[Qemu-devel] [PATCH v12 02/18] qapi: Guarantee NULL obj on input visitor callback error

[Eric Blake <eblake@redhat.com>]

Our existing input visitors were not very consistent on errors
in a function taking 'TYPE **obj'. While all of them set '*obj'
to allocated storage on success, it was not obvious whether
'*obj' was guaranteed safe on failure, or whether it was left
uninitialized.  But a future patch wants to guarantee that
visit_type_FOO() does not leak a partially-constructed obj back
to the caller; it is easier to implement this if we can reliably
state that '*obj' is assigned on exit, even on failures.

The opts-visitor start_struct() doesn't set an error, but it
also was doing a weird check for 0 size; all callers pass in
non-zero size if obj is non-NULL.

Signed-off-by: Eric Blake <eblake@redhat.com>

---
v12: new patch
---
 qapi/opts-visitor.c         | 3 ++-
 qapi/qmp-input-visitor.c    | 4 ++++
 qapi/string-input-visitor.c | 1 +
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/qapi/opts-visitor.c b/qapi/opts-visitor.c
index f9a2346..fd90608 100644
--- a/qapi/opts-visitor.c
+++ b/qapi/opts-visitor.c
@@ -132,7 +132,7 @@ opts_start_struct(Visitor *v, const char *name, void **obj,
     const QemuOpt *opt;

     if (obj) {
-        *obj = g_malloc0(size > 0 ? size : 1);
+        *obj = g_malloc0(size);
     }
     if (ov->depth++ > 0) {
         return;
@@ -313,6 +313,7 @@ opts_type_str(Visitor *v, const char *name, char **obj, Error **errp)

     opt = lookup_scalar(ov, name, errp);
     if (!opt) {
+        *obj = NULL;
         return;
     }
     *obj = g_strdup(opt->str ? opt->str : "");
diff --git a/qapi/qmp-input-visitor.c b/qapi/qmp-input-visitor.c
index 03dcb65..550aed6 100644
--- a/qapi/qmp-input-visitor.c
+++ b/qapi/qmp-input-visitor.c
@@ -119,6 +119,9 @@ static void qmp_input_start_struct(Visitor *v, const char *name, void **obj,
     QObject *qobj = qmp_input_get_object(qiv, name, true);
     Error *err = NULL;

+    if (obj) {
+        *obj = NULL;
+    }
     if (!qobj || qobject_type(qobj) != QTYPE_QDICT) {
         error_setg(errp, QERR_INVALID_PARAMETER_TYPE, name ? name : "null",
                    "QDict");
@@ -266,6 +269,7 @@ static void qmp_input_type_str(Visitor *v, const char *name, char **obj,
     QString *qstr = qobject_to_qstring(qmp_input_get_object(qiv, name, true));

     if (!qstr) {
+        *obj = NULL;
         error_setg(errp, QERR_INVALID_PARAMETER_TYPE, name ? name : "null",
                    "string");
         return;
diff --git a/qapi/string-input-visitor.c b/qapi/string-input-visitor.c
index d591e67..4087bf9 100644
--- a/qapi/string-input-visitor.c
+++ b/qapi/string-input-visitor.c
@@ -292,6 +292,7 @@ static void parse_type_str(Visitor *v, const char *name, char **obj,
     if (siv->string) {
         *obj = g_strdup(siv->string);
     } else {
+        *obj = NULL;
         error_setg(errp, QERR_INVALID_PARAMETER_TYPE, name ? name : "null",
                    "string");
     }
-- 
2.5.0