Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754254AbZFWRgG (ORCPT ); Tue, 23 Jun 2009 13:36:06 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752795AbZFWRfy (ORCPT ); Tue, 23 Jun 2009 13:35:54 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:38072 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751905AbZFWRfx (ORCPT ); Tue, 23 Jun 2009 13:35:53 -0400 Date: Tue, 23 Jun 2009 10:34:49 -0700 (PDT) From: Linus Torvalds X-X-Sender: torvalds@localhost.localdomain To: David Howells cc: Miklos Szeredi , alan@lxorguk.ukuu.org.uk, hch@infradead.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@ZenIV.linux.org.uk, adilger@sun.com, akpm@linux-foundation.org Subject: Re: [RFC] O_NOACC: open without any access In-Reply-To: <17310.1245776720@redhat.com> Message-ID: References: <20090623170610.7fd8a3f8@lxorguk.ukuu.org.uk> <20090623134640.GA13831@infradead.org> <20090623143408.GA2147@infradead.org> <16370.1245772337@redhat.com> <16755.1245773452@redhat.com> <17310.1245776720@redhat.com> User-Agent: Alpine 2.01 (LFD 1184 2008-12-16) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1935 Lines: 48 On Tue, 23 Jun 2009, David Howells wrote: > Miklos Szeredi wrote: > > > Define O_NOACC as 3. On open(..., O_FILESYSTEM | O_NOACC) require no > > privileges on the file. > > It must also work with O_NOFOLLOW, which I think your suggestion will. This does sound like a fairly natural extension of what we already do. We essentially already have O_NOACCESS (3), and use it exactly because we need to do operations on a file descriptor without "real" accesses (notably things like accessing /dev/cdrom without waiting/checking for the disk being present etc). O_FILESYSTEM I don't like as a name (to me, it doesn't say _what_ it is doing - of course an open works on a filesystem!), but the concept of saying "don't follow device nodes - just open the node itself" makes perfect sense. Together with O_NOFOLLOW it also fairly naturally means "give me the actual symlink _node_, don't return error or follow it". And we can trivially test at a higher level that O_FILESYSTEM (with a better name, please), is always paired with O_NOACCESS (not O_NOACC: we do not try to save three letters, there is no shortage). Because the raw node obviously must never really be "accessed" (ie you can't do read/write etc on it). That said, I do _not_ like the notion of > Add a new inode->i_filesystem_fop pointer regardless of whether it's in inode->i_op or wherever. I think we should just handle this in the regular "inode->f_op->open" routine, the same way we handle FMODE_EXCLUSIVE (O_EXCL), FMODE_NDELAY (O_NONBLOCK) and lack of access rights (O_NOACCESS) in the driver open routines that currently handle those specially (O_NDELAY is spe Al? Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/