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Provide more detailed specification for major(), minor() and makedev().

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Remove some statements which are no longer correct after ino64, and
clarify other.

The rewording is not in fact specific to ino64 and improvements are
useful on the stable branches.

Noted and reviewed by:	bde
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
This commit is contained in:
Konstantin Belousov 2017-08-05 07:52:15 +00:00
parent 0105034487
commit 1e94ddb453
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=322077
1 changed files with 21 additions and 9 deletions
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30
share/man/man3/makedev.3
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@ -24,7 +24,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd September 28, 2008
.Dd August 3, 2017
.Dt MAKEDEV 3
.Os
.Sh NAME
@ -43,7 +43,7 @@
.Sh DESCRIPTION
The
.Fn makedev
macro allows a unique device number to be generated based on its
macro returns a device number created from the provided
.Fa major
and
.Fa minor
@ -52,13 +52,26 @@ The
.Fn major
and
.Fn minor
macros can be used to obtain the original numbers from the device number
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
major and minor numbers.
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
@ -66,7 +79,8 @@ Later versions of
automatically generate a unique device number for each character device
visible in
.Pa /dev/ .
These numbers are not divided in device classes.
These numbers are not divided in device classes and are not guaranteed
to be stable upon reboot or driver reload.
.Pp
On
.Fx
@ -78,11 +92,9 @@ conventional way.
.Sh RETURN VALUES
The
.Fn major
macro returns a device major number that has a value between 0 and 255.
The
and
.Fn minor
macro returns a device minor number whose value can span the complete
range of an
macros return numbers whose value can span the complete range of an
.Vt int .
.Sh SEE ALSO
.Xr mknod 2 ,