Re: [PATCH 32/41] cpu: Make x86ModelFromCPU a bit smarter

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On 08/12/2016 09:33 AM, Jiri Denemark wrote:
> x86ModelFromCPU is used to provide CPUID data for features matching
> @policy. This patch allows callers to set @policy to -1 to get combined
> CPUID for all CPU features (including those implicitly provided a CPU
> model) specified in CPU def.
> 
> Signed-off-by: Jiri Denemark <jdenemar@xxxxxxxxxx>
> ---
>  src/cpu/cpu_x86.c | 44 +++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 39 insertions(+), 5 deletions(-)
> 
> diff --git a/src/cpu/cpu_x86.c b/src/cpu/cpu_x86.c
> index 914352d..dcf9c25 100644
> --- a/src/cpu/cpu_x86.c
> +++ b/src/cpu/cpu_x86.c
> @@ -1011,6 +1011,15 @@ x86ModelFind(virCPUx86MapPtr map,
>  }
>  
>  
> +/*
> + * Computes CPU model data from a CPU definition associated with features
> + * matching @policy. If @policy equals -1, the computed model will describe
> + * all CPU features, i.e., it will contain:
> + *
> + *      features from model
> + *      + required and forced features
> + *      - disabled and forbidden features
> + */
>  static virCPUx86ModelPtr
>  x86ModelFromCPU(const virCPUDef *cpu,
>                  virCPUx86MapPtr map,
> @@ -1023,10 +1032,11 @@ x86ModelFromCPU(const virCPUDef *cpu,
>       * just returns an empty model
>       */
>      if (cpu->type == VIR_CPU_TYPE_HOST &&
> -        policy != VIR_CPU_FEATURE_REQUIRE)
> +        policy != VIR_CPU_FEATURE_REQUIRE &&
> +        policy != -1)
>          return x86ModelNew();
>  
> -    if (policy == VIR_CPU_FEATURE_REQUIRE) {
> +    if (policy == VIR_CPU_FEATURE_REQUIRE || policy == -1) {
>          if (!(model = x86ModelFind(map, cpu->model))) {
>              virReportError(VIR_ERR_INTERNAL_ERROR,
>                             _("Unknown CPU model %s"), cpu->model);
> @@ -1043,9 +1053,15 @@ x86ModelFromCPU(const virCPUDef *cpu,
>  
>      for (i = 0; i < cpu->nfeatures; i++) {
>          virCPUx86FeaturePtr feature;
> +        virCPUFeaturePolicy fpol;
>  
> -        if (cpu->type == VIR_CPU_TYPE_GUEST
> -            && cpu->features[i].policy != policy)
> +        if (cpu->features[i].policy == -1)
> +            fpol = VIR_CPU_FEATURE_REQUIRE;
> +        else
> +            fpol = cpu->features[i].policy;
> +
> +        if ((policy == -1 && fpol == VIR_CPU_FEATURE_OPTIONAL) ||

[1]

> +            (policy != -1 && fpol != policy))
>              continue;
>  
>          if (!(feature = x86FeatureFind(map, cpu->features[i].name))) {
> @@ -1054,8 +1070,26 @@ x86ModelFromCPU(const virCPUDef *cpu,
>              goto error;
>          }
>  
> -        if (x86DataAdd(&model->data, &feature->data))
> +        if (policy == -1) {
> +            switch (fpol) {
> +            case VIR_CPU_FEATURE_FORCE:
> +            case VIR_CPU_FEATURE_REQUIRE:
> +                if (x86DataAdd(&model->data, &feature->data) < 0)
> +                    goto error;
> +                break;
> +
> +            case VIR_CPU_FEATURE_DISABLE:
> +            case VIR_CPU_FEATURE_FORBID:
> +                x86DataSubtract(&model->data, &feature->data);
> +                break;
> +
> +            case VIR_CPU_FEATURE_OPTIONAL:

[1]
Coverity happlily points out that OPTIONAL is a DEAD_CODE path
especially due to the prior check and continue;

I see no other sane way around it other than a comment before the case:

               /* coverity[dead_error_condition] */
               case VIR_CPU_FEATURE_OPTIONAL:


> +            case VIR_CPU_FEATURE_LAST:
> +                break;
> +            }
> +        } else if (x86DataAdd(&model->data, &feature->data) < 0) {
>              goto error;
> +        }
>      }
>  
>      return model;
> 

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