qemu-e2k/qapi/introspect.json
Eric Blake f545504420 qapi-introspect: Document lack of sorting
qapi-code-gen.txt already claims that types, commands, and
events share a common namespace; set this in stone by further
documenting that our introspection output will never have
collisions with the same name tied to more than one meta-type.

Our largest QMP enum currently has 125 values, our largest
object type has 27 members, and the mean for each is less than
10.  These sizes are small enough that the per-element overhead
of O(log n) binary searching probably outweighs the speed
possible with direct O(n) linear searching (a better algorithm
with more overhead will only beat a leaner naive algorithm only
as you scale to larger input sizes).

Arguably, the overall SchemaInfo array could be sorted by name;
there, we currently have 531 entities, large enough for a binary
search to be faster than linear.  However, remember that we have
mutually-recursive types, which means there is no topological
ordering that will allow clients to learn all information about
that type in a single linear pass; thus clients will want to do
random access over the data, and they will probably read the
introspection output into a hashtable for O(1) lookup rather
than O(log n) binary searching, at which point, pre-sorting our
introspection output doesn't help the client.

It doesn't help that sorting can be subjective if you introduce
locales into the mix (I'm not experienced enough with Python
to know for sure, but at least it looks like it defaults to
sorting in the C locale even when run under a different locale).
And while our current introspection output is deterministic
(because we visit entities in a sorted order), we may want
to change that order in the future (such as using OrderedDict
to stick to .json declaration order).

For these reasons, we simply document that clients should not
rely on any particular order of items in introspection output.
And since it is now a documented part of the contract, we have
the freedom to later rearrange output if needed, without
worrying about breaking well-written clients.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1446791754-23823-13-git-send-email-eblake@redhat.com>
[Commit message tweaked]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
2015-11-10 08:10:28 +01:00

281 lines
7.0 KiB
Python

# -*- Mode: Python -*-
#
# QAPI/QMP introspection
#
# Copyright (C) 2015 Red Hat, Inc.
#
# Authors:
# Markus Armbruster <armbru@redhat.com>
#
# This work is licensed under the terms of the GNU GPL, version 2 or later.
# See the COPYING file in the top-level directory.
##
# @query-qmp-schema
#
# Command query-qmp-schema exposes the QMP wire ABI as an array of
# SchemaInfo. This lets QMP clients figure out what commands and
# events are available in this QEMU, and their parameters and results.
#
# However, the SchemaInfo can't reflect all the rules and restrictions
# that apply to QMP. It's interface introspection (figuring out
# what's there), not interface specification. The specification is in
# the QAPI schema.
#
# Returns: array of @SchemaInfo, where each element describes an
# entity in the ABI: command, event, type, ...
#
# The order of the various SchemaInfo is unspecified; however, all
# names are guaranteed to be unique (no name will be duplicated with
# different meta-types).
#
# Note: the QAPI schema is also used to help define *internal*
# interfaces, by defining QAPI types. These are not part of the QMP
# wire ABI, and therefore not returned by this command.
#
# Since: 2.5
##
{ 'command': 'query-qmp-schema',
'returns': [ 'SchemaInfo' ],
'gen': false } # just to simplify qmp_query_json()
##
# @SchemaMetaType
#
# This is a @SchemaInfo's meta type, i.e. the kind of entity it
# describes.
#
# @builtin: a predefined type such as 'int' or 'bool'.
#
# @enum: an enumeration type
#
# @array: an array type
#
# @object: an object type (struct or union)
#
# @alternate: an alternate type
#
# @command: a QMP command
#
# @event: a QMP event
#
# Since: 2.5
##
{ 'enum': 'SchemaMetaType',
'data': [ 'builtin', 'enum', 'array', 'object', 'alternate',
'command', 'event' ] }
##
# @SchemaInfoBase
#
# Members common to any @SchemaInfo.
#
# Since: 2.5
##
{ 'struct': 'SchemaInfoBase',
'data': { 'name': 'str', 'meta-type': 'SchemaMetaType' } }
##
# @SchemaInfo
#
# @name: the entity's name, inherited from @base.
# Commands and events have the name defined in the QAPI schema.
# Unlike command and event names, type names are not part of
# the wire ABI. Consequently, type names are meaningless
# strings here, although they are still guaranteed unique
# regardless of @meta-type.
#
# All references to other SchemaInfo are by name.
#
# @meta-type: the entity's meta type, inherited from @base.
#
# Additional members depend on the value of @meta-type.
#
# Since: 2.5
##
{ 'union': 'SchemaInfo',
'base': 'SchemaInfoBase',
'discriminator': 'meta-type',
'data': {
'builtin': 'SchemaInfoBuiltin',
'enum': 'SchemaInfoEnum',
'array': 'SchemaInfoArray',
'object': 'SchemaInfoObject',
'alternate': 'SchemaInfoAlternate',
'command': 'SchemaInfoCommand',
'event': 'SchemaInfoEvent' } }
##
# @SchemaInfoBuiltin
#
# Additional SchemaInfo members for meta-type 'builtin'.
#
# @json-type: the JSON type used for this type on the wire.
#
# Since: 2.5
##
{ 'struct': 'SchemaInfoBuiltin',
'data': { 'json-type': 'JSONType' } }
##
# @JSONType
#
# The four primitive and two structured types according to RFC 7159
# section 1, plus 'int' (split off 'number'), plus the obvious top
# type 'value'.
#
# Since: 2.5
##
{ 'enum': 'JSONType',
'data': [ 'string', 'number', 'int', 'boolean', 'null',
'object', 'array', 'value' ] }
##
# @SchemaInfoEnum
#
# Additional SchemaInfo members for meta-type 'enum'.
#
# @values: the enumeration type's values, in no particular order.
#
# Values of this type are JSON string on the wire.
#
# Since: 2.5
##
{ 'struct': 'SchemaInfoEnum',
'data': { 'values': ['str'] } }
##
# @SchemaInfoArray
#
# Additional SchemaInfo members for meta-type 'array'.
#
# @element-type: the array type's element type.
#
# Values of this type are JSON array on the wire.
#
# Since: 2.5
##
{ 'struct': 'SchemaInfoArray',
'data': { 'element-type': 'str' } }
##
# @SchemaInfoObject
#
# Additional SchemaInfo members for meta-type 'object'.
#
# @members: the object type's (non-variant) members, in no particular order.
#
# @tag: #optional the name of the member serving as type tag.
# An element of @members with this name must exist.
#
# @variants: #optional variant members, i.e. additional members that
# depend on the type tag's value. Present exactly when
# @tag is present. The variants are in no particular order,
# and may even differ from the order of the values of the
# enum type of the @tag.
#
# Values of this type are JSON object on the wire.
#
# Since: 2.5
##
{ 'struct': 'SchemaInfoObject',
'data': { 'members': [ 'SchemaInfoObjectMember' ],
'*tag': 'str',
'*variants': [ 'SchemaInfoObjectVariant' ] } }
##
# @SchemaInfoObjectMember
#
# An object member.
#
# @name: the member's name, as defined in the QAPI schema.
#
# @type: the name of the member's type.
#
# @default: #optional default when used as command parameter.
# If absent, the parameter is mandatory.
# If present, the value must be null. The parameter is
# optional, and behavior when it's missing is not specified
# here.
# Future extension: if present and non-null, the parameter
# is optional, and defaults to this value.
#
# Since: 2.5
##
{ 'struct': 'SchemaInfoObjectMember',
'data': { 'name': 'str', 'type': 'str', '*default': 'any' } }
# @default's type must be null or match @type
##
# @SchemaInfoObjectVariant
#
# The variant members for a value of the type tag.
#
# @case: a value of the type tag.
#
# @type: the name of the object type that provides the variant members
# when the type tag has value @case.
#
# Since: 2.5
##
{ 'struct': 'SchemaInfoObjectVariant',
'data': { 'case': 'str', 'type': 'str' } }
##
# @SchemaInfoAlternate
#
# Additional SchemaInfo members for meta-type 'alternate'.
#
# @members: the alternate type's members, in no particular order.
# The members' wire encoding is distinct, see
# docs/qapi-code-gen.txt section Alternate types.
#
# On the wire, this can be any of the members.
#
# Since: 2.5
##
{ 'struct': 'SchemaInfoAlternate',
'data': { 'members': [ 'SchemaInfoAlternateMember' ] } }
##
# @SchemaInfoAlternateMember
#
# An alternate member.
#
# @type: the name of the member's type.
#
# Since: 2.5
##
{ 'struct': 'SchemaInfoAlternateMember',
'data': { 'type': 'str' } }
##
# @SchemaInfoCommand
#
# Additional SchemaInfo members for meta-type 'command'.
#
# @arg-type: the name of the object type that provides the command's
# parameters.
#
# @ret-type: the name of the command's result type.
#
# TODO @success-response (currently irrelevant, because it's QGA, not QMP)
#
# Since: 2.5
##
{ 'struct': 'SchemaInfoCommand',
'data': { 'arg-type': 'str', 'ret-type': 'str' } }
##
# @SchemaInfoEvent
#
# Additional SchemaInfo members for meta-type 'event'.
#
# @arg-type: the name of the object type that provides the event's
# parameters.
#
# Since: 2.5
##
{ 'struct': 'SchemaInfoEvent',
'data': { 'arg-type': 'str' } }