vfio/iommufd: Implement the iommufd backend

The iommufd backend is implemented based on the new /dev/iommu user API.
This backend obviously depends on CONFIG_IOMMUFD.

So far, the iommufd backend doesn't support dirty page sync yet.

Co-authored-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>

hw/vfio/common.c

@@ -19,6 +19,7 @@
  */
 
 #include "qemu/osdep.h"
+#include CONFIG_DEVICES /* CONFIG_IOMMUFD */
 #include <sys/ioctl.h>
 #ifdef CONFIG_KVM
 #include <linux/kvm.h>
@@ -1503,6 +1504,11 @@ int vfio_attach_device(char *name, VFIODevice *vbasedev,
 {
     const VFIOIOMMUOps *ops = &vfio_legacy_ops;
 
+#ifdef CONFIG_IOMMUFD
+    if (vbasedev->iommufd) {
+        ops = &vfio_iommufd_ops;
+    }
+#endif
     return ops->attach_device(name, vbasedev, as, errp);
 }