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

[Markus Armbruster <armbru@redhat.com>]

Eric Blake <eblake@redhat.com> writes:

> 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.

Okay.  Now work that into the documentation :)