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..543de1aa60579acd87f198908a3afdc341ff43a1 100644
--- a/lib/cros_vm_lib.sh
+++ b/lib/cros_vm_lib.sh
@@ -40,6 +40,7 @@ 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 +52,13 @@ function start_kvm() {
       snapshot="-snapshot"
     fi
 
+    if [ ${FLAGS_save_vm_state} -eq ${FLAGS_TRUE} ]; then
+      # Redirect the QEMU monitor to the guest usb serial port so tests
+      # can trigger a "savevm" command.
+      save_vm_state="-monitor telnet::4555,server,nowait
+                     -usbdevice serial::telnet:127.0.0.1:4555"
+    fi
+
     sudo kvm -m 1024 \
       -vga std \
       -pidfile "${KVM_PID_FILE}" \
@@ -58,6 +66,7 @@ function start_kvm() {
       -net nic,model=e1000 \
       ${nographics} \
       ${snapshot} \
+      ${save_vm_state} \
       -net user,hostfwd=tcp::${FLAGS_ssh_port}-:22 \
       -hda "${1}"