repair: reconstruct sparse inode records correctly on disk

repair: reconstruct sparse inode records correctly on disk

Phase 5 traverses all of the in-core inode records and regenerates the
inode btrees a record at a time. The record insertion code doesn't
account for sparse inodes which means the ir_holemask and ir_count
fields are not set on-disk and ir_freecount is set with an invalid value
for sparse inode records.

Update build_ino_tree() to handle sparse inode records correctly. We
must account real, allocated inodes only into the ir_freecount field.
The 64-bit in-core sparse inode bitmask must be converted to compressed
16-bit ir_holemask format. Finally, the ir_count field must set to the
total (non-sparse) inode count of the record.

If the fs does not support sparse inodes, both the ir_holemask and
ir_count field are initialized to zero to preserve backwards
compatibility. These bytes historically landed in the high order bytes
of ir_freecount and must be 0 to be interpreted correctly by older XFS
implementations without sparse inode support.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>