From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: O_TMPFILE detection Date: Tue, 11 Feb 2014 08:03:02 -0800 Message-ID: <20140211160302.GA18936@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org To: Alexander Viro , Linus Torvalds Cc: linux-fsdevel@vger.kernel.org, linux-man@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-man@vger.kernel.org I've started implementing support for O_TMPFILE in xfs_io in preparation for proper testcases and found something rather annoying: Given that we implicitly pass O_DIRECTORY as part of the full O_TMPFILE flag an open using O_TMPFILE will simply succeed on a kernel old enough to not have O_TMPFILE support, and give you a file descriptor for the directory passed in. Of course this only works if you open the fd read-only which isn't all that useful for real temporary files, but it would be the natural choice for a feature test. I guess we can't really fix this up any more, but does anyone have a good idea how to document this properly in the man page?