On Thu, May 07, 2020 at 05:22:28PM +0200, Stefan Haberland wrote:

OK, just thought again about your suggestion and also that
you have already been talking about a symbol lookup I just
have written a prototype that took your first two patches
as base, exports the symbol of dasd_biodasdinfo and in
ibm.c I do a kallsyms_lookup_name("dasd_biodasdinfo").

So I would not have to define a structure twice or rely on
MAJORs. Also we would not have to define an own file
operation only for DASD devices.

What do you think about this? If you agree I will polish
the patches, test them and send them for review.

How do you figure out a given gendisk is a DASD device?  I guess
dasd_biodasdinfo could just check the block_device_operations
pointer first thing.  That's still a little ugly, but seems the
least bad idea so far, so please at least post it for discussion.