Did anyone ever see this?
This is a relatively simple (and actually safe) change to make now, but
would be harder to do as ext4 becomes more widely used.
I think all that would be needed is that when accessing an extent with
ext_pblock() (ee_start | ee_start_hi) == 0 we return zeroes, just as if
For snapshot filesystems and in some cases where it is expected to do tree
rebalancing it would be desirable to allow a "whiteout" for an extent. That
means the extent would be present in the tree, and would explicitly list
the data blocks as a "hole" (i.e. ee_start == 0). This is useful because
