Automation

Command line alias

To facilitate faster development, we can set a group of alias commands in the host for common operations. Add the following to host shell startup file. Some commands require writing custom scripts.

export image_file=/path/to/my-linux.img
export mount_dir=/path/to/qemu-mount.dir
function mount_qemu_image() {
    sudo mount -o loop $image_file $mount_dir && \
    sudo mount -o bind,ro /dev $mount_dir/dev && \
    sudo mount -o bind,ro /dev/pts $mount_dir/dev/pts && \
    sudo mount -t proc none $mount_dir/proc
}
function unmount_qemu_image() {
    sudo umount $mount_dir/dev/pts
    sudo umount $mount_dir/dev
    sudo umount $mount_dir/proc
    sudo umount $mount_dir
}
# Mount/unmount disk image (do not mount if qemu is running)
alias m='pgrep qemu && echo "QEMU is running" || mount_qemu_image'
alias um=unmount_qemu_image
# Update image file (need to write custom cp/rsync scripts)
# You can also use (un)mount_qemu_image in the script.
alias ui='./updateimg.sh'
# Chroot into mounted disk image
# (`sudo' is used for setting $HOME and other variables correctly)
alias ch='sudo -i chroot $mount_dir'
# Run the VM (fail if still mounted) (need to write custom run.sh)
alias r='um; (mount | grep $mount_dir) || ./run.sh'
# Build the kernel
alias b='make -j`nproc`'
# Start gdb, attach to QEMU debug port, and boot the system
# (remove "-ex c" to stay in the gdb console)
alias g="gdb vmlinux -ex 'target remote 127.0.0.1:1234' -ex c"
# Force kill QEMU
alias k='killall qemu-system-x86_64'

Example run.sh

Combined with alias above, use r -d to start gdb server.

#!/bin/bash

if [[ $1 = '-d' ]]; then
        DBG='-s -S'  # gdb debug options (port 1234; stop cpu)
else
        DBG=
fi
# in gdb console, `break start_kernel`

KVM=--enable-kvm
#KVM=

qemu-system-x86_64 -kernel arch/x86/boot/bzImage \
    -hda qemu-image.img \
    -append "root=/dev/sda console=ttyS0 nokaslr" \
    ${DBG} \
    ${KVM} \
    -smp cores=10 -m 4096M \
    -nographic
    #-serial stdio -display none

Auto-login

To skip typing user name and password in the serial console every time we start QEMU, we can change to auto-login.

By default, Debian uses agetty with systemd. Edit the file /lib/systemd/system/serial-getty@.service. Find something like

[Service]
ExecStart=-/sbin/agetty -o '-p -- \\u' --keep-baud 115200,38400,9600 %I $TERM

Add -a root after agetty command (-a stands for --autologin):

[Service]
ExecStart=-/sbin/agetty -a root -o '-p -- \\u' --keep-baud 115200,38400,9600 %I $TERM

Auto-shutdown

To automatically shutdown the VM after Ctrl-D (or exit) in the login shell, add the following to ~/.bash_logout in the VM.

# Shutdown automatically (but do not shutdown when closing tmux pane)
if [[ $TMUX = "" ]]; then
    shutdown -h now
fi

Automatically run experiments

To automatically run experiments after login, we can add experiment commands to ~/.bash_login.

Note that ~/.bashrc has a different purpose and experiment commands should not be in this file. ~/.bashrc is sourced for non-login shells, and ~/.bash_login is for login shells. chroot from host uses non-login shell, while QEMU serial console uses a login shell. Running experiment code when chroot from the host is not a desired behavior, thus automated commands should only be in ~/.bash_login.

Conversely, we can put environment variable exports like export HISTSIZE=100000 in ~/.bashrc. If ~/.bashrc only contains common variables, we can even source ~/.bashrc in ~/.bash_login.

Tmux window

We can also automatically create Tmux layouts and run commands. See clustermanager.

This can also be added into ~/.bash_login.