From 39a65e2c243978a480e03cab865462d98873fc3c Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Wed, 11 Nov 2015 10:50:02 -0700 Subject: qapi: Document introspection stability considerations We are not ready (and might never be ready) to declare introspection stable between releases. Clients written to control multiple versions of qemu, and desiring to know whether a particular member is supported for a given command, must be prepared to locate that member in spite of qapi changes that may affect the member's location or type within the overall object, even though such changes did not break QMP wire back-compatibility. Signed-off-by: Eric Blake Message-Id: <1447264202-19554-1-git-send-email-eblake@redhat.com> Signed-off-by: Markus Armbruster --- docs/qapi-code-gen.txt | 11 +++++++++++ 1 file changed, 11 insertions(+) (limited to 'docs') diff --git a/docs/qapi-code-gen.txt b/docs/qapi-code-gen.txt index f9fa6f3..ceb9a78 100644 --- a/docs/qapi-code-gen.txt +++ b/docs/qapi-code-gen.txt @@ -514,6 +514,17 @@ exactly the server (QEMU) supports. For this purpose, QMP provides introspection via command query-qmp-schema. QGA currently doesn't support introspection. +While Client JSON Protocol wire compatibility should be maintained +between qemu versions, we cannot make the same guarantees for +introspection stability. For example, one version of qemu may provide +a non-variant optional member of a struct, and a later version rework +the member to instead be non-optional and associated with a variant. +Likewise, one version of qemu may list a member with open-ended type +'str', and a later version could convert it to a finite set of strings +via an enum type; or a member may be converted from a specific type to +an alternate that represents a choice between the original type and +something else. + query-qmp-schema returns a JSON array of SchemaInfo objects. These objects together describe the wire ABI, as defined in the QAPI schema. There is no specified order to the SchemaInfo objects returned; a -- cgit v1.1