Merge remote-tracking branch 'remotes/armbru/tags/pull-qapi-2019-06-12' into staging

QAPI patches for 2019-06-12

# gpg: Signature made Wed 12 Jun 2019 17:44:50 BST
# gpg:                using RSA key 354BC8B3D7EB2A6B68674E5F3870B400EB918653
# gpg:                issuer "armbru@redhat.com"
# gpg: Good signature from "Markus Armbruster <armbru@redhat.com>" [full]
# gpg:                 aka "Markus Armbruster <armbru@pond.sub.org>" [full]
# Primary key fingerprint: 354B C8B3 D7EB 2A6B 6867  4E5F 3870 B400 EB91 8653

* remotes/armbru/tags/pull-qapi-2019-06-12:
  qapi: Simplify how QAPIDoc implements its state machine
  file-posix: Add dynamic-auto-read-only QAPI feature
  qapi: Allow documentation for features
  qapi: Disentangle QAPIDoc code
  tests/qapi-schema: Error case tests for features in structs
  tests/qapi-schema: Test for good feature lists in structs
  qapi: Add feature flags to struct types
  block/gluster: update .help of BLOCK_OPT_PREALLOC option
  block/file-posix: update .help of BLOCK_OPT_PREALLOC option
  qapi/block-core: update documentation of preallocation parameter
  qdev: Delete unused LostTickPolicy "merge"

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

block/file-posix.c

@@ -2752,7 +2752,11 @@ static QemuOptsList raw_create_opts = {
         {
             .name = BLOCK_OPT_PREALLOC,
             .type = QEMU_OPT_STRING,
-            .help = "Preallocation mode (allowed values: off, falloc, full)"
+            .help = "Preallocation mode (allowed values: off"
+#ifdef CONFIG_POSIX_FALLOCATE
+                    ", falloc"
+#endif
+                    ", full)"
         },
         { /* end of list */ }
     }

block/gluster.c

@@ -98,7 +98,14 @@ static QemuOptsList qemu_gluster_create_opts = {
         {
             .name = BLOCK_OPT_PREALLOC,
             .type = QEMU_OPT_STRING,
-            .help = "Preallocation mode (allowed values: off, full)"
+            .help = "Preallocation mode (allowed values: off"
+#ifdef CONFIG_GLUSTERFS_FALLOCATE
+                    ", falloc"
+#endif
+#ifdef CONFIG_GLUSTERFS_ZEROFILL
+                    ", full"
+#endif
+                    ")"
         },
         {
             .name = GLUSTER_OPT_DEBUG,

docs/devel/qapi-code-gen.txt

@@ -719,6 +719,34 @@ any non-empty complex type (struct, union, or alternate), and a
 pointer to that QAPI type is passed as a single argument.
 
 
+=== Features ===
+
+Sometimes, the behaviour of QEMU changes compatibly, but 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 the extension is available.
+
+For this purpose, a list of features can be specified for a struct type.
+This is exposed to the client as a list of string, where each string
+signals that this build of QEMU shows a certain behaviour.
+
+In the schema, features can be specified as simple strings, for example:
+
+{ 'struct': 'TestType',
+  'data': { 'number': 'int' },
+  'features': [ 'allow-negative-numbers' ] }
+
+Another option is to specify features as dictionaries, where the key
+'name' specifies the feature string to be exposed to clients:
+
+{ 'struct': 'TestType',
+  'data': { 'number': 'int' },
+  'features': [ { 'name': 'allow-negative-numbers' } ] }
+
+This expanded form is necessary if you want to make the feature
+conditional (see below in "Configuring the schema").
+
+
 === Downstream extensions ===
 
 QAPI schema names that are externally visible, say in the Client JSON
@@ -771,6 +799,16 @@ Example: a conditional 'bar' enum member.
   [ 'foo',
     { 'name' : 'bar', 'if': 'defined(IFCOND)' } ] }
 
+Similarly, features can be specified as a dictionary with a 'name' and
+an 'if' key.
+
+Example: a conditional 'allow-negative-numbers' feature
+
+{ 'struct': 'TestType',
+  'data': { 'number': 'int' },
+  'features': [ { 'name': 'allow-negative-numbers',
+                  'if' 'defined(IFCOND)' } ] }
+
 Please note that you are responsible to ensure that the C code will
 compile with an arbitrary combination of conditions, since the
 generators are unable to check it at this point.

qapi/block-core.json

@@ -2859,6 +2859,15 @@
 #                         file is large, do not use in production.
 #                         (default: off) (since: 3.0)
 #
+# Features:
+# @dynamic-auto-read-only: If present, enabled auto-read-only means that the
+#                          driver will open the image read-only at first,
+#                          dynamically reopen the image file read-write when
+#                          the first writer is attached to the node and reopen
+#                          read-only when the last writer is detached. This
+#                          allows giving QEMU write permissions only on demand
+#                          when an operation actually needs write access.
+#
 # Since: 2.9
 ##
 { 'struct': 'BlockdevOptionsFile',
@@ -2868,7 +2877,9 @@
             '*aio': 'BlockdevAioOptions',
 	    '*drop-cache': {'type': 'bool',
 	                    'if': 'defined(CONFIG_LINUX)'},
-            '*x-check-cache-dropped': 'bool' } }
+            '*x-check-cache-dropped': 'bool' },
+  'features': [ { 'name': 'dynamic-auto-read-only',
+                  'if': 'defined(CONFIG_POSIX)' } ] }
 
 ##
 # @BlockdevOptionsNull:
@@ -4121,7 +4132,10 @@
 #
 # @filename         Filename for the new image file
 # @size             Size of the virtual disk in bytes
-# @preallocation    Preallocation mode for the new image (default: off)
+# @preallocation    Preallocation mode for the new image (default: off;
+#                   allowed values: off,
+#                   falloc (if defined CONFIG_POSIX_FALLOCATE),
+#                   full (if defined CONFIG_POSIX))
 # @nocow            Turn off copy-on-write (valid only on btrfs; default: off)
 #
 # Since: 2.12
@@ -4139,7 +4153,10 @@
 #
 # @location         Where to store the new image file
 # @size             Size of the virtual disk in bytes
-# @preallocation    Preallocation mode for the new image (default: off)
+# @preallocation    Preallocation mode for the new image (default: off;
+#                   allowed values: off,
+#                   falloc (if defined CONFIG_GLUSTERFS_FALLOCATE),
+#                   full (if defined CONFIG_GLUSTERFS_ZEROFILL))
 #
 # Since: 2.12
 ##
@@ -4243,7 +4260,8 @@
 # @backing-fmt      Name of the block driver to use for the backing file
 # @encrypt          Encryption options if the image should be encrypted
 # @cluster-size     qcow2 cluster size in bytes (default: 65536)
-# @preallocation    Preallocation mode for the new image (default: off)
+# @preallocation    Preallocation mode for the new image (default: off;
+#                   allowed values: off, falloc, full, metadata)
 # @lazy-refcounts   True if refcounts may be updated lazily (default: off)
 # @refcount-bits    Width of reference counts in bits (default: 16)
 #
@@ -4426,7 +4444,8 @@
 # @location         Where to store the new image file
 # @size             Size of the virtual disk in bytes
 # @backing-file     File name of a base image
-# @preallocation    Preallocation mode (allowed values: off, full)
+# @preallocation    Preallocation mode for the new image (default: off;
+#                   allowed values: off, full)
 # @redundancy       Redundancy of the image
 # @object-size      Object size of the image
 #
@@ -4461,8 +4480,8 @@
 #
 # @file             Node to create the image format on
 # @size             Size of the virtual disk in bytes
-# @preallocation    Preallocation mode for the new image (allowed values: off,
-#                   metadata; default: off)
+# @preallocation    Preallocation mode for the new image (default: off;
+#                   allowed values: off, metadata)
 #
 # Since: 2.12
 ##

qapi/introspect.json

@@ -174,6 +174,9 @@
 #            and may even differ from the order of the values of the
 #            enum type of the @tag.
 #
+# @features: names of features associated with the type, in no particular
+#            order. (since: 4.1)
+#
 # Values of this type are JSON object on the wire.
 #
 # Since: 2.5
@@ -181,7 +184,8 @@
 { 'struct': 'SchemaInfoObject',
   'data': { 'members': [ 'SchemaInfoObjectMember' ],
             '*tag': 'str',
-            '*variants': [ 'SchemaInfoObjectVariant' ] } }
+            '*variants': [ 'SchemaInfoObjectVariant' ],
+            '*features': [ 'str' ] } }
 
 ##
 # @SchemaInfoObjectMember:

qapi/misc.json

@@ -172,17 +172,13 @@
 # @delay: continue to deliver ticks at the normal rate.  Guest time will be
 #         delayed due to the late tick
 #
-# @merge: merge the missed tick(s) into one tick and inject.  Guest time
-#         may be delayed, depending on how the OS reacts to the merging
-#         of ticks
-#
 # @slew: deliver ticks at a higher rate to catch up with the missed tick. The
 #        guest time should not be delayed once catchup is complete.
 #
 # Since: 2.0
 ##
 { 'enum': 'LostTickPolicy',
-  'data': ['discard', 'delay', 'merge', 'slew' ] }
+  'data': ['discard', 'delay', 'slew' ] }
 
 ##
 # @add_client:

scripts/qapi/common.py

@@ -102,6 +102,24 @@ def __init__(self, info, msg):
 
 
 class QAPIDoc(object):
+    """
+    A documentation comment block, either expression or free-form
+
+    Expression documentation blocks consist of
+
+    * a body section: one line naming the expression, followed by an
+      overview (any number of lines)
+
+    * argument sections: a description of each argument (for commands
+      and events) or member (for structs, unions and alternates)
+
+    * features sections: a description of each feature flag
+
+    * additional (non-argument) sections, possibly tagged
+
+    Free-form documentation blocks consist only of a body section.
+    """
+
     class Section(object):
         def __init__(self, name=None):
             # optional section name (argument/member or section name)
@@ -131,10 +149,12 @@ def __init__(self, parser, info):
         self.body = QAPIDoc.Section()
         # dict mapping parameter name to ArgSection
         self.args = OrderedDict()
+        self.features = OrderedDict()
         # a list of Section
         self.sections = []
         # the current section
         self._section = self.body
+        self._append_line = self._append_body_line
 
     def has_section(self, name):
         """Return True if we have a section with this name."""
@@ -144,7 +164,16 @@ def has_section(self, name):
         return False
 
     def append(self, line):
-        """Parse a comment line and add it to the documentation."""
+        """
+        Parse a comment line and add it to the documentation.
+
+        The way that the line is dealt with depends on which part of
+        the documentation we're parsing right now:
+        * The body section: ._append_line is ._append_body_line
+        * An argument section: ._append_line is ._append_args_line
+        * A features section: ._append_line is ._append_features_line
+        * An additional section: ._append_line is ._append_various_line
+        """
         line = line[1:]
         if not line:
             self._append_freeform(line)
@@ -153,54 +182,155 @@ def append(self, line):
         if line[0] != ' ':
             raise QAPIParseError(self._parser, "Missing space after #")
         line = line[1:]
+        self._append_line(line)
+
+    def end_comment(self):
+        self._end_section()
 
+    @staticmethod
+    def _is_section_tag(name):
+        return name in ('Returns:', 'Since:',
+                        # those are often singular or plural
+                        'Note:', 'Notes:',
+                        'Example:', 'Examples:',
+                        'TODO:')
+
+    def _append_body_line(self, line):
+        """
+        Process a line of documentation text in the body section.
+
+        If this a symbol line and it is the section's first line, this
+        is an expression documentation block for that symbol.
+
+        If it's an expression documentation block, another symbol line
+        begins the argument section for the argument named by it, and
+        a section tag begins an additional section.  Start that
+        section and append the line to it.
+
+        Else, append the line to the current section.
+        """
+        name = line.split(' ', 1)[0]
         # FIXME not nice: things like '#  @foo:' and '# @foo: ' aren't
         # recognized, and get silently treated as ordinary text
-        if self.symbol:
-            self._append_symbol_line(line)
-        elif not self.body.text and line.startswith('@'):
+        if not self.symbol and not self.body.text and line.startswith('@'):
             if not line.endswith(':'):
                 raise QAPIParseError(self._parser, "Line should end with :")
             self.symbol = line[1:-1]
             # FIXME invalid names other than the empty string aren't flagged
             if not self.symbol:
                 raise QAPIParseError(self._parser, "Invalid name")
+        elif self.symbol:
+            # This is an expression documentation block
+            if name.startswith('@') and name.endswith(':'):
+                self._append_line = self._append_args_line
+                self._append_args_line(line)
+            elif line == 'Features:':
+                self._append_line = self._append_features_line
+            elif self._is_section_tag(name):
+                self._append_line = self._append_various_line
+                self._append_various_line(line)
+            else:
+                self._append_freeform(line.strip())
         else:
-            self._append_freeform(line)
+            # This is a free-form documentation block
+            self._append_freeform(line.strip())
 
-    def end_comment(self):
-        self._end_section()
+    def _append_args_line(self, line):
+        """
+        Process a line of documentation text in an argument section.
+
+        A symbol line begins the next argument section, a section tag
+        section or a non-indented line after a blank line begins an
+        additional section.  Start that section and append the line to
+        it.
+
+        Else, append the line to the current section.
 
-    def _append_symbol_line(self, line):
+        """
         name = line.split(' ', 1)[0]
 
         if name.startswith('@') and name.endswith(':'):
             line = line[len(name)+1:]
             self._start_args_section(name[1:-1])
-        elif name in ('Returns:', 'Since:',
-                      # those are often singular or plural
-                      'Note:', 'Notes:',
-                      'Example:', 'Examples:',
-                      'TODO:'):
+        elif self._is_section_tag(name):
+            self._append_line = self._append_various_line
+            self._append_various_line(line)
+            return
+        elif (self._section.text.endswith('\n\n')
+              and line and not line[0].isspace()):
+            if line == 'Features:':
+                self._append_line = self._append_features_line
+            else:
+                self._start_section()
+                self._append_line = self._append_various_line
+                self._append_various_line(line)
+            return
+
+        self._append_freeform(line.strip())
+
+    def _append_features_line(self, line):
+        name = line.split(' ', 1)[0]
+
+        if name.startswith('@') and name.endswith(':'):
+            line = line[len(name)+1:]
+            self._start_features_section(name[1:-1])
+        elif self._is_section_tag(name):
+            self._append_line = self._append_various_line
+            self._append_various_line(line)
+            return
+        elif (self._section.text.endswith('\n\n')
+              and line and not line[0].isspace()):
+            self._start_section()
+            self._append_line = self._append_various_line
+            self._append_various_line(line)
+            return
+
+        self._append_freeform(line.strip())
+
+    def _append_various_line(self, line):
+        """
+        Process a line of documentation text in an additional section.
+
+        A symbol line is an error.
+
+        A section tag begins an additional section.  Start that
+        section and append the line to it.
+
+        Else, append the line to the current section.
+        """
+        name = line.split(' ', 1)[0]
+
+        if name.startswith('@') and name.endswith(':'):
+            raise QAPIParseError(self._parser,
+                                 "'%s' can't follow '%s' section"
+                                 % (name, self.sections[0].name))
+        elif self._is_section_tag(name):
             line = line[len(name)+1:]
             self._start_section(name[:-1])
 
+        if (not self._section.name or
+                not self._section.name.startswith('Example')):
+            line = line.strip()
+
         self._append_freeform(line)
 
-    def _start_args_section(self, name):
+    def _start_symbol_section(self, symbols_dict, name):
         # FIXME invalid names other than the empty string aren't flagged
         if not name:
             raise QAPIParseError(self._parser, "Invalid parameter name")
-        if name in self.args:
+        if name in symbols_dict:
             raise QAPIParseError(self._parser,
                                  "'%s' parameter name duplicated" % name)
-        if self.sections:
-            raise QAPIParseError(self._parser,
-                                 "'@%s:' can't follow '%s' section"
-                                 % (name, self.sections[0].name))
+        assert not self.sections
         self._end_section()
         self._section = QAPIDoc.ArgSection(name)
-        self.args[name] = self._section
+        symbols_dict[name] = self._section
+
+    def _start_args_section(self, name):
+        self._start_symbol_section(self.args, name)
+
+    def _start_features_section(self, name):
+        self._start_symbol_section(self.features, name)
 
     def _start_section(self, name=None):
         if name in ('Returns', 'Since') and self.has_section(name):
@@ -219,13 +349,6 @@ def _end_section(self):
             self._section = None
 
     def _append_freeform(self, line):
-        in_arg = isinstance(self._section, QAPIDoc.ArgSection)
-        if (in_arg and self._section.text.endswith('\n\n')
-                and line and not line[0].isspace()):
-            self._start_section()
-        if (in_arg or not self._section.name
-                or not self._section.name.startswith('Example')):
-            line = line.strip()
         match = re.match(r'(@\S+:)', line)
         if match:
             raise QAPIParseError(self._parser,
@@ -886,12 +1009,26 @@ def check_enum(expr, info):
 def check_struct(expr, info):
     name = expr['struct']
     members = expr['data']
+    features = expr.get('features')
 
     check_type(info, "'data' for struct '%s'" % name, members,
                allow_dict=True, allow_optional=True)
     check_type(info, "'base' for struct '%s'" % name, expr.get('base'),
                allow_metas=['struct'])
 
+    if features:
+        if not isinstance(features, list):
+            raise QAPISemError(info,
+                               "Struct '%s' requires an array for 'features'" %
+                               name)
+        for f in features:
+            assert isinstance(f, dict)
+            check_known_keys(info, "feature of struct %s" % name, f,
+                             ['name'], ['if'])
+
+            check_if(f, info)
+            check_name(info, "Feature of struct %s" % name, f['name'])
+
 
 def check_known_keys(info, source, keys, required, optional):
 
@@ -948,6 +1085,12 @@ def normalize_members(members):
             members[key] = {'type': arg}
 
 
+def normalize_features(features):
+    if isinstance(features, list):
+        features[:] = [f if isinstance(f, dict) else {'name': f}
+                       for f in features]
+
+
 def check_exprs(exprs):
     global all_names
 
@@ -986,8 +1129,10 @@ def check_exprs(exprs):
             normalize_members(expr['data'])
         elif 'struct' in expr:
             meta = 'struct'
-            check_keys(expr_elem, 'struct', ['data'], ['base', 'if'])
+            check_keys(expr_elem, 'struct', ['data'],
+                       ['base', 'if', 'features'])
             normalize_members(expr['data'])
+            normalize_features(expr.get('features'))
             struct_types[expr[meta]] = expr
         elif 'command' in expr:
             meta = 'command'
@@ -1126,10 +1271,12 @@ def visit_enum_type(self, name, info, ifcond, members, prefix):
     def visit_array_type(self, name, info, ifcond, element_type):
         pass
 
-    def visit_object_type(self, name, info, ifcond, base, members, variants):
+    def visit_object_type(self, name, info, ifcond, base, members, variants,
+                          features):
         pass
 
-    def visit_object_type_flat(self, name, info, ifcond, members, variants):
+    def visit_object_type_flat(self, name, info, ifcond, members, variants,
+                               features):
         pass
 
     def visit_alternate_type(self, name, info, ifcond, variants):
@@ -1290,7 +1437,7 @@ def visit(self, visitor):
 
 class QAPISchemaObjectType(QAPISchemaType):
     def __init__(self, name, info, doc, ifcond,
-                 base, local_members, variants):
+                 base, local_members, variants, features):
         # struct has local_members, optional base, and no variants
         # flat union has base, variants, and no local_members
         # simple union has local_members, variants, and no base
@@ -1302,11 +1449,15 @@ def __init__(self, name, info, doc, ifcond,
         if variants is not None:
             assert isinstance(variants, QAPISchemaObjectTypeVariants)
             variants.set_owner(name)
+        for f in features:
+            assert isinstance(f, QAPISchemaFeature)
+            f.set_owner(name)
         self._base_name = base
         self.base = None
         self.local_members = local_members
         self.variants = variants
         self.members = None
+        self.features = features
 
     def check(self, schema):
         QAPISchemaType.check(self, schema)
@@ -1332,6 +1483,12 @@ def check(self, schema):
             self.variants.check(schema, seen)
             assert self.variants.tag_member in self.members
             self.variants.check_clash(self.info, seen)
+
+        # Features are in a name space separate from members
+        seen = {}
+        for f in self.features:
+            f.check_clash(self.info, seen)
+
         if self.doc:
             self.doc.check()
 
@@ -1368,12 +1525,15 @@ def json_type(self):
 
     def visit(self, visitor):
         visitor.visit_object_type(self.name, self.info, self.ifcond,
-                                  self.base, self.local_members, self.variants)
+                                  self.base, self.local_members, self.variants,
+                                  self.features)
         visitor.visit_object_type_flat(self.name, self.info, self.ifcond,
-                                       self.members, self.variants)
+                                       self.members, self.variants,
+                                       self.features)
 
 
 class QAPISchemaMember(object):
+    """ Represents object members, enum members and features """
     role = 'member'
 
     def __init__(self, name, ifcond=None):
@@ -1419,6 +1579,10 @@ def describe(self):
         return "'%s' %s" % (self.name, self._pretty_owner())
 
 
+class QAPISchemaFeature(QAPISchemaMember):
+    role = 'feature'
+
+
 class QAPISchemaObjectTypeMember(QAPISchemaMember):
     def __init__(self, name, typ, optional, ifcond=None):
         QAPISchemaMember.__init__(self, name, ifcond)
@@ -1675,7 +1839,7 @@ def _def_predefineds(self):
                   ('null',   'null',    'QNull' + pointer_suffix)]:
             self._def_builtin_type(*t)
         self.the_empty_object_type = QAPISchemaObjectType(
-            'q_empty', None, None, None, None, [], None)
+            'q_empty', None, None, None, None, [], None, [])
         self._def_entity(self.the_empty_object_type)
 
         qtypes = ['none', 'qnull', 'qnum', 'qstring', 'qdict', 'qlist',
@@ -1685,6 +1849,9 @@ def _def_predefineds(self):
         self._def_entity(QAPISchemaEnumType('QType', None, None, None,
                                             qtype_values, 'QTYPE'))
 
+    def _make_features(self, features):
+        return [QAPISchemaFeature(f['name'], f.get('if')) for f in features]
+
     def _make_enum_members(self, values):
         return [QAPISchemaMember(v['name'], v.get('if')) for v in values]
 
@@ -1721,7 +1888,7 @@ def _make_implicit_object_type(self, name, info, doc, ifcond,
             assert ifcond == typ._ifcond # pylint: disable=protected-access
         else:
             self._def_entity(QAPISchemaObjectType(name, info, doc, ifcond,
-                                                  None, members, None))
+                                                  None, members, None, []))
         return name
 
     def _def_enum_type(self, expr, info, doc):
@@ -1752,9 +1919,11 @@ def _def_struct_type(self, expr, info, doc):
         base = expr.get('base')
         data = expr['data']
         ifcond = expr.get('if')
+        features = expr.get('features', [])
         self._def_entity(QAPISchemaObjectType(name, info, doc, ifcond, base,
                                               self._make_members(data, info),
-                                              None))
+                                              None,
+                                              self._make_features(features)))
 
     def _make_variant(self, case, typ, ifcond):
         return QAPISchemaObjectTypeVariant(case, typ, ifcond)
@@ -1795,7 +1964,7 @@ def _def_union_type(self, expr, info, doc):
             QAPISchemaObjectType(name, info, doc, ifcond, base, members,
                                  QAPISchemaObjectTypeVariants(tag_name,
                                                               tag_member,
-                                                              variants)))
+                                                              variants), []))
 
     def _def_alternate_type(self, expr, info, doc):
         name = expr['alternate']

scripts/qapi/doc.py

@@ -182,6 +182,17 @@ def texi_members(doc, what, base, variants, member_func):
     return '\n@b{%s:}\n@table @asis\n%s@end table\n' % (what, items)
 
 
+def texi_features(doc):
+    """Format the table of features"""
+    items = ''
+    for section in doc.features.values():
+        desc = texi_format(section.text)
+        items += '@item @code{%s}\n%s' % (section.name, desc)
+    if not items:
+        return ''
+    return '\n@b{Features:}\n@table @asis\n%s@end table\n' % (items)
+
+
 def texi_sections(doc, ifcond):
     """Format additional sections following arguments"""
     body = ''
@@ -201,6 +212,7 @@ def texi_entity(doc, what, ifcond, base=None, variants=None,
                 member_func=texi_member):
     return (texi_body(doc)
             + texi_members(doc, what, base, variants, member_func)
+            + texi_features(doc)
             + texi_sections(doc, ifcond))
 
 
@@ -220,7 +232,8 @@ def visit_enum_type(self, name, info, ifcond, members, prefix):
                                body=texi_entity(doc, 'Values', ifcond,
                                                 member_func=texi_enum_value)))
 
-    def visit_object_type(self, name, info, ifcond, base, members, variants):
+    def visit_object_type(self, name, info, ifcond, base, members, variants,
+                          features):
         doc = self.cur_doc
         if base and base.is_implicit():
             base = None

scripts/qapi/introspect.py

@@ -188,11 +188,15 @@ def visit_array_type(self, name, info, ifcond, element_type):
         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):

scripts/qapi/types.py

@@ -227,7 +227,8 @@ def visit_array_type(self, name, info, ifcond, element_type):
             self._genh.add(gen_array(name, element_type))
             self._gen_type_cleanup(name)
 
-    def visit_object_type(self, name, info, ifcond, base, members, variants):
+    def visit_object_type(self, name, info, ifcond, base, members, variants,
+                          features):
         # Nothing to do for the special empty builtin
         if name == 'q_empty':
             return

scripts/qapi/visit.py

@@ -324,7 +324,8 @@ def visit_array_type(self, name, info, ifcond, element_type):
             self._genh.add(gen_visit_decl(name))
             self._genc.add(gen_visit_list(name, element_type))
 
-    def visit_object_type(self, name, info, ifcond, base, members, variants):
+    def visit_object_type(self, name, info, ifcond, base, members, variants,
+                          features):
         # Nothing to do for the special empty builtin
         if name == 'q_empty':
             return

tests/Makefile.include

@@ -378,6 +378,12 @@ qapi-schema += event-boxed-empty.json
 qapi-schema += event-case.json
 qapi-schema += event-member-invalid-dict.json
 qapi-schema += event-nest-struct.json
+qapi-schema += features-bad-type.json
+qapi-schema += features-duplicate-name.json
+qapi-schema += features-missing-name.json
+qapi-schema += features-name-bad-type.json
+qapi-schema += features-no-list.json
+qapi-schema += features-unknown-key.json
 qapi-schema += flat-union-array-branch.json
 qapi-schema += flat-union-bad-base.json
 qapi-schema += flat-union-bad-discriminator.json

tests/qapi-schema/double-type.err

@@ -1,2 +1,2 @@
 tests/qapi-schema/double-type.json:2: Unknown key 'command' in struct 'bar'
-Valid keys are 'base', 'data', 'if', 'struct'.
+Valid keys are 'base', 'data', 'features', 'if', 'struct'.

tests/qapi-schema/features-bad-type.err

@@ -0,0 +1 @@
+tests/qapi-schema/features-bad-type.json:1: Feature of struct FeatureStruct0 requires a string name

tests/qapi-schema/features-bad-type.exit

@@ -0,0 +1 @@
+1

tests/qapi-schema/features-bad-type.json

@@ -0,0 +1,3 @@
+{ 'struct': 'FeatureStruct0',
+  'data': { 'foo': 'int' },
+  'features': [ [ 'a feature cannot be an array' ] ] }

tests/qapi-schema/features-duplicate-name.err

@@ -0,0 +1 @@
+tests/qapi-schema/features-duplicate-name.json:1: 'foo' (feature of FeatureStruct0) collides with 'foo' (feature of FeatureStruct0)

tests/qapi-schema/features-duplicate-name.exit

@@ -0,0 +1 @@
+1

tests/qapi-schema/features-duplicate-name.json

@@ -0,0 +1,3 @@
+{ 'struct': 'FeatureStruct0',
+  'data': { 'foo': 'int' },
+  'features': [ 'foo', 'bar', 'foo' ] }

tests/qapi-schema/features-missing-name.err

@@ -0,0 +1 @@
+tests/qapi-schema/features-missing-name.json:1: Key 'name' is missing from feature of struct FeatureStruct0

tests/qapi-schema/features-missing-name.exit

@@ -0,0 +1 @@
+1

tests/qapi-schema/features-missing-name.json

@@ -0,0 +1,3 @@
+{ 'struct': 'FeatureStruct0',
+  'data': { 'foo': 'int' },
+  'features': [ { 'if': 'defined(NAMELESS_FEATURES)' } ] }

tests/qapi-schema/features-name-bad-type.err

@@ -0,0 +1 @@
+tests/qapi-schema/features-name-bad-type.json:1: Feature of struct FeatureStruct0 requires a string name

tests/qapi-schema/features-name-bad-type.exit

@@ -0,0 +1 @@
+1

tests/qapi-schema/features-name-bad-type.json

@@ -0,0 +1,3 @@
+{ 'struct': 'FeatureStruct0',
+  'data': { 'foo': 'int' },
+  'features': [ { 'name': { 'feature-type': 'object' } } ] }

tests/qapi-schema/features-no-list.err

@@ -0,0 +1 @@
+tests/qapi-schema/features-no-list.json:1: Struct 'FeatureStruct0' requires an array for 'features'

tests/qapi-schema/features-no-list.exit

@@ -0,0 +1 @@
+1

tests/qapi-schema/features-no-list.json

@@ -0,0 +1,3 @@
+{ 'struct': 'FeatureStruct0',
+  'data': { 'foo': 'int' },
+  'features': 'bar' }

tests/qapi-schema/features-unknown-key.err

@@ -0,0 +1,2 @@
+tests/qapi-schema/features-unknown-key.json:1: Unknown key 'colour' in feature of struct FeatureStruct0
+Valid keys are 'if', 'name'.

tests/qapi-schema/features-unknown-key.exit

@@ -0,0 +1 @@
+1

tests/qapi-schema/features-unknown-key.json

@@ -0,0 +1,3 @@
+{ 'struct': 'FeatureStruct0',
+  'data': { 'foo': 'int' },
+  'features': [ { 'name': 'bar', 'colour': 'red' } ] }

tests/qapi-schema/qapi-schema-test.json

@@ -242,3 +242,42 @@
   { 'foo': 'TestIfStruct',
     'bar': { 'type': ['TestIfEnum'], 'if': 'defined(TEST_IF_EVT_BAR)' } },
   'if': 'defined(TEST_IF_EVT) && defined(TEST_IF_STRUCT)' }
+
+# test 'features' for structs
+
+{ 'struct': 'FeatureStruct0',
+  'data': { 'foo': 'int' },
+  'features': [] }
+{ 'struct': 'FeatureStruct1',
+  'data': { 'foo': 'int' },
+  'features': [ 'feature1' ] }
+{ 'struct': 'FeatureStruct2',
+  'data': { 'foo': 'int' },
+  'features': [ { 'name': 'feature1' } ] }
+{ 'struct': 'FeatureStruct3',
+  'data': { 'foo': 'int' },
+  'features': [ 'feature1', 'feature2' ] }
+{ 'struct': 'FeatureStruct4',
+  'data': { 'namespace-test': 'int' },
+  'features': [ 'namespace-test', 'int', 'name', 'if' ] }
+
+{ 'struct': 'CondFeatureStruct1',
+  'data': { 'foo': 'int' },
+  'features': [ { 'name': 'feature1', 'if': 'defined(TEST_IF_FEATURE_1)'} ] }
+{ 'struct': 'CondFeatureStruct2',
+  'data': { 'foo': 'int' },
+  'features': [ { 'name': 'feature1', 'if': 'defined(TEST_IF_FEATURE_1)'},
+                { 'name': 'feature2', 'if': 'defined(TEST_IF_FEATURE_2)'} ] }
+{ 'struct': 'CondFeatureStruct3',
+  'data': { 'foo': 'int' },
+  'features': [ { 'name': 'feature1', 'if': [ 'defined(TEST_IF_COND_1)',
+                                              'defined(TEST_IF_COND_2)'] } ] }
+{ 'command': 'test-features',
+  'data': { 'fs0': 'FeatureStruct0',
+            'fs1': 'FeatureStruct1',
+            'fs2': 'FeatureStruct2',
+            'fs3': 'FeatureStruct3',
+            'fs4': 'FeatureStruct4',
+            'cfs1': 'CondFeatureStruct1',
+            'cfs2': 'CondFeatureStruct2',
+            'cfs3': 'CondFeatureStruct3' } }

tests/qapi-schema/qapi-schema-test.out

@@ -354,3 +354,46 @@ object q_obj_TestIfEvent-arg
 event TestIfEvent q_obj_TestIfEvent-arg
    boxed=False
     if ['defined(TEST_IF_EVT) && defined(TEST_IF_STRUCT)']
+object FeatureStruct0
+    member foo: int optional=False
+object FeatureStruct1
+    member foo: int optional=False
+    feature feature1
+object FeatureStruct2
+    member foo: int optional=False
+    feature feature1
+object FeatureStruct3
+    member foo: int optional=False
+    feature feature1
+    feature feature2
+object FeatureStruct4
+    member namespace-test: int optional=False
+    feature namespace-test
+    feature int
+    feature name
+    feature if
+object CondFeatureStruct1
+    member foo: int optional=False
+    feature feature1
+        if ['defined(TEST_IF_FEATURE_1)']
+object CondFeatureStruct2
+    member foo: int optional=False
+    feature feature1
+        if ['defined(TEST_IF_FEATURE_1)']
+    feature feature2
+        if ['defined(TEST_IF_FEATURE_2)']
+object CondFeatureStruct3
+    member foo: int optional=False
+    feature feature1
+        if ['defined(TEST_IF_COND_1)', 'defined(TEST_IF_COND_2)']
+object q_obj_test-features-arg
+    member fs0: FeatureStruct0 optional=False
+    member fs1: FeatureStruct1 optional=False
+    member fs2: FeatureStruct2 optional=False
+    member fs3: FeatureStruct3 optional=False
+    member fs4: FeatureStruct4 optional=False
+    member cfs1: CondFeatureStruct1 optional=False
+    member cfs2: CondFeatureStruct2 optional=False
+    member cfs3: CondFeatureStruct3 optional=False
+command test-features q_obj_test-features-arg -> None
+   gen=True success_response=True boxed=False oob=False preconfig=False

tests/qapi-schema/test-qapi.py

@@ -38,7 +38,8 @@ def visit_array_type(self, name, info, ifcond, element_type):
         print('array %s %s' % (name, element_type.name))
         self._print_if(ifcond)
 
-    def visit_object_type(self, name, info, ifcond, base, members, variants):
+    def visit_object_type(self, name, info, ifcond, base, members, variants,
+                          features):
         print('object %s' % name)
         if base:
             print('    base %s' % base.name)
@@ -48,6 +49,10 @@ def visit_object_type(self, name, info, ifcond, base, members, variants):
             self._print_if(m.ifcond, 8)
         self._print_variants(variants)
         self._print_if(ifcond)
+        if features:
+            for f in features:
+                print('    feature %s' % f.name)
+                self._print_if(f.ifcond, 8)
 
     def visit_alternate_type(self, name, info, ifcond, variants):
         print('alternate %s' % name)

tests/qapi-schema/unknown-expr-key.err

@@ -1,2 +1,2 @@
 tests/qapi-schema/unknown-expr-key.json:2: Unknown keys 'bogus', 'phony' in struct 'bar'
-Valid keys are 'base', 'data', 'if', 'struct'.
+Valid keys are 'base', 'data', 'features', 'if', 'struct'.

tests/test-qmp-cmds.c

@@ -43,6 +43,14 @@ void qmp_user_def_cmd1(UserDefOne * ud1, Error **errp)
 {
 }
 
+void qmp_test_features(FeatureStruct0 *fs0, FeatureStruct1 *fs1,
+                       FeatureStruct2 *fs2, FeatureStruct3 *fs3,
+                       FeatureStruct4 *fs4, CondFeatureStruct1 *cfs1,
+                       CondFeatureStruct2 *cfs2, CondFeatureStruct3 *cfs3,
+                       Error **errp)
+{
+}
+
 UserDefTwo *qmp_user_def_cmd2(UserDefOne *ud1a,
                               bool has_udb1, UserDefOne *ud1b,
                               Error **errp)