qapi: expose all schema features to code

This replaces use of the constants from the QapiSpecialFeatures
enum, with constants from the auto-generate QapiFeatures enum
in qapi-features.h

The 'deprecated' and 'unstable' features still have a little bit of
special handling, being force defined to be the 1st + 2nd features
in the enum, regardless of whether they're used in the schema. This
retains compatibility with common code that references the features
via the QapiSpecialFeatures constants.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20250205123550.2754387-5-berrange@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Imports tidied up with isort]
Signed-off-by: Markus Armbruster <armbru@redhat.com>

meson.build

@@ -3444,6 +3444,7 @@ qapi_gen_depends = [ meson.current_source_dir() / 'scripts/qapi/__init__.py',
                      meson.current_source_dir() / 'scripts/qapi/schema.py',
                      meson.current_source_dir() / 'scripts/qapi/source.py',
                      meson.current_source_dir() / 'scripts/qapi/types.py',
+                     meson.current_source_dir() / 'scripts/qapi/features.py',
                      meson.current_source_dir() / 'scripts/qapi/visit.py',
                      meson.current_source_dir() / 'scripts/qapi-gen.py'
 ]

scripts/qapi/commands.py

@@ -355,6 +355,7 @@ void %(c_prefix)sqmp_init_marshal(QmpCommandList *cmds);
 #include "qemu/osdep.h"
 #include "%(prefix)sqapi-commands.h"
 #include "%(prefix)sqapi-init-commands.h"
+#include "%(prefix)sqapi-features.h"
 
 void %(c_prefix)sqmp_init_marshal(QmpCommandList *cmds)
 {

scripts/qapi/features.py

@@ -0,0 +1,48 @@
+"""
+QAPI features generator
+
+Copyright 2024 Red Hat
+
+This work is licensed under the terms of the GNU GPL, version 2.
+# See the COPYING file in the top-level directory.
+"""
+
+from typing import ValuesView
+
+from .common import c_enum_const, c_name
+from .gen import QAPISchemaMonolithicCVisitor
+from .schema import QAPISchema, QAPISchemaFeature
+
+
+class QAPISchemaGenFeatureVisitor(QAPISchemaMonolithicCVisitor):
+
+    def __init__(self, prefix: str):
+        super().__init__(
+            prefix, 'qapi-features',
+            ' * Schema-defined QAPI features',
+            __doc__)
+
+        self.features: ValuesView[QAPISchemaFeature]
+
+    def visit_begin(self, schema: QAPISchema) -> None:
+        self.features = schema.features()
+        self._genh.add("#include \"qapi/util.h\"\n\n")
+
+    def visit_end(self) -> None:
+        self._genh.add("typedef enum {\n")
+        for f in self.features:
+            self._genh.add(f"    {c_enum_const('qapi_feature', f.name)}")
+            if f.name in QAPISchemaFeature.SPECIAL_NAMES:
+                self._genh.add(f" = {c_enum_const('qapi', f.name)},\n")
+            else:
+                self._genh.add(",\n")
+
+        self._genh.add("} " + c_name('QapiFeature') + ";\n")
+
+
+def gen_features(schema: QAPISchema,
+                 output_dir: str,
+                 prefix: str) -> None:
+    vis = QAPISchemaGenFeatureVisitor(prefix)
+    schema.visit(vis)
+    vis.write(output_dir)

scripts/qapi/gen.py

@@ -42,9 +42,9 @@ from .source import QAPISourceInfo
 
 
 def gen_features(features: Sequence[QAPISchemaFeature]) -> str:
-    featenum = [f"1u << {c_enum_const('qapi', feat.name)}"
-                for feat in features if feat.is_special()]
-    return ' | '.join(featenum) or '0'
+    feats = [f"1u << {c_enum_const('qapi_feature', feat.name)}"
+             for feat in features]
+    return ' | '.join(feats) or '0'
 
 
 class QAPIGen:

scripts/qapi/main.py

@@ -15,6 +15,7 @@ from .commands import gen_commands
 from .common import must_match
 from .error import QAPIError
 from .events import gen_events
+from .features import gen_features
 from .introspect import gen_introspect
 from .schema import QAPISchema
 from .types import gen_types
@@ -49,6 +50,7 @@ def generate(schema_file: str,
 
     schema = QAPISchema(schema_file)
     gen_types(schema, output_dir, prefix, builtins)
+    gen_features(schema, output_dir, prefix)
     gen_visit(schema, output_dir, prefix, builtins)
     gen_commands(schema, output_dir, prefix, gen_tracing)
     gen_events(schema, output_dir, prefix)

scripts/qapi/schema.py

@@ -29,6 +29,7 @@ from typing import (
     List,
     Optional,
     Union,
+    ValuesView,
     cast,
 )
 
@@ -933,8 +934,11 @@ class QAPISchemaEnumMember(QAPISchemaMember):
 class QAPISchemaFeature(QAPISchemaMember):
     role = 'feature'
 
+    # Features which are standardized across all schemas
+    SPECIAL_NAMES = ['deprecated', 'unstable']
+
     def is_special(self) -> bool:
-        return self.name in ('deprecated', 'unstable')
+        return self.name in QAPISchemaFeature.SPECIAL_NAMES
 
 
 class QAPISchemaObjectTypeMember(QAPISchemaMember):
@@ -1138,6 +1142,16 @@ class QAPISchema:
         self._entity_list: List[QAPISchemaEntity] = []
         self._entity_dict: Dict[str, QAPISchemaDefinition] = {}
         self._module_dict: Dict[str, QAPISchemaModule] = OrderedDict()
+        # NB, values in the dict will identify the first encountered
+        # usage of a named feature only
+        self._feature_dict: Dict[str, QAPISchemaFeature] = OrderedDict()
+
+        # All schemas get the names defined in the QapiSpecialFeature enum.
+        # Rely on dict iteration order matching insertion order so that
+        # the special names are emitted first when generating code.
+        for f in QAPISchemaFeature.SPECIAL_NAMES:
+            self._feature_dict[f] = QAPISchemaFeature(f, None)
+
         self._schema_dir = os.path.dirname(fname)
         self._make_module(QAPISchemaModule.BUILTIN_MODULE_NAME)
         self._make_module(fname)
@@ -1147,6 +1161,9 @@ class QAPISchema:
         self._def_exprs(exprs)
         self.check()
 
+    def features(self) -> ValuesView[QAPISchemaFeature]:
+        return self._feature_dict.values()
+
     def _def_entity(self, ent: QAPISchemaEntity) -> None:
         self._entity_list.append(ent)
 
@@ -1258,6 +1275,12 @@ class QAPISchema:
     ) -> List[QAPISchemaFeature]:
         if features is None:
             return []
+
+        for f in features:
+            feat = QAPISchemaFeature(f['name'], info)
+            if feat.name not in self._feature_dict:
+                self._feature_dict[feat.name] = feat
+
         return [QAPISchemaFeature(f['name'], info,
                                   QAPISchemaIfCond(f.get('if')))
                 for f in features]
@@ -1485,6 +1508,12 @@ class QAPISchema:
         for doc in self.docs:
             doc.check()
 
+        features = list(self._feature_dict.values())
+        if len(features) > 64:
+            raise QAPISemError(
+                features[64].info,
+                "Maximum of 64 schema features is permitted")
+
     def visit(self, visitor: QAPISchemaVisitor) -> None:
         visitor.visit_begin(self)
         for mod in self._module_dict.values():

scripts/qapi/types.py

@@ -304,11 +304,14 @@ class QAPISchemaGenTypeVisitor(QAPISchemaModularCVisitor):
 #include "qapi/dealloc-visitor.h"
 #include "%(types)s.h"
 #include "%(visit)s.h"
+#include "%(prefix)sqapi-features.h"
 ''',
-                                      types=types, visit=visit))
+                                      types=types, visit=visit,
+                                      prefix=self._prefix))
         self._genh.preamble_add(mcgen('''
 #include "qapi/qapi-builtin-types.h"
-'''))
+''',
+                                      prefix=self._prefix))
 
     def visit_begin(self, schema: QAPISchema) -> None:
         # gen_object() is recursive, ensure it doesn't visit the empty type

scripts/qapi/visit.py

@@ -356,8 +356,9 @@ class QAPISchemaGenVisitVisitor(QAPISchemaModularCVisitor):
 #include "qemu/osdep.h"
 #include "qapi/error.h"
 #include "%(visit)s.h"
+#include "%(prefix)sqapi-features.h"
 ''',
-                                      visit=visit))
+                                      visit=visit, prefix=self._prefix))
         self._genh.preamble_add(mcgen('''
 #include "qapi/qapi-builtin-visit.h"
 #include "%(types)s.h"

tests/meson.build

@@ -16,6 +16,8 @@ test_qapi_outputs = [
   'test-qapi-events-sub-sub-module.h',
   'test-qapi-events.c',
   'test-qapi-events.h',
+  'test-qapi-features.c',
+  'test-qapi-features.h',
   'test-qapi-init-commands.c',
   'test-qapi-init-commands.h',
   'test-qapi-introspect.c',

tests/qapi-schema/features-too-many.err

@@ -0,0 +1,2 @@
+features-too-many.json: In command 'go-fish':
+features-too-many.json:2: Maximum of 64 schema features is permitted

tests/qapi-schema/features-too-many.json

@@ -0,0 +1,13 @@
+# Max 64 features, with 2 specials, so 63rd custom is invalid
+{ 'command': 'go-fish',
+  'features': [
+      'f00', 'f01', 'f02', 'f03', 'f04', 'f05', 'f06', 'f07',
+      'f08', 'f09', 'f0a', 'f0b', 'f0c', 'f0d', 'f0e', 'f0f',
+      'f10', 'f11', 'f12', 'f13', 'f14', 'f15', 'f16', 'f17',
+      'f18', 'f19', 'f1a', 'f1b', 'f1c', 'f1d', 'f1e', 'f1f',
+      'f20', 'f21', 'f22', 'f23', 'f24', 'f25', 'f26', 'f27',
+      'f28', 'f29', 'f2a', 'f2b', 'f2c', 'f2d', 'f2e', 'f2f',
+      'f30', 'f31', 'f32', 'f33', 'f34', 'f35', 'f36', 'f37',
+      'f38', 'f39', 'f3a', 'f3b', 'f3c', 'f3d', 'f3e'
+  ]
+}

tests/qapi-schema/meson.build

@@ -105,6 +105,7 @@ schemas = [
   'event-case.json',
   'event-member-invalid-dict.json',
   'event-nest-struct.json',
+  'features-too-many.json',
   'features-bad-type.json',
   'features-deprecated-type.json',
   'features-duplicate-name.json',