Add an Epoll spec and some C interop code

This should help with resolving #2 and support running with Epoll

mozzoni.gpr

@@ -12,5 +12,7 @@ project Mozzoni is
       for Switches ("ada") use ("-gnato", "-gnat12", "-gnatf", "-fstack-check", "-g");
    end Compiler;
 
+   for Languages use ("Ada", "C");
+
 end Mozzoni;
 

src/epoll.ads

@@ -0,0 +1,72 @@
+
+with GNAT.Sockets,
+     Interfaces.C,
+     System;
+
+package Epoll is
+
+    subtype Epoll_Fd_Type is Integer;
+
+    type Epoll_Events_Type is (Epoll_In,
+                               Epoll_Pri,
+                               Epoll_Out,
+                               Epoll_Et,
+                               Epoll_In_And_Et
+                              );
+    for Epoll_Events_Type use (Epoll_In => 1,
+                                Epoll_Pri => 2,
+                                Epoll_Out => 4,
+                                Epoll_Et  => 2147483648,
+                                Epoll_In_And_Et => 2147483649);
+    for Epoll_Events_Type'Size use Interfaces.C.int'Size;
+
+    type Epoll_Ctl_Type is (Epoll_Ctl_Add,
+                            Epoll_Ctl_Del,
+                            Epoll_Ctl_Mod);
+    for Epoll_Ctl_Type use (Epoll_Ctl_Add => 1,
+                             Epoll_Ctl_Del => 2,
+                             Epoll_Ctl_Mod => 3);
+
+    type Data_Type (Discriminant : Interfaces.C.unsigned := 0) is record
+        case Discriminant is
+            when 0 =>
+                Ptr : System.Address;
+            when 1 =>
+                FD  : aliased GNAT.Sockets.Socket_Type; -- Interfaces.C.int
+            when 2 =>
+                U32 : aliased Interfaces.Unsigned_32;
+            when others =>
+                U64 : aliased Interfaces.Unsigned_64;
+        end case;
+    end record;
+    pragma Convention (C_Pass_By_Copy, Data_Type);
+    pragma Unchecked_Union (Data_Type);
+
+
+    type Event_Type is record
+        Events : aliased Epoll_Events_Type;
+        Data   : Data_Type;
+    end record;
+    pragma Convention (C_Pass_By_Copy, Event_Type);
+
+    type Event_Array_Type is array (Integer range <>) of aliased Event_Type;
+    pragma Convention (C, Event_Array_Type);
+
+
+    function Create (Size : Integer) return Epoll_Fd_Type;
+    pragma Import (C, Create, "epoll_create");
+
+
+    function Control (Epfd : Epoll_Fd_Type;
+                      Op : Epoll_Ctl_Type;
+                      Fd : Epoll_Fd_Type;
+                      Events : access Event_Type) return Integer;
+    pragma Import (C, Control, "epoll_ctl");
+
+
+    function Wait (Epfd : Epoll_Fd_Type;
+                   Events : access Event_Type;
+                   Max_Events : Integer;
+                   Timeout    : Integer) return Integer;
+    pragma Import (C, Wait, "epoll_wait");
+end Epoll;

src/interop.c

@@ -0,0 +1,7 @@
+#include <errno.h>
+
+/*
+ * errno is a macro on most modern GNU/libc's which means that we cannot
+ * Import it like other bindings from Ada
+ */
+int fetch_errno() { return errno; }