In kernel-2.4.20, the attribute d_hash in struct dentry is type of list_head. So you can use function list_empty defined in list.h to check whether the hash list is empty.

But in kernel-2.6.27, the type of the attribute d_hash has been changed to hlist_node, then if you want to check whether the hash list is empty, the function list_empty will not work any more.

What should I do to solve the problem??

Another question is that there are two function concerned with hlist defined in list.h: hlist_unhash and hlist_empty. What are the differences between the two functions?

Instead of this (old):
Use this (new: not a “literal” translation, but the preferred usage):
The first tells if a particular node is currently “headed” by a hash. The second tells if a particular head has a node. Also, the type struct hlist_node* may be safely cast to struct hlist_head*, so the first works only on nodes, yet the second works on nodes and heads.