blob: 6fa9bd1ddc0940a357a8f8c6dc4f9c8c73ac0a77 [file] [log] [blame]
# SPDX-License-Identifier: GPL-2.0+
# Create an initrd directory if one does not already exist.
# Copyright (C) IBM Corporation, 2013
# Author: Connor Shu <>
# Prerequisite checks
[ -z "$D" ] && echo >&2 "No argument supplied" && exit 1
if [ ! -d "$D" ]; then
echo >&2 "$D does not exist: Malformed kernel source tree?"
exit 1
if [ -s "$D/initrd/init" ]; then
echo "$D/initrd/init already exists, no need to create it"
exit 0
trap 'rm -rf $T' 0 2
mkdir $T
cat > $T/init << '__EOF___'
# Run in userspace a few milliseconds every second. This helps to
# exercise the NO_HZ_FULL portions of RCU. The 192 instances of "a" was
# empirically shown to give a nice multi-millisecond burst of user-mode
# execution on a 2GHz CPU, as desired. Modern CPUs will vary from a
# couple of milliseconds up to perhaps 100 milliseconds, which is an
# acceptable range.
# Why not calibrate an exact delay? Because within this initrd, we
# are restricted to Bourne-shell builtins, which as far as I know do not
# provide any means of obtaining a fine-grained timestamp.
a4="a a a a"
a16="$a4 $a4 $a4 $a4"
a64="$a16 $a16 $a16 $a16"
a192="$a64 $a64 $a64"
while :
for i in $a192
q="$q $i"
sleep 1
# Try using dracut to create initrd
if command -v dracut >/dev/null 2>&1
echo Creating $D/initrd using dracut.
# Filesystem creation
dracut --force --no-hostonly --no-hostonly-cmdline --module "base" $T/initramfs.img
cd $D
mkdir -p initrd
cd initrd
zcat $T/initramfs.img | cpio -id
cp $T/init init
chmod +x init
echo Done creating $D/initrd using dracut
exit 0
# No dracut, so create a C-language initrd/init program and statically
# link it. This results in a very small initrd, but might be a bit less
# future-proof than dracut.
echo "Could not find dracut, attempting C initrd"
cd $D
mkdir -p initrd
cd initrd
cat > init.c << '___EOF___'
#ifndef NOLIBC
#include <unistd.h>
#include <sys/time.h>
volatile unsigned long delaycount;
int main(int argc, int argv[])
int i;
struct timeval tv;
struct timeval tvb;
for (;;) {
/* Need some userspace time. */
if (gettimeofday(&tvb, NULL))
do {
for (i = 0; i < 1000 * 100; i++)
delaycount = i * i;
if (gettimeofday(&tv, NULL))
tv.tv_sec -= tvb.tv_sec;
if (tv.tv_sec > 1)
tv.tv_usec += tv.tv_sec * 1000 * 1000;
tv.tv_usec -= tvb.tv_usec;
} while (tv.tv_usec < 1000);
return 0;
# build using nolibc on supported archs (smaller executable) and fall
# back to regular glibc on other ones.
if echo -e "#if __x86_64__||__i386__||__i486__||__i586__||__i686__" \
"||__ARM_EABI__||__aarch64__\nyes\n#endif" \
| ${CROSS_COMPILE}gcc -E -nostdlib -xc - \
| grep -q '^yes'; then
# architecture supported by nolibc
${CROSS_COMPILE}gcc -fno-asynchronous-unwind-tables -fno-ident \
-nostdlib -include ../../../../include/nolibc/nolibc.h \
-lgcc -s -static -Os -o init init.c
${CROSS_COMPILE}gcc -s -static -Os -o init init.c
rm init.c
echo "Done creating a statically linked C-language initrd"
exit 0