peb_free_cmp
int peb_free_cmp(struct chfs_peb *peb1, struct chfs_peb *peb2);
RB_PROTOTYPE(peb_free_rbtree, chfs_peb, u.rb, peb_free_cmp);
RB_GENERATE(peb_free_rbtree, chfs_peb, u.rb, peb_free_cmp);