nixpkgs/nixos/modules/tasks/scsi-link-power-management.nix

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{ config, lib, pkgs, ... }:
with lib;
{
###### interface
options = {
powerManagement.scsiLinkPolicy = mkOption {
default = "";
example = "min_power";
type = types.str;
description = ''
Configure the SCSI link power management policy. By default,
the kernel configures "max_performance".
'';
};
};
###### implementation
config = mkIf (config.powerManagement.scsiLinkPolicy != "") {
jobs."scsi-link-pm" =
{ description = "SCSI Link Power Management Policy";
startOn = "stopped udevtrigger";
task = true;
unitConfig.ConditionPathIsReadWrite = "/sys/class/scsi_host";
script = ''
shopt -s nullglob
for x in /sys/class/scsi_host/host*/link_power_management_policy; do
echo ${config.powerManagement.scsiLinkPolicy} > $x
done
'';
};
};
}