implement Msrs as a FamStructWrapper over kvm_msrs

Since kvm_msrs contains a flexible array member, we can implement
Msrs as a FamStructWrapper<kvm_msrs>. This allows users of kvm-ioctls
to work with safe code even when dealing with kvm_msrs structures.

Signed-off-by: Adrian Catangiu <[email protected]>

Author: acatangiu

src/x86/fam_wrappers.rs

@@ -17,6 +17,9 @@ use super::bindings_v4_20_0::*;
 /// See arch/x86/include/asm/kvm_host.h
 pub const KVM_MAX_CPUID_ENTRIES: usize = 80;
 
+/// Maximum number of MSRs KVM supports (See arch/x86/kvm/x86.c).
+pub const KVM_MAX_MSR_ENTRIES: usize = 256;
+
 // Implement the FamStruct trait for kvm_cpuid2.
 generate_fam_struct_impl!(
     kvm_cpuid2,
@@ -35,3 +38,22 @@ generate_fam_struct_impl!(
 /// the array elements, this type is implemented using
 /// [FamStructWrapper](../vmm_sys_util/fam/struct.FamStructWrapper.html).
 pub type CpuId = FamStructWrapper<kvm_cpuid2>;
+
+// Implement the FamStruct trait for kvm_msrs.
+generate_fam_struct_impl!(
+    kvm_msrs,
+    kvm_msr_entry,
+    entries,
+    u32,
+    nmsrs,
+    KVM_MAX_MSR_ENTRIES
+);
+
+/// Wrapper over the `kvm_msrs` structure.
+///
+/// The `kvm_msrs` structure contains a flexible array member. For details check the
+/// [KVM API](https://www.kernel.org/doc/Documentation/virtual/kvm/api.txt)
+/// documentation on `kvm_msrs`. To provide safe access to
+/// the array elements, this type is implemented using
+/// [FamStructWrapper](../vmm_sys_util/fam/struct.FamStructWrapper.html).
+pub type Msrs = FamStructWrapper<kvm_msrs>;