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?
Cc: Alex Elder <aelder@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Signed-off-by: Tao Ma <tao.ma@xxxxxxxxxx>
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
@@ -672,9 +672,21 @@ xfs_vn_fiemap(
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;
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