[PATCH] xen/public: add comments regarding interface version bumps

[Juergen Gross <jgross@xxxxxxxx>]

domctl.h and sysctl.h have an interface version, which needs to be
bumped in case of incompatible modifications of the interface.

In order to avoid misunderstandings, add a comment to both headers
specifying in which cases a bump is needed.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 xen/include/public/domctl.h | 10 ++++++++++
 xen/include/public/sysctl.h | 10 ++++++++++
 2 files changed, 20 insertions(+)

diff --git a/xen/include/public/domctl.h b/xen/include/public/domctl.h
index e1028fc524..353f831e40 100644
--- a/xen/include/public/domctl.h
+++ b/xen/include/public/domctl.h
@@ -21,6 +21,16 @@
 #include "hvm/save.h"
 #include "memory.h"
 
+/*
+ * The interface version needs to be incremented by 1 in case the interface
+ * is modified in an incompatible way AND if the version hasn't been
+ * incremented in the current development cycle already.
+ * Pure additions (e.g. new sub-commands) or compatible interface changes
+ * (e.g. adding semantics to 0-checked input fields or data to zeroed output
+ * fields) don't require a change of the version.
+ *
+ * Last version bump: Xen 4.19
+ */
 #define XEN_DOMCTL_INTERFACE_VERSION 0x00000017
 
 /*
diff --git a/xen/include/public/sysctl.h b/xen/include/public/sysctl.h
index b2a5a724db..b0fec271d3 100644
--- a/xen/include/public/sysctl.h
+++ b/xen/include/public/sysctl.h
@@ -18,6 +18,16 @@
 #include "domctl.h"
 #include "physdev.h"
 
+/*
+ * The interface version needs to be incremented by 1 in case the interface
+ * is modified in an incompatible way AND if the version hasn't been
+ * incremented in the current development cycle already.
+ * Pure additions (e.g. new sub-commands) or compatible interface changes
+ * (e.g. adding semantics to 0-checked input fields or data to zeroed output
+ * fields) don't require a change of the version.
+ *
+ * Last version bump: Xen 4.17
+ */
 #define XEN_SYSCTL_INTERFACE_VERSION 0x00000015
 
 /*
-- 
2.43.0