Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753918AbaA3Wlt (ORCPT ); Thu, 30 Jan 2014 17:41:49 -0500 Received: from smtp1.Stanford.EDU ([171.67.219.81]:52595 "EHLO smtp.stanford.edu" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753109AbaA3Wlr convert rfc822-to-8bit (ORCPT ); Thu, 30 Jan 2014 17:41:47 -0500 X-Greylist: delayed 515 seconds by postgrey-1.27 at vger.kernel.org; Thu, 30 Jan 2014 17:41:47 EST From: Russ Allbery To: Pali =?utf-8?Q?Roh=C3=A1r?= Cc: Linus Torvalds , David Howells , linux-afs@lists.infradead.org, "Eric W. Biederman" , Linux Kernel Mailing List Subject: Re: [PATCH] afs: proc cells and rootcell are writeable In-Reply-To: ("Pali =?utf-8?Q?Roh=C3=A1r=22's?= message of "Thu, 30 Jan 2014 23:15:31 +0100") Organization: The Eyrie References: <20140126122729.32113.19659.stgit@warthog.procyon.org.uk> <8761p1m98f.fsf@xmission.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.4 (gnu/linux) Date: Thu, 30 Jan 2014 14:33:09 -0800 Message-ID: <871tzpf6ca.fsf@windlord.stanford.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Pali Rohár writes: > 2014-01-30 Linus Torvalds : >> Eric W. Biederman wrote: >>> These files have been read-only since this code was merged in 2002. >>> Over a decade of not being used seems like a strong indication that no >>> one cares about the write path. >> I think this is a pretty strong argument. Counter-arguments, anybody? The current in-tree AFS module is still something of an experiment and is not widely used by actual clients, essentially all of which are still using the (old, ugly, frustratingly-difficult-to-maintain) out-of-tree module. This is mostly because the in-kernel module is not yet sufficiently mature to support a variety of use cases. I think this is a (minor) step towards making it more mature. > In afs documentation is written that you need to write to these files. See: > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/filesystems/afs.txt#n82 > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/filesystems/afs.txt#n159 > Without cells file, you cannot specify other cell servers and you can > use only one rootcell which was specified in kernel cmdline. So for > mounting other server, you need to reboot kernel (if you compiled afs > driver statically) and without cells file there is no other option to > mount more afs servers... (or at least it is not written in that > documentation). So I think without write access it is hard or maybe > impossible to use afs driver. In the AFS world more generally, it is not common to change the root cell without restarting the client. It *is*, however, very common to add configuration for new cells on the fly. The most common implementation, OpenAFS, has a command-line tool for root to do that (fs newcell). The equivalent for the in-tree AFS module would be writing to this file, so to support the fs newcell command with the in-tree module, this file would need to be writable. This is a common action in some use cases. By comparison, there is not a standard fs command to set the current local cell, only to retrieve it. However, I suspect that's primarily due to design limitations in the OpenAFS client. If it's not difficult to support this operation in the in-tree kernel module, I think it would be a good idea to do so early, since it's the kind of thing that could be difficult to retroactively add later. -- Russ Allbery (eagle@eyrie.org) -- 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/