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>

diff --git a/Documentation/ABI/testing/sysfs-block-dm b/Documentation/ABI/testing/sysfs-block-dm
index ac4b6fe..f9f2339 100644 (file)
--- a/Documentation/ABI/testing/sysfs-block-dm
+++ b/Documentation/ABI/testing/sysfs-block-dm
@@ -37,3 +37,11 @@ Description: Allow control over how long a request that is a
                accounting.  This attribute is not applicable to
                bio-based DM devices so it will only ever report 0 for
                them.
+
+What:          /sys/block/dm-<num>/dm/use_blk_mq
+Date:          March 2015
+KernelVersion: 4.1
+Contact:       dm-devel@redhat.com
+Description:   Request-based Device-mapper blk-mq I/O path mode.
+               Contains the value 1 if the device is using blk-mq.
+               Otherwise it contains 0. Read-only attribute.

diff --cc drivers/md/Kconfig
Simple merge

diff --cc drivers/md/dm-sysfs.c
Simple merge

diff --cc drivers/md/dm-table.c
Simple merge

diff --cc drivers/md/dm.c
Simple merge

diff --cc drivers/md/dm.h
Simple merge