boot from iso doesn't work with snapshot with libvirt

[Yun Mao]

how to reproduce: boot from an iso image, then take a snapshot. error:

2012-07-11 11:48:39 TRACE nova.openstack.common.rpc.amqp Command: qemu-img convert -f qcow2 -O iso -s fb623355936c473fba1f805d097fb1db /opt/stack/nova/instances/instance-00000004/disk /opt/stack/nova/instances/snapshots/tmpBaLThN/fb623355936c473fba1f805d097fb1db
2012-07-11 11:48:39 TRACE nova.openstack.common.rpc.amqp Exit code: 1
2012-07-11 11:48:39 TRACE nova.openstack.common.rpc.amqp Stdout: ''
2012-07-11 11:48:39 TRACE nova.openstack.common.rpc.amqp Stderr: "qemu-img: Unknown file format 'iso'\n"
2012-07-11 11:48:39 TRACE nova.openstack.common.rpc.amqp

It tries to snapshot the root device which is the iso file.

[Douglas A. Maske (doug-maske-r)]

We are having the same issue right now, we built CentOS 6.2 64-bit from an ISO image, I try to snapshot it as a baseline image and I get the following:
2012-07-12 10:10:04 AUDIT nova.compute.manager [req-86422db7-f199-4870-a1b6-66cd26a27c43 b814182cb2ef4649add2f4194401cb8e 35dd40c123c74d90841c9802b1061229] instance 80aa96a7-405e-4231-a91a-ac8ca943541a: snapshotting
2012-07-12 10:11:09 WARNING nova.compute.manager [-] Found 1 in the database and 0 on the hypervisor.
2012-07-12 10:11:11 INFO nova.virt.libvirt.connection [-] Compute_service record updated for artim-cloud01.td.teradata.com
2012-07-12 10:11:11 INFO nova.compute.manager [-] Updating host status
2012-07-12 10:11:15 ERROR nova.rpc.amqp [req-86422db7-f199-4870-a1b6-66cd26a27c43 b814182cb2ef4649add2f4194401cb8e 35dd40c123c74d90841c9802b1061229] Exception during message handling
2012-07-12 10:11:15 TRACE nova.rpc.amqp Traceback (most recent call last):
2012-07-12 10:11:15 TRACE nova.rpc.amqp File "/usr/lib/python2.6/site-packages/nova/rpc/amqp.py", line 253, in _process_data
2012-07-12 10:11:15 TRACE nova.rpc.amqp rval = node_func(context=ctxt, **node_args)
2012-07-12 10:11:15 TRACE nova.rpc.amqp File "/usr/lib/python2.6/site-packages/nova/exception.py", line 114, in wrapped
2012-07-12 10:11:15 TRACE nova.rpc.amqp return f(*args, **kw)
2012-07-12 10:11:15 TRACE nova.rpc.amqp File "/usr/lib/python2.6/site-packages/nova/compute/manager.py", line 183, in decorated_function
2012-07-12 10:11:15 TRACE nova.rpc.amqp sys.exc_info())
2012-07-12 10:11:15 TRACE nova.rpc.amqp File "/usr/lib64/python2.6/contextlib.py", line 23, in __exit__
2012-07-12 10:11:15 TRACE nova.rpc.amqp self.gen.next()
2012-07-12 10:11:15 TRACE nova.rpc.amqp File "/usr/lib/python2.6/site-packages/nova/compute/manager.py", line 177, in decorated_function
2012-07-12 10:11:15 TRACE nova.rpc.amqp return function(self, context, instance_uuid, *args, **kwargs)
2012-07-12 10:11:15 TRACE nova.rpc.amqp File "/usr/lib/python2.6/site-packages/nova/compute/manager.py", line 952, in snapshot_instance
2012-07-12 10:11:15 TRACE nova.rpc.amqp self.driver.snapshot(context, instance_ref, image_id)
2012-07-12 10:11:15 TRACE nova.rpc.amqp File "/usr/lib/python2.6/site-packages/nova/exception.py", line 114, in wrapped
2012-07-12 10:11:15 TRACE nova.rpc.amqp return f(*args, **kw)
2012-07-12 10:11:15 TRACE nova.rpc.amqp File "/usr/lib/python2.6/site-packages/nova/virt/libvirt/connection.py", line 708, in snapshot
2012-07-12 10:11:15 TRACE nova.rpc.amqp image_format)
2012-07-12 10:11:15 TRACE nova.rpc.amqp File "/usr/lib/python2.6/site-packages/nova/virt/libvirt/utils.py", line 223, in extract_snapshot
2012-07-12 10:11:15 TRACE nova.rpc.amqp execute(*qemu_img_cmd)
2012-07-12 10:11:15 TRACE nova.rpc.amqp File "/usr/lib/python2.6/site-packages/nova/virt/libvirt/utils.py", line 35, in execute
2012-07-12 10:11:15 TRACE nova.rpc.amqp return utils.execute(*args, **kwargs)
2012-07-12 10:11:15 TRACE nova.rpc.amqp File "/usr/lib/python2.6/site-packages/nova/utils.py", line 243, in execute
2012-07-12 10:11:15 TRACE nova.rpc.amqp cmd=' '.join(cmd))
2012-07-12 10:11:15 TRACE nova.rpc.amqp Proc...

[Serge Hallyn (serge-hallyn)]

Hi,

did you mean to mark this as affecting the qemu-kvm package, or the project? (To mark it as affecting qemu-kvm package, choose 'Also affects distribution' and pick distribution Ubuntu and project qemu-kvm).

However, since qemu-kvm does not support an 'iso' output format for snapshots, I'm not sure that was your intent (so I won't do it for you as I'd likely be doing the wrong thing :).

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/10530

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/10530
Committed: http://github.com/openstack/nova/commit/af0651946010e6bcc966005aa9fc2a1f38d3748a
Submitter: Jenkins
Branch: master

commit af0651946010e6bcc966005aa9fc2a1f38d3748a
Author: Mark McLoughlin <email address hidden>
Date: Mon Jul 30 13:03:39 2012 +0100

    Avoid error during snapshot of ISO booted instance

    Fixes bug #1023492

    If you boot an instance from an image with disk_format=iso and then
    attempt to snapshot (i.e. nova image-create) you currently get a
    traceback because we do:

      qemu-img convert -f qcow2 -O iso -s $snap $disk $out

    and 'iso' is not a format that qemu-img knows anything about.

    When booting the image, we use qemu-img to detect that the file is
    a raw image so we avoid having to special case disk_format=iso
    there. However, there's no way of avoiding the special casing when
    extracting a snapshot.

    Note 1 - it's not very clever to take a snapshot of a read-only
    disk downloaded from glance and upload it back to glance again.
    Adding such smarts would be a nice enhancement.

    Note 2 - only the destination format is important here because
    we can only be extracting from a qcow2 image since snapshots
    only work where use_cow_images=True. See also #1030844.

    Change-Id: I21ff6db8ebb59a83d27f224283fb76f582c38a0e