From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60653) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dAIwP-0004lY-R6 for qemu-devel@nongnu.org; Mon, 15 May 2017 12:33:50 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dAIwM-0002x7-Ko for qemu-devel@nongnu.org; Mon, 15 May 2017 12:33:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53630) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dAIwM-0002wn-BX for qemu-devel@nongnu.org; Mon, 15 May 2017 12:33:46 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id DAF5C54E16 for ; Mon, 15 May 2017 16:33:44 +0000 (UTC) From: Juan Quintela In-Reply-To: <87k25iqf4m.fsf@dusky.pond.sub.org> (Markus Armbruster's message of "Mon, 15 May 2017 18:06:01 +0200") References: <20170511163228.6666-1-quintela@redhat.com> <20170511163228.6666-3-quintela@redhat.com> <20170512034033.GN28293@pxdev.xzpeter.org> <877f1mgx9h.fsf@secure.mitica> <5bab598f-30eb-fcf6-9d06-8f683b466414@redhat.com> <87lgpyfo28.fsf@secure.mitica> <87k25iqf4m.fsf@dusky.pond.sub.org> Reply-To: quintela@redhat.com Date: Mon, 15 May 2017 18:33:40 +0200 Message-ID: <87efvqdqqj.fsf@secure.mitica> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Qemu-devel] [PATCH 2/3] migration: Remove use of old MigrationParams List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Markus Armbruster Cc: Eric Blake , lvivier@redhat.com, qemu-devel@nongnu.org, Peter Xu , dgilbert@redhat.com Markus Armbruster wrote: > Juan Quintela writes: > >> Eric Blake wrote: >>> Or is the proposal that we are also going to simplify the QMP 'migrate' >>> command to get rid of crufty parameters? >> >> I didn't read it that way, but I would not oppose O:-) >> >> Later, Juan. > > I'm not too familiar with this stuff, so please correct my > misunderstandings. > > "Normal" migration configuration is global state, i.e. it applies to all > future migrations. > > Except the "migrate" command's flags apply to just the migration kicked > off by that command. > > QMP command "migrate" has two flags "blk" (HMP: -b) and "inc" (HMP: -i). > !blk && inc makes no sense and is silently treated like !blk && !inc. > > There's a third flag "detach" (HMP: -d), but it does nothing in QMP. As qmp command is asynchronous, you can think that -d is *always* on in QMP O:-) > You'd like to deprecate these flags in favour of "normal" configuration. > However, we need to maintain QMP backward compatibility at least for a > while. HMP backward compatibility is nice to have, but not required. > > First step is to design the new interface you want. Second step is to > figure out backward compatibility. > > The new interface adds a block migration tri-state (off, > non-incremental, incremental) to global state, default off. Whether > it's done as two bools or an enum of three values doesn't matter here. Tristates will complicate it. I still think that: - capability: block_migration - parameter: block_shared Makes more sense, no? If block_migration is not enabled, we ignore the shared parameter. We already do that for other parameters. > If the new interface isn't used, the old one still needs to work. If it > is used, the old one either has to do "the right thing", or fail > cleanly. > > We approximate "new interface isn't used" by "block migration is off in > global state". When it is off, the migration command needs to honor its > two flags for compatibility. It must leave block migration off in > global state. Yes, this will complicate the implementation until we > actually remove the deprecated flags. Par for the backward compatility > course. > > When block migration isn't off in global state, we can either > > * let the flags take precedence over the global state (one > interpretation of "do the right thing"), or > > * reject flags that conflict with global state (another interpretation), > or > > * reject *all* flags (fail cleanly). > > The last one looks perfectly servicable to me. Yeap, I think that makes sense. If you use capabilities, parameters, old interface don't work at all. We still have a problem that is what happens if the user does: migrate -b migrate_cancel (or error) migrate (without -b) With current patches, it will still use -b. Fixing it requires still anding more code. But I think that this use case is so weird what we should not even care about it. Later, Juan.