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

From: Max Reitz
Subject: Re: [Qemu-block] [PATCH 3/3] vpc: Do not return RAW from block_status
Date: Mon, 12 Aug 2019 17:56:12 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0

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?


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