+struct active_list * active_list_prev(struct active_list *head, struct active_list *ptr) {
+ struct active_list *prev=NULL;
+ if ( !head ) {
+ fprintf(stderr, "active_list_prev head = %p, ptr = %p invalid value!!\n", head, ptr);
+ return NULL;
+ }
+ if ( !ptr )
+ ptr = head;
+ if ( ptr->depend.prev != &ptr->depend ) {
+ prev = list_entry(ptr->depend.prev, struct active_list, node);
+ return prev;
+ }
+ if ( ptr->depended && ptr->depended != head && &ptr->depended->depend == ptr->node.prev ) {
+ prev = list_entry(ptr->depended->node.prev, struct active_list, node);
+ } else
+ prev = list_entry(ptr->node.prev, struct active_list, node);
+ if ( prev == head )
+ return NULL;
+ return prev;
+}
+