Script to start a virtual machine using virsh, and sample its $pc register until it seems to be idle.

virsh-start-and-wait-for-idle.sh

#!/bin/bash -e

# Check if we believe the VM has started after this number of samples.
CHECK_EVERY=500

# Consider the machine to be idle if MIN_IDLE_PCT% of sampled program counters
# were identical after at least MIN_IDLE_SAMPLES.
# 
MIN_IDLE_SAMPLES=450
MIN_IDLE_PCT=60

# Timeout (in seconds)
TIMEOUT=300

function monotonic_time_msecs {
    now=$(awk '/^now/ {print $3; exit}' /proc/timer_list)
    now_msecs="$(expr $now / 1000000)"
    echo $now_msecs
}

# Check if the user supplied a valid virtual machine.
virsh dumpxml $1 > /dev/null 2>&1 || (echo "Required argument: virtual machine name." ; exit 1)

# If the virtual machine hasn't been started, start it now.
# If it's already started, no big deal.
virsh start $1 > /dev/null 2>&1 || true

TEMPFILE="$(mktemp)"

function finish {
    rm -f "$TEMPFILE"
}

trap "finish \$?" EXIT

samples=0
start_time_msecs=$(monotonic_time_msecs)
while [ 1 ]; do
    virsh qemu-monitor-command $1 --hmp --cmd 'print $pc' | tr '\r' '\n' | head -1 >> $TEMPFILE
    let samples=$samples+1
    if [ "$(expr $samples % $CHECK_EVERY)" == "0" ]; then
        idle_info="$(cat $TEMPFILE | sort | uniq -c | sort -n | tail -1)"
        idle_samples="$(echo $idle_info | awk '{ print $1 }')"
        idle_pc="$(echo $idle_info | awk '{ print $2 }')"
        idle_pct="$(expr \( 100 \* $idle_samples \) / $samples)"
        now_msecs=$(monotonic_time_msecs)
        elapsed="$(expr $now_msecs - $start_time_msecs)"
        elapsed_secs="$(expr $elapsed / 1000)"
        printf "Idle pc=%s idle_samples=%s samples=%s idle=%s%%\n" \
            "$idle_pc" "$idle_samples" "$samples" "$idle_pct"
        if [ $idle_pct -ge $MIN_IDLE_PCT -a $idle_samples -gt $MIN_IDLE_SAMPLES ]; then
            printf "Virtual machine '%s' appears to be started after %d.%03ds.\n" \
                "$1" "$elapsed_secs" "$(expr $elapsed % 1000)"
            exit 0
        fi
        if [ $elapsed_secs -gt $TIMEOUT ]; then
             echo "$0: aborted waiting for virtual machine '$1' after waiting $TIMEOUT seconds." 1>&2
             exit 1
        fi
    fi
done