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Date: Wed, 02 Oct 2013 17:34:17 +0200
From: Peter Lieven <pl@kamp.de>
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Subject: Re: [Qemu-devel] [PATCHv4] block/get_block_status: avoid redundant
 callouts on raw devices
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: kwolf@redhat.com, stefanha@redhat.com, Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel@nongnu.org, anthony@codemonkey.ws, ronniesahlberg@gmail.com

Am 02.10.2013 17:13, schrieb Paolo Bonzini:
> Il 02/10/2013 17:06, Stefan Hajnoczi ha scritto:
>> Sorry I didn't review this earlier but this flag looks hacky and I'm not
>> confident about merging the patch yet.
>>
>> The patch makes me wonder if the raw_bsd driver should avoid calling
>> bs->file itself:
>>
>> return BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID |
>>        (sector_num << BDRV_SECTOR_BITS);
>>
>> Let block.c:bdrv_co_get_block_status() call down into bs->file.
>>
>> The problem is then the protocol cannot report unallocated sectors with
>> this approach.
>>
>> I think we want to preserve bs' offset while taking the other flags from
>> bs->file (DATA, ZERO).
> This would cause other changes.  For example, a qcow2 with full metadata
> preallocation (i.e. all L2 tables are there but it points to holes)
> would not return DATA anymore.  I think this is wrong, and especially a
> change from the old is_allocated API.
>
> However, a variant on this idea could be to return
>
>    BDRV_BLOCK_RAW | BDRV_BLOCK_OFFSET_VALID |
>         (sector_num << BDRV_SECTOR_BITS);
>
> and then BDRV_BLOCK_RAW would mean "take DATA and ZERO from bs->file".
I am fine with that.

Peter