diff mbox series

[v2,3/6] qapi: Remove wrapper struct for simple unions

Message ID 20201023161312.460406-4-kwolf@redhat.com
State New, archived
Headers show
Series qemu-storage-daemon: QAPIfy --chardev | expand

Commit Message

Kevin Wolf Oct. 23, 2020, 4:13 p.m. UTC
Variants of simple unions are always contained in a wrapper object
called 'data' that serves no real use. When mapping a QAPI object to the
command line, this becomes very visible to users because they have to
add one or more useless 'data.' to many option names.

As a first step towards avoiding this painful CLI experience, this gets
rid of the 'data' indirection internally: The QAPI parser doesn't use a
wrapper object as the variant type any more, so the indirection is
removed from the generated C types. As a result, the C type looks the
same for flat and simple unions now. A large part of this patch is
mechanical conversion of C code to remove the 'data' indirection.

Conceptually, the important change is that variants can now have flat
and wrapped representations. For a transitioning period, we'll allow
variants to support both representations in a later patch. Eventually,
the plan is to deprecate and remove wrapped representations entirely,
unifying simple and flat unions.

The externally visible interfaces stay unchanged: Visitors still expect
the 'data' wrappers, and introspection still shows it.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 docs/devel/qapi-code-gen.txt           | 32 ++++++++----
 docs/sphinx/qapidoc.py                 | 14 +++---
 backends/tpm/tpm_emulator.c            |  3 +-
 backends/tpm/tpm_passthrough.c         |  4 +-
 block/crypto.c                         |  3 +-
 block/qcow2.c                          |  9 ++--
 block/vmdk.c                           | 14 ++----
 blockdev.c                             | 36 ++++++-------
 chardev/char-file.c                    |  5 +-
 chardev/char-mux.c                     |  5 +-
 chardev/char-parallel.c                |  5 +-
 chardev/char-pipe.c                    |  7 ++-
 chardev/char-ringbuf.c                 |  5 +-
 chardev/char-serial.c                  |  5 +-
 chardev/char-socket.c                  | 13 ++---
 chardev/char-stdio.c                   |  5 +-
 chardev/char-udp.c                     | 11 ++--
 chardev/char.c                         | 10 ++--
 chardev/msmouse.c                      |  4 +-
 chardev/spice.c                        | 10 ++--
 chardev/wctablet.c                     |  4 +-
 hw/core/numa.c                         |  6 +--
 hw/display/xenfb.c                     |  8 +--
 hw/input/hid.c                         |  8 +--
 hw/input/ps2.c                         |  6 +--
 hw/input/virtio-input-hid.c            |  8 +--
 hw/mem/pc-dimm.c                       | 18 +++----
 hw/virtio/virtio-mem-pci.c             |  3 +-
 hw/virtio/virtio-pmem-pci.c            |  3 +-
 monitor/hmp-cmds.c                     | 14 +++---
 qemu-keymap.c                          |  2 +-
 replay/replay-input.c                  | 46 +++++++----------
 tests/test-char.c                      | 12 ++---
 tests/test-clone-visitor.c             | 14 +++---
 tests/test-qmp-cmds.c                  |  2 +-
 tests/test-qobject-input-visitor.c     | 24 ++++-----
 tests/test-qobject-output-visitor.c    | 24 ++++-----
 ui/console.c                           |  5 +-
 ui/input-keymap.c                      | 12 ++---
 ui/input-legacy.c                      | 12 ++---
 ui/input.c                             | 43 ++++++++--------
 ui/spice-app.c                         |  5 +-
 util/qemu-sockets.c                    |  8 +--
 scripts/qapi/introspect.py             |  7 ++-
 scripts/qapi/schema.py                 | 48 ++++++++++++++----
 scripts/qapi/visit.py                  | 28 +++++++++++
 tests/qapi-schema/doc-good.out         |  8 +--
 tests/qapi-schema/qapi-schema-test.out | 70 +++++++-------------------
 48 files changed, 322 insertions(+), 326 deletions(-)

Comments

Markus Armbruster Oct. 25, 2020, 9:16 a.m. UTC | #1
I apologize for writing so much.  It's the only way I know to figure out
how things work.

This may feel like I'm trying to shoot down your patch.  I'm not!  I'm
merely trying to understand and maybe improve it.  I'd love to get rid
of implicit wrapper objects, actually.  They complicate things in
places.  More on that below.

Kevin Wolf <kwolf@redhat.com> writes:

> Variants of simple unions are always contained in a wrapper object
> called 'data' that serves no real use.

Not quite.

Two aspects: on the wire, and in C.  Which aspect this patch is about is
not clear to me at this point.

1. One the wire

qapi-code-gen.txt documents:

    A simple union can always be re-written as a flat union where the base
    class has a single member named 'type', and where each branch of the
    union has a struct with a single member named 'data'.  That is,

     { 'union': 'Simple', 'data': { 'one': 'str', 'two': 'int' } }

    is identical on the wire to:

     { 'enum': 'Enum', 'data': ['one', 'two'] }
     { 'struct': 'Branch1', 'data': { 'data': 'str' } }
     { 'struct': 'Branch2', 'data': { 'data': 'int' } }
     { 'union': 'Flat', 'base': { 'type': 'Enum' }, 'discriminator': 'type',
       'data': { 'one': 'Branch1', 'two': 'Branch2' } }

Actual wire format:

    { "type": "one", "data": "some-string" }
    { "type": "two", "data": 1 }

"data" does serve a use here.

If we change the second branch from 'int' to some complex type, say

    { 'struct': 'Object', 'data': { 'x': 'int', 'y': 'int' } }
    { 'union': 'Simple', 'data': { 'one': 'str', 'two': 'Object' } }

    { 'struct': 'Branch2', 'data': { 'data': 'Object' } }

we get

    { "type": "one", "data": "some-string" }
    { "type": "two", "data": { "x": 1, "y": 2 } }

where the "data" wrapper is indeed pointless for branch "two".  We can
get rid of it by replacing the equivalent flat union by

    { 'union': 'Flatter', 'base': { 'type': 'Enum' }, 'discriminator': 'type',
      'data': { 'one': 'Branch1', 'two': 'Object' } }

to get

    { "type": "one", "data": "some-string" }
    { "type": "two", "x": 1, "y": 2 }

2. In C

The C types generated for the simple union and its corresponding flat
union are structurally equivalent (qapi-code-gen.txt doesn't document
this, maybe it should):

    typedef enum SimpleKind {
        SIMPLE_KIND_ONE,
        SIMPLE_KIND_TWO,
        SIMPLE_KIND__MAX,
    } SimpleKind;

    struct q_obj_str_wrapper {
        char *data;
    };

    struct q_obj_Object_wrapper {
        Object *data;
    };

    struct Simple {
        SimpleKind type;
        union { /* union tag is @type */
            q_obj_str_wrapper one;
            q_obj_Object_wrapper two;
        } u;
    };

and

    typedef enum Enum {
        ENUM_ONE,
        ENUM_TWO,
        ENUM__MAX,
    } Enum;

    struct Branch1 {
        char *data;
    };

    struct Branch2 {
        Object *data;
    };

    struct Flat {
        Enum type;
        union { /* union tag is @type */
            Branch1 one;
            Branch2 two;
        } u;
    };

Here, the wrapper is pointless for both branches.

For the "flatter" flat union, we get

    struct Flatter {
        Enum type;
        union { /* union tag is @type */
            Branch1 one;
            Object two;
        } u;
    };

One of two pointless wrappers are gone.

>                                        When mapping a QAPI object to the
> command line, this becomes very visible to users because they have to
> add one or more useless 'data.' to many option names.

It's useless in QMP, too.

> As a first step towards avoiding this painful CLI experience,

It's painful in CLI when you use dotted keys syntax, because that syntax
makes nesting painful.

I dislike pointless nesting even when the syntax makes it almost not
painful, like in QMP.

>                                                               this gets
> rid of the 'data' indirection internally: The QAPI parser doesn't use a
> wrapper object as the variant type any more, so the indirection is
> removed from the generated C types. As a result, the C type looks the
> same for flat and simple unions now.

Really?

For the simple union we now generate

    struct Simple {
        SimpleKind type;
        union { /* union tag is @type */
            char *one;
            Object two;
        } u;
    };

Same as what flat union?

Certainly not 'Flatter', which has branch 'one' wrapped in a struct.

The naive attempt to not wrap it

    { 'union': 'Flattest',
      'base': { 'type': 'Enum' }, 'discriminator': 'type',
      'data': { 'one': 'str', 'two': 'Object' } }

is invalid, because "All flat union branches must be of struct type"
(qapi-code-gen.txt).  qapi-gen.py duly rejects it with "branch 'one'
cannot use built-in type 'str'".  Remember, flat unions "splice in" the
variant members on the wire.  There have to be members for that.

>                                      A large part of this patch is
> mechanical conversion of C code to remove the 'data' indirection.

How did you do the conversion?  Coccinelle?  Regexps?  Manual until
compiler is happy?

> Conceptually, the important change is that variants can now have flat
> and wrapped representations. For a transitioning period, we'll allow
> variants to support both representations in a later patch.

Alright, now I'm confused.

What exactly is a "flat representation", and when is it used?

What's a "wrapped representation", and when is it used?

Are you talking about the internal representation,
i.e. QAPISchemaVariant?

>                                                            Eventually,
> the plan is to deprecate and remove wrapped representations entirely,
> unifying simple and flat unions.
>
> The externally visible interfaces stay unchanged: Visitors still expect
> the 'data' wrappers, and introspection still shows it.

Visitors are externally visible only indirectly: the QObject visitors
determine the wire format.  But that's detail.  Perhaps:

    The wire format remains the same.  The 'data' wrappers are still
    there, and introspection and documentation still show them.  This
    necessitates new special cases in visit.py, introspect.py, and
    qapidoc.py.

> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  docs/devel/qapi-code-gen.txt           | 32 ++++++++----
>  docs/sphinx/qapidoc.py                 | 14 +++---
>  backends/tpm/tpm_emulator.c            |  3 +-
>  backends/tpm/tpm_passthrough.c         |  4 +-
>  block/crypto.c                         |  3 +-
>  block/qcow2.c                          |  9 ++--
>  block/vmdk.c                           | 14 ++----
>  blockdev.c                             | 36 ++++++-------
>  chardev/char-file.c                    |  5 +-
>  chardev/char-mux.c                     |  5 +-
>  chardev/char-parallel.c                |  5 +-
>  chardev/char-pipe.c                    |  7 ++-
>  chardev/char-ringbuf.c                 |  5 +-
>  chardev/char-serial.c                  |  5 +-
>  chardev/char-socket.c                  | 13 ++---
>  chardev/char-stdio.c                   |  5 +-
>  chardev/char-udp.c                     | 11 ++--
>  chardev/char.c                         | 10 ++--
>  chardev/msmouse.c                      |  4 +-
>  chardev/spice.c                        | 10 ++--
>  chardev/wctablet.c                     |  4 +-
>  hw/core/numa.c                         |  6 +--
>  hw/display/xenfb.c                     |  8 +--
>  hw/input/hid.c                         |  8 +--
>  hw/input/ps2.c                         |  6 +--
>  hw/input/virtio-input-hid.c            |  8 +--
>  hw/mem/pc-dimm.c                       | 18 +++----
>  hw/virtio/virtio-mem-pci.c             |  3 +-
>  hw/virtio/virtio-pmem-pci.c            |  3 +-
>  monitor/hmp-cmds.c                     | 14 +++---
>  qemu-keymap.c                          |  2 +-
>  replay/replay-input.c                  | 46 +++++++----------
>  tests/test-char.c                      | 12 ++---
>  tests/test-clone-visitor.c             | 14 +++---
>  tests/test-qmp-cmds.c                  |  2 +-
>  tests/test-qobject-input-visitor.c     | 24 ++++-----
>  tests/test-qobject-output-visitor.c    | 24 ++++-----
>  ui/console.c                           |  5 +-
>  ui/input-keymap.c                      | 12 ++---
>  ui/input-legacy.c                      | 12 ++---
>  ui/input.c                             | 43 ++++++++--------
>  ui/spice-app.c                         |  5 +-
>  util/qemu-sockets.c                    |  8 +--
>  scripts/qapi/introspect.py             |  7 ++-
>  scripts/qapi/schema.py                 | 48 ++++++++++++++----
>  scripts/qapi/visit.py                  | 28 +++++++++++
>  tests/qapi-schema/doc-good.out         |  8 +--
>  tests/qapi-schema/qapi-schema-test.out | 70 +++++++-------------------
>  48 files changed, 322 insertions(+), 326 deletions(-)
>
> diff --git a/docs/devel/qapi-code-gen.txt b/docs/devel/qapi-code-gen.txt
> index c6438c6aa9..9722c1a204 100644
> --- a/docs/devel/qapi-code-gen.txt
> +++ b/docs/devel/qapi-code-gen.txt
> @@ -310,7 +310,20 @@ The BRANCH's STRING name is the branch name.
>  The BRANCH's value defines the branch's properties, in particular its
>  type.  The form TYPE-REF is shorthand for { 'type': TYPE-REF }.
>  
> -A simple union type defines a mapping from automatic discriminator
> +Each branch can have flat or wrapped representation in the Client JSON
> +Protocol.
> +
> +Wrapped representation of a branch means that it is represented by a
> +'data' member that is of the specified data type corresponding to the
> +discriminator value.
> +
> +Flat representation means that the union forms a single object that
> +contains both common members (from the base type) and the selected
> +branch's members, without any additional nesting.  The two sets of
> +member names must be disjoint.

You talk about representation of branches before saying anything about
representation of unions.  But let's focus on the contents now.  How to
best present it can wait.

> +
> +A simple union type automatically contains the 'type' member as a
> +discriminator and defines a mapping from automatic discriminator
>  values to data types like in this example:
>  
>   { 'struct': 'BlockdevOptionsFile', 'data': { 'filename': 'str' } }
> @@ -321,10 +334,8 @@ values to data types like in this example:
>     'data': { 'file': 'BlockdevOptionsFile',
>               'qcow2': 'BlockdevOptionsQcow2' } }
>  
> -In the Client JSON Protocol, a simple union is represented by an
> -object that contains the 'type' member as a discriminator, and a
> -'data' member that is of the specified data type corresponding to the
> -discriminator value, as in these examples:
> +In the Client JSON Protocol, all simple union branches have wrapped
> +representation, as in these examples:
>  
>   { "type": "file", "data": { "filename": "/some/place/my-image" } }
>   { "type": "qcow2", "data": { "backing": "/some/place/my-image",
> @@ -344,13 +355,12 @@ object, it defines common members just like a struct type's 'data'
>  member defines struct type members.  If it is a STRING, it names a
>  struct type whose members are the common members.
>  
> -All flat union branches must be of struct type.
> +Member 'discriminator' must name a non-optional enum-typed member of
> +the base struct and defines the option that should server as the
> +discrimiator.

s/server as the discrimiator/serve as discriminator/

>  
> -In the Client JSON Protocol, a flat union is represented by an object
> -with the common members (from the base type) and the selected branch's
> -members.  The two sets of member names must be disjoint.  Member
> -'discriminator' must name a non-optional enum-typed member of the base
> -struct.
> +All flat union branches must be of struct type.  They have always flat
> +representation.

So, simple unions use wrapped representation, flat unions use flat
representation, but I have to read the whole section at least twice to
figure that out :)  Let's not worry about that now.

>  
>  The following example enhances the above simple union example by
>  adding an optional common member 'read-only', renaming the
> diff --git a/docs/sphinx/qapidoc.py b/docs/sphinx/qapidoc.py
> index e03abcbb95..75f6721e29 100644
> --- a/docs/sphinx/qapidoc.py
> +++ b/docs/sphinx/qapidoc.py

Best to review the changes to the QAPI generator from frontend to
backends: schema.py first, then come back here.

> @@ -183,12 +183,14 @@ class QAPISchemaGenRSTVisitor(QAPISchemaVisitor):
>  
>          if variants:
>              for v in variants.variants:
> -                if v.type.is_implicit():
> -                    assert not v.type.base and not v.type.variants
> -                    for m in v.type.local_members:
> -                        term = self._nodes_for_one_member(m)
> -                        term.extend(self._nodes_for_variant_when(variants, v))
> -                        dlnode += self._make_dlitem(term, None)
> +                if v.wrapped:
> +                    term = [nodes.literal('', 'data'),
> +                            nodes.Text(': '),
> +                            nodes.literal('', v.type.doc_type())]
> +                    term.extend(self._nodes_for_variant_when(variants, v))
> +                    dlnode += self._make_dlitem(term, None)
> +                elif v.type.is_implicit():
> +                    assert v.type.name == 'q_empty'
>                  else:
>                      term = [nodes.Text('The members of '),
>                              nodes.literal('', v.type.doc_type())]
[...]
> diff --git a/scripts/qapi/introspect.py b/scripts/qapi/introspect.py
> index fafec94e02..1c4e3407a3 100644
> --- a/scripts/qapi/introspect.py
> +++ b/scripts/qapi/introspect.py
> @@ -188,7 +188,12 @@ const QLitObject %(c_name)s = %(c_string)s;
>                  'variants': [self._gen_variant(v) for v in variants]}
>  
>      def _gen_variant(self, variant):
> -        obj = {'case': variant.name, 'type': self._use_type(variant.type)}
> +        if variant.wrapped:
> +            obj = {'case': variant.name,
> +                   'type': self._use_type(variant.wrapper_type)}
> +        else:
> +            obj = {'case': variant.name,
> +                   'type': self._use_type(variant.type)}
>          return _make_tree(obj, variant.ifcond, None)
>  
>      def visit_builtin_type(self, name, info, json_type):
> diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
> index 720449feee..17525b4216 100644
> --- a/scripts/qapi/schema.py
> +++ b/scripts/qapi/schema.py
> @@ -216,6 +216,11 @@ class QAPISchemaBuiltinType(QAPISchemaType):
>          self._json_type_name = json_type
>          self._c_type_name = c_type
>  
> +    def check(self, schema):
> +        # Don't check twice, it would fail an assertion
> +        if not self._checked:
> +            super().check(schema)
> +

How can this get called twice?

I'm asking because I remember the last time I cleaned up .check()
recursion (commit f9d1743b9b0).  Just glancing at its commit message
brings back the headache.

>      def c_name(self):
>          return self.name
>  

Further down in QAPISchemaObjectType:

       @property
       def ifcond(self):
           assert self._checked
           if isinstance(self._ifcond, QAPISchemaType):
               # Simple union wrapper type inherits from wrapped type;
               # see _make_implicit_object_type()
               return self._ifcond.ifcond
           return self._ifcond

Is isinstance(self._ifcond, QAPISchemaType) still possible?  See
_make_implicit_object_type() below.

> @@ -593,18 +598,21 @@ class QAPISchemaVariants:
           if self._tag_name:    # flat union
               # branches that are not explicitly covered get an empty type
               cases = {v.name for v in self.variants}
               for m in self.tag_member.type.members:
                   if m.name not in cases:
                       v = QAPISchemaVariant(m.name, self.info,
                                             'q_empty', m.ifcond)

Note for later: the code to create a default empty variant stays the
same.

                       v.set_defined_in(self.tag_member.defined_in)
                       self.variants.append(v)
           [...]
           for v in self.variants:
               v.check(schema)
               # Union names must match enum values; alternate names are
               # checked separately. Use 'seen' to tell the two apart.
               if seen:
                   if v.name not in self.tag_member.type.member_names():
                       raise QAPISemError(
                           self.info,
>                          "branch '%s' is not a value of %s"
>                          % (v.name, self.tag_member.type.describe()))
>                  if (not isinstance(v.type, QAPISchemaObjectType)
> -                        or v.type.variants):
> +                        or v.type.variants) and v.flat:
>                      raise QAPISemError(
>                          self.info,
>                          "%s cannot use %s"
>                          % (v.describe(self.info), v.type.describe()))

Before the patch: check branch type is an object without variants.  For
flat unions, this is documented in qapi-code-gen.txt: "All flat union
branches must be of struct type".  For simple unions, the wrapper types
spliced in by the desugaring ensure this can't fail.

What the hunk does: permit arbitrary branch types when not v.flat.  To
make sense of it, we need to understand the meaning of v.flat.  See
below.

> -                v.type.check(schema)
> +                if isinstance(v.type, QAPISchemaObjectType):
> +                    v.type.check(schema)

Since we want to recurse only for object types (see commit f9d1743b9b0),
and other types are now possible when not v.flat, the recursion now
needs to be guarded.  Okay.

>  
>      def check_clash(self, info, seen):
>          for v in self.variants:
>              # Reset seen map for each variant, since qapi names from one
> -            # branch do not affect another branch
> -            v.type.check_clash(info, dict(seen))
> +            # branch do not affect another branch.  Variants that are
> +            # never flat don't even conflict with the base.

What do you mean by "never flat"?  Could a variant be sometimes flat?

> +            if isinstance(v.type, QAPISchemaObjectType):
> +                v.type.check_clash(info, dict(seen) if v.flat else {})

The guard is necessary because v.type has method .check_clash() only if
it's an object type.

.check() ensures that v.type is an object type without variants when
v.flat.

So:

* If v.flat, no change.

* If not v.flat and v.type is an object type (possibly with variants),
  we run its .check_clash() with an empty seen.  What does this
  accomplish?

* If not v.flat and v.type is not an object type, we do nothing.

>  
>  
>  class QAPISchemaMember:
> @@ -705,9 +713,22 @@ class QAPISchemaObjectTypeMember(QAPISchemaMember):
>  class QAPISchemaVariant(QAPISchemaObjectTypeMember):
>      role = 'branch'
>  
> -    def __init__(self, name, info, typ, ifcond=None):
> +    def __init__(self, name, info, typ, ifcond=None, flat=True,
> +                 wrapper_type=None):
>          super().__init__(name, info, typ, False, ifcond)
>  
> +        self.flat = flat
> +        self.wrapped = bool(wrapper_type)
> +        self.wrapper_type = wrapper_type
> +
> +        # For now, unions are either flat or wrapped, never both
> +        assert self.flat or self.wrapped
> +        assert not (self.flat and self.wrapped)

The comment makes me expect

           assert self.flat == not self.wrapped

Moreover, .flat and .wrapped seem to be redundant with .wrapper_type.

Hmm, I see the next patch will change this again.  I'm therefore
reserving judgement until the end of the series.

The constructor is called in three places:

* QAPISchema._make_variant(), call unchanged (see below), therefore flat

* QAPISchema._make_simple_variant(), now passes flat=False, see below
  for details

* QAPISchemaVariants.check(), call unchanged (see below), therefore flat

> +
> +    def check(self, schema):
> +        super().check(schema)
> +        if self.wrapped:
> +            self.wrapper_type.check(schema)

Commit f9d1743b9b0: "An entity's .check() recurses into another entity's
.check() only if the C struct generated for the former contains the C
struct generated for the latter (pointers don't count).  This is used to
detect "object contains itself".

Can you explain why we want to recurse here?

>  

pycodestyle-3 complains:

    scripts/qapi/schema.py:733:1: E302 expected 2 blank lines, found 1

>  class QAPISchemaCommand(QAPISchemaEntity):
>      meta = 'command'
> @@ -1017,14 +1038,19 @@ class QAPISchema:

Not changed:

       def _make_implicit_object_type(self, name, info, ifcond, role, members):
           if not members:
               return None
           # See also QAPISchemaObjectTypeMember.describe()
           name = 'q_obj_%s-%s' % (name, role)
           typ = self.lookup_entity(name, QAPISchemaObjectType)
           if typ:
               # The implicit object type has multiple users.  This can
               # happen only for simple unions' implicit wrapper types.
               # Its ifcond should be the disjunction of its user's
               # ifconds.  Not implemented.  Instead, we always pass the
               # wrapped type's ifcond, which is trivially the same for all
               # users.  It's also necessary for the wrapper to compile.
               # But it's not tight: the disjunction need not imply it.  We
               # may end up compiling useless wrapper types.
               # TODO kill simple unions or implement the disjunction

               # pylint: disable=protected-access
               assert (ifcond or []) == typ._ifcond
           else:
               self._def_entity(QAPISchemaObjectType(
                   name, info, None, ifcond, None, None, members, None))
           return name

Can typ still be non-None?

[...]
>      def _make_variant(self, case, typ, ifcond, info):
>          return QAPISchemaVariant(case, info, typ, ifcond)
>  
> -    def _make_simple_variant(self, case, typ, ifcond, info):
> +    def _make_simple_variant(self, union_name, case, typ, ifcond, info):
>          if isinstance(typ, list):
>              assert len(typ) == 1
>              typ = self._make_array_type(typ[0], info)
> -        typ = self._make_implicit_object_type(
> -            typ, info, self.lookup_type(typ),
> -            'wrapper', [self._make_member('data', typ, None, None, info)])
> -        return QAPISchemaVariant(case, info, typ, ifcond)
> +
> +        # The wrapper type is only used for introspection compatibility.
> +        # Don't add it to the entity list of the schema.
> +        wrapper_name = 'q_obj_%s-%s-wrapper' % (union_name, case)
> +        wrapper_member = self._make_member('data', typ, None, None, info)
> +        wrapper_type = QAPISchemaObjectType(wrapper_name, info, None, ifcond,
> +                                            None, None, [wrapper_member], None)

This adds another place where we create implicit object types.  Comments
need to be updated, e.g. in QAPISchemaObjectType.is_implicit().

> +        return QAPISchemaVariant(case, info, typ, ifcond, flat=False,
> +                                 wrapper_type=wrapper_type)

This changes argument @typ from wrapper to wrapped type.  The wrapper is
passed as @wrapped_type instead.

It's not the same wrapper, though.

Before the patch, we have a common q_obj_<wrapped-type>-wrapper.
_make_implicit_object_type() creates it unless it exists already.

After the patch, we have q_obj_<union-type>-<branch-name>-wrapper.  The
wrapper de-duplication is gone.  _make_implicit_object_type() is
bypassed.

But is this bypass necessary?  I suspect it's to not "add it to the
entity list of the schema".  Why not?

If the loss of de-duplication is intentional, the commit message should
mention it.

>  
>      def _def_union_type(self, expr, info, doc):
>          name = expr['union']
> @@ -1044,7 +1070,7 @@ class QAPISchema:
>                          for (key, value) in data.items()]
>              members = []
>          else:
> -            variants = [self._make_simple_variant(key, value['type'],
> +            variants = [self._make_simple_variant(name, key, value['type'],
>                                                    value.get('if'), info)
>                          for (key, value) in data.items()]
>              enum = [{'name': v.name, 'if': v.ifcond} for v in variants]
> diff --git a/scripts/qapi/visit.py b/scripts/qapi/visit.py
> index 339f152152..f72567cbcc 100644
> --- a/scripts/qapi/visit.py
> +++ b/scripts/qapi/visit.py
> @@ -118,6 +118,34 @@ bool visit_type_%(c_name)s_members(Visitor *v, %(c_name)s *obj, Error **errp)
           for var in variants.variants:
               case_str = c_enum_const(tag_member.type.name, var.name,
                                       tag_member.type.prefix)
               ret += gen_if(var.ifcond)

Before the patch, special case 'q_empty' (which has no visitor), general
case object type.

The patch adds two more cases.


This is special case 'q_empty':

               if var.type.name == 'q_empty':
                   # valid variant and nothing to do
                   ret += mcgen('''
       case %(case)s:
>          break;
>  ''',
>                               case=case_str)


New case "not an object type":

> +            elif not isinstance(var.type, QAPISchemaObjectType):
> +                assert not var.flat
> +                ret += mcgen('''
> +    case %(case)s:
> +        return visit_type_%(c_type)s(v, "data", &obj->u.%(c_name)s, errp);
> +''',
> +                             case=case_str,
> +                             c_type=var.type.c_name(), c_name=c_name(var.name))

Before the patch, we visit the implicit wrapper, using the general case
below, i.e.

           return visit_type_q_obj_T_wrapper_members(v, &obj->u.BRANCH, errp);

visit_type_q_obj_T_members() looks like this:

       bool visit_type_q_obj_T_wrapper_members(Visitor *v, q_obj_T_wrapper *obj, Error **errp)
       {
           if (!visit_type_T(v, "data", &obj->data, errp)) {
               return false;
           }
           return true;
       }

The new code calls visit_type_T() directly.  The only change (I think /
hope) is from &obj->u.BASE->data to &obj->u.BASE, which is what we want.


New case "wrapped object type":

> +            elif var.wrapped:
> +                ret += mcgen('''
> +    case %(case)s:
> +    {
> +        bool ok;
> +
> +        if (!visit_start_struct(v, "data", NULL, 0, errp)) {
> +            return false;
> +        }
> +        ok = visit_type_%(c_type)s_members(v, &obj->u.%(c_name)s, errp);
> +        if (ok) {
> +            ok = visit_check_struct(v, errp);
> +        }
> +        visit_end_struct(v, NULL);
> +        return ok;
> +    }
> +''',
> +                             case=case_str,
> +                             c_type=var.type.c_name(), c_name=c_name(var.name))
> +
>              else:
>                  ret += mcgen('''

To compensate for the implicit wrapper type's removal from the C type,
we splice in a virtual struct visit.

Before the patch, we visit the implicit wrapper, using the general case
below, i.e.

           return visit_type_q_obj_T_wrapper_members(v, &obj->u.BRANCH, errp);

visit_type_q_obj_T_members() looks like this:

       bool visit_type_q_obj_T_wrapper_members(Visitor *v, q_obj_T_wrapper *obj, Error **errp)
       {
           if (!visit_type_T(v, "data", &obj->data, errp)) {
               return false;
           }
           return true;
       }

When T is an object type, visit_type_T() looks like this:

       bool visit_type_T(Visitor *v, const char *name,
                        T **obj, Error **errp)
       {
           bool ok = false;

           if (!visit_start_struct(v, name, (void **)obj, sizeof(T), errp)) {
               return false;
           }
           if (!*obj) {
               /* incomplete */
               assert(visit_is_dealloc(v));
               ok = true;
               goto out_obj;
           }
           if (!visit_type_T_members(v, *obj, errp)) {
               goto out_obj;
           }
           ok = visit_check_struct(v, errp);
       out_obj:
           visit_end_struct(v, (void **)obj);
           if (!ok && visit_is_input(v)) {
               qapi_free_T(*obj);
               *obj = NULL;
           }
           return ok;
       }

Compare to the new code:

1. The new code passes NULL to visit_start_struct() and
   visit_end_struct(), i.e. the visit of "data" becomes virtual.

2. The new code passes &obj->u.BRANCH instead of &obj->u.BRANCH->data.

3. The new code doesn't have the /* incomplete */ conditional.

4. The new code doesn't have the conditional qapi_free_T().

The first two compensate for the wrapper type's removal from the C type.

Why are the last two not needed?


Case "unwrapped object type" (same as old general case):

>      case %(case)s:
           return visit_type_%(c_type)s_members(v, &obj->u.%(c_name)s, errp);
   ''',
                                case=case_str,
                                c_type=var.type.c_name(), c_name=c_name(var.name))

               ret += gen_endif(var.ifcond)
           ret += mcgen('''
       default:
           abort();
       }
   ''')

Now I should go back to qapidoc.py and introspect.py.  But I think we
have enough to discuss about this patch already, so I'm postponing their
review, and move on the the next patch.

> diff --git a/tests/qapi-schema/doc-good.out b/tests/qapi-schema/doc-good.out
> index 419284dae2..bcbcbd2fce 100644
> --- a/tests/qapi-schema/doc-good.out
> +++ b/tests/qapi-schema/doc-good.out
> @@ -31,10 +31,6 @@ object Object
>      case two: Variant2
>          if ['IFTWO']
>      feature union-feat1
> -object q_obj_Variant1-wrapper
> -    member data: Variant1 optional=False
> -object q_obj_Variant2-wrapper
> -    member data: Variant2 optional=False
>  enum SugaredUnionKind
>      member one
>      member two
> @@ -42,8 +38,8 @@ enum SugaredUnionKind
>  object SugaredUnion
>      member type: SugaredUnionKind optional=False
>      tag type
> -    case one: q_obj_Variant1-wrapper
> -    case two: q_obj_Variant2-wrapper
> +    case one: Variant1
> +    case two: Variant2
>          if ['IFTWO']
>      feature union-feat2
>  alternate Alternate
> diff --git a/tests/qapi-schema/qapi-schema-test.out b/tests/qapi-schema/qapi-schema-test.out
> index 8868ca0dca..a4e4051c61 100644
> --- a/tests/qapi-schema/qapi-schema-test.out
> +++ b/tests/qapi-schema/qapi-schema-test.out
> @@ -125,36 +125,6 @@ alternate AltStrObj
>      tag type
>      case s: str
>      case o: TestStruct
> -object q_obj_intList-wrapper
> -    member data: intList optional=False
> -object q_obj_int8List-wrapper
> -    member data: int8List optional=False
> -object q_obj_int16List-wrapper
> -    member data: int16List optional=False
> -object q_obj_int32List-wrapper
> -    member data: int32List optional=False
> -object q_obj_int64List-wrapper
> -    member data: int64List optional=False
> -object q_obj_uint8List-wrapper
> -    member data: uint8List optional=False
> -object q_obj_uint16List-wrapper
> -    member data: uint16List optional=False
> -object q_obj_uint32List-wrapper
> -    member data: uint32List optional=False
> -object q_obj_uint64List-wrapper
> -    member data: uint64List optional=False
> -object q_obj_numberList-wrapper
> -    member data: numberList optional=False
> -object q_obj_boolList-wrapper
> -    member data: boolList optional=False
> -object q_obj_strList-wrapper
> -    member data: strList optional=False
> -object q_obj_sizeList-wrapper
> -    member data: sizeList optional=False
> -object q_obj_anyList-wrapper
> -    member data: anyList optional=False
> -object q_obj_StatusList-wrapper
> -    member data: StatusList optional=False
>  enum UserDefListUnionKind
>      member integer
>      member s8
> @@ -174,21 +144,21 @@ enum UserDefListUnionKind
>  object UserDefListUnion
>      member type: UserDefListUnionKind optional=False
>      tag type
> -    case integer: q_obj_intList-wrapper
> -    case s8: q_obj_int8List-wrapper
> -    case s16: q_obj_int16List-wrapper
> -    case s32: q_obj_int32List-wrapper
> -    case s64: q_obj_int64List-wrapper
> -    case u8: q_obj_uint8List-wrapper
> -    case u16: q_obj_uint16List-wrapper
> -    case u32: q_obj_uint32List-wrapper
> -    case u64: q_obj_uint64List-wrapper
> -    case number: q_obj_numberList-wrapper
> -    case boolean: q_obj_boolList-wrapper
> -    case string: q_obj_strList-wrapper
> -    case sizes: q_obj_sizeList-wrapper
> -    case any: q_obj_anyList-wrapper
> -    case user: q_obj_StatusList-wrapper
> +    case integer: intList
> +    case s8: int8List
> +    case s16: int16List
> +    case s32: int32List
> +    case s64: int64List
> +    case u8: uint8List
> +    case u16: uint16List
> +    case u32: uint32List
> +    case u64: uint64List
> +    case number: numberList
> +    case boolean: boolList
> +    case string: strList
> +    case sizes: sizeList
> +    case any: anyList
> +    case user: StatusList
>  include include/sub-module.json
>  command user_def_cmd None -> None
>      gen=True success_response=True boxed=False oob=False preconfig=False
> @@ -263,14 +233,12 @@ object __org.qemu_x-Struct
>      base __org.qemu_x-Base
>      member __org.qemu_x-member2: str optional=False
>      member wchar-t: int optional=True
> -object q_obj_str-wrapper
> -    member data: str optional=False
>  enum __org.qemu_x-Union1Kind
>      member __org.qemu_x-branch
>  object __org.qemu_x-Union1
>      member type: __org.qemu_x-Union1Kind optional=False
>      tag type
> -    case __org.qemu_x-branch: q_obj_str-wrapper
> +    case __org.qemu_x-branch: str
>  alternate __org.qemu_x-Alt1
>      tag type
>      case __org.qemu_x-branch: str
> @@ -305,8 +273,6 @@ enum TestIfEnum
>      member bar
>          if ['defined(TEST_IF_ENUM_BAR)']
>      if ['defined(TEST_IF_ENUM)']
> -object q_obj_TestStruct-wrapper
> -    member data: TestStruct optional=False
>  enum TestIfUnionKind
>      member foo
>      member union_bar
> @@ -315,8 +281,8 @@ enum TestIfUnionKind
>  object TestIfUnion
>      member type: TestIfUnionKind optional=False
>      tag type
> -    case foo: q_obj_TestStruct-wrapper
> -    case union_bar: q_obj_str-wrapper
> +    case foo: TestStruct
> +    case union_bar: str
>          if ['defined(TEST_IF_UNION_BAR)']
>      if ['defined(TEST_IF_UNION) && defined(TEST_IF_STRUCT)']
>  object q_obj_TestIfUnionCmd-arg

Match what I'd expect.
Kevin Wolf Oct. 26, 2020, 11:04 a.m. UTC | #2
Am 25.10.2020 um 10:16 hat Markus Armbruster geschrieben:
> I apologize for writing so much.  It's the only way I know to figure out
> how things work.
> 
> This may feel like I'm trying to shoot down your patch.  I'm not!  I'm
> merely trying to understand and maybe improve it.  I'd love to get rid
> of implicit wrapper objects, actually.  They complicate things in
> places.  More on that below.
> 
> Kevin Wolf <kwolf@redhat.com> writes:
> 
> > Variants of simple unions are always contained in a wrapper object
> > called 'data' that serves no real use.
> 
> Not quite.
> 
> Two aspects: on the wire, and in C.  Which aspect this patch is about
> is not clear to me at this point.

After the first sentence, maybe it shouldn't be. I'm only starting to
describe the problem, not what the patch does to solve it. :-)

But to clarify, this patch aims to leave the wire protocol unchanged and
remove the indirection only internally.

> 1. One the wire
> 
> qapi-code-gen.txt documents:
> 
>     A simple union can always be re-written as a flat union where the base
>     class has a single member named 'type', and where each branch of the
>     union has a struct with a single member named 'data'.  That is,
> 
>      { 'union': 'Simple', 'data': { 'one': 'str', 'two': 'int' } }
> 
>     is identical on the wire to:
> 
>      { 'enum': 'Enum', 'data': ['one', 'two'] }
>      { 'struct': 'Branch1', 'data': { 'data': 'str' } }
>      { 'struct': 'Branch2', 'data': { 'data': 'int' } }
>      { 'union': 'Flat', 'base': { 'type': 'Enum' }, 'discriminator': 'type',
>        'data': { 'one': 'Branch1', 'two': 'Branch2' } }
> 
> Actual wire format:
> 
>     { "type": "one", "data": "some-string" }
>     { "type": "two", "data": 1 }
> 
> "data" does serve a use here.

Fair. This patch isn't about the wire format, but I wouldn't be
surprised if I'm talking about "variants" in other places where I should
say something like "object variants" to be more precise.

> If we change the second branch from 'int' to some complex type, say
> 
>     { 'struct': 'Object', 'data': { 'x': 'int', 'y': 'int' } }
>     { 'union': 'Simple', 'data': { 'one': 'str', 'two': 'Object' } }
> 
>     { 'struct': 'Branch2', 'data': { 'data': 'Object' } }
> 
> we get
> 
>     { "type": "one", "data": "some-string" }
>     { "type": "two", "data": { "x": 1, "y": 2 } }
> 
> where the "data" wrapper is indeed pointless for branch "two".  We can
> get rid of it by replacing the equivalent flat union by
> 
>     { 'union': 'Flatter', 'base': { 'type': 'Enum' }, 'discriminator': 'type',
>       'data': { 'one': 'Branch1', 'two': 'Object' } }
> 
> to get
> 
>     { "type": "one", "data": "some-string" }
>     { "type": "two", "x": 1, "y": 2 }
> 
> 2. In C
> 
> The C types generated for the simple union and its corresponding flat
> union are structurally equivalent (qapi-code-gen.txt doesn't document
> this, maybe it should):
> 
>     typedef enum SimpleKind {
>         SIMPLE_KIND_ONE,
>         SIMPLE_KIND_TWO,
>         SIMPLE_KIND__MAX,
>     } SimpleKind;
> 
>     struct q_obj_str_wrapper {
>         char *data;
>     };
> 
>     struct q_obj_Object_wrapper {
>         Object *data;
>     };
> 
>     struct Simple {
>         SimpleKind type;
>         union { /* union tag is @type */
>             q_obj_str_wrapper one;
>             q_obj_Object_wrapper two;
>         } u;
>     };
> 
> and
> 
>     typedef enum Enum {
>         ENUM_ONE,
>         ENUM_TWO,
>         ENUM__MAX,
>     } Enum;
> 
>     struct Branch1 {
>         char *data;
>     };
> 
>     struct Branch2 {
>         Object *data;
>     };
> 
>     struct Flat {
>         Enum type;
>         union { /* union tag is @type */
>             Branch1 one;
>             Branch2 two;
>         } u;
>     };
> 
> Here, the wrapper is pointless for both branches.
> 
> For the "flatter" flat union, we get
> 
>     struct Flatter {
>         Enum type;
>         union { /* union tag is @type */
>             Branch1 one;
>             Object two;
>         } u;
>     };
> 
> One of two pointless wrappers are gone.
> 
> >                                        When mapping a QAPI object to the
> > command line, this becomes very visible to users because they have to
> > add one or more useless 'data.' to many option names.
> 
> It's useless in QMP, too.

Not claiming otherwise.

> > As a first step towards avoiding this painful CLI experience,
> 
> It's painful in CLI when you use dotted keys syntax, because that syntax
> makes nesting painful.
> 
> I dislike pointless nesting even when the syntax makes it almost not
> painful, like in QMP.
> 
> >                                                               this gets
> > rid of the 'data' indirection internally: The QAPI parser doesn't use a
> > wrapper object as the variant type any more, so the indirection is
> > removed from the generated C types. As a result, the C type looks the
> > same for flat and simple unions now.
> 
> Really?

Only true for unions whose structure can be represented both as flat and
as simple unions. Flat unions don't allow 'str' as a variant type, so
there is no structurally equivalent flat union. (There is a flat union
that looks the same on the write, but has a wrapper object internally.)

In the future, I would like to solve this difference between flat and
simplie unions by allowing flat union variants to have non-object types,
too (allowing the simpler C code even for flat unions). We could allow
or even require setting an explicit name instead of the fixed 'data' we
use today for simple unions.

> For the simple union we now generate
> 
>     struct Simple {
>         SimpleKind type;
>         union { /* union tag is @type */
>             char *one;
>             Object two;
>         } u;
>     };
> 
> Same as what flat union?
> 
> Certainly not 'Flatter', which has branch 'one' wrapped in a struct.
> 
> The naive attempt to not wrap it
> 
>     { 'union': 'Flattest',
>       'base': { 'type': 'Enum' }, 'discriminator': 'type',
>       'data': { 'one': 'str', 'two': 'Object' } }
> 
> is invalid, because "All flat union branches must be of struct type"
> (qapi-code-gen.txt).  qapi-gen.py duly rejects it with "branch 'one'
> cannot use built-in type 'str'".  Remember, flat unions "splice in" the
> variant members on the wire.  There have to be members for that.
> 
> >                                      A large part of this patch is
> > mechanical conversion of C code to remove the 'data' indirection.
> 
> How did you do the conversion?  Coccinelle?  Regexps?  Manual until
> compiler is happy?

Manual. I considered Coccinelle, but imagined fighting with it would
take longer than just doing it myself for those few simple unions that
we have.

> > Conceptually, the important change is that variants can now have flat
> > and wrapped representations. For a transitioning period, we'll allow
> > variants to support both representations in a later patch.
> 
> Alright, now I'm confused.
> 
> What exactly is a "flat representation", and when is it used?
> 
> What's a "wrapped representation", and when is it used?
> 
> Are you talking about the internal representation,
> i.e. QAPISchemaVariant?

I'm talking about representation "on the wire" (I don't think we
generally use this term for the command line, but well...). Internal
representation is always flat after this patch.

> >                                                            Eventually,
> > the plan is to deprecate and remove wrapped representations entirely,
> > unifying simple and flat unions.
> >
> > The externally visible interfaces stay unchanged: Visitors still expect
> > the 'data' wrappers, and introspection still shows it.
> 
> Visitors are externally visible only indirectly: the QObject visitors
> determine the wire format.  But that's detail.  Perhaps:
> 
>     The wire format remains the same.  The 'data' wrappers are still
>     there, and introspection and documentation still show them.  This
>     necessitates new special cases in visit.py, introspect.py, and
>     qapidoc.py.

Ok, works for me. It's not true any more at the end of the series
depending on whether "wire format" can also mean CLI syntax, but for
this patch it's supposed to be true.

One major problem I noticed in the QAPI spec is that it's really tied to
QMP and QMP only. It doesn't know anything about the command line nor
about types that we use only internally in the C code. I felt addressing
this was out of scope for this series, though.

> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> > ---
> >  docs/devel/qapi-code-gen.txt           | 32 ++++++++----
> >  docs/sphinx/qapidoc.py                 | 14 +++---
> >  backends/tpm/tpm_emulator.c            |  3 +-
> >  backends/tpm/tpm_passthrough.c         |  4 +-
> >  block/crypto.c                         |  3 +-
> >  block/qcow2.c                          |  9 ++--
> >  block/vmdk.c                           | 14 ++----
> >  blockdev.c                             | 36 ++++++-------
> >  chardev/char-file.c                    |  5 +-
> >  chardev/char-mux.c                     |  5 +-
> >  chardev/char-parallel.c                |  5 +-
> >  chardev/char-pipe.c                    |  7 ++-
> >  chardev/char-ringbuf.c                 |  5 +-
> >  chardev/char-serial.c                  |  5 +-
> >  chardev/char-socket.c                  | 13 ++---
> >  chardev/char-stdio.c                   |  5 +-
> >  chardev/char-udp.c                     | 11 ++--
> >  chardev/char.c                         | 10 ++--
> >  chardev/msmouse.c                      |  4 +-
> >  chardev/spice.c                        | 10 ++--
> >  chardev/wctablet.c                     |  4 +-
> >  hw/core/numa.c                         |  6 +--
> >  hw/display/xenfb.c                     |  8 +--
> >  hw/input/hid.c                         |  8 +--
> >  hw/input/ps2.c                         |  6 +--
> >  hw/input/virtio-input-hid.c            |  8 +--
> >  hw/mem/pc-dimm.c                       | 18 +++----
> >  hw/virtio/virtio-mem-pci.c             |  3 +-
> >  hw/virtio/virtio-pmem-pci.c            |  3 +-
> >  monitor/hmp-cmds.c                     | 14 +++---
> >  qemu-keymap.c                          |  2 +-
> >  replay/replay-input.c                  | 46 +++++++----------
> >  tests/test-char.c                      | 12 ++---
> >  tests/test-clone-visitor.c             | 14 +++---
> >  tests/test-qmp-cmds.c                  |  2 +-
> >  tests/test-qobject-input-visitor.c     | 24 ++++-----
> >  tests/test-qobject-output-visitor.c    | 24 ++++-----
> >  ui/console.c                           |  5 +-
> >  ui/input-keymap.c                      | 12 ++---
> >  ui/input-legacy.c                      | 12 ++---
> >  ui/input.c                             | 43 ++++++++--------
> >  ui/spice-app.c                         |  5 +-
> >  util/qemu-sockets.c                    |  8 +--
> >  scripts/qapi/introspect.py             |  7 ++-
> >  scripts/qapi/schema.py                 | 48 ++++++++++++++----
> >  scripts/qapi/visit.py                  | 28 +++++++++++
> >  tests/qapi-schema/doc-good.out         |  8 +--
> >  tests/qapi-schema/qapi-schema-test.out | 70 +++++++-------------------
> >  48 files changed, 322 insertions(+), 326 deletions(-)
> >
> > diff --git a/docs/devel/qapi-code-gen.txt b/docs/devel/qapi-code-gen.txt
> > index c6438c6aa9..9722c1a204 100644
> > --- a/docs/devel/qapi-code-gen.txt
> > +++ b/docs/devel/qapi-code-gen.txt
> > @@ -310,7 +310,20 @@ The BRANCH's STRING name is the branch name.
> >  The BRANCH's value defines the branch's properties, in particular its
> >  type.  The form TYPE-REF is shorthand for { 'type': TYPE-REF }.
> >  
> > -A simple union type defines a mapping from automatic discriminator
> > +Each branch can have flat or wrapped representation in the Client JSON
> > +Protocol.
> > +
> > +Wrapped representation of a branch means that it is represented by a
> > +'data' member that is of the specified data type corresponding to the
> > +discriminator value.
> > +
> > +Flat representation means that the union forms a single object that
> > +contains both common members (from the base type) and the selected
> > +branch's members, without any additional nesting.  The two sets of
> > +member names must be disjoint.
> 
> You talk about representation of branches before saying anything about
> representation of unions.  But let's focus on the contents now.  How to
> best present it can wait.

Defining the branches first is intentional because the difference
between flat and simple is mostly just the representation of branches on
the wire. So it's hard to explain what the whole union looks like when
flat/wrapped representation hasn't been introduced yet.

Either way, I think this whole section is backwards. It should start
with unions in general, then flat unions, and then "simple" unions.
Fixing it should be a separate patch, either before this one or on top
of the series.

> > +
> > +A simple union type automatically contains the 'type' member as a
> > +discriminator and defines a mapping from automatic discriminator
> >  values to data types like in this example:
> >  
> >   { 'struct': 'BlockdevOptionsFile', 'data': { 'filename': 'str' } }
> > @@ -321,10 +334,8 @@ values to data types like in this example:
> >     'data': { 'file': 'BlockdevOptionsFile',
> >               'qcow2': 'BlockdevOptionsQcow2' } }
> >  
> > -In the Client JSON Protocol, a simple union is represented by an
> > -object that contains the 'type' member as a discriminator, and a
> > -'data' member that is of the specified data type corresponding to the
> > -discriminator value, as in these examples:
> > +In the Client JSON Protocol, all simple union branches have wrapped
> > +representation, as in these examples:
> >  
> >   { "type": "file", "data": { "filename": "/some/place/my-image" } }
> >   { "type": "qcow2", "data": { "backing": "/some/place/my-image",
> > @@ -344,13 +355,12 @@ object, it defines common members just like a struct type's 'data'
> >  member defines struct type members.  If it is a STRING, it names a
> >  struct type whose members are the common members.
> >  
> > -All flat union branches must be of struct type.
> > +Member 'discriminator' must name a non-optional enum-typed member of
> > +the base struct and defines the option that should server as the
> > +discrimiator.
> 
> s/server as the discrimiator/serve as discriminator/
> 
> >  
> > -In the Client JSON Protocol, a flat union is represented by an object
> > -with the common members (from the base type) and the selected branch's
> > -members.  The two sets of member names must be disjoint.  Member
> > -'discriminator' must name a non-optional enum-typed member of the base
> > -struct.
> > +All flat union branches must be of struct type.  They have always flat
> > +representation.
> 
> So, simple unions use wrapped representation, flat unions use flat
> representation, but I have to read the whole section at least twice to
> figure that out :)  Let's not worry about that now.
> 
> >  
> >  The following example enhances the above simple union example by
> >  adding an optional common member 'read-only', renaming the
> > diff --git a/docs/sphinx/qapidoc.py b/docs/sphinx/qapidoc.py
> > index e03abcbb95..75f6721e29 100644
> > --- a/docs/sphinx/qapidoc.py
> > +++ b/docs/sphinx/qapidoc.py
> 
> Best to review the changes to the QAPI generator from frontend to
> backends: schema.py first, then come back here.
> 
> > @@ -183,12 +183,14 @@ class QAPISchemaGenRSTVisitor(QAPISchemaVisitor):
> >  
> >          if variants:
> >              for v in variants.variants:
> > -                if v.type.is_implicit():
> > -                    assert not v.type.base and not v.type.variants
> > -                    for m in v.type.local_members:
> > -                        term = self._nodes_for_one_member(m)
> > -                        term.extend(self._nodes_for_variant_when(variants, v))
> > -                        dlnode += self._make_dlitem(term, None)
> > +                if v.wrapped:
> > +                    term = [nodes.literal('', 'data'),
> > +                            nodes.Text(': '),
> > +                            nodes.literal('', v.type.doc_type())]
> > +                    term.extend(self._nodes_for_variant_when(variants, v))
> > +                    dlnode += self._make_dlitem(term, None)
> > +                elif v.type.is_implicit():
> > +                    assert v.type.name == 'q_empty'
> >                  else:
> >                      term = [nodes.Text('The members of '),
> >                              nodes.literal('', v.type.doc_type())]
> [...]
> > diff --git a/scripts/qapi/introspect.py b/scripts/qapi/introspect.py
> > index fafec94e02..1c4e3407a3 100644
> > --- a/scripts/qapi/introspect.py
> > +++ b/scripts/qapi/introspect.py
> > @@ -188,7 +188,12 @@ const QLitObject %(c_name)s = %(c_string)s;
> >                  'variants': [self._gen_variant(v) for v in variants]}
> >  
> >      def _gen_variant(self, variant):
> > -        obj = {'case': variant.name, 'type': self._use_type(variant.type)}
> > +        if variant.wrapped:
> > +            obj = {'case': variant.name,
> > +                   'type': self._use_type(variant.wrapper_type)}
> > +        else:
> > +            obj = {'case': variant.name,
> > +                   'type': self._use_type(variant.type)}
> >          return _make_tree(obj, variant.ifcond, None)
> >  
> >      def visit_builtin_type(self, name, info, json_type):
> > diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
> > index 720449feee..17525b4216 100644
> > --- a/scripts/qapi/schema.py
> > +++ b/scripts/qapi/schema.py
> > @@ -216,6 +216,11 @@ class QAPISchemaBuiltinType(QAPISchemaType):
> >          self._json_type_name = json_type
> >          self._c_type_name = c_type
> >  
> > +    def check(self, schema):
> > +        # Don't check twice, it would fail an assertion
> > +        if not self._checked:
> > +            super().check(schema)
> > +
> 
> How can this get called twice?
> 
> I'm asking because I remember the last time I cleaned up .check()
> recursion (commit f9d1743b9b0).  Just glancing at its commit message
> brings back the headache.

This doesn't seem to happen any more, I can remove this hunk. I suppose
I hadn't made the recursion in QAPISchemaVariants.check() conditional on
instanceof(..., QAPISchemaObjectType) yet.

> >      def c_name(self):
> >          return self.name
> >  
> 
> Further down in QAPISchemaObjectType:
> 
>        @property
>        def ifcond(self):
>            assert self._checked
>            if isinstance(self._ifcond, QAPISchemaType):
>                # Simple union wrapper type inherits from wrapped type;
>                # see _make_implicit_object_type()
>                return self._ifcond.ifcond
>            return self._ifcond
> 
> Is isinstance(self._ifcond, QAPISchemaType) still possible?  See
> _make_implicit_object_type() below.

If the comment describe all possibly situations, probably not?

This is a case where John's type annotations would be helpful to find
the right answer quickly.

> > @@ -593,18 +598,21 @@ class QAPISchemaVariants:
>            if self._tag_name:    # flat union
>                # branches that are not explicitly covered get an empty type
>                cases = {v.name for v in self.variants}
>                for m in self.tag_member.type.members:
>                    if m.name not in cases:
>                        v = QAPISchemaVariant(m.name, self.info,
>                                              'q_empty', m.ifcond)
> 
> Note for later: the code to create a default empty variant stays the
> same.
> 
>                        v.set_defined_in(self.tag_member.defined_in)
>                        self.variants.append(v)
>            [...]
>            for v in self.variants:
>                v.check(schema)
>                # Union names must match enum values; alternate names are
>                # checked separately. Use 'seen' to tell the two apart.
>                if seen:
>                    if v.name not in self.tag_member.type.member_names():
>                        raise QAPISemError(
>                            self.info,
> >                          "branch '%s' is not a value of %s"
> >                          % (v.name, self.tag_member.type.describe()))
> >                  if (not isinstance(v.type, QAPISchemaObjectType)
> > -                        or v.type.variants):
> > +                        or v.type.variants) and v.flat:
> >                      raise QAPISemError(
> >                          self.info,
> >                          "%s cannot use %s"
> >                          % (v.describe(self.info), v.type.describe()))
> 
> Before the patch: check branch type is an object without variants.  For
> flat unions, this is documented in qapi-code-gen.txt: "All flat union
> branches must be of struct type".  For simple unions, the wrapper types
> spliced in by the desugaring ensure this can't fail.
> 
> What the hunk does: permit arbitrary branch types when not v.flat.  To
> make sense of it, we need to understand the meaning of v.flat.  See
> below.
> 
> > -                v.type.check(schema)
> > +                if isinstance(v.type, QAPISchemaObjectType):
> > +                    v.type.check(schema)
> 
> Since we want to recurse only for object types (see commit f9d1743b9b0),
> and other types are now possible when not v.flat, the recursion now
> needs to be guarded.  Okay.

By the way, it would be good if you didn't have to know commit
f9d1743b9b0 to figure out how this is supposed to work. Docstrings in
QAPISchemaEntity would probably go a long way.

> >  
> >      def check_clash(self, info, seen):
> >          for v in self.variants:
> >              # Reset seen map for each variant, since qapi names from one
> > -            # branch do not affect another branch
> > -            v.type.check_clash(info, dict(seen))
> > +            # branch do not affect another branch.  Variants that are
> > +            # never flat don't even conflict with the base.
> 
> What do you mean by "never flat"?  Could a variant be sometimes flat?

After the next patch, variants can support both flat and wrapped
representation in the generated C code. Which one is used depends on the
Visitor configuration then. (Not in this series, but further in the
future, input visitors can be able to accept both forms, which gives us
an opportunity to deprecate the wrapped form.)

> > +            if isinstance(v.type, QAPISchemaObjectType):
> > +                v.type.check_clash(info, dict(seen) if v.flat else {})
> 
> The guard is necessary because v.type has method .check_clash() only if
> it's an object type.
> 
> .check() ensures that v.type is an object type without variants when
> v.flat.
> 
> So:
> 
> * If v.flat, no change.
> 
> * If not v.flat and v.type is an object type (possibly with variants),
>   we run its .check_clash() with an empty seen.  What does this
>   accomplish?

Checking internal consistency, I guess.

If it's necessary depends on whether something else calls check_clash(),
too. Maybe it is already called for all entities? Then this would be
unnecessary.

> * If not v.flat and v.type is not an object type, we do nothing.
> 
> >  
> >  
> >  class QAPISchemaMember:
> > @@ -705,9 +713,22 @@ class QAPISchemaObjectTypeMember(QAPISchemaMember):
> >  class QAPISchemaVariant(QAPISchemaObjectTypeMember):
> >      role = 'branch'
> >  
> > -    def __init__(self, name, info, typ, ifcond=None):
> > +    def __init__(self, name, info, typ, ifcond=None, flat=True,
> > +                 wrapper_type=None):
> >          super().__init__(name, info, typ, False, ifcond)
> >  
> > +        self.flat = flat
> > +        self.wrapped = bool(wrapper_type)
> > +        self.wrapper_type = wrapper_type
> > +
> > +        # For now, unions are either flat or wrapped, never both
> > +        assert self.flat or self.wrapped
> > +        assert not (self.flat and self.wrapped)
> 
> The comment makes me expect
> 
>            assert self.flat == not self.wrapped
> 
> Moreover, .flat and .wrapped seem to be redundant with .wrapper_type.
> 
> Hmm, I see the next patch will change this again.  I'm therefore
> reserving judgement until the end of the series.
> 
> The constructor is called in three places:
> 
> * QAPISchema._make_variant(), call unchanged (see below), therefore flat
> 
> * QAPISchema._make_simple_variant(), now passes flat=False, see below
>   for details
> 
> * QAPISchemaVariants.check(), call unchanged (see below), therefore flat
> 
> > +
> > +    def check(self, schema):
> > +        super().check(schema)
> > +        if self.wrapped:
> > +            self.wrapper_type.check(schema)
> 
> Commit f9d1743b9b0: "An entity's .check() recurses into another entity's
> .check() only if the C struct generated for the former contains the C
> struct generated for the latter (pointers don't count).  This is used to
> detect "object contains itself".
> 
> Can you explain why we want to recurse here?

Because nothing else checks self.wrapper_type.

> pycodestyle-3 complains:
> 
>     scripts/qapi/schema.py:733:1: E302 expected 2 blank lines, found 1
> 
> >  class QAPISchemaCommand(QAPISchemaEntity):
> >      meta = 'command'
> > @@ -1017,14 +1038,19 @@ class QAPISchema:
> 
> Not changed:
> 
>        def _make_implicit_object_type(self, name, info, ifcond, role, members):
>            if not members:
>                return None
>            # See also QAPISchemaObjectTypeMember.describe()
>            name = 'q_obj_%s-%s' % (name, role)
>            typ = self.lookup_entity(name, QAPISchemaObjectType)
>            if typ:
>                # The implicit object type has multiple users.  This can
>                # happen only for simple unions' implicit wrapper types.
>                # Its ifcond should be the disjunction of its user's
>                # ifconds.  Not implemented.  Instead, we always pass the
>                # wrapped type's ifcond, which is trivially the same for all
>                # users.  It's also necessary for the wrapper to compile.
>                # But it's not tight: the disjunction need not imply it.  We
>                # may end up compiling useless wrapper types.
>                # TODO kill simple unions or implement the disjunction
> 
>                # pylint: disable=protected-access
>                assert (ifcond or []) == typ._ifcond
>            else:
>                self._def_entity(QAPISchemaObjectType(
>                    name, info, None, ifcond, None, None, members, None))
>            return name
> 
> Can typ still be non-None?

I don't know. I would have to understand all callers to tell. Again,
John's typing patches would make finding the answer easy.

> [...]
> >      def _make_variant(self, case, typ, ifcond, info):
> >          return QAPISchemaVariant(case, info, typ, ifcond)
> >  
> > -    def _make_simple_variant(self, case, typ, ifcond, info):
> > +    def _make_simple_variant(self, union_name, case, typ, ifcond, info):
> >          if isinstance(typ, list):
> >              assert len(typ) == 1
> >              typ = self._make_array_type(typ[0], info)
> > -        typ = self._make_implicit_object_type(
> > -            typ, info, self.lookup_type(typ),
> > -            'wrapper', [self._make_member('data', typ, None, None, info)])
> > -        return QAPISchemaVariant(case, info, typ, ifcond)
> > +
> > +        # The wrapper type is only used for introspection compatibility.
> > +        # Don't add it to the entity list of the schema.
> > +        wrapper_name = 'q_obj_%s-%s-wrapper' % (union_name, case)
> > +        wrapper_member = self._make_member('data', typ, None, None, info)
> > +        wrapper_type = QAPISchemaObjectType(wrapper_name, info, None, ifcond,
> > +                                            None, None, [wrapper_member], None)
> 
> This adds another place where we create implicit object types.  Comments
> need to be updated, e.g. in QAPISchemaObjectType.is_implicit().
> 
> > +        return QAPISchemaVariant(case, info, typ, ifcond, flat=False,
> > +                                 wrapper_type=wrapper_type)
> 
> This changes argument @typ from wrapper to wrapped type.  The wrapper is
> passed as @wrapped_type instead.
> 
> It's not the same wrapper, though.
> 
> Before the patch, we have a common q_obj_<wrapped-type>-wrapper.
> _make_implicit_object_type() creates it unless it exists already.
> 
> After the patch, we have q_obj_<union-type>-<branch-name>-wrapper.  The
> wrapper de-duplication is gone.  _make_implicit_object_type() is
> bypassed.
> 
> But is this bypass necessary?  I suspect it's to not "add it to the
> entity list of the schema".  Why not?

We don't really want it to be a type for almost all matters. For
example, having it in the entity list would generate C code that is
never used.

The only reason this type object is even created is because the
introspection code was too painful to change to work without it, and it
can't create the object locally because it would have to access private
attributes and/or methods to do so.

So pre-creating this type here is a compromise that I already dislike.
If you think it's bad, I can try and have another look at the
introspection code and if we can somehow make it work without having a
type.

But I certainly want code that wants to see this type do additional
steps, not code that wants to exclude it. It should be invisible by
default.

> If the loss of de-duplication is intentional, the commit message should
> mention it.

Not exactly intentional in the sense that it was the goal, but it
doesn't matter much either. Only the generated introspection code
becomes a bit longer.

> >  
> >      def _def_union_type(self, expr, info, doc):
> >          name = expr['union']
> > @@ -1044,7 +1070,7 @@ class QAPISchema:
> >                          for (key, value) in data.items()]
> >              members = []
> >          else:
> > -            variants = [self._make_simple_variant(key, value['type'],
> > +            variants = [self._make_simple_variant(name, key, value['type'],
> >                                                    value.get('if'), info)
> >                          for (key, value) in data.items()]
> >              enum = [{'name': v.name, 'if': v.ifcond} for v in variants]
> > diff --git a/scripts/qapi/visit.py b/scripts/qapi/visit.py
> > index 339f152152..f72567cbcc 100644
> > --- a/scripts/qapi/visit.py
> > +++ b/scripts/qapi/visit.py
> > @@ -118,6 +118,34 @@ bool visit_type_%(c_name)s_members(Visitor *v, %(c_name)s *obj, Error **errp)
>            for var in variants.variants:
>                case_str = c_enum_const(tag_member.type.name, var.name,
>                                        tag_member.type.prefix)
>                ret += gen_if(var.ifcond)
> 
> Before the patch, special case 'q_empty' (which has no visitor), general
> case object type.
> 
> The patch adds two more cases.
> 
> 
> This is special case 'q_empty':
> 
>                if var.type.name == 'q_empty':
>                    # valid variant and nothing to do
>                    ret += mcgen('''
>        case %(case)s:
> >          break;
> >  ''',
> >                               case=case_str)
> 
> 
> New case "not an object type":
> 
> > +            elif not isinstance(var.type, QAPISchemaObjectType):
> > +                assert not var.flat
> > +                ret += mcgen('''
> > +    case %(case)s:
> > +        return visit_type_%(c_type)s(v, "data", &obj->u.%(c_name)s, errp);
> > +''',
> > +                             case=case_str,
> > +                             c_type=var.type.c_name(), c_name=c_name(var.name))
> 
> Before the patch, we visit the implicit wrapper, using the general case
> below, i.e.
> 
>            return visit_type_q_obj_T_wrapper_members(v, &obj->u.BRANCH, errp);
> 
> visit_type_q_obj_T_members() looks like this:
> 
>        bool visit_type_q_obj_T_wrapper_members(Visitor *v, q_obj_T_wrapper *obj, Error **errp)
>        {
>            if (!visit_type_T(v, "data", &obj->data, errp)) {
>                return false;
>            }
>            return true;
>        }
> 
> The new code calls visit_type_T() directly.  The only change (I think /
> hope) is from &obj->u.BASE->data to &obj->u.BASE, which is what we want.
> 
> 
> New case "wrapped object type":
> 
> > +            elif var.wrapped:
> > +                ret += mcgen('''
> > +    case %(case)s:
> > +    {
> > +        bool ok;
> > +
> > +        if (!visit_start_struct(v, "data", NULL, 0, errp)) {
> > +            return false;
> > +        }
> > +        ok = visit_type_%(c_type)s_members(v, &obj->u.%(c_name)s, errp);
> > +        if (ok) {
> > +            ok = visit_check_struct(v, errp);
> > +        }
> > +        visit_end_struct(v, NULL);
> > +        return ok;
> > +    }
> > +''',
> > +                             case=case_str,
> > +                             c_type=var.type.c_name(), c_name=c_name(var.name))
> > +
> >              else:
> >                  ret += mcgen('''
> 
> To compensate for the implicit wrapper type's removal from the C type,
> we splice in a virtual struct visit.
> 
> Before the patch, we visit the implicit wrapper, using the general case
> below, i.e.
> 
>            return visit_type_q_obj_T_wrapper_members(v, &obj->u.BRANCH, errp);
> 
> visit_type_q_obj_T_members() looks like this:
> 
>        bool visit_type_q_obj_T_wrapper_members(Visitor *v, q_obj_T_wrapper *obj, Error **errp)
>        {
>            if (!visit_type_T(v, "data", &obj->data, errp)) {
>                return false;
>            }
>            return true;
>        }
> 
> When T is an object type, visit_type_T() looks like this:
> 
>        bool visit_type_T(Visitor *v, const char *name,
>                         T **obj, Error **errp)
>        {
>            bool ok = false;
> 
>            if (!visit_start_struct(v, name, (void **)obj, sizeof(T), errp)) {
>                return false;
>            }
>            if (!*obj) {
>                /* incomplete */
>                assert(visit_is_dealloc(v));
>                ok = true;
>                goto out_obj;
>            }
>            if (!visit_type_T_members(v, *obj, errp)) {
>                goto out_obj;
>            }
>            ok = visit_check_struct(v, errp);
>        out_obj:
>            visit_end_struct(v, (void **)obj);
>            if (!ok && visit_is_input(v)) {
>                qapi_free_T(*obj);
>                *obj = NULL;
>            }
>            return ok;
>        }
> 
> Compare to the new code:
> 
> 1. The new code passes NULL to visit_start_struct() and
>    visit_end_struct(), i.e. the visit of "data" becomes virtual.
> 
> 2. The new code passes &obj->u.BRANCH instead of &obj->u.BRANCH->data.
> 
> 3. The new code doesn't have the /* incomplete */ conditional.
> 
> 4. The new code doesn't have the conditional qapi_free_T().
> 
> The first two compensate for the wrapper type's removal from the C type.
> 
> Why are the last two not needed?

Because we're parsing fields for an pre-existing C struct now instead of
creating malloc'ed objects - which is also why visit_start/end_struct()
get NULL instead of obj.

> 
> Case "unwrapped object type" (same as old general case):
> 
> >      case %(case)s:
>            return visit_type_%(c_type)s_members(v, &obj->u.%(c_name)s, errp);
>    ''',
>                                 case=case_str,
>                                 c_type=var.type.c_name(), c_name=c_name(var.name))
> 
>                ret += gen_endif(var.ifcond)
>            ret += mcgen('''
>        default:
>            abort();
>        }
>    ''')
> 
> Now I should go back to qapidoc.py and introspect.py.  But I think we
> have enough to discuss about this patch already, so I'm postponing their
> review, and move on the the next patch.

Ok.

Kevin
diff mbox series

Patch

diff --git a/docs/devel/qapi-code-gen.txt b/docs/devel/qapi-code-gen.txt
index c6438c6aa9..9722c1a204 100644
--- a/docs/devel/qapi-code-gen.txt
+++ b/docs/devel/qapi-code-gen.txt
@@ -310,7 +310,20 @@  The BRANCH's STRING name is the branch name.
 The BRANCH's value defines the branch's properties, in particular its
 type.  The form TYPE-REF is shorthand for { 'type': TYPE-REF }.
 
-A simple union type defines a mapping from automatic discriminator
+Each branch can have flat or wrapped representation in the Client JSON
+Protocol.
+
+Wrapped representation of a branch means that it is represented by a
+'data' member that is of the specified data type corresponding to the
+discriminator value.
+
+Flat representation means that the union forms a single object that
+contains both common members (from the base type) and the selected
+branch's members, without any additional nesting.  The two sets of
+member names must be disjoint.
+
+A simple union type automatically contains the 'type' member as a
+discriminator and defines a mapping from automatic discriminator
 values to data types like in this example:
 
  { 'struct': 'BlockdevOptionsFile', 'data': { 'filename': 'str' } }
@@ -321,10 +334,8 @@  values to data types like in this example:
    'data': { 'file': 'BlockdevOptionsFile',
              'qcow2': 'BlockdevOptionsQcow2' } }
 
-In the Client JSON Protocol, a simple union is represented by an
-object that contains the 'type' member as a discriminator, and a
-'data' member that is of the specified data type corresponding to the
-discriminator value, as in these examples:
+In the Client JSON Protocol, all simple union branches have wrapped
+representation, as in these examples:
 
  { "type": "file", "data": { "filename": "/some/place/my-image" } }
  { "type": "qcow2", "data": { "backing": "/some/place/my-image",
@@ -344,13 +355,12 @@  object, it defines common members just like a struct type's 'data'
 member defines struct type members.  If it is a STRING, it names a
 struct type whose members are the common members.
 
-All flat union branches must be of struct type.
+Member 'discriminator' must name a non-optional enum-typed member of
+the base struct and defines the option that should server as the
+discrimiator.
 
-In the Client JSON Protocol, a flat union is represented by an object
-with the common members (from the base type) and the selected branch's
-members.  The two sets of member names must be disjoint.  Member
-'discriminator' must name a non-optional enum-typed member of the base
-struct.
+All flat union branches must be of struct type.  They have always flat
+representation.
 
 The following example enhances the above simple union example by
 adding an optional common member 'read-only', renaming the
diff --git a/docs/sphinx/qapidoc.py b/docs/sphinx/qapidoc.py
index e03abcbb95..75f6721e29 100644
--- a/docs/sphinx/qapidoc.py
+++ b/docs/sphinx/qapidoc.py
@@ -183,12 +183,14 @@  class QAPISchemaGenRSTVisitor(QAPISchemaVisitor):
 
         if variants:
             for v in variants.variants:
-                if v.type.is_implicit():
-                    assert not v.type.base and not v.type.variants
-                    for m in v.type.local_members:
-                        term = self._nodes_for_one_member(m)
-                        term.extend(self._nodes_for_variant_when(variants, v))
-                        dlnode += self._make_dlitem(term, None)
+                if v.wrapped:
+                    term = [nodes.literal('', 'data'),
+                            nodes.Text(': '),
+                            nodes.literal('', v.type.doc_type())]
+                    term.extend(self._nodes_for_variant_when(variants, v))
+                    dlnode += self._make_dlitem(term, None)
+                elif v.type.is_implicit():
+                    assert v.type.name == 'q_empty'
                 else:
                     term = [nodes.Text('The members of '),
                             nodes.literal('', v.type.doc_type())]
diff --git a/backends/tpm/tpm_emulator.c b/backends/tpm/tpm_emulator.c
index 201cd38503..7d2dc2b19d 100644
--- a/backends/tpm/tpm_emulator.c
+++ b/backends/tpm/tpm_emulator.c
@@ -629,7 +629,8 @@  static TpmTypeOptions *tpm_emulator_get_tpm_options(TPMBackend *tb)
     TpmTypeOptions *options = g_new0(TpmTypeOptions, 1);
 
     options->type = TPM_TYPE_OPTIONS_KIND_EMULATOR;
-    options->u.emulator.data = QAPI_CLONE(TPMEmulatorOptions, tpm_emu->options);
+    QAPI_CLONE_MEMBERS(TPMEmulatorOptions, &options->u.emulator,
+                       tpm_emu->options);
 
     return options;
 }
diff --git a/backends/tpm/tpm_passthrough.c b/backends/tpm/tpm_passthrough.c
index 8f6f4998a5..7fa7c84f5a 100644
--- a/backends/tpm/tpm_passthrough.c
+++ b/backends/tpm/tpm_passthrough.c
@@ -322,8 +322,8 @@  static TpmTypeOptions *tpm_passthrough_get_tpm_options(TPMBackend *tb)
     TpmTypeOptions *options = g_new0(TpmTypeOptions, 1);
 
     options->type = TPM_TYPE_OPTIONS_KIND_PASSTHROUGH;
-    options->u.passthrough.data = QAPI_CLONE(TPMPassthroughOptions,
-                                             TPM_PASSTHROUGH(tb)->options);
+    QAPI_CLONE_MEMBERS(TPMPassthroughOptions, &options->u.passthrough,
+                       TPM_PASSTHROUGH(tb)->options);
 
     return options;
 }
diff --git a/block/crypto.c b/block/crypto.c
index 0807557763..0e7838d70a 100644
--- a/block/crypto.c
+++ b/block/crypto.c
@@ -775,8 +775,7 @@  block_crypto_get_specific_info_luks(BlockDriverState *bs, Error **errp)
 
     spec_info = g_new(ImageInfoSpecific, 1);
     spec_info->type = IMAGE_INFO_SPECIFIC_KIND_LUKS;
-    spec_info->u.luks.data = g_new(QCryptoBlockInfoLUKS, 1);
-    *spec_info->u.luks.data = info->u.luks;
+    spec_info->u.luks = info->u.luks;
 
     /* Blank out pointers we've just stolen to avoid double free */
     memset(&info->u.luks, 0, sizeof(info->u.luks));
diff --git a/block/qcow2.c b/block/qcow2.c
index b05512718c..104fd8ad06 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -5052,10 +5052,9 @@  static ImageInfoSpecific *qcow2_get_specific_info(BlockDriverState *bs,
     spec_info = g_new(ImageInfoSpecific, 1);
     *spec_info = (ImageInfoSpecific){
         .type  = IMAGE_INFO_SPECIFIC_KIND_QCOW2,
-        .u.qcow2.data = g_new0(ImageInfoSpecificQCow2, 1),
     };
     if (s->qcow_version == 2) {
-        *spec_info->u.qcow2.data = (ImageInfoSpecificQCow2){
+        spec_info->u.qcow2 = (ImageInfoSpecificQCow2){
             .compat             = g_strdup("0.10"),
             .refcount_bits      = s->refcount_bits,
         };
@@ -5068,7 +5067,7 @@  static ImageInfoSpecific *qcow2_get_specific_info(BlockDriverState *bs,
             qapi_free_QCryptoBlockInfo(encrypt_info);
             return NULL;
         }
-        *spec_info->u.qcow2.data = (ImageInfoSpecificQCow2){
+        spec_info->u.qcow2 = (ImageInfoSpecificQCow2){
             .compat             = g_strdup("1.1"),
             .lazy_refcounts     = s->compatible_features &
                                   QCOW2_COMPAT_LAZY_REFCOUNTS,
@@ -5112,8 +5111,8 @@  static ImageInfoSpecific *qcow2_get_specific_info(BlockDriverState *bs,
         memset(&encrypt_info->u, 0, sizeof(encrypt_info->u));
         qapi_free_QCryptoBlockInfo(encrypt_info);
 
-        spec_info->u.qcow2.data->has_encrypt = true;
-        spec_info->u.qcow2.data->encrypt = qencrypt;
+        spec_info->u.qcow2.has_encrypt = true;
+        spec_info->u.qcow2.encrypt = qencrypt;
     }
 
     return spec_info;
diff --git a/block/vmdk.c b/block/vmdk.c
index a00dc00eb4..fc4ddcc351 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -2932,18 +2932,14 @@  static ImageInfoSpecific *vmdk_get_specific_info(BlockDriverState *bs,
 
     *spec_info = (ImageInfoSpecific){
         .type = IMAGE_INFO_SPECIFIC_KIND_VMDK,
-        .u = {
-            .vmdk.data = g_new0(ImageInfoSpecificVmdk, 1),
+        .u.vmdk = (ImageInfoSpecificVmdk) {
+            .create_type = g_strdup(s->create_type),
+            .cid = s->cid,
+            .parent_cid = s->parent_cid,
         },
     };
 
-    *spec_info->u.vmdk.data = (ImageInfoSpecificVmdk) {
-        .create_type = g_strdup(s->create_type),
-        .cid = s->cid,
-        .parent_cid = s->parent_cid,
-    };
-
-    next = &spec_info->u.vmdk.data->extents;
+    next = &spec_info->u.vmdk.extents;
     for (i = 0; i < s->num_extents; i++) {
         *next = g_new0(ImageInfoList, 1);
         (*next)->value = vmdk_get_extent_info(&s->extents[i]);
diff --git a/blockdev.c b/blockdev.c
index fe6fb5dc1d..2602298a26 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1090,7 +1090,7 @@  void qmp_blockdev_snapshot_sync(bool has_device, const char *device,
     };
     TransactionAction action = {
         .type = TRANSACTION_ACTION_KIND_BLOCKDEV_SNAPSHOT_SYNC,
-        .u.blockdev_snapshot_sync.data = &snapshot,
+        .u.blockdev_snapshot_sync = snapshot,
     };
     blockdev_do_action(&action, errp);
 }
@@ -1104,7 +1104,7 @@  void qmp_blockdev_snapshot(const char *node, const char *overlay,
     };
     TransactionAction action = {
         .type = TRANSACTION_ACTION_KIND_BLOCKDEV_SNAPSHOT,
-        .u.blockdev_snapshot.data = &snapshot_data,
+        .u.blockdev_snapshot = snapshot_data,
     };
     blockdev_do_action(&action, errp);
 }
@@ -1119,7 +1119,7 @@  void qmp_blockdev_snapshot_internal_sync(const char *device,
     };
     TransactionAction action = {
         .type = TRANSACTION_ACTION_KIND_BLOCKDEV_SNAPSHOT_INTERNAL_SYNC,
-        .u.blockdev_snapshot_internal_sync.data = &snapshot,
+        .u.blockdev_snapshot_internal_sync = snapshot,
     };
     blockdev_do_action(&action, errp);
 }
@@ -1289,7 +1289,7 @@  static void internal_snapshot_prepare(BlkActionState *common,
 
     g_assert(common->action->type ==
              TRANSACTION_ACTION_KIND_BLOCKDEV_SNAPSHOT_INTERNAL_SYNC);
-    internal = common->action->u.blockdev_snapshot_internal_sync.data;
+    internal = &common->action->u.blockdev_snapshot_internal_sync;
     state = DO_UPCAST(InternalSnapshotState, common, common);
 
     /* 1. parse input */
@@ -1453,7 +1453,7 @@  static void external_snapshot_prepare(BlkActionState *common,
     switch (action->type) {
     case TRANSACTION_ACTION_KIND_BLOCKDEV_SNAPSHOT:
         {
-            BlockdevSnapshot *s = action->u.blockdev_snapshot.data;
+            BlockdevSnapshot *s = &action->u.blockdev_snapshot;
             device = s->node;
             node_name = s->node;
             new_image_file = NULL;
@@ -1462,7 +1462,7 @@  static void external_snapshot_prepare(BlkActionState *common,
         break;
     case TRANSACTION_ACTION_KIND_BLOCKDEV_SNAPSHOT_SYNC:
         {
-            BlockdevSnapshotSync *s = action->u.blockdev_snapshot_sync.data;
+            BlockdevSnapshotSync *s = &action->u.blockdev_snapshot_sync;
             device = s->has_device ? s->device : NULL;
             node_name = s->has_node_name ? s->node_name : NULL;
             new_image_file = s->snapshot_file;
@@ -1507,7 +1507,7 @@  static void external_snapshot_prepare(BlkActionState *common,
     }
 
     if (action->type == TRANSACTION_ACTION_KIND_BLOCKDEV_SNAPSHOT_SYNC) {
-        BlockdevSnapshotSync *s = action->u.blockdev_snapshot_sync.data;
+        BlockdevSnapshotSync *s = &action->u.blockdev_snapshot_sync;
         const char *format = s->has_format ? s->format : "qcow2";
         enum NewImageMode mode;
         const char *snapshot_node_name =
@@ -1712,7 +1712,7 @@  static void drive_backup_prepare(BlkActionState *common, Error **errp)
     int ret;
 
     assert(common->action->type == TRANSACTION_ACTION_KIND_DRIVE_BACKUP);
-    backup = common->action->u.drive_backup.data;
+    backup = &common->action->u.drive_backup;
 
     if (!backup->has_mode) {
         backup->mode = NEW_IMAGE_MODE_ABSOLUTE_PATHS;
@@ -1907,7 +1907,7 @@  static void blockdev_backup_prepare(BlkActionState *common, Error **errp)
     int ret;
 
     assert(common->action->type == TRANSACTION_ACTION_KIND_BLOCKDEV_BACKUP);
-    backup = common->action->u.blockdev_backup.data;
+    backup = &common->action->u.blockdev_backup;
 
     bs = bdrv_lookup_bs(backup->device, backup->device, errp);
     if (!bs) {
@@ -2012,7 +2012,7 @@  static void block_dirty_bitmap_add_prepare(BlkActionState *common,
         return;
     }
 
-    action = common->action->u.block_dirty_bitmap_add.data;
+    action = &common->action->u.block_dirty_bitmap_add;
     /* AIO context taken and released within qmp_block_dirty_bitmap_add */
     qmp_block_dirty_bitmap_add(action->node, action->name,
                                action->has_granularity, action->granularity,
@@ -2033,7 +2033,7 @@  static void block_dirty_bitmap_add_abort(BlkActionState *common)
     BlockDirtyBitmapState *state = DO_UPCAST(BlockDirtyBitmapState,
                                              common, common);
 
-    action = common->action->u.block_dirty_bitmap_add.data;
+    action = &common->action->u.block_dirty_bitmap_add;
     /* Should not be able to fail: IF the bitmap was added via .prepare(),
      * then the node reference and bitmap name must have been valid.
      */
@@ -2053,7 +2053,7 @@  static void block_dirty_bitmap_clear_prepare(BlkActionState *common,
         return;
     }
 
-    action = common->action->u.block_dirty_bitmap_clear.data;
+    action = &common->action->u.block_dirty_bitmap_clear;
     state->bitmap = block_dirty_bitmap_lookup(action->node,
                                               action->name,
                                               &state->bs,
@@ -2098,7 +2098,7 @@  static void block_dirty_bitmap_enable_prepare(BlkActionState *common,
         return;
     }
 
-    action = common->action->u.block_dirty_bitmap_enable.data;
+    action = &common->action->u.block_dirty_bitmap_enable;
     state->bitmap = block_dirty_bitmap_lookup(action->node,
                                               action->name,
                                               NULL,
@@ -2136,7 +2136,7 @@  static void block_dirty_bitmap_disable_prepare(BlkActionState *common,
         return;
     }
 
-    action = common->action->u.block_dirty_bitmap_disable.data;
+    action = &common->action->u.block_dirty_bitmap_disable;
     state->bitmap = block_dirty_bitmap_lookup(action->node,
                                               action->name,
                                               NULL,
@@ -2174,7 +2174,7 @@  static void block_dirty_bitmap_merge_prepare(BlkActionState *common,
         return;
     }
 
-    action = common->action->u.block_dirty_bitmap_merge.data;
+    action = &common->action->u.block_dirty_bitmap_merge;
 
     state->bitmap = block_dirty_bitmap_merge(action->node, action->target,
                                              action->bitmaps, &state->backup,
@@ -2192,7 +2192,7 @@  static void block_dirty_bitmap_remove_prepare(BlkActionState *common,
         return;
     }
 
-    action = common->action->u.block_dirty_bitmap_remove.data;
+    action = &common->action->u.block_dirty_bitmap_remove;
 
     state->bitmap = block_dirty_bitmap_remove(action->node, action->name,
                                               false, &state->bs, errp);
@@ -2895,7 +2895,7 @@  void qmp_drive_backup(DriveBackup *backup, Error **errp)
 {
     TransactionAction action = {
         .type = TRANSACTION_ACTION_KIND_DRIVE_BACKUP,
-        .u.drive_backup.data = backup,
+        .u.drive_backup = *backup,
     };
     blockdev_do_action(&action, errp);
 }
@@ -2918,7 +2918,7 @@  void qmp_blockdev_backup(BlockdevBackup *backup, Error **errp)
 {
     TransactionAction action = {
         .type = TRANSACTION_ACTION_KIND_BLOCKDEV_BACKUP,
-        .u.blockdev_backup.data = backup,
+        .u.blockdev_backup = *backup,
     };
     blockdev_do_action(&action, errp);
 }
diff --git a/chardev/char-file.c b/chardev/char-file.c
index 2fd80707e5..3f0f0b6045 100644
--- a/chardev/char-file.c
+++ b/chardev/char-file.c
@@ -39,7 +39,7 @@  static void qmp_chardev_open_file(Chardev *chr,
                                   bool *be_opened,
                                   Error **errp)
 {
-    ChardevFile *file = backend->u.file.data;
+    ChardevFile *file = &backend->u.file;
 #ifdef _WIN32
     HANDLE out;
     DWORD accessmode;
@@ -100,14 +100,13 @@  static void qemu_chr_parse_file_out(QemuOpts *opts, ChardevBackend *backend,
                                     Error **errp)
 {
     const char *path = qemu_opt_get(opts, "path");
-    ChardevFile *file;
+    ChardevFile *file = &backend->u.file;
 
     backend->type = CHARDEV_BACKEND_KIND_FILE;
     if (path == NULL) {
         error_setg(errp, "chardev: file: no filename given");
         return;
     }
-    file = backend->u.file.data = g_new0(ChardevFile, 1);
     qemu_chr_parse_common(opts, qapi_ChardevFile_base(file));
     file->out = g_strdup(path);
 
diff --git a/chardev/char-mux.c b/chardev/char-mux.c
index 6f980bb836..bfb4bc6b8b 100644
--- a/chardev/char-mux.c
+++ b/chardev/char-mux.c
@@ -314,7 +314,7 @@  static void qemu_chr_open_mux(Chardev *chr,
                               bool *be_opened,
                               Error **errp)
 {
-    ChardevMux *mux = backend->u.mux.data;
+    ChardevMux *mux = &backend->u.mux;
     Chardev *drv;
     MuxChardev *d = MUX_CHARDEV(chr);
 
@@ -336,14 +336,13 @@  static void qemu_chr_parse_mux(QemuOpts *opts, ChardevBackend *backend,
                                Error **errp)
 {
     const char *chardev = qemu_opt_get(opts, "chardev");
-    ChardevMux *mux;
+    ChardevMux *mux = &backend->u.mux;
 
     if (chardev == NULL) {
         error_setg(errp, "chardev: mux: no chardev given");
         return;
     }
     backend->type = CHARDEV_BACKEND_KIND_MUX;
-    mux = backend->u.mux.data = g_new0(ChardevMux, 1);
     qemu_chr_parse_common(opts, qapi_ChardevMux_base(mux));
     mux->chardev = g_strdup(chardev);
 }
diff --git a/chardev/char-parallel.c b/chardev/char-parallel.c
index 05e7efbd6c..a17157a3be 100644
--- a/chardev/char-parallel.c
+++ b/chardev/char-parallel.c
@@ -244,7 +244,7 @@  static void qmp_chardev_open_parallel(Chardev *chr,
                                       bool *be_opened,
                                       Error **errp)
 {
-    ChardevHostdev *parallel = backend->u.parallel.data;
+    ChardevHostdev *parallel = &backend->u.parallel;
     int fd;
 
     fd = qmp_chardev_open_file_source(parallel->device, O_RDWR, errp);
@@ -258,14 +258,13 @@  static void qemu_chr_parse_parallel(QemuOpts *opts, ChardevBackend *backend,
                                     Error **errp)
 {
     const char *device = qemu_opt_get(opts, "path");
-    ChardevHostdev *parallel;
+    ChardevHostdev *parallel = &backend->u.parallel;
 
     if (device == NULL) {
         error_setg(errp, "chardev: parallel: no device path given");
         return;
     }
     backend->type = CHARDEV_BACKEND_KIND_PARALLEL;
-    parallel = backend->u.parallel.data = g_new0(ChardevHostdev, 1);
     qemu_chr_parse_common(opts, qapi_ChardevHostdev_base(parallel));
     parallel->device = g_strdup(device);
 }
diff --git a/chardev/char-pipe.c b/chardev/char-pipe.c
index 7eca5d9a56..eb19d9a526 100644
--- a/chardev/char-pipe.c
+++ b/chardev/char-pipe.c
@@ -109,7 +109,7 @@  static void qemu_chr_open_pipe(Chardev *chr,
                                bool *be_opened,
                                Error **errp)
 {
-    ChardevHostdev *opts = backend->u.pipe.data;
+    ChardevHostdev *opts = &backend->u.pipe;
     const char *filename = opts->device;
 
     if (win_chr_pipe_init(chr, filename, errp) < 0) {
@@ -124,7 +124,7 @@  static void qemu_chr_open_pipe(Chardev *chr,
                                bool *be_opened,
                                Error **errp)
 {
-    ChardevHostdev *opts = backend->u.pipe.data;
+    ChardevHostdev *opts = &backend->u.pipe;
     int fd_in, fd_out;
     char *filename_in;
     char *filename_out;
@@ -158,14 +158,13 @@  static void qemu_chr_parse_pipe(QemuOpts *opts, ChardevBackend *backend,
                                 Error **errp)
 {
     const char *device = qemu_opt_get(opts, "path");
-    ChardevHostdev *dev;
+    ChardevHostdev *dev = &backend->u.pipe;
 
     if (device == NULL) {
         error_setg(errp, "chardev: pipe: no device path given");
         return;
     }
     backend->type = CHARDEV_BACKEND_KIND_PIPE;
-    dev = backend->u.pipe.data = g_new0(ChardevHostdev, 1);
     qemu_chr_parse_common(opts, qapi_ChardevHostdev_base(dev));
     dev->device = g_strdup(device);
 }
diff --git a/chardev/char-ringbuf.c b/chardev/char-ringbuf.c
index d40d21d3cf..0ef2a17f90 100644
--- a/chardev/char-ringbuf.c
+++ b/chardev/char-ringbuf.c
@@ -97,7 +97,7 @@  static void qemu_chr_open_ringbuf(Chardev *chr,
                                   bool *be_opened,
                                   Error **errp)
 {
-    ChardevRingbuf *opts = backend->u.ringbuf.data;
+    ChardevRingbuf *opts = &backend->u.ringbuf;
     RingBufChardev *d = RINGBUF_CHARDEV(chr);
 
     d->size = opts->has_size ? opts->size : 65536;
@@ -210,10 +210,9 @@  static void qemu_chr_parse_ringbuf(QemuOpts *opts, ChardevBackend *backend,
                                    Error **errp)
 {
     int val;
-    ChardevRingbuf *ringbuf;
+    ChardevRingbuf *ringbuf = &backend->u.ringbuf;
 
     backend->type = CHARDEV_BACKEND_KIND_RINGBUF;
-    ringbuf = backend->u.ringbuf.data = g_new0(ChardevRingbuf, 1);
     qemu_chr_parse_common(opts, qapi_ChardevRingbuf_base(ringbuf));
 
     val = qemu_opt_get_size(opts, "size", 0);
diff --git a/chardev/char-serial.c b/chardev/char-serial.c
index 7c3d84ae24..baec955ecf 100644
--- a/chardev/char-serial.c
+++ b/chardev/char-serial.c
@@ -263,7 +263,7 @@  static void qmp_chardev_open_serial(Chardev *chr,
                                     bool *be_opened,
                                     Error **errp)
 {
-    ChardevHostdev *serial = backend->u.serial.data;
+    ChardevHostdev *serial = &backend->u.serial;
     int fd;
 
     fd = qmp_chardev_open_file_source(serial->device, O_RDWR | O_NONBLOCK,
@@ -283,14 +283,13 @@  static void qemu_chr_parse_serial(QemuOpts *opts, ChardevBackend *backend,
                                   Error **errp)
 {
     const char *device = qemu_opt_get(opts, "path");
-    ChardevHostdev *serial;
+    ChardevHostdev *serial = &backend->u.serial;
 
     if (device == NULL) {
         error_setg(errp, "chardev: serial/tty: no device path given");
         return;
     }
     backend->type = CHARDEV_BACKEND_KIND_SERIAL;
-    serial = backend->u.serial.data = g_new0(ChardevHostdev, 1);
     qemu_chr_parse_common(opts, qapi_ChardevHostdev_base(serial));
     serial->device = g_strdup(device);
 }
diff --git a/chardev/char-socket.c b/chardev/char-socket.c
index 95e45812d5..5332439d34 100644
--- a/chardev/char-socket.c
+++ b/chardev/char-socket.c
@@ -1301,7 +1301,7 @@  static void qmp_chardev_open_socket(Chardev *chr,
                                     Error **errp)
 {
     SocketChardev *s = SOCKET_CHARDEV(chr);
-    ChardevSocket *sock = backend->u.socket.data;
+    ChardevSocket *sock = &backend->u.socket;
     bool do_nodelay     = sock->has_nodelay ? sock->nodelay : false;
     bool is_listen      = sock->has_server  ? sock->server  : true;
     bool is_telnet      = sock->has_telnet  ? sock->telnet  : false;
@@ -1403,7 +1403,7 @@  static void qemu_chr_parse_socket(QemuOpts *opts, ChardevBackend *backend,
     }
 
     backend->type = CHARDEV_BACKEND_KIND_SOCKET;
-    sock = backend->u.socket.data = g_new0(ChardevSocket, 1);
+    sock = &backend->u.socket;
     qemu_chr_parse_common(opts, qapi_ChardevSocket_base(sock));
 
     sock->has_nodelay = qemu_opt_get(opts, "delay");
@@ -1435,16 +1435,14 @@  static void qemu_chr_parse_socket(QemuOpts *opts, ChardevBackend *backend,
 
     addr = g_new0(SocketAddressLegacy, 1);
     if (path) {
-        UnixSocketAddress *q_unix;
+        UnixSocketAddress *q_unix = &addr->u.q_unix;
         addr->type = SOCKET_ADDRESS_LEGACY_KIND_UNIX;
-        q_unix = addr->u.q_unix.data = g_new0(UnixSocketAddress, 1);
         q_unix->path = g_strdup(path);
         q_unix->tight = tight;
         q_unix->abstract = abstract;
     } else if (host) {
         addr->type = SOCKET_ADDRESS_LEGACY_KIND_INET;
-        addr->u.inet.data = g_new(InetSocketAddress, 1);
-        *addr->u.inet.data = (InetSocketAddress) {
+        addr->u.inet = (InetSocketAddress) {
             .host = g_strdup(host),
             .port = g_strdup(port),
             .has_to = qemu_opt_get(opts, "to"),
@@ -1456,8 +1454,7 @@  static void qemu_chr_parse_socket(QemuOpts *opts, ChardevBackend *backend,
         };
     } else if (fd) {
         addr->type = SOCKET_ADDRESS_LEGACY_KIND_FD;
-        addr->u.fd.data = g_new(String, 1);
-        addr->u.fd.data->str = g_strdup(fd);
+        addr->u.fd.str = g_strdup(fd);
     } else {
         g_assert_not_reached();
     }
diff --git a/chardev/char-stdio.c b/chardev/char-stdio.c
index 403da308c9..81ee655a21 100644
--- a/chardev/char-stdio.c
+++ b/chardev/char-stdio.c
@@ -87,7 +87,7 @@  static void qemu_chr_open_stdio(Chardev *chr,
                                 bool *be_opened,
                                 Error **errp)
 {
-    ChardevStdio *opts = backend->u.stdio.data;
+    ChardevStdio *opts = &backend->u.stdio;
     struct sigaction act;
 
     if (is_daemonized()) {
@@ -120,10 +120,9 @@  static void qemu_chr_open_stdio(Chardev *chr,
 static void qemu_chr_parse_stdio(QemuOpts *opts, ChardevBackend *backend,
                                  Error **errp)
 {
-    ChardevStdio *stdio;
+    ChardevStdio *stdio = &backend->u.stdio;
 
     backend->type = CHARDEV_BACKEND_KIND_STDIO;
-    stdio = backend->u.stdio.data = g_new0(ChardevStdio, 1);
     qemu_chr_parse_common(opts, qapi_ChardevStdio_base(stdio));
     stdio->has_signal = true;
     stdio->signal = qemu_opt_get_bool(opts, "signal", true);
diff --git a/chardev/char-udp.c b/chardev/char-udp.c
index 16b5dbce58..3b1bdddbbd 100644
--- a/chardev/char-udp.c
+++ b/chardev/char-udp.c
@@ -140,7 +140,7 @@  static void qemu_chr_parse_udp(QemuOpts *opts, ChardevBackend *backend,
     const char *localport = qemu_opt_get(opts, "localport");
     bool has_local = false;
     SocketAddressLegacy *addr;
-    ChardevUdp *udp;
+    ChardevUdp *udp = &backend->u.udp;
 
     backend->type = CHARDEV_BACKEND_KIND_UDP;
     if (host == NULL || strlen(host) == 0) {
@@ -161,13 +161,11 @@  static void qemu_chr_parse_udp(QemuOpts *opts, ChardevBackend *backend,
         has_local = true;
     }
 
-    udp = backend->u.udp.data = g_new0(ChardevUdp, 1);
     qemu_chr_parse_common(opts, qapi_ChardevUdp_base(udp));
 
     addr = g_new0(SocketAddressLegacy, 1);
     addr->type = SOCKET_ADDRESS_LEGACY_KIND_INET;
-    addr->u.inet.data = g_new(InetSocketAddress, 1);
-    *addr->u.inet.data = (InetSocketAddress) {
+    addr->u.inet = (InetSocketAddress) {
         .host = g_strdup(host),
         .port = g_strdup(port),
         .has_ipv4 = qemu_opt_get(opts, "ipv4"),
@@ -181,8 +179,7 @@  static void qemu_chr_parse_udp(QemuOpts *opts, ChardevBackend *backend,
         udp->has_local = true;
         addr = g_new0(SocketAddressLegacy, 1);
         addr->type = SOCKET_ADDRESS_LEGACY_KIND_INET;
-        addr->u.inet.data = g_new(InetSocketAddress, 1);
-        *addr->u.inet.data = (InetSocketAddress) {
+        addr->u.inet = (InetSocketAddress) {
             .host = g_strdup(localaddr),
             .port = g_strdup(localport),
         };
@@ -195,7 +192,7 @@  static void qmp_chardev_open_udp(Chardev *chr,
                                  bool *be_opened,
                                  Error **errp)
 {
-    ChardevUdp *udp = backend->u.udp.data;
+    ChardevUdp *udp = &backend->u.udp;
     SocketAddress *local_addr = socket_address_flatten(udp->local);
     SocketAddress *remote_addr = socket_address_flatten(udp->remote);
     QIOChannelSocket *sioc = qio_channel_socket_new();
diff --git a/chardev/char.c b/chardev/char.c
index 4d188bfa6f..34359818b6 100644
--- a/chardev/char.c
+++ b/chardev/char.c
@@ -238,7 +238,7 @@  static void qemu_char_open(Chardev *chr, ChardevBackend *backend,
 {
     ChardevClass *cc = CHARDEV_GET_CLASS(chr);
     /* Any ChardevCommon member would work */
-    ChardevCommon *common = backend ? backend->u.null.data : NULL;
+    ChardevCommon *common = backend ? &backend->u.null : NULL;
 
     if (common && common->has_logfile) {
         int flags = O_WRONLY | O_CREAT;
@@ -625,9 +625,8 @@  ChardevBackend *qemu_chr_parse_opts(QemuOpts *opts, Error **errp)
             return NULL;
         }
     } else {
-        ChardevCommon *ccom = g_new0(ChardevCommon, 1);
-        qemu_chr_parse_common(opts, ccom);
-        backend->u.null.data = ccom; /* Any ChardevCommon member would work */
+        /* Any ChardevCommon member would work */
+        qemu_chr_parse_common(opts, &backend->u.null);
     }
 
     return backend;
@@ -689,8 +688,7 @@  Chardev *qemu_chr_new_from_opts(QemuOpts *opts, GMainContext *context,
         qapi_free_ChardevBackend(backend);
         backend = g_new0(ChardevBackend, 1);
         backend->type = CHARDEV_BACKEND_KIND_MUX;
-        backend->u.mux.data = g_new0(ChardevMux, 1);
-        backend->u.mux.data->chardev = g_strdup(bid);
+        backend->u.mux.chardev = g_strdup(bid);
         mux = qemu_chardev_new(id, TYPE_CHARDEV_MUX, backend, context, errp);
         if (mux == NULL) {
             object_unparent(OBJECT(chr));
diff --git a/chardev/msmouse.c b/chardev/msmouse.c
index eb9231dcdb..98b0ef8cd7 100644
--- a/chardev/msmouse.c
+++ b/chardev/msmouse.c
@@ -111,12 +111,12 @@  static void msmouse_input_event(DeviceState *dev, QemuConsole *src,
 
     switch (evt->type) {
     case INPUT_EVENT_KIND_REL:
-        move = evt->u.rel.data;
+        move = &evt->u.rel;
         mouse->axis[move->axis] += move->value;
         break;
 
     case INPUT_EVENT_KIND_BTN:
-        btn = evt->u.btn.data;
+        btn = &evt->u.btn;
         mouse->btns[btn->button] = btn->down;
         mouse->btnc[btn->button] = true;
         break;
diff --git a/chardev/spice.c b/chardev/spice.c
index 1104426e3a..8d8502dca7 100644
--- a/chardev/spice.c
+++ b/chardev/spice.c
@@ -258,7 +258,7 @@  static void qemu_chr_open_spice_vmc(Chardev *chr,
                                     bool *be_opened,
                                     Error **errp)
 {
-    ChardevSpiceChannel *spicevmc = backend->u.spicevmc.data;
+    ChardevSpiceChannel *spicevmc = &backend->u.spicevmc;
     const char *type = spicevmc->type;
     const char **psubtype = spice_server_char_device_recognized_subtypes();
 
@@ -294,7 +294,7 @@  static void qemu_chr_open_spice_port(Chardev *chr,
                                      bool *be_opened,
                                      Error **errp)
 {
-    ChardevSpicePort *spiceport = backend->u.spiceport.data;
+    ChardevSpicePort *spiceport = &backend->u.spiceport;
     const char *name = spiceport->fqdn;
     SpiceChardev *s;
 
@@ -321,14 +321,13 @@  static void qemu_chr_parse_spice_vmc(QemuOpts *opts, ChardevBackend *backend,
                                      Error **errp)
 {
     const char *name = qemu_opt_get(opts, "name");
-    ChardevSpiceChannel *spicevmc;
+    ChardevSpiceChannel *spicevmc = &backend->u.spicevmc;
 
     if (name == NULL) {
         error_setg(errp, "chardev: spice channel: no name given");
         return;
     }
     backend->type = CHARDEV_BACKEND_KIND_SPICEVMC;
-    spicevmc = backend->u.spicevmc.data = g_new0(ChardevSpiceChannel, 1);
     qemu_chr_parse_common(opts, qapi_ChardevSpiceChannel_base(spicevmc));
     spicevmc->type = g_strdup(name);
 }
@@ -337,14 +336,13 @@  static void qemu_chr_parse_spice_port(QemuOpts *opts, ChardevBackend *backend,
                                       Error **errp)
 {
     const char *name = qemu_opt_get(opts, "name");
-    ChardevSpicePort *spiceport;
+    ChardevSpicePort *spiceport = &backend->u.spiceport;
 
     if (name == NULL) {
         error_setg(errp, "chardev: spice port: no name given");
         return;
     }
     backend->type = CHARDEV_BACKEND_KIND_SPICEPORT;
-    spiceport = backend->u.spiceport.data = g_new0(ChardevSpicePort, 1);
     qemu_chr_parse_common(opts, qapi_ChardevSpicePort_base(spiceport));
     spiceport->fqdn = g_strdup(name);
 }
diff --git a/chardev/wctablet.c b/chardev/wctablet.c
index 95e005f5a5..8479f59183 100644
--- a/chardev/wctablet.c
+++ b/chardev/wctablet.c
@@ -154,12 +154,12 @@  static void wctablet_input_event(DeviceState *dev, QemuConsole *src,
 
     switch (evt->type) {
     case INPUT_EVENT_KIND_ABS:
-        move = evt->u.abs.data;
+        move = &evt->u.abs;
         tablet->axis[move->axis] = move->value;
         break;
 
     case INPUT_EVENT_KIND_BTN:
-        btn = evt->u.btn.data;
+        btn = &evt->u.btn;
         tablet->btns[btn->button] = btn->down;
         break;
 
diff --git a/hw/core/numa.c b/hw/core/numa.c
index 7c4dd4e68e..24fe0e11d8 100644
--- a/hw/core/numa.c
+++ b/hw/core/numa.c
@@ -765,19 +765,19 @@  static void numa_stat_memory_devices(NumaNodeMem node_mem[])
             case MEMORY_DEVICE_INFO_KIND_DIMM:
             case MEMORY_DEVICE_INFO_KIND_NVDIMM:
                 pcdimm_info = value->type == MEMORY_DEVICE_INFO_KIND_DIMM ?
-                              value->u.dimm.data : value->u.nvdimm.data;
+                              &value->u.dimm : &value->u.nvdimm;
                 node_mem[pcdimm_info->node].node_mem += pcdimm_info->size;
                 node_mem[pcdimm_info->node].node_plugged_mem +=
                     pcdimm_info->size;
                 break;
             case MEMORY_DEVICE_INFO_KIND_VIRTIO_PMEM:
-                vpi = value->u.virtio_pmem.data;
+                vpi = &value->u.virtio_pmem;
                 /* TODO: once we support numa, assign to right node */
                 node_mem[0].node_mem += vpi->size;
                 node_mem[0].node_plugged_mem += vpi->size;
                 break;
             case MEMORY_DEVICE_INFO_KIND_VIRTIO_MEM:
-                vmi = value->u.virtio_mem.data;
+                vmi = &value->u.virtio_mem;
                 node_mem[vmi->node].node_mem += vmi->size;
                 node_mem[vmi->node].node_plugged_mem += vmi->size;
                 break;
diff --git a/hw/display/xenfb.c b/hw/display/xenfb.c
index 838260b6ad..6aa6010774 100644
--- a/hw/display/xenfb.c
+++ b/hw/display/xenfb.c
@@ -201,7 +201,7 @@  static void xenfb_key_event(DeviceState *dev, QemuConsole *src,
                             InputEvent *evt)
 {
     struct XenInput *xenfb = (struct XenInput *)dev;
-    InputKeyEvent *key = evt->u.key.data;
+    InputKeyEvent *key = &evt->u.key;
     int qcode = qemu_input_key_value_to_qcode(key->key);
     int lnx;
 
@@ -236,7 +236,7 @@  static void xenfb_mouse_event(DeviceState *dev, QemuConsole *src,
 
     switch (evt->type) {
     case INPUT_EVENT_KIND_BTN:
-        btn = evt->u.btn.data;
+        btn = &evt->u.btn;
         switch (btn->button) {
         case INPUT_BUTTON_LEFT:
             xenfb_send_key(xenfb, btn->down, BTN_LEFT);
@@ -263,7 +263,7 @@  static void xenfb_mouse_event(DeviceState *dev, QemuConsole *src,
         break;
 
     case INPUT_EVENT_KIND_ABS:
-        move = evt->u.abs.data;
+        move = &evt->u.abs;
         if (xenfb->raw_pointer_wanted) {
             xenfb->axis[move->axis] = move->value;
         } else {
@@ -289,7 +289,7 @@  static void xenfb_mouse_event(DeviceState *dev, QemuConsole *src,
         break;
 
     case INPUT_EVENT_KIND_REL:
-        move = evt->u.rel.data;
+        move = &evt->u.rel;
         xenfb->axis[move->axis] += move->value;
         break;
 
diff --git a/hw/input/hid.c b/hw/input/hid.c
index 89239b5634..2472c5a902 100644
--- a/hw/input/hid.c
+++ b/hw/input/hid.c
@@ -126,7 +126,7 @@  static void hid_pointer_event(DeviceState *dev, QemuConsole *src,
 
     switch (evt->type) {
     case INPUT_EVENT_KIND_REL:
-        move = evt->u.rel.data;
+        move = &evt->u.rel;
         if (move->axis == INPUT_AXIS_X) {
             e->xdx += move->value;
         } else if (move->axis == INPUT_AXIS_Y) {
@@ -135,7 +135,7 @@  static void hid_pointer_event(DeviceState *dev, QemuConsole *src,
         break;
 
     case INPUT_EVENT_KIND_ABS:
-        move = evt->u.abs.data;
+        move = &evt->u.abs;
         if (move->axis == INPUT_AXIS_X) {
             e->xdx = move->value;
         } else if (move->axis == INPUT_AXIS_Y) {
@@ -144,7 +144,7 @@  static void hid_pointer_event(DeviceState *dev, QemuConsole *src,
         break;
 
     case INPUT_EVENT_KIND_BTN:
-        btn = evt->u.btn.data;
+        btn = &evt->u.btn;
         if (btn->down) {
             e->buttons_state |= bmap[btn->button];
             if (btn->button == INPUT_BUTTON_WHEEL_UP) {
@@ -230,7 +230,7 @@  static void hid_keyboard_event(DeviceState *dev, QemuConsole *src,
     HIDState *hs = (HIDState *)dev;
     int scancodes[3], i, count;
     int slot;
-    InputKeyEvent *key = evt->u.key.data;
+    InputKeyEvent *key = &evt->u.key;
 
     count = qemu_input_key_value_to_scancode(key->key,
                                              key->down,
diff --git a/hw/input/ps2.c b/hw/input/ps2.c
index f8746d2f52..1176ccc88c 100644
--- a/hw/input/ps2.c
+++ b/hw/input/ps2.c
@@ -284,7 +284,7 @@  static void ps2_keyboard_event(DeviceState *dev, QemuConsole *src,
                                InputEvent *evt)
 {
     PS2KbdState *s = (PS2KbdState *)dev;
-    InputKeyEvent *key = evt->u.key.data;
+    InputKeyEvent *key = &evt->u.key;
     int qcode;
     uint16_t keycode = 0;
     int mod;
@@ -727,7 +727,7 @@  static void ps2_mouse_event(DeviceState *dev, QemuConsole *src,
 
     switch (evt->type) {
     case INPUT_EVENT_KIND_REL:
-        move = evt->u.rel.data;
+        move = &evt->u.rel;
         if (move->axis == INPUT_AXIS_X) {
             s->mouse_dx += move->value;
         } else if (move->axis == INPUT_AXIS_Y) {
@@ -736,7 +736,7 @@  static void ps2_mouse_event(DeviceState *dev, QemuConsole *src,
         break;
 
     case INPUT_EVENT_KIND_BTN:
-        btn = evt->u.btn.data;
+        btn = &evt->u.btn;
         if (btn->down) {
             s->mouse_buttons |= bmap[btn->button];
             if (btn->button == INPUT_BUTTON_WHEEL_UP) {
diff --git a/hw/input/virtio-input-hid.c b/hw/input/virtio-input-hid.c
index a7a244a95d..1c7b07cf42 100644
--- a/hw/input/virtio-input-hid.c
+++ b/hw/input/virtio-input-hid.c
@@ -83,7 +83,7 @@  static void virtio_input_handle_event(DeviceState *dev, QemuConsole *src,
 
     switch (evt->type) {
     case INPUT_EVENT_KIND_KEY:
-        key = evt->u.key.data;
+        key = &evt->u.key;
         qcode = qemu_input_key_value_to_qcode(key->key);
         if (qcode < qemu_input_map_qcode_to_linux_len &&
             qemu_input_map_qcode_to_linux[qcode]) {
@@ -99,7 +99,7 @@  static void virtio_input_handle_event(DeviceState *dev, QemuConsole *src,
         }
         break;
     case INPUT_EVENT_KIND_BTN:
-        btn = evt->u.btn.data;
+        btn = &evt->u.btn;
         if (vhid->wheel_axis &&
             (btn->button == INPUT_BUTTON_WHEEL_UP ||
              btn->button == INPUT_BUTTON_WHEEL_DOWN) &&
@@ -123,14 +123,14 @@  static void virtio_input_handle_event(DeviceState *dev, QemuConsole *src,
         }
         break;
     case INPUT_EVENT_KIND_REL:
-        move = evt->u.rel.data;
+        move = &evt->u.rel;
         event.type  = cpu_to_le16(EV_REL);
         event.code  = cpu_to_le16(axismap_rel[move->axis]);
         event.value = cpu_to_le32(move->value);
         virtio_input_send(vinput, &event);
         break;
     case INPUT_EVENT_KIND_ABS:
-        move = evt->u.abs.data;
+        move = &evt->u.abs;
         event.type  = cpu_to_le16(EV_ABS);
         event.code  = cpu_to_le16(axismap_abs[move->axis]);
         event.value = cpu_to_le32(move->value);
diff --git a/hw/mem/pc-dimm.c b/hw/mem/pc-dimm.c
index c30351070b..3d6f836621 100644
--- a/hw/mem/pc-dimm.c
+++ b/hw/mem/pc-dimm.c
@@ -236,11 +236,19 @@  static MemoryRegion *pc_dimm_md_get_memory_region(MemoryDeviceState *md,
 static void pc_dimm_md_fill_device_info(const MemoryDeviceState *md,
                                         MemoryDeviceInfo *info)
 {
-    PCDIMMDeviceInfo *di = g_new0(PCDIMMDeviceInfo, 1);
+    PCDIMMDeviceInfo *di;
     const DeviceClass *dc = DEVICE_GET_CLASS(md);
     const PCDIMMDevice *dimm = PC_DIMM(md);
     const DeviceState *dev = DEVICE(md);
 
+    if (object_dynamic_cast(OBJECT(dev), TYPE_NVDIMM)) {
+        di = &info->u.nvdimm;
+        info->type = MEMORY_DEVICE_INFO_KIND_NVDIMM;
+    } else {
+        di = &info->u.dimm;
+        info->type = MEMORY_DEVICE_INFO_KIND_DIMM;
+    }
+
     if (dev->id) {
         di->has_id = true;
         di->id = g_strdup(dev->id);
@@ -253,14 +261,6 @@  static void pc_dimm_md_fill_device_info(const MemoryDeviceState *md,
     di->size = object_property_get_uint(OBJECT(dimm), PC_DIMM_SIZE_PROP,
                                         NULL);
     di->memdev = object_get_canonical_path(OBJECT(dimm->hostmem));
-
-    if (object_dynamic_cast(OBJECT(dev), TYPE_NVDIMM)) {
-        info->u.nvdimm.data = di;
-        info->type = MEMORY_DEVICE_INFO_KIND_NVDIMM;
-    } else {
-        info->u.dimm.data = di;
-        info->type = MEMORY_DEVICE_INFO_KIND_DIMM;
-    }
 }
 
 static void pc_dimm_class_init(ObjectClass *oc, void *data)
diff --git a/hw/virtio/virtio-mem-pci.c b/hw/virtio/virtio-mem-pci.c
index 913f4a3326..f93572fc27 100644
--- a/hw/virtio/virtio-mem-pci.c
+++ b/hw/virtio/virtio-mem-pci.c
@@ -58,7 +58,7 @@  static uint64_t virtio_mem_pci_get_plugged_size(const MemoryDeviceState *md,
 static void virtio_mem_pci_fill_device_info(const MemoryDeviceState *md,
                                             MemoryDeviceInfo *info)
 {
-    VirtioMEMDeviceInfo *vi = g_new0(VirtioMEMDeviceInfo, 1);
+    VirtioMEMDeviceInfo *vi = &info->u.virtio_mem;
     VirtIOMEMPCI *pci_mem = VIRTIO_MEM_PCI(md);
     VirtIOMEM *vmem = VIRTIO_MEM(&pci_mem->vdev);
     VirtIOMEMClass *vpc = VIRTIO_MEM_GET_CLASS(vmem);
@@ -72,7 +72,6 @@  static void virtio_mem_pci_fill_device_info(const MemoryDeviceState *md,
     /* let the real device handle everything else */
     vpc->fill_device_info(vmem, vi);
 
-    info->u.virtio_mem.data = vi;
     info->type = MEMORY_DEVICE_INFO_KIND_VIRTIO_MEM;
 }
 
diff --git a/hw/virtio/virtio-pmem-pci.c b/hw/virtio/virtio-pmem-pci.c
index 2b2a0b1eae..adf17f873b 100644
--- a/hw/virtio/virtio-pmem-pci.c
+++ b/hw/virtio/virtio-pmem-pci.c
@@ -63,7 +63,7 @@  static uint64_t virtio_pmem_pci_get_plugged_size(const MemoryDeviceState *md,
 static void virtio_pmem_pci_fill_device_info(const MemoryDeviceState *md,
                                              MemoryDeviceInfo *info)
 {
-    VirtioPMEMDeviceInfo *vi = g_new0(VirtioPMEMDeviceInfo, 1);
+    VirtioPMEMDeviceInfo *vi = &info->u.virtio_pmem;
     VirtIOPMEMPCI *pci_pmem = VIRTIO_PMEM_PCI(md);
     VirtIOPMEM *pmem = VIRTIO_PMEM(&pci_pmem->vdev);
     VirtIOPMEMClass *vpc = VIRTIO_PMEM_GET_CLASS(pmem);
@@ -77,7 +77,6 @@  static void virtio_pmem_pci_fill_device_info(const MemoryDeviceState *md,
     /* let the real device handle everything else */
     vpc->fill_device_info(pmem, vi);
 
-    info->u.virtio_pmem.data = vi;
     info->type = MEMORY_DEVICE_INFO_KIND_VIRTIO_PMEM;
 }
 
diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
index 9789f4277f..0324caa114 100644
--- a/monitor/hmp-cmds.c
+++ b/monitor/hmp-cmds.c
@@ -918,7 +918,7 @@  void hmp_info_tpm(Monitor *mon, const QDict *qdict)
 
         switch (ti->options->type) {
         case TPM_TYPE_OPTIONS_KIND_PASSTHROUGH:
-            tpo = ti->options->u.passthrough.data;
+            tpo = &ti->options->u.passthrough;
             monitor_printf(mon, "%s%s%s%s",
                            tpo->has_path ? ",path=" : "",
                            tpo->has_path ? tpo->path : "",
@@ -926,7 +926,7 @@  void hmp_info_tpm(Monitor *mon, const QDict *qdict)
                            tpo->has_cancel_path ? tpo->cancel_path : "");
             break;
         case TPM_TYPE_OPTIONS_KIND_EMULATOR:
-            teo = ti->options->u.emulator.data;
+            teo = &ti->options->u.emulator;
             monitor_printf(mon, ",chardev=%s", teo->chardev);
             break;
         case TPM_TYPE_OPTIONS_KIND__MAX:
@@ -1728,14 +1728,14 @@  void hmp_sendkey(Monitor *mon, const QDict *qdict)
                 goto err_out;
             }
             keylist->value->type = KEY_VALUE_KIND_NUMBER;
-            keylist->value->u.number.data = value;
+            keylist->value->u.number = value;
         } else {
             int idx = index_from_key(keys, keyname_len);
             if (idx == Q_KEY_CODE__MAX) {
                 goto err_out;
             }
             keylist->value->type = KEY_VALUE_KIND_QCODE;
-            keylist->value->u.qcode.data = idx;
+            keylist->value->u.qcode = idx;
         }
 
         if (!*separator) {
@@ -1860,7 +1860,7 @@  void hmp_info_memory_devices(Monitor *mon, const QDict *qdict)
             case MEMORY_DEVICE_INFO_KIND_DIMM:
             case MEMORY_DEVICE_INFO_KIND_NVDIMM:
                 di = value->type == MEMORY_DEVICE_INFO_KIND_DIMM ?
-                     value->u.dimm.data : value->u.nvdimm.data;
+                     &value->u.dimm : &value->u.nvdimm;
                 monitor_printf(mon, "Memory device [%s]: \"%s\"\n",
                                MemoryDeviceInfoKind_str(value->type),
                                di->id ? di->id : "");
@@ -1875,7 +1875,7 @@  void hmp_info_memory_devices(Monitor *mon, const QDict *qdict)
                                di->hotpluggable ? "true" : "false");
                 break;
             case MEMORY_DEVICE_INFO_KIND_VIRTIO_PMEM:
-                vpi = value->u.virtio_pmem.data;
+                vpi = &value->u.virtio_pmem;
                 monitor_printf(mon, "Memory device [%s]: \"%s\"\n",
                                MemoryDeviceInfoKind_str(value->type),
                                vpi->id ? vpi->id : "");
@@ -1884,7 +1884,7 @@  void hmp_info_memory_devices(Monitor *mon, const QDict *qdict)
                 monitor_printf(mon, "  memdev: %s\n", vpi->memdev);
                 break;
             case MEMORY_DEVICE_INFO_KIND_VIRTIO_MEM:
-                vmi = value->u.virtio_mem.data;
+                vmi = &value->u.virtio_mem;
                 monitor_printf(mon, "Memory device [%s]: \"%s\"\n",
                                MemoryDeviceInfoKind_str(value->type),
                                vmi->id ? vmi->id : "");
diff --git a/qemu-keymap.c b/qemu-keymap.c
index 536e8f2385..52637c449c 100644
--- a/qemu-keymap.c
+++ b/qemu-keymap.c
@@ -38,7 +38,7 @@  static uint32_t qcode_to_number(uint32_t qcode)
     uint32_t number;
 
     keyvalue.type = KEY_VALUE_KIND_QCODE;
-    keyvalue.u.qcode.data = qcode;
+    keyvalue.u.qcode = qcode;
     number = qemu_input_key_value_to_number(&keyvalue);
     assert(number != 0);
     return number;
diff --git a/replay/replay-input.c b/replay/replay-input.c
index 1147e3d34e..c1eb1b79e1 100644
--- a/replay/replay-input.c
+++ b/replay/replay-input.c
@@ -26,16 +26,16 @@  void replay_save_input_event(InputEvent *evt)
 
     switch (evt->type) {
     case INPUT_EVENT_KIND_KEY:
-        key = evt->u.key.data;
+        key = &evt->u.key;
         replay_put_dword(key->key->type);
 
         switch (key->key->type) {
         case KEY_VALUE_KIND_NUMBER:
-            replay_put_qword(key->key->u.number.data);
+            replay_put_qword(key->key->u.number);
             replay_put_byte(key->down);
             break;
         case KEY_VALUE_KIND_QCODE:
-            replay_put_dword(key->key->u.qcode.data);
+            replay_put_dword(key->key->u.qcode);
             replay_put_byte(key->down);
             break;
         case KEY_VALUE_KIND__MAX:
@@ -44,17 +44,17 @@  void replay_save_input_event(InputEvent *evt)
         }
         break;
     case INPUT_EVENT_KIND_BTN:
-        btn = evt->u.btn.data;
+        btn = &evt->u.btn;
         replay_put_dword(btn->button);
         replay_put_byte(btn->down);
         break;
     case INPUT_EVENT_KIND_REL:
-        move = evt->u.rel.data;
+        move = &evt->u.rel;
         replay_put_dword(move->axis);
         replay_put_qword(move->value);
         break;
     case INPUT_EVENT_KIND_ABS:
-        move = evt->u.abs.data;
+        move = &evt->u.abs;
         replay_put_dword(move->axis);
         replay_put_qword(move->value);
         break;
@@ -68,26 +68,21 @@  InputEvent *replay_read_input_event(void)
 {
     InputEvent evt;
     KeyValue keyValue;
-    InputKeyEvent key;
-    key.key = &keyValue;
-    InputBtnEvent btn;
-    InputMoveEvent rel;
-    InputMoveEvent abs;
+    evt.u.key.key = &keyValue;
 
     evt.type = replay_get_dword();
     switch (evt.type) {
     case INPUT_EVENT_KIND_KEY:
-        evt.u.key.data = &key;
-        evt.u.key.data->key->type = replay_get_dword();
+        evt.u.key.key->type = replay_get_dword();
 
-        switch (evt.u.key.data->key->type) {
+        switch (evt.u.key.key->type) {
         case KEY_VALUE_KIND_NUMBER:
-            evt.u.key.data->key->u.number.data = replay_get_qword();
-            evt.u.key.data->down = replay_get_byte();
+            evt.u.key.key->u.number = replay_get_qword();
+            evt.u.key.down = replay_get_byte();
             break;
         case KEY_VALUE_KIND_QCODE:
-            evt.u.key.data->key->u.qcode.data = (QKeyCode)replay_get_dword();
-            evt.u.key.data->down = replay_get_byte();
+            evt.u.key.key->u.qcode = (QKeyCode)replay_get_dword();
+            evt.u.key.down = replay_get_byte();
             break;
         case KEY_VALUE_KIND__MAX:
             /* keep gcc happy */
@@ -95,19 +90,16 @@  InputEvent *replay_read_input_event(void)
         }
         break;
     case INPUT_EVENT_KIND_BTN:
-        evt.u.btn.data = &btn;
-        evt.u.btn.data->button = (InputButton)replay_get_dword();
-        evt.u.btn.data->down = replay_get_byte();
+        evt.u.btn.button = (InputButton)replay_get_dword();
+        evt.u.btn.down = replay_get_byte();
         break;
     case INPUT_EVENT_KIND_REL:
-        evt.u.rel.data = &rel;
-        evt.u.rel.data->axis = (InputAxis)replay_get_dword();
-        evt.u.rel.data->value = replay_get_qword();
+        evt.u.rel.axis = (InputAxis)replay_get_dword();
+        evt.u.rel.value = replay_get_qword();
         break;
     case INPUT_EVENT_KIND_ABS:
-        evt.u.abs.data = &abs;
-        evt.u.abs.data->axis = (InputAxis)replay_get_dword();
-        evt.u.abs.data->value = replay_get_qword();
+        evt.u.abs.axis = (InputAxis)replay_get_dword();
+        evt.u.abs.value = replay_get_qword();
         break;
     case INPUT_EVENT_KIND__MAX:
         /* keep gcc happy */
diff --git a/tests/test-char.c b/tests/test-char.c
index 9196e566e9..0e7a033a90 100644
--- a/tests/test-char.c
+++ b/tests/test-char.c
@@ -1220,7 +1220,7 @@  static void char_file_fifo_test(void)
                          .has_in = true,
                          .out = out };
     ChardevBackend backend = { .type = CHARDEV_BACKEND_KIND_FILE,
-                               .u.file.data = &file };
+                               .u.file = file };
     FeHandler fe = { 0, };
     int fd, ret;
 
@@ -1273,19 +1273,17 @@  static void char_file_test_internal(Chardev *ext_chr, const char *filepath)
     char *out;
     Chardev *chr;
     char *contents = NULL;
-    ChardevFile file = {};
-    ChardevBackend backend = { .type = CHARDEV_BACKEND_KIND_FILE,
-                               .u.file.data = &file };
+    ChardevBackend backend = { .type = CHARDEV_BACKEND_KIND_FILE };
     gsize length;
     int ret;
 
     if (ext_chr) {
         chr = ext_chr;
         out = g_strdup(filepath);
-        file.out = out;
+        backend.u.file.out = out;
     } else {
         out = g_build_filename(tmp_path, "out", NULL);
-        file.out = out;
+        backend.u.file.out = out;
         chr = qemu_chardev_new(NULL, TYPE_CHARDEV_FILE, &backend,
                                NULL, &error_abort);
     }
@@ -1384,7 +1382,7 @@  static void char_hotswap_test(void)
     char *filename = g_build_filename(tmp_path, "file", NULL);
     ChardevFile file = { .out = filename };
     ChardevBackend backend = { .type = CHARDEV_BACKEND_KIND_FILE,
-                               .u.file.data = &file };
+                               .u.file = file };
     ChardevReturn *ret;
 
     int port;
diff --git a/tests/test-clone-visitor.c b/tests/test-clone-visitor.c
index 5e1e8b2f5e..0a62704bed 100644
--- a/tests/test-clone-visitor.c
+++ b/tests/test-clone-visitor.c
@@ -110,7 +110,7 @@  static void test_clone_complex1(void)
     dst = QAPI_CLONE(UserDefListUnion, src);
     g_assert(dst);
     g_assert_cmpint(dst->type, ==, src->type);
-    g_assert(!dst->u.string.data);
+    g_assert(!dst->u.string);
 
     qapi_free_UserDefListUnion(src);
     qapi_free_UserDefListUnion(dst);
@@ -155,30 +155,30 @@  static void test_clone_complex3(void)
     tmp = src->array = g_new0(__org_qemu_x_Union1List, 1);
     tmp->value = g_new0(__org_qemu_x_Union1, 1);
     tmp->value->type = ORG_QEMU_X_UNION1_KIND___ORG_QEMU_X_BRANCH;
-    tmp->value->u.__org_qemu_x_branch.data = g_strdup("one");
+    tmp->value->u.__org_qemu_x_branch = g_strdup("one");
     tmp = tmp->next = g_new0(__org_qemu_x_Union1List, 1);
     tmp->value = g_new0(__org_qemu_x_Union1, 1);
     tmp->value->type = ORG_QEMU_X_UNION1_KIND___ORG_QEMU_X_BRANCH;
-    tmp->value->u.__org_qemu_x_branch.data = g_strdup("two");
+    tmp->value->u.__org_qemu_x_branch = g_strdup("two");
     tmp = tmp->next = g_new0(__org_qemu_x_Union1List, 1);
     tmp->value = g_new0(__org_qemu_x_Union1, 1);
     tmp->value->type = ORG_QEMU_X_UNION1_KIND___ORG_QEMU_X_BRANCH;
-    tmp->value->u.__org_qemu_x_branch.data = g_strdup("three");
+    tmp->value->u.__org_qemu_x_branch = g_strdup("three");
 
     dst = QAPI_CLONE(__org_qemu_x_Struct2, src);
     g_assert(dst);
     tmp = dst->array;
     g_assert(tmp);
     g_assert(tmp->value);
-    g_assert_cmpstr(tmp->value->u.__org_qemu_x_branch.data, ==, "one");
+    g_assert_cmpstr(tmp->value->u.__org_qemu_x_branch, ==, "one");
     tmp = tmp->next;
     g_assert(tmp);
     g_assert(tmp->value);
-    g_assert_cmpstr(tmp->value->u.__org_qemu_x_branch.data, ==, "two");
+    g_assert_cmpstr(tmp->value->u.__org_qemu_x_branch, ==, "two");
     tmp = tmp->next;
     g_assert(tmp);
     g_assert(tmp->value);
-    g_assert_cmpstr(tmp->value->u.__org_qemu_x_branch.data, ==, "three");
+    g_assert_cmpstr(tmp->value->u.__org_qemu_x_branch, ==, "three");
     tmp = tmp->next;
     g_assert(!tmp);
 
diff --git a/tests/test-qmp-cmds.c b/tests/test-qmp-cmds.c
index d3413bfef0..3d699fbb66 100644
--- a/tests/test-qmp-cmds.c
+++ b/tests/test-qmp-cmds.c
@@ -136,7 +136,7 @@  __org_qemu_x_Union1 *qmp___org_qemu_x_command(__org_qemu_x_EnumList *a,
     __org_qemu_x_Union1 *ret = g_new0(__org_qemu_x_Union1, 1);
 
     ret->type = ORG_QEMU_X_UNION1_KIND___ORG_QEMU_X_BRANCH;
-    ret->u.__org_qemu_x_branch.data = strdup("blah1");
+    ret->u.__org_qemu_x_branch = strdup("blah1");
 
     /* Also test that 'wchar-t' was munged to 'q_wchar_t' */
     if (b && b->value && !b->value->has_q_wchar_t) {
diff --git a/tests/test-qobject-input-visitor.c b/tests/test-qobject-input-visitor.c
index e41b91a2a6..b976ab9763 100644
--- a/tests/test-qobject-input-visitor.c
+++ b/tests/test-qobject-input-visitor.c
@@ -710,7 +710,7 @@  static void test_list_union_integer_helper(TestInputVisitorData *data,
     switch (kind) {
     case USER_DEF_LIST_UNION_KIND_INTEGER: {
         intList *elem = NULL;
-        for (i = 0, elem = cvalue->u.integer.data;
+        for (i = 0, elem = cvalue->u.integer;
              elem; elem = elem->next, i++) {
             g_assert_cmpint(elem->value, ==, i);
         }
@@ -718,56 +718,56 @@  static void test_list_union_integer_helper(TestInputVisitorData *data,
     }
     case USER_DEF_LIST_UNION_KIND_S8: {
         int8List *elem = NULL;
-        for (i = 0, elem = cvalue->u.s8.data; elem; elem = elem->next, i++) {
+        for (i = 0, elem = cvalue->u.s8; elem; elem = elem->next, i++) {
             g_assert_cmpint(elem->value, ==, i);
         }
         break;
     }
     case USER_DEF_LIST_UNION_KIND_S16: {
         int16List *elem = NULL;
-        for (i = 0, elem = cvalue->u.s16.data; elem; elem = elem->next, i++) {
+        for (i = 0, elem = cvalue->u.s16; elem; elem = elem->next, i++) {
             g_assert_cmpint(elem->value, ==, i);
         }
         break;
     }
     case USER_DEF_LIST_UNION_KIND_S32: {
         int32List *elem = NULL;
-        for (i = 0, elem = cvalue->u.s32.data; elem; elem = elem->next, i++) {
+        for (i = 0, elem = cvalue->u.s32; elem; elem = elem->next, i++) {
             g_assert_cmpint(elem->value, ==, i);
         }
         break;
     }
     case USER_DEF_LIST_UNION_KIND_S64: {
         int64List *elem = NULL;
-        for (i = 0, elem = cvalue->u.s64.data; elem; elem = elem->next, i++) {
+        for (i = 0, elem = cvalue->u.s64; elem; elem = elem->next, i++) {
             g_assert_cmpint(elem->value, ==, i);
         }
         break;
     }
     case USER_DEF_LIST_UNION_KIND_U8: {
         uint8List *elem = NULL;
-        for (i = 0, elem = cvalue->u.u8.data; elem; elem = elem->next, i++) {
+        for (i = 0, elem = cvalue->u.u8; elem; elem = elem->next, i++) {
             g_assert_cmpint(elem->value, ==, i);
         }
         break;
     }
     case USER_DEF_LIST_UNION_KIND_U16: {
         uint16List *elem = NULL;
-        for (i = 0, elem = cvalue->u.u16.data; elem; elem = elem->next, i++) {
+        for (i = 0, elem = cvalue->u.u16; elem; elem = elem->next, i++) {
             g_assert_cmpint(elem->value, ==, i);
         }
         break;
     }
     case USER_DEF_LIST_UNION_KIND_U32: {
         uint32List *elem = NULL;
-        for (i = 0, elem = cvalue->u.u32.data; elem; elem = elem->next, i++) {
+        for (i = 0, elem = cvalue->u.u32; elem; elem = elem->next, i++) {
             g_assert_cmpint(elem->value, ==, i);
         }
         break;
     }
     case USER_DEF_LIST_UNION_KIND_U64: {
         uint64List *elem = NULL;
-        for (i = 0, elem = cvalue->u.u64.data; elem; elem = elem->next, i++) {
+        for (i = 0, elem = cvalue->u.u64; elem; elem = elem->next, i++) {
             g_assert_cmpint(elem->value, ==, i);
         }
         break;
@@ -868,7 +868,7 @@  static void test_visitor_in_list_union_bool(TestInputVisitorData *data,
     g_assert(cvalue != NULL);
     g_assert_cmpint(cvalue->type, ==, USER_DEF_LIST_UNION_KIND_BOOLEAN);
 
-    for (i = 0, elem = cvalue->u.boolean.data; elem; elem = elem->next, i++) {
+    for (i = 0, elem = cvalue->u.boolean; elem; elem = elem->next, i++) {
         g_assert_cmpint(elem->value, ==, (i % 3 == 0) ? 1 : 0);
     }
 
@@ -900,7 +900,7 @@  static void test_visitor_in_list_union_string(TestInputVisitorData *data,
     g_assert(cvalue != NULL);
     g_assert_cmpint(cvalue->type, ==, USER_DEF_LIST_UNION_KIND_STRING);
 
-    for (i = 0, elem = cvalue->u.string.data; elem; elem = elem->next, i++) {
+    for (i = 0, elem = cvalue->u.string; elem; elem = elem->next, i++) {
         gchar str[8];
         sprintf(str, "%d", i);
         g_assert_cmpstr(elem->value, ==, str);
@@ -936,7 +936,7 @@  static void test_visitor_in_list_union_number(TestInputVisitorData *data,
     g_assert(cvalue != NULL);
     g_assert_cmpint(cvalue->type, ==, USER_DEF_LIST_UNION_KIND_NUMBER);
 
-    for (i = 0, elem = cvalue->u.number.data; elem; elem = elem->next, i++) {
+    for (i = 0, elem = cvalue->u.number; elem; elem = elem->next, i++) {
         GString *double_expected = g_string_new("");
         GString *double_actual = g_string_new("");
 
diff --git a/tests/test-qobject-output-visitor.c b/tests/test-qobject-output-visitor.c
index 1c856d9bd2..202f848062 100644
--- a/tests/test-qobject-output-visitor.c
+++ b/tests/test-qobject-output-visitor.c
@@ -444,7 +444,7 @@  static void init_list_union(UserDefListUnion *cvalue)
     int i;
     switch (cvalue->type) {
     case USER_DEF_LIST_UNION_KIND_INTEGER: {
-        intList **list = &cvalue->u.integer.data;
+        intList **list = &cvalue->u.integer;
         for (i = 0; i < 32; i++) {
             *list = g_new0(intList, 1);
             (*list)->value = i;
@@ -454,7 +454,7 @@  static void init_list_union(UserDefListUnion *cvalue)
         break;
     }
     case USER_DEF_LIST_UNION_KIND_S8: {
-        int8List **list = &cvalue->u.s8.data;
+        int8List **list = &cvalue->u.s8;
         for (i = 0; i < 32; i++) {
             *list = g_new0(int8List, 1);
             (*list)->value = i;
@@ -464,7 +464,7 @@  static void init_list_union(UserDefListUnion *cvalue)
         break;
     }
     case USER_DEF_LIST_UNION_KIND_S16: {
-        int16List **list = &cvalue->u.s16.data;
+        int16List **list = &cvalue->u.s16;
         for (i = 0; i < 32; i++) {
             *list = g_new0(int16List, 1);
             (*list)->value = i;
@@ -474,7 +474,7 @@  static void init_list_union(UserDefListUnion *cvalue)
         break;
     }
     case USER_DEF_LIST_UNION_KIND_S32: {
-        int32List **list = &cvalue->u.s32.data;
+        int32List **list = &cvalue->u.s32;
         for (i = 0; i < 32; i++) {
             *list = g_new0(int32List, 1);
             (*list)->value = i;
@@ -484,7 +484,7 @@  static void init_list_union(UserDefListUnion *cvalue)
         break;
     }
     case USER_DEF_LIST_UNION_KIND_S64: {
-        int64List **list = &cvalue->u.s64.data;
+        int64List **list = &cvalue->u.s64;
         for (i = 0; i < 32; i++) {
             *list = g_new0(int64List, 1);
             (*list)->value = i;
@@ -494,7 +494,7 @@  static void init_list_union(UserDefListUnion *cvalue)
         break;
     }
     case USER_DEF_LIST_UNION_KIND_U8: {
-        uint8List **list = &cvalue->u.u8.data;
+        uint8List **list = &cvalue->u.u8;
         for (i = 0; i < 32; i++) {
             *list = g_new0(uint8List, 1);
             (*list)->value = i;
@@ -504,7 +504,7 @@  static void init_list_union(UserDefListUnion *cvalue)
         break;
     }
     case USER_DEF_LIST_UNION_KIND_U16: {
-        uint16List **list = &cvalue->u.u16.data;
+        uint16List **list = &cvalue->u.u16;
         for (i = 0; i < 32; i++) {
             *list = g_new0(uint16List, 1);
             (*list)->value = i;
@@ -514,7 +514,7 @@  static void init_list_union(UserDefListUnion *cvalue)
         break;
     }
     case USER_DEF_LIST_UNION_KIND_U32: {
-        uint32List **list = &cvalue->u.u32.data;
+        uint32List **list = &cvalue->u.u32;
         for (i = 0; i < 32; i++) {
             *list = g_new0(uint32List, 1);
             (*list)->value = i;
@@ -524,7 +524,7 @@  static void init_list_union(UserDefListUnion *cvalue)
         break;
     }
     case USER_DEF_LIST_UNION_KIND_U64: {
-        uint64List **list = &cvalue->u.u64.data;
+        uint64List **list = &cvalue->u.u64;
         for (i = 0; i < 32; i++) {
             *list = g_new0(uint64List, 1);
             (*list)->value = i;
@@ -534,7 +534,7 @@  static void init_list_union(UserDefListUnion *cvalue)
         break;
     }
     case USER_DEF_LIST_UNION_KIND_BOOLEAN: {
-        boolList **list = &cvalue->u.boolean.data;
+        boolList **list = &cvalue->u.boolean;
         for (i = 0; i < 32; i++) {
             *list = g_new0(boolList, 1);
             (*list)->value = QEMU_IS_ALIGNED(i, 3);
@@ -544,7 +544,7 @@  static void init_list_union(UserDefListUnion *cvalue)
         break;
     }
     case USER_DEF_LIST_UNION_KIND_STRING: {
-        strList **list = &cvalue->u.string.data;
+        strList **list = &cvalue->u.string;
         for (i = 0; i < 32; i++) {
             *list = g_new0(strList, 1);
             (*list)->value = g_strdup_printf("%d", i);
@@ -554,7 +554,7 @@  static void init_list_union(UserDefListUnion *cvalue)
         break;
     }
     case USER_DEF_LIST_UNION_KIND_NUMBER: {
-        numberList **list = &cvalue->u.number.data;
+        numberList **list = &cvalue->u.number;
         for (i = 0; i < 32; i++) {
             *list = g_new0(numberList, 1);
             (*list)->value = (double)i / 3;
diff --git a/ui/console.c b/ui/console.c
index 820e408170..2f93723ed6 100644
--- a/ui/console.c
+++ b/ui/console.c
@@ -2212,7 +2212,7 @@  static void vc_chr_open(Chardev *chr,
                         bool *be_opened,
                         Error **errp)
 {
-    ChardevVC *vc = backend->u.vc.data;
+    ChardevVC *vc = &backend->u.vc;
     VCChardev *drv = VC_CHARDEV(chr);
     QemuConsole *s;
     unsigned width = 0;
@@ -2362,10 +2362,9 @@  void qemu_display_help(void)
 void qemu_chr_parse_vc(QemuOpts *opts, ChardevBackend *backend, Error **errp)
 {
     int val;
-    ChardevVC *vc;
+    ChardevVC *vc = &backend->u.vc;
 
     backend->type = CHARDEV_BACKEND_KIND_VC;
-    vc = backend->u.vc.data = g_new0(ChardevVC, 1);
     qemu_chr_parse_common(opts, qapi_ChardevVC_base(vc));
 
     val = qemu_opt_get_number(opts, "width", 0);
diff --git a/ui/input-keymap.c b/ui/input-keymap.c
index 1b756a6970..0232e25124 100644
--- a/ui/input-keymap.c
+++ b/ui/input-keymap.c
@@ -33,13 +33,13 @@  int qemu_input_linux_to_qcode(unsigned int lnx)
 int qemu_input_key_value_to_number(const KeyValue *value)
 {
     if (value->type == KEY_VALUE_KIND_QCODE) {
-        if (value->u.qcode.data >= qemu_input_map_qcode_to_qnum_len) {
+        if (value->u.qcode >= qemu_input_map_qcode_to_qnum_len) {
             return 0;
         }
-        return qemu_input_map_qcode_to_qnum[value->u.qcode.data];
+        return qemu_input_map_qcode_to_qnum[value->u.qcode];
     } else {
         assert(value->type == KEY_VALUE_KIND_NUMBER);
-        return value->u.number.data;
+        return value->u.number;
     }
 }
 
@@ -54,10 +54,10 @@  int qemu_input_key_number_to_qcode(unsigned int nr)
 int qemu_input_key_value_to_qcode(const KeyValue *value)
 {
     if (value->type == KEY_VALUE_KIND_QCODE) {
-        return value->u.qcode.data;
+        return value->u.qcode;
     } else {
         assert(value->type == KEY_VALUE_KIND_NUMBER);
-        return qemu_input_key_number_to_qcode(value->u.number.data);
+        return qemu_input_key_number_to_qcode(value->u.number);
     }
 }
 
@@ -68,7 +68,7 @@  int qemu_input_key_value_to_scancode(const KeyValue *value, bool down,
     int count = 0;
 
     if (value->type == KEY_VALUE_KIND_QCODE &&
-        value->u.qcode.data == Q_KEY_CODE_PAUSE) {
+        value->u.qcode == Q_KEY_CODE_PAUSE) {
         /* specific case */
         int v = down ? 0 : 0x80;
         codes[count++] = 0xe1;
diff --git a/ui/input-legacy.c b/ui/input-legacy.c
index 9fc78a639b..5a32b010d4 100644
--- a/ui/input-legacy.c
+++ b/ui/input-legacy.c
@@ -75,9 +75,9 @@  static KeyValue *copy_key_value(KeyValue *src)
     KeyValue *dst = g_new(KeyValue, 1);
     memcpy(dst, src, sizeof(*src));
     if (dst->type == KEY_VALUE_KIND_NUMBER) {
-        QKeyCode code = qemu_input_key_number_to_qcode(dst->u.number.data);
+        QKeyCode code = qemu_input_key_number_to_qcode(dst->u.number);
         dst->type = KEY_VALUE_KIND_QCODE;
-        dst->u.qcode.data = code;
+        dst->u.qcode = code;
     }
     return dst;
 }
@@ -113,7 +113,7 @@  static void legacy_kbd_event(DeviceState *dev, QemuConsole *src,
 {
     QEMUPutKbdEntry *entry = (QEMUPutKbdEntry *)dev;
     int scancodes[3], i, count;
-    InputKeyEvent *key = evt->u.key.data;
+    InputKeyEvent *key = &evt->u.key;
 
     if (!entry || !entry->put_kbd) {
         return;
@@ -159,7 +159,7 @@  static void legacy_mouse_event(DeviceState *dev, QemuConsole *src,
 
     switch (evt->type) {
     case INPUT_EVENT_KIND_BTN:
-        btn = evt->u.btn.data;
+        btn = &evt->u.btn;
         if (btn->down) {
             s->buttons |= bmap[btn->button];
         } else {
@@ -181,11 +181,11 @@  static void legacy_mouse_event(DeviceState *dev, QemuConsole *src,
         }
         break;
     case INPUT_EVENT_KIND_ABS:
-        move = evt->u.abs.data;
+        move = &evt->u.abs;
         s->axis[move->axis] = move->value;
         break;
     case INPUT_EVENT_KIND_REL:
-        move = evt->u.rel.data;
+        move = &evt->u.rel;
         s->axis[move->axis] += move->value;
         break;
     default:
diff --git a/ui/input.c b/ui/input.c
index 4791b089c7..a4078780ee 100644
--- a/ui/input.c
+++ b/ui/input.c
@@ -164,10 +164,10 @@  void qmp_input_send_event(bool has_device, const char *device,
         InputEvent *evt = e->value;
 
         if (evt->type == INPUT_EVENT_KIND_KEY &&
-            evt->u.key.data->key->type == KEY_VALUE_KIND_NUMBER) {
-            KeyValue *key = evt->u.key.data->key;
-            QKeyCode code = qemu_input_key_number_to_qcode(key->u.number.data);
-            qemu_input_event_send_key_qcode(con, code, evt->u.key.data->down);
+            evt->u.key.key->type == KEY_VALUE_KIND_NUMBER) {
+            KeyValue *key = evt->u.key.key;
+            QKeyCode code = qemu_input_key_number_to_qcode(key->u.number);
+            qemu_input_event_send_key_qcode(con, code, evt->u.key.down);
         } else {
             qemu_input_event_send(con, evt);
         }
@@ -183,7 +183,7 @@  static int qemu_input_transform_invert_abs_value(int value)
 
 static void qemu_input_transform_abs_rotate(InputEvent *evt)
 {
-    InputMoveEvent *move = evt->u.abs.data;
+    InputMoveEvent *move = &evt->u.abs;
     switch (graphic_rotate) {
     case 90:
         if (move->axis == INPUT_AXIS_X) {
@@ -220,16 +220,16 @@  static void qemu_input_event_trace(QemuConsole *src, InputEvent *evt)
     }
     switch (evt->type) {
     case INPUT_EVENT_KIND_KEY:
-        key = evt->u.key.data;
+        key = &evt->u.key;
         switch (key->key->type) {
         case KEY_VALUE_KIND_NUMBER:
-            qcode = qemu_input_key_number_to_qcode(key->key->u.number.data);
+            qcode = qemu_input_key_number_to_qcode(key->key->u.number);
             name = QKeyCode_str(qcode);
-            trace_input_event_key_number(idx, key->key->u.number.data,
+            trace_input_event_key_number(idx, key->key->u.number,
                                          name, key->down);
             break;
         case KEY_VALUE_KIND_QCODE:
-            name = QKeyCode_str(key->key->u.qcode.data);
+            name = QKeyCode_str(key->key->u.qcode);
             trace_input_event_key_qcode(idx, name, key->down);
             break;
         case KEY_VALUE_KIND__MAX:
@@ -238,17 +238,17 @@  static void qemu_input_event_trace(QemuConsole *src, InputEvent *evt)
         }
         break;
     case INPUT_EVENT_KIND_BTN:
-        btn = evt->u.btn.data;
+        btn = &evt->u.btn;
         name = InputButton_str(btn->button);
         trace_input_event_btn(idx, name, btn->down);
         break;
     case INPUT_EVENT_KIND_REL:
-        move = evt->u.rel.data;
+        move = &evt->u.rel;
         name = InputAxis_str(move->axis);
         trace_input_event_rel(idx, name, move->value);
         break;
     case INPUT_EVENT_KIND_ABS:
-        move = evt->u.abs.data;
+        move = &evt->u.abs;
         name = InputAxis_str(move->axis);
         trace_input_event_abs(idx, name, move->value);
         break;
@@ -355,7 +355,7 @@  void qemu_input_event_send(QemuConsole *src, InputEvent *evt)
     /* Expect all parts of QEMU to send events with QCodes exclusively.
      * Key numbers are only supported as end-user input via QMP */
     assert(!(evt->type == INPUT_EVENT_KIND_KEY &&
-             evt->u.key.data->key->type == KEY_VALUE_KIND_NUMBER));
+             evt->u.key.key->type == KEY_VALUE_KIND_NUMBER));
 
 
     /*
@@ -367,8 +367,8 @@  void qemu_input_event_send(QemuConsole *src, InputEvent *evt)
      * neeed to deal with this mistake
      */
     if (evt->type == INPUT_EVENT_KIND_KEY &&
-        evt->u.key.data->key->u.qcode.data == Q_KEY_CODE_SYSRQ) {
-        evt->u.key.data->key->u.qcode.data = Q_KEY_CODE_PRINT;
+        evt->u.key.key->u.qcode == Q_KEY_CODE_SYSRQ) {
+        evt->u.key.key->u.qcode = Q_KEY_CODE_PRINT;
     }
 
     if (!runstate_is_running() && !runstate_check(RUN_STATE_SUSPENDED)) {
@@ -407,10 +407,9 @@  void qemu_input_event_sync(void)
 static InputEvent *qemu_input_event_new_key(KeyValue *key, bool down)
 {
     InputEvent *evt = g_new0(InputEvent, 1);
-    evt->u.key.data = g_new0(InputKeyEvent, 1);
     evt->type = INPUT_EVENT_KIND_KEY;
-    evt->u.key.data->key = key;
-    evt->u.key.data->down = down;
+    evt->u.key.key = key;
+    evt->u.key.down = down;
     return evt;
 }
 
@@ -440,7 +439,7 @@  void qemu_input_event_send_key_qcode(QemuConsole *src, QKeyCode q, bool down)
 {
     KeyValue *key = g_new0(KeyValue, 1);
     key->type = KEY_VALUE_KIND_QCODE;
-    key->u.qcode.data = q;
+    key->u.qcode = q;
     qemu_input_event_send_key(src, key, down);
 }
 
@@ -469,7 +468,7 @@  void qemu_input_queue_btn(QemuConsole *src, InputButton btn, bool down)
     };
     InputEvent evt = {
         .type = INPUT_EVENT_KIND_BTN,
-        .u.btn.data = &bevt,
+        .u.btn = bevt,
     };
 
     qemu_input_event_send(src, &evt);
@@ -520,7 +519,7 @@  void qemu_input_queue_rel(QemuConsole *src, InputAxis axis, int value)
     };
     InputEvent evt = {
         .type = INPUT_EVENT_KIND_REL,
-        .u.rel.data = &move,
+        .u.rel = move,
     };
 
     qemu_input_event_send(src, &evt);
@@ -537,7 +536,7 @@  void qemu_input_queue_abs(QemuConsole *src, InputAxis axis, int value,
     };
     InputEvent evt = {
         .type = INPUT_EVENT_KIND_ABS,
-        .u.abs.data = &move,
+        .u.abs = move,
     };
 
     qemu_input_event_send(src, &evt);
diff --git a/ui/spice-app.c b/ui/spice-app.c
index 026124ef56..b542e927e5 100644
--- a/ui/spice-app.c
+++ b/ui/spice-app.c
@@ -60,7 +60,6 @@  chr_spice_backend_new(void)
     ChardevBackend *be = g_new0(ChardevBackend, 1);
 
     be->type = CHARDEV_BACKEND_KIND_SPICEPORT;
-    be->u.spiceport.data = g_new0(ChardevSpicePort, 1);
 
     return be;
 }
@@ -83,7 +82,7 @@  static void vc_chr_open(Chardev *chr,
     }
 
     be = chr_spice_backend_new();
-    be->u.spiceport.data->fqdn = fqdn ?
+    be->u.spiceport.fqdn = fqdn ?
         g_strdup(fqdn) : g_strdup_printf("org.qemu.console.%s", chr->label);
     vc->parent_open(chr, be, be_opened, errp);
     qapi_free_ChardevBackend(be);
@@ -182,7 +181,7 @@  static void spice_app_display_init(DisplayState *ds, DisplayOptions *opts)
     GError *err = NULL;
     gchar *uri;
 
-    be->u.spiceport.data->fqdn = g_strdup("org.qemu.monitor.qmp.0");
+    be->u.spiceport.fqdn = g_strdup("org.qemu.monitor.qmp.0");
     qemu_chardev_new("org.qemu.monitor.qmp", TYPE_CHARDEV_SPICEPORT,
                      be, NULL, &error_abort);
     qopts = qemu_opts_create(qemu_find_opts("mon"),
diff --git a/util/qemu-sockets.c b/util/qemu-sockets.c
index 05e5c73f9d..59e317cbb8 100644
--- a/util/qemu-sockets.c
+++ b/util/qemu-sockets.c
@@ -1365,21 +1365,21 @@  SocketAddress *socket_address_flatten(SocketAddressLegacy *addr_legacy)
     case SOCKET_ADDRESS_LEGACY_KIND_INET:
         addr->type = SOCKET_ADDRESS_TYPE_INET;
         QAPI_CLONE_MEMBERS(InetSocketAddress, &addr->u.inet,
-                           addr_legacy->u.inet.data);
+                           &addr_legacy->u.inet);
         break;
     case SOCKET_ADDRESS_LEGACY_KIND_UNIX:
         addr->type = SOCKET_ADDRESS_TYPE_UNIX;
         QAPI_CLONE_MEMBERS(UnixSocketAddress, &addr->u.q_unix,
-                           addr_legacy->u.q_unix.data);
+                           &addr_legacy->u.q_unix);
         break;
     case SOCKET_ADDRESS_LEGACY_KIND_VSOCK:
         addr->type = SOCKET_ADDRESS_TYPE_VSOCK;
         QAPI_CLONE_MEMBERS(VsockSocketAddress, &addr->u.vsock,
-                           addr_legacy->u.vsock.data);
+                           &addr_legacy->u.vsock);
         break;
     case SOCKET_ADDRESS_LEGACY_KIND_FD:
         addr->type = SOCKET_ADDRESS_TYPE_FD;
-        QAPI_CLONE_MEMBERS(String, &addr->u.fd, addr_legacy->u.fd.data);
+        QAPI_CLONE_MEMBERS(String, &addr->u.fd, &addr_legacy->u.fd);
         break;
     default:
         abort();
diff --git a/scripts/qapi/introspect.py b/scripts/qapi/introspect.py
index fafec94e02..1c4e3407a3 100644
--- a/scripts/qapi/introspect.py
+++ b/scripts/qapi/introspect.py
@@ -188,7 +188,12 @@  const QLitObject %(c_name)s = %(c_string)s;
                 'variants': [self._gen_variant(v) for v in variants]}
 
     def _gen_variant(self, variant):
-        obj = {'case': variant.name, 'type': self._use_type(variant.type)}
+        if variant.wrapped:
+            obj = {'case': variant.name,
+                   'type': self._use_type(variant.wrapper_type)}
+        else:
+            obj = {'case': variant.name,
+                   'type': self._use_type(variant.type)}
         return _make_tree(obj, variant.ifcond, None)
 
     def visit_builtin_type(self, name, info, json_type):
diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
index 720449feee..17525b4216 100644
--- a/scripts/qapi/schema.py
+++ b/scripts/qapi/schema.py
@@ -216,6 +216,11 @@  class QAPISchemaBuiltinType(QAPISchemaType):
         self._json_type_name = json_type
         self._c_type_name = c_type
 
+    def check(self, schema):
+        # Don't check twice, it would fail an assertion
+        if not self._checked:
+            super().check(schema)
+
     def c_name(self):
         return self.name
 
@@ -593,18 +598,21 @@  class QAPISchemaVariants:
                         "branch '%s' is not a value of %s"
                         % (v.name, self.tag_member.type.describe()))
                 if (not isinstance(v.type, QAPISchemaObjectType)
-                        or v.type.variants):
+                        or v.type.variants) and v.flat:
                     raise QAPISemError(
                         self.info,
                         "%s cannot use %s"
                         % (v.describe(self.info), v.type.describe()))
-                v.type.check(schema)
+                if isinstance(v.type, QAPISchemaObjectType):
+                    v.type.check(schema)
 
     def check_clash(self, info, seen):
         for v in self.variants:
             # Reset seen map for each variant, since qapi names from one
-            # branch do not affect another branch
-            v.type.check_clash(info, dict(seen))
+            # branch do not affect another branch.  Variants that are
+            # never flat don't even conflict with the base.
+            if isinstance(v.type, QAPISchemaObjectType):
+                v.type.check_clash(info, dict(seen) if v.flat else {})
 
 
 class QAPISchemaMember:
@@ -705,9 +713,22 @@  class QAPISchemaObjectTypeMember(QAPISchemaMember):
 class QAPISchemaVariant(QAPISchemaObjectTypeMember):
     role = 'branch'
 
-    def __init__(self, name, info, typ, ifcond=None):
+    def __init__(self, name, info, typ, ifcond=None, flat=True,
+                 wrapper_type=None):
         super().__init__(name, info, typ, False, ifcond)
 
+        self.flat = flat
+        self.wrapped = bool(wrapper_type)
+        self.wrapper_type = wrapper_type
+
+        # For now, unions are either flat or wrapped, never both
+        assert self.flat or self.wrapped
+        assert not (self.flat and self.wrapped)
+
+    def check(self, schema):
+        super().check(schema)
+        if self.wrapped:
+            self.wrapper_type.check(schema)
 
 class QAPISchemaCommand(QAPISchemaEntity):
     meta = 'command'
@@ -1017,14 +1038,19 @@  class QAPISchema:
     def _make_variant(self, case, typ, ifcond, info):
         return QAPISchemaVariant(case, info, typ, ifcond)
 
-    def _make_simple_variant(self, case, typ, ifcond, info):
+    def _make_simple_variant(self, union_name, case, typ, ifcond, info):
         if isinstance(typ, list):
             assert len(typ) == 1
             typ = self._make_array_type(typ[0], info)
-        typ = self._make_implicit_object_type(
-            typ, info, self.lookup_type(typ),
-            'wrapper', [self._make_member('data', typ, None, None, info)])
-        return QAPISchemaVariant(case, info, typ, ifcond)
+
+        # The wrapper type is only used for introspection compatibility.
+        # Don't add it to the entity list of the schema.
+        wrapper_name = 'q_obj_%s-%s-wrapper' % (union_name, case)
+        wrapper_member = self._make_member('data', typ, None, None, info)
+        wrapper_type = QAPISchemaObjectType(wrapper_name, info, None, ifcond,
+                                            None, None, [wrapper_member], None)
+        return QAPISchemaVariant(case, info, typ, ifcond, flat=False,
+                                 wrapper_type=wrapper_type)
 
     def _def_union_type(self, expr, info, doc):
         name = expr['union']
@@ -1044,7 +1070,7 @@  class QAPISchema:
                         for (key, value) in data.items()]
             members = []
         else:
-            variants = [self._make_simple_variant(key, value['type'],
+            variants = [self._make_simple_variant(name, key, value['type'],
                                                   value.get('if'), info)
                         for (key, value) in data.items()]
             enum = [{'name': v.name, 'if': v.ifcond} for v in variants]
diff --git a/scripts/qapi/visit.py b/scripts/qapi/visit.py
index 339f152152..f72567cbcc 100644
--- a/scripts/qapi/visit.py
+++ b/scripts/qapi/visit.py
@@ -118,6 +118,34 @@  bool visit_type_%(c_name)s_members(Visitor *v, %(c_name)s *obj, Error **errp)
         break;
 ''',
                              case=case_str)
+            elif not isinstance(var.type, QAPISchemaObjectType):
+                assert not var.flat
+                ret += mcgen('''
+    case %(case)s:
+        return visit_type_%(c_type)s(v, "data", &obj->u.%(c_name)s, errp);
+''',
+                             case=case_str,
+                             c_type=var.type.c_name(), c_name=c_name(var.name))
+            elif var.wrapped:
+                ret += mcgen('''
+    case %(case)s:
+    {
+        bool ok;
+
+        if (!visit_start_struct(v, "data", NULL, 0, errp)) {
+            return false;
+        }
+        ok = visit_type_%(c_type)s_members(v, &obj->u.%(c_name)s, errp);
+        if (ok) {
+            ok = visit_check_struct(v, errp);
+        }
+        visit_end_struct(v, NULL);
+        return ok;
+    }
+''',
+                             case=case_str,
+                             c_type=var.type.c_name(), c_name=c_name(var.name))
+
             else:
                 ret += mcgen('''
     case %(case)s:
diff --git a/tests/qapi-schema/doc-good.out b/tests/qapi-schema/doc-good.out
index 419284dae2..bcbcbd2fce 100644
--- a/tests/qapi-schema/doc-good.out
+++ b/tests/qapi-schema/doc-good.out
@@ -31,10 +31,6 @@  object Object
     case two: Variant2
         if ['IFTWO']
     feature union-feat1
-object q_obj_Variant1-wrapper
-    member data: Variant1 optional=False
-object q_obj_Variant2-wrapper
-    member data: Variant2 optional=False
 enum SugaredUnionKind
     member one
     member two
@@ -42,8 +38,8 @@  enum SugaredUnionKind
 object SugaredUnion
     member type: SugaredUnionKind optional=False
     tag type
-    case one: q_obj_Variant1-wrapper
-    case two: q_obj_Variant2-wrapper
+    case one: Variant1
+    case two: Variant2
         if ['IFTWO']
     feature union-feat2
 alternate Alternate
diff --git a/tests/qapi-schema/qapi-schema-test.out b/tests/qapi-schema/qapi-schema-test.out
index 8868ca0dca..a4e4051c61 100644
--- a/tests/qapi-schema/qapi-schema-test.out
+++ b/tests/qapi-schema/qapi-schema-test.out
@@ -125,36 +125,6 @@  alternate AltStrObj
     tag type
     case s: str
     case o: TestStruct
-object q_obj_intList-wrapper
-    member data: intList optional=False
-object q_obj_int8List-wrapper
-    member data: int8List optional=False
-object q_obj_int16List-wrapper
-    member data: int16List optional=False
-object q_obj_int32List-wrapper
-    member data: int32List optional=False
-object q_obj_int64List-wrapper
-    member data: int64List optional=False
-object q_obj_uint8List-wrapper
-    member data: uint8List optional=False
-object q_obj_uint16List-wrapper
-    member data: uint16List optional=False
-object q_obj_uint32List-wrapper
-    member data: uint32List optional=False
-object q_obj_uint64List-wrapper
-    member data: uint64List optional=False
-object q_obj_numberList-wrapper
-    member data: numberList optional=False
-object q_obj_boolList-wrapper
-    member data: boolList optional=False
-object q_obj_strList-wrapper
-    member data: strList optional=False
-object q_obj_sizeList-wrapper
-    member data: sizeList optional=False
-object q_obj_anyList-wrapper
-    member data: anyList optional=False
-object q_obj_StatusList-wrapper
-    member data: StatusList optional=False
 enum UserDefListUnionKind
     member integer
     member s8
@@ -174,21 +144,21 @@  enum UserDefListUnionKind
 object UserDefListUnion
     member type: UserDefListUnionKind optional=False
     tag type
-    case integer: q_obj_intList-wrapper
-    case s8: q_obj_int8List-wrapper
-    case s16: q_obj_int16List-wrapper
-    case s32: q_obj_int32List-wrapper
-    case s64: q_obj_int64List-wrapper
-    case u8: q_obj_uint8List-wrapper
-    case u16: q_obj_uint16List-wrapper
-    case u32: q_obj_uint32List-wrapper
-    case u64: q_obj_uint64List-wrapper
-    case number: q_obj_numberList-wrapper
-    case boolean: q_obj_boolList-wrapper
-    case string: q_obj_strList-wrapper
-    case sizes: q_obj_sizeList-wrapper
-    case any: q_obj_anyList-wrapper
-    case user: q_obj_StatusList-wrapper
+    case integer: intList
+    case s8: int8List
+    case s16: int16List
+    case s32: int32List
+    case s64: int64List
+    case u8: uint8List
+    case u16: uint16List
+    case u32: uint32List
+    case u64: uint64List
+    case number: numberList
+    case boolean: boolList
+    case string: strList
+    case sizes: sizeList
+    case any: anyList
+    case user: StatusList
 include include/sub-module.json
 command user_def_cmd None -> None
     gen=True success_response=True boxed=False oob=False preconfig=False
@@ -263,14 +233,12 @@  object __org.qemu_x-Struct
     base __org.qemu_x-Base
     member __org.qemu_x-member2: str optional=False
     member wchar-t: int optional=True
-object q_obj_str-wrapper
-    member data: str optional=False
 enum __org.qemu_x-Union1Kind
     member __org.qemu_x-branch
 object __org.qemu_x-Union1
     member type: __org.qemu_x-Union1Kind optional=False
     tag type
-    case __org.qemu_x-branch: q_obj_str-wrapper
+    case __org.qemu_x-branch: str
 alternate __org.qemu_x-Alt1
     tag type
     case __org.qemu_x-branch: str
@@ -305,8 +273,6 @@  enum TestIfEnum
     member bar
         if ['defined(TEST_IF_ENUM_BAR)']
     if ['defined(TEST_IF_ENUM)']
-object q_obj_TestStruct-wrapper
-    member data: TestStruct optional=False
 enum TestIfUnionKind
     member foo
     member union_bar
@@ -315,8 +281,8 @@  enum TestIfUnionKind
 object TestIfUnion
     member type: TestIfUnionKind optional=False
     tag type
-    case foo: q_obj_TestStruct-wrapper
-    case union_bar: q_obj_str-wrapper
+    case foo: TestStruct
+    case union_bar: str
         if ['defined(TEST_IF_UNION_BAR)']
     if ['defined(TEST_IF_UNION) && defined(TEST_IF_STRUCT)']
 object q_obj_TestIfUnionCmd-arg