On a Friday in 2021, Daniel P. Berrangé wrote:
Libvirt has a notion of "tainting" which we use to mark a guest which
has some undesirable configuration or behaviour from libvirt's POV.
This ends up in the libvirtd logs and in the per-VM log file, but is
not exposed to management applications directly.
QMP has the ability to report whether a CPU or machine type is
deprecated.
QEMU itself prints warnings to stderr which end up in the per VM log:
2021-01-22T12:22:53.566239Z qemu-system-x86_64: Machine type 'pc-1.3' is depr=
ecated: use a newer machine type instead
2021-01-22T12:22:53.566613Z qemu-system-x86_64: warning: CPU model Icelake-Cl=
ient-x86_64-cpu is deprecated -- use Icelake-Server instead
We can use the deprecation info from QMP to add tainting to the
domain too. This will appear in the pre-VM log file again:
2021-01-22 12:22:53.492+0000: Domain id=3D2 is tainted: deprecated-configurat=
ion (machine type 'pc-1.3')
2021-01-22 12:22:53.492+0000: Domain id=3D2 is tainted: deprecated-configurat=
ion (CPU model 'Icelake-Client')
and more usefully in the libvirtd log
2021-01-22 13:18:09.619+0000: 3299849: warning :
qemuDomainObjTaintMsg:6208 :
Domain id=3D3 name=3D'demo' uuid=3Deadf8ef0-bf14-4c5f-9708-4a19bacf9e81
is tainted: deprecated-configuration (machine type 'pc-1.3')
2021-01-22 13:18:09.619+0000: 3299849: warning :
qemuDomainObjTaintMsg:6208 :
Domain id=3D3 name=3D'demo' uuid=3Deadf8ef0-bf14-4c5f-9708-4a19bacf9e81
is tainted: deprecated-configuration (CPU model 'Icelake-Client')
This series goes further and also exposes the deprecation info in the
capabilities (machine types) or domain capabilities (CPU) XML. This
lets mgmt apps avoid using the feature upfront if desired.
Finally both deprecation messages and tainting flags are exposed in
new public APIs, and wired into virsh
$ virsh dominfo demo
Id: 3
Name: demo
UUID: eadf8ef0-bf14-4c5f-9708-4a19bacf9e81
OS Type: hvm
State: running
CPU(s): 2
CPU time: 1.3s
Max memory: 1536000 KiB
Used memory: 1536000 KiB
Persistent: yes
Autostart: disable
Managed save: no
Security model: selinux
Security DOI: 0
Security label: unconfined_u:unconfined_r:svirt_t:s0:c578,c807 (permissive)
Tainting: custom-monitor
deprecated-config
Deprecations: CPU model 'Icelake-Client'
machine type 'pc-1.3'
The deprecations API is simple, just returning a list of free form
opaque strings, which are eeffectively warning messages.
I'm not entirely convinced by tainting API though. I didn't especially
want to expose the virDomainTaintFlags enum in the public API since it
feels like the enum flags are (almost) all QEMU driver specific. I thus
took the approach of having an API return opaque strings which are
declared to be hypervisor specific.
I'm worried though that mgmt apps will none the less simply match on
the strings to detect things, at which point we might as well just use
an enum after all.
Depending on the app, there might be no need to even call GetTainting in the first place - the app already has the power not to use any of the tainted features, with the exception of the newly-added deprecated-config, which can happen after migration to a newer QEMU. So they can just query for deprecations directly. Also, with the deprecations being an opaque string, can the apps take any different action than just passing them to the user? It seems to me the APIs are better for humans and the XML in capabilities is better for apps, but I've never really written one.
So perhaps it should just be turned into
virDomainGetTainting(virDomainPtr obj,
int **codes,
unsigned int flags);
enum virDomainTaintCodes {
....
}
Daniel P. Berrang=C3=A9 (16):
qemu: report whether a CPU model is deprecated in dom capabilities
qemu: report whether a machine type is deprecated in capabilities
conf: introduce new taint flag for deprecated configuration
qemu: add ability to associate a string message with taint warning
qemu: taint the VM if it is using a deprecated CPU model
qemu: taint the VM if it is using a deprecated machine type
conf: record deprecation messages against the domain
qemu: record deprecation messages against the domain
src: define virDomainGetDeprecations API
remote: add RPC support for the virDomainGetDeprecations API
qemu: implement virDomainGetDeprecations API
tools: report deprecations for 'dominfo' command
src: define virDomainGetTainting API
remote: add RPC support for the virDomainGetTainting API
qemu: implement virDomainGetTainting API
tools: report tainting for 'dominfo' command
Reviewed-by: Ján Tomko <jtomko@xxxxxxxxxx> Jano
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