Index: kernel/generic/include/ipc/ipc.h
===================================================================
--- kernel/generic/include/ipc/ipc.h	(revision 86939b1cfc4e60d1449f2f92c6a1e36462943230)
+++ kernel/generic/include/ipc/ipc.h	(revision ffc1b1dbcf8a3ea33f630e7788d4e62f80c5da37)
@@ -106,5 +106,9 @@
 
 typedef struct {
-	/** Task link. */
+	/**
+	 * Task link.
+	 * Valid only when the call is not forgotten.
+	 * Protected by the task's active_calls_lock.
+	 */
 	link_t ta_link;
 
@@ -113,6 +117,23 @@
 	
 	unsigned int flags;
+
+	/** Protects the forget member. */
+	SPINLOCK_DECLARE(forget_lock);
+
+	/**
+	 * True if the caller 'forgot' this call and donated it to the callee.
+	 * Forgotten calls are discarded upon answering (the answer is not
+	 * delivered) and answered calls cannot be forgotten. Forgotten calls
+	 * also do not figure on the task's active call list.
+	 *
+	 * We keep this separate from the flags so that it is not necessary
+	 * to take a lock when accessing them.
+	 */
+	bool forget;
 	
-	/** Identification of the caller. */
+	/**
+	 * Identification of the caller.
+	 * Valid only when the call is not forgotten.
+	 */
 	struct task *sender;