Re: [PATCH v6 03/12] libs/guest: allow fetching a specific CPUID leaf from a cpu policy

[Jan Beulich <jbeulich@xxxxxxxx>]

On 17.01.2022 10:48, Roger Pau Monne wrote:
> Introduce an interface that returns a specific leaf/subleaf from a cpu
> policy in xen_cpuid_leaf_t format.
> 
> This is useful to callers can peek data from the opaque
> xc_cpu_policy_t type.
> 
> No caller of the interface introduced on this patch.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
with a nit:

> --- a/tools/libs/guest/xg_cpuid_x86.c
> +++ b/tools/libs/guest/xg_cpuid_x86.c
> @@ -855,6 +855,31 @@ int xc_cpu_policy_update_msrs(xc_interface *xch, 
> xc_cpu_policy_t *policy,
>      return rc;
>  }
>  
> +int xc_cpu_policy_get_cpuid(xc_interface *xch, const xc_cpu_policy_t *policy,
> +                            uint32_t leaf, uint32_t subleaf,
> +                            xen_cpuid_leaf_t *out)
> +{
> +    const struct cpuid_leaf *tmp;
> +
> +    *out = (xen_cpuid_leaf_t){};
> +
> +    tmp = x86_cpuid_get_leaf(&policy->cpuid, leaf, subleaf);
> +    if ( !tmp )
> +    {
> +        /* Unable to find a matching leaf. */
> +        errno = ENOENT;
> +        return -1;
> +    }
> +
> +    out->leaf = leaf;
> +    out->subleaf = subleaf;
> +    out->a = tmp->a;
> +    out->b = tmp->b;
> +    out->c = tmp->c;
> +    out->d = tmp->d;
> +    return 0;
> +}

Hypervisor style, which aiui also applies to libxc, would prefer a blank
line before the main "return" of a function.

Jan