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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 14.0-RELEASE-p11 August 3, 2017 FreeBSD 14.0-RELEASE-p11