_DEV_BSHIFT
cdb->cdb[7] = ((nblk >> _DEV_BSHIFT) & 0xff00) >> 8;
cdb->cdb[8] = ((nblk >> _DEV_BSHIFT) & 0x00ff);
#define DEV_BSIZE (1 << _DEV_BSHIFT)
#define DEV_BSHIFT _DEV_BSHIFT
#define ctod(x) ((x) << (PAGE_SHIFT - _DEV_BSHIFT))
#define dtoc(x) ((x) >> (PAGE_SHIFT - _DEV_BSHIFT))
#define btodb(x) ((x) >> _DEV_BSHIFT)
#define dbtob(x) ((x) << _DEV_BSHIFT)