svn commit: r322422 - stable/11/share/man/man3
Konstantin Belousov
kib at FreeBSD.org
Sat Aug 12 08:51:20 UTC 2017
Author: kib
Date: Sat Aug 12 08:51:19 2017
New Revision: 322422
URL: https://svnweb.freebsd.org/changeset/base/322422
Log:
MFC r322077:
Provide more detailed specification for major(), minor() and makedev().
Modified:
stable/11/share/man/man3/makedev.3
Directory Properties:
stable/11/ (props changed)
Modified: stable/11/share/man/man3/makedev.3
==============================================================================
--- stable/11/share/man/man3/makedev.3 Fri Aug 11 23:12:28 2017 (r322421)
+++ stable/11/share/man/man3/makedev.3 Sat Aug 12 08:51:19 2017 (r322422)
@@ -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 ,
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