python/ovs/util.py

   1 # Copyright (c) 2010, 2011, 2012 Nicira, Inc.
   2 #
   3 # Licensed under the Apache License, Version 2.0 (the "License");
   4 # you may not use this file except in compliance with the License.
   5 # You may obtain a copy of the License at:
   6 #
   7 #     http://www.apache.org/licenses/LICENSE-2.0
   8 #
   9 # Unless required by applicable law or agreed to in writing, software
  10 # distributed under the License is distributed on an "AS IS" BASIS,
  11 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  12 # See the License for the specific language governing permissions and
  13 # limitations under the License.
  14
  15 import os
  16 import os.path
  17 import sys
  18
  19 PROGRAM_NAME = os.path.basename(sys.argv[0])
  20 EOF = -1
  21
  22
  23 def abs_file_name(dir_, file_name):
  24     """If 'file_name' starts with '/', returns a copy of 'file_name'.
  25     Otherwise, returns an absolute path to 'file_name' considering it relative
  26     to 'dir_', which itself must be absolute.  'dir_' may be None or the empty
  27     string, in which case the current working directory is used.
  28
  29     Returns None if 'dir_' is None and getcwd() fails.
  30
  31     This differs from os.path.abspath() in that it will never change the
  32     meaning of a file name."""
  33     if file_name.startswith('/'):
  34         return file_name
  35     else:
  36         if dir_ is None or dir_ == "":
  37             try:
  38                 dir_ = os.getcwd()
  39             except OSError:
  40                 return None
  41
  42         if dir_.endswith('/'):
  43             return dir_ + file_name
  44         else:
  45             return "%s/%s" % (dir_, file_name)
  46
  47
  48 def ovs_retval_to_string(retval):
  49     """Many OVS functions return an int which is one of:
  50     - 0: no error yet
  51     - >0: errno value
  52     - EOF: end of file (not necessarily an error; depends on the function
  53       called)
  54
  55     Returns the appropriate human-readable string."""
  56
  57     if not retval:
  58         return ""
  59     if retval > 0:
  60         return os.strerror(retval)
  61     if retval == EOF:
  62         return "End of file"
  63     return "***unknown return value: %s***" % retval
  64
  65
  66 def ovs_error(err_no, message, vlog=None):
  67     """Prints 'message' on stderr and emits an ERROR level log message to
  68     'vlog' if supplied.  If 'err_no' is nonzero, then it is formatted with
  69     ovs_retval_to_string() and appended to the message inside parentheses.
  70
  71     'message' should not end with a new-line, because this function will add
  72     one itself."""
  73
  74     err_msg = "%s: %s" % (PROGRAM_NAME, message)
  75     if err_no:
  76         err_msg += " (%s)" % ovs_retval_to_string(err_no)
  77
  78     sys.stderr.write("%s\n" % err_msg)
  79     if vlog:
  80         vlog.err(err_msg)
  81
  82
  83 def ovs_fatal(*args, **kwargs):
  84     """Prints 'message' on stderr and emits an ERROR level log message to
  85     'vlog' if supplied.  If 'err_no' is nonzero, then it is formatted with
  86     ovs_retval_to_string() and appended to the message inside parentheses.
  87     Then, terminates with exit code 1 (indicating a failure).
  88
  89     'message' should not end with a new-line, because this function will add
  90     one itself."""
  91
  92     ovs_error(*args, **kwargs)
  93     sys.exit(1)