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

From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
To: Eric Blake <eblake@redhat.com>, Markus Armbruster <armbru@redhat.com>
Cc: "fam@euphon.net" <fam@euphon.net>,
	"kwolf@redhat.com" <kwolf@redhat.com>,
	"qemu-block@nongnu.org" <qemu-block@nongnu.org>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
	"mreitz@redhat.com" <mreitz@redhat.com>,
	Denis Lunev <den@virtuozzo.com>,
	Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>,
	"jsnow@redhat.com" <jsnow@redhat.com>
Subject: Re: [Qemu-devel] [PATCH v11 2/3] qemu-img info lists bitmap directory entries
Date: Mon, 4 Feb 2019 16:35:03 +0000	[thread overview]
Message-ID: <bed5c588-b41b-bb93-92a8-e1ffc6f4fac7@virtuozzo.com> (raw)
In-Reply-To: <8db32102-7daa-6b5a-8752-46727cbef106@redhat.com>

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 :).

-- 
Best regards,
Vladimir