kernel: add k_thread_access_grant()

This is a runtime counterpart to K_THREAD_ACCESS_GRANT().
This function takes a thread and a NULL-terminated list of kernel
objects and runs k_object_access_grant() on each of them.
This function doesn't require any special permissions and doesn't
need to become a system call.

__attribute__((sentinel)) added to warn users if they omit the
required NULL termination.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>

include/kernel.h

@@ -615,6 +615,22 @@ extern FUNC_NORETURN void k_thread_user_mode_enter(k_thread_entry_t entry,
 						   void *p1, void *p2,
 						   void *p3);
 
+/**
+ * @brief Grant a thread access to a NULL-terminated  set of kernel objects
+ *
+ * This is a convenience function. For the provided thread, grant access to
+ * the remaining arguments, which must be pointers to kernel objects.
+ * The final argument must be a NULL.
+ *
+ * The thread object must be initialized (i.e. running). The objects don't
+ * need to be.
+ *
+ * @param thread Thread to grant access to objects
+ * @param ... NULL-terminated list of kernel object pointers
+ */
+extern void __attribute__((sentinel))
+	k_thread_access_grant(struct k_thread *thread, ...);
+
 /**
  * @brief Put the current thread to sleep.
  *

kernel/thread.c

@@ -692,6 +692,25 @@ void _k_thread_group_leave(u32_t groups, struct k_thread *thread)
 	thread_data->init_groups &= groups;
 }
 
+void k_thread_access_grant(struct k_thread *thread, ...)
+{
+#ifdef CONFIG_USERSPACE
+	va_list args;
+	va_start(args, thread);
+
+	while (1) {
+		void *object = va_arg(args, void *);
+		if (object == NULL) {
+			break;
+		}
+		k_object_access_grant(object, thread);
+	}
+	va_end(args);
+#else
+	ARG_UNUSED(thread);
+#endif
+}
+
 FUNC_NORETURN void k_thread_user_mode_enter(k_thread_entry_t entry,
 					    void *p1, void *p2, void *p3)
 {