Re: [RFC 3/5] livepatch: Allow to distinguish different version of system state changes

It might happen that an older change is not enough and the same system
state has to be modified another way. Different changes need to get
distinguished by a version number added to struct klp_state.

The version can also be used to prevent loading incompatible livepatches.
The check is done when the livepatch is enabled. The rules are:

  + Any completely new system state modification is allowed.

  + System state modifications with the same or higher version are allowed
    for already modified system states.

  + Cumulative livepatches must handle all system state modifications from
    already installed livepatches.

  + Non-cumulative livepatches are allowed to touch already modified
    system states.

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 include/linux/livepatch.h |  2 ++
 kernel/livepatch/core.c   |  8 ++++++++
 kernel/livepatch/state.c  | 40 +++++++++++++++++++++++++++++++++++++++-
 kernel/livepatch/state.h  |  9 +++++++++
 4 files changed, 58 insertions(+), 1 deletion(-)
 create mode 100644 kernel/livepatch/state.h

diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 591abdee30d7..8bc4c6cc3f3f 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h

@@ -135,10 +135,12 @@ struct klp_object {
 /**
  * struct klp_state - state of the system modified by the livepatch
  * @id:		system state identifier (non zero)
+ * @version:	version of the change (non-zero)
  * @data:	custom data
  */
 struct klp_state {
 	int id;