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Date: Thu, 16 Sep 2010 09:54:42 +0200
From: Kevin Wolf <kwolf@redhat.com>
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Subject: [Qemu-devel] Re: [PATCH 1/3] block: allow migration to work with
	image files
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To: Juan Quintela <quintela@redhat.com>
Cc: Anthony Liguori <aliguori@us.ibm.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

Am 15.09.2010 18:03, schrieb Juan Quintela:
> Kevin Wolf <kwolf@redhat.com> wrote:
>> Am 11.09.2010 16:04, schrieb Anthony Liguori:
> 
>> There is a simple generic implementation:
>>
>> drv = bs->drv;
>> drv->close(bs);
>> drv->open(bs, bs->open_flags);
>>
>> Note that this only reopens e.g. the qcow2 layer, but not the image
>> file, which is bs->file.
>>
>> This works for all simple case, that is, one format on top of one or
>> more protocols, where the protocols don't need invalidation. I think
>> this includes everything that is possible today. With -blockdev we might
>> need to revise this to include the lower layers, too. (But only
>> sometimes, because we don't want to reopen the file)
> 
> we require it for nfs consistency.  We need to:
> 
> source: fsync()
> target: open() (after the fsync).
> 
> About your 1st comment, I am doing:
> 
> bdrv_close(bdrv);
> bdrv_open(bdrv);
> 
> Do you mean that this don't close and open again the file with qcow2?

It does. bdrv_open/close take care of the whole stack.

Kevin