dm: add 'use_blk_mq' module param and expose in per-device ro sysfs attr

Request-based DM's blk-mq support defaults to off; but a user can easily
change the default using the dm_mod.use_blk_mq module/boot option.

Also, you can check what mode a given request-based DM device is using
with: cat /sys/block/dm-X/dm/use_blk_mq

This change enabled further cleanup and reduced work (e.g. the
md->io_pool and md->rq_pool isn't created if using blk-mq).

Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/drivers/md/dm.h b/drivers/md/dm.h
index 5522422cc6c4..6123c2bf9150 100644
--- a/drivers/md/dm.h
+++ b/drivers/md/dm.h
@@ -211,6 +211,8 @@ int dm_kobject_uevent(struct mapped_device *md, enum kobject_action action,
 void dm_internal_suspend(struct mapped_device *md);
 void dm_internal_resume(struct mapped_device *md);
 
+bool dm_use_blk_mq(struct mapped_device *md);
+
 int dm_io_init(void);
 void dm_io_exit(void);
 
@@ -220,7 +222,8 @@ void dm_kcopyd_exit(void);
 /*
  * Mempool operations
  */
-struct dm_md_mempools *dm_alloc_md_mempools(unsigned type, unsigned integrity, unsigned per_bio_data_size);
+struct dm_md_mempools *dm_alloc_md_mempools(struct mapped_device *md, unsigned type,
+                                            unsigned integrity, unsigned per_bio_data_size);
 void dm_free_md_mempools(struct dm_md_mempools *pools);
 
 /*