[PATCH v2] Cygwin: Have tmpfile(3) use O_TMPFILE

[Corinna Vinschen]

On Feb 10 22:53, Mark Geisert wrote:
> 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.
> ---
>  winsup/cygwin/release/3.2.0 |  4 ++++
>  winsup/cygwin/syscalls.cc   | 17 +++++++++++++++++
>  2 files changed, 21 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..4cda69033 100644
> --- a/winsup/cygwin/syscalls.cc
> +++ b/winsup/cygwin/syscalls.cc
> @@ -5225,3 +5225,20 @@ 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;
> +}

The patch was missing the EXPORT_ALIAS for tmpfile64, as outlined in
https://cygwin.com/pipermail/cygwin-developers/2021-February/012039.html
I added this to the patch and pushed it.

Thanks,
Corinna