Samba Team developer Namjae Jeon implemented support in KSMBD for supporting durable handles v1 and v2 of the specification, a feature that's long been sought for this in-kernel SMB server. The durable handles functionality allow for SMB clients to survive a temporary client-side connection loss after opening a file and for transparent client reconnection.
Samba has supported durable handles while now the KSMBD server does too for dealing with brief client disconnects. This data integrity feature is the main change of the KSMBD changes for Linux 6.9 while the rest of the merge amounts to the usual bug fixing.