qapi: Implement boxed types for commands/events

Turn on the ability to pass command and event arguments in
a single boxed parameter, which must name a non-empty type
(although the type can be a struct with all optional members).
For structs, it makes it possible to pass a single qapi type
instead of a breakout of all struct members (useful if the
arguments are already in a struct or if the number of members
is large); for other complex types, it is now possible to use
a union or alternate as the data for a command or event.

The empty type may be technically feasible if needed down the
road, but it's easier to forbid it now and relax things to allow
it later, than it is to allow it now and have to special case
how the generated 'q_empty' type is handled (see commit 7ce106a9
for reasons why nothing is generated for the empty type).  An
alternate type is never considered empty, but now that a boxed
type can be either an object or an alternate, we have to provide
a trivial QAPISchemaAlternateType.is_empty().  The new call to
arg_type.is_empty() during QAPISchemaCommand.check() requires
that we first check the type in question; but there is no chance
of introducing a cycle since objects do not refer back to commands.

We still have a split in syntax checking between ad-hoc parsing
up front (merely validates that 'boxed' has a sane value) and
during .check() methods (if 'boxed' is set, then 'data' must name
a non-empty user-defined type).

Generated code is unchanged, as long as no client uses the
new feature.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1468468228-27827-10-git-send-email-eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Test files renamed to *-boxed-*]
Signed-off-by: Markus Armbruster <armbru@redhat.com>

docs/qapi-code-gen.txt

@@ -410,7 +410,7 @@ following example objects:
 === Commands ===
 
 Usage: { 'command': STRING, '*data': COMPLEX-TYPE-NAME-OR-DICT,
-         '*returns': TYPE-NAME,
+         '*returns': TYPE-NAME, '*boxed': true,
          '*gen': false, '*success-response': false }
 
 Commands are defined by using a dictionary containing several members,
@@ -461,6 +461,20 @@ which would validate this Client JSON Protocol transaction:
  => { "execute": "my-second-command" }
  <= { "return": [ { "value": "one" }, { } ] }
 
+The generator emits a prototype for the user's function implementing
+the command.  Normally, 'data' is a dictionary for an anonymous type,
+or names a struct type (possibly empty, but not a union), and its
+members are passed as separate arguments to this function.  If the
+command definition includes a key 'boxed' with the boolean value true,
+then 'data' is instead the name of any non-empty complex type
+(struct, union, or alternate), and a pointer to that QAPI type is
+passed as a single argument.
+
+The generator also emits a marshalling function that extracts
+arguments for the user's function out of an input QDict, calls the
+user's function, and if it succeeded, builds an output QObject from
+its return value.
+
 In rare cases, QAPI cannot express a type-safe representation of a
 corresponding Client JSON Protocol command.  You then have to suppress
 generation of a marshalling function by including a key 'gen' with
@@ -484,7 +498,8 @@ use of this member.
 
 === Events ===
 
-Usage: { 'event': STRING, '*data': COMPLEX-TYPE-NAME-OR-DICT }
+Usage: { 'event': STRING, '*data': COMPLEX-TYPE-NAME-OR-DICT,
+         '*boxed': true }
 
 Events are defined with the keyword 'event'.  It is not allowed to
 name an event 'MAX', since the generator also produces a C enumeration
@@ -505,6 +520,14 @@ Resulting in this JSON object:
   "data": { "b": "test string" },
   "timestamp": { "seconds": 1267020223, "microseconds": 435656 } }
 
+The generator emits a function to send the event.  Normally, 'data' is
+a dictionary for an anonymous type, or names a struct type (possibly
+empty, but not a union), and its members are passed as separate
+arguments to this function.  If the event definition includes a key
+'boxed' with the boolean value true, then 'data' is instead the name of
+any non-empty complex type (struct, union, or alternate), and a
+pointer to that QAPI type is passed as a single argument.
+
 
 == Client JSON Protocol introspection ==
 

scripts/qapi-commands.py

@@ -30,7 +30,8 @@ def gen_call(name, arg_type, boxed, ret_type):
 
     argstr = ''
     if boxed:
-        assert False    # not implemented
+        assert arg_type and not arg_type.is_empty()
+        argstr = '&arg, '
     elif arg_type:
         assert not arg_type.variants
         for memb in arg_type.members:

scripts/qapi-event.py

@@ -79,7 +79,10 @@ def gen_event_send(name, arg_type, boxed):
     QObject *obj;
     Visitor *v;
 ''')
-        ret += gen_param_var(arg_type)
+        if not boxed:
+            ret += gen_param_var(arg_type)
+    else:
+        assert not boxed
 
     ret += mcgen('''
 

scripts/qapi.py

@@ -522,10 +522,14 @@ def check_type(expr_info, source, value, allow_array=False,
 
 def check_command(expr, expr_info):
     name = expr['command']
+    boxed = expr.get('boxed', False)
 
+    args_meta = ['struct']
+    if boxed:
+        args_meta += ['union', 'alternate']
     check_type(expr_info, "'data' for command '%s'" % name,
-               expr.get('data'), allow_dict=True, allow_optional=True,
-               allow_metas=['struct'])
+               expr.get('data'), allow_dict=not boxed, allow_optional=True,
+               allow_metas=args_meta)
     returns_meta = ['union', 'struct']
     if name in returns_whitelist:
         returns_meta += ['built-in', 'alternate', 'enum']
@@ -537,11 +541,15 @@ def check_command(expr, expr_info):
 def check_event(expr, expr_info):
     global events
     name = expr['event']
+    boxed = expr.get('boxed', False)
 
+    meta = ['struct']
+    if boxed:
+        meta += ['union', 'alternate']
     events.append(name)
     check_type(expr_info, "'data' for event '%s'" % name,
-               expr.get('data'), allow_dict=True, allow_optional=True,
-               allow_metas=['struct'])
+               expr.get('data'), allow_dict=not boxed, allow_optional=True,
+               allow_metas=meta)
 
 
 def check_union(expr, expr_info):
@@ -694,6 +702,10 @@ def check_keys(expr_elem, meta, required, optional=[]):
             raise QAPIExprError(info,
                                 "'%s' of %s '%s' should only use false value"
                                 % (key, meta, name))
+        if key == 'boxed' and value is not True:
+            raise QAPIExprError(info,
+                                "'%s' of %s '%s' should only use true value"
+                                % (key, meta, name))
     for key in required:
         if key not in expr:
             raise QAPIExprError(info,
@@ -725,10 +737,10 @@ def check_exprs(exprs):
             add_struct(expr, info)
         elif 'command' in expr:
             check_keys(expr_elem, 'command', [],
-                       ['data', 'returns', 'gen', 'success-response'])
+                       ['data', 'returns', 'gen', 'success-response', 'boxed'])
             add_name(expr['command'], info, 'command')
         elif 'event' in expr:
-            check_keys(expr_elem, 'event', [], ['data'])
+            check_keys(expr_elem, 'event', [], ['data', 'boxed'])
             add_name(expr['event'], info, 'event')
         else:
             raise QAPIExprError(expr_elem['info'],
@@ -1163,6 +1175,9 @@ class QAPISchemaAlternateType(QAPISchemaType):
     def visit(self, visitor):
         visitor.visit_alternate_type(self.name, self.info, self.variants)
 
+    def is_empty(self):
+        return False
+
 
 class QAPISchemaCommand(QAPISchemaEntity):
     def __init__(self, name, info, arg_type, ret_type, gen, success_response,
@@ -1181,9 +1196,19 @@ class QAPISchemaCommand(QAPISchemaEntity):
     def check(self, schema):
         if self._arg_type_name:
             self.arg_type = schema.lookup_type(self._arg_type_name)
-            assert isinstance(self.arg_type, QAPISchemaObjectType)
-            assert not self.arg_type.variants   # not implemented
-            assert not self.boxed               # not implemented
+            assert (isinstance(self.arg_type, QAPISchemaObjectType) or
+                    isinstance(self.arg_type, QAPISchemaAlternateType))
+            self.arg_type.check(schema)
+            if self.boxed:
+                if self.arg_type.is_empty():
+                    raise QAPIExprError(self.info,
+                                        "Cannot use 'boxed' with empty type")
+            else:
+                assert not isinstance(self.arg_type, QAPISchemaAlternateType)
+                assert not self.arg_type.variants
+        elif self.boxed:
+            raise QAPIExprError(self.info,
+                                "Use of 'boxed' requires 'data'")
         if self._ret_type_name:
             self.ret_type = schema.lookup_type(self._ret_type_name)
             assert isinstance(self.ret_type, QAPISchemaType)
@@ -1205,9 +1230,19 @@ class QAPISchemaEvent(QAPISchemaEntity):
     def check(self, schema):
         if self._arg_type_name:
             self.arg_type = schema.lookup_type(self._arg_type_name)
-            assert isinstance(self.arg_type, QAPISchemaObjectType)
-            assert not self.arg_type.variants   # not implemented
-            assert not self.boxed               # not implemented
+            assert (isinstance(self.arg_type, QAPISchemaObjectType) or
+                    isinstance(self.arg_type, QAPISchemaAlternateType))
+            self.arg_type.check(schema)
+            if self.boxed:
+                if self.arg_type.is_empty():
+                    raise QAPIExprError(self.info,
+                                        "Cannot use 'boxed' with empty type")
+            else:
+                assert not isinstance(self.arg_type, QAPISchemaAlternateType)
+                assert not self.arg_type.variants
+        elif self.boxed:
+            raise QAPIExprError(self.info,
+                                "Use of 'boxed' requires 'data'")
 
     def visit(self, visitor):
         visitor.visit_event(self.name, self.info, self.arg_type, self.boxed)
@@ -1648,11 +1683,13 @@ extern const char *const %(c_name)s_lookup[];
 
 def gen_params(arg_type, boxed, extra):
     if not arg_type:
+        assert not boxed
         return extra
     ret = ''
     sep = ''
     if boxed:
-        assert False     # not implemented
+        ret += '%s arg' % arg_type.c_param_type()
+        sep = ', '
     else:
         assert not arg_type.variants
         for memb in arg_type.members:

tests/Makefile.include

@@ -284,6 +284,10 @@ qapi-schema += args-alternate.json
 qapi-schema += args-any.json
 qapi-schema += args-array-empty.json
 qapi-schema += args-array-unknown.json
+qapi-schema += args-bad-boxed.json
+qapi-schema += args-boxed-anon.json
+qapi-schema += args-boxed-empty.json
+qapi-schema += args-boxed-string.json
 qapi-schema += args-int.json
 qapi-schema += args-invalid.json
 qapi-schema += args-member-array-bad.json
@@ -317,6 +321,7 @@ qapi-schema += enum-wrong-data.json
 qapi-schema += escape-outside-string.json
 qapi-schema += escape-too-big.json
 qapi-schema += escape-too-short.json
+qapi-schema += event-boxed-empty.json
 qapi-schema += event-case.json
 qapi-schema += event-nest-struct.json
 qapi-schema += flat-union-array-branch.json

tests/qapi-schema/args-bad-boxed.err

@@ -0,0 +1 @@
+tests/qapi-schema/args-bad-boxed.json:2: 'boxed' of command 'foo' should only use true value

tests/qapi-schema/args-bad-boxed.exit

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

tests/qapi-schema/args-bad-boxed.json

@@ -0,0 +1,2 @@
+# 'boxed' should only appear with value true
+{ 'command': 'foo', 'boxed': false }

tests/qapi-schema/args-boxed-anon.err

@@ -0,0 +1 @@
+tests/qapi-schema/args-boxed-anon.json:2: 'data' for command 'foo' should be a type name

tests/qapi-schema/args-boxed-anon.exit

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

tests/qapi-schema/args-boxed-anon.json

@@ -0,0 +1,2 @@
+# 'boxed' can only be used with named types
+{ 'command': 'foo', 'boxed': true, 'data': { 'string': 'str' } }

tests/qapi-schema/args-boxed-empty.err

@@ -0,0 +1 @@
+tests/qapi-schema/args-boxed-empty.json:3: Cannot use 'boxed' with empty type

tests/qapi-schema/args-boxed-empty.exit

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

tests/qapi-schema/args-boxed-empty.json

@@ -0,0 +1,3 @@
+# 'boxed' requires a non-empty type
+{ 'struct': 'Empty', 'data': {} }
+{ 'command': 'foo', 'boxed': true, 'data': 'Empty' }

tests/qapi-schema/args-boxed-string.err

@@ -0,0 +1 @@
+tests/qapi-schema/args-boxed-string.json:2: 'data' for command 'foo' cannot use built-in type 'str'

tests/qapi-schema/args-boxed-string.exit

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

tests/qapi-schema/args-boxed-string.json

@@ -0,0 +1,2 @@
+# 'boxed' requires a complex (not built-in) type
+{ 'command': 'foo', 'boxed': true, 'data': 'str' }

tests/qapi-schema/args-union.err

@@ -1 +1 @@
-tests/qapi-schema/args-union.json:4: 'data' for command 'oops' cannot use union type 'Uni'
+tests/qapi-schema/args-union.json:3: 'data' for command 'oops' cannot use union type 'Uni'

tests/qapi-schema/args-union.json

@@ -1,4 +1,3 @@
-# we do not allow union arguments
-# TODO should we support this?
+# use of union arguments requires 'boxed':true
 { 'union': 'Uni', 'data': { 'case1': 'int', 'case2': 'str' } }
 { 'command': 'oops', 'data': 'Uni' }

tests/qapi-schema/event-boxed-empty.err

@@ -0,0 +1 @@
+tests/qapi-schema/event-boxed-empty.json:2: Use of 'boxed' requires 'data'

tests/qapi-schema/event-boxed-empty.exit

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

tests/qapi-schema/event-boxed-empty.json

@@ -0,0 +1,2 @@
+# 'boxed' requires a non-empty type
+{ 'event': 'FOO', 'boxed': true }

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

@@ -127,6 +127,8 @@
 { 'command': 'guest-get-time', 'data': {'a': 'int', '*b': 'int' },
   'returns': 'int' }
 { 'command': 'guest-sync', 'data': { 'arg': 'any' }, 'returns': 'any' }
+{ 'command': 'boxed-struct', 'boxed': true, 'data': 'UserDefZero' }
+{ 'command': 'boxed-union', 'data': 'UserDefNativeListUnion', 'boxed': true }
 
 # For testing integer range flattening in opts-visitor. The following schema
 # corresponds to the option format:
@@ -154,6 +156,8 @@
   'data': { '*a': 'int', '*b': 'UserDefOne', 'c': 'str' } }
 { 'event': 'EVENT_D',
   'data': { 'a' : 'EventStructOne', 'b' : 'str', '*c': 'str', '*enum3': 'EnumOne' } }
+{ 'event': 'EVENT_E', 'boxed': true, 'data': 'UserDefZero' }
+{ 'event': 'EVENT_F', 'boxed': true, 'data': 'UserDefAlternate' }
 
 # test that we correctly compile downstream extensions, as well as munge
 # ticklish names

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

@@ -30,6 +30,10 @@ event EVENT_C q_obj_EVENT_C-arg
    boxed=False
 event EVENT_D q_obj_EVENT_D-arg
    boxed=False
+event EVENT_E UserDefZero
+   boxed=True
+event EVENT_F UserDefAlternate
+   boxed=True
 object Empty1
 object Empty2
     base Empty1
@@ -153,6 +157,10 @@ object __org.qemu_x-Union2
     case __org.qemu_x-value: __org.qemu_x-Struct2
 command __org.qemu_x-command q_obj___org.qemu_x-command-arg -> __org.qemu_x-Union1
    gen=True success_response=True boxed=False
+command boxed-struct UserDefZero -> None
+   gen=True success_response=True boxed=True
+command boxed-union UserDefNativeListUnion -> None
+   gen=True success_response=True boxed=True
 command guest-get-time q_obj_guest-get-time-arg -> int
    gen=True success_response=True boxed=False
 command guest-sync q_obj_guest-sync-arg -> any

tests/test-qmp-commands.c

@@ -59,6 +59,14 @@ QObject *qmp_guest_sync(QObject *arg, Error **errp)
     return arg;
 }
 
+void qmp_boxed_struct(UserDefZero *arg, Error **errp)
+{
+}
+
+void qmp_boxed_union(UserDefNativeListUnion *arg, Error **errp)
+{
+}
+
 __org_qemu_x_Union1 *qmp___org_qemu_x_command(__org_qemu_x_EnumList *a,
                                               __org_qemu_x_StructList *b,
                                               __org_qemu_x_Union2 *c,