vfio: Add struct device to vfio_device

and replace kref. With it a 'vfio-dev/vfioX' node is created under the
sysfs path of the parent, indicating the device is bound to a vfio
driver, e.g.:

/sys/devices/pci0000\:6f/0000\:6f\:01.0/vfio-dev/vfio0

It is also a preparatory step toward adding cdev for supporting future
device-oriented uAPI.

Add Documentation/ABI/testing/sysfs-devices-vfio-dev.

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Signed-off-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20220921104401.38898-16-kevin.tian@intel.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

Documentation/ABI/testing/sysfs-devices-vfio-dev

@@ -0,0 +1,8 @@
+What:		 /sys/.../<device>/vfio-dev/vfioX/
+Date:		 September 2022
+Contact:	 Yi Liu <yi.l.liu@intel.com>
+Description:
+		 This directory is created when the device is bound to a
+		 vfio driver. The layout under this directory matches what
+		 exists for a standard 'struct device'. 'X' is a unique
+		 index marking this device in vfio.

MAINTAINERS

@@ -21312,6 +21312,7 @@ R:	Cornelia Huck <cohuck@redhat.com>
 L:	kvm@vger.kernel.org
 S:	Maintained
 T:	git git://github.com/awilliam/linux-vfio.git
+F:	Documentation/ABI/testing/sysfs-devices-vfio-dev
 F:	Documentation/driver-api/vfio.rst
 F:	drivers/vfio/
 F:	include/linux/vfio.h

drivers/vfio/vfio_main.c

@@ -49,6 +49,8 @@ static struct vfio {
 	struct mutex			group_lock; /* locks group_list */
 	struct ida			group_ida;
 	dev_t				group_devt;
+	struct class			*device_class;
+	struct ida			device_ida;
 } vfio;
 
 struct vfio_iommu_driver {
@@ -485,12 +487,13 @@ static struct vfio_device *vfio_group_get_device(struct vfio_group *group,
  * VFIO driver API
  */
 /* Release helper called by vfio_put_device() */
-void vfio_device_release(struct kref *kref)
+static void vfio_device_release(struct device *dev)
 {
 	struct vfio_device *device =
-			container_of(kref, struct vfio_device, kref);
+			container_of(dev, struct vfio_device, device);
 
 	vfio_release_device_set(device);
+	ida_free(&vfio.device_ida, device->index);
 
 	/*
 	 * kvfree() cannot be done here due to a life cycle mess in
@@ -500,7 +503,6 @@ void vfio_device_release(struct kref *kref)
 	 */
 	device->ops->release(device);
 }
-EXPORT_SYMBOL_GPL(vfio_device_release);
 
 /*
  * Allocate and initialize vfio_device so it can be registered to vfio
@@ -548,6 +550,13 @@ int vfio_init_device(struct vfio_device *device, struct device *dev,
 {
 	int ret;
 
+	ret = ida_alloc_max(&vfio.device_ida, MINORMASK, GFP_KERNEL);
+	if (ret < 0) {
+		dev_dbg(dev, "Error to alloc index\n");
+		return ret;
+	}
+
+	device->index = ret;
 	init_completion(&device->comp);
 	device->dev = dev;
 	device->ops = ops;
@@ -558,11 +567,15 @@ int vfio_init_device(struct vfio_device *device, struct device *dev,
 			goto out_uninit;
 	}
 
-	kref_init(&device->kref);
+	device_initialize(&device->device);
+	device->device.release = vfio_device_release;
+	device->device.class = vfio.device_class;
+	device->device.parent = device->dev;
 	return 0;
 
 out_uninit:
 	vfio_release_device_set(device);
+	ida_free(&vfio.device_ida, device->index);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(vfio_init_device);
@@ -659,6 +672,7 @@ static int __vfio_register_dev(struct vfio_device *device,
 		struct vfio_group *group)
 {
 	struct vfio_device *existing_device;
+	int ret;
 
 	if (IS_ERR(group))
 		return PTR_ERR(group);
@@ -675,16 +689,21 @@ static int __vfio_register_dev(struct vfio_device *device,
 		dev_WARN(device->dev, "Device already exists on group %d\n",
 			 iommu_group_id(group->iommu_group));
 		vfio_device_put_registration(existing_device);
-		if (group->type == VFIO_NO_IOMMU ||
-		    group->type == VFIO_EMULATED_IOMMU)
-			iommu_group_remove_device(device->dev);
-		vfio_group_put(group);
-		return -EBUSY;
+		ret = -EBUSY;
+		goto err_out;
 	}
 
 	/* Our reference on group is moved to the device */
 	device->group = group;
 
+	ret = dev_set_name(&device->device, "vfio%d", device->index);
+	if (ret)
+		goto err_out;
+
+	ret = device_add(&device->device);
+	if (ret)
+		goto err_out;
+
 	/* Refcounting can't start until the driver calls register */
 	refcount_set(&device->refcount, 1);
 
@@ -693,6 +712,12 @@ static int __vfio_register_dev(struct vfio_device *device,
 	mutex_unlock(&group->device_lock);
 
 	return 0;
+err_out:
+	if (group->type == VFIO_NO_IOMMU ||
+	    group->type == VFIO_EMULATED_IOMMU)
+		iommu_group_remove_device(device->dev);
+	vfio_group_put(group);
+	return ret;
 }
 
 int vfio_register_group_dev(struct vfio_device *device)
@@ -779,6 +804,9 @@ void vfio_unregister_group_dev(struct vfio_device *device)
 	list_del(&device->group_next);
 	mutex_unlock(&group->device_lock);
 
+	/* Balances device_add in register path */
+	device_del(&device->device);
+
 	if (group->type == VFIO_NO_IOMMU || group->type == VFIO_EMULATED_IOMMU)
 		iommu_group_remove_device(device->dev);
 
@@ -2362,6 +2390,7 @@ static int __init vfio_init(void)
 	int ret;
 
 	ida_init(&vfio.group_ida);
+	ida_init(&vfio.device_ida);
 	mutex_init(&vfio.group_lock);
 	mutex_init(&vfio.iommu_drivers_lock);
 	INIT_LIST_HEAD(&vfio.group_list);
@@ -2377,11 +2406,18 @@ static int __init vfio_init(void)
 	vfio.class = class_create(THIS_MODULE, "vfio");
 	if (IS_ERR(vfio.class)) {
 		ret = PTR_ERR(vfio.class);
-		goto err_class;
+		goto err_group_class;
 	}
 
 	vfio.class->devnode = vfio_devnode;
 
+	/* /sys/class/vfio-dev/vfioX */
+	vfio.device_class = class_create(THIS_MODULE, "vfio-dev");
+	if (IS_ERR(vfio.device_class)) {
+		ret = PTR_ERR(vfio.device_class);
+		goto err_dev_class;
+	}
+
 	ret = alloc_chrdev_region(&vfio.group_devt, 0, MINORMASK + 1, "vfio");
 	if (ret)
 		goto err_alloc_chrdev;
@@ -2398,9 +2434,12 @@ static int __init vfio_init(void)
 err_driver_register:
 	unregister_chrdev_region(vfio.group_devt, MINORMASK + 1);
 err_alloc_chrdev:
+	class_destroy(vfio.device_class);
+	vfio.device_class = NULL;
+err_dev_class:
 	class_destroy(vfio.class);
 	vfio.class = NULL;
-err_class:
+err_group_class:
 	misc_deregister(&vfio_dev);
 	return ret;
 }
@@ -2412,8 +2451,11 @@ static void __exit vfio_cleanup(void)
 #ifdef CONFIG_VFIO_NOIOMMU
 	vfio_unregister_iommu_driver(&vfio_noiommu_ops);
 #endif
+	ida_destroy(&vfio.device_ida);
 	ida_destroy(&vfio.group_ida);
 	unregister_chrdev_region(vfio.group_devt, MINORMASK + 1);
+	class_destroy(vfio.device_class);
+	vfio.device_class = NULL;
 	class_destroy(vfio.class);
 	vfio.class = NULL;
 	misc_deregister(&vfio_dev);

include/linux/vfio.h

@@ -47,7 +47,8 @@ struct vfio_device {
 	struct kvm *kvm;
 
 	/* Members below here are private, not for driver use */
-	struct kref kref;	/* object life cycle */
+	unsigned int index;
+	struct device device;	/* device.kref covers object life circle */
 	refcount_t refcount;	/* user count on registered device*/
 	unsigned int open_count;
 	struct completion comp;
@@ -178,10 +179,9 @@ struct vfio_device *_vfio_alloc_device(size_t size, struct device *dev,
 int vfio_init_device(struct vfio_device *device, struct device *dev,
 		     const struct vfio_device_ops *ops);
 void vfio_free_device(struct vfio_device *device);
-void vfio_device_release(struct kref *kref);
 static inline void vfio_put_device(struct vfio_device *device)
 {
-	kref_put(&device->kref, vfio_device_release);
+	put_device(&device->device);
 }
 
 int vfio_register_group_dev(struct vfio_device *device);