From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=47754 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Q4Fov-000657-Cf for qemu-devel@nongnu.org; Mon, 28 Mar 2011 13:01:39 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Q4Fot-0004JV-Dd for qemu-devel@nongnu.org; Mon, 28 Mar 2011 13:01:36 -0400 Received: from e39.co.us.ibm.com ([32.97.110.160]:59356) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Q4Fot-0004I2-7z for qemu-devel@nongnu.org; Mon, 28 Mar 2011 13:01:35 -0400 Received: from d03relay02.boulder.ibm.com (d03relay02.boulder.ibm.com [9.17.195.227]) by e39.co.us.ibm.com (8.14.4/8.13.1) with ESMTP id p2SGmLHS022443 for ; Mon, 28 Mar 2011 10:48:21 -0600 Received: from d03av05.boulder.ibm.com (d03av05.boulder.ibm.com [9.17.195.85]) by d03relay02.boulder.ibm.com (8.13.8/8.13.8/NCO v9.1) with ESMTP id p2SH1Ij7076468 for ; Mon, 28 Mar 2011 11:01:21 -0600 Received: from d03av05.boulder.ibm.com (loopback [127.0.0.1]) by d03av05.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p2SH1IKE024045 for ; Mon, 28 Mar 2011 11:01:18 -0600 Message-ID: <4D90BEDC.6050207@us.ibm.com> Date: Mon, 28 Mar 2011 12:01:16 -0500 From: Anthony Liguori MIME-Version: 1.0 References: <1301082479-4058-1-git-send-email-mdroth@linux.vnet.ibm.com> <1301082479-4058-6-git-send-email-mdroth@linux.vnet.ibm.com> <4D8D0788.7070700@us.ibm.com> <20110328134747.5c9fbc8e@doriath> In-Reply-To: <20110328134747.5c9fbc8e@doriath> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: [Qemu-devel] Re: [RFC][PATCH v1 05/12] qapi: fix handling for null-return async callbacks List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Luiz Capitulino Cc: aliguori@linux.vnet.ibm.com, agl@linux.vnet.ibm.com, Michael Roth , Jes.Sorensen@redhat.com, qemu-devel@nongnu.org On 03/28/2011 11:47 AM, Luiz Capitulino wrote: > On Fri, 25 Mar 2011 16:22:16 -0500 > Anthony Liguori wrote: > >> On 03/25/2011 02:47 PM, Michael Roth wrote: >>> Async commands like 'guest-ping' have NULL retvals. Handle these by >>> inserting an empty dictionary in the response's "return" field. >>> >>> Signed-off-by: Michael Roth >>> --- >>> qmp-core.c | 5 ++++- >>> 1 files changed, 4 insertions(+), 1 deletions(-) >>> >>> diff --git a/qmp-core.c b/qmp-core.c >>> index e33f7a4..9f3d182 100644 >>> --- a/qmp-core.c >>> +++ b/qmp-core.c >>> @@ -922,9 +922,12 @@ void qmp_async_complete_command(QmpCommandState *cmd, QObject *retval, Error *er >>> rsp = qdict_new(); >>> if (err) { >>> qdict_put_obj(rsp, "error", error_get_qobject(err)); >>> - } else { >>> + } else if (retval) { >>> qobject_incref(retval); >>> qdict_put_obj(rsp, "return", retval); >>> + } else { >>> + /* add empty "return" dict, this is the standard for NULL returns */ >>> + qdict_put_obj(rsp, "return", QOBJECT(qdict_new())); >> Luiz, I know we decided to return empty dicts because it lets us extend >> things better, but did we want to rule out the use of a 'null' return >> value entirely? > For asynchronous commands you mean? No we didn't. No, nothing to do with asynchronous commands. Just in general. The question is, is it legal for a command to return 'null'. It's certain valid JSON, but is it valid QMP? Regards, Anthony Liguori > *iirc*, what happens today is that no command using this api is truly async, > for two reasons. First, changing from sync to async can break clients (that > happened to query-balloon). Second, although I can't remember the exact > details, the api that exists in the tree today is limited. > > But for a new thing, like QAPI, having different semantics for async commands > seems the right thing to be done (ie. delaying the response). >> For a command like this, I can't imagine ever wanting to extend the >> return value... >> >> Regards, >> >> Anthony Liguori >> >>> } >>> if (cmd->tag) { >>> qdict_put_obj(rsp, "tag", cmd->tag);