1
、
MKDEV
（
ma, mi
）
Constructs a device number, converting the major and minor numbers to the device number type (dev_t).
The MKDEV
macro shifts the major device number ( ma
) to the left by
20
bits, and then ANDs it with the minor device number (
mi
) to get the device number.
dev_t
structure
12
digits of major equipment number