Current File : //usr/lib/udev/rules.d/40-elevator.rules

# We aren't adding devices skip the elevator check
ACTION!="add", GOTO="sched_out"

SUBSYSTEM!="block", GOTO="sched_out"
ENV{DEVTYPE}!="disk", GOTO="sched_out"

# Technically, dm-multipath can be configured to use an I/O scheduler.
# However, there are races between the 'add' uevent and the linking in
# of the queue/scheduler sysfs file.  For now, just skip dm- devices.
KERNEL=="dm-*|md*", GOTO="sched_out"

# Skip bio-based devices, which don't support an I/O scheduler.
ATTR{queue/scheduler}=="none", GOTO="sched_out"

# If elevator= is specified on the kernel command line, change the
# scheduler to the one specified.
IMPORT{cmdline}="elevator"
ENV{elevator}!="", ATTR{queue/scheduler}="$env{elevator}"

LABEL="sched_out"