Implement Register, which will handle adding descriptors and callbacks to the hub

src/epoll.adb

@@ -1,10 +1,30 @@
+--
+--  epoll.adb - Loose binding on top of the epoll(7) interface in the Linux
+--  kernel
+--
 
 
 package body Epoll is
 
-    procedure Register (This : in Hub; Descriptor : in C.int) is
+    procedure Register (This : in out Hub; Descriptor : in C.int; Cb : in Callback) is
+        Event : aliased Epoll_Event;
     begin
-        null;
+        Validate_Hub (This);
+
+        Event.Events := EPOLLIN;
+        Event.Data.Fd := Descriptor;
+
+        declare
+            Status : C.int;
+        begin
+            Status := Epoll_Ctl (This.Epoll_fd, EPOLL_CTL_ADD, Descriptor, Event'Access);
+
+            if Status = -1 then
+                raise Descriptor_Registration_Falied;
+            end if;
+        end;
+
+        Callback_Registry.Insert (This.Callbacks, Descriptor, Cb);
     end Register;
 
     procedure Run (This : in Hub) is
@@ -29,4 +49,11 @@ package body Epoll is
         return Created_Hub;
     end Create;
 
+    procedure Validate_Hub (H : in Hub) is
+    begin
+        if H.Epoll_Fd < 0 then
+            raise Hub_Invalid;
+        end if;
+    end Validate_Hub;
+
 end Epoll;

src/epoll.ads

@@ -4,29 +4,44 @@
 
 with Interfaces.C;
 with System;
+with Ada.Containers.Vectors;
 
+use Ada.Containers;
 use Interfaces;
 
 package Epoll is
     type Callback is access procedure (Descriptor : C.int);
     -- My_Callback.all (Fd);
+    package Callback_Registry is new Vectors (C.int, Callback);
+
 
     type Hub is tagged private;
 
-    procedure Register (This : in Hub; Descriptor : C.int);
+    procedure Register (This : in out Hub;
+                            Descriptor : in C.int;
+                            Cb : in Callback);
     procedure Run (This : in Hub);
 
     function Create return Hub;
 
     Hub_Create_Failed : exception;
+    Hub_Invalid : exception;
+    Descriptor_Registration_Falied : exception;
 
     private
         use Interfaces.C;
 
+        --  Callback_Registry will be used to determine "who" to invoke when a
+        --  specific descriptor receives data in the `Run` loop
+
         type Hub is tagged record
             Epoll_Fd : C.int := -1;
+            Should_Continue : Boolean := True;
+            Callbacks : Callback_Registry.Vector;
         end record;
 
+        procedure Validate_Hub (H: in Hub);
+
         subtype EPOLL_CTL_OPS is C.unsigned;
         EPOLL_CTL_ADD : constant EPOLL_CTL_OPS := 1;
         EPOLL_CTL_DEL : constant EPOLL_CTL_OPS := 2;
@@ -58,18 +73,18 @@ package Epoll is
                 when Pointer =>
                     Ptr : System.Address;
                 when File_Descriptor =>
-                    Fd : C.int;
+                    Fd : aliased C.int;
                 when Int_32 =>
-                    u32 : C.int;
+                    u32 : aliased C.int;
                 when Int_64 =>
-                    u64 : C.int;
+                    u64 : aliased C.int;
             end case;
         end record;
         pragma Convention (C_Pass_By_Copy, Epoll_Data);
         pragma Unchecked_Union (Epoll_Data);
 
         type Epoll_Event is record
-            Events : Integer;
+            Events : aliased C.unsigned;
             Data : Epoll_Data;
         end record;
         pragma Convention (C_Pass_By_Copy, Epoll_Event);