vfio: factor out a vfio_group_find_or_alloc helper

Factor out a helper to find or allocate the vfio_group to reduce the
spagetthi code in vfio_register_group_dev a little.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20210924155705.4258-5-hch@lst.deSigned-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/vfio.c

@@ -823,49 +823,59 @@ void vfio_uninit_group_dev(struct vfio_device *device)
 }
 EXPORT_SYMBOL_GPL(vfio_uninit_group_dev);
 
-int vfio_register_group_dev(struct vfio_device *device)
+struct vfio_group *vfio_group_find_or_alloc(struct device *dev)
 {
-	struct vfio_device *existing_device;
 	struct iommu_group *iommu_group;
 	struct vfio_group *group;
 
-	/*
-	 * If the driver doesn't specify a set then the device is added to a
-	 * singleton set just for itself.
-	 */
-	if (!device->dev_set)
-		vfio_assign_device_set(device, device);
-
-	iommu_group = vfio_iommu_group_get(device->dev);
+	iommu_group = vfio_iommu_group_get(dev);
 	if (!iommu_group)
-		return -EINVAL;
+		return ERR_PTR(-EINVAL);
 
+	/* a found vfio_group already holds a reference to the iommu_group */
 	group = vfio_group_get_from_iommu(iommu_group);
-	if (!group) {
+	if (group)
+		goto out_put;
+
+	/* a newly created vfio_group keeps the reference. */
 	group = vfio_create_group(iommu_group);
-		if (IS_ERR(group)) {
+	if (IS_ERR(group))
+		goto out_remove;
+	return group;
+
+out_remove:
 #ifdef CONFIG_VFIO_NOIOMMU
 	if (iommu_group_get_iommudata(iommu_group) == &noiommu)
-				iommu_group_remove_device(device->dev);
+		iommu_group_remove_device(dev);
 #endif
+out_put:
 	iommu_group_put(iommu_group);
-			return PTR_ERR(group);
-		}
-	} else {
+	return group;
+}
+
+int vfio_register_group_dev(struct vfio_device *device)
+{
+	struct vfio_device *existing_device;
+	struct vfio_group *group;
+
 	/*
-		 * A found vfio_group already holds a reference to the
-		 * iommu_group.  A created vfio_group keeps the reference.
+	 * If the driver doesn't specify a set then the device is added to a
+	 * singleton set just for itself.
 	 */
-		iommu_group_put(iommu_group);
-	}
+	if (!device->dev_set)
+		vfio_assign_device_set(device, device);
+
+	group = vfio_group_find_or_alloc(device->dev);
+	if (IS_ERR(group))
+		return PTR_ERR(group);
 
 	existing_device = vfio_group_get_device(group, device->dev);
 	if (existing_device) {
 		dev_WARN(device->dev, "Device already exists on group %d\n",
-			 iommu_group_id(iommu_group));
+			 iommu_group_id(group->iommu_group));
 		vfio_device_put(existing_device);
 #ifdef CONFIG_VFIO_NOIOMMU
-		if (iommu_group_get_iommudata(iommu_group) == &noiommu)
+		if (iommu_group_get_iommudata(group->iommu_group) == &noiommu)
 			iommu_group_remove_device(device->dev);
 #endif
 		vfio_group_put(group);