Implement syscall for file opening and refactor open_files initialisation in thread.c w/ S.

src/threads/thread.c

@@ -238,6 +238,7 @@ thread_create (const char *name, int priority,
   struct thread *parent_thread = thread_current ();
   init_thread (t, name, parent_thread->nice, priority, parent_thread->recent_cpu);
   tid = t->tid = allocate_tid ();
+  hash_init (&t->open_files, fd_hash, fd_less, NULL);
 
   /* Prepare thread for first run by initializing its stack.
      Do this atomically so intermediate values for the 'stack' 
@@ -662,7 +663,6 @@ init_thread (struct thread *t, const char *name, int nice, int priority,
   t->priority = t->base_priority;
 
   t->exit_status = -1;
-  hash_init (&t->open_files, fd_hash, fd_less, NULL);
 
   old_level = intr_disable ();
   list_push_back (&all_list, &t->allelem);