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diff --git a/sysdeps/unix/sysv/linux/unlockpt.c b/sysdeps/unix/sysv/linux/unlockpt.c
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+/* Copyright (C) 1998 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+ Contributed by Zack Weinberg <zack@rabi.phys.columbia.edu>, 1998.
+
+ 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 <sys/ioctl.h>
+#include <termios.h>
+#include <errno.h>
+#include <stdlib.h>
+
+/* Given a fd on a master pseudoterminal, clear a kernel lock so that
+ the slave can be opened. This is to avoid a race between opening the
+ master and calling grantpt() to take possession of the slave. */
+int
+unlockpt (fd)
+ int fd __attribute__ ((unused));
+{
+#ifdef TIOCSPTLCK
+ int serrno = errno;
+ int unlock = 0;
+
+ if (ioctl (fd, TIOCSPTLCK, &unlock))
+ {
+ if(errno == EINVAL)
+ {
+ __set_errno (serrno);
+ return 0;
+ }
+ else
+ return -1;
+ }
+#else
+ /* On pre-/dev/ptmx kernels this function should be a no-op. */
+ return 0;
+#endif
+}