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

[Markus Armbruster]

Marc-André Lureau <address@hidden> writes:

> 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

Okay.  I expected a few more than two.

>> > 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.

Hmm.  I found g_hash_table_steal(), but it's a bit different: it
"Removes a key and its associated value from a GHashTable without
calling the key and value destroy functions" (that part seems close
enough), but returns a bool rather than the value.  Feels like sub-par
design to me.  Is this the precedence you have in mind?

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