examples: extract common features for running QEMU VMs

Needed by commit: "examples: add deploy-krops.sh"

examples/qemu-vm/run-vm.sh

@@ -0,0 +1,48 @@
+qemuDir=$(cd "${BASH_SOURCE[0]%/*}" && pwd)
+
+tmpDir=/tmp/nix-bitcoin-qemu-vm
+mkdir -p $tmpDir
+
+# Cleanup on exit
+cleanup() {
+    set +eu
+    if [[ $qemuPID ]]; then
+        kill -9 $qemuPID
+    fi
+    rm -rf $tmpDir
+}
+trap "cleanup" EXIT
+
+identityFile=$qemuDir/id-vm
+chmod 0600 $identityFile
+
+runVM() {
+    vm=$1
+    vmNumCPUs=$2
+    vmMemoryMiB=$3
+    sshPort=$4
+
+    export NIX_DISK_IMAGE=$tmpDir/img
+    export QEMU_NET_OPTS=hostfwd=tcp::$sshPort-:22
+    </dev/null $vm/bin/run-*-vm -m $vmMemoryMiB -smp $vmNumCPUs &>/dev/null &
+    qemuPID=$!
+}
+
+vmWaitForSSH() {
+    echo
+    printf "Waiting for SSH connection..."
+    while ! c : 2>/dev/null; do :; done
+    echo
+}
+
+# Run command in VM
+c() {
+    ssh -p $sshPort -i $identityFile -o ConnectTimeout=1 \
+        -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -o LogLevel=ERROR \
+        -o ControlMaster=auto -o ControlPath=$tmpDir/ssh-connection -o ControlPersist=60 \
+        root@127.0.0.1 "$@"
+}
+export identityFile
+export sshPort
+export tmpDir
+export -f c

examples/qemu-vm/vm-config.nix

@@ -0,0 +1,7 @@
+{
+  virtualisation.graphics = false;
+  services.mingetty.autologinUser = "root";
+  users.users.root = {
+    openssh.authorizedKeys.keyFiles = [ ./id-vm.pub ];
+  };
+}