path: root/src/util/pty/update_utmp.c

/*
 * pty_update_utmp: Update or create a utmp entry
 * 
 * Copyright 1995, 2001 by the Massachusetts Institute of Technology.
 * 
 * Permission to use, copy, modify, and distribute this software and
 * its documentation for any purpose and without fee is hereby
 * granted, provided that the above copyright notice appear in all
 * copies and that both that copyright notice and this permission
 * notice appear in supporting documentation, and that the name of
 * M.I.T. not be used in advertising or publicity pertaining to
 * distribution of the software without specific, written prior
 * permission.  Furthermore if you modify this software you must label
 * your software as modified software and not distribute it in such a
 * fashion that it might be confused with the original M.I.T. software.
 * M.I.T. makes no representations about the suitability
 * of this software for any purpose.  It is provided "as is" without
 * express or implied warranty.
 */

/*
 * Rant about the historical vagaries of utmp:
 * -------------------------------------------
 *
 * There exist many subtly incompatible incarnations of utmp, ranging
 * from BSD to System V to Unix98 and everywhere in between.  This
 * rant attempts to collect in one place as much knowledge as possible
 * about this portability nightmare.
 *
 * BSD:
 * ----
 *
 * The simplest (and earliest? possibly dating back to Version 7...)
 * case is 4.x BSD utmp/wtmp.  There are no auxiliary files.  There is
 * only a struct utmp, declared in utmp.h.  Its contents usually
 * include:
 *
 *	char ut_line[]
 *	char ut_name[]
 *	char ut_host[]
 *	long ut_time
 *
 * The meanings of these fields follow their names reasonbly well.
 * The ut_line field usually is the pathname of the tty device
 * associated with the login, with the leading "/dev/" stripped off.
 *
 * It is believed that ut_host is nul-terminated, while the other
 * strings are merely nul-padded.
 *
 * Generally, ut_name is an empty string for a logout record in both
 * utmp and wtmp.  For entries made by the window system or other
 * terminal emulation stuff, ut_host is an empty string (at least
 * under SunOS 4.x, it seems).  The macro nonuser() is used to
 * determine this if a utmp entry is made by the window system on at
 * least SunOS 4.x.
 *
 * The native login never clears its own utmp entry or writes its own
 * logout record; its parent (one of init, rlogind, telnetd, etc.)
 * should handle that.  In theory, getty could do that, but getty
 * usually doesn't fork to exec login.
 *
 * Old (c. 1984) System V:
 * -----------------------
 *
 * This is partially conjecture, based on some reading of
 * /usr/xpg2include/utmp.h on a SunOS 4.x system.  There appears to
 * only be a struct utmp, declared in utmp.h.  It is likely used for
 * both utmp and wtmp files.  It is quite likely that the utmp is only
 * supposed to be accessed via the getutline()/pututline() API.  The
 * contents of struct utmp seem to include:
 *
 *	char	ut_user[]
 *	char	ut_id[]
 *	char	ut_line[]
 *	short	ut_pid
 *	short	ut_type
 *	struct exit_status ut_exit
 *	time_t	ut_time
 *
 * On these systems, ut_name is often #define'ed to be ut_user to be
 * somewhat compatible with the BSD-style utmp.  Note that there is
 * not necessarily a ut_host field in this utmp structure.
 *
 * The ut_id field bears some explanation.  The systems that use this
 * style of utmp also use a sysV-ish init, which starts processes out
 * of /etc/inittab rather than /etc/ttys, and has the concept of
 * runlevels.  The first field in each line of /etc/inittab contains a
 * unique ID field.  init probably gets really confused if there are
 * conflicts here.  Every process that init starts gets its own entry
 * written to utmp.
 *
 * It is possible for multiple entries to have the same ut_line but
 * different ut_id values, since the sysadmin will be responsible for
 * assigning values to ut_id.  Usually, ut_id is four characters,
 * while the permissible unique ID values for entries in /etc/inittab
 * are constrained to two characters, but this is not always the
 * case.  In the case where we are emulating the vendor's login
 * program and being run out of getty, we need to account for which
 * value of ut_id was used by the getty, since pututline() will search
 * based on ut_id and not ut_line for some reason.
 *
 * The ut_pid and ut_type fields are used for bookkeeping by init.
 * The ut_type field gets the value INIT_PROCESS for processes started
 * by init.  It gets the value LOGIN_PROCESS if it is a process that
 * is prompting for a login name, and it gets the value USER_PROCESS
 * for an actual valid login.  When the process dies, either init
 * cleans up after it and records a DEAD_PROCESS entry in utmp, or the
 * process itself does so.  It's not completely clear which actually
 * happens, though it is quite possible that init only cleans up after
 * processes that it starts itself.
 *
 * Other values of ut_type exist; they're largely internal bookkeeping
 * for init's runlevels and such, and don't really interest this
 * library at all.
 *
 * The ut_exit field contains the following members:
 *
 *	short	e_termination
 *	short	e_exit
 *
 * It is not clear how these values are used; presumably they record
 * the process termination status of dead processes.
 *
 * There is no uniform API for manipulating wtmp on systems that use
 * this sort of utmp structure; it can be assumed that the structure
 * can be directly written to the wtmp file.
 *
 * Unix98:
 * -------
 *
 * This description also likely applies to later System V derivatives
 * as well as systems conforming to earlier X/Open standards such as
 * XPG4.  There is a new header, utmpx.h, which defines a struct utmpx
 * and a new getutxline()/pututxline() API for accessing it.  Some
 * systems actually have a utmpx file on disk; others use the utmpx
 * API to access a file named utmp, just to further confuse matters.
 *
 * The utmpx structure is guaranteed (by Unix98) to contain at least
 * the following:
 *
 *	char	ut_user[]
 *	char	ut_line[]
 *	char	ut_id[]
 *	pid_t	ut_pid
 *	short	ut_type
 *	struct timeval ut_tv
 *
 * It is not guaranteed to contain, but often does contain, the
 * following:
 *
 *	char	ut_host[]
 *	int	ut_syslen
 *	int	ut_session
 *	struct exit_status ut_exit
 *
 * The ut_syslen field, on systems that contain it, contains the
 * number of significant characters in ut_host, including the
 * terminating nul character.
 *
 * The main difference between this struct utmpx and the struct utmp
 * used by early sysV derivatives is the change from a time_t or long
 * for ut_time to a struct timeval for ut_tv.
 *
 * Comments in various header files imply that ut_session is used for
 * window systems, but it's not clear how.  Perhaps it contains the
 * session ID of the session running the window system, e.g. the xdm
 * or X server on an X11 system.
 *
 * Most of the description of the earlier sysV format probably applies
 * here, with suitable changes of names.  On systems that maintain
 * utmpx and utmp files in parallel, it is assumed that using the
 * pututxline() API is sufficient to keep them in sync.  There are no
 * known counterexamples to this.
 *
 * Nevertheless, there are, on some systems, API functions getutmp()
 * and getutmpx() that appear to convert from struct utmpx to struct
 * utmp and vice versa.  This could be useful when there is a wtmp
 * file but not a corresponding wtmpx file.
 *
 * Incidentally, ut_exit is sometimes present in the struct utmp but
 * not the struct utmpx for a given system.  Sometimes, it exists in
 * both, but contains differently named members.  It's probably one of
 * the least portable pieces in this whole mess.
 *
 * Known Quirks of Specific OSes:
 * ------------------------------
 *
 * Solaris 2.x:
 *
 * Has utmpd, which will automatically clean up utmpx, utmp, wtmpx,
 * wtmp after process termination, provided that pututxline() was
 * used.
 *
 * Solaris 8 seems to have a bug in utmpname() that causes
 * garbage filenames to be generated.  Solaris 7 (and possibly Solaris
 * 8) have a bug in utmpxname() that prevents them from looking at
 * anything other than /var/adm/utmpx, it seems.  For some reason,
 * though, utmpname() goes and looks at the corresponding utmpx file.
 *
 * Solaris 7 (and may be 8 as well) has a bug in pututline() that
 * interacts badly with prior invocation of getutline(): if
 * getutline() finds an entry, calling pututline() without first
 * calling setutent() will overwrite the record following the one that
 * was intended.
 *
 * Also, ut_exit in utmpx contains ut_e_termination and
 * ut_e_exit (otherwise it contains the expected e_termination and
 * e_exit) only if _XPG4_2 is defined and __EXTENSIONS__ is not, which
 * is not a compilation environment we're likely to encourage.  The
 * ut_exit field of utmp contains the expected fields.
 *
 * If _XPG4_2 is not defined or __EXTENSIONS__ is defined, the
 * functions getutmp(), getutmpx(), updwtmp(), and updwtmpx() are
 * available, as well as the undocumented functions makeutx() and
 * modutx().
 *
 * All the files utmp, utmpx, wtmp, and wtmpx exist.
 *
 * HP-UX 10.x:
 *
 * There is a curious interaction between how we allocate pty masters
 * and how ttyname() works.  It seems that if /dev/ptmx/clone is
 * opened, a call to ptsname() on the master fd gets a filename of the
 * form /dev/pty/tty[pqrs][0-9a-f], while ttyname() called on a fd
 * opened with that filename returns a filename of the form
 * /dev/tty[pqrs][0-9a-f] instead.  These two filenames are actually
 * hardlinks to the same special device node, so it shouldn't be a
 * security problem.
 *
 * We can't call ttyname() in the parent because it would involve
 * possibly acquiring a controlling terminal (which would be
 * potentially problematic), so we have to resort to some trickery in
 * order to ensure that the ut_line in the wtmp logout and login
 * records match.  If they don't match, various utilities such as last
 * will get confused.  Of course it's likely an OS bug that ttyname()
 * and ptsname() are inconsistent in this way, but it's one that isn't
 * too painful to work around.
 *
 * It seems that the HP-UX native telnetd has problems similar to ours
 * in this area, though it manages to write the correct logout record
 * to wtmp somehow.  It probably does basically what we do here:
 * search for a record with a matching ut_pid and grab its ut_line for
 * writing into the logout record.  Interestingly enough, its
 * LOGIN_PROCESS record is of the form pty/tty[pqrs][0-9][a-f].
 *
 * Uses four-character unique IDs for /etc/inittab, which means that
 * programs not running out of init should use two-character ut_id
 * fields to avoid conflict.
 *
 * In utmpx, ut_exit contains __e_termination and __e_exit, while
 * ut_exit in utmp contains the expected fields.
 *
 * There is no wtmpx file, despite there being utmp and utmpx files.
 *
 * Irix 6.x:
 *
 * In utmpx, ut_exit contains __e_termination and __e_exit, which get
 * #define aliases e_termination and e_exit if _NO_XOPEN4 is true.
 * Curiously enough, utmp.h declares ut_exit to have __e_termination
 * and __e_exit as well, but does #define e_termination
 * __e_termination, etc. if another header (utmpx.h) hasn't already
 * declared struct __exit_status.  It seems that the default
 * compilation environment has the effect of making _NO_XOPEN4 true
 * though.
 *
 * If _NO_XOPEN4 is true, getutmp(), getutmpx(), updwtmp(), and
 * updwtmpx() are available, as well as the undocumented functions
 * makeutx() and modutx().
 *
 * All the files utmp, utmpx, wtmp, and wtmpx exist.
 *
 * Tru64 Unix 4.x:
 *
 * In utmpx, ut_exit contains ut_termination and ut_exit, while utmp
 * contains the expected fields.  The files utmp and wtmp seem to
 * exist, but not utmpx or wtmpx.
 *
 * When writing a logout entry, the presence of a non-empty username
 * confuses last.
 *
 * AIX 4.3.x:
 *
 * The ut_exit field seems to exist in utmp, but not utmpx. The files
 * utmp and wtmp seem to exist, but not utmpx, or wtmpx.
 *
 * libpty Implementation Decisions:
 * --------------------------------
 *
 * We choose to use the pututxline() whenever possible, falling back
 * to pututline() and calling write() to write out struct utmp if
 * necessary.  The code to handle pututxline() and pututline() is
 * rather similar, since the structure members are quite similar, and
 * we make the assumption that it will never be necessary to call
 * both.  This allows us to avoid duplicating lots of code, by means
 * of some slightly demented macros.
 *
 * If neither pututxline() nor pututline() are available, we assume
 * BSD-style utmp files and behave accordingly, writing the structure
 * out to disk ourselves.
 *
 * On systems where updwtmpx() or updwtmp() are available, we use
 * those to update the wtmpx or wtmp file.  When they're not
 * available, we write the utmpx or utmp structure out to disk
 * ourselves, though sometimes conversion from utmpx to utmp format is
 * needed.
 *
 * We assume that at logout the system is ok with with having an empty
 * username both in utmp and wtmp.
 */

#include "com_err.h"
#include "libpty.h"
#include "pty-int.h"

#if !defined(UTMP_FILE) && defined(_PATH_UTMP)
#define UTMP_FILE _PATH_UTMP
#endif

/* if it is *still* missing, assume SunOS */
#ifndef UTMP_FILE
#define	UTMP_FILE	"/etc/utmp"
#endif

/*
 * The following grossness exists to avoid duplicating lots of code
 * between the cases where we have an old-style sysV utmp and where we
 * have a modern (Unix98 or XPG4) utmpx.  See the above history rant
 * for further explanation.
 */
#if defined(HAVE_SETUTXENT) || defined(HAVE_SETUTENT)
#ifdef HAVE_SETUTXENT
#define PTY_STRUCT_UTMPX struct utmpx
#define PTY_SETUTXENT setutxent
#define PTY_GETUTXENT getutxent
#define PTY_GETUTXLINE getutxline
#define PTY_PUTUTXLINE pututxline
#define PTY_ENDUTXENT endutxent
#else
#define PTY_STRUCT_UTMPX struct utmp
#define PTY_SETUTXENT setutent
#define PTY_GETUTXENT getutent
#define PTY_GETUTXLINE getutline
#define PTY_PUTUTXLINE pututline
#define PTY_ENDUTXENT endutent
#endif

static int better(const PTY_STRUCT_UTMPX *, const PTY_STRUCT_UTMPX *,
		  const PTY_STRUCT_UTMPX *);
static int match_pid(const PTY_STRUCT_UTMPX *,
		     const PTY_STRUCT_UTMPX *);
static PTY_STRUCT_UTMPX *best_utxent(const PTY_STRUCT_UTMPX *);

/*
 * Utility function to determine whether A is a better match for
 * SEARCH than B.  Should only be called by best_utxent().
 */
static int
better(const PTY_STRUCT_UTMPX *search,
       const PTY_STRUCT_UTMPX *a, const PTY_STRUCT_UTMPX *b)
{
    if (strncmp(search->ut_id, b->ut_id, sizeof(b->ut_id))) {
	if (!strncmp(search->ut_id, a->ut_id, sizeof(a->ut_id))) {
	    return 1;
	}
    }

    if (strncmp(a->ut_id, b->ut_id, sizeof(b->ut_id))) {
	/* Got different UT_IDs; find the right one. */
	if (!strncmp(search->ut_id, b->ut_id, sizeof(b->ut_id))) {
	    /* Old entry already matches; use it. */
	    return 0;
	}
	if (a->ut_type == LOGIN_PROCESS
	    && b->ut_type != LOGIN_PROCESS) {
	    /* Prefer LOGIN_PROCESS */
	    return 1;
	}
	if (search->ut_type == DEAD_PROCESS
	    && a->ut_type == USER_PROCESS
	    && b->ut_type != USER_PROCESS) {
	    /*
	     * Try USER_PROCESS if we're entering a DEAD_PROCESS.
	     */
	    return 1;
	}
	return 0;
    } else {
	/*
	 * Bad juju.  We shouldn't get two entries with identical
	 * ut_id fields for the same value of ut_line.  pututxline()
	 * will probably pick the first entry, in spite of the strange
	 * state of utmpx, if we rewind with setutxent() first.
	 *
	 * For now, return 0, to force the earlier entry to be used.
	 */
	return 0;
    }
}

static int
match_pid(const PTY_STRUCT_UTMPX *search, const PTY_STRUCT_UTMPX *u)
{
    if (u->ut_type != LOGIN_PROCESS && u->ut_type != USER_PROCESS)
	return 0;
    if (u->ut_pid == search->ut_pid) {
	/*
	 * One of ut_line or ut_id should match, else some nastiness
	 * may result.  We can fall back to searching by ut_line if
	 * need be.  This should only really break if we're login.krb5
	 * running out of getty, or we're cleaning up after the vendor
	 * login, and either the vendor login or the getty has
	 * different ideas than we do of what both ut_id and ut_line
	 * should be.  It should be rare, though.  We may want to
	 * remove this restriction later.
	 */
	if (!strncmp(u->ut_line, search->ut_line, sizeof(u->ut_line)))
	    return 1;
	if (!strncmp(u->ut_id, search->ut_id, sizeof(u->ut_id)))
	    return 1;
    }
    return 0;
}

/*
 * This expects to be called with SEARCH pointing to a struct utmpx
 * with its ut_type equal to USER_PROCESS or DEAD_PROCESS, since if
 * we're making a LOGIN_PROCESS entry, we presumably don't care about
 * preserving existing state.  At the very least, the ut_pid, ut_line,
 * ut_id, and ut_type fields must be filled in by the caller.
 */
static PTY_STRUCT_UTMPX *
best_utxent(const PTY_STRUCT_UTMPX *search)
{
    PTY_STRUCT_UTMPX utxtmp, *utxp;
    int i, best;

    memset(&utxtmp, 0, sizeof(utxtmp));

    /*
     * First, search based on pid, but only if non-zero.
     */
    if (search->ut_pid) {
	i = 0;
	PTY_SETUTXENT();
	while ((utxp = PTY_GETUTXENT()) != NULL) {
	    if (match_pid(search, utxp)) {
		return utxp;
	    }
	    i++;
	}
    }
    /*
     * Uh-oh, someone didn't enter our pid.  Try valiantly to search
     * by terminal line.
     */
    i = 0;
    best = -1;
    PTY_SETUTXENT();
    while ((utxp = PTY_GETUTXLINE(search)) != NULL) {
	if (better(search, utxp, &utxtmp)) {
	    utxtmp = *utxp;
	    best = i;
	}
	memset(utxp, 0, sizeof(*utxp));
	i++;
    }
    if (best == -1)
	return NULL;
    PTY_SETUTXENT();
    for (i = 0; i <= best; i++) {
	if (utxp != NULL)
	    memset(utxp, 0, sizeof(*utxp));
	utxp = PTY_GETUTXLINE(search);
    }
    return utxp;
}

/*
 * All calls to this function for a given login session must have the
 * pids be equal; various things will break if this is not the case,
 * since we do some searching based on the pid.  Note that if a parent
 * process calls this via pty_cleanup(), it should still pass the
 * child's pid rather than its own.
 */
long
pty_update_utmp(int process_type, int pid, const char *username,
		    const char *line, const char *host, int flags)
{
    PTY_STRUCT_UTMPX utx, *utxtmp, utx2;
    const char *cp;
    size_t len;
    char utmp_id[5];

    /*
     * Zero things out in case there are fields we don't handle here.
     * They tend to be non-portable anyway.
     */
    memset(&utx, 0, sizeof(utx));
    utxtmp = NULL;
    cp = line;
    if (strncmp(cp, "/dev/", sizeof("/dev/") - 1) == 0)
	cp += sizeof("/dev/") - 1;
    strncpy(utx.ut_line, cp, sizeof(utx.ut_line));
    utx.ut_pid = pid;
    switch (process_type) {
    case PTY_LOGIN_PROCESS:
	utx.ut_type = LOGIN_PROCESS;
	break;
    case PTY_USER_PROCESS:
	utx.ut_type = USER_PROCESS;
	break;
    case PTY_DEAD_PROCESS:
	utx.ut_type = DEAD_PROCESS;
	break;
    default:
	return PTY_UPDATE_UTMP_PROCTYPE_INVALID;
    }
    len = strlen(line);
    if (len >= 2) {
	cp = line + len - 1;
	if (*(cp - 1) != '/')
	    cp--;		/* last two characters, unless it's a / */
    } else
	cp = line;
    /*
     * HP-UX has mostly 4-character inittab ids, while most other sysV
     * variants use only 2-charcter inittab ids, so to avoid
     * conflicts, we pick 2-character ut_ids for our own use.  We may
     * want to feature-test for this, but it would be somewhat of a
     * pain, and would eit cross-compiling.
     */
#ifdef __hpux
    strcpy(utmp_id, cp);
#else
    if (len > 2 && *(cp - 1) != '/')
      sprintf(utmp_id, "k%s", cp - 1);
    else
      sprintf(utmp_id, "k0%s", cp);
#endif
    strncpy(utx.ut_id, utmp_id, sizeof(utx.ut_id));
    /*
     * Get existing utmpx entry for PID or LINE, if any, so we can
     * copy some stuff from it.  This is particularly important if we
     * are login.krb5 and are running out of getty, since getty will
     * have written the entry for the line with ut_type ==
     * LOGIN_PROCESS, and what it has recorded in ut_id may not be
     * what we come up with, since that's up to the whim of the
     * sysadmin who writes the inittab entry.
     *
     * Note that we may be screwed if we try to write a logout record
     * for a vendor's login program, since it may construct ut_line
     * and ut_id differently from us; even though we search on ut_pid,
     * we validate against ut_id or ut_line to sanity-check.  We may
     * want to rethink whether to actually include this check, since
     * it should be highly unlikely that there will be a bogus entry
     * in utmpx matching our pid.
     */
    if (process_type != PTY_LOGIN_PROCESS)
	utxtmp = best_utxent(&utx);

#ifdef HAVE_SETUTXENT
    if (gettimeofday(&utx.ut_tv, NULL))
	return errno;
#else
    (void)time(&utx.ut_time);
#endif
    /*
     * On what system is there not ut_host?  Unix98 doesn't mandate
     * this field, but we have yet to see a system that supports utmpx
     * that doesn't have it.  For what it's worth, some ancient utmp
     * headers on svr4 systems imply that there's no ut_host in struct
     * utmp...
     */
#if (defined(HAVE_SETUTXENT) && defined(HAVE_STRUCT_UTMPX_UT_HOST))	\
	|| (!defined(HAVE_SETUTXENT) && defined(HAVE_STRUCT_UTMP_UT_HOST))
    if (host != NULL) {
	strncpy(utx.ut_host, host, sizeof(utx.ut_host));
	/* Unlike other things in utmpx, ut_host is nul-terminated? */
	utx.ut_host[sizeof(utx.ut_host) - 1] = '\0';
    } else
	utx.ut_host[0] = '\0';
#if (defined(HAVE_SETUTXENT) && defined(HAVE_STRUCT_UTMPX_UT_SYSLEN))	\
	|| (!defined (HAVE_SETUTXENT) && defined(HAVE_STRUCT_UTMP_UT_SYSLEN))
    if (host != NULL)
	utx.ut_syslen = strlen(utx.ut_host) + 1;
    else
	utx.ut_syslen = 0;
#endif
#endif

    /* XXX deal with ut_addr? */

    if (utxtmp != NULL) {
	/*
	 * For entries not of type LOGIN_PROCESS, override some stuff
	 * with what was in the previous entry we found, if any.
	 */
	strncpy(utx.ut_id, utxtmp->ut_id, sizeof(utx.ut_id));
	utx.ut_pid = utxtmp->ut_pid;
    }

    strncpy(utx.ut_user, username, sizeof(utx.ut_user));

    /*
     * Make a copy now and deal with copying relevant things out of
     * utxtmp in case setutxline() or pututxline() clobbers utxtmp.
     * (After all, the returned pointer from the getutx*() functions
     * is allowed to point to static storage that may get overwritten
     * by subsequent calls to related functions.)
     */
    utx2 = utx;
    if (process_type == PTY_DEAD_PROCESS && utxtmp != NULL) {
	/*
	 * Use ut_line from old entry to avoid confusing last on
	 * HP-UX.
	 */
	strncpy(utx2.ut_line, utxtmp->ut_line, sizeof(utx2.ut_line));
    }

    PTY_SETUTXENT();
    PTY_PUTUTXLINE(&utx);
    PTY_ENDUTXENT();

    /* Don't record LOGIN_PROCESS entries. */
    if (process_type == PTY_LOGIN_PROCESS)
	return 0;

#ifdef HAVE_SETUTXENT
    return ptyint_update_wtmpx(&utx2);
#else
    return ptyint_update_wtmp(&utx2);
#endif
}

#else /* !(HAVE_SETUTXENT || HAVE_SETUTENT) */

long
pty_update_utmp(int process_type, int pid, const char *username,
		const char *line, const char *host, int flags)
{
    struct utmp ent, ut;
    const char *cp;
    int tty, lc, fd;
    off_t seekpos;
    ssize_t ret;
    struct stat statb;

    memset(&ent, 0, sizeof(ent));
#ifdef HAVE_STRUCT_UTMP_UT_HOST
    if (host)
	strncpy(ent.ut_host, host, sizeof(ent.ut_host));
#endif
    strncpy(ent.ut_name, username, sizeof(ent.ut_name));
    cp = line;
    if (strncmp(cp, "/dev/", sizeof("/dev/") - 1) == 0)
	cp += sizeof("/dev/") - 1;
    strncpy(ent.ut_line, cp, sizeof(ent.ut_line));
    (void)time(&ent.ut_time);

    if (flags & PTY_TTYSLOT_USABLE)
	tty = ttyslot();
    else {
	tty = -1;
	fd = open(UTMP_FILE, O_RDONLY);
	if (fd == -1)
	    return errno;
	for (lc = 0; ; lc++) {
	    seekpos = lseek(fd, (off_t)(lc * sizeof(struct utmp)), SEEK_SET);
	    if (seekpos != (off_t)(lc * sizeof(struct utmp)))
		break;
	    if (read(fd, (char *) &ut, sizeof(struct utmp))
		!= sizeof(struct utmp))
		break;
	    if (strncmp(ut.ut_line, ent.ut_line, sizeof(ut.ut_line)) == 0) {
		tty = lc;
		break;
	    }
	}
	close(fd);
    }
    if (tty > 0) {
	fd = open(UTMP_FILE, O_WRONLY);
	if (fd == -1)
	    return 0;
	if (fstat(fd, &statb)) {
	    close(fd);
	    return 0;
	}
	seekpos = lseek(fd, (off_t)(tty * sizeof(struct utmp)), SEEK_SET);
	if (seekpos != (off_t)(tty * sizeof(struct utmp))) {
	    close(fd);
	    return 0;
	}
	ret = write(fd, (char *)&ent, sizeof(struct utmp));
	if (ret != sizeof(struct utmp)) {
	    ftruncate(fd, statb.st_size);
	}
	close(fd);
    }
    /* Don't record LOGIN_PROCESS entries. */
    if (process_type == PTY_LOGIN_PROCESS)
	return 0;
    else
	return ptyint_update_wtmp(&ent);
}
#endif