Table 2 Structure of the minor device byte
15 7 6 5 4 3 2 1 0
Unit # BSD Reserved Density Density No rewind Unit #
Bits 7-15 behavior Select Select on Close Bits 0-1
/*
* Layout of minor device byte:
*/
#define MTUNIT (dev) (((minor(dev) & 0xff80) >> 5) +(minor(dev) & 0x3))
#define MT_NOREWIND (1 <<2)
#define MT_DENSITY_MASK (3 <<3)
#define MT_DENSITY1 (0 <<3) /* Lowest density/format */
#define MT_DENSITY2 (1 <<3)
#define MT_DENSITY3 (2 <<3)
#define MT_DENSITY4 (3 <<3) /* Highest density/format */
#define MTMINOR (unit) (((unit & 0x7fc) << 5) + (unit & 0x3))
#define MT_BSD (1 <<6) /* BSD behavior on close */
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