kvm: add kvm_device_supported() helper function

This can be used when probing whether KVM support specific device. Here,
a raw vmfd is used.

Signed-off-by: Peter Xu <peterx@redhat.com>
Acked-by: Sergey Fedorov <serge.fdrv@gmail.com>
Message-id: 1458788142-17509-4-git-send-email-peterx@redhat.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

include/sysemu/kvm.h

@@ -306,6 +306,15 @@ void kvm_device_access(int fd, int group, uint64_t attr,
  */
 int kvm_create_device(KVMState *s, uint64_t type, bool test);
 
+/**
+ * kvm_device_supported - probe whether KVM supports specific device
+ *
+ * @vmfd: The fd handler for VM
+ * @type: type of device
+ *
+ * @return: true if supported, otherwise false.
+ */
+bool kvm_device_supported(int vmfd, uint64_t type);
 
 /* Arch specific hooks */
 

kvm-all.c

@@ -2339,6 +2339,21 @@ int kvm_create_device(KVMState *s, uint64_t type, bool test)
     return test ? 0 : create_dev.fd;
 }
 
+bool kvm_device_supported(int vmfd, uint64_t type)
+{
+    struct kvm_create_device create_dev = {
+        .type = type,
+        .fd = -1,
+        .flags = KVM_CREATE_DEVICE_TEST,
+    };
+
+    if (ioctl(vmfd, KVM_CHECK_EXTENSION, KVM_CAP_DEVICE_CTRL) <= 0) {
+        return false;
+    }
+
+    return (ioctl(vmfd, KVM_CREATE_DEVICE, &create_dev) >= 0);
+}
+
 int kvm_set_one_reg(CPUState *cs, uint64_t id, void *source)
 {
     struct kvm_one_reg reg;