From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cuda.sgi.com (cuda2.sgi.com [192.48.176.25]) by oss.sgi.com (8.14.3/8.14.3/SuSE Linux 0.8) with ESMTP id o5BNaVZp168345 for ; Fri, 11 Jun 2010 18:36:31 -0500 Received: from rcsinet10.oracle.com (localhost [127.0.0.1]) by cuda.sgi.com (Spam Firewall) with ESMTP id A86A03C0B11 for ; Fri, 11 Jun 2010 16:39:05 -0700 (PDT) Received: from rcsinet10.oracle.com (rcsinet10.oracle.com [148.87.113.121]) by cuda.sgi.com with ESMTP id GREdij0JwM14QOT0 for ; Fri, 11 Jun 2010 16:39:05 -0700 (PDT) Message-ID: <4C12C8BB.50604@oracle.com> Date: Sat, 12 Jun 2010 07:37:31 +0800 From: Tao Ma MIME-Version: 1.0 Subject: Re: [PATCH] xfs: Make fiemap works with sparse file. References: <1276236135-12051-1-git-send-email-tao.ma@oracle.com> <4C125C0D.4080600@sandeen.net> In-Reply-To: <4C125C0D.4080600@sandeen.net> 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: Eric Sandeen Cc: linux-kernel@vger.kernel.org, Alex Elder , Christoph Hellwig , xfs@oss.sgi.com Eric Sandeen wrote: > 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) > oh, yes, I will change the commit log and send a v2. and can I add your ack for this patch? Regards, Tao > -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/ > _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs