From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43515) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fNPZj-0006Tw-Oi for qemu-devel@nongnu.org; Mon, 28 May 2018 17:21:08 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fNPZi-0003G8-Gk for qemu-devel@nongnu.org; Mon, 28 May 2018 17:21:07 -0400 Date: Mon, 28 May 2018 22:20:54 +0100 From: "Richard W.M. Jones" Message-ID: <20180528212054.GH2209@redhat.com> References: <20180518180440-mutt-send-email-mst@kernel.org> <20180524113251.GB4660@redhat.com> <20180528183058.GG2209@redhat.com> <20180528183833.GJ4580@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180528183833.GJ4580@localhost.localdomain> 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: Max Reitz , "Michael S. Tsirkin" , ehabkost@redhat.com, stefanha@redhat.com, qemu-devel@nongnu.org, qemu-block@nongnu.org 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 Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com Fedora Windows cross-compiler. Compile Windows programs, test, and build Windows installers. Over 100 libraries supported. http://fedoraproject.org/wiki/MinGW