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Heads up! Implement universal device attachment and autoconfiguration machinery.
This is somewhat similar to traditional BSD autoconf but much more simple.
Three basic data structures involved in autoconfiguration process are:
struct device, which represents abstract device and its private (driver softc) data;
struct driver, which holds {attach,match,detach} entries, name and softc size;
struct attachment, which tells us how drivers are interacted with each other.
Attachment basically describes how to attach devices in system.
Machine specified part should export arrays config_table[] and *drivers[] for config.

This might have broken i386 & gba tree, but there is only a question of time.

/*
 * $Id: config_rootdev.c,v 1.1 2008/08/08 12:37:11 nbrk Exp $
 */
/*
 * 'root' is the parent to all devices in system.
 * Device module calls config_attach_rootdev() to initiate recursive 
 * autoconfiguration process.
 */
#include <driver.h>

/*
 * rootdev driver.
 */
struct driver	root_drv = {
	"root",	/* name */
	0,		/* datasize */
	NULL,	/* match */
	NULL,	/* attach */
	NULL,	/* detach */
	-1		/* nunits XXX */
};

/*
 * rootdev device.
 */
struct device	*root_dev;


void
config_attach_rootdev()
{
	/*
	 * Attach our one and only child, 'hostio'.
	 * Panic if attachment failed.
	 */
	int	ndevs;

	/*
	 * Allocate and construct ourselfes.
	 */
	root_dev = config_alloc_device(&root_drv);
	root_dev->dv_parent = root_dev;

	ndevs = config_search_children(root_dev, NULL);
	if (ndevs == 0)
		panic("rootdev: can't find hostio");
}