This patch implements the core mechanism for managing preserved
files throughout the live update lifecycle. It provides the logic to
invoke the file handler callbacks (preserve, unpreserve, freeze,
unfreeze, retrieve, and finish) at the appropriate stages.

During the reboot phase, luo_file_freeze() serializes the final
metadata for each file (handler compatible string, token, and data
handle) into a memory region preserved by KHO. In the new kernel,
luo_file_deserialize() reconstructs the in-memory file list from this
data, preparing the session for retrieval.

Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
 include/linux/kho/abi/luo.h      |  39 +-
 include/linux/liveupdate.h       |  98 ++++
 kernel/liveupdate/Makefile       |   1 +
 kernel/liveupdate/luo_file.c     | 882 +++++++++++++++++++++++++++++++
 kernel/liveupdate/luo_internal.h |  38 ++
 5 files changed, 1057 insertions(+), 1 deletion(-)
 create mode 100644 kernel/liveupdate/luo_file.c

diff --git a/include/linux/kho/abi/luo.h b/include/linux/kho/abi/luo.h
index a2d2940eca6b..fc143f243871 100644
--- a/include/linux/kho/abi/luo.h
+++ b/include/linux/kho/abi/luo.h

@@ -65,6 +65,11 @@
  *     Metadata for a single session, including its name and a physical pointer
  *     to another preserved memory block containing an array of
  *     `struct luo_file_ser` for all files in that session.
+ *
+ *   - struct luo_file_ser:
+ *     Metadata for a single preserved file. Contains the `compatible` string to
+ *     find the correct handler in the new kernel, a user-provided `token` for
+ *     identification, and an opaque `data` handle for the handler to use.
  */
 
 #ifndef _LINUX_KHO_ABI_LUO_H

@@ -82,13 +87,43 @@
 #define LUO_FDT_COMPATIBLE	"luo-v1"
 #define LUO_FDT_LIVEUPDATE_NUM	"liveupdate-number"
 
+#define LIVEUPDATE_HNDL_COMPAT_LENGTH	48
+
+/**
+ * struct luo_file_ser - Represents the serialized preserves files.
+ * @compatible:  File handler compatible string.
+ * @data:        Private data
+ * @token:       User provided token for this file
+ *
+ * If this structure is modified, LUO_SESSION_COMPATIBLE must be updated.
+ */
+struct luo_file_ser {
+	char compatible[LIVEUPDATE_HNDL_COMPAT_LENGTH];
+	u64 data;
+	u64 token;
+} __packed;
+
+/**
+ * struct luo_file_set_ser - Represents the serialized metadata for file set
+ * @files:   The physical address of a contiguous memory block that holds
+ *           the serialized state of files (array of luo_file_ser) in this file
+ *           set.
+ * @count:   The total number of files that were part of this session during
+ *           serialization. Used for iteration and validation during
+ *           restoration.
+ */
+struct luo_file_set_ser {
+	u64 files;
+	u64 count;
+} __packed;