ext4: make ext4_es_cache_extent() support overwrite existing extents

ext4: make ext4_es_cache_extent() support overwrite existing extents

Currently, ext4_es_cache_extent() is used to load extents into the
extent status tree when reading on-disk extent blocks. But it inserts
information into the extent status tree if and only if there isn't
information about the specified range already. So it only used for the
initial loading and does not support overwrit extents.

However, there are many other places in ext4 where on-disk extents are
inserted into the extent status tree, such as in ext4_map_query_blocks().
Currently, they call ext4_es_insert_extent() to perform the insertion,
but they don't modify the extents, so ext4_es_cache_extent() would be a
more appropriate choice. However, when ext4_map_query_blocks() inserts
an extent, it may overwrite a short existing extent of the same type.
Therefore, to prepare for the replacements, we need to extend
ext4_es_cache_extent() to allow it to overwrite existing extents with
the same status. So it checks the found extents before removing and
inserting. (There is one exception, a hole in the on-disk extent but a
delayed extent in the extent status tree is allowed.)

In addition, since cached extents can be more lenient than the extents
they modify and do not involve modifying reserved blocks, it is not
necessary to ensure that the insertion operation succeeds as strictly as
in the ext4_es_insert_extent() function.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Baokun Li <libaokun1@huawei.com>
Message-ID: <20251129103247.686136-12-yi.zhang@huaweicloud.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>