[Qemu-block] [PATCH 2/2] qobject: modify qobject_ref() to assert on NULL

[Marc-André Lureau]

While it may be convenient to accept NULL value in
qobject_unref() (for similar reasons as free() accepts NULL), it is
not such a good idea for qobject_ref(): now assert() on NULL.

Some code relied on that behaviour, but it's best to be explicit that
NULL is accepted.  We have to rely on testing, and manual inspection
of qobject_ref() usage:

* block.c:
 - bdrv_refresh_filename(): guarded
 - append_open_options(): it depends if qdict values could be NULL,
   handled for extra safety, might be unnecessary

* block/blkdebug.c:
 - blkdebug_refresh_filename(): depends if qdict values could be NULL,
   full_open_options could be NULL apparently, handled

* block/blkverify.c: guarded

* block/{null,nvme}.c: guarded, previous qdict_del() (actually
  qdict_find()) guarantee non-NULL)

* block/quorum.c: full_open_options could be NULL, handled for extra
  safety, might be unnecessary

* monitor: events have associated qdict, but may not have 'data' dict
  entry. Command 'id' is already guarded. A queued response is
  non-NULL.

* qapi/qmp-dispatch.c: if "arguments" exists, it can't be NULL during
  json parsing

* qapi/qobject-input-visitor.c: guarded by assert in visit_type_any()

* qapi/qobject-output-visitor.c: guarded by assert() in visit_type_any()
  qobject_output_complete(): guarded by pre-condition assert()

* qmp.c: guarded, error out before if NULL

* qobject/q{list,dict}.c: can accept NULL values apparently, what's
  the reason? how are you supposed to handle that? no test?

  Some code, such as qdict_flatten_qdict(), assume the value is always
  non-NULL for example.

- tests/*: considered to be covered by make check, not critical

- util/keyval.c: guarded, if (!elt[i]) before

Signed-off-by: Marc-André Lureau <address@hidden>
Reviewed-by: Eric Blake <address@hidden>
---
 include/qapi/qmp/qobject.h | 7 ++++---
 block.c                    | 6 ++++--
 block/blkdebug.c           | 3 ++-
 block/quorum.c             | 3 ++-
 monitor.c                  | 2 +-
 5 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/include/qapi/qmp/qobject.h b/include/qapi/qmp/qobject.h
index fcfd549220..2fe5b42579 100644
--- a/include/qapi/qmp/qobject.h
+++ b/include/qapi/qmp/qobject.h
@@ -74,9 +74,8 @@ static inline void qobject_init(QObject *obj, QType type)
 
 static inline void qobject_ref_impl(QObject *obj)
 {
-    if (obj) {
-        obj->base.refcnt++;
-    }
+    assert(obj);
+    obj->base.refcnt++;
 }
 
 /**
@@ -103,6 +102,7 @@ static inline void qobject_unref_impl(QObject *obj)
 
 /**
  * qobject_ref(): Increment QObject's reference count
+ * @obj: a #QObject or child type instance (must not be NULL)
  *
  * Returns: the same @obj. The type of @obj will be propagated to the
  * return type.
@@ -116,6 +116,7 @@ static inline void qobject_unref_impl(QObject *obj)
 /**
  * qobject_unref(): Decrement QObject's reference count, deallocate
  * when it reaches zero
+ * @obj: a #QObject or child type instance (can be NULL)
  */
 #define qobject_unref(obj) qobject_unref_impl(QOBJECT(obj))
 
diff --git a/block.c b/block.c
index 6161dbe3eb..f1e35c3c1e 100644
--- a/block.c
+++ b/block.c
@@ -5154,6 +5154,8 @@ static bool append_open_options(QDict *d, 
BlockDriverState *bs)
     for (entry = qdict_first(bs->options); entry;
          entry = qdict_next(bs->options, entry))
     {
+        QObject *val;
+
         /* Exclude node-name references to children */
         QLIST_FOREACH(child, &bs->children, next) {
             if (!strcmp(entry->key, child->name)) {
@@ -5174,8 +5176,8 @@ static bool append_open_options(QDict *d, 
BlockDriverState *bs)
             continue;
         }
 
-        qdict_put_obj(d, qdict_entry_key(entry),
-                      qobject_ref(qdict_entry_value(entry)));
+        val = qdict_entry_value(entry);
+        qdict_put_obj(d, qdict_entry_key(entry), val ? qobject_ref(val) : 
NULL);
         found_any = true;
     }
 
diff --git a/block/blkdebug.c b/block/blkdebug.c
index 0759452925..062263f7e1 100644
--- a/block/blkdebug.c
+++ b/block/blkdebug.c
@@ -846,7 +846,8 @@ static void blkdebug_refresh_filename(BlockDriverState *bs, 
QDict *options)
     opts = qdict_new();
     qdict_put_str(opts, "driver", "blkdebug");
 
-    qdict_put(opts, "image", qobject_ref(bs->file->bs->full_open_options));
+    qdict_put(opts, "image", bs->file->bs->full_open_options ?
+              qobject_ref(bs->file->bs->full_open_options) : NULL);
 
     for (e = qdict_first(options); e; e = qdict_next(options, e)) {
         if (strcmp(qdict_entry_key(e), "x-image")) {
diff --git a/block/quorum.c b/block/quorum.c
index 9152da8c58..96cd094ede 100644
--- a/block/quorum.c
+++ b/block/quorum.c
@@ -1089,7 +1089,8 @@ static void quorum_refresh_filename(BlockDriverState *bs, 
QDict *options)
     children = qlist_new();
     for (i = 0; i < s->num_children; i++) {
         qlist_append(children,
-                     qobject_ref(s->children[i]->bs->full_open_options));
+                     s->children[i]->bs->full_open_options ?
+                     qobject_ref(s->children[i]->bs->full_open_options) : 
NULL);
     }
 
     opts = qdict_new();
diff --git a/monitor.c b/monitor.c
index eab2dc7b7b..be4bcd82a0 100644
--- a/monitor.c
+++ b/monitor.c
@@ -675,7 +675,7 @@ monitor_qapi_event_queue_no_reenter(QAPIEvent event, QDict 
*qdict)
 
             evstate = g_new(MonitorQAPIEventState, 1);
             evstate->event = event;
-            evstate->data = qobject_ref(data);
+            evstate->data = data ? qobject_ref(data) : NULL;
             evstate->qdict = NULL;
             evstate->timer = timer_new_ns(monitor_get_event_clock(),
                                           monitor_qapi_event_handler,
-- 
2.18.0.547.g1d89318c48