Re: [PATCH 1/7] block: add a ->get_unique_id method

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

On 10/12/21 5:04 AM, Christoph Hellwig wrote:
> Add a method to query query uniqueue IDs from block devices.  It will be
> used to remove code that deeply pokes into SCSI internals in the NFS
> server.  The implementation in the sd driver itself can also be much
> nicer as it can use the cached VPD page instead of always sending a
> command as the current NFS code does.
> 
> For now the interface is kept very minimal but could be easily
> extended when other users like a block-layer sysfs interface for
> uniquue IDs shows up.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   include/linux/blkdev.h | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 17705c970d7e1..81f94a7c54521 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -1188,6 +1188,7 @@ struct block_device_operations {
>   	int (*report_zones)(struct gendisk *, sector_t sector,
>   			unsigned int nr_zones, report_zones_cb cb, void *data);
>   	char *(*devnode)(struct gendisk *disk, umode_t *mode);
> +	int (*get_unique_id)(struct gendisk *disk, u8 id[16], u8 id_type);
>   	struct module *owner;
>   	const struct pr_ops *pr_ops;

Please document the meaning of the 'u8 id_type' argument, how callers 
can determine the length of the unique ID and what the meaning of the 
return value is.

Thanks,

Bart.