Bug 524734

I've now tried this a few more times, and continued to get errors with the
disk using virtio (not always the journal errors above, sometimes it would
hang at boot or flake out randomy in other ways).

I converted the disk to use an emulated ide mode such as is used by
default with windows xp, and the problems all disappeared.

I should probably add that I was using kernel 2.6.31-33.fc12.x86_64 for
all this testing, and I have a 4 processor machine with the ubuntu
KVM also set to use 4 vcpus.

Tom: could you give us more details about the guest? Could you also supply /var/log/libvirt/qemu/$guest.log ?

Perhaps also worth trying Fedora 11 and Fedora 12 guests

hch, kwolf: any ideas on this? sounds like it only happens with qcow2+virtio. My guess is that no cache= parameter is supplied

I'll give it another try to get a log, but I'm pretty sure I remember
looking in the log when it happened and the only thing in it was the
initial qemu-kvm command line - no messages after that.

The guest is 64 bit ubuntu 9.04 installed via the "alternate" text based
installer iso image.

Also, this may be something silly I did wrong. I only recently managed to
discover the deeply nested, jargon camouflaged, dialog in virt-manager
that would let me create a qcow2 image at install time, so this qcow2
image is really the result of used qemu-img to convert the raw image
I got in initial install to a qcow2 image. I didn't change any parameters in
the xml definition of the storage for the virtual machine, I just made
the file it referred to be a qcow2 image. If changes to other attributes
were required, they didn't happen (though I did sort of assume it ought to
recognize the image format and do whatever was necessary automagically).

Tom: it's always best to include the guest XML config and log file, so we can spot whether the config is correct

If you have:

    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>

then you need to change it to:

    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>

but I assume you don't have the <driver> line at all

You could try making it:

    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2' cache='none'/>

and see if that helps

OK, I've narrowed it down. What I really need to make it fail is not
just a single qcow2 image but a qcow2 image with another qcow2 image
backing it up. I reinstalled (running on a rawhide system) a new ubuntu
image from scratch, this time using a qcow2 image in the initial install
by diving down into the use existing storage button and creating one
in there. That image worked fine with all the virt-manager created
defaults. The disk definition looked like:

    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/u2.img.img'/>
      <target dev='vda' bus='virtio'/>
    </disk>

But then I shutdown the machine, and diddled the disk images to rename the
original image and make a new image based on it, so that I had this
combination:

[root@zooty images]# ls -l u2*
-r--r--r-- 1 root root 2801205248 2009-10-01 21:42 u2-base.img
-rw-rw-rw- 1 root root    6946816 2009-10-01 22:04 u2.img.img
[root@zooty images]# qemu-img info u2-base.img
image: u2-base.img
file format: qcow2
virtual size: 20G (20971520000 bytes)
disk size: 2.6G
cluster_size: 65536
[root@zooty images]# qemu-img info u2.img.img 
image: u2.img.img
file format: qcow2
virtual size: 20G (20971520000 bytes)
disk size: 6.5M
cluster_size: 65536
backing file: u2-base.img (actual path: u2-base.img)

Now when I boot the kvm, it randomly fails, sometimes during boot, sometimes
later. Adding cache='none' does not change this behavior, I still get random
failures.

However, if I change the disk device to look like this:

    <disk type='file' device='disk'>
      <source file='/var/lib/libvirt/images/ubu.img.img'/>
      <target dev='hda' bus='ide'/>
    </disk>

then everything works perfectly fine, even with the qcow2 based on another
qcow2.

Created attachment 363413 [details]
The xml definition for the new "u2" ubuntu machine

Here's the current incarnation of the xml definition. This one has the
cache=none attribute (which didn't help).

Created attachment 363416 [details]
The qemu log file for the u2 virtual machine

Nothing much in here but qemu command lines, but I add it for completeness.

Great stuff, Tom - thanks

Christoph: summary seems to be that this is specific to virtio and qcow2 with a backing file

Kevin is looking at this, I think

http://lists.gnu.org/archive/html/qemu-devel/2009-10/msg00767.html

Kevin, it sounds like Anthony is fine with this patch for the stable branch, so I'll go ahead and pull it into F-12 today

I was going to ask you to apply it today, but you're just too quick for me. :-)

Yes, please do. It's the only sane thing we can do for a code base that will be used by real users soon.

* Fri Oct  9 2009 Mark McLoughlin <markmc> - 2:0.11.0-6
- Fix fs errors with virtio and qcow2 backing file (#524734)
- Fix ksm initscript errors on kernel missing ksm (#527653)
- Add missing Requires(post): getent, useradd, groupadd (#527087)

tag request: https://fedorahosted.org/rel-eng/ticket/2429

tagged now for F12 GA