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Re: [Qemu-block] [PATCH 12/22] qcow2-bitmap: add IN_USE flag

From: Max Reitz
Subject: Re: [Qemu-block] [PATCH 12/22] qcow2-bitmap: add IN_USE flag
Date: Mon, 24 Oct 2016 18:54:32 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0

On 24.10.2016 12:32, Vladimir Sementsov-Ogievskiy wrote:
> 21.10.2016 22:58, Max Reitz пишет:
>> On 21.10.2016 17:34, Vladimir Sementsov-Ogievskiy wrote:
>>> 07.10.2016 22:44, Max Reitz пишет:
>>>> On 30.09.2016 12:53, Vladimir Sementsov-Ogievskiy wrote:
>>>>> This flag means that the bitmap is now in use by the software or
>>>>> was not
>>>>> successfully saved. In any way, with this flag set the bitmap data
>>>>> must
>>>>> be considered inconsistent and should not be loaded.
>>>>> With current implementation this flag is never set, as we just remove
>>>>> bitmaps from the image after loading. But it defined in qcow2 spec and
>>>>> must be handled. Also, it can be used in future, if async schemes of
>>>>> bitmap loading/saving are implemented.
>>>>> We also remove in-use bitmaps from the image on open.
>>>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
>>>>> ---
>>>>>    block/qcow2-bitmap.c | 17 ++++++++++++++++-
>>>>>    1 file changed, 16 insertions(+), 1 deletion(-)
>>>> Don't you want to make use of this flag? It would appear useful to
>>>> me if
>>>> you just marked autoload bitmaps as in_use instead of deleting them
>>>> from
>>>> the image when it's opened and then overwrite them when the image is
>>>> closed.
>>> And what is the use of it?
>> You don't need to free any bitmaps when opening the file, and you don't
>> need to allocate any new bitmap space when closing it.
> As bitmaps are sparce in file, I need to allocate new space when
> closing. Or free it...

May happen. But not necessarily, and it will probably still save time as
you can reuse existing allocations and don't have to free everything.


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