Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756525Ab0KJTVx (ORCPT ); Wed, 10 Nov 2010 14:21:53 -0500 Received: from mail-ww0-f44.google.com ([74.125.82.44]:38473 "EHLO mail-ww0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756262Ab0KJTVv (ORCPT ); Wed, 10 Nov 2010 14:21:51 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; b=ePa9+0iS+tee5mwwmgX4hVnxgox+IV88ed8JYkza/CZHPG5o9ZAJN11GaOezHsKf2y 8vpSkKYN8QRjJRU7CAJdU2tBFBOTumLhrqDXoRilJmyIhXFlwrdtGuZbv8klFLp81vbD eBxL7k/6Ac5Wrtk1nh/cJ2TvMaVIwrDKQsYeY= MIME-Version: 1.0 In-Reply-To: References: <20101106050721.GA2194@kroah.com> Date: Wed, 10 Nov 2010 11:21:49 -0800 Message-ID: Subject: Re: [RFC] rbd sysfs interface From: Yehuda Sadeh Weinraub To: Greg KH Cc: ceph-devel@vger.kernel.org, Sage Weil , linux-kernel@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2958 Lines: 68 On Fri, Nov 5, 2010 at 10:51 PM, Yehuda Sadeh Weinraub wrote: > On Fri, Nov 5, 2010 at 10:07 PM, Greg KH wrote: >> On Fri, Nov 05, 2010 at 04:09:31PM -0700, Yehuda Sadeh Weinraub wrote: >>> >>> Does this seem sane? Any comments would be greatly appreciated. >> >> It sounds like you need to use configfs instead of sysfs, as your model >> was the reason it was created. >> >> Have you tried that? > > Oh, will look at it now. With ceph (although for a different purpose) > we went through proc -> sysfs -> debugfs, however, it seems that we've > missed at least one userspace-kernel channel. > Well, we looked a bit at what configfs does, and from what we see it doesn't really fit our needs. Configfs would be more suitable to configuring a static system than to control a dynamic one. The main problem is that items creation is only driven by userspace. That would be ok if we had a static mapping of the images and snapshots, however, we don't. We need the system to reflect any state change with the running configuration (e.g., a new snapshot was created by a different client), and it doesn't seem possible with configfs as long as items creation is only driven by userspace operations. We need a system that would be able to reflect changes that happened due to some external operation, and this doesn't seem to be the case here. There is second issue and that's committable items are not implemented there yet. So the interface itself would be a bit weird. E.g., had committable items been implemented we would have done something like the following: /config/rbd# mkdir pending/myimage /config/rbd# echo foo > pending/myimage/name /config/rbd# cat ~/mykey > pending/myimge/key /config/rbd# echo 10.0.0.1 > pending/myimage/addr ... /config/rbd# mv pending/myimage live/ and that would do what we need in terms of initial configuration. However, as this is not really implemented yet, there is no distinction between images that are pending and images that are live, so configuration would look something like: /config/rbd# mkdir myimage /config/rbd# echo foo > myimage/name /config/rbd# cat ~/mykey > myimge/key /config/rbd# echo 10.0.0.1 > myimage/addr ... /config/rbd# echo 1 > myimage/go And having that, the myimage/ directory will still hold all those config options that are moot after the image went live. It doesn't seem to offer a significant improvement over the current sysfs one liner configuration and with sysfs we can have it reflect any dynamic change that occurred within the system. So we tend to opt for an improved sysfs solution, similar to the one I described before. Any thoughts? Am I completely off the tracks? Thanks, Yehuda -- 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/