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From: "Nicholas A. Bellinger" <nab@linux-iscsi.org>
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Date: Thu, 26 Jul 2012 13:15:26 -0700
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Subject: Re: [Qemu-devel] [PATCH] tcm_vhost: Expose ABI version via
 VHOST_SCSI_GET_ABI_VERSION
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To: Avi Kivity <avi@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>, kvm-devel <kvm@vger.kernel.org>, "Michael S. Tsirkin" <mst@redhat.com>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>, qemu-devel <qemu-devel@nongnu.org>, lf-virt <virtualization@lists.linux-foundation.org>, Anthony Liguori <aliguori@linux.vnet.ibm.com>, target-devel <target-devel@vger.kernel.org>, Hannes Reinecke <hare@suse.de>, linux-scsi <linux-scsi@vger.kernel.org>, Paolo Bonzini <pbonzini@redhat.com>, Zhi Yong Wu <wuzhy@cn.ibm.com>, Christoph Hellwig <hch@lst.de>

On Thu, 2012-07-26 at 11:58 +0300, Avi Kivity wrote:
> On 07/26/2012 05:34 AM, Nicholas A. Bellinger wrote:
> > 
> > In that case, respinning a -v5 for tcm_vhost to start from ABI=0 and
> > will post an updated patch shortly.
> > 
> >> The main thing I would like to confirm is that this only versions the
> >> tcm_vhost ioctls?  In that case a single version number works.
> >> 
> > 
> > Correct, the GET_ABI_VERSION call is only intended to identify the
> > changing of tcm_vhost ioctls.
> 
> Why use version numbers at all?
> 

This was a request by QEMU folks.. 


> Feature maps are better, because you can get very fine granularity.
> 
> 

Example..?  If there is a better way to handle ioctl compat I'd
certainly like to hear about it.