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[14/26] qapi: Document that input visitor semantics are prone to leaks

Message ID 1438679896-5077-15-git-send-email-armbru@redhat.com
State New
Headers show

Commit Message

Markus Armbruster Aug. 4, 2015, 9:18 a.m. UTC 
From: Eric Blake <eblake@redhat.com>

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>
---
 scripts/qapi-visit.py          | 4 ++++
 tests/test-qmp-input-visitor.c | 2 ++
 2 files changed, 6 insertions(+)
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Patch

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 @@  out:
 
 
 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 @@  static void test_visitor_in_errors(TestInputVisitorData *data,
 
     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);