__ARM_MAXDISKS
#define DISKUNIT(dev) ((minor(dev) / OLDMAXPARTITIONS) % __ARM_MAXDISKS)
((minor(dev) / (__ARM_MAXDISKS * OLDMAXPARTITIONS)) * OLDMAXPARTITIONS))
((part) / OLDMAXPARTITIONS) * (__ARM_MAXDISKS * OLDMAXPARTITIONS))