Add simple page allocator and doubly-linked list implementation.

kernel/list.c

@@ -0,0 +1,58 @@
+#include <list.h>
+
+void init_list(struct dlist_node *n) {
+	n->prev = n;
+	n->next = n;
+}
+
+int list_empty(struct dlist_node *n) {
+	return n->next == n;
+}
+
+void insert_after(struct dlist_node *n, struct dlist_node *to_add) {
+	to_add->next = n->next;
+	to_add->next->prev = to_add;
+	n->next = to_add;
+	to_add->prev = n;
+}
+
+void insert_before(struct dlist_node *n, struct dlist_node *to_add) {
+	to_add->prev = n->prev;
+	to_add->prev->next = to_add;
+	n->prev = to_add;
+	to_add->next = n;
+}
+
+void remove(struct dlist_node *to_remove) {
+	if (!list_empty(to_remove)) {
+		to_remove->next->prev = to_remove->prev;
+		to_remove->prev->next = to_remove->next;
+		init_list(to_remove);
+	}
+}
+
+/*
+ * Remove a series of nodes from a list. Note that this assumes the list is not
+ * empty, and that 'from' comes before 'to' in the list. 'from' and 'to' will
+ * both be removed from the list, along with any nodes which come after 'from'
+ * but before 'to'.
+ */
+void remove_splice(struct dlist_node *from, struct dlist_node *to) {
+	to->next->prev = from->prev;
+	from->prev->next = to->next;
+
+	//make the removed splice become its own wrap-around list, for easy access to the last member when re-splicing
+	to->next = from;
+	from->prev = to;
+}
+
+/*
+ * Add a splice of nodes to a list (most likely a series previously removed via
+ * remove_splice()).
+ */
+void insert_splice_before(struct dlist_node *n, struct dlist_node *first, struct dlist_node *last) {
+	first->prev = n->prev;
+	first->prev->next = first;
+	n->prev = last;
+	last->next = n;
+}