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Date: Mon, 01 Feb 2010 11:05:11 +0100
From: Alexander Graf <agraf@suse.de>
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Subject: Re: [Qemu-devel] Re: [PATCH] block: Enable fall-back to read-only
	for backing file
References: <4B65B4B7.2030700@redhat.com> <4B6694C8.4010703@redhat.com>
	<20100201090649.GA20918@lst.de>
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To: Christoph Hellwig <hch@lst.de>
Cc: Kevin Wolf <kwolf@redhat.com>, Naphtali Sprei <nsprei@redhat.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, Sheng Yang <sheng@linux.intel.com>

Christoph Hellwig wrote:
> On Mon, Feb 01, 2010 at 10:25:52AM +0100, Alexander Graf wrote:
>   
>> We don't know beforehand if a user will use the commit comnand during  
>> tje runtime of the vm.
>>
>> IMHO it'd be best to always open backing files read only and try to  
>> open them for write access on the commit command. That command can  
>> then fail gaciously.
>>     
>
> That's another option.  Basically this means opening another
> BlockDriverState for the backing device that is writeable inside
> bdrv_commit().
>   

Or another function call hook to change the backing device state from RO
to RW.

Alex