From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58777) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1g82zw-0002zv-0W for qemu-devel@nongnu.org; Thu, 04 Oct 2018 08:44:58 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1g82zt-0006QQ-T7 for qemu-devel@nongnu.org; Thu, 04 Oct 2018 08:44:55 -0400 Date: Thu, 4 Oct 2018 14:44:21 +0200 From: Kevin Wolf Message-ID: <20181004124421.GC6009@localhost.localdomain> References: <20181001102928.20533-1-vsementsov@virtuozzo.com> <20181001102928.20533-14-vsementsov@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181001102928.20533-14-vsementsov@virtuozzo.com> Subject: Re: [Qemu-devel] [PATCH v3 13/18] block: introduce new filter driver: fleecing-hook List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Vladimir Sementsov-Ogievskiy Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, eblake@redhat.com, armbru@redhat.com, xiechanglong.d@gmail.com, wencongyang2@huawei.com, stefanha@redhat.com, jsnow@redhat.com, famz@redhat.com, jcody@redhat.com, mreitz@redhat.com, den@openvz.org Am 01.10.2018 um 12:29 hat Vladimir Sementsov-Ogievskiy geschrieben: > Fleecing-hook filter does copy-before-write operation. It should be > inserted above active disk and has a target node for CBW, like the > following: > > +-------+ > | Guest | > +---+---+ > |r,w > v > +---+-----------+ target +---------------+ > | Fleecing hook |---------->| target(qcow2) | > +---+-----------+ CBW +---+-----------+ > | | > backing |r,w | > v | > +---+---------+ backing | > | Active disk |<----------------+ > +-------------+ r > > Target's backing may point to active disk (should be set up > separately), which gives fleecing-scheme. > > Signed-off-by: Vladimir Sementsov-Ogievskiy This lacks an explanation why we need a specialised fleecing hook driver rather than just a generic bdrv_backup_top block driver in analogy to what commit and mirror are already doing. In fact, if I'm reading the last patch of the series right, backup doesn't even restrict the use of the fleecing-hook driver to actual fleecing scenarios. Maybe what doesn't feel right to me is just that it's a misnomer, and if you rename it into bdrv_backup_top (and make it internal to the block job), it is very close to what I actually have in mind? Kevin