rcutorture: Automatically create initrd directory

The rcutorture scripts currently expect the user to create the
tools/testing/selftests/rcutorture/initrd directory.  Should the user
fail to do this, the kernel build will fail with obscure and confusing
error messages.  This commit therefore adds explicit checks for the
tools/testing/selftests/rcutorture/initrd directory, and if not present,
creates one on systems on which dracut is installed.  If this directory
could not be created, a less obscure error message is emitted and the
test is aborted.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Connor Shu <Connor.Shu@ibm.com>
[ paulmck: Adapt the script to fit into the rcutorture framework and
  severely abbreviate the initrd/init script. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

tools/testing/selftests/rcutorture/bin/kvm.sh

@@ -194,6 +194,14 @@ do
 	shift
 done
 
+if test -z "$TORTURE_INITRD" || tools/testing/selftests/rcutorture/bin/mkinitrd.sh
+then
+	:
+else
+	echo No initrd and unable to create one, aborting test >&2
+	exit 1
+fi
+
 CONFIGFRAG=${KVM}/configs/${TORTURE_SUITE}; export CONFIGFRAG
 
 if test -z "$configs"

tools/testing/selftests/rcutorture/bin/mkinitrd.sh

@@ -0,0 +1,60 @@
+#!/bin/bash
+#
+# Create an initrd directory if one does not already exist.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, you can access it online at
+# http://www.gnu.org/licenses/gpl-2.0.html.
+#
+# Copyright (C) IBM Corporation, 2013
+#
+# Author: Connor Shu <Connor.Shu@ibm.com>
+
+D=tools/testing/selftests/rcutorture
+
+# Prerequisite checks
+[ -z "$D" ] && echo >&2 "No argument supplied" && exit 1
+if [ ! -d "$D" ]; then
+    echo >&2 "$D does not exist: Malformed kernel source tree?"
+    exit 1
+fi
+if [ -d "$D/initrd" ]; then
+    echo "$D/initrd already exists, no need to create it"
+    exit 0
+fi
+
+T=${TMPDIR-/tmp}/mkinitrd.sh.$$
+trap 'rm -rf $T' 0 2
+mkdir $T
+
+cat > $T/init << '__EOF___'
+#!/bin/sh
+while :
+do
+	sleep 1000000
+done
+__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.
+
+# 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
+echo Done creating $D/initrd using dracut
+exit 0