Re: [PATCH v11 23/26] block/rnbd: server: sysfs interface functions

[Bart Van Assche <bvanassche@acm.org>]

On 2020-03-20 05:16, Jack Wang wrote:
> This is the sysfs interface to rnbd mapped devices on server side:
> 
>   /sys/devices/virtual/rnbd-server/ctl/devices/<device_name>/
>     |- block_dev
>     |  *** link pointing to the corresponding block device sysfs entry
>     |
>     |- sessions/<session-name>/
>     |  *** sessions directory
>        |
>        |- read_only
>        |  *** is devices mapped as read only
>        |
>        |- mapping_path
>           *** relative device path provided by the client during mapping
> 

> +static struct kobj_type ktype = {
> +	.sysfs_ops	= &kobj_sysfs_ops,
> +};

From Documentation/kobject.txt: "One important point cannot be
overstated: every kobject must have a release() method." I think this is
something that Greg KH feels very strongly about. Please fix this.

> +int rnbd_srv_create_dev_sysfs(struct rnbd_srv_dev *dev,
> +			       struct block_device *bdev,
> +			       const char *dir_name)
> +{
> +	struct kobject *bdev_kobj;
> +	int ret;
> +
> +	ret = kobject_init_and_add(&dev->dev_kobj, &ktype,
> +				   rnbd_devs_kobj, dir_name);
> +	if (ret)
> +		return ret;
> +
> +	ret = kobject_init_and_add(&dev->dev_sessions_kobj,
> +				   &ktype,
> +				   &dev->dev_kobj, "sessions");
> +	if (ret)
> +		goto err;
> +
> +	bdev_kobj = &disk_to_dev(bdev->bd_disk)->kobj;
> +	ret = sysfs_create_link(&dev->dev_kobj, bdev_kobj, "block_dev");
> +	if (ret)
> +		goto err2;
> +
> +	return 0;
> +
> +err2:
> +	kobject_put(&dev->dev_sessions_kobj);
> +err:
> +	kobject_put(&dev->dev_kobj);
> +	return ret;
> +}

Please choose more descriptive names for the goto labels, e.g.
put_sess_kobj and put_dev_kobj.

> +static ssize_t read_only_show(struct kobject *kobj, struct kobj_attribute *attr,
> +			      char *page)
> +{
> +	struct rnbd_srv_sess_dev *sess_dev;
> +
> +	sess_dev = container_of(kobj, struct rnbd_srv_sess_dev, kobj);
> +
> +	return scnprintf(page, PAGE_SIZE, "%s\n",
> +			 (sess_dev->open_flags & FMODE_WRITE) ? "0" : "1");
> +}

The scnprintf() statement looks overcomplicated. How about the following?

return scnprintf(page, PAGE_SIZE, "%d\n",
                 (sess_dev->open_flags & FMODE_WRITE) != 0);

> +void rnbd_srv_destroy_dev_session_sysfs(struct rnbd_srv_sess_dev *sess_dev)
> +{
> +	DECLARE_COMPLETION_ONSTACK(sysfs_compl);
> +
> +	sysfs_remove_group(&sess_dev->kobj,
> +			   &rnbd_srv_default_dev_session_attr_group);
> +
> +	sess_dev->sysfs_release_compl = &sysfs_compl;
> +	kobject_del(&sess_dev->kobj);
> +	kobject_put(&sess_dev->kobj);
> +	wait_for_completion(&sysfs_compl);
> +}

Why is there a wait_for_completion() call in the above function? I think
Greg KH strongly disagrees with such calls in functions that remove
sysfs attributes.

> +int rnbd_srv_create_sysfs_files(void)
> +{
> +	int err;
> +
> +	rnbd_dev_class = class_create(THIS_MODULE, "rnbd-server");
> +	if (IS_ERR(rnbd_dev_class))
> +		return PTR_ERR(rnbd_dev_class);
> +
> +	rnbd_dev = device_create(rnbd_dev_class, NULL,
> +				  MKDEV(0, 0), NULL, "ctl");
> +	if (IS_ERR(rnbd_dev)) {
> +		err = PTR_ERR(rnbd_dev);
> +		goto cls_destroy;
> +	}
> +	rnbd_devs_kobj = kobject_create_and_add("devices", &rnbd_dev->kobj);
> +	if (!rnbd_devs_kobj) {
> +		err = -ENOMEM;
> +		goto dev_destroy;
> +	}
> +
> +	return 0;
> +
> +dev_destroy:
> +	device_destroy(rnbd_dev_class, MKDEV(0, 0));
> +cls_destroy:
> +	class_destroy(rnbd_dev_class);
> +
> +	return err;
> +}

Please mention the device class in the description of this patch.

Thanks,

Bart.