[libvirt-users] How to explain this libvirt oddity w.r.t machine types?
Context: The baremetal host previously had QEMU 2.11. But I manually downgraded the QEMU version (via `dnf downgrade qemu-system-x86`); now it is at 2.10: $ rpm -q qemu-system-x86 qemu-system-x86-2.10.2-1.fc27.x86_64 The guest is offline. Let's see (in a couple of ways) what machine type it has while it is dormant: # virsh dumpxml cirros | grep -i machine= <type arch='x86_64' machine='pc-i440fx-2.10'>hvm</type> # grep machine= /etc/libvirt/qemu/cirros.xml <type arch='x86_64' machine='pc-i440fx-2.10'>hvm</type> Okay, now edit the guest XML and carefully remove the "machine='pc-i440fx-2.10'" bit---to see what machine type will libvirt (libvirt-daemon-kvm-4.0.0-2.fc27.x86_64) default to: # virsh edit cirros Domain cirros XML configuration edited. Now check the machine type again. Bizarrely enough, libvirt "helpfully" auto-adds QEMU *2.11* machine type, which is obviously no longer on the system! # grep machine= /etc/libvirt/qemu/cirros.xml <type arch='x86_64' machine='pc-i440fx-2.11'>hvm</type> # virsh dumpxml cirros | grep -i machine= <type arch='x86_64' machine='pc-i440fx-2.11'>hvm</type> How to explain this? Is this even a "valid test"? (To undo the nuisance, obviously, I had to `virsh edit cirros` again and change it to 2.10.) Note, I *don't* have 2.11 QEMU on the system: # rpm -qa | grep -E 'qemu.*2.11' # echo $? 1 * * * It's getting late, and I should stop staring at screens. -- /kashyap
On Fri, 2018-10-12 at 22:38 +0200, Kashyap Chamarthy wrote:
Context: The baremetal host previously had QEMU 2.11. But I manually downgraded the QEMU version (via `dnf downgrade qemu-system-x86`); now it is at 2.10:
$ rpm -q qemu-system-x86 qemu-system-x86-2.10.2-1.fc27.x86_64
The guest is offline. Let's see (in a couple of ways) what machine type it has while it is dormant:
# virsh dumpxml cirros | grep -i machine= <type arch='x86_64' machine='pc-i440fx-2.10'>hvm</type>
# grep machine= /etc/libvirt/qemu/cirros.xml <type arch='x86_64' machine='pc-i440fx-2.10'>hvm</type>
Okay, now edit the guest XML and carefully remove the "machine='pc-i440fx-2.10'" bit---to see what machine type will libvirt (libvirt-daemon-kvm-4.0.0-2.fc27.x86_64) default to:
# virsh edit cirros Domain cirros XML configuration edited.
Now check the machine type again. Bizarrely enough, libvirt "helpfully" auto-adds QEMU *2.11* machine type, which is obviously no longer on the system!
# grep machine= /etc/libvirt/qemu/cirros.xml <type arch='x86_64' machine='pc-i440fx-2.11'>hvm</type>
# virsh dumpxml cirros | grep -i machine= <type arch='x86_64' machine='pc-i440fx-2.11'>hvm</type>
How to explain this? Is this even a "valid test"?
(To undo the nuisance, obviously, I had to `virsh edit cirros` again and change it to 2.10.)
Note, I *don't* have 2.11 QEMU on the system:
# rpm -qa | grep -E 'qemu.*2.11' # echo $? 1
* * *
It's getting late, and I should stop staring at screens.
If I had to guess, I would say the <emulator> element of your guest is probably pointing to a custom-built QEMU 2.11 binary rather than the default one installed from RPMs. -- Andrea Bolognani / Red Hat / Virtualization
On Sun, Oct 14, 2018 at 02:28:07PM +0200, Andrea Bolognani wrote:
On Fri, 2018-10-12 at 22:38 +0200, Kashyap Chamarthy wrote:
[...]
Now check the machine type again. Bizarrely enough, libvirt "helpfully" auto-adds QEMU *2.11* machine type, which is obviously no longer on the system!
# grep machine= /etc/libvirt/qemu/cirros.xml <type arch='x86_64' machine='pc-i440fx-2.11'>hvm</type>
# virsh dumpxml cirros | grep -i machine= <type arch='x86_64' machine='pc-i440fx-2.11'>hvm</type>
How to explain this? Is this even a "valid test"?
(To undo the nuisance, obviously, I had to `virsh edit cirros` again and change it to 2.10.)
Note, I *don't* have 2.11 QEMU on the system:
[...]
If I had to guess, I would say the <emulator> element of your guest is probably pointing to a custom-built QEMU 2.11 binary rather than the default one installed from RPMs.
Your guess made me curious enough to check the remote machine one last time before I went to sleep, but unfortunately the <emulator> element is pointing to the plain `/usr/bin/qemu-kvm`, which in turn exec()'s `/usr/bin/qemu-system-x86_64`. (I attached the nothing-special, full guest XML.) -- /kashyap
On Mon, 2018-10-15 at 08:21 +0200, Kashyap Chamarthy wrote:
On Sun, Oct 14, 2018 at 02:28:07PM +0200, Andrea Bolognani wrote:
If I had to guess, I would say the <emulator> element of your guest is probably pointing to a custom-built QEMU 2.11 binary rather than the default one installed from RPMs.
Your guess made me curious enough to check the remote machine one last time before I went to sleep, but unfortunately the <emulator> element is pointing to the plain `/usr/bin/qemu-kvm`, which in turn exec()'s `/usr/bin/qemu-system-x86_64`.
(I attached the nothing-special, full guest XML.)
Interesting. What is the output of 'virsh capabilities'? More interesting still is the fact that the guest XML you shared looks like an *active* XML, ie. one taken from a running guest... Does that mean the guest can start even though it's using the 2.11 machine type? -- Andrea Bolognani / Red Hat / Virtualization
On Mon, Oct 15, 2018 at 09:05:16AM +0200, Andrea Bolognani wrote: [...]
Interesting. What is the output of 'virsh capabilities'?
In attachment.
More interesting still is the fact that the guest XML you shared looks like an *active* XML, ie. one taken from a running guest... Does that mean the guest can start even though it's using the 2.11 machine type?
No, of course it doesn't; the guest is running because I `virsh-edit`ed it to use 2.10 machine type :-) -- /kashyap
On Mon, 2018-10-15 at 11:46 +0200, Kashyap Chamarthy wrote:
On Mon, Oct 15, 2018 at 09:05:16AM +0200, Andrea Bolognani wrote:
Interesting. What is the output of 'virsh capabilities'?
In attachment.
Looks reasonable enough.
More interesting still is the fact that the guest XML you shared looks like an *active* XML, ie. one taken from a running guest... Does that mean the guest can start even though it's using the 2.11 machine type?
No, of course it doesn't; the guest is running because I `virsh-edit`ed it to use 2.10 machine type :-)
Should have noticed that. Welp, I'm fresh out of ideas then :/ -- Andrea Bolognani / Red Hat / Virtualization
participants (2)
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Andrea Bolognani -
Kashyap Chamarthy