random: use the right rng device by default

When users provide mclock and time, build a default random generator
using these.

lib/mirage/mirage.mli

@@ -363,9 +363,9 @@ val tcpv4 : tcpv4 typ
 val tcpv6 : tcpv6 typ
 
 val direct_tcp :
-  ?clock:mclock impl ->
-  ?random:random impl ->
+  ?mclock:mclock impl ->
   ?time:time impl ->
+  ?random:random impl ->
   'a ip impl ->
   'a tcp impl
 
@@ -379,9 +379,9 @@ val stackv4 : stackv4 typ
 (** Implementation of the [Mirage_types.STACKV4] signature. *)
 
 val direct_stackv4 :
-  ?clock:mclock impl ->
-  ?random:random impl ->
+  ?mclock:mclock impl ->
   ?time:time impl ->
+  ?random:random impl ->
   network impl ->
   ethernet impl ->
   arpv4 impl ->
@@ -446,9 +446,9 @@ val resolver : resolver typ
 val resolver_dns :
   ?ns:Ipaddr.V4.t ->
   ?ns_port:int ->
-  ?random:random impl ->
   ?time:time impl ->
   ?mclock:mclock impl ->
+  ?random:random impl ->
   stackv4 impl ->
   resolver impl
 

lib/mirage/mirage_impl_resolver.ml

@@ -43,8 +43,8 @@ let resolver_dns_conf ~ns ~ns_port =
   impl ~packages ~keys ~connect "Resolver_mirage.Make_with_stack"
     (random @-> time @-> mclock @-> stackv4 @-> resolver)
 
-let resolver_dns ?ns ?ns_port ?(random = default_random) ?(time = default_time)
-    ?(mclock = default_monotonic_clock) stack =
+let resolver_dns ?ns ?ns_port ?(time = default_time)
+    ?(mclock = default_monotonic_clock) ?(random = rng ~time ~mclock ()) stack =
   let ns = Key.resolver ?default:ns ()
   and ns_port = Key.resolver_port ?default:ns_port () in
   resolver_dns_conf ~ns ~ns_port $ random $ time $ mclock $ stack

lib/mirage/mirage_impl_resolver.mli

@@ -10,9 +10,9 @@ val resolver : resolver typ
 val resolver_dns :
   ?ns:Ipaddr.V4.t ->
   ?ns_port:int ->
-  ?random:random impl ->
   ?time:time impl ->
   ?mclock:mclock impl ->
+  ?random:random impl ->
   Mirage_impl_stackv4.stackv4 impl ->
   resolver impl
 

lib/mirage/mirage_impl_stackv4.ml

@@ -36,8 +36,8 @@ let stackv4_direct_conf () =
     @-> tcpv4
     @-> stackv4 )
 
-let direct_stackv4 ?(clock = default_monotonic_clock) ?(random = default_random)
-    ?(time = default_time) network eth arp ip =
+let direct_stackv4 ?(mclock = default_monotonic_clock) ?(time = default_time)
+    ?(random = rng ~time ~mclock ()) network eth arp ip =
   stackv4_direct_conf ()
   $ time
   $ random
@@ -47,7 +47,7 @@ let direct_stackv4 ?(clock = default_monotonic_clock) ?(random = default_random)
   $ ip
   $ Mirage_impl_icmp.direct_icmpv4 ip
   $ direct_udp ~random ip
-  $ direct_tcp ~clock ~random ~time ip
+  $ direct_tcp ~mclock ~random ~time ip
 
 let dhcp_ipv4_stack ?(random = default_random) ?(time = default_time)
     ?(arp = arp ?time:None) tap =

lib/mirage/mirage_impl_stackv4.mli

@@ -3,9 +3,9 @@ type stackv4
 val stackv4 : stackv4 Functoria.typ
 
 val direct_stackv4 :
-  ?clock:Mirage_impl_mclock.mclock Functoria.impl ->
-  ?random:Mirage_impl_random.random Functoria.impl ->
+  ?mclock:Mirage_impl_mclock.mclock Functoria.impl ->
   ?time:Mirage_impl_time.time Functoria.impl ->
+  ?random:Mirage_impl_random.random Functoria.impl ->
   Mirage_impl_network.network Functoria.impl ->
   Mirage_impl_ethernet.ethernet Functoria.impl ->
   Mirage_impl_arpv4.arpv4 Functoria.impl ->

lib/mirage/mirage_impl_tcp.ml

@@ -28,9 +28,9 @@ let tcp_direct_func () =
   impl ~packages_v ~connect "Tcp.Flow.Make"
     (ip @-> time @-> mclock @-> random @-> tcp)
 
-let direct_tcp ?(clock = default_monotonic_clock) ?(random = default_random)
-    ?(time = default_time) ip =
-  tcp_direct_func () $ ip $ time $ clock $ random
+let direct_tcp ?(mclock = default_monotonic_clock) ?(time = default_time)
+    ?(random = rng ~time ~mclock ()) ip =
+  tcp_direct_func () $ ip $ time $ mclock $ random
 
 let tcpv4_socket_conf ipv4_key =
   let keys = [ Key.v ipv4_key ] in

lib/mirage/mirage_impl_tcp.mli

@@ -11,9 +11,9 @@ val tcpv4 : tcpv4 Functoria.typ
 val tcpv6 : tcpv6 Functoria.typ
 
 val direct_tcp :
-  ?clock:Mirage_impl_mclock.mclock Functoria.impl ->
-  ?random:Mirage_impl_random.random Functoria.impl ->
+  ?mclock:Mirage_impl_mclock.mclock Functoria.impl ->
   ?time:Mirage_impl_time.time Functoria.impl ->
+  ?random:Mirage_impl_random.random Functoria.impl ->
   'a Mirage_impl_ip.ip Functoria.impl ->
   'a tcp Functoria.impl