From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44581) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fNPdr-0007lD-O0 for qemu-devel@nongnu.org; Mon, 28 May 2018 17:25:24 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fNPdq-0006Bu-DL for qemu-devel@nongnu.org; Mon, 28 May 2018 17:25:23 -0400 Date: Mon, 28 May 2018 22:25:10 +0100 From: "Richard W.M. Jones" Message-ID: <20180528212510.GC4660@redhat.com> References: <20180518180440-mutt-send-email-mst@kernel.org> <20180524113251.GB4660@redhat.com> <20180528183058.GG2209@redhat.com> <20180528183833.GJ4580@localhost.localdomain> <20180528212054.GH2209@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180528212054.GH2209@redhat.com> Subject: Re: [Qemu-devel] storing machine data in qcow images? List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: ehabkost@redhat.com, qemu-block@nongnu.org, "Michael S. Tsirkin" , qemu-devel@nongnu.org, Max Reitz , stefanha@redhat.com On Mon, May 28, 2018 at 10:20:54PM +0100, Richard W.M. Jones wrote: > On Mon, May 28, 2018 at 08:38:33PM +0200, Kevin Wolf wrote: > > Just accessing the image file within a tar archive is possible and we > > could write a block driver for that (I actually think we should do > > this), but it restricts you because certain operations like resizing > > aren't really possible in tar. Unfortunately, resizing is a really > > common operation for non-raw image formats. > > We do this already in virt-v2v (using file.offset and file.size > parameters in the raw driver). > > For virt-v2v we only need to read the source so resizing isn't an > issue. For most of the cases we're talking about the downloaded image > would also be a template / base image, so I suppose only reading would > be required too. > > I also wrote an nbdkit tar file driver (supports writes, but not > resizing). > https://manpages.debian.org/testing/nbdkit-plugin-perl/nbdkit-tar-plugin.1.en.html I should add the other thorny issue with OVA files is that the metadata contains a checksum (SHA1 or SHA256) of the disk images. If you modify the disk images in-place in the tar file then you need to recalculate those. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://people.redhat.com/~rjones/virt-df/