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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 n 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.
p 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
a /dev/ . These numbers are not divided in device classes and are not guaranteed to be stable upon reboot or driver reload.
p 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 5