Re: [Qemu-devel] [PATCH 2/5] block/qcow2-bitmap: Allow bitmap flushing

[Vladimir Sementsov-Ogievskiy]

06.03.2019 18:59, John Snow wrote:
> 
> 
> On 3/6/19 7:58 AM, Eric Blake wrote:
>> On 3/5/19 5:43 PM, John Snow wrote:
>>> Usually, we only write out bitmaps when we're about to close out the file,
>>> so we always remove the bitmaps after to make it easier to determine the
>>> source of truth for migration purposes.
>>>
>>> However, there may be times we want to flush bitmap data more aggressively,
>>> like after a truncate event where we need to make the metadata consistent
>>> again.
>>
>> Or, as I've mentioned in other threads, after every
>> bitmap-add/bitmap-delete operation, so that 'qemu-img info -U' can see
>> which persistent bitmaps exist. But that's one step further than this
>> series, so I won't insist on it today.
>>
> 
> Yes, I was keeping that in mind as I wrote this. I think it extends to
> those cases trivially, so long as Vladimir is OK with what I'm trying to do.
> 

I still don't see the point of flushing bitmaps, the only thing is optimizing
qemu-img info --force-share, which should never used except for debugging.

So, at least, if we'll have it, I'd prefer bitmap flushing to be optional,
and other code should not rely on it.


-- 
Best regards,
Vladimir