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authorEric Blake <eblake@redhat.com>2015-12-01 22:20:48 -0700
committerMarkus Armbruster <armbru@redhat.com>2015-12-17 08:21:28 +0100
commit0426d53c6530606bf7641b83f2b755fe61c280ee (patch)
tree3d99a418cb2bf4bfaeb27a26d4ca943164299cd4 /scripts/qapi.py
parent7264f5c50cc1be0f1406e3ebb45aedcca02f603a (diff)
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>
Diffstat (limited to 'scripts/qapi.py')
-rw-r--r--scripts/qapi.py18
1 files changed, 13 insertions, 5 deletions
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,