From: Theodore Ts'o Subject: Re: [PATCH] ext4: add fallocate mode blocking for debugging purposes Date: Tue, 15 Apr 2014 14:44:42 -0400 Message-ID: <20140415184442.GC4456@thunk.org> References: <1397420518-29218-1-git-send-email-tytso@mit.edu> <20140413220016.GD8122@thunk.org> <534D5B2D.70408@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: =?utf-8?B?THVrw6HFoQ==?= Czerner , Ext4 Developers List , Namjae Jeon To: Eric Sandeen Return-path: Received: from imap.thunk.org ([74.207.234.97]:54702 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754551AbaDOSor (ORCPT ); Tue, 15 Apr 2014 14:44:47 -0400 Content-Disposition: inline In-Reply-To: <534D5B2D.70408@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Tue, Apr 15, 2014 at 11:15:41AM -0500, Eric Sandeen wrote: > > I tend to agree, better to fix the kernel than to add a knob to turn it > off. And fsx changes can happen a lot quicker than kernel changes. [1] > > And if it's really unsafe, and you really want to add a knob, I'd at least > default it to off until it's non-corrupting, and add a message that > this tunable will go away as soon as it's stable, so you'll have no > qualms about quickly deprecating it... Yeah, I went back and forth on this. One of there reasons why I added a kernel knob is that *I* can make the kernel change a lot faster than it would be to tweak all of the various xfstests program to globally disable certain operations in fsx, fstress, etc. I also had a sneaking suspicion that we might have a similar issue with the INSERT RANGE patches which are coming down the pike, and so having a general way of also being able INSERT RANGE if to be able to quickly determine whether a potential bug was caused by INSERT RANGE or some other pending changes might also be useful. I freely admit it is a bit of a hack, though. Does the hack smell less bad if we wrap it in CONFIG_EXT4FS_DEBUG? > [1] it'd be nifty to make an env. var in xfstests which can globally > disable certain fsx operations across all tests which run fsx... Yes, although as I mentioned above, it would be really nice if it worked across all of the various tests, and not just be limited to fsx, or even just fsx and fstress. - Ted