From 3a85fd262cf759135879a7dae35426b1ac5e13f5 Mon Sep 17 00:00:00 2001
From: Poul-Henning Kamp <phk@FreeBSD.org>
Date: Sat, 29 Jan 2005 15:07:13 +0000
Subject: [PATCH] Add MAXMINOR #define, we should have had this long time ago.

Add minor2unit() in addition to dev2unit() and unit2minor().

If it wasn't such a hazzle we should redefine minor numbers in
the kernel without the gap for the major number, but it's not worth
the bother (yet).
---
 sys/kern/kern_conf.c | 12 +++++++++---
 sys/sys/conf.h       |  3 +++
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/sys/kern/kern_conf.c b/sys/kern/kern_conf.c
index d8083816a843..07ddc91ca44e 100644
--- a/sys/kern/kern_conf.c
+++ b/sys/kern/kern_conf.c
@@ -258,12 +258,18 @@ minor(struct cdev *x)
 int
 dev2unit(struct cdev *x)
 {
-	int i;
 
 	if (x == NULL)
 		return NODEV;
-	i = minor(x);
-	return ((i & 0xff) | (i >> 8));
+	return (minor2unit(minor(x));
+}
+
+int
+minor2unit(int _minor)
+{
+
+	KASSERT((_minor & 0xff00) == 0, ("Illegal minor %x", _minor));
+	return ((_minor & 0xff) | (_minor >> 8));
 }
 
 int
diff --git a/sys/sys/conf.h b/sys/sys/conf.h
index d7ecddc3b84b..143faf5ef556 100644
--- a/sys/sys/conf.h
+++ b/sys/sys/conf.h
@@ -219,6 +219,8 @@ struct cdevsw {
 
 #define NUMCDEVSW 256
 
+#define MAXMINOR	0xffff00ff
+
 /*
  * XXX: do not use MAJOR_AUTO unless you have no choice.  In general drivers
  * should just not initialize .d_maj and that will DTRT.
@@ -266,6 +268,7 @@ int	dev2unit(struct cdev *_dev);
 void	dev_lock(void);
 void	dev_unlock(void);
 int	unit2minor(int _unit);
+int	minor2unit(int _minor);
 void	setconf(void);
 
 void devfs_create(struct cdev *dev);