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Re: [Qemu-devel] [Nbd] [PATCH v2] doc: Add NBD_CMD_BLOCK_STATUS extensio

From: Alex Bligh
Subject: Re: [Qemu-devel] [Nbd] [PATCH v2] doc: Add NBD_CMD_BLOCK_STATUS extension
Date: Mon, 4 Apr 2016 21:08:03 +0100

On 4 Apr 2016, at 21:04, Denis V. Lunev <address@hidden> wrote:

>> Sure, but given you can't report dirtiness without also reporting
>> allocation, if they are are at different blocksize I'd rather they
>> were in different commands, because otherwise the code to report
>> block size needs to work at two different granularities.
> 'dirty' could come after the data was 'trimmed' from the region!
> thus we could have dirty unallocated data.

Let me rephrase.

Under the current proposal it is not possible to report whether or
not a region is dirty without also reporting whether or not it
is allocated. As these two concepts exist at potentially
different block sizes, the code to support reporting on allocation
must now be able to run both at the allocation blocksize and
the dirtiness blocksize, which is going to be a pain.

If these were two different commands, they could each run at their
natural block size.

Alex Bligh

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