Implement the mlock2 function

Fallback using mlock is provided if the flags argument is zero.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

sysdeps/unix/sysv/linux/mlock2.c

@@ -0,0 +1,40 @@
+/* Wrapper for the mlock2 system call with fallback to mlock.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <sys/mman.h>
+#include <errno.h>
+#include <sysdep.h>
+
+int
+mlock2 (const void *addr, size_t length, unsigned int flags)
+{
+#ifdef __ASSUME_MLOCK2
+  return INLINE_SYSCALL_CALL (mlock2, addr, length, flags);
+#else
+  if (flags == 0)
+    return INLINE_SYSCALL_CALL (mlock, addr, length);
+# ifdef __NR_mlock2
+  int ret = INLINE_SYSCALL_CALL (mlock2, addr, length, flags);
+  if (ret == 0 || errno != ENOSYS)
+    return ret;
+# endif /* __NR_mlock2 */
+  /* Treat the missing system call as an invalid (non-zero) flag
+     argument.  */
+  __set_errno (EINVAL);
+  return -1;
+#endif /* __ASSUME_MLOCK2 */
+}