dm mpath: add optional "queue_mode" feature

Allow a user to specify an optional feature 'queue_mode <mode>' where
<mode> may be "bio", "rq" or "mq" -- which corresponds to bio-based,
request_fn rq-based, and blk-mq rq-based respectively.

If the queue_mode feature isn't specified the default for the
"multipath" target is still "rq" but if dm_mod.use_blk_mq is set to Y
it'll default to mode "mq".

This new queue_mode feature introduces the ability for each multipath
device to have its own queue_mode (whereas before this feature all
multipath devices effectively had to have the same queue_mode).

This commit also goes a long way to eliminate the awkward (ab)use of
DM_TYPE_*, the associated filter_md_type() and other relatively fragile
and difficult to maintain code.

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

1 files changed, 2 insertions, 13 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 8f22527134e9..2c907bc10fe9 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1738,23 +1738,14 @@ struct queue_limits *dm_get_queue_limits(struct mapped_device *md)
 }
 EXPORT_SYMBOL_GPL(dm_get_queue_limits);
 
-static unsigned filter_md_type(unsigned type, struct mapped_device *md)
-{
-	if (type == DM_TYPE_BIO_BASED)
-		return type;
-
-	return !md->use_blk_mq ? DM_TYPE_REQUEST_BASED : DM_TYPE_MQ_REQUEST_BASED;
-}
-
 /*
  * Setup the DM device's queue based on md's type
  */
 int dm_setup_md_queue(struct mapped_device *md, struct dm_table *t)
 {
 	int r;
-	unsigned md_type = filter_md_type(dm_get_md_type(md), md);
 
-	switch (md_type) {
+	switch (dm_get_md_type(md)) {
 	case DM_TYPE_REQUEST_BASED:
 		r = dm_old_init_request_queue(md);
 		if (r) {
@@ -1763,7 +1754,7 @@ int dm_setup_md_queue(struct mapped_device *md, struct dm_table *t)
 		}
 		break;
 	case DM_TYPE_MQ_REQUEST_BASED:
-		r = dm_mq_init_request_queue(md, dm_table_get_immutable_target(t));
+		r = dm_mq_init_request_queue(md, t);
 		if (r) {
 			DMERR("Cannot initialize queue for request-based dm-mq mapped device");
 			return r;
@@ -2472,8 +2463,6 @@ struct dm_md_mempools *dm_alloc_md_mempools(struct mapped_device *md, unsigned t
 	if (!pools)
 		return NULL;
 
-	type = filter_md_type(type, md);
-
 	switch (type) {
 	case DM_TYPE_BIO_BASED:
 		cachep = _io_cache;