[Qemu-devel] [PATCH] qapi: Document optional arguments' backwards compatibility

[Fam Zheng]

Signed-off-by: Fam Zheng <address@hidden>
---
 docs/qapi-code-gen.txt | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/docs/qapi-code-gen.txt b/docs/qapi-code-gen.txt
index d78921f..d7b19ab 100644
--- a/docs/qapi-code-gen.txt
+++ b/docs/qapi-code-gen.txt
@@ -51,8 +51,10 @@ example of a complex type is:
 
 The use of '*' as a prefix to the name means the member is optional.  Optional
 members should always be added to the end of the dictionary to preserve
-backwards compatibility.
-
+backwards compatibility. Even there is no strict restriction for default values
+of those optional arguments between QEMU's versions, the backwards
+compatibility should be preserved by keeping the user visible behavior
+unchanged.
 
 A complex type definition can specify another complex type as its base.
 In this case, the fields of the base type are included as top-level fields
-- 
1.9.2