If a SCSI device handler module is loaded after some SCSI devices have
already been probed (e.g. via request_module() by dm-multipath), the
"access_state" and "preferred_path" sysfs attributes remain invisible for
these devices, although the handler is attached and live. The reason is
that the visibility is only checked when the sysfs attribute group is first
created. This results in an inconsistent user experience depending on the
load order of SCSI low-level drivers vs. device handler modules.

This patch changes user space API: attempting to read the "access_state" or
"preferred_path" attributes will now result in -EINVAL rather than -ENODEV
for devices that have no device handler, and tests for the existence of
these attributes will have a different result.

Link: https://lore.kernel.org/r/20220127141351.30706-1-mwilck@suse.comReviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin Wilck <mwilck@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>