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.Dd August 3, 2017
.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 returns a device number created from the provided
.Fa major
and
.Fa minor
number.
The
.Fn major
and
.Fn minor
macros return the original numbers from the device number
.Fa dev .
In other words, for a value
.Va dev
of the type
.Vt dev_t ,
and values
.Va ma , mi
of the type
.Vt int ,
the assertions
.Dl dev == makedev(major(dev), minor(dev))
.Dl ma == major(makedev(ma, mi))
.Dl mi == minor(makedev(ma, mi))
are valid.
.Pp
In previous implementations of
.Fx
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
.Fx
automatically generate a unique device number for each character device
visible in
.Pa /dev/ .
These numbers are not divided in device classes and are not guaranteed
to be stable upon reboot or driver reload.
.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
and
.Fn minor
macros return numbers whose value can span the complete range of an
.Vt int .
.Sh SEE ALSO
.Xr mknod 2 ,
.Xr devname 3 ,
.Xr devfs 4