From 39a65e2c243978a480e03cab865462d98873fc3c Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Wed, 11 Nov 2015 10:50:02 -0700 Subject: [PATCH 1/2] 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 +++++++++++ qapi/introspect.json | 9 +++++++++ 2 files changed, 20 insertions(+) diff --git a/docs/qapi-code-gen.txt b/docs/qapi-code-gen.txt index f9fa6f3d96..ceb9a782d0 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 diff --git a/qapi/introspect.json b/qapi/introspect.json index e7c4c3e998..9e9369e160 100644 --- a/qapi/introspect.json +++ b/qapi/introspect.json @@ -22,6 +22,15 @@ # what's there), not interface specification. The specification is in # the QAPI schema. # +# Furthermore, while we strive to keep the QMP wire format +# backwards-compatible across qemu versions, the introspection output +# is not guaranteed to have the same stability. For example, one +# version of qemu may list an object member as an optional +# non-variant, while another lists the same member only through the +# object's variants; or the type of a member may change from a generic +# string into a specific enum or from one specific type into an +# alternate that includes the original type alongside something else. +# # Returns: array of @SchemaInfo, where each element describes an # entity in the ABI: command, event, type, ... # From 513e7cdbaeec56c77e4cf26f151d7ee79f3a6be9 Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Thu, 12 Nov 2015 11:50:43 -0700 Subject: [PATCH 2/2] input: Document why x-input-send-event is still experimental The x-input-send-event command was introduced in 2.2 with mention that it is experimental, but now that several releases have elapsed without any changes, it would be nice to document why that was done and should still remain experimental in 2.5. Meanwhile, our documentation states that we prefer 'lower-case', rather than 'CamelCase', for qapi enum values. The InputButton and InputAxis enums violate this convention. However, because they are currently used primarily for generating code that is used internally; and their only exposure through QMP is via the experimental 'x-input-send-event' command, we are free to change their spelling. Of course, it would be nicer to delay such a change until the same time we promote the command to non-experimental. Adding documentation will help us remember to do that rename. We have plans to tighten the qapi generator to flag instances of inconsistent use of naming conventions; if that lands first, it will just need to whitelist these exceptions until the time we settle on the final interface. Fix a typo in the docs for InputAxis while at it. Signed-off-by: Eric Blake Message-Id: <1447354243-31825-1-git-send-email-eblake@redhat.com> Reviewed-by: Gerd Hoffmann Signed-off-by: Markus Armbruster --- qapi-schema.json | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/qapi-schema.json b/qapi-schema.json index b65905f4d6..8b1a423fa7 100644 --- a/qapi-schema.json +++ b/qapi-schema.json @@ -3579,16 +3579,22 @@ # Button of a pointer input device (mouse, tablet). # # Since: 2.0 +# +# Note that the spelling of these values may change when the +# x-input-send-event is promoted out of experimental status. ## { 'enum' : 'InputButton', 'data' : [ 'Left', 'Middle', 'Right', 'WheelUp', 'WheelDown' ] } ## -# @InputButton +# @InputAxis # # Position axis of a pointer input device (mouse, tablet). # # Since: 2.0 +# +# Note that the spelling of these values may change when the +# x-input-send-event is promoted out of experimental status. ## { 'enum' : 'InputAxis', 'data' : [ 'X', 'Y' ] } @@ -3679,7 +3685,10 @@ # # Since: 2.2 # -# Note: this command is experimental, and not a stable API. +# Note: this command is experimental, and not a stable API. Things that +# might change before it becomes stable include the spelling of enum +# values for InputButton and InputAxis, and the notion of how to designate +# which console will receive the event. # ## { 'command': 'x-input-send-event',