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@citrix.com>
---
Changes since v5:
 - Zero out parameter.

Changes since v3:
 - Use x86_cpuid_get_leaf.

Changes since v1:
 - Use find leaf.
---
 tools/include/xenguest.h        |  3 +++
 tools/libs/guest/xg_cpuid_x86.c | 25 +++++++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/tools/include/xenguest.h b/tools/include/xenguest.h
index e01f494b77..0a6fd99306 100644
--- a/tools/include/xenguest.h
+++ b/tools/include/xenguest.h
@@ -807,6 +807,9 @@ int xc_cpu_policy_update_cpuid(xc_interface *xch, xc_cpu_policy_t *policy,
                                uint32_t nr);
 int xc_cpu_policy_update_msrs(xc_interface *xch, xc_cpu_policy_t *policy,
                               const xen_msr_entry_t *msrs, uint32_t nr);
+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);
 
 /* Compatibility calculations. */
 bool xc_cpu_policy_is_compatible(xc_interface *xch, xc_cpu_policy_t *host,
diff --git a/tools/libs/guest/xg_cpuid_x86.c b/tools/libs/guest/xg_cpuid_x86.c
index b9e827ce7e..aff4efe78d 100644
--- 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;
+}
+
 bool xc_cpu_policy_is_compatible(xc_interface *xch, xc_cpu_policy_t *host,
                                  xc_cpu_policy_t *guest)
 {
-- 
2.34.1

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@citrix.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>
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