logwtmp.c

/* Copyright (C) 1996 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@cygnus.com>, 1996.

The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.

The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Library General Public License for more details.

You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB.  If
not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */

#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <utmp.h>
#include <sys/file.h>
#include <sys/stat.h>

void
logwtmp (const char *line, const char *name, const char *host)
{
  struct utmp ut;
  struct stat st;
  size_t written;
  int fd;

  /* Open WTMP file.  */
  fd = __open (_PATH_WTMP, O_WRONLY | O_APPEND);
  if (fd < 0)
      return;

  /* Set information in new entry.  */
  memset (&ut, 0, sizeof (ut));
  ut.ut_pid = getpid ();
#if _HAVE_UT_TYPE - 0
  ut.ut_type = name[0] ? USER_PROCESS : DEAD_PROCESS;
#endif
  strncpy (ut.ut_line, line, sizeof ut.ut_line);
  strncpy (ut.ut_name, name, sizeof ut.ut_name);
#if _HAVE_UT_HOST - 0
  strncpy (ut.ut_host, host, sizeof ut.ut_host);
#endif

#if _HAVE_UT_TV - 0
  __gettimeofday (&ut.ut_tv, NULL);
#else
  __time (&ut.ut_time);
#endif

  /* Try to lock the file.  */
  if (__flock (fd, LOCK_EX | LOCK_NB) < 0 && errno != ENOSYS)
    {
      /* Oh, oh.  The file is already locked.  Wait a bit and try again.  */
      sleep (1);

      /* This time we ignore the error.  */
      __flock (fd, LOCK_EX | LOCK_NB);
    }

  /* Remeber original size of log file: */
  if (__fstat (fd, &st) < 0)
    goto done;

  /* Write the entry.  If we can't write all the bytes, reset the file
     size back to the original size.  That way, no partial entries
     will remain.  */
  written = __write (fd, &ut, sizeof (ut));
  if (written > 0 && written != sizeof (ut))
    ftruncate (fd, st.st_size);

done:
  /* And unlock the file.  */
  __flock (fd, LOCK_UN);

  /* Close WTMP file.  */
  __close (fd);
}