Re: [Qemu-devel] [PATCH 3/3] vpc: Do not return RAW from block_status

[Vladimir Sementsov-Ogievskiy]

12.08.2019 18:56, Max Reitz wrote:
> On 12.08.19 17:33, Vladimir Sementsov-Ogievskiy wrote:
>> 25.07.2019 18:55, Max Reitz wrote:
>>> vpc is not really a passthrough driver, even when using the fixed
>>> subformat (where host and guest offsets are equal).  It should handle
>>> preallocation like all other drivers do, namely by returning
>>> DATA | RECURSE instead of RAW.
>>>
>>> There is no tangible difference but the fact that bdrv_is_allocated() no
>>> longer falls through to the protocol layer.
>>
>> Hmm. Isn't a real bug (fixed by this patch) ?
>>
>> Assume vpc->file is qcow2 with backing, which have "unallocated" region, 
>> which is
>> backed by actual data in backing file.
> 
> Come on now.
> 
>> So, this region will be reported as not allocated and will be skipped by any 
>> copying
>> loop using block-status? Is it a bug of BDRV_BLOCK_RAW itself? Or I don't 
>> understand
>> something..
> 
> I think what you don’t understand is that if you have a vpc file inside
> of a qcow2 file, you’re doing basically everything wrong. ;-)
> 
> But maybe we should drop BDRV_BLOCK_RAW...  Does it do anything good for
> us in the raw driver?  Shouldn’t it too just return DATA | RECURSE?
> 

And if I have raw driver above qcow2, it will not work, like I've described 
above..


-- 
Best regards,
Vladimir