[PATCH V2] nvme: enable char device per namespace

[Christoph Hellwig]

A bunch of nitpicks (mostly naming as usual, sorry..):

> +static int __nvme_ns_ioctl(struct gendisk *disk, unsigned int cmd,
> +			   unsigned long arg)
>  {

What about nvme_disk_ioctl instead as that is what it operates on?

> +static int nvme_ioctl(struct block_device *bdev, fmode_t mode,
> +		      unsigned int cmd, unsigned long arg)
> +{
> +	return __nvme_ns_ioctl(bdev->bd_disk, cmd, arg);
> +}
> +
> +static long nvme_cdev_ioctl(struct file *file, unsigned int cmd,
> +			    unsigned long arg)
> +{
> +	return __nvme_ns_ioctl((struct gendisk *)file->private_data, cmd, arg);
> +}

No need for the cast.

Also can we keep all the char device methods together close to the
struct file_operations declaration?  I just prefer to keep the code
a little grouped.

> -static int nvme_open(struct block_device *bdev, fmode_t mode)
> +static int __nvme_open(struct nvme_ns *ns)
>  {
> -	struct nvme_ns *ns = bdev->bd_disk->private_data;
> -
>  #ifdef CONFIG_NVME_MULTIPATH
>  	/* should never be called due to GENHD_FL_HIDDEN */
>  	if (WARN_ON_ONCE(ns->head->disk))
> @@ -1846,12 +1859,24 @@ static int nvme_open(struct block_device *bdev, fmode_t mode)
>  	return -ENXIO;
>  }
>  
> +static void __nvme_release(struct nvme_ns *ns)
> +{
> +	module_put(ns->ctrl->ops->module);
> +	nvme_put_ns(ns);
> +}

nvme_ns_open and nvme_ns_release?

> +
> +static int nvme_open(struct block_device *bdev, fmode_t mode)
> +{
> +	struct nvme_ns *ns = bdev->bd_disk->private_data;
> +
> +	return __nvme_open(ns);
> +}
> +
>  static void nvme_release(struct gendisk *disk, fmode_t mode)
>  {
>  	struct nvme_ns *ns = disk->private_data;
>  
> -	module_put(ns->ctrl->ops->module);
> -	nvme_put_ns(ns);
> +	__nvme_release(ns);

No need for the local ns variable in both cases.

> +static int nvme_cdev_open(struct inode *inode, struct file *file)
> +{
> +	struct nvme_ns *ns = container_of(inode->i_cdev, struct nvme_ns, cdev);
> +	int ret;
> +
> +	ret = __nvme_open(ns);
> +	if (!ret)
> +		file->private_data = ns->disk;
> +
> +	return ret;

Do we need the ->private_data assignment at all?  I think the ioctl
handler could just grab it directly from i_cdev.

> +	sprintf(cdisk_name, "nvme%dn%dc", ctrl->instance, ns->head->instance);

And the most important naming decision is this.  I have two issues with
naming still:

 - we aready use the c for controller in the hidden disk naming.  Although
   that is in a different position, but I think this not super intuitive.
 - this is missing multipath support entirely, so once we want to add
   multipath support we'll run into issues.  So maybe use something
   based off the hidden node naming?  E.g.:

	sprintf(disk_name, "nvme-generic-%dc%dn%d", ctrl->subsys->instance,
		ctrl->instance, ns->head->instance);

> +	/* When the device does not support any of the features required by the
> +	 * kernel (or viceversa), hide the block device. We can still rely on
> +	 * the namespace char device for submitting IOCTLs
> +	 */

Normal kernel comment style is the opening

	/*

on its own line.

>  	if (nvme_update_ns_info(ns, id))
> -		goto out_put_disk;
> +		disk->flags |= GENHD_FL_HIDDEN;

I don't think we can do this based on all the error returns.  I think
we'll have to move the flags manipulation into nvme_update_ns_info to
also cover the revalidate case.