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

[Vladimir Sementsov-Ogievskiy]

04.02.2019 19:35, Vladimir Sementsov-Ogievskiy wrote:
> 04.02.2019 19:24, Eric Blake wrote:
>> On 2/4/19 10:03 AM, Vladimir Sementsov-Ogievskiy wrote:
>>
>>>>>> 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.
>>
>> The grammar still feels awkward.  Maybe:
>>
>> @unknown-flags: If present, this is the value of additional bitmap flags
>> that were set in the image but not reported in @flags, implying that the
>> image was created with a newer version of software (that supports new
>> flags) or has been corrupted. Modifying the image without upgrading qemu
>> first will likely break the contents of the bitmap.
>>
> 
> Thank you!
> 
> Oops, hm, I now doubt, how Andrey's patches work, if bitmap_list_load function
> fails when unknown flags are found. So, can we really show unknown-flags,
> or we'll fail if there any?
> 
> And if we fail (I hope we fail) on unknown flags, than we don't need this
> field :).
> 

But we can update bitmap_list_load, to have a flag, and show bitmaps with
unknown flags in qemu-img info.. And we have to somehow not fail on open before
it. I'm very sorry that I understand it all only now :(.

So, do we really need unknown-flags field? If yes, may be, do it as a next step?
And proceed now without them?


-- 
Best regards,
Vladimir