arc-patches/iosched-trampoline.sh
2024-01-22 19:07:12 +01:00

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#!/usr/bin/sh
# This script is saved to /sbin/modprobe which is a so called UMH (user-mode-helper) for kmod (kernel/kmod.c)
# The kmod subsystem in the kernel is used to load modules from kernel. We exploit it a bit to load RP as soon as
# possible (which turns out to be via init/main.c => load_default_modules => load_default_elevator_module
# When the kernel is booted with "elevator=elevator" it will attempt to load a module "elevator-iosched"... and the rest
# should be obvious from the code below. DO NOT print anything here (kernel doesn't attach STDOUT)
for arg in "$@"; do
if [ "${arg}" = "elevator-iosched" ]; then
insmod /usr/lib/modules/rp.ko
rm /usr/lib/modules/rp.ko
rm /usr/sbin/modprobe
ln -s /usr/bin/kmod /usr/sbin/modprobe
exit 0
fi
done
exit 1