[newlib-cygwin] Cygwin: Have tmpfile(3) use O_TMPFILE

[Corinna Vinschen <corinna@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=62ee6581a5701342c17790116f847e9d40c387d7

commit 62ee6581a5701342c17790116f847e9d40c387d7
Author: Mark Geisert <mark@maxrnd.com>
Date:   Wed Feb 10 22:53:05 2021 -0800

    Cygwin: Have tmpfile(3) use O_TMPFILE
    
    Per discussion on cygwin-developers, a Cygwin tmpfile(3) implementation
    has been added to syscalls.cc.  This overrides the one supplied by
    newlib.  Then the open(2) flag O_TMPFILE was added to the open call that
    tmpfile internally makes.
    
    This v2 patch removes O_CREAT from open() call as O_TMPFILE obviates it.
    Note that open() takes a directory's path but returns an fd to a file.

Diff:
---
 winsup/cygwin/release/3.2.0 |  4 ++++
 winsup/cygwin/syscalls.cc   | 19 +++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/winsup/cygwin/release/3.2.0 b/winsup/cygwin/release/3.2.0
index f748a9bc8..d02d16863 100644
--- a/winsup/cygwin/release/3.2.0
+++ b/winsup/cygwin/release/3.2.0
@@ -19,6 +19,10 @@ What changed:
 
 - A few FAQ updates.
 
+- Have tmpfile(3) make use of Win32 FILE_ATTRIBUTE_TEMPORARY via open(2)
+  flag O_TMPFILE.
+  Addresses: https://cygwin.com/pipermail/cygwin/2021-January/247304.html
+
 
 Bug Fixes
 ---------
diff --git a/winsup/cygwin/syscalls.cc b/winsup/cygwin/syscalls.cc
index 52a020f07..d04b2d9b3 100644
--- a/winsup/cygwin/syscalls.cc
+++ b/winsup/cygwin/syscalls.cc
@@ -5225,3 +5225,22 @@ pipe2 (int filedes[2], int mode)
   syscall_printf ("%R = pipe2([%d, %d], %y)", res, read, write, mode);
   return res;
 }
+
+extern "C" FILE *
+tmpfile (void)
+{
+  char *dir = getenv ("TMPDIR");
+  if (!dir)
+    dir = P_tmpdir;
+  int fd = open (dir, O_RDWR | O_BINARY | O_TMPFILE, S_IRUSR | S_IWUSR);
+  if (fd < 0)
+    return NULL;
+  FILE *fp = fdopen (fd, "wb+");
+  int e = errno;
+  if (!fp)
+    close (fd); // ..will remove tmp file
+  set_errno (e);
+  return fp;
+}
+
+EXPORT_ALIAS (tmpfile, tmpfile64)