Attempt to boot kvm even when NBD is not available

slapos/recipe/kvm/template/kvm_run.in

-#!%(shell_path)s
+#!%(python_path)s
 # BEWARE: This file is operated by slapgrid
 # BEWARE: It will be overwritten automatically
 
-if [ ! -e "%(disk_path)s" ]
-  then "%(qemu_img_path)s" create -f qcow2 "%(disk_path)s" %(disk_size)sG
-fi
+# Echo client program
+import os
+import socket
+import subprocess
 
-# TODO: -net nic,model=virtio, but OS installer has to provide the virtio_net
-# module
-exec %(qemu_path)s \
-  -net nic,macaddr=%(mac_address)s \
-  -net tap,ifname=%(tap_interface)s,script=no,downscript=no \
-  -smp %(smp_count)s \
-  -m %(ram_size)s \
-  -cdrom nbd:[%(nbd_ip)s]:%(nbd_port)s \
-  -drive file=%(disk_path)s,if=virtio,boot=on \
-  -vnc %(vnc_ip)s:1,ipv4,password \
-  -boot menu=on \
-  -qmp unix:%(socket_path)s,server \
-  -pidfile %(pid_file_path)s \
-  -no-kvm
+def getSocketStatus(host, port):
+  s = None
+  for res in socket.getaddrinfo(host, port,
+      socket.AF_UNSPEC, socket.SOCK_STREAM):
+    af, socktype, proto, canonname, sa = res
+    try:
+      s = socket.socket(af, socktype, proto)
+    except socket.error, msg:
+      s = None
+      continue
+    try:
+      s.connect(sa)
+    except socket.error, msg:
+      s.close()
+      s = None
+      continue
+    break
+  return s
+
+# create disk if doesn't exist
+disk_path = '%(disk_path)s'
+if not os.path.exists(disk_path):
+  subprocess.Popen(['%(qemu_img_path)s', 'create' ,'-f', 'qcow2',
+      '%(disk_path)s', '%(disk_size)sG'])
+
+kvm_argument_list = ['%(qemu_path)s',
+  '-net' 'nic,macaddr=%(mac_address)s',
+  '-net' 'tap,ifname=%(tap_interface)s,script=no,downscript=no',
+  '-smp' '%(smp_count)s',
+  '-m' '%(ram_size)s',
+  '-drive' 'file=%(disk_path)s,if=virtio,boot=on',
+  '-vnc' '%(vnc_ip)s:1,ipv4,password',
+  '-boot' 'menu=on',
+  '-qmp' 'unix:%(socket_path)s,server',
+  '-pidfile' '%(pid_file_path)s',
+  '-no-kvm']
+
+# Try to connect to NBD server
+s = getSocketStatus('%(nbd_ip)s', %(nbd_port)s)
+if s is None:
+  # NBD is not available : launch kvm without it
+  print 'Warning : Nbd is not available.'
+  os.execv(kvm_argument_list)
+else:
+  # NBD is available
+  kvm_argument_list.extend(['-cdrom' 'nbd:[%(nbd_ip)s]:%(nbd_port)s'])
+  os.execv(kvm_argument_list)