Re: [Qemu-devel] [Qemu-block] [PATCH v3 1/3] block: add bdrv_get_format_alloc_stat format interface

[John Snow <jsnow@redhat.com>]

On 06/29/2017 02:59 AM, Vladimir Sementsov-Ogievskiy wrote:
> 29.06.2017 03:15, John Snow wrote:
>>
>> Alright, let me see if I have this straight...
>>
>> used-data: Normal data. We are standing on terra-firma.
>> used-zero: Data that is defined to be zeroes in some way.
>>
>> (Does not necessarily include data clusters if they were not actually
>> zeroed out, I think. May not include regions that ARE zero, even if they
>> are literally zero, because the driver may not especially recognize them
>> as such. Anything marked as zero will DEFINITELY be zero, though. Yes?)
>>
>> used-discarded: I'm not actually sure in this case.
>>
>> used-overrun: Data that is defined to exist, but appears to fall outside
>> of or beyond EOF. Appears to happen with qcow2 metadata before any
>> writes occur.
>>
>> unused-data: Normal data, but not in-use by the schema anywhere. Leaked
>> clusters and the like, effectively.
>>
>> unused-zero: Similar to the above, but definitely zeroes.
>>
>> unused-discarded: Not really sure.
> 
> yes, something like this. again, -data, -zero and -discarded are just
> corresponding to return value of bdrv_get_block_status(bs->file),
> 
> if status & BDRV_BLOCK_DATA
>    it is  -data
> else if status & BDRV_BLOCK_ZERO
>    it is -zero (should be holes for raw)
> else
>    it is -discarded (impossible for raw)
> end
> 

Understood, but I was not too clear on the exact nature of block status,
so I needed to clarify. I'm a lot clearer now, thanks.