Re: [Qemu-devel] [PATCH] qemu-img: let qemu-img behave as the manual advertise

[Kevin Wolf]

Am 11.04.2012 12:33, schrieb Kevin Wolf:
> Am 11.04.2012 12:05, schrieb Liu Yuan:
>> On 04/11/2012 03:49 PM, Kevin Wolf wrote:
>>
>>> I don't agree with this patch. If the documentation says that qemu-img
>>> always uses writeback, then the documentation must be fixed.
>>>
>>> We really don't care about flushes during an image conversion. It should
>>> just go as fast as it can. If any error happens in the middle, you'll
>>> have to throw the image away anyway, because it contains only half of
>>> what you need. So not having flushed doesn't really make any difference.
>>>
>>> As soon as a guest begins using the image with data that we really care
>>> about, it's probably running in a VM with non-unsafe mode, and then it
>>> gets flushed.
>>
>>
>> But we can set cache mode for qemu-img convert. So at least if we set
>> explicitly with other modes(for e.g, writeback) that ask to flush the
>> dirty bits, I think we should call brdv_flush().
>>
>> If you agree, I'll update the patch with this modification.
> 
> Yes, adding the flush is fine, I just wouldn't change the default cache
> mode.

On second thought, wouldn't make it more sense to add the flush in
bdrv_close(), so that all callers get it?

Kevin