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author | Eric Blake <eblake@redhat.com> | 2015-12-01 22:20:48 -0700 |
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committer | Timothy Pearson <tpearson@raptorengineering.com> | 2019-11-29 19:28:19 -0600 |
commit | c2ee6c7c2da2aef4240a32b63ff017baaf2317e5 (patch) | |
tree | 8dd260cf1d4c4364a90fae106f1f7fda9fe358be /include/qapi/visitor.h | |
parent | 2fbc567c329267e4a802cb1dfa28743c394e120a (diff) | |
download | hqemu-c2ee6c7c2da2aef4240a32b63ff017baaf2317e5.zip hqemu-c2ee6c7c2da2aef4240a32b63ff017baaf2317e5.tar.gz |
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 'include/qapi/visitor.h')
-rw-r--r-- | include/qapi/visitor.h | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h index a2ad66c..6d25ad2 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); |