Re: [Qemu-devel] [PATCH v11 2/3] qemu-img info lists bitmap directory entries

[Eric Blake]

On 2/1/19 1:23 PM, Markus Armbruster wrote:

>>>> +# @unknown-flags: any remaining flags not recognized by the current qemu 
>>>> version
>>>
>>> Intended use cases for @unknown-flags?
>>
>> The qcow2 spec defines bit 2 extra_data_compatible; and also leaves the
>> door open for future extensions that may define other bits. If a new
>> version of qemu (or some non-qemu qcow2 creation app) creates an image
>> with additional feature bits set, THIS version of qemu doesn't know what
>> name to give those bits, but can still inform the user that those bits
>> are set via this field. It will be omitted for all images created by
>> this version of qemu.
> 
> What would QMP clients do with this information?

'qemu-img info' is the intended QMP client; and it will print the
unknown-flags along with everything else. In other words, we're trying
to make qemu-img become useful for inspecting as much useful information
as possible from an image with unknown origins.  Knowing that an image
uses bitmaps with flags unknown to THIS version of qemu is a good
indication that you should be careful about using/altering the image
without first upgrading qemu, as it may destroy data that some other
product desires to utilize.

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

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