[PATCH v2] xfs: Make fiemap works with sparse file.
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From: Tao Ma on 11 Jun 2010 22:20 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 + 2(one more the header). Cc: Alex Elder <aelder(a)sgi.com> Cc: Christoph Hellwig <hch(a)lst.de> Cc: Dave Chinner <david(a)fromorbit.com> Acked-by: Eric Sandeen <sandeen(a)redhat.com> Signed-off-by: Tao Ma <tao.ma(a)oracle.com> --- 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; -- 1.5.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |