On Wed, Jul 23, 2025 at 02:46:27PM +0000, Pasha Tatashin wrote:

+/**
+ * struct liveupdate_file_ops - Callbacks for for live-updatable files.
+ * @prepare:       Optional. Saves state for a specific file instance (@file,
+ *                 @arg) before update, potentially returning value via @data.
+ *                 Returns 0 on success, negative errno on failure.
+ * @freeze:        Optional. Performs final actions just before kernel
+ *                 transition, potentially reading/updating the handle via
+ *                 @data.
+ *                 Returns 0 on success, negative errno on failure.
+ * @cancel:        Optional. Cleans up state/resources if update is aborted
+ *                 after prepare/freeze succeeded, using the @data handle (by
+ *                 value) from the successful prepare. Returns void.
+ * @finish:        Optional. Performs final cleanup in the new kernel using the
+ *                 preserved @data handle (by value). Returns void.
+ * @retrieve:      Retrieve the preserved file. Must be called before finish.
+ * @can_preserve:  callback to determine if @file with associated context (@arg)
+ *                 can be preserved by this handler.
+ *                 Return bool (true if preservable, false otherwise).
+ */
+struct liveupdate_file_ops {
+	int (*prepare)(struct file *file, void *arg, u64 *data);
+	int (*freeze)(struct file *file, void *arg, u64 *data);
+	void (*cancel)(struct file *file, void *arg, u64 data);
+	void (*finish)(struct file *file, void *arg, u64 data, bool reclaimed);
+	int (*retrieve)(void *arg, u64 data, struct file **file);
+	bool (*can_preserve)(struct file *file, void *arg);
+};

ops structures often have an owner = THIS_MODULE

It wouldn't hurt to add it here too, and some appropriate module_get's
though I didn't try to figure what happens if userspace races a module
unload with other luo operations.

+
+/**
+ * struct liveupdate_file_handler - Represents a handler for a live-updatable
+ * file type.
+ * @ops:           Callback functions
+ * @compatible:    The compatibility string (e.g., "memfd-v1", "vfiofd-v1")
+ *                 that uniquely identifies the file type this handler supports.
+ *                 This is matched against the compatible string associated with
+ *                 individual &struct liveupdate_file instances.
+ * @arg:           An opaque pointer to implementation-specific context data
+ *                 associated with this file handler registration.

Why? This is not the normal way, if you want context data then
allocate a struct driver_liveupdate_file_handler and embed a normal
struct liveupdate_file_handler inside it, then use container_of.

+	fdt_for_each_subnode(file_node_offset, luo_file_fdt_in, 0) {
+		bool handler_found = false;
+		u64 token;
+
+		node_name = fdt_get_name(luo_file_fdt_in, file_node_offset,
+					 NULL);
+		if (!node_name) {
+			panic("FDT subnode at offset %d: Cannot get name\n",
+			      file_node_offset);

I think this approach will raise lots of questions..

I'd introduce a new function "luo_deserialize_failure" that does panic
internally.

Only called by places that are parsing the FDT & related but run into
trouble that cannot be savely recovered from.

Jason