string_t uuid_str;
+    uuid_unparse(cliopt->vmnet_network_uuid, uuid_str);
+    INFOF("Using network identifier \"%s\" and no vmnet gateway -> NO DHCP will be enabled on this vmnet", uuid_str);
+  } else  {
+    if (cliopt->vmnet_gateway != NULL) {
+      xpc_dictionary_set_string(dict, vmnet_start_address_key, cliopt->vmnet_gateway);
+      xpc_dictionary_set_string(dict, vmnet_end_address_key, cliopt->vmnet_dhcp_end);
+      xpc_dictionary_set_string(dict, vmnet_subnet_mask_key, cliopt->vmnet_mask);
+    }
   }
 
   xpc_dictionary_set_uuid(dict, vmnet_interface_id_key, cliopt->vmnet_interface_id);