[Qemu-devel] [PATCH v14 03/19] qapi: Guarantee NULL obj on input visitor callback error

[Eric Blake]

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 <address@hidden>

---
v14: no change
v13: no change
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 f98cf2e..cdb6e42 100644
--- a/qapi/opts-visitor.c
+++ b/qapi/opts-visitor.c
@@ -133,7 +133,7 @@ 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;
@@ -314,6 +314,7 @@ 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 02d4233..77cce8b 100644
--- a/qapi/qmp-input-visitor.c
+++ b/qapi/qmp-input-visitor.c
@@ -120,6 +120,9 @@ 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");
@@ -267,6 +270,7 @@ 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 d604575..797973a 100644
--- a/qapi/string-input-visitor.c
+++ b/qapi/string-input-visitor.c
@@ -293,6 +293,7 @@ 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");
     }
-- 
2.5.5