Add in syscall hash helper functions for open_file struct: fd_hash and fd_less, w/ E

src/userprog/syscall.c

@@ -13,6 +13,13 @@
 
 static struct lock filesys_lock;
 
+struct open_file
+  {
+    int fd;              /* File Descriptor / Identifier */
+    struct file *file;   /* Pointer to the associated file */
+    struct hash_elem elem;      /* elem for a hash table */
+  };
+
 static void syscall_handler (struct intr_frame *);
 
 /* A syscall_function is a function that receives up to 3 arguments, the
@@ -239,6 +246,22 @@ syscall_close (int fd UNUSED)
   //TODO
 }
 
+unsigned
+fd_hash (const struct hash_elem *element, void *aux UNUSED)
+{
+  return hash_int (hash_entry (element, struct open_file, elem)->fd);
+}
+
+bool
+fd_less (const struct hash_elem *a_, const struct hash_elem *b_,
+        void *aux UNUSED)
+{
+  struct open_file *a = hash_entry (a_, struct open_file, elem);
+  struct open_file *b = hash_entry (b_, struct open_file, elem);
+
+  return a->fd < b->fd;
+}
+
 /* Validates if a block of memory starting at PTR and of size SIZE bytes is
    fully contained within user virtual memory. Kills the thread (by calling
    thread_exit) if the memory is invalid. Otherwise, returns the PTR given.