CA-416532: Revert #6586, overwrites /etc/resolve.conf (#6643)

This reverts @psafont's PR, #6586, this causing the `/etc/resolve.conf`
to be overwritten during update, after the dhclient writes it. This
happens because `set_dns` no longer checks the mode before applying the
DNS config,

This reverts commit 05e6317, reversing
changes made to 1fbdaae.

Author: GabrielBuica

ocaml/networkd/bin/network_server.ml

@@ -554,8 +554,7 @@ module Interface = struct
   let set_dns _ dbg ~name ~nameservers ~domains =
     Debug.with_thread_associated dbg
       (fun () ->
-        update_config name
-          {(get_config name) with dns= Some (nameservers, domains)} ;
+        update_config name {(get_config name) with dns= (nameservers, domains)} ;
         debug "Configuring DNS for %s: nameservers: [%s]; domains: [%s]" name
           (String.concat ", " (List.map Unix.string_of_inet_addr nameservers))
           (String.concat ", " domains) ;
@@ -728,7 +727,7 @@ module Interface = struct
                   ; ipv6_conf
                   ; ipv6_gateway
                   ; ipv4_routes
-                  ; dns
+                  ; dns= nameservers, domains
                   ; mtu
                   ; ethtool_settings
                   ; ethtool_offload
@@ -737,10 +736,15 @@ module Interface = struct
                 ) ) ->
                 update_config name c ;
                 exec (fun () ->
-                    match dns with
-                    | Some (nameservers, domains) ->
+                    (* We only apply the DNS settings when not in a DHCP mode
+                       to avoid conflicts. The `dns` field
+                       should really be an option type so that we don't have to
+                       derive the intention of the caller by looking at other
+                       fields. *)
+                    match (ipv4_conf, ipv6_conf) with
+                    | Static4 _, _ | _, Static6 _ | _, Autoconf6 ->
                         set_dns () dbg ~name ~nameservers ~domains
-                    | None ->
+                    | _ ->
                         ()
                 ) ;
                 exec (fun () -> set_ipv4_conf dbg name ipv4_conf) ;

ocaml/networkd/bin_db/networkd_db.ml

@@ -74,25 +74,20 @@ let _ =
                     [("gateway", Unix.string_of_inet_addr addr)]
               in
               let dns =
-                interface_config.dns
-                |> Option.map fst
-                |> Option.map (List.map Unix.string_of_inet_addr)
-                |> Option.fold ~none:[] ~some:(function
-                     | [] ->
-                         []
-                     | dns' ->
-                         [("dns", String.concat "," dns')]
-                     )
+                let dns' =
+                  List.map Unix.string_of_inet_addr (fst interface_config.dns)
+                in
+                if dns' = [] then
+                  []
+                else
+                  [("dns", String.concat "," dns')]
               in
               let domains =
-                interface_config.dns
-                |> Option.map snd
-                |> Option.fold ~none:[] ~some:(function
-                     | [] ->
-                         []
-                     | domains' ->
-                         [("domain", String.concat "," domains')]
-                     )
+                let domains' = snd interface_config.dns in
+                if domains' = [] then
+                  []
+                else
+                  [("domain", String.concat "," domains')]
               in
               mode @ addrs @ gateway @ dns @ domains
           | None4 ->

ocaml/networkd/lib/network_config.ml

@@ -37,6 +37,7 @@ let bridge_naming_convention (device : string) =
 let get_list_from ~sep ~key args =
   List.assoc_opt key args
   |> Option.map (fun v -> Astring.String.cuts ~empty:false ~sep v)
+  |> Option.value ~default:[]
 
 let parse_ipv4_config args = function
   | Some "static" ->
@@ -72,13 +73,11 @@ let parse_ipv6_config args = function
       (None6, None)
 
 let parse_dns_config args =
-  let ( let* ) = Option.bind in
-  let* nameservers =
-    get_list_from ~sep:"," ~key:"DNS" args
-    |> Option.map (List.map Unix.inet_addr_of_string)
+  let nameservers =
+    get_list_from ~sep:"," ~key:"DNS" args |> List.map Unix.inet_addr_of_string
   in
-  let* domains = get_list_from ~sep:" " ~key:"DOMAIN" args in
-  Some (nameservers, domains)
+  let domains = get_list_from ~sep:" " ~key:"DOMAIN" args in
+  (nameservers, domains)
 
 let read_management_conf () =
   try
@@ -104,15 +103,15 @@ let read_management_conf () =
     let device =
       (* Take 1st member of bond *)
       match (bond_mode, bond_members) with
-      | None, _ | _, (None | Some []) -> (
+      | None, _ | _, [] -> (
         match List.assoc_opt "LABEL" args with
         | Some x ->
             x
         | None ->
             error "%s: missing LABEL in %s" __FUNCTION__ management_conf ;
             raise Read_error
       )
-      | _, Some (hd :: _) ->
+      | _, hd :: _ ->
           hd
     in
     Inventory.reread_inventory () ;

ocaml/xapi-idl/network/network_interface.ml

@@ -158,10 +158,7 @@ type interface_config_t = {
   ; ipv6_conf: ipv6 [@default None6]
   ; ipv6_gateway: Unix.inet_addr option [@default None]
   ; ipv4_routes: ipv4_route_t list [@default []]
-  ; dns: (Unix.inet_addr list * string list) option [@default None]
-        (** the list
-  of nameservers and domains to persist in /etc/resolv.conf. Must be None when
-  using a DHCP mode *)
+  ; dns: Unix.inet_addr list * string list [@default [], []]
   ; mtu: int [@default 1500]
   ; ethtool_settings: (string * string) list [@default []]
   ; ethtool_offload: (string * string) list [@default [("lro", "off")]]
@@ -203,7 +200,7 @@ let default_interface =
   ; ipv6_conf= None6
   ; ipv6_gateway= None
   ; ipv4_routes= []
-  ; dns= None
+  ; dns= ([], [])
   ; mtu= 1500
   ; ethtool_settings= []
   ; ethtool_offload= [("lro", "off")]

ocaml/xapi/nm.ml

@@ -634,25 +634,28 @@ let bring_pif_up ~__context ?(management_interface = false) (pif : API.ref_PIF)
                     rc.API.pIF_ip_configuration_mode = `Static
                 | `IPv6 ->
                     rc.API.pIF_ipv6_configuration_mode = `Static
-                    || rc.API.pIF_ipv6_configuration_mode = `Autoconf
               in
               let dns =
                 match (static, rc.API.pIF_DNS) with
                 | false, _ | true, "" ->
-                    None
+                    ([], [])
                 | true, pif_dns ->
                     let nameservers =
                       List.map Unix.inet_addr_of_string
-                        (String.split_on_char ',' pif_dns)
+                        (String.split ',' pif_dns)
                     in
                     let domains =
                       match List.assoc_opt "domain" rc.API.pIF_other_config with
-                      | None | Some "" ->
+                      | None ->
                           []
-                      | Some domains ->
-                          String.split_on_char ',' domains
+                      | Some domains -> (
+                        try String.split ',' domains
+                        with _ ->
+                          warn "Invalid DNS search domains: %s" domains ;
+                          []
+                      )
                     in
-                    Some (nameservers, domains)
+                    (nameservers, domains)
               in
               let mtu = determine_mtu rc net_rc in
               let ethtool_settings, ethtool_offload =