From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44700) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZWXSb-0004lG-SM for qemu-devel@nongnu.org; Mon, 31 Aug 2015 18:21:55 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZWXSX-0002uI-Lz for qemu-devel@nongnu.org; Mon, 31 Aug 2015 18:21:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45615) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZWXSX-0002tv-El for qemu-devel@nongnu.org; Mon, 31 Aug 2015 18:21:49 -0400 References: <1433776886-27239-1-git-send-email-vsementsov@virtuozzo.com> <1433776886-27239-2-git-send-email-vsementsov@virtuozzo.com> From: Eric Blake Message-ID: <55E4D370.4000904@redhat.com> Date: Mon, 31 Aug 2015 16:21:36 -0600 MIME-Version: 1.0 In-Reply-To: <1433776886-27239-2-git-send-email-vsementsov@virtuozzo.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="1jqXC1H1GecXURAqlXdcnmQwWld3KLK2g" Subject: Re: [Qemu-devel] [PATCH 1/8] spec: add qcow2-dirty-bitmaps specification List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Vladimir Sementsov-Ogievskiy , qemu-devel@nongnu.org Cc: kwolf@redhat.com, Vladimir Sementsov-Ogievskiy , stefanha@redhat.com, pbonzini@redhat.com, den@openvz.org, jsnow@redhat.com This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --1jqXC1H1GecXURAqlXdcnmQwWld3KLK2g Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 06/08/2015 09:21 AM, Vladimir Sementsov-Ogievskiy wrote: > From: Vladimir Sementsov-Ogievskiy >=20 > Persistent dirty bitmaps will be saved into qcow2 files. It may be used= > as 'internal' bitmaps (for qcow2 drives) or as 'external' bitmaps for > other drives (there may be qcow2 file with zero disk size but with > several dirty bitmaps for other drives). >=20 > Signed-off-by: Vladimir Sementsov-Ogievskiy > --- > docs/specs/qcow2.txt | 66 ++++++++++++++++++++++++++++++++++++++++++++= ++++++++ > 1 file changed, 66 insertions(+) >=20 > +=3D=3D Dirty bitmaps =3D=3D > + > +Dirty bitmaps is an optional header extension. It provides a possibili= ty of > +storing dirty bitmaps in qcow2 image. The fields are: > + > + 0 - 3: nb_dirty_bitmaps > + Number of dirty bitmaps contained in the image > + > + 4 - 11: dirty_bitmaps_offset > + Offset into the image file at which the dirty bitma= ps table > + starts. Must be aligned to a cluster boundary. To date, all 8-byte fields in qcow2 have been 8-byte aligned; this would break that nice feature. You could keep that nice property by swapping the order of these two fields. [Note that the spec on header extensions already requires clients to recognize that a header extension of 12 bytes implicitly pads out an additional 4 bytes, so that the next header extension type field once again lands on 8-byte alignment] > +=3D=3D Dirty bitmaps =3D=3D > + > +The feature supports storing several dirty bitmaps in the qcow2 file. Is it possible to have a qcow2 file that stores JUST dirty bitmap(s) and no guest data (that is, no L1 table, no backing file)? It might make sense, if we intend to allow persistent bitmap files that can be associated with a raw disk. But right now, the spec seems to require that l1_table_offset must be non-zero. --=20 Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org --1jqXC1H1GecXURAqlXdcnmQwWld3KLK2g Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 Comment: Public key at http://people.redhat.com/eblake/eblake.gpg Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBCAAGBQJV5NNwAAoJEKeha0olJ0NqlDUH+wfqkU/yY74b8ZlVzPz2WQiN R/Le/2L7nQ7n28Pl2jh5Ysluc3v7WrMVdBwewZfjIaCevwXEJqloYm/2oL34F3Ri v61sLcKWJCSl+RaE5nZbBls75V183gaDNK0zs9Oc688pEKEYuKUQ/ojCXeMaQBZn TR8559Df+81mJM42B+Y0O9YQ7zxR6UjfRdG2FdjDhyl13qQY3nhJukCJZG5yhl6y bpTLb371QOpwWTHWqsNmIfpegujb/9vfTu+dndvjA8NGNjq93eInse8qYPrJE3Ew XhsTMbT13WjsIu5po3Ezu5wzfS5wVuCIigB6BhTBWRydxP9u5YO6ud7Q2L3kEFA= =N9jd -----END PGP SIGNATURE----- --1jqXC1H1GecXURAqlXdcnmQwWld3KLK2g--