Don't use O_EXCL when using O_TMPFILE

Feature or enhancement

Proposal:

I was working on a tool on Linux where I'm updating yaml files on disk. I need to replace the file when the data changes. I was looking into using a tempfile created with O_TMPFILE, writing the content, and then replacing the original file using linkat. This would provide a simple atomic replacement of the file without needing to do a lot of file handshaking, etc.

However, at the moment tempfile.TemporaryFile passes the O_EXCL flag to io.open, this prevents the file descriptor from being used in a linkat call.

The TemporaryFile code already removes the O_CREAT flags from the standard open flags when using O_TMPFILE.

Would it be okay to remove O_EXCL from the open flags as well?

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-136281
• gh-136430
• gh-136534

Start at Python's tempfile.TemporaryFile implementation and inspect how it passes flags to io.open when O_TMPFILE is used. Confirm that O_EXCL is omitted only for this path, then verify that the resulting descriptor can be used with linkat without changing other TemporaryFile behavior.