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.Dd September 28, 2008
.Dt MAKEDEV 3
.Os
.Sh NAME
.Nm makedev ,
.Nm major ,
.Nm minor
.Nd device number conversion
.Sh SYNOPSIS
.In sys/types.h
.Ft dev_t
.Fn makedev "int major" "int minor"
.Ft int
.Fn major "dev_t dev"
.Ft int
.Fn minor "dev_t dev"
.Sh DESCRIPTION
The
.Fn makedev
macro allows a unique device number to be generated based on its
.Fa major
and
.Fa minor
number.
The
.Fn major
and
.Fn minor
macros can be used to obtain the original numbers from the device number
.Fa dev .
.Pp
In previous implementations of
.Fx
all block and character devices were uniquely identified by a pair of
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
.Fx
automatically generate a unique device number for each character device
visible in
.Pa /dev/ .
These numbers are not divided in device classes.
.Pp
On
.Fx
these macros are only used by utilities that need to exchange numbers
with other operating systems that may use different encodings for
.Vt dev_t ,
but also applications that present these numbers to the user in a more
conventional way.
.Sh RETURN VALUES
The
.Fn major
macro returns a device major number that has a value between 0 and 255.
The
.Fn minor
macro returns a device minor number whose value can span the complete
range of an
.Vt int .
.Sh SEE ALSO
.Xr devfs 5 ,
.Xr devname 3 ,
.Xr mknod 2