114 lines
3.6 KiB
Plaintext
Executable file
114 lines
3.6 KiB
Plaintext
Executable file
This document describes one way to create the initrd directory hierarchy
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in order to allow an initrd to be built into your kernel. The trick
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here is to steal the initrd file used on your Linux laptop, Ubuntu in
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this case. There are probably much better ways of doing this.
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That said, here are the commands:
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------------------------------------------------------------------------
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cd tools/testing/selftests/rcutorture
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zcat /initrd.img > /tmp/initrd.img.zcat
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mkdir initrd
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cd initrd
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cpio -id < /tmp/initrd.img.zcat
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------------------------------------------------------------------------
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Another way to create an initramfs image is using "dracut"[1], which is
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available on many distros, however the initramfs dracut generates is a cpio
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archive with another cpio archive in it, so an extra step is needed to create
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the initrd directory hierarchy.
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Here are the commands to create a initrd directory for rcutorture using
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dracut:
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------------------------------------------------------------------------
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dracut --no-hostonly --no-hostonly-cmdline --module "base bash shutdown" /tmp/initramfs.img
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cd tools/testing/selftests/rcutorture
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mkdir initrd
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cd initrd
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/usr/lib/dracut/skipcpio /tmp/initramfs.img | zcat | cpio -id < /tmp/initramfs.img
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------------------------------------------------------------------------
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Interestingly enough, if you are running rcutorture, you don't really
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need userspace in many cases. Running without userspace has the
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advantage of allowing you to test your kernel independently of the
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distro in place, the root-filesystem layout, and so on. To make this
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happen, put the following script in the initrd's tree's "/init" file,
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with 0755 mode.
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------------------------------------------------------------------------
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#!/bin/sh
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[ -d /dev ] || mkdir -m 0755 /dev
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[ -d /root ] || mkdir -m 0700 /root
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[ -d /sys ] || mkdir /sys
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[ -d /proc ] || mkdir /proc
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[ -d /tmp ] || mkdir /tmp
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mkdir -p /var/lock
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mount -t sysfs -o nodev,noexec,nosuid sysfs /sys
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mount -t proc -o nodev,noexec,nosuid proc /proc
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# Some things don't work properly without /etc/mtab.
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ln -sf /proc/mounts /etc/mtab
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# Note that this only becomes /dev on the real filesystem if udev's scripts
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# are used; which they will be, but it's worth pointing out
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if ! mount -t devtmpfs -o mode=0755 udev /dev; then
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echo "W: devtmpfs not available, falling back to tmpfs for /dev"
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mount -t tmpfs -o mode=0755 udev /dev
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[ -e /dev/console ] || mknod --mode=600 /dev/console c 5 1
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[ -e /dev/kmsg ] || mknod --mode=644 /dev/kmsg c 1 11
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[ -e /dev/null ] || mknod --mode=666 /dev/null c 1 3
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fi
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mkdir /dev/pts
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mount -t devpts -o noexec,nosuid,gid=5,mode=0620 devpts /dev/pts || true
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mount -t tmpfs -o "nosuid,size=20%,mode=0755" tmpfs /run
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mkdir /run/initramfs
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# compatibility symlink for the pre-oneiric locations
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ln -s /run/initramfs /dev/.initramfs
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# Export relevant variables
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export ROOT=
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export ROOTDELAY=
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export ROOTFLAGS=
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export ROOTFSTYPE=
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export IP=
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export BOOT=
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export BOOTIF=
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export UBIMTD=
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export break=
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export init=/sbin/init
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export quiet=n
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export readonly=y
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export rootmnt=/root
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export debug=
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export panic=
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export blacklist=
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export resume=
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export resume_offset=
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export recovery=
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for i in /sys/devices/system/cpu/cpu*/online
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do
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case $i in
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'/sys/devices/system/cpu/cpu0/online')
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;;
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'/sys/devices/system/cpu/cpu*/online')
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;;
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*)
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echo 1 > $i
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;;
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esac
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done
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while :
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do
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sleep 10
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done
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------------------------------------------------------------------------
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References:
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[1]: https://dracut.wiki.kernel.org/index.php/Main_Page
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[2]: http://blog.elastocloud.org/2015/06/rapid-linux-kernel-devtest-with-qemu.html
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[3]: https://www.centos.org/forums/viewtopic.php?t=51621
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