xfs: Make fiemap work with sparse files

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.

This patch add a new parameter BMV_IF_NO_HOLES for bvm_iflags.
So with this flags, we don't use our 'out' in xfs_getbmap for
a hole. The solution is a bit ugly by just don't increasing
index of 'out' vector. I felt that it is not easy to skip it
at the very beginning since we have the complicated check and
some function like xfs_getbmapx_fix_eof_hole to adjust 'out'.

Cc: Dave Chinner <david@fromorbit.com>
Signed-off-by: Tao Ma <tao.ma@oracle.com>
Signed-off-by: Alex Elder <aelder@sgi.com>

1 files changed, 13 insertions, 1 deletions

diff --git a/fs/xfs/xfs_bmap.c b/fs/xfs/xfs_bmap.c
index 23f14e595c18..f90dadd5a968 100644
--- a/fs/xfs/xfs_bmap.c
+++ b/fs/xfs/xfs_bmap.c
@@ -5533,12 +5533,24 @@ xfs_getbmap(
                                         map[i].br_startblock))
                                 goto out_free_map;
 
-                        nexleft--;
                         bmv->bmv_offset =
                                 out[cur_ext].bmv_offset +
                                 out[cur_ext].bmv_length;
                         bmv->bmv_length =
                                 max_t(__int64_t, 0, bmvend - bmv->bmv_offset);
+
+                        /*
+                         * In case we don't want to return the hole,
+                         * don't increase cur_ext so that we can reuse
+                         * it in the next loop.
+                         */
+                        if ((iflags & BMV_IF_NO_HOLES) &&
+                            map[i].br_startblock == HOLESTARTBLOCK) {
+                                memset(&out[cur_ext], 0, sizeof(out[cur_ext]));
+                                continue;
+                        }
+
+                        nexleft--;
                         bmv->bmv_entries++;
                         cur_ext++;
                 }