From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cuda.sgi.com (cuda1.sgi.com [192.48.157.11]) by oss.sgi.com (8.14.3/8.14.3/SuSE Linux 0.8) with ESMTP id o5EDZMa0042655 for ; Mon, 14 Jun 2010 08:35:22 -0500 Received: from rcsinet10.oracle.com (localhost [127.0.0.1]) by cuda.sgi.com (Spam Firewall) with ESMTP id 0FA88FB1D9F for ; Mon, 14 Jun 2010 06:41:25 -0700 (PDT) Received: from rcsinet10.oracle.com (rcsinet10.oracle.com [148.87.113.121]) by cuda.sgi.com with ESMTP id FmuMDG26zAHCNQx3 for ; Mon, 14 Jun 2010 06:41:25 -0700 (PDT) Message-ID: <4C16308E.1030305@oracle.com> Date: Mon, 14 Jun 2010 21:37:18 +0800 From: Tao Ma MIME-Version: 1.0 Subject: Re: [PATCH v2] xfs: Make fiemap works with sparse file. References: <1276308495-14267-1-git-send-email-tao.ma@oracle.com> <20100614002705.GA6590@dastard> <20100614122912.GD6590@dastard> In-Reply-To: <20100614122912.GD6590@dastard> List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: xfs-bounces@oss.sgi.com Errors-To: xfs-bounces@oss.sgi.com To: Dave Chinner Cc: Christoph Hellwig , Alex Elder , sandeen@sandeen.net, linux-kernel@vger.kernel.org, xfs@oss.sgi.com Hi Dave, Dave Chinner wrote: > On Mon, Jun 14, 2010 at 10:27:06AM +1000, Dave Chinner wrote: > >> On Sat, Jun 12, 2010 at 10:08:15AM +0800, Tao Ma wrote: >> >>> The reason is that in xfs_getbmap we will >>> calculate holes and set it in 'out', while out is malloced by >>> bmv_count(fi_extent_max+1) which didn't consider holes. So in the >>> worst case, if 'out' vector looks like >>> [hole, extent, hole, extent, hole, ... hole, extent, hole], >>> we will only return half of fi_extent_max extents. >>> >> Right, it's not broken, we simply return less than fi_extent_mex >> extents when there are holes. I don't see that as a problem as >> applications have to handle that case anyway, and.... >> >> >>> So in xfs_vn_fiemap, we should consider this worst case. If the >>> user wants fi_extent_max extents, we need a 'out' with size of >>> 2 *fi_extent_max + 2(one more the header). >>> >> That's rather dangerous, I think. It relies on other code to catch >> the buffer overrun that this sets up for fragmented, non-sparse >> files. Personally I'd much prefer to return fewer extents for sparse >> files than to add a landmine like this into the kernel code.... >> > > I just had a thought - if you want to avoid holes being reported to > fiemap, then add a BMV_IF_NO_HOLES flag to xfs_getbmap() and skip > holes in the mappin gloop when this flag is set. That will make > fiemap fill in the full number of extents without hacking the > extent count... > yeah, that should work and I will try to generate a patch for it. I am not quite familiar with xfs, so please be kind to me if I make some stupid mistake in the patch. ;) Regards, Tao _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs