From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Snitzer Subject: Re: [PATCH v2] dm: Fix alignment stacking on partitioned devices Date: Fri, 8 Jan 2010 15:28:07 -0500 Message-ID: <20100108202807.GA21439@redhat.com> References: <20100106025731.GA16154@redhat.com> <20100106041050.GA21438@redhat.com> <20100106051605.GB21438@redhat.com> <20100106132508.GA3589@redhat.com> <20100107185505.GA15181@redhat.com> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: "Martin K. Petersen" Cc: device-mapper development , "Alasdair G. Kergon" List-Id: dm-devel.ids On Fri, Jan 08 2010 at 1:41pm -0500, Martin K. Petersen wrote: > >>>>> "Mike" == Mike Snitzer writes: > > Mike, > > Mike> Seems I took the time to add a comment whose FIXME doesn't ring > Mike> many bells now! But ignoring that, the comment before the FIXME > Mike> is making a veiled reference to userspace having consumed > Mike> alignment_offset. > > I read and understood the comment. But even then explicitly zeroing out > those two values didn't make sense (because if user space did in fact do > the right thing they'd always be zero). > > I know that the DM utilities take care of business. And that DM devices > are special because they are always set up by user space and not a > kernel discovery process. > > But since the code *is* in place to validate things I'm not so keen on > you clearing fields that have been calculated and have a meaning. For > me it masked a case where the DM utilities did the wrong thing (because > they were old). > > With the Enterprise Linux hat on it is easy for us to specify that you > must use this version of the kernel and the device mapper utilities. > But reality is that lots of people are running upstream kernels on > distributions with older userland. And some distributions get things > wrong, ship broken bits, etc. > > It's great that new DM utils will transparently adjust the starting > offset. That's the way it's supposed to work. No arguments there. > > My main concern is making sure that we never get into a case where we > run with misaligned components without indicating that there is a > problem. Ever! Regardless of which DM utils might be in place. > > We have the power to get that right. All the pieces are in place. I'd > simply like us to stop making assumptions about user space always doing > the right thing. Yeap, I already agreed that those 2 lines should be removed (in the p.s. of my previous mail). They really aren't serving any purpose and their justification was/is tenuous at best. I'll get the fix, for 2.6.33, to Alasdair shortly. Mike