From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:51512) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gqeCC-00011N-QT for qemu-devel@nongnu.org; Mon, 04 Feb 2019 08:21:57 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gqdx8-0006kw-1i for qemu-devel@nongnu.org; Mon, 04 Feb 2019 08:06:22 -0500 From: Markus Armbruster References: <1548942405-760115-1-git-send-email-andrey.shinkevich@virtuozzo.com> <1548942405-760115-3-git-send-email-andrey.shinkevich@virtuozzo.com> <87pnsbxsi7.fsf@dusky.pond.sub.org> <3ed70b8e-f778-f942-2841-905223d3af8d@redhat.com> <87womjwbwj.fsf@dusky.pond.sub.org> Date: Mon, 04 Feb 2019 14:05:58 +0100 In-Reply-To: (Eric Blake's message of "Fri, 1 Feb 2019 13:28:32 -0600") Message-ID: <877eefsnyh.fsf@dusky.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Qemu-devel] [PATCH v11 2/3] qemu-img info lists bitmap directory entries List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eric Blake Cc: fam@euphon.net, kwolf@redhat.com, vsementsov@virtuozzo.com, qemu-block@nongnu.org, qemu-devel@nongnu.org, mreitz@redhat.com, den@openvz.org, Andrey Shinkevich , jsnow@redhat.com Eric Blake 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 :)