Here is the "utmpentry.h" I got in my source tree ( updated today ) :

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/*      $NetBSD: utmpentry.h,v 1.5 2006/09/20 19:39:23 christos Exp  
$   */

/*-
* Copyright (c) 2002 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD  
Foundation
* by Christos Zoulas.
*
* 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 the NetBSD
*        Foundation, Inc. and its contributors.
* 4. Neither the name of The NetBSD Foundation nor the names of its
*    contributors may be used to endorse or promote products derived
*    from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND  
CONTRIBUTORS
* ``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 FOUNDATION OR  
CONTRIBUTORS
* 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.
*/

#if defined(SUPPORT_UTMPX)
# include <utmpx.h>
# define WHO_NAME_LEN           _UTX_USERSIZE
# define WHO_LINE_LEN           _UTX_LINESIZE
# define WHO_HOST_LEN           _UTX_HOSTSIZE
#elif defined(SUPPORT_UTMP)
# include <utmp.h>
# define WHO_NAME_LEN           UT_NAMESIZE
# define WHO_LINE_LEN           UT_LINESIZE
# define WHO_HOST_LEN           UT_HOSTSIZE
#else
# error Either SUPPORT_UTMPX or SUPPORT_UTMP must be defined!
#endif


struct utmpentry {
         char name[WHO_NAME_LEN + 1];
         char line[WHO_LINE_LEN + 1];
         char host[WHO_HOST_LEN + 1];
         struct timeval tv;
         pid_t pid;
         uint16_t term;
         uint16_t exit;
         uint16_t sess;
         uint16_t type;
         struct utmpentry *next;
};

extern int maxname, maxline, maxhost;
extern int etype;

int getutentries(const char *, struct utmpentry **);
void freeutentries(struct utmpentry *);
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Best regards