From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755652AbZB1Uxt (ORCPT ); Sat, 28 Feb 2009 15:53:49 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753700AbZB1Uxk (ORCPT ); Sat, 28 Feb 2009 15:53:40 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:33268 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753675AbZB1Uxj (ORCPT ); Sat, 28 Feb 2009 15:53:39 -0500 Date: Sat, 28 Feb 2009 15:53:29 -0500 From: Christoph Hellwig To: Dave Hansen Cc: Ingo Molnar , containers , "linux-kernel@vger.kernel.org" , "Serge E. Hallyn" , Oren Laadan , Alexey Dobriyan , hch@infradead.org Subject: Re: [RFC][PATCH 5/8] add f_op for checkpointability Message-ID: <20090228205329.GB4254@infradead.org> References: <20090227203425.F3B51176@kernel> <20090227203431.D1E697CB@kernel> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090227203431.D1E697CB@kernel> User-Agent: Mutt/1.5.18 (2008-05-17) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 27, 2009 at 12:34:31PM -0800, Dave Hansen wrote: > > We have set up sane defaults for how filesystems should > be checkpointed. However, as usual in the VFS, there > are specialized places that will always need an ability > to override these defaults. > > This adds a new 'file_operations' function for > checkpointing a file. I did this under the assumption > that we should have a dirt-simple way to make something > (un)checkpointable that fits in with current code. > > As you can see in the /dev/null patch in a second, all > that we have to do to make something like /dev/null > supported is add a single "generic" f_op entry. Please don't do the fallback to allow checkpointing without file operations. We've never had luck with these fallbacks, and I'm in the process of getting of the last default file operation (llseek, which has a very bad default) currently. Incidentally that should also allow you to get rid of the per-fs flag by just checking for the presence of the operation to check if checkpointing is allowed. Also the double-use of the op seem not very nice to me. Is there any real life use case were you would have the operation on a file but sometimes not allow checkpoiting?