[libvirt] [PATCH v2 3/7] cpu_x86: Introduce virCPUx86FeatureIsMSR

[Jiri Denemark]

On Thu, Jun 20, 2019 at 10:16:36 +0200, Ján Tomko wrote:
> On Thu, Jun 20, 2019 at 12:53:38AM +0200, Jiri Denemark wrote:
> >This function may be used as a virCPUDefFeatureFilter callback for
> >virCPUDefCheckFeatures, virCPUDefFilerFeatures, and similar functions to
> >filter or pick out features reported via MSR.
> >
> >Signed-off-by: Jiri Denemark <jdenemar at redhat.com>
> >---
> > src/cpu/cpu_x86.c        | 40 ++++++++++++++++++++++++++++++++++++++++
> > src/cpu/cpu_x86.h        |  3 +++
> > src/libvirt_private.syms |  1 +
> > 3 files changed, 44 insertions(+)
> >
> >diff --git a/src/cpu/cpu_x86.c b/src/cpu/cpu_x86.c
> >index 6eef5cef00..a7ec0f7095 100644
> >--- a/src/cpu/cpu_x86.c
> >+++ b/src/cpu/cpu_x86.c
> >@@ -3362,6 +3362,46 @@ virCPUx86DataAddFeature(virCPUDataPtr cpuData,
> > }
> >
> >
> >+/**
> >+ * virCPUx86FeatureIsMSR:
> >+ * @name CPU feature name
> >+ * @opaque NULL or a pointer to bool
> >+ *
> >+ * This is a callback for functions filtering features in virCPUDef.
> >+ *
> >+ * Checks whether a given CPU feature is reported via MSR. When @opaque is NULL
> >+ * or a pointer to true, the function will pick out (return true for) MSR
> >+ * features. If @opaque is a pointer to false, the logic will be inverted and
> >+ * the function will filter out (return false for) MSR features.
> >+ */
> 
> Uhm. What? Do I understand it correctly?
> 
> @opaque | *opaque | IsMSR | return
> --------+---------+-------+--------
> NULL    | SEGV    | true  | true
> 0xBEEF  | true    | true  | true
> 0xBEEF  | false   | true  | false
> --------+---------+-------+--------
> 
> First, it feels odd that 'false' is the value resulting in
> changed behavior. I'd rather see it act differently when the bool
> pointer is present and points to true.

I actually tried both variants and could not decide which one is better.
And this means both are in fact ugly :-) So when changing
virCPUx86FeatureIsMSR into a helper, I created two simple wrappers
instead of playing with opaque pointer.

Jirka