From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41599) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cjqdt-00089z-Gd for qemu-devel@nongnu.org; Fri, 03 Mar 2017 12:05:22 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cjqdq-0007DG-DK for qemu-devel@nongnu.org; Fri, 03 Mar 2017 12:05:21 -0500 Received: from mx1.redhat.com ([209.132.183.28]:48448) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cjqdq-0007D9-4v for qemu-devel@nongnu.org; Fri, 03 Mar 2017 12:05:18 -0500 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 386F083F3E for ; Fri, 3 Mar 2017 17:05:18 +0000 (UTC) From: Markus Armbruster References: <20170301123223.12489-1-berrange@redhat.com> <20170302123300.GJ29835@redhat.com> <87d1dys9mr.fsf@dusky.pond.sub.org> <20170303161857.GC13631@redhat.com> Date: Fri, 03 Mar 2017 18:05:15 +0100 In-Reply-To: <20170303161857.GC13631@redhat.com> (Daniel P. Berrange's message of "Fri, 3 Mar 2017 16:18:57 +0000") Message-ID: <874lzanvec.fsf@dusky.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Qemu-devel] [PATCH] migration: allow clearing migration string parameters List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Daniel P. Berrange" Cc: qemu-devel@nongnu.org, "Dr. David Alan Gilbert" , Juan Quintela "Daniel P. Berrange" writes: > On Fri, Mar 03, 2017 at 03:44:12PM +0100, Markus Armbruster 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". >> >> 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? > > Not really - we need this fix so libvirt can enable TLS migration, > in addition we'll be wanting to add it to stable branches upstream > and downstream. Alternatives: (a) We support null in 2.9, and use it to solve this problem. (b) We use "", support null in 2.10, immediately deprecate "" in favor of null. PRO (a): Less churn, less variation, less overall work. PRO (b): Might be easier to backport to really old versions. Soft freeze. Non-alternative: use "" forever. Sorry, I hate it.