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Re: [PATCH v4 2/7] nbd: Add new qemu:allocation-depth metadata context

From: Eric Blake
Subject: Re: [PATCH v4 2/7] nbd: Add new qemu:allocation-depth metadata context
Date: Thu, 22 Oct 2020 16:45:21 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1

On 10/14/20 6:52 AM, Vladimir Sementsov-Ogievskiy wrote:

>>   docs/interop/nbd.txt | 27 ++++++++++---
> [..]
>> +In the allocation depth context, bits 0 and 1 form a tri-state value:
>> +
>> +    bits 0-1: 00: NBD_STATE_DEPTH_UNALLOC, the extent is unallocated
>> +              01: NBD_STATE_DEPTH_LOCAL, the extent is allocated in the
>> +                  top level of the image
> Hmm. I always thought that "image" == file, so backing chain is a chain
> of images,
> not a several levels of one image. If it is so, than it should be "the
> top level image".
> And "levels of the image" may designate internal qcow2 snapshots
> unrelated here..

It's fuzzy.  From the guest point of view, we are serving a single guest
image by use of multiple files in the host.  I will do s/level/layer/,
to match the wording I already had on the next line:

>               10: NBD_STATE_DEPTH_BACKING, the extent is inherited from a
>                   backing layer

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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