Obtained from: well it has a relationship with the LKM code..

This is a place for all things to do with conf.c and conf.h
that are not machine specific.
Other things that are at present in i386/isa/conf.c might
migrate into here..
It's the first small step in cleaning up the device interface
to make it more dynamic and to assist in more modular drivers
(i.e. both loadable via LKMs and linked in..
e.g able to add a device without having to edit conf.c)

this code is not yet used and the whole thing will be conditionally
compiled in for a while till proven useful :)

sys/kern/kern_conf.c

@@ -0,0 +1,79 @@
+/*-
+ * Parts Copyright (c) 1995 Terrence R. Lambert
+ * Copyright (c) 1995 Julian R. Elischer
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. All advertising materials mentioning features or use of this software
+ *    must display the following acknowledgement:
+ *      This product includes software developed by Terrence R. Lambert.
+ * 4. The name Terrence R. Lambert may not be used to endorse or promote
+ *    products derived from this software without specific prior written
+ *    permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY Julian R. Elischer ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE TERRENCE R. LAMBERT BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $Id: kern_lkm.c,v 1.15 1995/09/08 11:08:34 bde Exp $
+ */
+
+#include <sys/param.h>
+#include <sys/conf.h>
+extern d_open_t lkmenodev;
+
+/*
+ * (re)place an entry in the bdevsw or cdevsw table
+ * return the slot used in MAJOR(*descrip)
+ */
+#define ADDENTRY(TTYPE,NXXXDEV) \
+int TTYPE##_add(dev_t *descrip,						\
+		struct TTYPE *cdeventry,				\
+		cdevsw_t *oldentry)					\
+{									\
+	if ( (int)*decsrip == -1) {	/* auto (0 is valid) */		\
+		/*							\
+		 * Search the table looking for a slot...		\
+		 */							\
+		for (i = 0; i < NXXXDEV; i++)				\
+			if (TTYPE[i].d_open == lkmenodev)		\
+				break;		/* found it! */		\
+		/* out of allocable slots? */				\
+		if (i == NXXXDEV) {					\
+			return ENFILE;					\
+		}							\
+	} else {				/* assign */		\
+		if (i < 0 || i >= NXXXDEV) {				\
+			return EINVAL;					\
+		}							\
+	}								\
+									\
+	/* save old */							\
+        if (oldentry) {							\
+		bcopy(&TTYPE[i], oldentry, sizeof(struct TTYPE));	\
+	}								\
+	/* replace with new */						\
+	bcopy(cdeventry, &TTYPE[i], sizeof(struct TTYPE));		\
+									\
+	/* done! */							\
+	*descrip = makedev(i,0);					\
+	return 0							\
+} \
+
+ADDENTRY(cdevsw, nblkdev)
+ADDENTRY(bdevsw, nchrdev)