From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [RFC] O_NOACC: open without any access Date: Tue, 23 Jun 2009 09:46:40 -0400 Message-ID: <20090623134640.GA13831@infradead.org> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, viro@ZenIV.linux.org.uk, adilger@sun.com, dhowells@redhat.com, alan@lxorguk.ukuu.org.uk, akpm@linux-foundation.org To: Miklos Szeredi Return-path: Received: from bombadil.infradead.org ([18.85.46.34]:54279 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752775AbZFWNqk (ORCPT ); Tue, 23 Jun 2009 09:46:40 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Thu, Jun 18, 2009 at 08:55:37AM +0200, Miklos Szeredi wrote: > Implement a new open flag that doesn't require any access on the file. > It works on any file type including symlinks. > > The sole purpose is to help race free "userspace lookup" type > operations. So fstat, fch*, *at work but nothing else. Filesystem's > ->open() is not called and f_op is set to NULL. we guarantee that f_op is never NULL, so you'll need to assign a file operations structure that is empty to it to avoid crashed in various places. > It would be logical to reuse the open_flag=3 value, but that has > historically been used with different semantics so I'm afraid of > touching it. I think the historical semantics are exactly that you can open it an issue ioctls + stat / etc on it ut not actually read/write it.