Re: [Qemu-devel] [PATCH 1/2] qdict: add qdict_steal()

[Markus Armbruster]

Marc-André Lureau <address@hidden> writes:

> Add a new function qdict_steal(), that deletes a key from a dict, and
> returns the associated value, if any. Simplify related code.
>
> Signed-off-by: Marc-André Lureau <address@hidden>
> ---
>  include/qapi/qmp/qdict.h |  1 +
>  monitor.c                |  3 +--
>  qobject/block-qdict.c    |  7 ++-----
>  qobject/qdict.c          | 22 ++++++++++++++++++++++
>  4 files changed, 26 insertions(+), 7 deletions(-)

Missing: tests/check-qdict.c update.

> diff --git a/include/qapi/qmp/qdict.h b/include/qapi/qmp/qdict.h
> index 7f3ec10a10..84644bfba6 100644
> --- a/include/qapi/qmp/qdict.h
> +++ b/include/qapi/qmp/qdict.h
> @@ -37,6 +37,7 @@ QObject *qdict_entry_value(const QDictEntry *entry);
>  size_t qdict_size(const QDict *qdict);
>  void qdict_put_obj(QDict *qdict, const char *key, QObject *value);
>  void qdict_del(QDict *qdict, const char *key);
> +QObject *qdict_steal(QDict *qdict, const char *key);
>  int qdict_haskey(const QDict *qdict, const char *key);
>  QObject *qdict_get(const QDict *qdict, const char *key);
>  bool qdict_is_equal(const QObject *x, const QObject *y);
> diff --git a/monitor.c b/monitor.c
> index a1999e396c..eab2dc7b7b 100644
> --- a/monitor.c
> +++ b/monitor.c
> @@ -4262,8 +4262,7 @@ static void handle_qmp_command(JSONMessageParser 
> *parser, GQueue *tokens)
>  
>      qdict = qobject_to(QDict, req);
>      if (qdict) {
> -        id = qobject_ref(qdict_get(qdict, "id"));
> -        qdict_del(qdict, "id");
> +        id = qdict_steal(qdict, "id");
>      } /* else will fail qmp_dispatch() */
>  
>      if (req && trace_event_get_state_backends(TRACE_HANDLE_QMP_COMMAND)) {
> diff --git a/qobject/block-qdict.c b/qobject/block-qdict.c
> index 42054cc274..a07664ee6a 100644
> --- a/qobject/block-qdict.c
> +++ b/qobject/block-qdict.c
> @@ -692,8 +692,6 @@ void qdict_join(QDict *dest, QDict *src, bool overwrite)
>   */
>  bool qdict_rename_keys(QDict *qdict, const QDictRenames *renames, Error 
> **errp)
>  {
> -    QObject *qobj;
> -
>      while (renames->from) {
>          if (qdict_haskey(qdict, renames->from)) {
>              if (qdict_haskey(qdict, renames->to)) {
> @@ -702,9 +700,8 @@ bool qdict_rename_keys(QDict *qdict, const QDictRenames 
> *renames, Error **errp)
>                  return false;
>              }
>  
> -            qobj = qdict_get(qdict, renames->from);
> -            qdict_put_obj(qdict, renames->to, qobject_ref(qobj));
> -            qdict_del(qdict, renames->from);
> +            qdict_put_obj(qdict, renames->to,
> +                          qdict_steal(qdict, renames->from));
>          }
>  
>          renames++;

How did you find possible uses for qdict_steal()?

> diff --git a/qobject/qdict.c b/qobject/qdict.c
> index 3d8c2f7bbc..322f23f094 100644
> --- a/qobject/qdict.c
> +++ b/qobject/qdict.c
> @@ -406,6 +406,28 @@ void qdict_del(QDict *qdict, const char *key)
>      }
>  }
>  
> +/**
> + * qdict_steal(): Steal a 'key:value' pair from the dictionary

"Steal" is cute, but perhaps qdict_get_and_del() would be clearer.

> + *
> + * Return the associated entry value and remove it, or NULL.

Suggest

    * If @qdict has @key, return its value, and delete it from @qdict.
    * Else, return NULL.

> + */
> +QObject *qdict_steal(QDict *qdict, const char *key)
> +{
> +    QDictEntry *entry;
> +    QObject *val = NULL;
> +
> +    entry = qdict_find(qdict, key, tdb_hash(key) % QDICT_BUCKET_MAX);
> +    if (entry) {
> +        QLIST_REMOVE(entry, next);
> +        val = qobject_ref(entry->value);
> +        qentry_destroy(entry);
> +        qdict->size--;
> +    }
> +
> +    return val;
> +}

This is a slightly extended qdict_del().

   void qdict_del(QDict *qdict, const char *key)
   {
       QDictEntry *entry;

       entry = qdict_find(qdict, key, tdb_hash(key) % QDICT_BUCKET_MAX);
       if (entry) {
           QLIST_REMOVE(entry, next);
           qentry_destroy(entry);
           qdict->size--;
       }
   }

Heavy-handed de-duplication:

   QObject *qdict_get_and_del(QDict *qdict, const char *key)
   {
       QDictEntry *entry;
       QObject *val;

       entry = qdict_find(qdict, key, tdb_hash(key) % QDICT_BUCKET_MAX);
       if (!entry) {
           return NULL;
       }

       QLIST_REMOVE(entry, next);
       val = qobject_ref(entry->value);
       qentry_destroy(entry);
       qdict->size--;
       return val;
   }

   void qdict_del(QDict *qdict, const char *key)
   {
       qobject_unref(qdict_get_and_del(qdict, key));
   }

Makes qdict_del() execute an additional qobject_ref() / qobject_unref(),
but that shouldn't matter.

> +
> +

Just one blank line, please.

>  /**
>   * qdict_is_equal(): Test whether the two QDicts are equal
>   *