hd_private
qfp->q_tab.hd_private = 0;
qfp->q_tab.hd_private = 0;
qfp->q_tab.hd_private = (void *)private;
#define BP_LT_HD(a, b) (DBLK(a) < (unsigned long)((b)->hd_private))
#define BP_GT_HD(a, b) (DBLK(a) > (unsigned long)((b)->hd_private))
qfp->q_tab.hd_private = 0;