WindowServer: Begin refactoring towards a fully asynchronous protocol.

In order to move the WindowServer to userspace, I have to eliminate its
dependence on system call facilities. The communication channel with each
client needs to be message-based in both directions.

Kernel/GUIEventDevice.cpp

@@ -2,6 +2,7 @@
 #include <Kernel/Process.h>
 #include <AK/Lock.h>
 #include <LibC/errno_numbers.h>
+#include <WindowServer/WSMessageLoop.h>
 
 //#define GUIEVENTDEVICE_DEBUG
 
@@ -32,7 +33,7 @@ ssize_t GUIEventDevice::read(Process& process, byte* buffer, size_t size)
     return size;
 }
 
-ssize_t GUIEventDevice::write(Process&, const byte*, size_t)
+ssize_t GUIEventDevice::write(Process& process, const byte* data, size_t size)
 {
-    return -EINVAL;
+    return WSMessageLoop::the().on_receive_from_client(process.gui_client_id(), data, size);
 }

Kernel/GUIEventDevice.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <Kernel/CharacterDevice.h>
+#include <Kernel/DoubleBuffer.h>
 
 class GUIEventDevice final : public CharacterDevice {
 public:

Kernel/GUITypes.h

@@ -68,6 +68,8 @@ struct GUI_Event {
         WindowDeactivated,
         WindowCloseRequest,
         MenuItemActivated,
+        DidCreateMenubar,
+        DidDestroyMenubar,
     };
     Type type { Invalid };
     int window_id { -1 };
@@ -90,12 +92,30 @@ struct GUI_Event {
             bool shift : 1;
         } key;
         struct {
+            int menubar_id;
             int menu_id;
             unsigned identifier;
         } menu;
     };
 };
 
+struct GUI_ClientMessage {
+    enum Type : unsigned {
+        Invalid,
+        CreateMenubar,
+        DestroyMenubar,
+    };
+    Type type { Invalid };
+    int window_id { -1 };
+
+    union {
+        struct {
+            int menubar_id;
+            int menu_id;
+        } menu;
+    };
+};
+
 inline Rect::Rect(const GUI_Rect& r) : Rect(r.location, r.size) { }
 inline Point::Point(const GUI_Point& p) : Point(p.x, p.y) { }
 inline Size::Size(const GUI_Size& s) : Size(s.width, s.height) { }

Kernel/Process.h

@@ -230,8 +230,6 @@ public:
     int gui$get_window_rect(int window_id, GUI_Rect*);
     int gui$set_window_rect(int window_id, const GUI_Rect*);
     int gui$set_global_cursor_tracking_enabled(int window_id, bool enabled);
-    int gui$menubar_create();
-    int gui$menubar_destroy(int menubar_id);
     int gui$menubar_add_menu(int menubar_id, int menu_id);
     int gui$menu_create(const char* name);
     int gui$menu_destroy(int menu_id);
@@ -313,6 +311,8 @@ public:
     bool has_used_fpu() const { return m_has_used_fpu; }
     void set_has_used_fpu(bool b) { m_has_used_fpu = b; }
 
+    int gui_client_id() const { return (int)this; }
+
 private:
     friend class MemoryManager;
     friend class Scheduler;
@@ -420,7 +420,6 @@ private:
     Vector<GUI_Event> m_gui_events;
     Lock m_gui_events_lock;
     int m_next_window_id { 1 };
-    bool m_has_created_menus { false };
 
     dword m_wakeup_requested { false };
     bool m_has_used_fpu { false };

Kernel/ProcessGUI.cpp

@@ -259,7 +259,7 @@ int Process::gui$set_global_cursor_tracking_enabled(int window_id, bool enabled)
 
 void Process::destroy_all_menus()
 {
-    if (!m_has_created_menus)
+    if (!WSMessageLoop::the().running())
         return;
     WSWindowManager::the().destroy_all_menus(*this);
 }
@@ -292,17 +292,6 @@ DisplayInfo Process::set_video_resolution(int width, int height)
     return info;
 }
 
-int Process::gui$menubar_create()
-{
-    m_has_created_menus = true;
-    return WSWindowManager::the().api$menubar_create();
-}
-
-int Process::gui$menubar_destroy(int menubar_id)
-{
-    return WSWindowManager::the().api$menubar_destroy(menubar_id);
-}
-
 int Process::gui$menubar_add_menu(int menubar_id, int menu_id)
 {
     return WSWindowManager::the().api$menubar_add_menu(menubar_id, menu_id);
@@ -312,7 +301,6 @@ int Process::gui$menu_create(const char* name)
 {
     if (!validate_read_str(name))
         return -EFAULT;
-    m_has_created_menus = true;
     return WSWindowManager::the().api$menu_create(String(name));
 }
 

Kernel/Syscall.cpp

@@ -223,10 +223,6 @@ static dword handle(RegisterDump& regs, dword function, dword arg1, dword arg2,
         return current->sys$rmdir((const char*)arg1);
     case Syscall::SC_chmod:
         return current->sys$chmod((const char*)arg1, (mode_t)arg2);
-    case Syscall::SC_gui_menubar_create:
-        return current->gui$menubar_create();
-    case Syscall::SC_gui_menubar_destroy:
-        return current->gui$menubar_destroy((int)arg1);
     case Syscall::SC_gui_menubar_add_menu:
         return current->gui$menubar_add_menu((int)arg1, (int)arg2);
     case Syscall::SC_gui_menu_create:

Kernel/Syscall.h

@@ -85,8 +85,6 @@
     __ENUMERATE_SYSCALL(rmdir) \
     __ENUMERATE_SYSCALL(chmod) \
     __ENUMERATE_SYSCALL(usleep) \
-    __ENUMERATE_SYSCALL(gui_menubar_create) \
-    __ENUMERATE_SYSCALL(gui_menubar_destroy) \
     __ENUMERATE_SYSCALL(gui_menubar_add_menu) \
     __ENUMERATE_SYSCALL(gui_menu_create) \
     __ENUMERATE_SYSCALL(gui_menu_destroy) \