Re: [Qemu-devel] [PATCH] KVM: Add wrapper script around Qemu to test kernels

[Alexander Graf]

On 24.08.2011, at 12:40, Blue Swirl wrote:

> On Tue, Aug 23, 2011 at 10:16 PM, Alexander Graf <address@hidden> wrote:
>> On LinuxCon I had a nice chat with Linus on what he thinks kvm-tool
>> would be doing and what he expects from it. Basically he wants a
>> small and simple tool he and other developers can run to try out and
>> see if the kernel they just built actually works.
>> 
>> Fortunately, Qemu can do that today already! The only piece that was
>> missing was the "simple" piece of the equation, so here is a script
>> that wraps around Qemu and executes a kernel you just built.
>> 
>> If you do have KVM around and are not cross-compiling, it will use
>> KVM. But if you don't, you can still fall back to emulation mode and
>> at least check if your kernel still does what you expect. I only
>> implemented support for s390x and ppc there, but it's easily extensible
>> to more platforms, as Qemu can emulate (and virtualize) pretty much
>> any platform out there.
>> 
>> If you don't have qemu installed, please do so before using this script. Your
>> distro should provide a package for it (might even call it "kvm"). If not,
>> just compile it from source - it's not hard!
>> 
>> To quickly get going, just execute the following as user:
>> 
>>    $ ./Documentation/run-qemu.sh -r / -a init=/bin/bash
>> 
>> This will drop you into a shell on your rootfs.
>> 
>> Happy hacking!
>> 
>> Signed-off-by: Alexander Graf <address@hidden>
>> ---
>>  Documentation/run-qemu.sh |  284 
>> +++++++++++++++++++++++++++++++++++++++++++++
>>  1 files changed, 284 insertions(+), 0 deletions(-)
>>  create mode 100755 Documentation/run-qemu.sh
>> 
>> diff --git a/Documentation/run-qemu.sh b/Documentation/run-qemu.sh
>> new file mode 100755
>> index 0000000..0bac924
>> --- /dev/null
>> +++ b/Documentation/run-qemu.sh
>> @@ -0,0 +1,284 @@
>> +#!/bin/bash
>> +#
>> +# QEMU Launcher
>> +#
>> +# This script enables simple use of the KVM and Qemu tool stack for
> 
> QEMU
> 
>> +# easy kernel testing. It allows to pass either a host directory to
>> +# the guest or a disk image. Example usage:
>> +#
>> +# Run the host root fs inside a VM:
>> +#
>> +# $ ./Documentation/run-qemu.sh -r /
>> +#
>> +# Run the same with SDL:
>> +#
>> +# $ ./Documentation/run-qemu.sh -r / --sdl
>> +#
>> +# Or with a PPC build:
>> +#
>> +# $ ARCH=ppc ./Documentation/run-qemu.sh -r /
>> +#
>> +#
>> +
>> +USE_SDL=
>> +USE_VNC=
>> +KERNEL_BIN=arch/x86/boot/bzImage
>> +MON_STDIO=
>> +KERNEL_APPEND2=
>> +SERIAL=ttyS0
>> +SERIAL_KCONFIG=SERIAL_8250
>> +
>> +function usage() {
>> +       echo "
>> +Run-Qemu allows you to execute a virtual machine with the Linux kernel
> 
> run-qemu.sh or $0
> 
>> +that you just built. To only execute a simple VM, you can just run it
>> +on your root fs with \"-r / -a init=/bin/bash\"
>> +
>> +       -a, --append parameters
>> +               Append the given parameters to the kernel command line
>> +
>> +       -d, --disk image
>> +               Add the image file as disk into the VM
>> +
>> +       -r, --root directory
>> +               Use the specified directory as root directory inside the 
>> guest.
>> +
>> +       -s, --sdl
>> +               Enable SDL graphical output.
>> +
>> +       -S, --smp cpus
>> +               Set number of virtual CPUs
>> +
>> +       -v, --vnc
>> +               Enable VNC graphical output.
>> +
>> +Examples:
>> +
>> +       Run the host root fs inside a VM:
>> +       $ ./Documentation/run-qemu.sh -r /
>> +
>> +       Run the same with SDL:
>> +       $ ./Documentation/run-qemu.sh -r / --sdl
>> +
>> +       Or with a PPC build:
>> +       $ ARCH=ppc ./Documentation/run-qemu.sh -r /
>> +"
>> +}
>> +
>> +function require_config() {
>> +       if [ "$(grep CONFIG_$1=y .config)" ]; then
>> +               return
>> +       fi
>> +
>> +       echo "You need to enable CONFIG_$1 for run-qemu to work properly"
>> +       exit 1
>> +}
>> +
>> +function has_config() {
>> +       grep "CONFIG_$1=y" .config
>> +}
>> +
>> +function drive_if() {
>> +       if [ "$(has_config VIRTIO_BLK)" ]; then
>> +               echo virtio
>> +       elif [ "$(has_config ATA_PIIX)" ]; then
>> +               echo ide
>> +       else
>> +               echo "\
>> +Your kernel must have either VIRTIO_BLK or ATA_PIIX
>> +enabled for block device assignment" >&2
>> +               exit 1
>> +       fi
>> +}
>> +
>> +GETOPT=`getopt -o a:d:hr:sS:v --long append,disk:,help,root:,sdl,smp:,vnc \
>> +       -n "$(basename \"$0\")" -- "$@"`
>> +
>> +if [ $? != 0 ]; then
>> +       echo "Terminating..." >&2
>> +       exit 1
>> +fi
>> +
>> +eval set -- "$GETOPT"
>> +
>> +while true; do
>> +       case "$1" in
>> +       -a|--append)
>> +               KERNEL_APPEND2="$2"
>> +               shift 2
>> +               ;;
>> +       -d|--disk)
>> +               QEMU_OPTIONS="$QEMU_OPTIONS -drive \
>> +                       file=$2,if=$(drive_if),cache=unsafe"
>> +               USE_DISK=1
>> +               shift 2
>> +               ;;
>> +       -h|--help)
>> +               usage
>> +               exit 0
>> +               ;;
>> +       -r|--root)
>> +               ROOTFS="$2"
>> +               shift 2
>> +               ;;
>> +       -s|--sdl)
>> +               USE_SDL=1
>> +               shift
>> +               ;;
>> +       -S|--smp)
>> +               SMP="$2"
>> +               shift 2
>> +               ;;
>> +       -v|--vnc)
>> +               USE_VNC=1
>> +               shift
>> +               ;;
>> +       --)
>> +               shift
>> +               break
>> +               ;;
>> +       *)
>> +               echo "Could not parse option: $1" >&2
>> +               exit 1
>> +               ;;
>> +       esac
>> +done
>> +
>> +if [ ! "$ROOTFS" -a ! "$USE_DISK" ]; then
>> +       echo "\
>> +Error: Please specify at least -r or -d with a target \
>> +FS to run off of" >&2
>> +       exit 1
>> +fi
>> +
>> +# Try to find the KVM accelerated Qemu binary
>> +
>> +[ "$ARCH" ] || ARCH=$(uname -m)
>> +case $ARCH in
>> +i*86|x86_64)
>> +       KERNEL_BIN=arch/x86/boot/bzImage
>> +       # SUSE and Red Hat call the binary qemu-kvm
>> +       [ "$QEMU_BIN" ] || QEMU_BIN=$(which qemu-kvm 2>/dev/null)
>> +
>> +       # Debian and Gentoo call it kvm
>> +       [ "$QEMU_BIN" ] || QEMU_BIN=$(which kvm 2>/dev/null)
>> +
>> +       # Qemu's own build system calls it qemu-system-x86_64
>> +       [ "$QEMU_BIN" ] || QEMU_BIN=$(which qemu-system-x86_64 2>/dev/null)
> 
> If you run qemu-system-x86_64 on an i386 host, will it use kvm at all?
> If testing kvm  is not needed, then why don't you just grab the target
> CPU from .config and use qemu-system-$CPU?

Well, how do you find out if it's needed? The goal is to use as few command 
line parameters as possible to get a kernel test going. And most people will 
want to use KVM if it's available, right? Plus, on x86_64, there are very few 
machines that don't support KVM these days.

Also, how would you fetch $CPU from .config? I haven't found anything in 
.config that is explicitly telling me the ARCH for the respective build.

> 
>> +
>> +       # i386 version of Qemu
>> +       if [ ! "$(has_config X86_64)" ]; then
>> +               [ "$QEMU_BIN" ] || QEMU_BIN=$(which qemu 2>/dev/null)
> 
> I'd just make a separate case for i386, even if the first two checks
> are duplicated.

Hrm. On i386 we can just always fall back to the qemu binary I'd say. You're 
pretty unlikely to get KVM there and if you do, -machine accel= should sort 
that one out for you.

> 
>> +       fi
>> +       ;;
>> +s390*)
>> +       KERNEL_BIN=arch/s390/boot/image
>> +       [ "$QEMU_BIN" ] || QEMU_BIN=$(which qemu-system-s390x 2>/dev/null)
>> +       ;;
>> +ppc*)
>> +       KERNEL_BIN=vmlinux
>> +
>> +       IS_64BIT=
>> +       [ "$(has_config PPC64)" ] && IS_64BIT=64
>> +       if [ "$(has_config PPC_85xx)" ]; then
>> +               QEMU_OPTIONS="$QEMU_OPTIONS -M mpc8544ds"
>> +       elif [ "$(has_config PPC_PSERIES)" ]; then
>> +               QEMU_OPTIONS="$QEMU_OPTIONS -M pseries"
>> +               SERIAL=hvc0
>> +               SERIAL_KCONFIG=HVC_CONSOLE
>> +       elif [ "$(has_config PPC_PMAC)" ]; then
>> +               [ "$(has_config SERIAL_PMACZILOG_TTYS)" ] || SERIAL=ttyPZ0
>> +               SERIAL_KCONFIG=SERIAL_PMACZILOG
>> +       else
>> +               echo "Unknown PPC board" >&2
>> +               exit 1
>> +       fi
>> +
>> +       [ "$QEMU_BIN" ] || QEMU_BIN=$(which qemu-system-ppc${IS_64BIT} 
>> 2>/dev/null)
>> +       ;;
>> +esac
>> +
>> +if [ ! "$QEMU_BIN" ]; then
>> +       echo "\
>> +Could not find a usable Qemu binary. Please install one from \
>> +your distro or from source code." >&2
>> +       exit 1
>> +fi
>> +
>> +# The binaries without kvm in their name can be too old to support KVM, so
>> +# check for that before the user gets confused
>> +if [ ! "$(echo $QEMU_BIN | grep kvm)" -a \
>> +     ! "$($QEMU_BIN --help | egrep '^-machine')" ]; then
>> +       echo "Your Qemu binary is too old, please update to at least 0.15." 
>> >&2
>> +       exit 1
>> +fi
>> +QEMU_OPTIONS="$QEMU_OPTIONS -machine accel=kvm:tcg"
>> +
>> +# We need to check some .config variables to make sure we actually work
>> +# on the respective kernel.
>> +if [ ! -e .config ]; then
>> +       echo "\
>> +Please run this script on a fully compiled and configured
>> +Linux kernel build directory" >&2
>> +       exit 1
>> +fi
>> +
>> +if [ ! -e "$KERNEL_BIN" ]; then
>> +       echo "Could not find kernel binary: $KERNEL_BIN" >&2
>> +       exit 1
>> +fi
>> +
>> +QEMU_OPTIONS="$QEMU_OPTIONS -kernel $KERNEL_BIN"
>> +
>> +if [ "$USE_SDL" ]; then
>> +       # SDL is the default, so nothing to do
>> +       :
>> +elif [ "$USE_VNC" ]; then
>> +       QEMU_OPTIONS="$QEMU_OPTIONS -vnc :5"
>> +else
>> +       # When emulating a serial console, tell the kernel to use it as well
>> +       QEMU_OPTIONS="$QEMU_OPTIONS -nographic"
>> +       KERNEL_APPEND="$KERNEL_APPEND console=$SERIAL earlyprintk=serial"
>> +       MON_STDIO=1
>> +       require_config "$SERIAL_KCONFIG"
>> +fi
>> +
>> +if [ "$ROOTFS" ]; then
>> +       # Using rootfs with 9p
>> +       require_config "NET_9P_VIRTIO"
>> +       KERNEL_APPEND="$KERNEL_APPEND \
>> +root=/dev/root rootflags=rw,trans=virtio,version=9p2000.L rootfstype=9p"
>> +
>> +#Usage: -virtfs 
>> fstype,path=/share_path/,security_model=[mapped|passthrough|none],mount_tag=tag.
>> +
>> +
>> +       QEMU_OPTIONS="$QEMU_OPTIONS \
>> +-virtfs 
>> local,id=root,path=$ROOTFS,mount_tag=root,security_model=passthrough \
>> +-device virtio-9p-pci,fsdev=root,mount_tag=/dev/root"
>> +fi
>> +
>> +[ "$SMP" ] || SMP=1
>> +
>> +# User append args come last
>> +KERNEL_APPEND="$KERNEL_APPEND $KERNEL_APPEND2"
>> +
>> +############### Execution #################
>> +
>> +echo "
>> +       ################# Linux Qemu launcher #################
>> +
>> +This script executes your currently built Linux kernel using Qemu. If KVM is
>> +available, it will also use KVM for fast virtualization of your guest.
>> +
>> +The intent is to make it very easy to run your kernel. If you need to do 
>> more
>> +advanced things, such as passing through real devices, please take the 
>> command
>> +line shown below and modify it to your needs. This tool is for simplicity, 
>> not
>> +world dominating functionality coverage.
> 
> Please add this:
> (just a hobby, won't be big and professional like libvirt)
> 
> Though usually Unix tools should be terse unless the user specifies -v.
> 
>> +"
>> +echo "\
>> +Your guest is bound to the current foreground shell. To quit the guest,
>> +please use Ctrl-A x"
>> +echo "  Executing: $QEMU_BIN $QEMU_OPTIONS -append \"$KERNEL_APPEND\" -smp 
>> $SMP"
>> +echo
>> +
>> +exec $QEMU_BIN $QEMU_OPTIONS -append "$KERNEL_APPEND -smp $SMP"
> 
> How about something like this (modulo quoting to allow compiling the
> kernel in C:\Documents and Settings\agraf\):
> CMD="$QEMU_BIN $QEMU_OPTIONS -append $KERNEL_APPEND -smp $SMP"
> echo "  Executing: $CMD"
> exec $CMD

Yeah, I tried that, but my bash foo is not good enough :(. The quoting isn't 
quite as simple. I think I'd have to make this be an array - and before I do 
that I'd rather have the code be slightly more verbose.


Alex