[PATCH] Cygwin: Have tmpfile(3) use O_TMPFILE
Corinna Vinschen
corinna-cygwin@cygwin.com
Tue Feb 9 15:25:10 GMT 2021
Hi Mark,
On Feb 9 02:50, 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.
> ---
> winsup/cygwin/release/3.2.0 | 4 ++++
> winsup/cygwin/syscalls.cc | 20 ++++++++++++++++++++
> 2 files changed, 24 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..b79c1c7cd 100644
> --- a/winsup/cygwin/syscalls.cc
> +++ b/winsup/cygwin/syscalls.cc
> @@ -5225,3 +5225,23 @@ 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");
This isn't what Linux tmpfile does. Per the man page, it tries to
create the file in P_tmpdir first, and if that fails, it tries
"/tmp".
> + if (!dir)
> + dir = P_tmpdir;
> + int fd = open (dir, O_RDWR | O_CREAT | O_BINARY | O_TMPFILE,
You have to specify O_EXCL here. The idea is that this file cannot be
made permanent, and missing the O_EXCL flag allows exactly that. See
https://man7.org/linux/man-pages/man2/open.2.html, the lengthy
description in terms of O_TMPFILE.
Thanks,
Corinna
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