• Damien Le Moal's avatar
    block: Introduce elevator features · 68c43f13
    Damien Le Moal authored
    Introduce the definition of elevator features through the
    elevator_features flags in the elevator_type structure. Each flag can
    represent a feature supported by an elevator. The first feature defined
    by this patch is support for zoned block device sequential write
    constraint with the flag ELEVATOR_F_ZBD_SEQ_WRITE, which is implemented
    by the mq-deadline elevator using zone write locking.
    
    Other possible features are IO priorities, write hints, latency targets
    or single-LUN dual-actuator disks (for which the elevator could maintain
    one LBA ordered list per actuator).
    
    The required_elevator_features field is also added to the request_queue
    structure to allow a device driver to specify elevator feature flags
    that an elevator must support for the correct operation of the device
    (e.g. device drivers for zoned block devices can have the
    ELEVATOR_F_ZBD_SEQ_WRITE flag as a required feature).
    The helper function blk_queue_required_elevator_features() is
    defined for setting this new field.
    
    With these two new fields in place, the elevator functions
    elevator_match() and elevator_find() are modified to allow a user to set
    only an elevator with a set of features that satisfies the device
    required features. Elevators not matching the device requirements are
    not shown in the device sysfs queue/scheduler file to prevent their use.
    
    The "none" elevator can always be selected as before.
    Reviewed-by: default avatarJohannes Thumshirn <jthumshirn@suse.de>
    Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
    Reviewed-by: default avatarMing Lei <ming.lei@redhat.com>
    Signed-off-by: default avatarDamien Le Moal <damien.lemoal@wdc.com>
    Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
    68c43f13
blk-settings.c 27.4 KB