04.02.2019 16:05, Markus Armbruster wrote:
> Eric Blake <ebl...@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 :)
>
I'll try:
@unknown-flags: any flags except 'in-use' and 'auto' set for the bitmap.
Presence of non-zero @unknown-flags definitely shows that
image was created by newer version of software (which
supports more bitmap flags) or corrupted. Image can't be
used for r-w with non-zero @unknown-flags in any bitmap.
--
Best regards,
Vladimir
