qemu-devel
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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


From: Markus Armbruster
Subject: Re: [Qemu-devel] [PATCH 2/2] qobject: modify qobject_ref() to assert on NULL
Date: Fri, 24 Aug 2018 10:12:15 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)

Marc-André Lureau <address@hidden> writes:

> 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.

Why is it not such a good idea?

Is it unsafe?  Unclean?  Ugly?

If unsafe, can you point to actual problems, present or past?

If you consider it unclean or ugly, can you point to established
convention?

> 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>

That's a lot of analysis to support a change...

> ---
>  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,

... that only complicates code.  By not much, granted.  My problem with
it is that the commit message doesn't convince me it's an improvement.



reply via email to

[Prev in Thread] Current Thread [Next in Thread]