From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andreas Dilger Subject: Re: [PATCH 0/4] Fiemap, an extent mapping ioctl - round 2 Date: Wed, 02 Jul 2008 00:26:12 -0600 Message-ID: <20080702062612.GP6239@webber.adilger.int> References: <20080625221835.GQ28100@wotan.suse.de> <4863A1C5.7020403@redhat.com> <20080627014119.GW29319@disturbed> <20080627094156.GA30200@shareable.org> <20080627224843.GZ6239@webber.adilger.int> <4865BC50.2030804@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7BIT Cc: Jamie Lokier , Mark Fasheh , linux-fsdevel@vger.kernel.org, Andreas Dilger , Kalpak Shah , Josef Bacik To: Eric Sandeen Return-path: Received: from sca-es-mail-1.Sun.COM ([192.18.43.132]:63533 "EHLO sca-es-mail-1.sun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1762610AbYGBG0R (ORCPT ); Wed, 2 Jul 2008 02:26:17 -0400 Received: from fe-sfbay-09.sun.com ([192.18.43.129]) by sca-es-mail-1.sun.com (8.13.7+Sun/8.12.9) with ESMTP id m626QF2a025172 for ; Tue, 1 Jul 2008 23:26:16 -0700 (PDT) Received: from conversion-daemon.fe-sfbay-09.sun.com by fe-sfbay-09.sun.com (Sun Java System Messaging Server 6.2-8.04 (built Feb 28 2007)) id <0K3D00K018ER5500@fe-sfbay-09.sun.com> (original mail from adilger@sun.com) for linux-fsdevel@vger.kernel.org; Tue, 01 Jul 2008 23:26:15 -0700 (PDT) In-reply-to: <4865BC50.2030804@redhat.com> Content-disposition: inline Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Jun 27, 2008 23:21 -0500, Eric Sandeen wrote: > even w/ metadata out of the way the ext4 extent format is still > capped at 128M per extent right, even if they're contiguous. Which led > me to the little though experiment about hm, is this 1G file 1 extent or > 8 and what should fiemap return... The current FIEMAP code will return 8 extents, which mirrors the number of physical extents on disk. This could be important to the person looking at the file, as it will be clear that there are too many extents to fit into the inode and the extent tree will include an index block. I was a bit on the fence about this, but I agree with David that if userspace has more information (e.g. all of the on-disk extent data) it can always merge it, but it can't "un-merge" the data returned from the kernel. Cheers, Andreas -- Andreas Dilger Sr. Staff Engineer, Lustre Group Sun Microsystems of Canada, Inc.