KVM: Add method to check for backwards-compatible API extensions

Signed-off-by: Avi Kivity <avi@qumranet.com>

2 files changed, 11 insertions, 0 deletions

diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index 5d24203afd20..39cf8fd343a3 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -2416,6 +2416,12 @@ static long kvm_dev_ioctl(struct file *filp,
                 r = 0;
                 break;
         }
+        case KVM_CHECK_EXTENSION:
+                /*
+                 * No extensions defined at present.
+                 */
+                r = 0;
+                break;
         default:
                 ;
         }
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 93472daec120..c93cf53953af 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -232,6 +232,11 @@ struct kvm_cpuid {
 #define KVM_GET_API_VERSION       _IO(KVMIO,   0x00)
 #define KVM_CREATE_VM             _IO(KVMIO,   0x01) /* returns a VM fd */
 #define KVM_GET_MSR_INDEX_LIST    _IOWR(KVMIO, 0x02, struct kvm_msr_list)
+/*
+ * Check if a kvm extension is available.  Argument is extension number,
+ * return is 1 (yes) or 0 (no, sorry).
+ */
+#define KVM_CHECK_EXTENSION       _IO(KVMIO,   0x03)
 
 /*
  * ioctls for VM fds