Returning a partial object on error is an invitation for a careless
caller to leak memory. As no one outside the testsuite was actually
relying on these semantics, it is cleaner to just document and
guarantee that ALL pointer-based visit_type_FOO() functions always
leave a safe value in *obj during an input visitor (either the new
object on success, or NULL if an error is encountered), so callers
can now unconditionally use qapi_free_FOO() to clean up regardless
of whether an error occurred.
The decision is done by enhancing qapi-visit-core to return true
for input visitors (the callbacks themselves do not need
modification); since we've documented that visit_end_* must be
called after any successful visit_start_*, that is a sufficient
point for knowing that something was allocated during start.
Note that we still leave *obj unchanged after a scalar-based
visit_type_FOO(); I did not feel like auditing all uses of
visit_type_Enum() to see if the callers would tolerate a specific
sentinel value (not to mention having to decide whether it would
be better to use 0 or ENUM__MAX as that sentinel).
Signed-off-by: Eric Blake <ebl...@redhat.com>
---
v13: rebase to latest, documentation tweaks
v12: rebase to latest, don't modify callback signatures, use newer
approach for detecting input visitors, avoid 'allocated' boolean
[no v10, v11]
v9: fix bug in use of errp
v8: rebase to earlier changes
v7: rebase to earlier changes, enhance commit message, also fix
visit_type_str() and visit_type_any()
v6: rebase on top of earlier doc and formatting improvements, mention
that *obj can be uninitialized on entry to an input visitor, rework
semantics to keep valgrind happy on uninitialized input, break some
long lines
---
include/qapi/visitor.h | 42 ++++++++++++++++++++++++++++++------------
include/qapi/visitor-impl.h | 8 +++++---
scripts/qapi-visit.py | 25 +++++++++++++------------
qapi/qapi-visit-core.c | 41 ++++++++++++++++++++++++++++++++++-------
tests/test-qmp-commands.c | 13 ++++++-------
tests/test-qmp-input-strict.c | 19 ++++++++-----------
tests/test-qmp-input-visitor.c | 10 ++--------
docs/qapi-code-gen.txt | 10 ++++++++--
8 files changed, 106 insertions(+), 62 deletions(-)
diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h
index 8d4837d..5b7c86e 100644
--- a/include/qapi/visitor.h
+++ b/include/qapi/visitor.h
@@ -66,14 +66,16 @@
* }' if an error is encountered on "value" (or to have the visitor
* core auto-generate the nicer name).
*
- * FIXME: At present, input visitors may allocate an incomplete *@obj
- * even when visit_type_FOO() reports an error. Using an output
- * visitor with an incomplete object has undefined behavior; callers
- * must call qapi_free_FOO() (which uses the dealloc visitor, and
- * safely handles an incomplete object) to avoid a memory leak.
+ * If an error is detected during visit_type_FOO() with an input
+ * visitor, then *@obj will be NULL for pointer types, and left
+ * unchanged for scalar types. Using an output visitor with an
+ * incomplete object has undefined behavior (other than a special case
+ * for visit_type_str() treating NULL like ""), while the dealloc
+ * visitor safely handles incomplete objects.
*
- * Likewise, the QAPI object types (structs, unions, and alternates)
- * have a generated function in qapi-visit.h compatible with:
+ * Additionally, the QAPI object types (structs, unions, and
+ * alternates) have a generated function in qapi-visit.h compatible
+ * with:
*
* void visit_type_FOO_members(Visitor *v, FOO *obj, Error **errp);
*
@@ -105,7 +107,6 @@
* v = ...obtain input visitor...
* visit_type_Foo(v, NULL, &f, &err);
* if (err) {
- * qapi_free_Foo(f);
* ...handle error...
* } else {
* ...use f...
@@ -113,7 +114,6 @@
* v = ...obtain input visitor...
* visit_type_FooList(v, NULL, &l, &err);
* if (err) {
- * qapi_free_FooList(l);
* ...handle error...
* } else {
* while (l) {
@@ -257,8 +257,14 @@ void visit_check_struct(Visitor *v, Error **errp);
* even if intermediate processing was skipped due to errors, to allow
* the backend to release any resources. Destroying the visitor may
* behave as if this was implicitly called.
+ *
+ * Returns true if this is an input visitor (that is, an allocation
+ * occurred during visit_start_struct() if obj was non-NULL). The
+ * caller can use this, along with tracking whether a local error
+ * occurred in the meantime, to decide when to undo allocation before
+ * returning control from a visit_type_FOO() function.
*/
-void visit_end_struct(Visitor *v);
+bool visit_end_struct(Visitor *v);
/* === Visiting lists */
@@ -314,8 +320,14 @@ GenericList *visit_next_list(Visitor *v, GenericList
*tail, size_t size);
* even if intermediate processing was skipped due to errors, to allow
* the backend to release any resources. Destroying the visitor may
* behave as if this was implicitly called.
+ *
+ * Returns true if this is an input visitor (that is, an allocation
+ * occurred during visit_start_list() if list was non-NULL). The
+ * caller can use this, along with tracking whether a local error
+ * occurred in the meantime, to decide when to undo allocation before
+ * returning control from a visit_type_FOO() function.
*/
-void visit_end_list(Visitor *v);
+bool visit_end_list(Visitor *v);
/* === Visiting alternates */
@@ -348,10 +360,16 @@ void visit_start_alternate(Visitor *v, const char *name,
* the backend to release any resources. Destroying the visitor may
* behave as if this was implicitly called.
*
+ * Returns true if this is an input visitor (that is, an allocation
+ * occurred during visit_start_alternate() if obj was non-NULL). The
+ * caller can use this, along with tracking whether a local error
+ * occurred in the meantime, to decide when to undo allocation before
+ * returning control from a visit_type_FOO() function.
+ *
* TODO: Should all the visit_end_* interfaces take obj parameter, so
* that dealloc visitor need not track what was passed in visit_start?
*/
-void visit_end_alternate(Visitor *v);
+bool visit_end_alternate(Visitor *v);
/* === Other helpers */
diff --git a/include/qapi/visitor-impl.h b/include/qapi/visitor-impl.h
index 0471465..f113869 100644
--- a/include/qapi/visitor-impl.h
+++ b/include/qapi/visitor-impl.h
@@ -42,7 +42,8 @@ struct Visitor
/* Optional; intended for input visitors. */
void (*check_struct)(Visitor *v, Error **errp);
- /* Must be set to visit structs. */
+ /* Must be set to visit structs. The core takes care of the
+ * return value. */
void (*end_struct)(Visitor *v);
/* Must be set; document if @list may not be NULL. */
@@ -52,7 +53,7 @@ struct Visitor
/* Must be set. */
GenericList *(*next_list)(Visitor *v, GenericList *tail, size_t size);
- /* Must be set. */
+ /* Must be set. The core takes care of the return value. */
void (*end_list)(Visitor *v);
/* Must be set by input and dealloc visitors to visit alternates;
@@ -61,7 +62,8 @@ struct Visitor
GenericAlternate **obj, size_t size,
bool promote_int, Error **errp);
- /* Optional, needed for dealloc visitor. */
+ /* Optional, needed for dealloc visitor. The core takes care of
+ * the return value. */
void (*end_alternate)(Visitor *v);
/* Must be set. */
diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py
index fdb10c0..e95285e 100644
--- a/scripts/qapi-visit.py
+++ b/scripts/qapi-visit.py
@@ -91,10 +91,6 @@ out:
def gen_visit_list(name, element_type):
- # FIXME: if *obj is NULL on entry, and the first visit_next_list()
- # assigns to *obj, while a later one fails, we should clean up *obj
- # rather than leaving it non-NULL. As currently written, the caller must
- # call qapi_free_FOOList() to avoid a memory leak of the partial FOOList.
return mcgen('''
void visit_type_%(c_name)s(Visitor *v, const char *name, %(c_name)s **obj,
Error **errp)
@@ -114,7 +110,10 @@ void visit_type_%(c_name)s(Visitor *v, const char *name,
%(c_name)s **obj, Error
break;
}
}
- visit_end_list(v);
+ if (visit_end_list(v) && err) {
+ qapi_free_%(c_name)s(*obj);
+ *obj = NULL;
+ }
out:
error_propagate(errp, err);
}
@@ -191,21 +190,20 @@ void visit_type_%(c_name)s(Visitor *v, const char *name,
%(c_name)s **obj, Error
error_setg(&err, QERR_INVALID_PARAMETER_TYPE, name ? name : "null",
"%(name)s");
}
- visit_end_alternate(v);
+ if (visit_end_alternate(v) && err) {
+ qapi_free_%(c_name)s(*obj);
+ *obj = NULL;
+ }
out:
error_propagate(errp, err);
}
''',
- name=name)
+ name=name, c_name=c_name(name))
return ret
def gen_visit_object(name, base, members, variants):
- # FIXME: if *obj is NULL on entry, and visit_start_struct() assigns to
- # *obj, but then visit_type_FOO_members() fails, we should clean up *obj
- # rather than leaving it non-NULL. As currently written, the caller must
- # call qapi_free_FOO() to avoid a memory leak of the partial FOO.
return mcgen('''
void visit_type_%(c_name)s(Visitor *v, const char *name, %(c_name)s **obj,
Error **errp)
@@ -225,7 +223,10 @@ void visit_type_%(c_name)s(Visitor *v, const char *name,
%(c_name)s **obj, Error
}
visit_check_struct(v, &err);
out_obj:
- visit_end_struct(v);
+ if (visit_end_struct(v) && err) {
+ qapi_free_%(c_name)s(*obj);
+ *obj = NULL;
+ }
out:
error_propagate(errp, err);
}
diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c
index bbcedb1..7c36b24 100644
--- a/qapi/qapi-visit-core.c
+++ b/qapi/qapi-visit-core.c
@@ -22,11 +22,17 @@
void visit_start_struct(Visitor *v, const char *name, void **obj,
size_t size, Error **errp)
{
+ Error *err = NULL;
+
if (obj) {
assert(size);
assert(v->type != VISITOR_OUTPUT || *obj);
}
- v->start_struct(v, name, obj, size, errp);
+ v->start_struct(v, name, obj, size, &err);
+ if (obj && v->type == VISITOR_INPUT) {
+ assert(err || *obj);
+ }
+ error_propagate(errp, err);
}
void visit_check_struct(Visitor *v, Error **errp)
@@ -36,11 +42,13 @@ void visit_check_struct(Visitor *v, Error **errp)
}
}
-void visit_end_struct(Visitor *v)
+bool visit_end_struct(Visitor *v)
{
v->end_struct(v);
+ return v->type == VISITOR_INPUT;
}
+
void visit_start_list(Visitor *v, const char *name, GenericList **list,
size_t size, Error **errp)
{
@@ -54,26 +62,34 @@ GenericList *visit_next_list(Visitor *v, GenericList *tail,
size_t size)
return v->next_list(v, tail, size);
}
-void visit_end_list(Visitor *v)
+bool visit_end_list(Visitor *v)
{
v->end_list(v);
+ return v->type == VISITOR_INPUT;
}
void visit_start_alternate(Visitor *v, const char *name,
GenericAlternate **obj, size_t size,
bool promote_int, Error **errp)
{
+ Error *err = NULL;
+
assert(obj && size >= sizeof(GenericAlternate));
if (v->start_alternate) {
- v->start_alternate(v, name, obj, size, promote_int, errp);
+ v->start_alternate(v, name, obj, size, promote_int, &err);
+ if (v->type == VISITOR_INPUT) {
+ assert(err || *obj);
+ }
+ error_propagate(errp, err);
}
}
-void visit_end_alternate(Visitor *v)
+bool visit_end_alternate(Visitor *v)
{
if (v->end_alternate) {
v->end_alternate(v);
}
+ return v->type == VISITOR_INPUT;
}
bool visit_optional(Visitor *v, const char *name, bool *present)
@@ -205,12 +221,17 @@ void visit_type_bool(Visitor *v, const char *name, bool
*obj, Error **errp)
void visit_type_str(Visitor *v, const char *name, char **obj, Error **errp)
{
+ Error *err = NULL;
assert(obj);
/* TODO: Fix callers to not pass NULL when they mean "", so that we
* can enable:
assert(v->type != VISITOR_OUTPUT || *obj);
*/
- v->type_str(v, name, obj, errp);
+ v->type_str(v, name, obj, &err);
+ if (v->type == VISITOR_INPUT) {
+ assert(err || *obj);
+ }
+ error_propagate(errp, err);
}
void visit_type_number(Visitor *v, const char *name, double *obj,
@@ -222,9 +243,15 @@ void visit_type_number(Visitor *v, const char *name,
double *obj,
void visit_type_any(Visitor *v, const char *name, QObject **obj, Error **errp)
{
+ Error *err = NULL;
+
assert(obj);
assert(v->type != VISITOR_OUTPUT || *obj);
- v->type_any(v, name, obj, errp);
+ v->type_any(v, name, obj, &err);
+ if (v->type == VISITOR_INPUT) {
+ assert(err || *obj);
+ }
+ error_propagate(errp, err);
}
void visit_type_null(Visitor *v, const char *name, Error **errp)
diff --git a/tests/test-qmp-commands.c b/tests/test-qmp-commands.c
index 14a9ebb..d6c494d 100644
--- a/tests/test-qmp-commands.c
+++ b/tests/test-qmp-commands.c
@@ -228,14 +228,13 @@ static void test_dealloc_partial(void)
QDECREF(ud2_dict);
}
- /* verify partial success */
- assert(ud2 != NULL);
- assert(ud2->string0 != NULL);
- assert(strcmp(ud2->string0, text) == 0);
- assert(ud2->dict1 == NULL);
-
- /* confirm & release construction error */
+ /* verify that visit_type_XXX() cleans up properly on error */
error_free_or_abort(&err);
+ assert(!ud2);
+
+ /* Manually create a partial object, leaving ud2->dict1 at NULL */
+ ud2 = g_new0(UserDefTwo, 1);
+ ud2->string0 = g_strdup(text);
/* tear down partial object */
qapi_free_UserDefTwo(ud2);
diff --git a/tests/test-qmp-input-strict.c b/tests/test-qmp-input-strict.c
index 6a33aa4..9587b14 100644
--- a/tests/test-qmp-input-strict.c
+++ b/tests/test-qmp-input-strict.c
@@ -181,10 +181,7 @@ static void test_validate_fail_struct(TestInputVisitorData
*data,
visit_type_TestStruct(v, NULL, &p, &err);
error_free_or_abort(&err);
- if (p) {
- g_free(p->string);
- }
- g_free(p);
+ g_assert(!p);
}
static void test_validate_fail_struct_nested(TestInputVisitorData *data,
@@ -198,7 +195,7 @@ static void
test_validate_fail_struct_nested(TestInputVisitorData *data,
visit_type_UserDefTwo(v, NULL, &udp, &err);
error_free_or_abort(&err);
- qapi_free_UserDefTwo(udp);
+ g_assert(!udp);
}
static void test_validate_fail_list(TestInputVisitorData *data,
@@ -212,7 +209,7 @@ static void test_validate_fail_list(TestInputVisitorData
*data,
visit_type_UserDefOneList(v, NULL, &head, &err);
error_free_or_abort(&err);
- qapi_free_UserDefOneList(head);
+ g_assert(!head);
}
static void test_validate_fail_union_native_list(TestInputVisitorData *data,
@@ -227,7 +224,7 @@ static void
test_validate_fail_union_native_list(TestInputVisitorData *data,
visit_type_UserDefNativeListUnion(v, NULL, &tmp, &err);
error_free_or_abort(&err);
- qapi_free_UserDefNativeListUnion(tmp);
+ g_assert(!tmp);
}
static void test_validate_fail_union_flat(TestInputVisitorData *data,
@@ -241,7 +238,7 @@ static void
test_validate_fail_union_flat(TestInputVisitorData *data,
visit_type_UserDefFlatUnion(v, NULL, &tmp, &err);
error_free_or_abort(&err);
- qapi_free_UserDefFlatUnion(tmp);
+ g_assert(!tmp);
}
static void test_validate_fail_union_flat_no_discrim(TestInputVisitorData
*data,
@@ -256,13 +253,13 @@ static void
test_validate_fail_union_flat_no_discrim(TestInputVisitorData *data,
visit_type_UserDefFlatUnion2(v, NULL, &tmp, &err);
error_free_or_abort(&err);
- qapi_free_UserDefFlatUnion2(tmp);
+ g_assert(!tmp);
}
static void test_validate_fail_alternate(TestInputVisitorData *data,
const void *unused)
{
- UserDefAlternate *tmp = NULL;
+ UserDefAlternate *tmp;
Visitor *v;
Error *err = NULL;
@@ -270,7 +267,7 @@ static void
test_validate_fail_alternate(TestInputVisitorData *data,
visit_type_UserDefAlternate(v, NULL, &tmp, &err);
error_free_or_abort(&err);
- qapi_free_UserDefAlternate(tmp);
+ g_assert(!tmp);
}
static void do_test_validate_qmp_introspect(TestInputVisitorData *data,
diff --git a/tests/test-qmp-input-visitor.c b/tests/test-qmp-input-visitor.c
index a62c2b1..19bed0a 100644
--- a/tests/test-qmp-input-visitor.c
+++ b/tests/test-qmp-input-visitor.c
@@ -759,18 +759,12 @@ static void test_visitor_in_errors(TestInputVisitorData
*data,
visit_type_TestStruct(v, NULL, &p, &err);
error_free_or_abort(&err);
- /* FIXME - a failed parse should not leave a partially-allocated p
- * for us to clean up; this could cause callers to leak memory. */
- g_assert(p->string == NULL);
-
- g_free(p->string);
- g_free(p);
+ g_assert(!p);
v = visitor_input_test_init(data, "[ '1', '2', false, '3' ]");
visit_type_strList(v, NULL, &q, &err);
error_free_or_abort(&err);
- assert(q);
- qapi_free_strList(q);
+ assert(!q);
}
static void test_visitor_in_wrong_type(TestInputVisitorData *data,
diff --git a/docs/qapi-code-gen.txt b/docs/qapi-code-gen.txt
index 6107fa4..b702885 100644
--- a/docs/qapi-code-gen.txt
+++ b/docs/qapi-code-gen.txt
@@ -904,7 +904,10 @@ Example:
}
visit_check_struct(v, &err);
out_obj:
- visit_end_struct(v);
+ if (visit_end_struct(v) && err) {
+ qapi_free_UserDefOne(*obj);
+ *obj = NULL;
+ }
out:
error_propagate(errp, err);
}
@@ -927,7 +930,10 @@ Example:
}
}
- visit_end_list(v);
+ if (visit_end_list(v) && err) {
+ qapi_free_UserDefOneList(*obj);
+ *obj = NULL;
+ }
out:
error_propagate(errp, err);
}
--
2.5.0
