commonlib/list: Add list_length() and more to API

In a follow-up patch (CB:90962), the list will be changed to a circular
one, and list_node fields 'next' and 'prev' will become private to the
implementation.

To allow smooth transition to circular lists for all call sites, add the
following functions to the list API:

- list_is_empty()
- list_next()
- list_prev()
- list_first()
- list_last()
- list_length()

All list API call sites are expected to use the public API instead of
the raw 'next' and 'prev' pointers.

Change-Id: Ib1040f5caab8550ea52db9b55a074d7d79c591e5
Signed-off-by: Yu-Ping Wu <yupingso@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/90961
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Jakub "Kuba" Czapiga <czapiga@google.com>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/commonlib/include/commonlib/list.h

@@ -5,6 +5,7 @@
 #define __COMMONLIB_LIST_H__
 
 #include <commonlib/helpers.h>
+#include <stdbool.h>
 #include <stdint.h>
 
 struct list_node {
@@ -18,9 +19,41 @@ void list_remove(struct list_node *node);
 void list_insert_after(struct list_node *node, struct list_node *after);
 // Insert list_node node before list_node before in a doubly linked list.
 void list_insert_before(struct list_node *node, struct list_node *before);
-// Appends the node to the end of the list.
+// Append the node to the end of the list.
 void list_append(struct list_node *node, struct list_node *head);
 
+// Return if the list is empty.
+static inline bool list_is_empty(const struct list_node *head)
+{
+	return !head->next;
+}
+
+// Get next node.
+static inline const struct list_node *list_next(const struct list_node *node,
+						const struct list_node *head)
+{
+	return node->next;
+};
+
+// Get prev node.
+static inline const struct list_node *list_prev(const struct list_node *node,
+						const struct list_node *head)
+{
+	return node->prev == head ? NULL : node->prev;
+};
+
+// Get first node.
+static inline const struct list_node *list_first(const struct list_node *head)
+{
+	return list_is_empty(head) ? NULL : head->next;
+}
+
+// Get last node.
+const struct list_node *list_last(const struct list_node *head);
+
+// Get the number of list elements.
+size_t list_length(const struct list_node *head);
+
 #define list_for_each(ptr, head, member)                                      \
 	for ((ptr) = container_of((head).next, typeof(*(ptr)), member);       \
 		(uintptr_t)ptr + (uintptr_t)offsetof(typeof(*(ptr)), member); \

src/commonlib/list.c

@@ -36,3 +36,24 @@ void list_append(struct list_node *node, struct list_node *head)
 
 	list_insert_after(node, head);
 }
+
+const struct list_node *list_last(const struct list_node *head)
+{
+	const struct list_node *ptr = head;
+	while (ptr->next)
+		ptr = ptr->next;
+	return ptr == head ? NULL : ptr;
+}
+
+size_t list_length(const struct list_node *head)
+{
+	struct {
+		struct list_node node;
+	} const *ptr;
+	size_t len = 0;
+
+	list_for_each(ptr, *head, node)
+		len++;
+
+	return len;
+}