libvirt Xen have to use "file" disk driver in the case of compute node doesn't support blktap.

[Nikita Gerasimov]

There are Xen servers which do not support http://wiki.xen.org/wiki/Blktap (e.g. Oracle VM Server for x86) but are still operational with simple file driver. To support those xen servers as compute platform we have to change method pick_disk_driver_name() in nova/virt/libvirt/utils.py to return "file" in the case hypervisor is Xen and Blktap is not operational.
The side effect is: file driver does not support "qcow2" disk format. So we also have to force 'use_cow_images' config to False for those compute nodes.

[Vasily Isaenko (vasily-isaenko)]

there is a partial fix for this issue pending integration:
     https://review.openstack.org/#/c/96400/

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/96400
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=09f8089a9a55902ee3e39371cefc19ed6d292842
Submitter: Jenkins
Branch: master

commit 09f8089a9a55902ee3e39371cefc19ed6d292842
Author: Nikita Gerasimov <email address hidden>
Date: Mon Jan 12 20:01:05 2015 +0300

    Adds "file" disk driver support to Xen libvirt driver.

    There are Xen servers which do not support
    http://wiki.xen.org/wiki/Blktap (e.g. Oracle VM Server for x86) but
    are still operational with simple file driver. So, if Xen node do not
    support Blktap then method pick_disk_driver_name return "file" instead
    of "tap" or "tap2" in case of "qemu" is not available.

    Change-Id: If8fbb058ed7e78e4a80d54f0561e2d8b9055ecb9
    Partial-Bug: #1323722

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/157436

[Nikita Gerasimov (nikita-gerasimov)]

Related to https://bugs.launchpad.net/nova/+bug/1253571

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/157436
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=675d23ecfeb373446690362226e9b7d23e170979
Submitter: Jenkins
Branch: master

commit 675d23ecfeb373446690362226e9b7d23e170979
Author: Nikita Gerasimov <email address hidden>
Date: Thu Feb 19 19:14:28 2015 +0300

    Adds xend to rootwrap.d/compute.filters.

    nova/virt/libvirt/utils.py call 'xend status' to guess which toolstack
    (xend or libxl) libvirtd will use.

    Change-Id: I860d86e3c59afbf71f283531f6e10841ad2dba38
    Partial-Bug: #1323722

[Davanum Srinivas (DIMS) (dims-v)]

Hi, What else needs to be done for this bug? (to close it?) Thanks, dims

[Nikita Gerasimov (nikita-gerasimov)]

There is still a problem with COW images. Only qemu and tap2 does support qcow2. So when "file" used as disk backed nova have to convert images to RAW format.
It's not clear where to put this logic.

Also, as mentioned in #1253571, COW ability depends on guest type. Only HVM guests may work from qcow2 image out of box. That makes COW image choice logic even more complex.

[sstabellini (stefano-stabellini)]

Using a newer libvirt with libxl support should fix your issues: libvirt and libxl should be able to deal with QCOW and QCOW2 disk images for both PV and HVM guests. No need for blktap unless a VHD image is specified.

[Markus Zoeller (markus_z) (mzoeller)]

Cleanup
=======

There are no open reviews for this bug report since more than 2 weeks.
To signal that to other contributors which might provide patches for
this bug, I switch the status from "In Progress" to "Confirmed" and
remove the assignee.
Feel free to add yourself as assignee and to push a review for it.

[Markus Zoeller (markus_z) (mzoeller)]

This is an automated cleanup. This bug report has been closed because it
is older than 18 months and there is no open code change to fix this.
After this time it is unlikely that the circumstances which lead to
the observed issue can be reproduced.

If you can reproduce the bug, please:
* reopen the bug report (set to status "New")
* AND add the detailed steps to reproduce the issue (if applicable)
* AND leave a comment "CONFIRMED FOR: <RELEASE_NAME>"
  Only still supported release names are valid (LIBERTY, MITAKA, OCATA, NEWTON).
  Valid example: CONFIRMED FOR: LIBERTY