From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:59695) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QjyQ1-0003bn-Km for qemu-devel@nongnu.org; Thu, 21 Jul 2011 14:56:26 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QjyQ0-0005ER-Qk for qemu-devel@nongnu.org; Thu, 21 Jul 2011 14:56:21 -0400 Received: from e5.ny.us.ibm.com ([32.97.182.145]:57739) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QjyQ0-0005ED-Lm for qemu-devel@nongnu.org; Thu, 21 Jul 2011 14:56:20 -0400 Received: from d01relay04.pok.ibm.com (d01relay04.pok.ibm.com [9.56.227.236]) by e5.ny.us.ibm.com (8.14.4/8.13.1) with ESMTP id p6LIRL5O009021 for ; Thu, 21 Jul 2011 14:27:21 -0400 Received: from d03av03.boulder.ibm.com (d03av03.boulder.ibm.com [9.17.195.169]) by d01relay04.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p6LIuI5S150668 for ; Thu, 21 Jul 2011 14:56:18 -0400 Received: from d03av03.boulder.ibm.com (loopback [127.0.0.1]) by d03av03.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p6LCu8s7013693 for ; Thu, 21 Jul 2011 06:56:08 -0600 Message-ID: <4E287648.4050708@linux.vnet.ibm.com> Date: Thu, 21 Jul 2011 13:56:08 -0500 From: Michael Roth MIME-Version: 1.0 References: <4E2055AE.8090107@redhat.com> <4E253136.4080509@redhat.com> <4E258635.2040108@redhat.com> <4E258D70.6000205@redhat.com> <4E25902D.2000403@redhat.com> <4E2593B0.1030508@redhat.com> <4E2594FB.4050203@redhat.com> <20110719164755.GF12026@redhat.com> In-Reply-To: <20110719164755.GF12026@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] live snapshot wiki updated List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Daniel P. Berrange" Cc: Stefan Hajnoczi , "libvir-list@redhat.com" , Jes Sorensen , QEMU Developers , Stefan Hajnoczi , Eric Blake On 07/19/2011 11:47 AM, Daniel P. Berrange wrote: > On Tue, Jul 19, 2011 at 04:30:19PM +0200, Jes Sorensen wrote: >> On 07/19/11 16:24, Eric Blake wrote: >>> [adding the libvir-list] >>> On 07/19/2011 08:09 AM, Jes Sorensen wrote: >>>> Urgh, libvirt parsing image files is really unfortunate, it really >>>> doesn't give me warm fuzzy feelings :( libvirt really should not know >>>> about internals of image formats. >>> >>> But even if you add new features to qemu to avoid needing this in the >>> future, it doesn't change the past - libvirt will always have to know >>> how to parse image files understood by older qemu, and so as long as >>> libvirt already knows how to do that parsing, we might as well take >>> advantage of it. >> >> What has been done here in the past is plain wrong. Continuing to do it >> isn't the right thing to do here. >> >>> Besides, I feel that having a well-documented file format, so that >>> independent applications can both parse the same file with the same >>> semantics by obeying the file format specification, is a good design goal. >> >> We all know that documentation is rarely uptodate, new features may not >> get added and libvirt will never be able to keep up. The driver for a >> file format belongs in QEMU and nowhere else. > > This would be possible if QEMU to provide a libblockformat.so library > which allowed apps to extract metadata from file formats using a stable > API. How wrong would it be to call out to qemu-img to handle this instead? Seems like a more stable interface (assuming the output of `qemu-img info` is treated as an API of sorts, or perhaps some other output mode is added to qemu-img that is considered stable). > > Daniel