old_contents: #!/usr/bin/env python
  
  import os, random, sys
  from subprocess import Popen, PIPE
  
  if len(sys.argv) != 3:
      print "Usage: %s xfs|ext4|btrfs file.img"%sys.argv[0]
      sys.exit(1) 
  
  format = sys.argv[1]
  if format not in ['xfs', 'ext4', 'btrfs']:
      print "format must be xfs or ext4 or btrfs"
      sys.exit(1)
  
  image  = os.path.abspath(sys.argv[2])
  
  if not os.path.exists(image):
      print "image file %s doesn't exist"%image
      sys.exit(1)
  
  def cmd(s):
      print s
      if os.system(s):
          raise RuntimeError('failed: "%s"'%s)
  
  def cmd2(s):
      print s
      out = Popen(s, stdin=PIPE, stdout=PIPE, stderr=PIPE, shell=True)
      e = out.wait()
      x = out.stdout.read() + out.stderr.read()
      return x,e
  
  max_part = 64
  def nbd(n):
      cmd("modprobe nbd max_part=%s"%max_part)
      dev = '/dev/nbd%s'%n 
      cmd("qemu-nbd -c %s '%s'"%(dev,image))
      return dev
  
  def fdisk(dev):
      x,e = cmd2('echo "n\np\n1\n\n\n\nw" | fdisk %s'%dev)
      if "is already defined" in x.lower():
          raise ValueError("already partitioned-- refusing to format.")
      if e:
          raise RuntimeError(x)
   
  def mkfs(dev):
      cmd("mkfs.%s -f %sp1"%(format, dev))
  
  def nbd_disconnect(dev):
      cmd("qemu-nbd -d %s"%dev)
  
  dev = None
  try:
      for i in range(max_part):
          # we try until success, since nbd is flakie.
          try:
              dev = nbd(i)
              fdisk(dev)
              mkfs(dev)
              break
          except RuntimeError:
              pass
  finally:
      if dev is not None:
          nbd_disconnect(dev)
  
  
  
new_contents: #!/usr/bin/env python
  
  """
  Put this in visudo and make damned sure only root can edit this script:
  
      salvus ALL=(ALL)   NOPASSWD:  /usr/local/bin/salvus_nbd_format.py *
  """
  
  import os, random, sys
  from subprocess import Popen, PIPE
  
  if len(sys.argv) != 3:
      print "Usage: %s xfs|ext4|btrfs file.img"%sys.argv[0]
      sys.exit(1) 
  
  format = sys.argv[1]
  if format not in ['xfs', 'ext4', 'btrfs']:
      print "format must be xfs or ext4 or btrfs"
      sys.exit(1)
  
  image  = os.path.abspath(sys.argv[2])
  
  if not os.path.exists(image):
      print "image file %s doesn't exist"%image
      sys.exit(1)
  
  def cmd(s):
      print s
      if os.system(s):
          raise RuntimeError('failed: "%s"'%s)
  
  def cmd2(s):
      print s
      if isinstance(s, str):
         out = Popen(s, stdin=PIPE, stdout=PIPE, stderr=PIPE, shell=True)
      else: 
         out = Popen(s, stdin=PIPE, stdout=PIPE, stderr=PIPE, shell=False)
      e = out.wait()
      x = out.stdout.read() + out.stderr.read()
      return x,e
  
  max_part = 64
  def nbd(n):
      cmd("modprobe nbd max_part=%s"%max_part)
      dev = '/dev/nbd%s'%n 
      if cmd2(['qemu-nbd', '-c', dev, image])[1]:
          raise RuntimeError(out.stdout.read() + out.stderr.read())
      else:
          return dev
  
  def fdisk(dev):
      x,e = cmd2('echo "n\np\n1\n\n\n\nw" | fdisk %s'%dev)
      if "is already defined" in x.lower():
          raise ValueError("already partitioned-- refusing to format.")
      if e:
          raise RuntimeError(x)
   
  def mkfs(dev):
      cmd("mkfs.%s -f %sp1"%(format, dev))
  
  def nbd_disconnect(dev):
      cmd("qemu-nbd -d %s"%dev)
  
  dev = None
  try:
      for i in range(max_part):
          # we try until success, since nbd is flakie.
          try:
              dev = nbd(i)
              fdisk(dev)
              mkfs(dev)
              break
          except RuntimeError:
              pass
  finally:
      if dev is not None:
          nbd_disconnect(dev)
  
  
  
subject: make nbd format script more robust against attacks.