From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [RFC-v2 0/4] tcm_vhost+cmwq fabric driver code for-3.6
Date: Wed, 18 Jul 2012 11:53:38 -0400
Message-ID: <20120718155338.GA21817@infradead.org>
References: <1342041304-29728-1-git-send-email-nab@linux-iscsi.org>
 <20120717150548.GA11587@redhat.com>
 <5005B52E.20509@us.ibm.com>
 <1342561819.18004.470.camel@haakon2.linux-iscsi.org>
 <5006BD3D.7090104@us.ibm.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: "Nicholas A. Bellinger" <nab@linux-iscsi.org>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	target-devel <target-devel@vger.kernel.org>,
	linux-scsi <linux-scsi@vger.kernel.org>,
	lf-virt <virtualization@lists.linux-foundation.org>,
	kvm-devel <kvm@vger.kernel.org>,
	Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>,
	Zhi Yong Wu <wuzhy@cn.ibm.com>,
	Anthony Liguori <aliguori@linux.vnet.ibm.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
	Hannes Reinecke <hare@suse.de>
To: Anthony Liguori <aliguori@us.ibm.com>
Return-path: <kvm-owner@vger.kernel.org>
Received: from 173-166-109-252-newengland.hfc.comcastbusiness.net ([173.166.109.252]:57850
	"EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK)
	by vger.kernel.org with ESMTP id S1751687Ab2GRPxr (ORCPT
	<rfc822;kvm@vger.kernel.org>); Wed, 18 Jul 2012 11:53:47 -0400
Content-Disposition: inline
In-Reply-To: <5006BD3D.7090104@us.ibm.com>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

On Wed, Jul 18, 2012 at 08:42:21AM -0500, Anthony Liguori wrote:
> 
> If you add support for a new command, you need to provide userspace
> a way to disable this command.  If you change what gets reported for
> VPD, you need to provide userspace a way to make VPD look like what
> it did in a previous version.
> 
> Basically, you need to be able to make a TCM device behave 100% the
> same as it did in an older version of the kernel.
> 
> This is unique to virtualization due to live migration.  If you
> migrate from a 3.6 kernel to a 3.8 kernel, you need to make sure
> that the 3.8 kernel's TCM device behaves exactly like the 3.6 kernel
> because the guest that is interacting with it does not realize that
> live migration happened.

I don't think these strict live migration rules apply to SCSI targets.

Real life storage systems get new features and different behaviour with
firmware upgrades all the time, and SCSI initiators deal with that just
fine.  I don't see any reason to be more picky just because we're
virtualized.