[PATCH v2 1/1] liveupdate: luo_file: Add documentation for dependencies

[Samiullah Khawaja <skhawaja@google.com>]

Add documentation for dependencies between FDs preserved by file
handlers. This supplements the previously added
liveupdate_get_token_outgoing() and liveupdate_get_file_incoming()
internal APIs to allow file handlers to resolve dependencies.

Signed-off-by: Samiullah Khawaja <skhawaja@google.com>
---
 kernel/liveupdate/luo_file.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
index dbae0715220b..a39992da504f 100644
--- a/kernel/liveupdate/luo_file.c
+++ b/kernel/liveupdate/luo_file.c
@@ -91,6 +91,21 @@
  *    again later. If the issue cannot be resolved, these resources will be held
  *    by LUO until the next live update cycle, at which point they will be
  *    discarded.
+ *
+ * Dependencies:
+ *
+ * Preserved files may have dependencies on other files that also need to be
+ * preserved during a live update. A file handler can resolve these dependencies
+ * by querying the token of the dependency. That token can then be serialized
+ * and used to fetch the dependency during the .retrieve() callback in the next
+ * kernel.
+ *
+ * Some of these dependencies can be resolved late during file handler's
+ * .freeze() callback, but some of these might need resolution during file
+ * handler's .preserve() callback based on constraints such as immutability and
+ * performance. This introduces an order of preservation. Note that the order of
+ * preservation of dependencies can be safely relaxed later, but it cannot be
+ * enforced later.
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
-- 
2.55.0.1032.g73a4cd73de-goog