diff options
author | Eric Blake <eblake@redhat.com> | 2015-12-01 22:20:48 -0700 |
---|---|---|
committer | Markus Armbruster <armbru@redhat.com> | 2015-12-17 08:21:28 +0100 |
commit | 0426d53c6530606bf7641b83f2b755fe61c280ee (patch) | |
tree | 3d99a418cb2bf4bfaeb27a26d4ca943164299cd4 /scripts/qapi.py | |
parent | 7264f5c50cc1be0f1406e3ebb45aedcca02f603a (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.py | 18 |
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, |