That being said ->make_request basically doesn't care about actual
limits at all, it mostly care about support features (e.g. discard, fua,
etc). So I think a lot of these limits could porbably be lifted,
but I'd need to add the check to generic_make_request_checks back.
Different virt_boundary capabilities will trigger bio splits which
can make make_request blocking (due to lack of tags).
All the bio splitting is done in blk_queue_split, and other things
related to limits are done even later in blk_mq_make_request when
building the request. For normal make_request based stacking drivers
nothing of this matters, although a few drivers t call blk_queue_split
manually from their make_request method.
Maybe I misunderstood the change log comment, but didn't it said that
the caller is not allowed to submit a bio that might split?
