python: Add ovs_error() helper function to Python.

The ovs_error() and ovs_fatal() helper functions are useful enough
to be ported to Python.  A user will be added in a future commit.

Signed-off-by: Ethan Jackson <ethan@nicira.com>

python/ovs/jsonrpc.py

@@ -1,4 +1,4 @@
-# Copyright (c) 2010, 2011 Nicira Networks
+# Copyright (c) 2010, 2011, 2012 Nicira Networks
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -20,9 +20,10 @@ import ovs.poller
 import ovs.reconnect
 import ovs.stream
 import ovs.timeval
+import ovs.util
 import ovs.vlog
 
-EOF = -1
+EOF = ovs.util.EOF
 vlog = ovs.vlog.Vlog("jsonrpc")
 
 

python/ovs/reconnect.py

@@ -1,4 +1,4 @@
-# Copyright (c) 2010, 2011 Nicira Networks
+# Copyright (c) 2010, 2011, 2012 Nicira Networks
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -15,13 +15,14 @@
 import os
 
 import ovs.vlog
+import ovs.util
 
 # Values returned by Reconnect.run()
 CONNECT = 'connect'
 DISCONNECT = 'disconnect'
 PROBE = 'probe'
 
-EOF = -1
+EOF = ovs.util.EOF
 vlog = ovs.vlog.Vlog("reconnect")
 
 

python/ovs/util.py

@@ -1,4 +1,4 @@
-# Copyright (c) 2010, 2011 Nicira Networks
+# Copyright (c) 2010, 2011, 2012 Nicira Networks
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -17,6 +17,7 @@ import os.path
 import sys
 
 PROGRAM_NAME = os.path.basename(sys.argv[0])
+EOF = -1
 
 
 def abs_file_name(dir_, file_name):
@@ -42,3 +43,51 @@ def abs_file_name(dir_, file_name):
             return dir_ + file_name
         else:
             return "%s/%s" % (dir_, file_name)
+
+
+def ovs_retval_to_string(retval):
+    """Many OVS functions return an int which is one of:
+    - 0: no error yet
+    - >0: errno value
+    - EOF: end of file (not necessarily an error; depends on the function
+      called)
+
+    Returns the appropriate human-readable string."""
+
+    if not retval:
+        return ""
+    if retval > 0:
+        return os.strerror(retval)
+    if retval == EOF:
+        return "End of file"
+    return "***unknown return value: %s***" % retval
+
+
+def ovs_error(err_no, message, vlog=None):
+    """Prints 'message' on stderr and emits an ERROR level log message to
+    'vlog' if supplied.  If 'err_no' is nonzero, then it is formatted with
+    ovs_retval_to_string() and appended to the message inside parentheses.
+
+    'message' should not end with a new-line, because this function will add
+    one itself."""
+
+    err_msg = "%s: %s" % (PROGRAM_NAME, message)
+    if err_no:
+        err_msg += " (%s)" % ovs_retval_to_string(err_no)
+
+    sys.stderr.write("%s\n" % err_msg)
+    if vlog:
+        vlog.err(err_msg)
+
+
+def ovs_fatal(*args, **kwargs):
+    """Prints 'message' on stderr and emits an ERROR level log message to
+    'vlog' if supplied.  If 'err_no' is nonzero, then it is formatted with
+    ovs_retval_to_string() and appended to the message inside parentheses.
+    Then, terminates with exit code 1 (indicating a failure).
+
+    'message' should not end with a new-line, because this function will add
+    one itself."""
+
+    ovs_error(*args, **kwargs)
+    sys.exit(1)