From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from relay.sgi.com (relay2.corp.sgi.com [137.38.102.29]) by oss.sgi.com (Postfix) with ESMTP id EA8007CA2 for ; Mon, 15 Feb 2016 14:40:49 -0600 (CST) Received: from cuda.sgi.com (cuda3.sgi.com [192.48.176.15]) by relay2.corp.sgi.com (Postfix) with ESMTP id ADD10304039 for ; Mon, 15 Feb 2016 12:40:49 -0800 (PST) Received: from ipmail07.adl2.internode.on.net (ipmail07.adl2.internode.on.net [150.101.137.131]) by cuda.sgi.com with ESMTP id hB1HjRTdjmhbh4Zh for ; Mon, 15 Feb 2016 12:40:47 -0800 (PST) Date: Tue, 16 Feb 2016 07:40:09 +1100 From: Dave Chinner Subject: Re: XFS fiemap issue with Linux 3.10.0-327.el7.x86_64 (CentOS 7) Message-ID: <20160215204009.GJ14668@dastard> References: <56C219F0.3050002@sandeen.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: xfs-bounces@oss.sgi.com Sender: xfs-bounces@oss.sgi.com To: Jim Wilcoxson Cc: Eric Sandeen , xfs@oss.sgi.com On Mon, Feb 15, 2016 at 02:28:36PM -0500, Jim Wilcoxson wrote: > Thanks Eric. > > I ran xfs_bmap -v and it returned extents 0-19999, alternating data > with holes. The holes and data were various sizes, I suppose for xfs > alignment reasons, but everything was there. > > Running fiemap again after xfs_bmap still returned 1364 extents. Yes, fiemap in XFS uses a buffer size of: bm.bmv_count = min_t(__s32, bm.bmv_count, (PAGE_SIZE * 16 / sizeof(struct getbmapx))); i.e. limits a single fiemap fetch to a maximum of 64k of extent data. I think you have an incorrect assumption about fiemap behaviour. fiemap is not designed to return or even count all the extents in a file in a single call; on XFS it returns how many extents it can return in a single call. When you then map the file, if the FIEMAP_EXTENT_LAST is not set on the last extent returned, then the application needs to make another FIEMAP call from the end offset of last extent mapping returned in the last call, and it will then return the next N extents in the file. IOWs, you have to keep calling FIEMAP to map the entire file, not assume a single call will return an arbitrary amount of data to you in a single call. But, as Eric said - fiemap is a diagnosis tool, not an interface you can rely on for anything involving data movement. Cheers, Dave. -- Dave Chinner david@fromorbit.com _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs