[list] Add list_next_entry() and list_prev_entry()

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

src/include/ipxe/list.h

@@ -348,6 +348,34 @@ extern void extern_list_splice_tail_init ( struct list_head *list,
 	  ( type * ) NULL :					\
 	  list_entry ( (list)->prev, type, member ) )
 
+/**
+ * Get the container of the next entry in a list
+ *
+ * @v pos		Current list entry
+ * @v head		List head
+ * @v member		Name of list field within iterator's type
+ * @ret next		Next list entry, or NULL at end of list
+ */
+#define list_next_entry( pos, head, member ) ( {		\
+	typeof (pos) next = list_entry ( (pos)->member.next,	\
+					 typeof ( *(pos) ),	\
+					 member );		\
+	( ( &next->member == (head) ) ? NULL : next ); } )
+
+/**
+ * Get the container of the previous entry in a list
+ *
+ * @v pos		Current list entry
+ * @v head		List head
+ * @v member		Name of list field within iterator's type
+ * @ret next		Next list entry, or NULL at end of list
+ */
+#define list_prev_entry( pos, head, member ) ( {		\
+	typeof (pos) prev = list_entry ( (pos)->member.prev,	\
+					 typeof ( *(pos) ),	\
+					 member );		\
+	( ( &prev->member == (head) ) ? NULL : prev ); } )
+
 /**
  * Iterate over a list
  *

src/tests/list_test.c

@@ -396,6 +396,29 @@ static void list_test_exec ( void ) {
 	ok ( list_first_entry ( list, struct list_test, list ) == NULL );
 	ok ( list_last_entry ( list, struct list_test, list ) == NULL );
 
+	/* Test list_next_entry() and list_prev_entry() */
+	INIT_LIST_HEAD ( list );
+	list_add_tail ( &list_tests[5].list, list );
+	list_add_tail ( &list_tests[3].list, list );
+	list_add_tail ( &list_tests[1].list, list );
+	list_add_tail ( &list_tests[7].list, list );
+	ok ( list_prev_entry ( &list_tests[5], list, list ) == NULL );
+	ok ( list_next_entry ( &list_tests[5], list, list ) == &list_tests[3] );
+	ok ( list_prev_entry ( &list_tests[3], list, list ) == &list_tests[5] );
+	ok ( list_next_entry ( &list_tests[3], list, list ) == &list_tests[1] );
+	ok ( list_prev_entry ( &list_tests[1], list, list ) == &list_tests[3] );
+	ok ( list_next_entry ( &list_tests[1], list, list ) == &list_tests[7] );
+	ok ( list_prev_entry ( &list_tests[7], list, list ) == &list_tests[1] );
+	ok ( list_next_entry ( &list_tests[7], list, list ) == NULL );
+	list_del ( &list_tests[7].list );
+	ok ( list_prev_entry ( &list_tests[1], list, list ) == &list_tests[3] );
+	ok ( list_next_entry ( &list_tests[1], list, list ) == NULL );
+	list_del ( &list_tests[3].list );
+	ok ( list_prev_entry ( &list_tests[5], list, list ) == NULL );
+	ok ( list_next_entry ( &list_tests[5], list, list ) == &list_tests[1] );
+	ok ( list_prev_entry ( &list_tests[1], list, list ) == &list_tests[5] );
+	ok ( list_next_entry ( &list_tests[1], list, list ) == NULL );
+
 	/* Test list_for_each() */
 	INIT_LIST_HEAD ( list );
 	list_add_tail ( &list_tests[6].list, list );