The CentOS stream 4.18.0-257 kernel appears to have backported
the Linux 5.9 change to make_request_fn and the associated API.
To maintain weak modules compatibility the original symbol was
retained and the new interface blk_alloc_queue_rh() was added.
Unfortunately, blk_alloc_queue() was replaced in the blkdev.h
header by blk_alloc_queue_bh() so there doesn't seem to be a way
to build new kmods against the old interfces. Even though they
appear to still be available for weak module binding.
To accommodate this a configure check is added for the new _rh()
variant of the function and used if available. If compatibility
code gets added to the kernel for the original blk_alloc_queue()
interface this should be fine. OpenZFS will simply continue to
prefer the new interface and only fallback to blk_alloc_queue()
when blk_alloc_queue_rh() isn't available.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#11374
6152014d1a