[PATCH block/for-5.2-fixes] bfq: use io.weight interface file instead of io.bfq.weight

[Tejun Heo <tj@kernel.org>]

(Description mostly stolen from 19e9da9e86c4 ("block, bfq: add weight
symlink to the bfq.weight cgroup parameter")

Many userspace tools and services use the proportional-share policy of
the blkio/io cgroups controller. The CFQ I/O scheduler implemented
this policy for the legacy block layer. To modify the weight of a
group in case CFQ was in charge, the 'weight' parameter of the group
must be modified. On the other hand, the BFQ I/O scheduler implements
the same policy in blk-mq, but, with BFQ, the parameter to modify has
a different name: bfq.weight (forced choice until legacy block was
present, because two different policies cannot share a common
parameter in cgroups).

Due to CFQ legacy, most if not all userspace configurations still use
the parameter 'weight', and for the moment do not seem likely to be
changed. But, when CFQ went away with legacy block, such a parameter
ceased to exist.

19e9da9e86c4 ("block, bfq: add weight symlink to the bfq.weight cgroup
parameter") tried to solve the problem by creating a symlink but there
doesn't seem to be a good reason for the added complexity.  Make bfq
simply create interface file io.weight instead of io.bfq.weight.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Paolo Valente <paolo.valente@linaro.org>
Cc: Angelo Ruocco <angeloruocco90@gmail.com>
---
 block/bfq-cgroup.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index b3796a40a61a..c68c6aa22154 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -1045,8 +1045,8 @@ struct blkcg_policy blkcg_policy_bfq = {
 
 struct cftype bfq_blkcg_legacy_files[] = {
 	{
-		.name = "bfq.weight",
-		.flags = CFTYPE_NOT_ON_ROOT,
+		.name = "io.weight",
+		.flags = CFTYPE_NOT_ON_ROOT | CFTYPE_NO_PREFIX,
 		.seq_show = bfq_io_show_weight,
 		.write_u64 = bfq_io_set_weight_legacy,
 	},
@@ -1165,8 +1165,8 @@ struct cftype bfq_blkcg_legacy_files[] = {
 
 struct cftype bfq_blkg_files[] = {
 	{
-		.name = "bfq.weight",
-		.flags = CFTYPE_NOT_ON_ROOT,
+		.name = "io.weight",
+		.flags = CFTYPE_NOT_ON_ROOT | CFTYPE_NO_PREFIX,
 		.seq_show = bfq_io_show_weight,
 		.write = bfq_io_set_weight,
 	},