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qapi: Document that input visitor semantics are prone to leaks

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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>
This commit is contained in:
Eric Blake 2015-07-30 16:33:07 -06:00 committed by Markus Armbruster
parent 999387782f
commit 2f52e20597
2 changed files with 6 additions and 0 deletions
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4
scripts/qapi-visit.py
View File

@ -115,6 +115,10 @@ out:
def generate_visit_struct_body(name): 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(''' ret = mcgen('''
Error *err = NULL; Error *err = NULL;

2
tests/test-qmp-input-visitor.c
View File

@ -636,6 +636,8 @@ static void test_visitor_in_errors(TestInputVisitorData *data,
visit_type_TestStruct(v, &p, NULL, &err); visit_type_TestStruct(v, &p, NULL, &err);
g_assert(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); g_assert(p->string == NULL);
error_free(err); error_free(err);