Hi Pasha,

On Mon, Sep 29 2025, Pasha Tatashin wrote:

Introducing the userspace interface and internal logic required to
manage the lifecycle of file descriptors within a session. Previously, a
session was merely a container; this change makes it a functional
management unit.

The following capabilities are added:

A new set of ioctl commands are added, which operate on the file
descriptor returned by CREATE_SESSION. This allows userspace to:
- LIVEUPDATE_SESSION_PRESERVE_FD: Add a file descriptor to a session
  to be preserved across the live update.
- LIVEUPDATE_SESSION_UNPRESERVE_FD: Remove a previously added file
  descriptor from the session.
- LIVEUPDATE_SESSION_RESTORE_FD: Retrieve a preserved file in the
  new kernel using its unique token.

A state machine for each individual session, distinct from the global
LUO state. This enables more granular control, allowing userspace to
prepare or freeze specific sessions independently. This is managed via:
- LIVEUPDATE_SESSION_SET_EVENT: An ioctl to send PREPARE, FREEZE,
  CANCEL, or FINISH events to a single session.
- LIVEUPDATE_SESSION_GET_STATE: An ioctl to query the current state
  of a single session.

The global subsystem callbacks (luo_session_prepare, luo_session_freeze)
are updated to iterate through all existing sessions. They now trigger
the appropriate per-session state transitions for any sessions that
haven't already been transitioned individually by userspace.

The session's .release handler is enhanced to be state-aware. When a
session's file descriptor is closed, it now correctly cancels or
finishes the session based on its current state before freeing all
associated file resources, preventing resource leaks.

Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>

[...]

+/**
+ * struct liveupdate_session_get_state - ioctl(LIVEUPDATE_SESSION_GET_STATE)
+ * @size:     Input; sizeof(struct liveupdate_session_get_state)
+ * @incoming: Input; If 1, query the state of a restored file from the incoming
+ *            (previous kernel's) set. If 0, query a file being prepared for
+ *            preservation in the current set.

Spotted this when working on updating my test suite for LUO. This seems
to be a leftover from a previous version. I don't see it being used
anywhere in the code.

Also, I think the model we should have is to only allow new sessions in
normal state. Currently luo_session_create() allows creating a new
session in updated state. This would end up mixing sessions from a
previous boot and sessions from current boot. I don't really see a
reason for that and I think the userspace should first call finish
before starting new serialization. Keeps things simpler.

+ * @reserved: Must be zero.
+ * @state:    Output; The live update state of this FD.
+ *
+ * Query the current live update state of a specific preserved file descriptor.
+ *
+ * - %LIVEUPDATE_STATE_NORMAL:   Default state
+ * - %LIVEUPDATE_STATE_PREPARED: Prepare callback has been performed on this FD.
+ * - %LIVEUPDATE_STATE_FROZEN:   Freeze callback ahs been performed on this FD.
+ * - %LIVEUPDATE_STATE_UPDATED:  The system has successfully rebooted into the
+ *                               new kernel.
+ *
+ * See the definition of &enum liveupdate_state for more details on each state.
+ *
+ * Return: 0 on success, negative error code on failure.
+ */
+struct liveupdate_session_get_state {
+	__u32		size;
+	__u8		incoming;
+	__u8		reserved[3];
+	__u32		state;
+};
+
+#define LIVEUPDATE_SESSION_GET_STATE					\
+	_IO(LIVEUPDATE_IOCTL_TYPE, LIVEUPDATE_CMD_SESSION_GET_STATE)

[...]

-- 
Regards,
Pratyush Yadav