Service: Add new ServiceFramework framework for writing HLE services

The old "Interface" class had a few problems such as using free
functions (Which didn't allow you to write the service handler as if it
were a regular class.) which weren't very extensible. (Only received one
parameter with a pointer to the Interface object.)

The new ServiceFramework aims to solve these problems by working with
member functions and passing a generic context struct as parameter. This
struct can be extended in the future without having to update all
existing service implementations.

src/core/hle/kernel/hle_ipc.cpp

@@ -21,4 +21,6 @@ void SessionRequestHandler::ClientDisconnected(SharedPtr<ServerSession> server_s
     boost::range::remove_erase(connected_sessions, server_session);
 }
 
+HLERequestContext::~HLERequestContext() = default;
+
 } // namespace Kernel

src/core/hle/kernel/hle_ipc.h

@@ -7,11 +7,14 @@
 #include <memory>
 #include <vector>
 #include "core/hle/kernel/kernel.h"
+#include "core/hle/kernel/server_session.h"
+
+namespace Service {
+class ServiceFrameworkBase;
+}
 
 namespace Kernel {
 
-class ServerSession;
-
 /**
  * Interface implemented by HLE Session handlers.
  * This can be provided to a ServerSession in order to hook into several relevant events
@@ -52,4 +55,33 @@ protected:
     std::vector<SharedPtr<ServerSession>> connected_sessions;
 };
 
+/**
+ * Class containing information about an in-flight IPC request being handled by an HLE service
+ * implementation. Services should avoid using old global APIs (e.g. Kernel::GetCommandBuffer()) and
+ * when possible use the APIs in this class to service the request.
+ */
+class HLERequestContext {
+public:
+    ~HLERequestContext();
+
+    /// Returns a pointer to the IPC command buffer for this request.
+    u32* CommandBuffer() const {
+        return cmd_buf;
+    }
+
+    /**
+     * Returns the session through which this request was made. This can be used as a map key to
+     * access per-client data on services.
+     */
+    SharedPtr<ServerSession> Session() const {
+        return session;
+    }
+
+private:
+    friend class Service::ServiceFrameworkBase;
+
+    u32* cmd_buf = nullptr;
+    SharedPtr<ServerSession> session;
+};
+
 } // namespace Kernel