[kernel] Simplify mailbox code, and messages

A number of simplifications of mailboxes now that the interface is much
simpler, and synchronous.

* call and respond can now only transfer one handle at a time
* mailbox objects got rid of the message queue, and just have
  wait_queues of blocked threads, and a reply_to map.
* threads now have a message_data struct on them for use by mailboxes

src/user/drv.uart/main.cpp

@@ -61,10 +61,7 @@ channel_pump_loop()
 
     uint64_t tag = j6_proto_sl_register;
     uint64_t proto_id = "jsix.protocol.stream.ouput"_id;
-    size_t handle_count = 1;
-    result = j6_mailbox_call(slp,
-            &tag, &proto_id,
-            &cout_write, &handle_count);
+    result = j6_mailbox_call(slp, &tag, &proto_id, &cout_write);
     if (result != j6_status_ok)
         return 4;
 

src/user/srv.init/service_locator.cpp

@@ -25,23 +25,17 @@ service_locator_start(j6_handle_t mb)
 
     uint64_t tag = 0;
     uint64_t subtag = 0;
-    uint16_t reply_tag = 0;
-
-    j6_handle_t handles[10] = {0};
-    const size_t handles_capacity = sizeof(handles)/sizeof(j6_handle_t);
-    size_t handles_count = 0;
+    uint64_t reply_tag = 0;
 
+    j6_handle_t give_handle = j6_handle_invalid;
     uint64_t proto_id;
 
     while (true) {
-        size_t handles_in = handles_count;
-        handles_count = handles_capacity;
+        j6_status_t s = j6_mailbox_respond(mb, &tag, &subtag, &give_handle,
+                &reply_tag, j6_mailbox_block);
 
-        j6_status_t s = j6_mailbox_respond(mb,
-                &tag, &subtag,
-                handles, &handles_count,
-                handles_in, &reply_tag,
-                j6_mailbox_block);
+        if (s != j6_status_ok)
+            while (1);
 
         handle_entry *found = nullptr;
 
@@ -49,22 +43,21 @@ service_locator_start(j6_handle_t mb)
         case j6_proto_base_get_proto_id:
             tag = j6_proto_base_proto_id;
             subtag = j6_proto_sl_id;
-            handles_count = 0;
+            give_handle = j6_handle_invalid;
             break;
 
         case j6_proto_sl_register:
             proto_id = subtag;
-            if (handles_count != 1) {
+            if (give_handle == j6_handle_invalid) {
                 tag = j6_proto_base_status;
                 subtag = j6_err_invalid_arg;
-                handles_count = 0;
                 break;
             }
 
-            services.insert( {proto_id, handles[0]} );
+            services.insert( {proto_id, give_handle} );
             tag = j6_proto_base_status;
             subtag = j6_status_ok;
-            handles_count = 0;
+            give_handle = j6_handle_invalid;
             break;
 
         case j6_proto_sl_find:
@@ -72,18 +65,16 @@ service_locator_start(j6_handle_t mb)
             tag = j6_proto_sl_result;
 
             found = services.find(proto_id);
-            if (found) {
-                handles_count = 1;
-                handles[0] = found->handle;
-            } else {
-                handles_count = 0;
-            }
+            if (found)
+                give_handle = found->handle;
+            else
+                give_handle = j6_handle_invalid;
             break;
 
         default:
             tag = j6_proto_base_status;
             subtag = j6_err_invalid_arg;
-            handles_count = 0;
+            give_handle = j6_handle_invalid;
             break;
         }
     }

src/user/srv.logger/main.cpp

@@ -125,13 +125,11 @@ main(int argc, const char **argv)
     for (unsigned i = 0; i < 100; ++i) {
         uint64_t tag = j6_proto_sl_find;
         uint64_t proto_id = "jsix.protocol.stream.ouput"_id;
-        size_t handle_count = 0;
 
-        j6_status_t s = j6_mailbox_call(slp, &tag,
-                &proto_id, &cout, &handle_count);
+        j6_status_t s = j6_mailbox_call(slp, &tag, &proto_id, &cout);
         if (s == j6_status_ok &&
             tag == j6_proto_sl_result &&
-            handle_count == 1)
+            cout != j6_handle_invalid)
             break;
 
         cout = j6_handle_invalid;