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qapi: Add feature flags to struct types

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Sometimes, the behaviour of QEMU changes without a change in the QMP
syntax (usually by allowing values or operations that previously
resulted in an error). QMP clients may still need to know whether
they can rely on the changed behavior.

Let's add feature flags to the QAPI schema language, so that we can make
such changes visible with schema introspection.

An example for a schema definition using feature flags looks like this:

    { 'struct': 'TestType',
      'data': { 'number': 'int' },
      'features': [ 'allow-negative-numbers' ] }

Introspection information then looks like this:

    { "name": "TestType", "meta-type": "object",
      "members": [
          { "name": "number", "type": "int" } ],
      "features": [ "allow-negative-numbers" ] }

This patch implements feature flags only for struct types. We'll
implement them more widely as needed.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20190606153803.5278-2-armbru@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
This commit is contained in:
Kevin Wolf 2019-06-06 17:37:57 +02:00 • committed by Markus Armbruster
parent 2ea8e96da2
commit 6a8c0b5102
10 changed files with 114 additions and 18 deletions
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6
scripts/qapi/introspect.py
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@ -188,11 +188,15 @@ const QLitObject %(c_name)s = %(c_string)s;
self._gen_qlit('[' + element + ']', 'array', {'element-type': element},
ifcond)
def visit_object_type_flat(self, name, info, ifcond, members, variants):
def visit_object_type_flat(self, name, info, ifcond, members, variants,
features):
obj = {'members': [self._gen_member(m) for m in members]}
if variants:
obj.update(self._gen_variants(variants.tag_member.name,
variants.variants))
if features:
obj['features'] = [(f.name, {'if': f.ifcond}) for f in features]
self._gen_qlit(name, 'object', obj, ifcond)
def visit_alternate_type(self, name, info, ifcond, variants):