From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45744) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dAI54-0006ec-JB for qemu-devel@nongnu.org; Mon, 15 May 2017 11:38:44 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dAI51-0003d6-Gf for qemu-devel@nongnu.org; Mon, 15 May 2017 11:38:42 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41972) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dAI51-0003c1-7Y for qemu-devel@nongnu.org; Mon, 15 May 2017 11:38:39 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 34244369CD for ; Mon, 15 May 2017 15:38:38 +0000 (UTC) From: Markus Armbruster References: <20170511163228.6666-1-quintela@redhat.com> <20170511163228.6666-2-quintela@redhat.com> <0bbb5f93-83bb-47b9-e7dd-d0824f3d8b61@redhat.com> <87pofafoek.fsf@secure.mitica> <20170515094655.GC2089@work-vm> <6ad3d1a1-ae63-b01d-b6a0-72a017b343aa@redhat.com> Date: Mon, 15 May 2017 17:38:34 +0200 In-Reply-To: <6ad3d1a1-ae63-b01d-b6a0-72a017b343aa@redhat.com> (Eric Blake's message of "Mon, 15 May 2017 09:24:56 -0500") Message-ID: <87r2zqqged.fsf@dusky.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Qemu-devel] [PATCH 1/3] migration: Create block capabilities for shared and enable List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eric Blake Cc: "Dr. David Alan Gilbert" , Juan Quintela , lvivier@redhat.com, qemu-devel@nongnu.org, peterx@redhat.com Eric Blake writes: > On 05/15/2017 04:46 AM, Dr. David Alan Gilbert wrote: >> * Juan Quintela (quintela@redhat.com) wrote: >>> Eric Blake wrote: >>>> On 05/11/2017 11:32 AM, Juan Quintela wrote: >>>>> Those two capabilities were added through the command line. Notice that >>>>> we just created them. This is just the boilerplate. >>>>> >>>>> Signed-off-by: Juan Quintela >>>>> Reviewed-by: Eric Blake >>>>> >>>>> -- >>>>> >>>>> Make migrate_set_block_* take a boolean argument. >>>> >>>> Question - do we support the orthogonal selection of all 4 combinations >>>> under HMP 'migrate' (no argument, -b alone, -i alone, -b and -i >>>> together), or are there only 3 actual states? If the latter, should we >>>> represent this as a single enum-valued property, rather than as two >>>> independent boolean properties? >>> >>> { 'enum': 'MigrationCapability', >>> 'data': ['xbzrle', 'rdma-pin-all', 'auto-converge', 'zero-blocks', >>> 'compress', 'events', 'postcopy-ram', 'x-colo', 'release-ram'] } >>> >>> >>> My understanding is that we can only have boolean capabilities here. >>> Or, how could we put a non-boolean capability? > > If we want a non-boolean, then we make it a migration parameter rather > than a migration capability. There may be other advantages to using > MigrationParameter instead of MigrationCapability (such as making it > easier to figure out whether the parameter settings are persistent or > apply per-migration). What makes a migration knob a MigrationCapability rather than a MigrationParameter? Type bool, or is there more to it? >> >> Lets keep this simple and stick with the booleans. >> >> Dave >> >>> There are three states as far as I can see. Begs the question how the fourth state behaves. Documentation is of no help: diff --git a/qapi-schema.json b/qapi-schema.json index 5728b7f..109852e 100644 --- a/qapi-schema.json +++ b/qapi-schema.json @@ -894,11 +894,16 @@ # @release-ram: if enabled, qemu will free the migrated ram pages on the source # during postcopy-ram migration. (since 2.9) # +# @block-enabled: enable block migration (Since 2.10) +# +# @block-shared: enable block shared migration (Since 2.10) +# # Since: 1.2 ## Please explain all four states clearly there. > I'll leave it up to you as maintainers which way you prefer, I'm just > offering the potential design tradeoffs for simplicity of booleans (but > complexity in an unused state) vs. simplicity of design (but complexity > in code). For what it's worth, I dislike entangled booleans.