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;