python/ovs/socket_util.py

   1 # Copyright (c) 2010 Nicira Networks
   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 errno
  16 import logging
  17 import os
  18 import select
  19 import socket
  20 import sys
  21
  22 import ovs.fatal_signal
  23
  24
  25 def make_unix_socket(style, nonblock, bind_path, connect_path):
  26     """Creates a Unix domain socket in the given 'style' (either
  27     socket.SOCK_DGRAM or socket.SOCK_STREAM) that is bound to 'bind_path' (if
  28     'bind_path' is not None) and connected to 'connect_path' (if 'connect_path'
  29     is not None).  If 'nonblock' is true, the socket is made non-blocking.
  30
  31     Returns (error, socket): on success 'error' is 0 and 'socket' is a new
  32     socket object, on failure 'error' is a positive errno value and 'socket' is
  33     None."""
  34
  35     try:
  36         sock = socket.socket(socket.AF_UNIX, style)
  37     except socket.error, e:
  38         return get_exception_errno(e), None
  39
  40     try:
  41         if nonblock:
  42             set_nonblocking(sock)
  43         if bind_path is not None:
  44             # Delete bind_path but ignore ENOENT.
  45             try:
  46                 os.unlink(bind_path)
  47             except OSError, e:
  48                 if e.errno != errno.ENOENT:
  49                     return e.errno, None
  50
  51             ovs.fatal_signal.add_file_to_unlink(bind_path)
  52             sock.bind(bind_path)
  53
  54             try:
  55                 if sys.hexversion >= 0x02060000:
  56                     os.fchmod(sock.fileno(), 0700)
  57                 else:
  58                     os.chmod("/dev/fd/%d" % sock.fileno(), 0700)
  59             except OSError, e:
  60                 pass
  61         if connect_path is not None:
  62             try:
  63                 sock.connect(connect_path)
  64             except socket.error, e:
  65                 if get_exception_errno(e) != errno.EINPROGRESS:
  66                     raise
  67         return 0, sock
  68     except socket.error, e:
  69         sock.close()
  70         try:
  71             os.unlink(bind_path)
  72         except OSError, e:
  73             pass
  74         if bind_path is not None:
  75             ovs.fatal_signal.add_file_to_unlink(bind_path)
  76         return get_exception_errno(e), None
  77
  78
  79 def check_connection_completion(sock):
  80     p = select.poll()
  81     p.register(sock, select.POLLOUT)
  82     if len(p.poll(0)) == 1:
  83         return get_socket_error(sock)
  84     else:
  85         return errno.EAGAIN
  86
  87
  88 def get_socket_error(sock):
  89     """Returns the errno value associated with 'socket' (0 if no error) and
  90     resets the socket's error status."""
  91     return sock.getsockopt(socket.SOL_SOCKET, socket.SO_ERROR)
  92
  93
  94 def get_exception_errno(e):
  95     """A lot of methods on Python socket objects raise socket.error, but that
  96     exception is documented as having two completely different forms of
  97     arguments: either a string or a (errno, string) tuple.  We only want the
  98     errno."""
  99     if type(e.args) == tuple:
 100         return e.args[0]
 101     else:
 102         return errno.EPROTO
 103
 104
 105 null_fd = -1
 106
 107
 108 def get_null_fd():
 109     """Returns a readable and writable fd for /dev/null, if successful,
 110     otherwise a negative errno value.  The caller must not close the returned
 111     fd (because the same fd will be handed out to subsequent callers)."""
 112     global null_fd
 113     if null_fd < 0:
 114         try:
 115             null_fd = os.open("/dev/null", os.O_RDWR)
 116         except OSError, e:
 117             logging.error("could not open /dev/null: %s"
 118                           % os.strerror(e.errno))
 119             return -e.errno
 120     return null_fd
 121
 122
 123 def write_fully(fd, buf):
 124     """Returns an (error, bytes_written) tuple where 'error' is 0 on success,
 125     otherwise a positive errno value, and 'bytes_written' is the number of
 126     bytes that were written before the error occurred.  'error' is 0 if and
 127     only if 'bytes_written' is len(buf)."""
 128     bytes_written = 0
 129     if len(buf) == 0:
 130         return 0, 0
 131     while True:
 132         try:
 133             retval = os.write(fd, buf)
 134             assert retval >= 0
 135             if retval == len(buf):
 136                 return 0, bytes_written + len(buf)
 137             elif retval == 0:
 138                 logging.warning("write returned 0")
 139                 return errno.EPROTO, bytes_written
 140             else:
 141                 bytes_written += retval
 142                 buf = buf[:retval]
 143         except OSError, e:
 144             return e.errno, bytes_written
 145
 146
 147 def set_nonblocking(sock):
 148     try:
 149         sock.setblocking(0)
 150     except socket.error, e:
 151         logging.error("could not set nonblocking mode on socket: %s"
 152                       % os.strerror(get_socket_error(e)))