From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:36555) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZqpA2-0008Ho-Mw for qemu-devel@nongnu.org; Mon, 26 Oct 2015 17:18:35 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZqpA1-000320-JM for qemu-devel@nongnu.org; Mon, 26 Oct 2015 17:18:34 -0400 References: <1445883177-11795-1-git-send-email-jsnow@redhat.com> From: Max Reitz Message-ID: <562E989F.5010000@redhat.com> Date: Mon, 26 Oct 2015 22:18:23 +0100 MIME-Version: 1.0 In-Reply-To: <1445883177-11795-1-git-send-email-jsnow@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="LQlHnuLXJM4fewSbRKu0XkhHmtDCJHlKT" Subject: Re: [Qemu-devel] [PATCH] block: allow best-effort query List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: John Snow , qemu-block@nongnu.org Cc: kwolf@redhat.com, qemu-devel@nongnu.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --LQlHnuLXJM4fewSbRKu0XkhHmtDCJHlKT Content-Type: text/plain; charset=iso-8859-15 Content-Transfer-Encoding: quoted-printable On 26.10.2015 19:12, John Snow wrote: > For more complex BDS trees that can be created under normal circumstanc= es, > we lose the ability to issue query commands because of our inability to= > re-construct the absolute filename. >=20 > Instead, omit this field when it is a problem and present as much infor= mation > as we can. >=20 > This will change the expected output in iotest 110, where we will now s= ee a > json filename and the lack of an absolute filename instead of an error.= >=20 > Signed-off-by: John Snow > --- > block/qapi.c | 10 ++++++---- > tests/qemu-iotests/110.out | 5 ++++- > 2 files changed, 10 insertions(+), 5 deletions(-) One problem I see now is that qemu-img --backing-chain uses the full backing name if it is available and if it isn't, it resorts to the non-full backing name (which was good until this patch, as far as I can see). But now that's not necessarily a valid substitution anymore: $ mkdir foo $ ./qemu-img create -f qcow2 foo/base.qcow2 64M $ ./qemu-img create -f qcow2 -b base.qcow2 foo/top.qcow2 $ ./qemu-img create -f qcow2 base.qcow2 64M $ ./qemu-img info --backing-chain foo/top.qcow2 image: foo/top.qcow2 file format: qcow2 virtual size: 64M (67108864 bytes) disk size: 196K cluster_size: 65536 backing file: base.qcow2 (actual path: foo/base.qcow2) Format specific information: compat: 1.1 lazy refcounts: false refcount bits: 16 corrupt: false image: foo/base.qcow2 file format: qcow2 virtual size: 64M (67108864 bytes) disk size: 196K cluster_size: 65536 Format specific information: compat: 1.1 lazy refcounts: false refcount bits: 16 corrupt: false $ ./qemu-img info --backing-chain \ "json:{'file.filename':'foo/top.qcow2', 'driver':'qcow2','lazy-refcounts':true}" image: json:{"lazy-refcounts": true, "driver": "qcow2", "file": {"driver": "file", "filename": "foo/top.qcow2"}} file format: qcow2 virtual size: 64M (67108864 bytes) disk size: 196K cluster_size: 65536 backing file: base.qcow2 Format specific information: compat: 1.1 lazy refcounts: false refcount bits: 16 corrupt: false image: base.qcow2 file format: qcow2 virtual size: 32M (33554432 bytes) disk size: 196K cluster_size: 65536 Format specific information: compat: 1.1 lazy refcounts: false refcount bits: 16 corrupt: false As you can see, in the second case, the wrong base.qcow2 was used. I think qemu-img info --backing-chain should abort once it hits a point where has_full_backing_filename is false; but for that to work, we need to set info->full_backing_filename even if the "relative" and the absolute backing filename (backing_filename and backing_filename2) are equal. (By the way: It's actually some kind of a bug that you can open images with JSON filenames and backing files; this only works because bdrv_open_backing_file() is called before bdrv_refresh_filename(). Actually, after my "Drop BDS.filename" series it will no longer work. This is bad. I need to fix this before I can continue the series...) ((It is bad because that means: $ x86_64-softmmu/qemu-system-x86_64 \ -drive if=3Dnone,file.filename=3Dfoo/top.qcow2,lazy-refcounts=3Don qemu-system-x86_64: -drive if=3Dnone,file.filename=3Dfoo/top.qcow2,lazy-refcounts=3Don: Cannot use relative backing file names for 'json:{"lazy-refcounts": "on", "driver": "qcow2", "file": {"driver": "file", "filename": "foo/top.qcow2"}}' And that's bad.)) (((So for this patch that means I guess we should just fix bdrv_get_full_backing_filename() instead.))) Max --LQlHnuLXJM4fewSbRKu0XkhHmtDCJHlKT 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 iQEcBAEBCAAGBQJWLpifAAoJEDuxQgLoOKyt2ewH/jDPb9HNh89GBg/+YQNBc96i 1ImlzKPSMVD92MEJtHJUYjCiYCzBvhXeHHXfSIfIbNoPoD+1fWCilJVn9gk44N8k S190Kw3FkpV0M0e5nWMvUAa/tCM1KpUx9sSULoWX6cuQQZ49xn7qd2+DA9+nmw1q 36/K8IQpHDT1k2avKqLJ4ZgPKriMZAx3hXRGASEm/BOghy+5M9GIZLsVUe7YnzMv CnOeG5cCbta6fjQ24aRaXNqkxTs+S26tf+BmWsIYG+COzyfXuBqx79FAAICbse2Y Bxtx+HjsLCJDgx+OqbvYWAOcVDt2TAePizBjEjuslM2WkWOqhgjlOVJzEDJhGqU= =m8S7 -----END PGP SIGNATURE----- --LQlHnuLXJM4fewSbRKu0XkhHmtDCJHlKT--