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Pull in patch from current (even more to come):
Fix (millert):
warnx?/errx? paranoia (use "%s" not a bare string unless it is a
constant).  These are not security holes but it is worth fixing
them anyway both for robustness and so folks looking for examples
in the tree are not misled into doing something potentially dangerous.
Furthermore, it is a bad idea to assume that pathnames will not
include '%' in them and that error routines don't return strings
with '%' in them (especially in light of the possibility of locales).

/*	$OpenBSD: dkstats.c,v 1.6.4.1 2000/10/06 21:16:17 jason Exp $	*/
/*	$NetBSD: dkstats.c,v 1.1 1996/05/10 23:19:27 thorpej Exp $	*/

/*
 * Copyright (c) 1996 John M. Vinopal
 * 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 for the NetBSD Project
 *      by John M. Vinopal.
 * 4. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
 */

#include <sys/dkstat.h>
#include <sys/time.h>
#include <sys/disk.h>

#include <err.h>
#include <fcntl.h>
#include <kvm.h>
#include <limits.h>
#include <nlist.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "dkstats.h"

static struct nlist namelist[] = {
#define	X_TK_NIN	0
	{ "_tk_nin" },		/* tty characters in */
#define	X_TK_NOUT	1
	{ "_tk_nout" },		/* tty characters out */
#define	X_CP_TIME	2
	{ "_cp_time" },		/* system timer ticks */
#define	X_HZ		3
	{ "_hz" },		/* ticks per second */
#define	X_STATHZ	4
	{ "_stathz" },
#define X_DISK_COUNT	5
	{ "_disk_count" },	/* number of disks */
#define X_DISKLIST	6
	{ "_disklist" },	/* TAILQ of disks */
	{ NULL },
};

/* Structures to hold the statistics. */
struct _disk	cur, last;

/* Kernel pointers: nlistf and memf defined in calling program. */
static kvm_t	*kd = NULL;
extern char	*nlistf;
extern char	*memf;

/* Pointer to list of disks. */
static struct disk	*dk_drivehead = NULL;

/* Backward compatibility references. */
int	  	dk_ndrive = 0;
int		*dk_select;
char		**dr_name;

#define	KVM_ERROR(_string) {						\
	warnx((_string));						\
	errx(1, "%s", kvm_geterr(kd));					\
}

/*
 * Dereference the namelist pointer `v' and fill in the local copy 
 * 'p' which is of size 's'.
 */
#define deref_nl(v, p, s) deref_kptr((void *)namelist[(v)].n_value, (p), (s));

/* Missing from <sys/time.h> */
#define timerset(tvp, uvp) ((uvp)->tv_sec = (tvp)->tv_sec);		\
			   ((uvp)->tv_usec = (tvp)->tv_usec)

static void deref_kptr __P((void *, void *, size_t));

/*
 * Take the delta between the present values and the last recorded
 * values, storing the present values in the 'last' structure, and
 * the delta values in the 'cur' structure.
 */
void
dkswap()
{
#define SWAP(fld)		tmp = cur.fld;				\
				cur.fld -= last.fld;			\
				last.fld = tmp
	u_int64_t tmp;
	int	i;

	for (i = 0; i < dk_ndrive; i++) {
		struct timeval	tmp_timer;

		if (!cur.dk_select[i])
			continue;

		/* Delta Values. */
		SWAP(dk_xfer[i]);
		SWAP(dk_seek[i]);
		SWAP(dk_bytes[i]);

		/* Delta Time. */
		timerclear(&tmp_timer);
		timerset(&(cur.dk_time[i]), &tmp_timer);
		timersub(&tmp_timer, &(last.dk_time[i]), &(cur.dk_time[i]));
		timerclear(&(last.dk_time[i]));
		timerset(&tmp_timer, &(last.dk_time[i]));
	}
	for (i = 0; i < CPUSTATES; i++) {
		SWAP(cp_time[i]);
	}
	SWAP(tk_nin);
	SWAP(tk_nout);

#undef SWAP
}

/*
 * Read the disk statistics for each disk in the disk list. 
 * Also collect statistics for tty i/o and cpu ticks.
 */
void
dkreadstats()
{
	struct disk	cur_disk, *p;
	int		i;

	p = dk_drivehead;

	for (i = 0; i < dk_ndrive; i++) {
		deref_kptr(p, &cur_disk, sizeof(cur_disk));
		cur.dk_xfer[i] = cur_disk.dk_xfer;
		cur.dk_seek[i] = cur_disk.dk_seek;
		cur.dk_bytes[i] = cur_disk.dk_bytes;
		timerset(&(cur_disk.dk_time), &(cur.dk_time[i]));
		p = cur_disk.dk_link.tqe_next;
	}
	deref_nl(X_CP_TIME, cur.cp_time, sizeof(cur.cp_time));
	deref_nl(X_TK_NIN, &cur.tk_nin, sizeof(cur.tk_nin));
	deref_nl(X_TK_NOUT, &cur.tk_nout, sizeof(cur.tk_nout));
}

/*
 * Perform all of the initialization and memory allocation needed to
 * track disk statistics.
 */
int
dkinit(select)
int	select;
{
	struct disklist_head disk_head;
	struct disk	cur_disk, *p;
        char		errbuf[_POSIX2_LINE_MAX];
	static int	once = 0;
	extern int	hz;
	int		i;

	if (once)
		return(1);

	/* Open the kernel. */
        if ((kd = kvm_openfiles(nlistf, memf, NULL, O_RDONLY, errbuf)) == NULL)
		errx(1, "kvm_openfiles: %s", errbuf);

	/* Obtain the namelist symbols from the kernel. */
	if (kvm_nlist(kd, namelist))
		KVM_ERROR("kvm_nlist failed to read symbols.");

	/* Get the number of attached drives. */
	deref_nl(X_DISK_COUNT, &dk_ndrive, sizeof(dk_ndrive));

	if (dk_ndrive < 0)
		errx(1, "invalid _disk_count %d.", dk_ndrive);
	else {
		/* Get a pointer to the first disk. */
		deref_nl(X_DISKLIST, &disk_head, sizeof(disk_head));
		dk_drivehead = disk_head.tqh_first;
	}

	/* Get ticks per second. */
	deref_nl(X_STATHZ, &hz, sizeof(hz));
	if (!hz)
		deref_nl(X_HZ, &hz, sizeof(hz));

	/* allocate space for the statistics */
	cur.dk_time = calloc(dk_ndrive, sizeof(struct timeval));
	cur.dk_xfer = calloc(dk_ndrive, sizeof(u_int64_t));
	cur.dk_seek = calloc(dk_ndrive, sizeof(u_int64_t));
	cur.dk_bytes = calloc(dk_ndrive, sizeof(u_int64_t));
	last.dk_time = calloc(dk_ndrive, sizeof(struct timeval));
	last.dk_xfer = calloc(dk_ndrive, sizeof(u_int64_t));
	last.dk_seek = calloc(dk_ndrive, sizeof(u_int64_t));
	last.dk_bytes = calloc(dk_ndrive, sizeof(u_int64_t));
	cur.dk_select = calloc(dk_ndrive, sizeof(int));
	cur.dk_name = calloc(dk_ndrive, sizeof(char *));
	
	if (!cur.dk_time || !cur.dk_xfer || !cur.dk_seek || !cur.dk_bytes
	    || !last.dk_time || !last.dk_xfer || !last.dk_seek || !last.dk_bytes
	    || !cur.dk_select || !cur.dk_name)
		errx(1, "Memory allocation failure.");

	/* Set up the compatibility interfaces. */
	dk_select = cur.dk_select;
	dr_name = cur.dk_name;

	/* Read the disk names and set intial selection. */
	p = dk_drivehead;
	for (i = 0; i < dk_ndrive; i++) {
		char	buf[10];
		deref_kptr(p, &cur_disk, sizeof(cur_disk));
		deref_kptr(cur_disk.dk_name, buf, sizeof(buf));
		cur.dk_name[i] = strdup(buf);
		cur.dk_select[i] = select;

		p = cur_disk.dk_link.tqe_next;
	}

	/* Never do this initalization again. */
	once = 1;
	return(1);
}

/*
 * Dereference the kernel pointer `kptr' and fill in the local copy 
 * pointed to by `ptr'.  The storage space must be pre-allocated,
 * and the size of the copy passed in `len'.
 */
static void
deref_kptr(kptr, ptr, len)
	void *kptr, *ptr;
	size_t len;
{
	char buf[128];

	if (kvm_read(kd, (u_long)kptr, ptr, len) != len) {
		bzero(buf, sizeof(buf));
		snprintf(buf, (sizeof(buf) - 1),
		     "can't dereference kptr 0x%lx", (u_long)kptr);
		KVM_ERROR(buf);
	}
}