[list] Add list_last_entry()

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/list.h

 	  ( type * ) NULL :				\
 	  list_entry ( (list)->next, type, member ) )
 
+/**
+ * Get the container of the last entry in a list
+ *
+ * @v list		List head
+ * @v type		Containing type
+ * @v member		Name of list field within containing type
+ * @ret first		First list entry, or NULL
+ */
+#define list_last_entry( list, type, member )		\
+	( list_empty ( (list) ) ?			\
+	  ( type * ) NULL :				\
+	  list_entry ( (list)->prev, type, member ) )
+
 /**
  * Iterate over a list
  *

src/tests/list_test.c

 	ok ( list_entry ( &list_tests[3].list, struct list_test, list )
 	     == &list_tests[3] );
 
-	/* Test list_first_entry() */
+	/* Test list_first_entry() and list_last_entry() */
 	INIT_LIST_HEAD ( list );
 	list_add_tail ( &list_tests[9].list, list );
 	list_add_tail ( &list_tests[5].list, list );
 	list_add_tail ( &list_tests[6].list, list );
 	ok ( list_first_entry ( list, struct list_test, list )
 	     == &list_tests[9] );
+	ok ( list_last_entry ( list, struct list_test, list )
+	     == &list_tests[6] );
 	list_del ( &list_tests[9].list );
 	ok ( list_first_entry ( list, struct list_test, list )
 	     == &list_tests[5] );
+	ok ( list_last_entry ( list, struct list_test, list )
+	     == &list_tests[6] );
+	list_del ( &list_tests[6].list );
+	ok ( list_first_entry ( list, struct list_test, list )
+	     == &list_tests[5] );
+	ok ( list_last_entry ( list, struct list_test, list )
+	     == &list_tests[5] );
+	list_del ( &list_tests[5].list );
+	ok ( list_first_entry ( list, struct list_test, list ) == NULL );
+	ok ( list_last_entry ( list, struct list_test, list ) == NULL );
 
 	/* Test list_for_each() */
 	INIT_LIST_HEAD ( list );