From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50546) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1co5II-0002lv-92 for qemu-devel@nongnu.org; Wed, 15 Mar 2017 05:32:35 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1co5IF-00027C-6D for qemu-devel@nongnu.org; Wed, 15 Mar 2017 05:32:34 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49700) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1co5IE-00025j-TT for qemu-devel@nongnu.org; Wed, 15 Mar 2017 05:32:31 -0400 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (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 EAB74C05AA5B for ; Wed, 15 Mar 2017 09:32:30 +0000 (UTC) Date: Wed, 15 Mar 2017 09:32:26 +0000 From: "Dr. David Alan Gilbert" Message-ID: <20170315093226.GB2430@work-vm> References: <20170301123223.12489-1-berrange@redhat.com> <20170302123300.GJ29835@redhat.com> <87d1dys9mr.fsf@dusky.pond.sub.org> <20170314184909.GC7576@work-vm> <87bmt3t5r0.fsf@dusky.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87bmt3t5r0.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: qemu-devel@nongnu.org, Juan Quintela * Markus Armbruster (armbru@redhat.com) wrote: > "Dr. David Alan Gilbert" writes: > > > * 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. > > You argue syntax, I'm arguing semantics. > > The command means "set parameter P to value V". *Except* when V is "", > it means something else, namely "reset parameter P to its default, > whatever that may be". > > This is (a) not general, because it won't do for cases where "" may > occur as value, and (b) ugly. > > Ugliness is the eye of the beholder. Lack of generality isn't. No, I'm questioning why it's defined as 'reset parameter P to its default'; why do we need a way to do that? Dave > >> 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 -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK