On Sun, Aug 25, 2019 at 11:07:46PM -0600, Andreas Dilger wrote:

This may not always detect empty directory blocks properly, because
ext4_generic_delete_entry() will only merge deleted entries with the
previous entry.  It at least appears possible that if entries are not
deleted in the proper order (e.g. in reverse of the order they are
listed in the directory) there may be multiple empty entries in a block,
and the above check will fail.

I don't think that's a problem.  We always merge with the previous
entry, whether it's an empty/deleted entry or an in-use entry.  So
long as all implementations do this, it works just fine.  If there is
an ext2/3/4 implementation which deletes the entry by simply clearing
the inode number *without* merging with the previous one, it's
possible that we might get confused.

But that's easily fixed, too.  In ext4_generic_delete_entry(), we just
need to add a check so that we check to see if the subsequent entry
(if it exists) has a zero de->inode value.  If so, then we absorb the
current directory entry to include the deleted subsequent entry and
repeat the check.

						- Ted