From: Theodore Tso Subject: Re: [Ext4 punch hole 1/5] Ext4 Punch Hole Support: Convert Blocks to Uninit Exts Date: Thu, 3 Mar 2011 09:27:27 -0500 Message-ID: References: <4D6C6318.2010105@linux.vnet.ibm.com> <02A57041-5FC1-419D-89D2-47D541616DD4@dilger.ca> <20110302202313.GA15097@dastard> Mime-Version: 1.0 (Apple Message framework v1082) Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: Andreas Dilger , Allison Henderson , linux-ext4@vger.kernel.org To: Dave Chinner Return-path: Received: from DMZ-MAILSEC-SCANNER-2.MIT.EDU ([18.9.25.13]:65411 "EHLO dmz-mailsec-scanner-2.mit.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758331Ab1CCOg2 (ORCPT ); Thu, 3 Mar 2011 09:36:28 -0500 In-Reply-To: <20110302202313.GA15097@dastard> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Mar 2, 2011, at 3:23 PM, Dave Chinner wrote: > > XFS_IOC_ZERO_RANGE converts a range to unwritten extents, not > uninitialised extents. An uninitialised extent is one that is > allocated but had not data written to it (i.e. contains stale data), > while an unwritten/preallocated extent is guaranteed to contain > zeros. This may be just a terminology issue, but we should try to > use the same jargon across all filesystems... What is the difference from the user's perspective? If the read from from an uninitialized extent, what do they get back? And if the read from an unwritten extent, what do they get back? In ext4, in both cases we would return all zero's. For XFS, why is it important to maintain the distinction between these two concept? Just trying to understand, -- Ted