Issue #21515: Elaborate tempfile.TemporaryFile() comment
Explain why calling os.open() with os.O_TMPFILE is a safe test to check if
O_TMPFILE is supported by the running kernel.
diff --git a/Lib/tempfile.py b/Lib/tempfile.py
index 2f1f9fd..e87eb09 100644
--- a/Lib/tempfile.py
+++ b/Lib/tempfile.py
@@ -591,12 +591,20 @@
flags2 = (flags | _os.O_TMPFILE) & ~_os.O_CREAT
fd = _os.open(dir, flags2, 0o600)
except IsADirectoryError:
- # Linux kernel older than 3.11 ignores O_TMPFILE flag.
- # Set flag to False to not try again.
+ # Linux kernel older than 3.11 ignores the O_TMPFILE flag:
+ # O_TMPFILE is read as O_DIRECTORY. Trying to open a directory
+ # with O_RDWR|O_DIRECTORY fails with IsADirectoryError, a
+ # directory cannot be open to write. Set flag to False to not
+ # try again.
_O_TMPFILE_WORKS = False
except OSError:
# The filesystem of the directory does not support O_TMPFILE.
# For example, OSError(95, 'Operation not supported').
+ #
+ # On Linux kernel older than 3.11, trying to open a regular
+ # file (or a symbolic link to a regular file) with O_TMPFILE
+ # fails with NotADirectoryError, because O_TMPFILE is read as
+ # O_DIRECTORY.
pass
else:
try: