1 This document describes one way to create the initrd directory hierarchy 2 in order to allow an initrd to be built into your kernel. The trick 3 here is to steal the initrd file used on your Linux laptop, Ubuntu in 4 this case. There are probably much better ways of doing this. 5 6 That said, here are the commands: 7 8 ------------------------------------------------------------------------ 9 cd tools/testing/selftests/rcutorture 10 zcat /initrd.img > /tmp/initrd.img.zcat 11 mkdir initrd 12 cd initrd 13 cpio -id < /tmp/initrd.img.zcat 14 ------------------------------------------------------------------------ 15 16 Another way to create an initramfs image is using "dracut"[1], which is 17 available on many distros, however the initramfs dracut generates is a cpio 18 archive with another cpio archive in it, so an extra step is needed to create 19 the initrd directory hierarchy. 20 21 Here are the commands to create a initrd directory for rcutorture using 22 dracut: 23 24 ------------------------------------------------------------------------ 25 dracut --no-hostonly --no-hostonly-cmdline --module "base bash shutdown" /tmp/initramfs.img 26 cd tools/testing/selftests/rcutorture 27 mkdir initrd 28 cd initrd 29 /usr/lib/dracut/skipcpio /tmp/initramfs.img | zcat | cpio -id < /tmp/initramfs.img 30 ------------------------------------------------------------------------ 31 32 Interestingly enough, if you are running rcutorture, you don't really 33 need userspace in many cases. Running without userspace has the 34 advantage of allowing you to test your kernel independently of the 35 distro in place, the root-filesystem layout, and so on. To make this 36 happen, put the following script in the initrd's tree's "/init" file, 37 with 0755 mode. 38 39 ------------------------------------------------------------------------ 40 #!/bin/sh 41 42 [ -d /dev ] || mkdir -m 0755 /dev 43 [ -d /root ] || mkdir -m 0700 /root 44 [ -d /sys ] || mkdir /sys 45 [ -d /proc ] || mkdir /proc 46 [ -d /tmp ] || mkdir /tmp 47 mkdir -p /var/lock 48 mount -t sysfs -o nodev,noexec,nosuid sysfs /sys 49 mount -t proc -o nodev,noexec,nosuid proc /proc 50 # Some things don't work properly without /etc/mtab. 51 ln -sf /proc/mounts /etc/mtab 52 53 # Note that this only becomes /dev on the real filesystem if udev's scripts 54 # are used; which they will be, but it's worth pointing out 55 if ! mount -t devtmpfs -o mode=0755 udev /dev; then 56 echo "W: devtmpfs not available, falling back to tmpfs for /dev" 57 mount -t tmpfs -o mode=0755 udev /dev 58 [ -e /dev/console ] || mknod --mode=600 /dev/console c 5 1 59 [ -e /dev/kmsg ] || mknod --mode=644 /dev/kmsg c 1 11 60 [ -e /dev/null ] || mknod --mode=666 /dev/null c 1 3 61 fi 62 63 mkdir /dev/pts 64 mount -t devpts -o noexec,nosuid,gid=5,mode=0620 devpts /dev/pts || true 65 mount -t tmpfs -o "nosuid,size=20%,mode=0755" tmpfs /run 66 mkdir /run/initramfs 67 # compatibility symlink for the pre-oneiric locations 68 ln -s /run/initramfs /dev/.initramfs 69 70 # Export relevant variables 71 export ROOT= 72 export ROOTDELAY= 73 export ROOTFLAGS= 74 export ROOTFSTYPE= 75 export IP= 76 export BOOT= 77 export BOOTIF= 78 export UBIMTD= 79 export break= 80 export init=/sbin/init 81 export quiet=n 82 export readonly=y 83 export rootmnt=/root 84 export debug= 85 export panic= 86 export blacklist= 87 export resume= 88 export resume_offset= 89 export recovery= 90 91 for i in /sys/devices/system/cpu/cpu*/online 92 do 93 case $i in 94 '/sys/devices/system/cpu/cpu0/online') 95 ;; 96 '/sys/devices/system/cpu/cpu*/online') 97 ;; 98 *) 99 echo 1 > $i 100 ;; 101 esac 102 done 103 104 while : 105 do 106 sleep 10 107 done 108 ------------------------------------------------------------------------ 109 110 References: 111 [1]: https://dracut.wiki.kernel.org/index.php/Main_Page 112 [2]: http://blog.elastocloud.org/2015/06/rapid-linux-kernel-devtest-with-qemu.html 113 [3]: https://www.centos.org/forums/viewtopic.php?t=51621 114
