MAKEDEV(3)             FreeBSD Library Functions Manual             MAKEDEV(3)

NAME
     makedev, major, minor - device number conversion

SYNOPSIS
     #include <sys/types.h>

     dev_t
     makedev(int major, int minor);

     int
     major(dev_t dev);

     int
     minor(dev_t dev);

DESCRIPTION
     The makedev() macro returns a device number created from the provided
     major and minor number.  The major() and minor() macros return the
     original numbers from the device number dev.  In other words, for a value
     dev of the type dev_t, and values ma, mi of the type int, the assertions
           dev == makedev(major(dev), minor(dev))
           ma == major(makedev(ma, mi))
           mi == minor(makedev(ma, mi))
     are valid.

     In previous implementations of FreeBSD all block and character devices
     were uniquely identified by a pair of stable major and minor numbers.
     The major number referred to a certain device class (e.g. disks, TTYs)
     while the minor number identified an instance within the device class.
     Later versions of FreeBSD automatically generate a unique device number
     for each character device visible in /dev/.  These numbers are not
     divided in device classes and are not guaranteed to be stable upon reboot
     or driver reload.

     On FreeBSD these macros are only used by utilities that need to exchange
     numbers with other operating systems that may use different encodings for
     dev_t, but also applications that present these numbers to the user in a
     more conventional way.

RETURN VALUES
     The major() and minor() macros return numbers whose value can span the
     complete range of an int.

SEE ALSO
     mknod(2), devname(3), devfs(5)

FreeBSD 13.1-RELEASE-p6         August 3, 2017         FreeBSD 13.1-RELEASE-p6