[PATCH 0/7] Elevator cleanups and improvements

[Damien Le Moal <damien.lemoal@wdc.com>]

This patch series implements some cleanup of the elevator initialization
code and introduces elevator features identification and device matching
to enhance checks for elevator/device compatibility and fitness.

The first 3 patches of the series are simple cleanups which simplify and
streamline elevator initialization for newly allocated device queues.

The following two patches introduce elevator features control which
allow defining features and function that an elevator supports and match
these against features required by a block device driver. With this, the
sysfs elevator list for a device always only shows elevators matching
the features that a particular device requires, with the exception of
the none elevator which has no features but is always available for use
with any device.

The first feature defined is for zoned block device write order control
through zone write locking which prevents the use of any scheduler that
does not support this feature with zoned devices.

The last 2 patches of this series rework the default elevator selection
and initialization to allow for the feature matching to work,
simultaneously addressing cases not currently well supported, namely,
multi-queue zoned block devices.

Damien Le Moal (7):
  block: Cleanup elevator_init_mq() use
  block: Change elevator_init_mq() to always succeed
  block: Remove sysfs lock from elevator_init_rq()
  block: Introduce elevator features
  block: Introduce zoned block device elevator feature
  block: Improve default elevator selection
  block: Delay default elevator initialization

 block/blk-mq.c                |  10 ---
 block/blk-settings.c          |  15 ++++
 block/blk.h                   |   2 +-
 block/elevator.c              | 144 +++++++++++++++++++++++++---------
 block/genhd.c                 |   3 +
 block/mq-deadline.c           |   1 +
 drivers/block/null_blk_main.c |   5 ++
 drivers/scsi/sd_zbc.c         |   2 +
 include/linux/blkdev.h        |   4 +
 include/linux/elevator.h      |   8 ++
 10 files changed, 147 insertions(+), 47 deletions(-)

-- 
2.21.0