Add support for saving VM state when a test fails.

lib/cros_vm_lib.sh

Index: lib/cros_vm_lib.sh
diff --git a/lib/cros_vm_lib.sh b/lib/cros_vm_lib.sh
index 7a99cbebe25774791d68a0892780977a8a402f22..0ed87891bb10395d4bbdbd83e998f3f510baccfd 100644
--- a/lib/cros_vm_lib.sh
+++ b/lib/cros_vm_lib.sh
@@ -14,6 +14,7 @@ DEFINE_string vnc "" "VNC Server to display to instead of SDL."
 
 KVM_PID_FILE=/tmp/kvm.$$.pid
 LIVE_VM_IMAGE=
+KVM_MONITOR_SOCKET=
 
 function get_pid() {
   sudo cat "${KVM_PID_FILE}"
@@ -40,6 +41,7 @@ function start_kvm() {
     echo "Starting a KVM instance" >&2
     local nographics=""
     local usesnapshot=""
+    local save_vm_state=""
     if [ ${FLAGS_no_graphics} -eq ${FLAGS_TRUE} ]; then
       nographics="-nographic -serial none"
     fi
@@ -51,6 +53,14 @@ function start_kvm() {
       snapshot="-snapshot"
     fi
 
+    if [ ${FLAGS_save_vm_state} -eq ${FLAGS_TRUE} ]; then
+      # Redirect the QEMU monitor to the guest usb serial port so tests
+      # can trigger a "savevm" command from inside the guest.
+      KVM_MONITOR_SOCKET=/tmp/kvm.mon.socket.$$
+      save_vm_state="-monitor unix:${KVM_MONITOR_SOCKET},server,nowait
+                     -usbdevice serial::unix:${KVM_MONITOR_SOCKET}"
+    fi
+
     sudo kvm -m 1024 \
       -vga std \
       -pidfile "${KVM_PID_FILE}" \
@@ -58,6 +68,7 @@ function start_kvm() {
       -net nic,model=e1000 \
       ${nographics} \
       ${snapshot} \
+      ${save_vm_state} \
       -net user,hostfwd=tcp::${FLAGS_ssh_port}-:22 \
       -hda "${1}"
 
@@ -100,6 +111,9 @@ function stop_kvm() {
       echo "Killing ${pid}" >&2
       sudo kill ${pid}
       sudo rm "${KVM_PID_FILE}"
+      if [ -n "${KVM_MONITOR_SOCKET}" ]; then
+        sudo rm "${KVM_MONITOR_SOCKET}"
+      fi
     else
       echo "No kvm pid found to stop." >&2
       return 1