From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:59852) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SV1EL-0003sD-6c for qemu-devel@nongnu.org; Thu, 17 May 2012 09:59:06 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1SV1EG-00043F-8y for qemu-devel@nongnu.org; Thu, 17 May 2012 09:59:00 -0400 Received: from mx1.redhat.com ([209.132.183.28]:25259) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SV1EG-00042u-0S for qemu-devel@nongnu.org; Thu, 17 May 2012 09:58:56 -0400 Message-ID: <4FB5041D.3050402@redhat.com> Date: Thu, 17 May 2012 07:58:53 -0600 From: Eric Blake MIME-Version: 1.0 References: <1337262266-32227-1-git-send-email-rjones@redhat.com> In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="------------enig22047F248523E0DB21C6C9C9" Subject: Re: [Qemu-devel] [PATCH] qemu-img: Implement 'diff' operation. List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Maydell Cc: "Richard W.M. Jones" , qemu-devel@nongnu.org This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig22047F248523E0DB21C6C9C9 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 05/17/2012 07:52 AM, Peter Maydell wrote: > On 17 May 2012 14:44, Richard W.M. Jones wrote: >> From: "Richard W.M. Jones" >> >> This produces a qcow2 file which is the different between >> two disk images. ie, if: >> >> original.img - is a disk image (in any format) >> modified.img - is a modified version of original.img >> >> then: >> >> qemu-img diff -b original.img modified.img diff.qcow2 >> >> creates 'diff.qcow2' which contains just the differences. Note that >> 'diff.qcow2' has 'original.img' set as the backing file. >=20 > Any chance of some more detailed explanation in the docs patch > about what this actually means and why it's useful? I spent > several minutes going "huh, does it even mean anything to > calculate the difference between two binary disk images?" > before realising that it's the presence of the backing file > that makes it actually make sense... Even something as simple as: Useful for converting a monolithic image back into a thin image on top of a common base. --=20 Eric Blake eblake@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org --------------enig22047F248523E0DB21C6C9C9 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) Comment: Public key at http://people.redhat.com/eblake/eblake.gpg Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iQEcBAEBCAAGBQJPtQQdAAoJEKeha0olJ0NqFfQH/0U6Fm2DwwOIbWzKi+3BKiKg R6rinTxkpHNQcl6SnFEl+8OeWMFEveR2/vMsTLBYsOlE4GpUW341EFyTiag1HM3A RMQQgWPSoSsnQQtoj0rQg1vW0KRAXbQs60XvbP78rKD4Gvda4ZD3xmB/KsyE9c4M 7buO/blWE7ajIPLVlRMEWjZy9I55pIVU2p2+zGueit9Ec/YZn0Sslotbf8+NF5Hp B3PkUj9H9LsV4FuhshxDtME+rsxH/yY297C7NOIOsEZ3UXoE9xuxmkT98aH26buX 7YTh4ffnaEgIyhq+sH9/w5tjTzuYvq+uEpk63flQfL/AYRwyH1pOyXUnaxBm7bw= =Ut5H -----END PGP SIGNATURE----- --------------enig22047F248523E0DB21C6C9C9--