qapi: Simplify visiting of alternate types

Previously, working with alternates required two lookup arrays
and some indirection: for type Foo, we created Foo_qtypes[]
which maps each qtype to a value of the generated FooKind enum,
then look up that value in FooKind_lookup[] like we do for other
union types.

This has a couple of subtle bugs.  First, the generator was
creating a call with a parameter '(int *) &(*obj)->type' where
type is an enum type; this is unsafe if the compiler chooses
to store the enum type in a different size than int, where
assigning through the wrong size pointer can corrupt data or
cause a SIGBUS.

Related bug, not not fixed in this patch: qapi-visit.py's
gen_visit_enum() generates a cast of its enum * argument to
int *. Marked FIXME.

Second, since the values of the FooKind enum start at zero, all
entries of the Foo_qtypes[] array that were not explicitly
initialized will map to the same branch of the union as the
first member of the alternate, rather than triggering a desired
failure in visit_get_next_type().  Fortunately, the bug seldom
bites; the very next thing the input visitor does is try to
parse the incoming JSON with the wrong parser, which normally
fails; the output visitor is not used with a C struct in that
state, and the dealloc visitor has nothing to clean up (so
there is no leak).

However, the second bug IS observable in one case: parsing an
integer causes unusual behavior in an alternate that contains
at least a 'number' member but no 'int' member, because the
'number' parser accepts QTYPE_QINT in addition to the expected
QTYPE_QFLOAT (that is, since 'int' is not a member, the type
QTYPE_QINT accidentally maps to FooKind 0; if this enum value
is the 'number' branch the integer parses successfully, but if
the 'number' branch is not first, some other branch tries to
parse the integer and rejects it).  A later patch will worry
about fixing alternates to always parse all inputs that a
non-alternate 'number' would accept, for now this is still
marked FIXME in the updated test-qmp-input-visitor.c, to
merely point out that new undesired behavior of 'ans' matches
the existing undesired behavior of 'asn'.

This patch fixes the default-initialization bug by deleting the
indirection, and modifying get_next_type() to directly assign a
QTypeCode parameter.  This in turn fixes the type-casting bug,
as we are no longer casting a pointer to enum to a questionable
size. There is no longer a need to generate an implicit FooKind
enum associated with the alternate type (since the QMP wire
format never uses the stringized counterparts of the C union
member names).  Since the updated visit_get_next_type() does not
know which qtypes are expected, the generated visitor is
modified to generate an error statement if an unexpected type is
encountered.

Callers now have to know the QTYPE_* mapping when looking at the
discriminator; but so far, only the testsuite was even using the
C struct of an alternate types.  I considered the possibility of
keeping the internal enum FooKind, but initialized differently
than most generated arrays, as in:
  typedef enum FooKind {
      FOO_KIND_A = QTYPE_QDICT,
      FOO_KIND_B = QTYPE_QINT,
  } FooKind;
to create nicer aliases for knowing when to use foo->a or foo->b
when inspecting foo->type; but it turned out to add too much
complexity, especially without a client.

There is a user-visible side effect to this change, but I
consider it to be an improvement. Previously,
the invalid QMP command:
  {"execute":"blockdev-add", "arguments":{"options":
    {"driver":"raw", "id":"a", "file":true}}}
failed with:
  {"error": {"class": "GenericError",
    "desc": "Invalid parameter type for 'file', expected: QDict"}}
(visit_get_next_type() succeeded, and the error comes from the
visit_type_BlockdevOptions() expecting {}; there is no mention of
the fact that a string would also work).  Now it fails with:
  {"error": {"class": "GenericError",
    "desc": "Invalid parameter type for 'file', expected: BlockdevRef"}}
(the error when the next type doesn't match any expected types for
the overall alternate).

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1449033659-25497-5-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

12 files changed, 54 insertions, 79 deletions

diff --git a/docs/qapi-code-gen.txt b/docs/qapi-code-gen.txt
index 79bf072695..128f074a2d 100644
--- a/docs/qapi-code-gen.txt
+++ b/docs/qapi-code-gen.txt
@@ -384,9 +384,6 @@ where each branch of the union names a QAPI type.  For example:
    'data': { 'definition': 'BlockdevOptions',
              'reference': 'str' } }
 
-Just like for a simple union, an implicit C enum 'NameKind' is created
-to enumerate the branches for the alternate 'Name'.
-
 Unlike a union, the discriminator string is never passed on the wire
 for the Client JSON Protocol.  Instead, the value's JSON type serves
 as an implicit discriminator, which in turn means that an alternate
diff --git a/include/qapi/visitor-impl.h b/include/qapi/visitor-impl.h
index 8c0ba57292..7cd1313129 100644
--- a/include/qapi/visitor-impl.h
+++ b/include/qapi/visitor-impl.h
@@ -32,7 +32,8 @@ struct Visitor
 
     void (*type_enum)(Visitor *v, int *obj, const char * const strings[],
                       const char *kind, const char *name, Error **errp);
-    void (*get_next_type)(Visitor *v, int *kind, const int *qobjects,
+    /* May be NULL; only needed for input visitors. */
+    void (*get_next_type)(Visitor *v, QType *type,
                           const char *name, Error **errp);
 
     void (*type_int)(Visitor *v, int64_t *obj, const char *name, Error **errp);
diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h
index a2ad66cf8f..6d25ad27a2 100644
--- a/include/qapi/visitor.h
+++ b/include/qapi/visitor.h
@@ -38,7 +38,13 @@ GenericList *visit_next_list(Visitor *v, GenericList **list, Error **errp);
 void visit_end_list(Visitor *v, Error **errp);
 void visit_optional(Visitor *v, bool *present, const char *name,
                     Error **errp);
-void visit_get_next_type(Visitor *v, int *obj, const int *qtypes,
+
+/**
+ * Determine the qtype of the item @name in the current object visit.
+ * For input visitors, set *@type to the correct qtype of a qapi
+ * alternate type; for other visitors, leave *@type unchanged.
+ */
+void visit_get_next_type(Visitor *v, QType *type,
                          const char *name, Error **errp);
 void visit_type_enum(Visitor *v, int *obj, const char * const strings[],
                      const char *kind, const char *name, Error **errp);
diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c
index 59ed5067fa..850ca034cb 100644
--- a/qapi/qapi-visit-core.c
+++ b/qapi/qapi-visit-core.c
@@ -81,11 +81,11 @@ void visit_optional(Visitor *v, bool *present, const char *name,
     }
 }
 
-void visit_get_next_type(Visitor *v, int *obj, const int *qtypes,
+void visit_get_next_type(Visitor *v, QType *type,
                          const char *name, Error **errp)
 {
     if (v->get_next_type) {
-        v->get_next_type(v, obj, qtypes, name, errp);
+        v->get_next_type(v, type, name, errp);
     }
 }
 
diff --git a/qapi/qmp-input-visitor.c b/qapi/qmp-input-visitor.c
index eb6e110300..d398de743d 100644
--- a/qapi/qmp-input-visitor.c
+++ b/qapi/qmp-input-visitor.c
@@ -208,7 +208,7 @@ static void qmp_input_end_list(Visitor *v, Error **errp)
     qmp_input_pop(qiv, errp);
 }
 
-static void qmp_input_get_next_type(Visitor *v, int *kind, const int *qobjects,
+static void qmp_input_get_next_type(Visitor *v, QType *type,
                                     const char *name, Error **errp)
 {
     QmpInputVisitor *qiv = to_qiv(v);
@@ -218,7 +218,7 @@ static void qmp_input_get_next_type(Visitor *v, int *kind, const int *qobjects,
         error_setg(errp, QERR_MISSING_PARAMETER, name ? name : "null");
         return;
     }
-    *kind = qobjects[qobject_type(qobj)];
+    *type = qobject_type(qobj);
 }
 
 static void qmp_input_type_int(Visitor *v, int64_t *obj, const char *name,
diff --git a/scripts/qapi-types.py b/scripts/qapi-types.py
index 2071846250..84ec858419 100644
--- a/scripts/qapi-types.py
+++ b/scripts/qapi-types.py
@@ -101,38 +101,6 @@ static inline %(base)s *qapi_%(c_name)s_base(const %(c_name)s *obj)
                  c_name=c_name(name), base=base.c_name())
 
 
-def gen_alternate_qtypes_decl(name):
-    return mcgen('''
-
-extern const int %(c_name)s_qtypes[];
-''',
-                 c_name=c_name(name))
-
-
-def gen_alternate_qtypes(name, variants):
-    ret = mcgen('''
-
-const int %(c_name)s_qtypes[QTYPE__MAX] = {
-''',
-                c_name=c_name(name))
-
-    for var in variants.variants:
-        qtype = var.type.alternate_qtype()
-        assert qtype
-
-        ret += mcgen('''
-    [%(qtype)s] = %(enum_const)s,
-''',
-                     qtype=qtype,
-                     enum_const=c_enum_const(variants.tag_member.type.name,
-                                             var.name))
-
-    ret += mcgen('''
-};
-''')
-    return ret
-
-
 def gen_variants(variants):
     # FIXME: What purpose does data serve, besides preventing a union that
     # has a branch named 'data'? We use it in qapi-visit.py to decide
@@ -264,9 +232,7 @@ class QAPISchemaGenTypeVisitor(QAPISchemaVisitor):
 
     def visit_alternate_type(self, name, info, variants):
         self._fwdecl += gen_fwd_object_or_array(name)
-        self._fwdefn += gen_alternate_qtypes(name, variants)
         self.decl += gen_object(name, None, [variants.tag_member], variants)
-        self.decl += gen_alternate_qtypes_decl(name)
         self._gen_type_cleanup(name)
 
 # If you link code generated from multiple schemata, you want only one
diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py
index 7ceda18bdb..4797d6e050 100644
--- a/scripts/qapi-visit.py
+++ b/scripts/qapi-visit.py
@@ -172,6 +172,7 @@ out:
 
 
 def gen_visit_enum(name):
+    # FIXME cast from enum *obj to int * invalidly assumes enum is int
     return mcgen('''
 
 void visit_type_%(c_name)s(Visitor *v, %(c_name)s *obj, const char *name, Error **errp)
@@ -193,7 +194,7 @@ void visit_type_%(c_name)s(Visitor *v, %(c_name)s **obj, const char *name, Error
     if (err) {
         goto out;
     }
-    visit_get_next_type(v, (int*) &(*obj)->type, %(c_name)s_qtypes, name, &err);
+    visit_get_next_type(v, &(*obj)->type, name, &err);
     if (err) {
         goto out_obj;
     }
@@ -201,20 +202,22 @@ void visit_type_%(c_name)s(Visitor *v, %(c_name)s **obj, const char *name, Error
 ''',
                 c_name=c_name(name))
 
+    # FIXME: When 'number' but not 'int' is present in the alternate, we
+    # should allow QTYPE_INT to promote to QTYPE_FLOAT.
     for var in variants.variants:
         ret += mcgen('''
     case %(case)s:
         visit_type_%(c_type)s(v, &(*obj)->u.%(c_name)s, name, &err);
         break;
 ''',
-                     case=c_enum_const(variants.tag_member.type.name,
-                                       var.name),
+                     case=var.type.alternate_qtype(),
                      c_type=var.type.c_name(),
                      c_name=c_name(var.name))
 
     ret += mcgen('''
     default:
-        abort();
+        error_setg(&err, QERR_INVALID_PARAMETER_TYPE, name ? name : "null",
+                   "%(name)s");
     }
 out_obj:
     error_propagate(errp, err);
@@ -223,7 +226,8 @@ out_obj:
 out:
     error_propagate(errp, err);
 }
-''')
+''',
+                 name=name)
 
     return ret
 
@@ -437,6 +441,7 @@ fdef.write(mcgen('''
 
 fdecl.write(mcgen('''
 #include "qapi/visitor.h"
+#include "qapi/qmp/qerror.h"
 #include "%(prefix)sqapi-types.h"
 
 ''',
diff --git a/scripts/qapi.py b/scripts/qapi.py
index c9e4ad2d9e..2b46dd095f 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -635,8 +635,8 @@ def check_alternate(expr, expr_info):
     for (key, value) in members.items():
         check_name(expr_info, "Member of alternate '%s'" % name, key)
 
-        # Check for conflicts in the generated enum
-        c_key = camel_to_upper(key)
+        # Check for conflicts in the branch names
+        c_key = c_name(key)
         if c_key in values:
             raise QAPIExprError(expr_info,
                                 "Alternate '%s' member '%s' clashes with '%s'"
@@ -1092,8 +1092,11 @@ class QAPISchemaObjectTypeVariants(object):
         assert isinstance(self.tag_member.type, QAPISchemaEnumType)
         for v in self.variants:
             v.check(schema)
-            assert v.name in self.tag_member.type.values
-            if isinstance(v.type, QAPISchemaObjectType):
+            # Union names must match enum values; alternate names are
+            # checked separately. Use 'seen' to tell the two apart.
+            if seen:
+                assert v.name in self.tag_member.type.values
+                assert isinstance(v.type, QAPISchemaObjectType)
                 v.type.check(schema)
 
     def check_clash(self, schema, info, seen):
@@ -1135,6 +1138,11 @@ class QAPISchemaAlternateType(QAPISchemaType):
         # Not calling self.variants.check_clash(), because there's nothing
         # to clash with
         self.variants.check(schema, {})
+        # Alternate branch names have no relation to the tag enum values;
+        # so we have to check for potential name collisions ourselves.
+        seen = {}
+        for v in self.variants.variants:
+            v.check_clash(self.info, seen)
 
     def json_type(self):
         return 'value'
@@ -1342,7 +1350,7 @@ class QAPISchema(object):
         data = expr['data']
         variants = [self._make_variant(key, value)
                     for (key, value) in data.iteritems()]
-        tag_member = self._make_implicit_tag(name, info, variants)
+        tag_member = QAPISchemaObjectTypeMember('type', 'QType', False)
         self._def_entity(
             QAPISchemaAlternateType(name, info,
                                     QAPISchemaObjectTypeVariants(None,
diff --git a/tests/qapi-schema/alternate-empty.out b/tests/qapi-schema/alternate-empty.out
index 02b9876e76..f78f174111 100644
--- a/tests/qapi-schema/alternate-empty.out
+++ b/tests/qapi-schema/alternate-empty.out
@@ -1,6 +1,5 @@
 object :empty
 alternate Alt
     case i: int
-enum AltKind ['i']
 enum QType ['none', 'qnull', 'qint', 'qstring', 'qdict', 'qlist', 'qfloat', 'qbool']
     prefix QTYPE
diff --git a/tests/qapi-schema/qapi-schema-test.out b/tests/qapi-schema/qapi-schema-test.out
index b87cfba599..2c546b708a 100644
--- a/tests/qapi-schema/qapi-schema-test.out
+++ b/tests/qapi-schema/qapi-schema-test.out
@@ -56,27 +56,21 @@ object :obj-user_def_cmd2-arg
 alternate AltIntNum
     case i: int
     case n: number
-enum AltIntNumKind ['i', 'n']
 alternate AltNumInt
     case n: number
     case i: int
-enum AltNumIntKind ['n', 'i']
 alternate AltNumStr
     case n: number
     case s: str
-enum AltNumStrKind ['n', 's']
 alternate AltStrBool
     case s: str
     case b: bool
-enum AltStrBoolKind ['s', 'b']
 alternate AltStrInt
     case s: str
     case i: int
-enum AltStrIntKind ['s', 'i']
 alternate AltStrNum
     case s: str
     case n: number
-enum AltStrNumKind ['s', 'n']
 event EVENT_A None
 event EVENT_B None
 event EVENT_C :obj-EVENT_C-arg
@@ -114,7 +108,6 @@ alternate UserDefAlternate
     case uda: UserDefA
     case s: str
     case i: int
-enum UserDefAlternateKind ['uda', 's', 'i']
 object UserDefB
     member intb: int optional=False
     member a-b: bool optional=True
@@ -180,7 +173,6 @@ event __ORG.QEMU_X-EVENT __org.qemu_x-Struct
 alternate __org.qemu_x-Alt
     case __org.qemu_x-branch: str
     case b: __org.qemu_x-Base
-enum __org.qemu_x-AltKind ['__org.qemu_x-branch', 'b']
 object __org.qemu_x-Base
     member __org.qemu_x-member1: __org.qemu_x-Enum optional=False
 enum __org.qemu_x-Enum ['__org.qemu_x-value']
diff --git a/tests/test-qmp-input-visitor.c b/tests/test-qmp-input-visitor.c
index d48ebdd62f..43b9e18912 100644
--- a/tests/test-qmp-input-visitor.c
+++ b/tests/test-qmp-input-visitor.c
@@ -312,13 +312,13 @@ static void test_visitor_in_alternate(TestInputVisitorData *data,
 
     v = visitor_input_test_init(data, "42");
     visit_type_UserDefAlternate(v, &tmp, NULL, &error_abort);
-    g_assert_cmpint(tmp->type, ==, USER_DEF_ALTERNATE_KIND_I);
+    g_assert_cmpint(tmp->type, ==, QTYPE_QINT);
     g_assert_cmpint(tmp->u.i, ==, 42);
     qapi_free_UserDefAlternate(tmp);
 
     v = visitor_input_test_init(data, "'string'");
     visit_type_UserDefAlternate(v, &tmp, NULL, &error_abort);
-    g_assert_cmpint(tmp->type, ==, USER_DEF_ALTERNATE_KIND_S);
+    g_assert_cmpint(tmp->type, ==, QTYPE_QSTRING);
     g_assert_cmpstr(tmp->u.s, ==, "string");
     qapi_free_UserDefAlternate(tmp);
 
@@ -347,36 +347,37 @@ static void test_visitor_in_alternate_number(TestInputVisitorData *data,
     error_free_or_abort(&err);
     qapi_free_AltStrBool(asb);
 
-    /* FIXME: Order of alternate should not affect semantics; asn should
-     * parse the same as ans */
+    /* FIXME: integer should parse as number */
     v = visitor_input_test_init(data, "42");
     visit_type_AltStrNum(v, &asn, NULL, &err);
-    /* FIXME g_assert_cmpint(asn->type, == ALT_STR_NUM_KIND_N); */
+    /* FIXME g_assert_cmpint(asn->type, ==, QTYPE_QFLOAT); */
     /* FIXME g_assert_cmpfloat(asn->u.n, ==, 42); */
     error_free_or_abort(&err);
     qapi_free_AltStrNum(asn);
 
+    /* FIXME: integer should parse as number */
     v = visitor_input_test_init(data, "42");
-    visit_type_AltNumStr(v, &ans, NULL, &error_abort);
-    g_assert_cmpint(ans->type, ==, ALT_NUM_STR_KIND_N);
-    g_assert_cmpfloat(ans->u.n, ==, 42);
+    visit_type_AltNumStr(v, &ans, NULL, &err);
+    /* FIXME g_assert_cmpint(ans->type, ==, QTYPE_QFLOAT); */
+    /* FIXME g_assert_cmpfloat(ans->u.n, ==, 42); */
+    error_free_or_abort(&err);
     qapi_free_AltNumStr(ans);
 
     v = visitor_input_test_init(data, "42");
     visit_type_AltStrInt(v, &asi, NULL, &error_abort);
-    g_assert_cmpint(asi->type, ==, ALT_STR_INT_KIND_I);
+    g_assert_cmpint(asi->type, ==, QTYPE_QINT);
     g_assert_cmpint(asi->u.i, ==, 42);
     qapi_free_AltStrInt(asi);
 
     v = visitor_input_test_init(data, "42");
     visit_type_AltIntNum(v, &ain, NULL, &error_abort);
-    g_assert_cmpint(ain->type, ==, ALT_INT_NUM_KIND_I);
+    g_assert_cmpint(ain->type, ==, QTYPE_QINT);
     g_assert_cmpint(ain->u.i, ==, 42);
     qapi_free_AltIntNum(ain);
 
     v = visitor_input_test_init(data, "42");
     visit_type_AltNumInt(v, &ani, NULL, &error_abort);
-    g_assert_cmpint(ani->type, ==, ALT_NUM_INT_KIND_I);
+    g_assert_cmpint(ani->type, ==, QTYPE_QINT);
     g_assert_cmpint(ani->u.i, ==, 42);
     qapi_free_AltNumInt(ani);
 
@@ -389,13 +390,13 @@ static void test_visitor_in_alternate_number(TestInputVisitorData *data,
 
     v = visitor_input_test_init(data, "42.5");
     visit_type_AltStrNum(v, &asn, NULL, &error_abort);
-    g_assert_cmpint(asn->type, ==, ALT_STR_NUM_KIND_N);
+    g_assert_cmpint(asn->type, ==, QTYPE_QFLOAT);
     g_assert_cmpfloat(asn->u.n, ==, 42.5);
     qapi_free_AltStrNum(asn);
 
     v = visitor_input_test_init(data, "42.5");
     visit_type_AltNumStr(v, &ans, NULL, &error_abort);
-    g_assert_cmpint(ans->type, ==, ALT_NUM_STR_KIND_N);
+    g_assert_cmpint(ans->type, ==, QTYPE_QFLOAT);
     g_assert_cmpfloat(ans->u.n, ==, 42.5);
     qapi_free_AltNumStr(ans);
 
@@ -406,13 +407,13 @@ static void test_visitor_in_alternate_number(TestInputVisitorData *data,
 
     v = visitor_input_test_init(data, "42.5");
     visit_type_AltIntNum(v, &ain, NULL, &error_abort);
-    g_assert_cmpint(ain->type, ==, ALT_INT_NUM_KIND_N);
+    g_assert_cmpint(ain->type, ==, QTYPE_QFLOAT);
     g_assert_cmpfloat(ain->u.n, ==, 42.5);
     qapi_free_AltIntNum(ain);
 
     v = visitor_input_test_init(data, "42.5");
     visit_type_AltNumInt(v, &ani, NULL, &error_abort);
-    g_assert_cmpint(ani->type, ==, ALT_NUM_INT_KIND_N);
+    g_assert_cmpint(ani->type, ==, QTYPE_QFLOAT);
     g_assert_cmpfloat(ani->u.n, ==, 42.5);
     qapi_free_AltNumInt(ani);
 }
diff --git a/tests/test-qmp-output-visitor.c b/tests/test-qmp-output-visitor.c
index 4196e66dde..30784424e4 100644
--- a/tests/test-qmp-output-visitor.c
+++ b/tests/test-qmp-output-visitor.c
@@ -428,7 +428,7 @@ static void test_visitor_out_alternate(TestOutputVisitorData *data,
     UserDefAlternate *tmp;
 
     tmp = g_new0(UserDefAlternate, 1);
-    tmp->type = USER_DEF_ALTERNATE_KIND_I;
+    tmp->type = QTYPE_QINT;
     tmp->u.i = 42;
 
     visit_type_UserDefAlternate(data->ov, &tmp, NULL, &error_abort);
@@ -441,7 +441,7 @@ static void test_visitor_out_alternate(TestOutputVisitorData *data,
     qobject_decref(arg);
 
     tmp = g_new0(UserDefAlternate, 1);
-    tmp->type = USER_DEF_ALTERNATE_KIND_S;
+    tmp->type = QTYPE_QSTRING;
     tmp->u.s = g_strdup("hello");
 
     visit_type_UserDefAlternate(data->ov, &tmp, NULL, &error_abort);