Re: [PATCH] dm: add support for get_unique_id

[Christoph Hellwig <hch@lst.de>]

On Wed, Oct 30, 2024 at 08:57:56AM -0400, Benjamin Coddington wrote:
> This adds support to obtain a device's unique id through dm, similar to the
> existing ioctl and persistent resevation handling.  We limit this to
> single-target devices.
> 
> This enables knfsd to export pNFS SCSI luns that have been exported from
> multipath devices.

Is there anything that ensures that the underlying IDs actually
match?

> +	struct dm_unique_id *dmuuid = data;
> +	const struct block_device_operations *fops = dev->bdev->bd_disk->fops;
> +
> +	if (fops->get_unique_id)
> +		return fops->get_unique_id(dev->bdev->bd_disk, dmuuid->id, dmuuid->type);
> +
> +	return 0;

Overly long line here.  Also maybe just personal, but I find code easier
to read when the exit early condition is in the branch, e.g.

	strut gendisk *disk = dev->bdev->bd_disk

	if (!disk->fops->get_unique_id)
		return 0;
	return disk->fops->get_unique_id(disk, dmuuid->id, dmuuid->type);