Definition of updwtmp function.

login/updwtmp.c

@@ -0,0 +1,69 @@
+/* Copyright (C) 1997 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Mark Kettenis <kettenis@phys.uva.nl>, 1997.
+
+   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 <fcntl.h>
+#include <unistd.h>
+#include <utmp.h>
+#include <sys/file.h>
+#include <sys/stat.h>
+
+#include "utmp-private.h"
+
+
+void
+updwtmp (const char *wtmp_file, const struct utmp *utmp)
+{
+  struct stat st;
+  size_t written;
+  int fd;
+
+  /* Open WTMP file.  */
+  fd = __open (wtmp_file, O_WRONLY | O_APPEND);
+  if (fd < 0)
+      return;
+
+  /* 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);
+    }
+
+  /* Remember 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, utmp, sizeof (struct utmp));
+  if (written > 0 && written != sizeof (struct utmp))
+    ftruncate (fd, st.st_size);
+
+done:
+  /* And unlock the file.  */
+  __flock (fd, LOCK_UN);
+
+  /* Close WTMP file.  */
+  __close (fd);
+}