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Re: [Qemu-devel] [Nbd] [PATCH 2/2] NBD proto: add GET_LBA_STATUS extensi

From: Eric Blake
Subject: Re: [Qemu-devel] [Nbd] [PATCH 2/2] NBD proto: add GET_LBA_STATUS extension
Date: Mon, 4 Apr 2016 14:36:52 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.1

On 04/04/2016 02:16 PM, Denis V. Lunev wrote:

>> +    The following request types are currently defined for the command:
>> +
>> +    1. Block provisioning state
>> +
>> +    Upon receiving an `NBD_CMD_GET_LBA_STATUS` command with command flags
>> +    field set to `NBD_FLAG_GET_ALLOCATED` (0x0), the server MUST return
>> +    the provisioning state of the device. The following provisionnig states
>> +    are defined for the command:
>> +
>> +      - `NBD_STATE_ALLOCATED` (0x0), LBA extent is present on the block 
>> device;
>> +      - `NBD_STATE_ZEROED` (0x1), LBA extent is present on the block device
>> +        and contains zeroes;
>> +      - `NBD_STATE_DEALLOCATED` (0x2), LBA extent is not present on the
>> +        block device. A client MUST NOT make any assumptions about the
>> +        contents of the extent.

> we can add 'NBD_STATE_DIRTY_DEALLOCATED' (0x2) here as additional hint

No, DEALLOCATED and HOLE are the same thing, and we really want the
status to be a bitwise-OR of flags (bit 0: is it allocated or
deallocated. bit 1: is it unknown content or all 0), rather than a set
of 3 states, since it really is possible to have all four combinations
of those two orthognal status information. That was one of the topics
already hashed out in the v1 conversation, and fixed in v2.

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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