ext4: pass out extent seq counter when mapping blocks

ext4: pass out extent seq counter when mapping blocks

When creating or querying mapping blocks using the ext4_map_blocks() and
ext4_map_{query|create}_blocks() helpers, also pass out the extent
sequence number of the block mapping info through the ext4_map_blocks
structure. This sequence number can later serve as a valid cookie within
iomap infrastructure and the move extents procedure.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Message-ID: <20251013015128.499308-5-yi.zhang@huaweicloud.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>