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Date: Sat, 11 Sep 2010 12:45:48 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] [PATCH 2/3] block-nbd: fix use of protocols in
	backing files and nbd probing
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To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>, Juan Quintela <quintela@redhat.com>

On 09/11/2010 12:27 PM, Anthony Liguori wrote:
> I think the better solution is to explicitly specific raw with nbd.  
> IOW, I think -drive file=nbd:localhost:1026,format=raw should work the 
> same way.  I still feel slightly weird about probing happening with 
> nbd.  It seems like it could only result in badness.

Yeah, w/o this patch, 'qemu-img create -f qcow2 -b nbd:localhost:1026 -o 
backing_fmt=raw foo.img' doesn't generate any reads although if you drop 
-o backing_fmt, it will.

Not sure I agree it's the most useful thing, but I'm not going to claim 
it's never useful so this patch is not a good idea.

Regards,

Anthony Liguori

>
> The specific scenario is migration.  I'm using a copy-on-read file on 
> the destination and I want to be sure that I don't read any blocks 
> (since they're copied) until the source stops execution.
>
> Regards,
>
> Anthony Liguori
>
>> Stefan
>>
>