Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758804Ab0FKPxw (ORCPT ); Fri, 11 Jun 2010 11:53:52 -0400 Received: from 64-131-60-146.usfamily.net ([64.131.60.146]:39033 "EHLO mail.sandeen.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758537Ab0FKPxv (ORCPT ); Fri, 11 Jun 2010 11:53:51 -0400 Message-ID: <4C125C0D.4080600@sandeen.net> Date: Fri, 11 Jun 2010 10:53:49 -0500 From: Eric Sandeen User-Agent: Thunderbird 2.0.0.24 (Macintosh/20100228) MIME-Version: 1.0 To: Tao Ma CC: xfs@oss.sgi.com, Christoph Hellwig , linux-kernel@vger.kernel.org, Alex Elder Subject: Re: [PATCH] xfs: Make fiemap works with sparse file. References: <1276236135-12051-1-git-send-email-tao.ma@oracle.com> In-Reply-To: <1276236135-12051-1-git-send-email-tao.ma@oracle.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2555 Lines: 61 Tao Ma wrote: > In xfs_vn_fiemap, we set bvm_count to fi_extent_max + 1 and want > to return fi_extent_max extents, but actually it won't work for > a sparse file. 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. > > 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 + 1. This all seems right to me, though your commit message above (+1) doesn't match the comment and code in the patch (+2) -Eric > Cc: Alex Elder > Cc: Christoph Hellwig > Cc: Dave Chinner > Signed-off-by: Tao Ma > --- > fs/xfs/linux-2.6/xfs_iops.c | 16 ++++++++++++++-- > 1 files changed, 14 insertions(+), 2 deletions(-) > > diff --git a/fs/xfs/linux-2.6/xfs_iops.c b/fs/xfs/linux-2.6/xfs_iops.c > index 9c8019c..1db92e3 100644 > --- a/fs/xfs/linux-2.6/xfs_iops.c > +++ b/fs/xfs/linux-2.6/xfs_iops.c > @@ -672,9 +672,21 @@ xfs_vn_fiemap( > else > bm.bmv_length = BTOBB(length); > > - /* We add one because in getbmap world count includes the header */ > + /* > + * It is a bit tricky for us to calculate the bmv_count from > + * fi_extent_max. > + * If we support to return fi_extent_max extents to the user, > + * we need at most 2 * fi_extent_max + 1 for bmv_count since > + * in xfs_getbmap we will calculate holes while fi_extent_max > + * don't have them. So in the worst case, bmv can looks like > + * [hole, extent, hole, extent, hole, ... hole, extent, hole]. > + * So there will be 2 *fi_extent_max + 1. > + * What's more, in getbmap world count have to include the > + * header, so we need another bmv. So the total number will > + * be 2 * fieinfo->fi_extents_max + 2. > + */ > bm.bmv_count = !fieinfo->fi_extents_max ? MAXEXTNUM : > - fieinfo->fi_extents_max + 1; > + 2 * fieinfo->fi_extents_max + 2; > bm.bmv_count = min_t(__s32, bm.bmv_count, > (PAGE_SIZE * 16 / sizeof(struct getbmapx))); > bm.bmv_iflags = BMV_IF_PREALLOC; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/