From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754429AbcJEAkI (ORCPT ); Tue, 4 Oct 2016 20:40:08 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53320 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754113AbcJEAkH (ORCPT ); Tue, 4 Oct 2016 20:40:07 -0400 Date: Wed, 5 Oct 2016 01:40:05 +0100 From: Alasdair G Kergon To: Andy Grover Cc: Greg KH , dm-devel@redhat.com, linux-kernel@vger.kernel.org, snitzer@redhat.com Subject: Re: [dm-devel] [PATCH 0/9] Generate uevents for all DM events Message-ID: <20161005004004.GC28416@agk-dp.fab.redhat.com> Mail-Followup-To: Andy Grover , Greg KH , dm-devel@redhat.com, linux-kernel@vger.kernel.org, snitzer@redhat.com References: <1475522580-16723-1-git-send-email-agrover@redhat.com> <20161004072015.GA11216@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Organization: Red Hat UK Ltd. Registered in England and Wales, number 03798903. Registered Office: Peninsular House, 30-36 Monument Street, 4th Floor, London, England, EC3R 8NB. User-Agent: Mutt/1.5.18 (2008-05-17) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Wed, 05 Oct 2016 00:40:07 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 04, 2016 at 04:39:28PM -0700, Andy Grover wrote: > devicemapper is using uevents for: > a. dm-verity detected corruption > b. dm-multipath: path failed or reinstated > c. dm device renamed > d. there's also some use in md and bcache. > > devicemapper uses DM_EVENT ioctl (yuck) for: > 1. dm-thin pool data/metadata filling up (hit a threshold) > 2. dm-cache is now clean > 3. dm-log flushed or log failed > 4. dm-raid error detected or sync complete > there doesn't seem to be much technical differentiation between the > two lists. The distinction in dm is that events in the first category may affect the availability of the device: they represent major (and hopefully rare) changes. Events in the second category are just notifications: no impact on /dev, no need to trigger udev rules, and their use will continue to be extended, and (rarely at the moment) could be frequent (which is no problem for the existing polling-based mechanism). > Instead of using uevent for everything, we could go to a separate > genetlink for 1-4 instead of making them use uevent like a-d, but we'd > end up with two different userspace notification techniques. We see these as two different categories of notifications, and prefer the greater flexibility a mechanism independent of uevents would provide. The team has discussed several alternatives over the years but didn't make a decision as we've not yet reached a point where we're straining the existing mechanism too far. Alasdair