[PATCH v2 00/30] Configurable policy for handling deprecated interfaces

[Peter Krempa]

On Tue, Mar 03, 2020 at 17:34:35 +0100, Markus Armbruster wrote:
> Based-on: <20200227144531.24309-1-armbru at redhat.com>
> 
> This series extends QMP introspection to cover deprecation.
> Additionally, new option -compat lets you configure what to do when
> deprecated interfaces get used.  This is intended for testing users of
> the management interfaces.  It is experimental.

I've quickly hacked up support for the 'deprecated' feature in libvirt's
QMP validator. I've found a few uses of deprecated commands but they
might very well be in code paths that are no longer invoked in modern
qemus:

Offenders from qemumonitorjsontest:

44) qemuMonitorJSONSetCPU                                             ... libvirt: QEMU Driver error : internal error: unable to execute QEMU command 'cpu-add': failed to validate arguments of 'cpu-add' against QAPI schema: ERROR: 'cpu-add' is deprecated
FAILED
46) qemuMonitorJSONChangeMedia                                        ... libvirt: QEMU Driver error : internal error: unable to execute QEMU command 'change': failed to validate arguments of 'change' against QAPI schema: ERROR: 'change' is deprecated
FAILED
49) qemuMonitorJSONSetMigrationSpeed                                  ... libvirt: QEMU Driver error : internal error: unable to execute QEMU command 'migrate_set_speed': failed to validate arguments of 'migrate_set_speed' against QAPI schema: ERROR: 'migrate_set_speed' is deprecated
FAILED
50) qemuMonitorJSONSetMigrationDowntime                               ... libvirt: QEMU Driver error : internal error: unable to execute QEMU command 'migrate_set_downtime': failed to validate arguments of 'migrate_set_downtime' against QAPI schema: ERROR: 'migrate_set_downtime' is deprecated
FAILED
77) qemuMonitorJSONGetMigrationCacheSize                              ... libvirt: QEMU Driver error : internal error: unable to execute QEMU command 'query-migrate-cache-size': failed to validate arguments of 'query-migrate-cache-size' against QAPI schema: ERROR: 'query-migrate-cache-size' is deprecated
FAILED
83) qemuMonitorJSONQueryCPUs                                          ... libvirt: QEMU Driver error : internal error: unable to execute QEMU command 'query-cpus': failed to validate arguments of 'query-cpus' against QAPI schema: ERROR: 'query-cpus' is deprecated
FAILED
93) GetCPUInfo(x86-basic-pluggable)                                   ... libvirt: QEMU Driver error : internal error: unable to execute QEMU command 'query-cpus': failed to validate arguments of 'query-cpus' against QAPI schema: ERROR: 'query-cpus' is deprecated
FAILED
94) GetCPUInfo(x86-full)                                              ... libvirt: QEMU Driver error : internal error: unable to execute QEMU command 'query-cpus': failed to validate arguments of 'query-cpus' against QAPI schema: ERROR: 'query-cpus' is deprecated
FAILED
95) GetCPUInfo(x86-node-full)                                         ... libvirt: QEMU Driver error : internal error: unable to execute QEMU command 'query-cpus': failed to validate arguments of 'query-cpus' against QAPI schema: ERROR: 'query-cpus' is deprecated
FAILED
97) GetCPUInfo(ppc64-basic)                                           ... libvirt: QEMU Driver error : internal error: unable to execute QEMU command 'query-cpus': failed to validate arguments of 'query-cpus' against QAPI schema: ERROR: 'query-cpus' is deprecated
FAILED
98) GetCPUInfo(ppc64-hotplug-1)                                       ... libvirt: QEMU Driver error : internal error: unable to execute QEMU command 'query-cpus': failed to validate arguments of 'query-cpus' against QAPI schema: ERROR: 'query-cpus' is deprecated
FAILED
99) GetCPUInfo(ppc64-hotplug-2)                                       ... libvirt: QEMU Driver error : internal error: unable to execute QEMU command 'query-cpus': failed to validate arguments of 'query-cpus' against QAPI schema: ERROR: 'query-cpus' is deprecated
FAILED
100) GetCPUInfo(ppc64-hotplug-4)                                       ... libvirt: QEMU Driver error : internal error: unable to execute QEMU command 'query-cpus': failed to validate arguments of 'query-cpus' against QAPI schema: ERROR: 'query-cpus' is deprecated
FAILED
101) GetCPUInfo(ppc64-no-threads)                                      ... libvirt: QEMU Driver error : internal error: unable to execute QEMU command 'query-cpus': failed to validate arguments of 'query-cpus' against QAPI schema: ERROR: 'query-cpus' is deprecated
FAILED

Here all commands are tested just for legacy reasons. query-cpus-fast is
used on any live codebase, cpu-add is no longer used, change is not used
with -blockdev. I'm not sure about the migration parameter APIs but I
didn't check either.

The above shows that we can't enable this without thinking even in our
test-suite.

I'll try to come up with a solution where we can enable the reporting of
use of deprecated commands through /etc/qemu.conf so that I as an
developer can always use it.

I'm currently busy but I plan to follow up later.

I've pushed the test change here:

https://gitlab.com/pipo.sk/libvirt/-/commits/qmp-deprecated

The unfortunate part is that we'll need to manually inspect the codebase
for any deprecation in returned values. Our parser is 'artisanaly
handcrafted' so it can't be introspected.