qapi: Document that input visitor semantics are prone to leaks
Most functions that can return a pointer or set an Error ** value
are decent enough to guarantee a NULL return when reporting an error.
Not so with our generated qapi visitor functions. If the caller
is not careful to clean up partially-allocated objects on error,
then the caller suffers a memory leak.
Properly fixing it is probably complex enough to save for a later
day, so merely document it for now.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1438295587-19069-1-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py
index 73f136f..eec5f1f 100644
--- a/scripts/qapi-visit.py
+++ b/scripts/qapi-visit.py
@@ -115,6 +115,10 @@
def generate_visit_struct_body(name):
+ # FIXME: if *obj is NULL on entry, and visit_start_struct() assigns to
+ # *obj, but then visit_type_FOO_fields() 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.
ret = mcgen('''
Error *err = NULL;
diff --git a/tests/test-qmp-input-visitor.c b/tests/test-qmp-input-visitor.c
index b7a87ee..a5cfefa 100644
--- a/tests/test-qmp-input-visitor.c
+++ b/tests/test-qmp-input-visitor.c
@@ -636,6 +636,8 @@
visit_type_TestStruct(v, &p, NULL, &err);
g_assert(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);
error_free(err);
