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Date: Mon, 27 Feb 2012 10:06:45 -0300
From: Luiz Capitulino <lcapitulino@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 2/2 v2] Add the blockdev-reopen and
 blockdev-migrate commands
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: kwolf@redhat.com, Federico Simoncelli <fsimonce@redhat.com>, mtosatti@redhat.com, qemu-devel@nongnu.org, armbru@redhat.com

On Mon, 27 Feb 2012 13:49:17 +0100
Paolo Bonzini <pbonzini@redhat.com> wrote:

> On 02/27/2012 01:12 PM, Luiz Capitulino wrote:
> > > If I didn't make any mistake in the code I'm just enforcing that when
> > > you specify "incremental" you also need a new image.
> > > There are still other valid cases where they are optional.
> > 
> > Which operation will be performed if 'incremental' is not passed? If
> > it's passed, which operation will be performed if 'new_image_file' is not?
> 
> There are four cases:
> 
> 1) incremental=false, new_image_file not passed:
>    right now fail; in the future:
>    - create an image on dest with no backing file;
>    - writes will be mirrored to current_image_file and dest
>    - start streaming from current_image_file to dest
> 
> 2) incremental=false, new_image_file passed:
>    right now fail; in the future:
>    - create an image on dest with no backing file;
>    - live-snapshot based on current_image_file to new_image_file;
>    - writes will be mirrored to new_image_file and dest
>    - start streaming from current_image_file to dest
>
> 
> 3) incremental=true, new_image_file not passed:
>    - error
> 
> 4) incremental=true, new_image_file passed:
>    - no images will be created
>    - writes will be mirrored to new_image_file and dest

IMHO, this is asking for two commands, where cases 1 & 2 is one of them
and cases 3 & 4 is the other one. Note how 'incremental' goes away and
'new_image_file' really becomes an optional.