From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [Qemu-devel] [RFC PATCH 1/1] ceph/rbd block driver for qemu-kvm Date: Tue, 25 May 2010 16:36:33 +0300 Message-ID: <4BFBD261.9040908@redhat.com> References: <20100519192222.GD61706@ncolin.muc.de> <4BF5A9D2.5080609@codemonkey.ws> <4BF91937.2070801@redhat.com> <87wrutg4dk.wl%morita.kazutaka@lab.ntt.co.jp> <4BFA5D96.3030603@redhat.com> <4BFA696D.2060606@redhat.com> <4BFAD59E.2010706@codemonkey.ws> <4BFB94D9.5080904@redhat.com> <4BFBCDD9.4070104@codemonkey.ws> <4BFBCFB9.6020104@redhat.com> <4BFBD0C6.9000105@codemonkey.ws> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Christian Brunner , MORITA Kazutaka , Blue Swirl , kvm@vger.kernel.org, qemu-devel@nongnu.org, ceph-devel@vger.kernel.org To: Anthony Liguori Return-path: In-Reply-To: <4BFBD0C6.9000105@codemonkey.ws> Sender: ceph-devel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 05/25/2010 04:29 PM, Anthony Liguori wrote: >> The current situation is that those block format drivers only exist >> in qemu.git or as patches. Surely that's even more unhappiness. >> >> Confusion could be mitigated: >> >> $ qemu -module my-fancy-block-format-driver.so >> my-fancy-block-format-driver.so does not support this version of >> qemu (0.19.2). Please contact >> my-fancy-block-format-driver-devel@example.org. >> >> The question is how many such block format drivers we expect. We now >> have two in the pipeline (ceph, sheepdog), it's reasonable to assume >> we'll want an lvm2 driver and btrfs driver. This is an area with a >> lot of activity and a relatively simply interface. > > > If we expose a simple interface, I'm all for it. But BlockDriver is > not simple and things like the snapshoting API need love. > > Of course, there's certainly a question of why we're solving this in > qemu at all. Wouldn't it be more appropriate to either (1) implement > a kernel module for ceph/sheepdog if performance matters We'd need a kernel-level generic snapshot API for this eventually. > or (2) implement BUSE to complement FUSE and CUSE to enable proper > userspace block devices. Likely slow due do lots of copying. Also needs a snapshot API. (ABUSE was proposed a while ago by Zach). > If you want to use a block device within qemu, you almost certainly > want to be able to manipulate it on the host using standard tools > (like mount and parted) so it stands to reason that addressing this in > the kernel makes more sense. qemu-nbd also allows this. This reasoning also applies to qcow2, btw. -- error compiling committee.c: too many arguments to function