From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39336) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cnrVW-00039V-Eh for qemu-devel@nongnu.org; Tue, 14 Mar 2017 14:49:19 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cnrVT-0001O4-Bp for qemu-devel@nongnu.org; Tue, 14 Mar 2017 14:49:18 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34792) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cnrVT-0001MR-3e for qemu-devel@nongnu.org; Tue, 14 Mar 2017 14:49:15 -0400 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 076166AAC2 for ; Tue, 14 Mar 2017 18:49:15 +0000 (UTC) Date: Tue, 14 Mar 2017 18:49:10 +0000 From: "Dr. David Alan Gilbert" Message-ID: <20170314184909.GC7576@work-vm> References: <20170301123223.12489-1-berrange@redhat.com> <20170302123300.GJ29835@redhat.com> <87d1dys9mr.fsf@dusky.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87d1dys9mr.fsf@dusky.pond.sub.org> Subject: Re: [Qemu-devel] [PATCH] migration: allow clearing migration string parameters List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Markus Armbruster Cc: "Daniel P. Berrange" , Eric Blake , Juan Quintela , qemu-devel@nongnu.org * Markus Armbruster (armbru@redhat.com) wrote: > "Daniel P. Berrange" writes: > > > On Wed, Mar 01, 2017 at 08:36:03AM -0600, Eric Blake wrote: > >> On 03/01/2017 06:32 AM, Daniel P. Berrange wrote: > >> > } > >> > if (params->has_tls_creds) { > >> > g_free(s->parameters.tls_creds); > >> > - s->parameters.tls_creds = g_strdup(params->tls_creds); > >> > + if (*params->tls_creds == '\0') { > >> > + s->parameters.tls_creds = NULL; > >> > >> I'm wondering if you should also do s->parameters.has_tls_creds = false > >> at this point? The visitors expect that if has_tls_creds is true, then > >> the string is non-NULL. > > > > The fact that s->parameters contains has_* fields is completely ignored > > by the migration code afaict. IOW the code behaves as if all the has_* > > fields are hardwired to true in s->parameters, even though that is not > > the case :-) The has_* fields are only used when the various migration > > QMP methods are executed, and those all use a separate MigrationParameters > > struct instance. > > Not keeping the has_ members up-to-date is harmless as long as you don't > pass the thing to visitors, including the one hiding in qapi_free_FOO(). > That one ignores scalars, though. > > > From a more abstract point of view, we have two related data types: one > for the state, and one for state changes requests. > > In state, members are always present. > > A state change request is a bag of state member change requests, and > each request can either specify the new value or ask for a reset to > default. Absent member means no change. > > We press the same QAPI type into service for both by making all members > optional. > > For the state case, we hardwire the has_ to true. Or even ignore them > completely. > > For the state change request, we use has_ = false for "no change", has_ > = true with a special value for "reset to default" (new in this patch) > and has_ = true with a non-special value for "set to this value". I'm confused why we need a 'reset to default' - all we need is the ability to change each parameter, and for the new value of that parameter to be an empty string. > Requires a special value outside the set of non-special values. The > obvious one is JSON null, but the QAPI generator doesn't quite support > that, yet. "" works here, but is not general. > > I think I can get you null support in 2.10. Would that work for you? Dave -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK