vfio/platform: Make vfio cdev pre-openable by passing a file handle

This gives management tools like libvirt a chance to open the vfio
cdev with privilege and pass FD to qemu. This way qemu never needs
to have privilege to open a VFIO or iommu cdev node.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>

hw/vfio/platform.c

@@ -531,14 +531,13 @@ static VFIODeviceOps vfio_platform_ops = {
  */
 static int vfio_base_device_init(VFIODevice *vbasedev, Error **errp)
 {
-    struct stat st;
     int ret;
 
-    /* @sysfsdev takes precedence over @host */
-    if (vbasedev->sysfsdev) {
+    /* @fd takes precedence over @sysfsdev which takes precedence over @host */
+    if (vbasedev->fd < 0 && vbasedev->sysfsdev) {
         g_free(vbasedev->name);
         vbasedev->name = g_path_get_basename(vbasedev->sysfsdev);
-    } else {
+    } else if (vbasedev->fd < 0) {
         if (!vbasedev->name || strchr(vbasedev->name, '/')) {
             error_setg(errp, "wrong host device name");
             return -EINVAL;
@@ -548,10 +547,9 @@ static int vfio_base_device_init(VFIODevice *vbasedev, Error **errp)
                                              vbasedev->name);
     }
 
-    if (stat(vbasedev->sysfsdev, &st) < 0) {
-        error_setg_errno(errp, errno,
-                         "failed to get the sysfs host device file status");
-        return -errno;
+    ret = vfio_device_get_name(vbasedev, errp);
+    if (ret) {
+        return ret;
     }
 
     ret = vfio_attach_device(vbasedev->name, vbasedev,
@@ -658,13 +656,30 @@ static Property vfio_platform_dev_properties[] = {
     DEFINE_PROP_END_OF_LIST(),
 };
 
+static void vfio_platform_instance_init(Object *obj)
+{
+    VFIOPlatformDevice *vdev = VFIO_PLATFORM_DEVICE(obj);
+
+    vdev->vbasedev.fd = -1;
+}
+
+#ifdef CONFIG_IOMMUFD
+static void vfio_platform_set_fd(Object *obj, const char *str, Error **errp)
+{
+    vfio_device_set_fd(&VFIO_PLATFORM_DEVICE(obj)->vbasedev, str, errp);
+}
+#endif
+
 static void vfio_platform_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
     SysBusDeviceClass *sbc = SYS_BUS_DEVICE_CLASS(klass);
 
     dc->realize = vfio_platform_realize;
     device_class_set_props(dc, vfio_platform_dev_properties);
+#ifdef CONFIG_IOMMUFD
+    object_class_property_add_str(klass, "fd", NULL, vfio_platform_set_fd);
+#endif
     dc->vmsd = &vfio_platform_vmstate;
     dc->desc = "VFIO-based platform device assignment";
     sbc->connect_irq_notifier = vfio_start_irqfd_injection;
@@ -677,6 +692,7 @@ static const TypeInfo vfio_platform_dev_info = {
     .name = TYPE_VFIO_PLATFORM,
     .parent = TYPE_SYS_BUS_DEVICE,
     .instance_size = sizeof(VFIOPlatformDevice),
+    .instance_init = vfio_platform_instance_init,
     .class_init = vfio_platform_class_init,
     .class_size = sizeof(VFIOPlatformDeviceClass),
 };