rcutorture: Add KVM-based test framework

This commit adds the test framework that I used to test RCU under KVM.
This consists of a group of scripts and Kconfig fragments.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Greg KH <gregkh@linuxfoundation.org>

tools/testing/selftests/rcutorture/doc/initrd.txt

@@ -0,0 +1,90 @@
+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.
+
+That said, here are the commands:
+
+------------------------------------------------------------------------
+zcat /initrd.img > /tmp/initrd.img.zcat
+mkdir initrd
+cd initrd
+cpio -id < /tmp/initrd.img.zcat
+------------------------------------------------------------------------
+
+Interestingly enough, if you are running rcutorture, you don't really
+need userspace in many cases.  Running without userspace has the
+advantage of allowing you to test your kernel independently of the
+distro in place, the root-filesystem layout, and so on.  To make this
+happen, put the following script in the initrd's tree's "/init" file,
+with 0755 mode.
+
+------------------------------------------------------------------------
+#!/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

tools/testing/selftests/rcutorture/doc/rcu-test-image.txt

@@ -0,0 +1,42 @@
+This document describes one way to created the rcu-test-image file
+that contains the filesystem used by the guest-OS kernel.  There are
+probably much better ways of doing this, and this filesystem could no
+doubt be smaller.  It is probably also possible to simply download
+an appropriate image from any number of places.
+
+That said, here are the commands:
+
+------------------------------------------------------------------------
+dd if=/dev/zero of=rcu-test-image bs=400M count=1
+mkfs.ext3 ./rcu-test-image
+sudo mount -o loop ./rcu-test-image /mnt
+
+# Replace "precise" below with your favorite Ubuntu release.
+# Empirical evidence says this image will work for 64-bit, but...
+# Note that debootstrap does take a few minutes to run.  Or longer.
+sudo debootstrap --verbose --arch i386 precise /mnt http://archive.ubuntu.com/ubuntu
+cat << '___EOF___' | sudo dd of=/mnt/etc/fstab
+# UNCONFIGURED FSTAB FOR BASE SYSTEM
+#
+/dev/vda        /               ext3    defaults        1 1
+dev             /dev            tmpfs   rw              0 0
+tmpfs           /dev/shm        tmpfs   defaults        0 0
+devpts          /dev/pts        devpts  gid=5,mode=620  0 0
+sysfs           /sys            sysfs   defaults        0 0
+proc            /proc           proc    defaults        0 0
+___EOF___
+sudo umount /mnt
+------------------------------------------------------------------------
+
+
+References:
+
+	http://sripathikodi.blogspot.com/2010/02/creating-kvm-bootable-fedora-system.html
+	https://help.ubuntu.com/community/KVM/CreateGuests
+	https://help.ubuntu.com/community/JeOSVMBuilder
+	http://wiki.libvirt.org/page/UbuntuKVMWalkthrough
+	http://www.moe.co.uk/2011/01/07/pci_add_option_rom-failed-to-find-romfile-pxe-rtl8139-bin/ -- "apt-get install kvm-pxe"
+	http://www.landley.net/writing/rootfs-howto.html
+	http://en.wikipedia.org/wiki/Initrd
+	http://en.wikipedia.org/wiki/Cpio
+	http://wiki.libvirt.org/page/UbuntuKVMWalkthrough