[libvirt PATCH v2 1/2] qemu: remove use of (+|-)name syntax for -cpu featres

[Jiri Denemark]

On Thu, Oct 07, 2021 at 11:09:19 +0100, Daniel P. Berrangé wrote:
> On Thu, Oct 07, 2021 at 11:53:00AM +0200, Jiri Denemark wrote:
> > On Thu, Oct 07, 2021 at 10:05:12 +0100, Daniel P. Berrangé wrote:
> > > The -cpu arg gained support for feature=on|off syntax for the x86
> > > emulator in 2.4.0
> > > 
> > >   commit 38e5c119c2925812bd441450ab9e5e00fc79e662
> > >   Author: Eduardo Habkost <ehabkost at redhat.com>
> > >   Date:   Mon Mar 23 17:29:32 2015 -0300
> > > 
> > >     target-i386: Register QOM properties for feature flags
> > > 
> > > Most other targets gained this syntax even earlier in 1.4.1
> > > 
> > >   commit 1590bbcb02921dfe8e3cf66e3a3aafd31193babf
> > >   Author: Andreas Färber <afaerber at suse.de>
> > >   Date:   Mon Mar 3 23:33:51 2014 +0100
> > > 
> > >     cpu: Implement CPUClass::parse_features() for the rest of CPUs
> > > 
> > >     CPUs who do not provide their own implementation of feature parsing
> > >     will treat each option as a QOM property and set it to the supplied
> > >     value.
> > > 
> > > There appears no reason to keep supporting "+|-feature" syntax,
> > > given the current minimum QEMU version.
> > > 
> > > Signed-off-by: Daniel P. Berrangé <berrange at redhat.com>
> > > ---
> > >  src/qemu/qemu_command.c                       | 34 ++++++-------------
> > >  tests/qemuxml2argvdata/cpu-Haswell2.args      |  2 +-
> > >  tests/qemuxml2argvdata/cpu-Haswell3.args      |  2 +-
> > >  .../qemuxml2argvdata/cpu-cache-disable3.args  |  2 +-
> > >  .../cpu-check-default-partial.args            |  2 +-
> > >  tests/qemuxml2argvdata/cpu-eoi-disabled.args  |  2 +-
> > >  tests/qemuxml2argvdata/cpu-eoi-enabled.args   |  2 +-
> > >  tests/qemuxml2argvdata/cpu-exact1.args        |  2 +-
> > >  .../cpu-exact2-nofallback.args                |  2 +-
> > >  tests/qemuxml2argvdata/cpu-exact2.args        |  2 +-
> > >  tests/qemuxml2argvdata/cpu-fallback.args      |  2 +-
> > >  tests/qemuxml2argvdata/cpu-host-kvmclock.args |  2 +-
> > >  .../qemuxml2argvdata/cpu-host-model-cmt.args  |  2 +-
> > >  .../cpu-host-model-fallback.args              |  2 +-
> > >  .../cpu-host-model-vendor.args                |  2 +-
> > >  tests/qemuxml2argvdata/cpu-host-model.args    |  2 +-
> > >  .../cpu-host-passthrough-features.args        |  2 +-
> > >  tests/qemuxml2argvdata/cpu-kvmclock.args      |  2 +-
> > >  tests/qemuxml2argvdata/cpu-minimum1.args      |  2 +-
> > >  tests/qemuxml2argvdata/cpu-minimum2.args      |  2 +-
> > >  tests/qemuxml2argvdata/cpu-strict1.args       |  2 +-
> > >  .../cpu-translation.x86_64-latest.args        |  2 +-
> > >  tests/qemuxml2argvdata/cpu-tsc-frequency.args |  2 +-
> > >  .../eoi-disabled.x86_64-latest.args           |  2 +-
> > >  .../eoi-enabled.x86_64-latest.args            |  2 +-
> > >  .../graphics-spice-timeout.args               |  2 +-
> > >  .../kvmclock+eoi-disabled.x86_64-latest.args  |  2 +-
> > >  tests/qemuxml2argvdata/kvmclock.args          |  2 +-
> > >  .../pci-bridge-many-disks.args                |  2 +-
> > >  .../pv-spinlock-disabled.x86_64-latest.args   |  2 +-
> > >  .../pv-spinlock-enabled.x86_64-latest.args    |  2 +-
> > >  31 files changed, 41 insertions(+), 53 deletions(-)
> > > 
> > > diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
> > > index eaa1e0deb9..0f1cdd9372 100644
> > > --- a/src/qemu/qemu_command.c
> > > +++ b/src/qemu/qemu_command.c
> > > @@ -6242,21 +6242,6 @@ qemuBuildGlobalControllerCommandLine(virCommand *cmd,
> > >  }
> > >  
> > >  
> > > -static void
> > > -qemuBuildCpuFeature(virQEMUCaps *qemuCaps,
> > > -                    virBuffer *buf,
> > > -                    const char *name,
> > > -                    bool state)
> > > -{
> > > -    name = virQEMUCapsCPUFeatureToQEMU(qemuCaps, name);
> > > -
> > > -    if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_QUERY_CPU_MODEL_EXPANSION))
> > > -        virBufferAsprintf(buf, ",%s=%s", name, state ? "on" : "off");
> > > -    else
> > > -        virBufferAsprintf(buf, ",%c%s", state ? '+' : '-', name);
> > > -}
> > 
> > I guess it would have been easier and perhaps clearer to just remove the
> > else branch and the test itself, because...
> > 
> > > @@ -6433,13 +6420,14 @@ qemuBuildCpuCommandLine(virCommand *cmd,
> > >      }
> > >  
> > >      if (def->apic_eoi) {
> > > -        qemuBuildCpuFeature(qemuCaps, &buf, "kvm_pv_eoi",
> > > -                            def->apic_eoi == VIR_TRISTATE_SWITCH_ON);
> > > +        virBufferAsprintf(&buf, ",kvm_pv_eoi=%s", def->apic_eoi ==
> > > +                          VIR_TRISTATE_SWITCH_ON ? "on" : "off");
> > 
> > This is affected by the same issue spotted by Peter in v1. In other
> > words, when replacing qemuBuildCpuFeature you need to make sure the
> > feature name goes through virQEMUCapsCPUFeatureToQEMU().
> 
> virQEMUCapsCPUFeatureToQEMU() is a constant mapping. It makes sense
> to use it in the earlier loop, because we're getting feature names
> dynamically from the XML config.
> 
> In this case though, we've just got a constant string. Seems better
> to just pass the right constant string in directly rather than send
> it through this remapping.

Well, only when QEMU_CAPS_CANONICAL_CPU_FEATURES is set. If it is always
set for any QEMU we deal with, we can just drop it too, though.

BTW the same applies to VIR_CPU_x86_KVM_PV_UNHALT just a few lines below
and I can't guarantee I spotted all cases :-)

As I said, keeping qemuBuildCpuFeature would be easier for reviewers as
chances for making a mistake would be significantly lower...

Jirka