linux: Implement tmpfile with O_TMPFILE (BZ#21530)

This patch adds O_TMPFILE support to tmpfile on Linux.  This is
similar to the previous suggestion by Andreas Schwab [1] with the
difference the file descriptor creation is parameterized to
compartmentalize Linux only open flags (O_TMPFILE) on sysdeps.

Checked on x86_64-linux-gnu.

	Adhemerval Zanella  <adhemerval.zanella@linaro.org>
	Andreas Schwab  <schwab@suse.de>

	[BZ #21530]
	* include/stdio.h (__gen_tempfd): New function.
	* stdio-common/Makefile (routines): Add gentempfd.
	* stdio-common/gentempfd.c: New file.
	* sysdeps/unix/sysv/linux/gentempfd.c: Likewise.
	* stdio-common/tmpfile.c (tmpfile): First try to use a system specific
	unnamed file first.

[1] https://sourceware.org/ml/libc-alpha/2017-06/msg01293.html

1 files changed, 34 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/gentempfd.c b/sysdeps/unix/sysv/linux/gentempfd.c
new file mode 100644
index 0000000000..902cbe286e
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/gentempfd.c
@@ -0,0 +1,34 @@
+/* Generate a temporary file descriptor.  Linux version.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   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 <stdio.h>
+#include <fcntl.h>
+#include <errno.h>
+
+int
+__gen_tempfd (int flags)
+{
+  int fd = __open (P_tmpdir, O_RDWR | O_TMPFILE | O_EXCL | flags,
+		   S_IRUSR | S_IWUSR);
+  if (fd < 0 && errno == ENOENT && strcmp (P_tmpdir, "/tmp") != 0)
+    fd = __open ("/tmp", O_RDWR | O_TMPFILE | O_EXCL | flags,
+		 S_IRUSR | S_IWUSR);
+
+  return fd;
+}
+libc_hidden_def (__gen_tempfd)