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

[Marc-André Lureau]

Hi

On Fri, Aug 24, 2018 at 10:05 AM Markus Armbruster <address@hidden> wrote:
>
> 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.

ok

>
> > 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()?

manual review

>
> > 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.

"steal" is common in glib. I don't mind renaming.

>
> > + *
> > + * 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.

ok

>
> > +
> > +
>
> Just one blank line, please.

ok

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

thanks

-- 
Marc-André Lureau