Remove the "extra_dns" IPs

These were a remnant of an earlier attempt to make DNS more reliable.
The idea was to map the "extra_dns" IPs onto the real external DNS IPs
and use the VM's resolvers to query them. Unfortunately this failed
because many common resolvers (including the musl one) only use the
first 3 IPs and a Mac/Windows host may have more than that.

On Windows we use a resolver library and on Mac we use the macOS APIs
directly, exposing both as a single DNS IP. This code is redundant and
can be removed.

Signed-off-by: David Scott <[email protected]>

Author: djs55

src/hostnet/configuration.ml

@@ -44,7 +44,6 @@ type t = {
   (* TODO: remove this from the record since it is not constant across all clients *)
   lowest_ip: Ipaddr.V4.t;
   highest_ip: Ipaddr.V4.t;
-  extra_dns: Ipaddr.V4.t list;
   dhcp_json_path: string option;
   dhcp_configuration: Dhcp_configuration.t option;
   mtu: int;
@@ -55,7 +54,7 @@ type t = {
 }
 
 let to_string t =
-  Printf.sprintf "server_macaddr = %s; max_connection = %s; dns_path = %s; dns = %s; resolver = %s; domain = %s; allowed_bind_addresses = %s; gateway_ip = %s; lowest_ip = %s; highest_ip = %s; extra_dns = %s; dhcp_json_path = %s; dhcp_configuration = %s; mtu = %d; http_intercept = %s; http_intercept_path = %s; port_max_idle_time = %s; host_names = %s"
+  Printf.sprintf "server_macaddr = %s; max_connection = %s; dns_path = %s; dns = %s; resolver = %s; domain = %s; allowed_bind_addresses = %s; gateway_ip = %s; lowest_ip = %s; highest_ip = %s; dhcp_json_path = %s; dhcp_configuration = %s; mtu = %d; http_intercept = %s; http_intercept_path = %s; port_max_idle_time = %s; host_names = %s"
     (Macaddr.to_string t.server_macaddr)
     (match t.max_connections with None -> "None" | Some x -> string_of_int x)
     (match t.dns_path with None -> "None" | Some x -> x)
@@ -66,7 +65,6 @@ let to_string t =
     (Ipaddr.V4.to_string t.gateway_ip)
     (Ipaddr.V4.to_string t.lowest_ip)
     (Ipaddr.V4.to_string t.highest_ip)
-    (String.concat ", " (List.map Ipaddr.V4.to_string t.extra_dns))
     (match t.dhcp_json_path with None -> "None" | Some x -> x)
     (match t.dhcp_configuration with None -> "None" | Some x -> Dhcp_configuration.to_string x)
     t.mtu
@@ -81,7 +79,6 @@ let no_dns_servers =
 let default_lowest_ip = Ipaddr.V4.of_string_exn "192.168.65.2"
 let default_gateway_ip = Ipaddr.V4.of_string_exn "192.168.65.1"
 let default_highest_ip = Ipaddr.V4.of_string_exn "192.168.65.254"
-let default_extra_dns = []
 (* The default MTU is limited by the maximum message size on a Hyper-V
    socket. On currently available windows versions, we need to stay
    below 8192 bytes *)
@@ -103,7 +100,6 @@ let default = {
   gateway_ip = default_gateway_ip;
   lowest_ip = default_lowest_ip;
   highest_ip = default_highest_ip;
-  extra_dns = default_extra_dns;
   dhcp_json_path = None;
   dhcp_configuration = None;
   mtu = default_mtu;

src/hostnet/hostnet_dhcp.ml

@@ -46,7 +46,7 @@ module Make (Clock: Mirage_clock_lwt.MCLOCK) (Netif: Mirage_net_lwt.S) = struct
        resolved in the future *)
     let low_ip, high_ip =
       let open Ipaddr.V4 in
-      let all_static_ips = c.Configuration.gateway_ip :: c.Configuration.lowest_ip :: c.Configuration.extra_dns in
+      let all_static_ips = [ c.Configuration.gateway_ip; c.Configuration.lowest_ip ] in
       let highest = maximum_ip all_static_ips in
       let i32 = to_int32 highest in
       of_int32 @@ Int32.succ i32, of_int32 @@ Int32.succ @@ Int32.succ i32 in
@@ -73,7 +73,7 @@ module Make (Clock: Mirage_clock_lwt.MCLOCK) (Netif: Mirage_net_lwt.S) = struct
         | _, _ -> Configuration.default_domain in
       let options = [
         Dhcp_wire.Routers [ c.Configuration.gateway_ip ];
-        Dhcp_wire.Dns_servers (c.Configuration.gateway_ip :: c.Configuration.extra_dns);
+        Dhcp_wire.Dns_servers [ c.Configuration.gateway_ip ];
         Dhcp_wire.Ntp_servers [ c.Configuration.gateway_ip ];
         Dhcp_wire.Broadcast_addr (Ipaddr.V4.Prefix.broadcast prefix);
         Dhcp_wire.Subnet_mask (Ipaddr.V4.Prefix.netmask prefix);

src/hostnet/slirp.ml

@@ -862,12 +862,12 @@ struct
     let local_arp_table = [
       c.Configuration.lowest_ip, client_macaddr;
       c.Configuration.gateway_ip, c.Configuration.server_macaddr;
-    ] @ (List.map (fun ip -> ip, c.Configuration.server_macaddr) c.Configuration.extra_dns) in
+    ] in
     Global_arp_ethif.connect switch
     >>= fun global_arp_ethif ->
 
     (* Listen on local IPs *)
-    let local_ips = c.Configuration.gateway_ip :: c.Configuration.extra_dns in
+    let local_ips = [ c.Configuration.gateway_ip ] in
 
     let dhcp = Dhcp.make ~configuration:c clock switch in
 
@@ -1305,15 +1305,6 @@ struct
     Active_config.map (Configuration.Parse.ipv4 Configuration.default_highest_ip) string_highest_ips
     >>= fun highest_ips ->
     on_change highest_ips (fun highest_ip -> update (fun c -> { c with highest_ip }));
-    let extra_dns_ips_path = driver @ [ "slirp"; "extra_dns" ] in
-    Config.string config ~default:""
-      extra_dns_ips_path
-    >>= fun string_extra_dns_ips ->
-    Active_config.map
-      (fun x -> Lwt.return @@ Configuration.Parse.ipv4_list (List.map Ipaddr.V4.of_string_exn Configuration.default_extra_dns) x)
-      string_extra_dns_ips
-    >>= fun extra_dns_ips ->
-    on_change extra_dns_ips (fun extra_dns -> update (fun c -> { c with extra_dns }));
     let resolver_path = driver @ [ "slirp"; "resolver" ] in
     Config.string_option config resolver_path
     >>= fun string_resolver_settings ->

src/hostnet_test/slirp_stack.ml

@@ -134,17 +134,11 @@ module DNS = Dns_resolver_mirage.Make(Host.Time)(Client)
 
 let primary_dns_ip = Ipaddr.V4.of_string_exn "192.168.65.1"
 
-let extra_dns_ip = List.map Ipaddr.V4.of_string_exn [
-    "192.168.65.3"; "192.168.65.4"; "192.168.65.5"; "192.168.65.6";
-    "192.168.65.7"; "192.168.65.8"; "192.168.65.9"; "192.168.65.10";
-  ]
-
 let preferred_ip1 = Ipaddr.V4.of_string_exn "192.168.65.250"
 
 let config =
   let configuration = {
     Configuration.default with
-    extra_dns = extra_dns_ip;
     domain = Some "local";
   } in
   Mclock.connect () >>= fun clock ->