__EOF___
# Try using dracut to create initrd
-command -v dracut >/dev/null 2>&1 || { echo >&2 "Dracut not installed"; exit 1; }
-echo Creating $D/initrd using dracut.
+if command -v dracut >/dev/null 2>&1
+then
+ echo Creating $D/initrd using dracut.
+ # Filesystem creation
+ dracut --force --no-hostonly --no-hostonly-cmdline --module "base" $T/initramfs.img
+ cd $D
+ mkdir 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
+fi
-# Filesystem creation
-dracut --force --no-hostonly --no-hostonly-cmdline --module "base" $T/initramfs.img
+# 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 initrd
cd initrd
-zcat $T/initramfs.img | cpio -id
-cp $T/init init
-echo Done creating $D/initrd using dracut
+cat > init.c << '___EOF___'
+#include <unistd.h>
+
+int main(int argc, int argv[])
+{
+ for (;;)
+ sleep(1000*1000*1000); /* One gigasecond is ~30 years. */
+ return 0;
+}
+___EOF___
+gcc -static -Os -o init init.c
+strip init
+rm init.c
+echo "Done creating a statically linked C-language initrd"
+
exit 0
-This document describes one way to create the initrd directory hierarchy
-in order to allow an initrd to be built into your kernel. The trick
-here is to steal the initrd file used on your Linux laptop, Ubuntu in
-this case. There are probably much better ways of doing this.
+The rcutorture scripting tools automatically create the needed initrd
+directory using dracut. Failing that, this tool will create an initrd
+containing a single statically linked binary named "init" that loops
+over a very long sleep() call. In both cases, this creation is done
+by tools/testing/selftests/rcutorture/bin/mkinitrd.sh.
-That said, here are the commands:
+However, if you are attempting to run rcutorture on a system that does
+not have dracut installed, and if you don't like the notion of static
+linking, you might wish to press an existing initrd into service:
------------------------------------------------------------------------
cd tools/testing/selftests/rcutorture
mkdir initrd
cd initrd
cpio -id < /tmp/initrd.img.zcat
-------------------------------------------------------------------------
-
-Another way to create an initramfs image is using "dracut"[1], which is
-available on many distros, however the initramfs dracut generates is a cpio
-archive with another cpio archive in it, so an extra step is needed to create
-the initrd directory hierarchy.
-
-Here are the commands to create a initrd directory for rcutorture using
-dracut:
-
-------------------------------------------------------------------------
-dracut --no-hostonly --no-hostonly-cmdline --module "base bash shutdown" /tmp/initramfs.img
-cd tools/testing/selftests/rcutorture
-mkdir initrd
-cd initrd
-/usr/lib/dracut/skipcpio /tmp/initramfs.img | zcat | cpio -id < /tmp/initramfs.img
+# Manually verify that initrd contains needed binaries and libraries.
------------------------------------------------------------------------
Interestingly enough, if you are running rcutorture, you don't really
------------------------------------------------------------------------
#!/bin/sh
-[ -d /dev ] || mkdir -m 0755 /dev
-[ -d /root ] || mkdir -m 0700 /root
-[ -d /sys ] || mkdir /sys
-[ -d /proc ] || mkdir /proc
-[ -d /tmp ] || mkdir /tmp
-mkdir -p /var/lock
-mount -t sysfs -o nodev,noexec,nosuid sysfs /sys
-mount -t proc -o nodev,noexec,nosuid proc /proc
-# Some things don't work properly without /etc/mtab.
-ln -sf /proc/mounts /etc/mtab
-
-# Note that this only becomes /dev on the real filesystem if udev's scripts
-# are used; which they will be, but it's worth pointing out
-if ! mount -t devtmpfs -o mode=0755 udev /dev; then
- echo "W: devtmpfs not available, falling back to tmpfs for /dev"
- mount -t tmpfs -o mode=0755 udev /dev
- [ -e /dev/console ] || mknod --mode=600 /dev/console c 5 1
- [ -e /dev/kmsg ] || mknod --mode=644 /dev/kmsg c 1 11
- [ -e /dev/null ] || mknod --mode=666 /dev/null c 1 3
-fi
-
-mkdir /dev/pts
-mount -t devpts -o noexec,nosuid,gid=5,mode=0620 devpts /dev/pts || true
-mount -t tmpfs -o "nosuid,size=20%,mode=0755" tmpfs /run
-mkdir /run/initramfs
-# compatibility symlink for the pre-oneiric locations
-ln -s /run/initramfs /dev/.initramfs
-
-# Export relevant variables
-export ROOT=
-export ROOTDELAY=
-export ROOTFLAGS=
-export ROOTFSTYPE=
-export IP=
-export BOOT=
-export BOOTIF=
-export UBIMTD=
-export break=
-export init=/sbin/init
-export quiet=n
-export readonly=y
-export rootmnt=/root
-export debug=
-export panic=
-export blacklist=
-export resume=
-export resume_offset=
-export recovery=
-
-for i in /sys/devices/system/cpu/cpu*/online
-do
- case $i in
- '/sys/devices/system/cpu/cpu0/online')
- ;;
- '/sys/devices/system/cpu/cpu*/online')
- ;;
- *)
- echo 1 > $i
- ;;
- esac
-done
-
while :
do
sleep 10
done
------------------------------------------------------------------------
-References:
-[1]: https://dracut.wiki.kernel.org/index.php/Main_Page
-[2]: http://blog.elastocloud.org/2015/06/rapid-linux-kernel-devtest-with-qemu.html
-[3]: https://www.centos.org/forums/viewtopic.php?t=51621
+This approach also allows most of the binaries and libraries in the
+initrd filesystem to be dispensed with, which can save significant
+space in rcutorture's "res" directory.